Positive pole piece, battery and electric device

Abstract

The embodiment of the invention provides a positive pole piece, a battery and an electric device, and relates to the field of batteries. The positive pole piece comprises a current collector and an active material layer arranged on the surface of at least one side of the current collector, the active material layer comprises at least two sub-layers, and in the mixed active material layer, a positive active material comprises a first positive active material and a second positive active material; the shrinking percentage T2 of the second positive electrode active material is larger than the shrinking percentage T1 of the first positive electrode active material, T2-T1 is larger than or equal to 0.3%, and the first positive electrode active material or the second positive electrode active material accounts for 55%-95% of the total mass of the positive electrode active materials in the mixed active material layer. The positive pole piece can improve the dynamic performance of the battery.

Description

Positive electrode, battery and electrical device Technical Field

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

[0002] Energy conservation and emission reduction are key to the sustainable development of the automotive industry. Electric vehicles, due to their energy-saving and environmentally friendly advantages, have become an important component of the sustainable development of the automotive industry. For electric vehicles, battery technology is a key factor in their development.

[0003] The positive electrode active material layer made by mixing two positive electrode active materials has certain optimization improvements in energy density or safety performance compared with the positive electrode active material layer made by a single active material.

[0004] Summary of the Invention

[0005] The inventors of this application have discovered that when positive electrode active materials with large shrinkage differences are mixed in similar amounts, the overall battery kinