Positive electrode sheet, battery cell, battery, and electric device

Abstract

A positive electrode sheet, a battery cell, a battery, and an electric device, relating to the technical field of batteries. 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 which are sequentially arranged on the surface of the current collector. The lattice volume shrinkage of a first positive electrode active material is greater than that of a second positive electrode active material, and the mass percentage of a binder in the first positive electrode active material layer is 0.8 wt%-1.5 wt%. By limiting the upper limit of the amount of the binder in the first positive electrode active material layer, the first positive electrode active material layer would not be allowed to comprise more other components such as a positive electrode active material, and the overall energy density and specific capacity of the battery cell or the battery are met. Additionally, the lower limit of the amount of the binder in the first positive electrode active material layer can also be limited, thereby improving the binding performance between the first positive electrode active material layer and the positive electrode current collector and between the first positive electrode active material layer and the second positive electrode active material layer, preventing a coating from falling off.

Description

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

[0001] Cross-references

[0002] This application claims priority to Chinese Patent Application No. 202310882443.7, filed on July 18, 2023, entitled “A positive electrode sheet, battery cell, battery and electric device,” the entire contents of which are incorporated herein by reference. Technical Field

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

[0004] Positive electrode active materials with higher energy density, such as ternary materials, have the characteristics of low cost and long life, but lack of safety performance and controllability of production process. Positive electrode active materials with lower energy density, such as lithium manganese phosphate, have the characteristics of high safety performance. Combining 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.

[0005] However, due to the differences in electrochemical properties of the two positive electrode active materials, directly physically mixing the two positive electrode active materials to form a positive electrode active material layer can lead to rapid degradation of the battery cell or battery in the early stages of cycling. Separately coating the two positive electrode active materials to form two independent positive electrode active material layers requires consideration of the bonding effect between the different positive electrode active material layers.

[0006] Summary of the Invention

[0007] 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 the positive electrode active material and increase the energy density.

[0008] 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 a surface of the current collector, the first positive electrode active material layer comprising a first positive electrode active material and a binder, and the second positive electrode active material layer comprising a second positive electrode active material. A lattice volume shrinkage rate of the first positive electrode active material is greater than a lattice volume shrinkage rate of the second positive electrode active material, and a mass percentage of the binder in the first positive electrode active material layer is 0.8 wt% to 1.5 wt%.

[0009] In the technical solution of the embodiments of the present application, the positive electrode sheet of the present application disposes a first positive electrode active material layer formed of a first positive electrode active material having a large lattice volume shrinkage rate between a positive electrode current collector and a second positive electrode active material layer. This reduces the risk of particle shedding of the first positive electrode active material due to large volume changes during the intercalation and deintercalation of a battery cell or battery, effectively reducing the probability of cycle drop, improving the cycle capacity of the battery cell or battery, and increasing the cycle life. Furthermore, when the mass percentage of the binder in the first positive electrode active material layer is between 0.8 wt% and 1.5 wt%, this not only limits the upper limit of the binder usage in the first positive electrode active material layer, thereby preventing the first positive electrode active material layer from containing more other components such as the positive electrode active material, thereby meeting the energy density and capacity of the battery cell or battery as a whole, but also limits the lower limit of the binder usage in the first positive electrode active material layer, thereby improving the bonding performance of the first positive electrode active material layer with the positive electrode current collector and the second positive active material layer, and preventing coating shedding.

[0010] 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 resulting battery or battery cell has a higher energy density and capacity.

[0011] 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 first positive electrode active material and the second positive electrode active material are used, 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 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.

[0012] 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 battery can be improved.

[0013] 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.

[0014] In some embodiments, the Dv50 of the first positive electrode active material is greater than the Dv50 of the second positive electrode active material. A first positive electrode active material layer formed from the first positive electrode active material having a larger particle size is bonded to the positive electrode current collector, and a second positive electrode active material layer formed from the second positive electrode active material having a smaller particle size is bonded to the first positive electrode active material layer. The second positive electrode active material layer can enhance the adhesion of the first positive electrode active material layer, thereby preventing or improving the shedding of the first positive electrode active material and reducing the risk of battery cell or battery failure.

[0015] In some embodiments, the first positive electrode active material contains Mn and Ni, and the positive electrode sheet meets 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 problems in the synthesis process, 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 material with lower energy density, such as lithium manganese phosphate, reacts with the electrolyte to generate hydrogen fluoride, which will corrode the ternary material 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 When manufacturing a battery, the cost of the positive electrode sheet, as well as the safety and cycle stability of the battery cell or battery can be controlled.

[0016] In some embodiments, the first positive electrode active material contains Ni and Co, and 2wt% ≤ w(Co) ≤ 15wt%, and 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% and 20wt% ≤ w(Ni) ≤ 55wt%, the first positive electrode active material can achieve both good energy density and rate cycling performance.

[0017] 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 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 enhance the electrical conductivity and rate performance of the cathode active material.

[0018] 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 . Where 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.

[0019] In some embodiments, the first cathode active material is in a single crystal form. In a high-voltage working environment, high-nickel polycrystals are prone to phase changes 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 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 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 the battery cell or the battery.

[0020] 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, and 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 specified, the cycle stability of the battery cell or battery can be improved, the voltage platform can be increased, and the energy density of the battery cell or battery can be increased.

[0021] In a second aspect, the present application provides a battery cell comprising the positive electrode plate in the above embodiment.

[0022] In a third aspect, the present application provides a battery comprising the battery cell in the above embodiment.

[0023] In a fourth 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.

[0024] 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

[0025] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present application. The same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0026] FIG1 is a schematic structural diagram of a vehicle according to some embodiments of the present application;

[0027] FIG2 is a schematic diagram of the exploded structure of a battery according to some embodiments of the present application;

[0028] FIG3 is a schematic diagram of the exploded structure of a battery cell according to some embodiments of the present application;

[0029] FIG4 is a cross-sectional view of a positive electrode sheet according to some embodiments of the present application.

[0030] The figure numbers in the specific embodiment are as follows: 1000-vehicle; 100-battery; 200-controller; 300-motor; 10-housing; 11-first part; 12-second part; 20-battery cell; 21-end cover; 22-housing; 23-electrode assembly; 30-positive electrode sheet; 31-positive electrode current collector; 32-first positive electrode active material layer; 33-second positive electrode active material layer. DETAILED DESCRIPTION

[0031] The following embodiments of the technical solution of the present application will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only examples and are not intended to limit the scope of protection of the present application.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned figure descriptions are intended to cover non-exclusive inclusions.

[0033] In the description of the embodiments of this application, the technical terms "first" and "second" are used only to distinguish different objects and should not be understood to indicate or imply relative importance or implicitly specify the quantity, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "plurality" is more than two, unless otherwise clearly and specifically defined.

[0034] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0035] In the description of the embodiments of this application, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent the following three situations: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0036] 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).

[0037] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present application.

[0038] In the description of the embodiments of the present application, unless otherwise expressly specified or limited, technical terms such as "installed," "connected," "connected," and "fixed" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integration; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; internal connections between two components or interactions between two components. Those skilled in the art can understand the specific meanings of the above terms in the embodiments of the present application based on specific circumstances.

[0039] Currently, market developments indicate that power batteries are becoming increasingly widely used. They are not only used in energy storage systems such as hydropower, thermal, wind, and solar power plants, but are also widely used in electric vehicles like electric bicycles, electric motorcycles, and electric vehicles, as well as in military equipment and aerospace. As power battery applications continue to expand, market demand is also growing.

[0040] Positive electrode active materials with higher energy density, such as ternary materials, have the characteristics of low cost and long life, but lack of safety performance and controllability of production process. Positive electrode active materials with lower energy density, such as lithium manganese phosphate, have the characteristics of high safety performance. Combining 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.

[0041] However, due to the differences in electrochemical properties of the two positive electrode active materials, directly physically mixing the two positive electrode active materials to form a positive electrode active material layer can lead to rapid degradation of the battery cell or battery in the early stages of cycling. Separately coating the two positive electrode active materials to form two independent positive electrode active material layers requires consideration of the bonding effect between the different positive electrode active material layers.

[0042] 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 disposes a first positive electrode active material layer formed of a first positive electrode active material having a large lattice volume shrinkage rate between the positive electrode current collector and the second positive electrode active material layer. This can reduce the risk of particle shedding of the first positive electrode active material due to large volume changes during the cyclic insertion and removal of the battery cell or battery, effectively reducing the probability of cycle drop, improving the cycle capacity of the battery cell or battery, and increasing 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%. This can not only limit the upper limit of the binder usage in the first positive electrode active material layer, thereby preventing the first positive electrode active material layer from containing more positive electrode active material and other components, thereby meeting the energy density and capacity of the battery cell or battery as a whole, but also limit the lower limit of the binder usage in the first positive electrode active material layer, improving the bonding performance of the first positive electrode active material layer to the positive electrode current collector and the second positive active material layer, and preventing the coating from shedding.

[0043] 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 an 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 layered and coated, 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.

[0044] 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 positive electrode active material in the second positive electrode active material are directly in contact with the cold pressing roller, which avoids the cold pressing roller directly acting on the large particles of positive electrode active material in the first positive electrode active material, reducing the risk of cold pressing damage to the large particles of positive electrode active material in the first positive electrode active material.

[0045] 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-scale side reactions between the first positive electrode active material and water, hydrogen fluoride and electrolyte, and optimize the electrochemical performance of the battery cell or battery.

[0046] The battery referred to in the embodiments of this application refers to a single physical module that includes multiple battery cells to provide higher voltage and capacity. The battery can be in the form of a battery module or battery pack. A battery generally includes a battery case that encloses the multiple battery cells. The battery case prevents liquids or other foreign matter from affecting the charging or discharging of the battery cells.

[0047] Each battery cell is a secondary battery; it can be a lithium-ion battery or a lithium-sulfur battery, but is not limited to these. Battery cells can be cylindrical, flat, rectangular, or other shapes. Battery cells are generally categorized into three types based on packaging: cylindrical, prismatic, and pouch-type.

[0048] A battery cell includes an electrode assembly and an electrolyte. The electrode assembly consists of a positive electrode sheet, a negative electrode sheet, and a separator. A battery cell primarily operates by the movement of metal ions between the positive and negative electrode sheets. The positive electrode sheet includes a positive current collector and a positive active material layer. The positive active material layer is coated on the surface of the positive electrode collector. The uncoated positive electrode collector protrudes from the coated positive electrode collector. This serves as the positive electrode tab. For lithium-ion batteries, for example, the positive electrode current collector can be made of 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 current collector and a negative active material layer. The negative active material layer is coated on the surface of the negative electrode collector. The uncoated negative electrode collector protrudes from the coated negative electrode collector. This serves as the negative electrode tab. The negative electrode current collector can be made of copper. To ensure that high currents can pass without melting, multiple positive electrode tabs are stacked together, and multiple negative electrode tabs are stacked together. The separator can be made of polypropylene (PP) or polyethylene (PE). In addition, the electrode assembly can be a wound structure or a laminated structure, but the embodiments of the present application are not limited to this.

[0049] 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 the current collecting component to realize series, parallel or mixed connection of multiple battery cells.

[0050] The battery also includes sampling terminals and a battery management system. The sampling terminals are connected to the busbar and are used to collect information about the battery cells, such as voltage or temperature. The sampling terminals transmit the collected battery cell information to the battery management system. If the battery management system detects that the battery cell information is outside the normal range, it will limit the battery's output power for safety protection.

[0051] It will be appreciated that the electrical devices applicable to the batteries described in the embodiments of the present application may be in various forms, for example, mobile phones, portable devices, laptop computers, electric 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, for example, game consoles, electric car toys, electric ship toys and electric airplane toys, etc. Electric tools include metal cutting power tools, grinding power tools, assembly power tools and railway power tools, for example, electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators and electric planers.

[0052] 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 an example.

[0053] Please refer to Figure 1, which is a structural diagram of a vehicle provided in some embodiments of the present application. The vehicle 1000 can be a fuel vehicle, a gas vehicle or a new energy vehicle. The new energy vehicle can be a pure electric vehicle, a hybrid vehicle or an extended-range vehicle, etc. A battery 100 is provided inside the vehicle 1000, and the battery 100 can be provided at the bottom, head or tail of the vehicle 1000. The battery 100 can be used to power the vehicle 1000. For example, the battery 100 can serve as an operating power source for the vehicle 1000. The vehicle 1000 may also include a controller 200 and a motor 300. 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.

[0054] In some embodiments of the present application, the battery 100 can not only serve as the operating power source of the vehicle 1000, but also serve as the driving power source of the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

[0055] Please refer to Figure 2, which is an exploded view of a battery provided in some embodiments of the present application. Battery 100 includes a housing 10 and a battery cell 20, with battery cell 20 housed within housing 10. Housing 10 provides storage space for battery cell 20 and can have various structures. In some embodiments, housing 10 can include a first portion 11 and a second portion 12, which overlap each other and together define a storage space for battery cell 20. Second portion 12 can be a hollow structure with one end open. First portion 11 can be a plate-like structure, with first portion 11 overlapping the open side of second portion 12, so that the first and second portions 11 and 12 together define a storage space. Alternatively, first portion 11 and second portion 12 can each be a hollow structure with one end open, with the open side of first portion 11 overlapping the open side of second portion 12. Housing 10 formed by first portion 11 and second portion 12 can have various shapes, such as a cylinder or a rectangular parallelepiped.

[0056] 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 hybrid connection. A hybrid connection refers to a combination of series and parallel connections among the multiple battery cells 20. The multiple battery cells 20 may be directly connected in series, in parallel, or in a hybrid connection, and then the entire battery cell 20 may be housed within the housing 10. Alternatively, the battery 100 may be constructed by first connecting multiple battery cells 20 in series, in parallel, or in a hybrid connection to form a battery module, which is then connected in series, in parallel, or in a hybrid connection to form a complete battery module, and then housed within the housing 10. The battery 100 may also include other structures, such as a busbar assembly for electrically connecting the multiple battery cells 20.

[0057] 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.

[0058] Please refer to Figure 3, which is a schematic diagram of the exploded structure of a first type of battery cell provided in some embodiments of the present application. A battery cell 20 is the smallest unit that makes up a battery. As shown in Figure 3, a battery cell 20 includes an end cap 21, a housing 22, an electrode assembly 23, and other functional components.

[0059] The end cap 21 is a component that covers the opening of the housing 22 to isolate the internal environment of the battery cell 20 from the external environment. The shape of the end cap 21 can be adapted to the shape of the housing 22 to fit the housing 22. Optionally, the end cap 21 can be made of a material with a certain hardness and strength (such as an aluminum alloy). This prevents the end cap 21 from deforming when subjected to compression or collision, thereby enhancing the structural strength and safety of the battery cell 20. Functional components such as electrode terminals can be provided on the end cap 21. The electrode terminals can be used to electrically connect to the electrode assembly 23 to output or input electrical energy to the battery cell 20. In some embodiments, the end cap 21 can also be provided with a pressure relief mechanism for relieving internal pressure when the internal pressure or temperature of the battery cell 20 reaches a threshold. The end cap 21 can also be made of a variety of materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and this embodiment of the present application does not impose any specific limitations on this. In some embodiments, an insulating member may be provided inside the end cap 21 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 made of plastic, rubber, or the like.

[0060] The housing 22 is a component that cooperates with the end cap 21 to form the internal environment of the battery cell 20. This internal environment can be used to accommodate the electrode assembly 23, electrolyte, and other components. The housing 22 and end cap 21 can be separate components. An opening can be provided in the housing 22, and the end cap 21 is placed over the opening to form the internal environment of the battery cell 20. Alternatively, the end cap 21 and housing 22 can be integrated. Specifically, the end cap 21 and housing 22 can form a common connection surface before other components are inserted into the housing. When the interior of the housing 22 needs to be enclosed, the end cap 21 is placed over the housing 22. The housing 22 can have a variety of shapes and sizes, such as a rectangular parallelepiped, a cylindrical shape, or a hexagonal prism. Specifically, the shape of the housing 22 can be determined based on the specific shape and size of the electrode assembly 23. The housing 22 can be made of a variety of materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and this embodiment of the present application does not impose any particular limitations on this.

[0061] 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 and negative electrode tabs 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 electrode active material and the negative electrode active material react with the electrolyte, and the tabs connect the electrode terminals to form a current loop.

[0062] According to some embodiments of the present application, please refer to FIG. 4 , which is a cross-sectional view of the positive electrode sheet 30 of some embodiments of the present application.

[0063] 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 0.8 wt% to 1.5 wt%.

[0064] 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:

[0065] A soft-pack laminated battery is made using the first positive electrode active material or the second positive electrode active material respectively. The battery is charged to 4.4 V at 0.5C0 at 2.5-4.4 V in a constant temperature environment of 25°C, and then charged at a constant voltage at 4.4 V to a current ≤ 0.05C0. The battery is then disassembled to remove the positive electrode sheet and perform an XRD test. 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, and the lattice volume shrinkage rate C1 = (Vfresh-Vfull charge) / Vfresh.

[0066] 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 %.

[0067] 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)).

[0068] Here, 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 .

[0069] The positive electrode sheet 30 of the present application disposes a first positive active material layer 32 formed of a first positive active material having a large lattice volume shrinkage rate between a positive current collector 31 and a second positive active material layer 33. This reduces the risk of particle shedding of the first positive active material due to large volume changes during the intercalation and deintercalation of a battery cell or battery, effectively mitigating the probability of cycling failure, improving the cycling capability of the battery cell or battery, and increasing the cycle life. Furthermore, when the mass percentage of the binder in the first positive active material layer 32 is between 0.8 wt% and 1.5 wt%, this not only limits the upper limit of the binder content in the first positive active material layer 32, thereby preventing the first positive active material layer 32 from containing excessive amounts of other components such as positive active material, thereby meeting the energy density and capacity requirements of the battery cell or battery as a whole, but also limits the lower limit of the binder content in the first positive active material layer 32, thereby improving the bonding performance of the first positive active material layer 32 to the positive current collector 31 and the second positive active material layer 33, and preventing coating shedding.

[0070] 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%.

[0071] According to some embodiments of the present application, optionally, 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.

[0072] As an example, the first positive active material layer 32 may include 95.5 wt%, 95.6 wt%, 95.7 wt%, 95.8 wt%, 95.9 wt%, 96 wt%, 96.1 wt%, 96.2 wt%, 96.3 wt%, 96.4 wt%, 96.5 wt%, 96.6 wt%, 96.7 wt%, 96.8 wt%, 96.9 wt% or 97 wt% of the first positive active material, and 2.5 wt%, 2.6 wt%, 2.7 wt%, 2.8 wt%, 2.9 wt% or 3 wt% of the conductive agent.

[0073] 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.

[0074] According to some embodiments of the present application, optionally, the positive electrode plate 30 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.

[0075] 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.

[0076] 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:

[0077] Place a certain amount of powder in a special compaction mold, place the mold on the compaction density instrument, set the pressure to 4T, and read the thickness of the powder under 4T pressure on the device. Calculate the compaction density through density = mass / volume.

[0078] When the positive electrode sheet 30 meets the following conditions: When the first positive electrode active material and the second positive electrode active material are used, 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.

[0079] According to some embodiments of the present application, optionally, 0.5≤w1≤0.95, 0.05≤w2≤0.5.

[0080] As an example, 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.

[0081] 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.

[0082] 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.

[0083] Optionally, 0.6≤w1≤0.8, 0.2≤w2≤0.4.

[0084] According to some embodiments of the present application, optionally, 3g / cc≤P1≤4g / cc, 2g / cc≤P2≤2.5g / cc.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] According to some embodiments of the present application, optionally, the first positive electrode active material contains Mn and Ni elements, and the positive electrode plate 30 meets the following conditions:

[0092]

[0093] 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 .

[0094] 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.

[0095] Since some positive electrode active materials with lower energy density, such as lithium manganese phosphate, have higher water content due to synthesis process problems 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 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 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, the cost, safety and cycle stability of the battery cell or battery can be controlled.

[0096] Optionally, 5wt%≤w(Ni)≤25wt%, 20wt%≤w(Ni)≤55wt%.

[0097] Optionally, 20 μm≤H1≤70 μm, 5 μm≤H2≤60 μm.

[0098] Optionally, 25 μm≤H1≤55 μm, 20 μm≤H2≤50 μm.

[0099] Optionally, the thickness of the positive electrode current collector 31 is 10 μm to 15 μm.

[0100] Optionally, the thickness of the positive electrode current collector 31 is 13 μm.

[0101] According to some embodiments of the present application, the first positive electrode active material optionally contains Ni and Co, and 2 wt % ≤ w(Co) ≤ 15 wt %, and 20 wt % ≤ w(Ni) ≤ 55 wt %, where 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.

[0102] As an example, the value of w(Co) can be 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt% or 15 wt%.

[0103] The value of w(Ni) may be 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt%, 25 wt%, 26 wt%, 27 wt%, 28 wt%, 29 wt%, 30 wt%, 31 wt%, 32 wt%, 33 wt%, 34 wt%, 35 wt%, 36 wt%, 37 wt%, 38 wt%, 39 wt%, 40 wt%, 41 wt%, 42 wt%, 43 wt%, 44 wt%, 45 wt%, 46 wt%, 47 wt%, 48 wt%, 49 wt%, 50 wt%, 51 wt%, 52 wt%, 53 wt%, 54 wt% or 55 wt%.

[0104] 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.

[0105] Optionally, 3wt%≤w(Co)≤12.5wt%, 25wt%≤w(Ni)≤50wt%.

[0106] Optionally, 30wt%≤w(Ni)≤45wt%.

[0107] Optionally, 30wt%≤w(Ni)≤40wt%.

[0108] According to some embodiments of the present application, optionally, the positive electrode plate 30 meets the following conditions:

[0109] 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.

[0110] The performance of positive electrode active materials with different Ni contents varies greatly. Among positive electrode active materials with the same Ni content, when the positive electrode sheet 30 meets the following conditions: When the cathode material is used as the cathode material, it can not only reduce the cost and improve the low temperature performance, but also improve the conductivity and rate performance of the cathode active material.

[0111] Optionally,

[0112] Optionally,

[0113] 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 . Where, 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.

[0114] The first positive electrode active material is a ternary material, and the Ni content is relatively low. Using a medium-low nickel ternary material can improve the safety performance while meeting the energy requirements.

[0115] According to some embodiments of the present application, optionally, the first positive electrode active material is in a single crystal form.

[0116] In a high-voltage working environment, high-nickel polycrystals are prone to phase changes 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 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 under high voltage. 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 battery.

[0117] 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. Where, -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.

[0118] 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 increasing the energy density of the battery cell or battery.

[0119] Optionally, 0.2≤y≤0.5.

[0120] Optionally, the surface of the second positive electrode active material has a coating layer, the material of the coating layer is pyrophosphate, phosphate or carbon, and the number of the coating layers is ≥1.

[0121] The battery's charge and discharge processes involve the intercalation and deintercalation of lithium, leading to different molar Li contents at different discharge states. The molar Li contents listed in this application for cathode materials refer to the initial state of the material, i.e., the state before addition of the materials. When the cathode material is used in a battery system, the molar Li content will change after charge and discharge cycles.

[0122] In the list of positive electrode materials in this application, the molar content of O is only a theoretical value. Lattice oxygen release will cause the molar content of oxygen to change, and the actual molar content of O will fluctuate.

[0123] The following is a further detailed description of a positive electrode plate of the present application in conjunction with embodiments.

[0124] 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.

[0125] Table 1 Parameters of the first part of the positive electrode sheets of Examples 1 to 14 and Comparative Examples 1 to 2

[0126]

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

[0128]

[0129] Table 3 Parameters of the third part of the positive electrode sheets of Examples 1 to 14 and Comparative Examples 1 to 2

[0130]

[0131] 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 all conductive carbon black, and the binder is all polyvinylidene fluoride.

[0132] The positive electrode sheets of Examples 1 to 14 and Comparative Examples 1 to 2 were prepared by the following method:

[0133] S1. Prepare the first positive electrode active material slurry

[0134] A first positive electrode active material, conductive carbon black and polyvinylidene fluoride are mixed to prepare a first mixture, N-methylpyrrolidone is added to the first mixture and stirred uniformly to prepare a first positive electrode active material slurry, wherein the viscosity of the first positive electrode active material slurry is 3000mPa·S to 10000mPa·S.

[0135] S2. Preparation of second positive electrode active material slurry

[0136] A second mixture was prepared by mixing 96.7 wt% of a second positive electrode active material, 0.4 wt% of conductive carbon black and 2.9 wt% of polyvinylidene fluoride. N-methylpyrrolidone was added to the second mixture and stirred uniformly to prepare a second positive electrode active material slurry. The viscosity of the second positive electrode active material slurry was 3000 mPa·S to 10000 mPa·S.

[0137] S3. Preparation of positive electrode sheet

[0138] 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.

[0139] Detection method of the content of the element to be measured:

[0140] 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) until the positive electrode sheet is digested, add 0.5ml of perchloric acid, and heat to 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. Depending on the content of the element to be measured, the volume is fixed to an appropriate volume and then the test is started on the ICP-OES test instrument.

[0141] Test Example 1

[0142] The content of the elements to be tested in the positive electrode sheets of Examples 1 to 14 and Comparative Examples 1 to 2 was measured. 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.

[0143] 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:

[0144] (1) Preparation of negative electrode sheet

[0145] Graphite, sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and conductive carbon were added to a certain amount of deionized water. The mass ratio of graphite: sodium carboxymethyl cellulose: styrene-butadiene rubber: conductive agent was 90:2:3:5. The mixture was stirred to form a uniform slurry with a viscosity controlled at 3000-10000 mPa·s. The slurry was then coated on copper foil and dried to form a negative electrode sheet.

[0146] (2) Preparation of soft-pack laminated batteries

[0147] The prepared positive electrode sheet, negative electrode sheet and separator (polyethylene (PE) porous polymer film) are made into corresponding battery cells according to a 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 appropriate size for top-side sealing. The top-side sealing temperature is 145°C, and the electrolyte is injected (the electrolyte is 1 mol / L LiPF6 / (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 after standing, formation, aging, exhaust, secondary sealing, and capacity testing.

[0148] Testing method for bonding strength of positive electrode sheet:

[0149] 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 surface facing down. Insert a paper tape with a width equal to the electrode and a length 80-200mm greater than the length of the sample under the electrode and fix it with wrinkle glue. Turn on the power of the Sansi tensile testing machine, the indicator light will light up, 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 that comes with the tensile testing machine to adjust the position of the upper clamp and start the tensile test.

[0150] Method for testing capacity retention after 500 cycles:

[0151] The prepared soft-pack laminated battery was 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 was recorded as Cn (n = 1, 2, 3 ...). The above operation was repeated. The capacity retention rate after 500 cycles was = C500 / C3, where C3 is the cell capacity at the 3rd cycle, and C500 is the cell capacity at the 500th cycle.

[0152] Battery capacity detection method:

[0153] The cell capacity is the cell capacity of the third cycle, which is C3.

[0154] Table 4 Adhesion strength of the positive electrode sheets of Examples 1 to 14 and Comparative Examples 1 to 2 and performance of the prepared soft-pack laminated batteries

[0155]

[0156] 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.

[0157] 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 make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions 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, wherein: 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, wherein: The first positive active material layer includes 95.5 wt % to 97 wt % of the first positive active material and 2.5 wt % to 3 wt % of a conductive agent.

3. The positive electrode sheet according to claim 1 or 2, wherein: 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, wherein: 0.5≤w1≤0.95, 0.05≤w2≤0.

5.

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

6. The positive electrode sheet according to claim 3, wherein: 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 any one of claims 1 to 6, wherein: 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 any one of claims 1 to 7, wherein: 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, wherein: The positive electrode sheet meets the following conditions:

10. The positive electrode sheet according to any one of claims 1 to 9, wherein: 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, wherein: The first positive electrode active material is in a single crystal form.

12. The positive electrode sheet according to any one of claims 1 to 11, wherein: 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, wherein: The battery cell comprises the positive electrode sheet as claimed in any one of claims 1 to 12.

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

15. An electrical device, wherein: 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.

Images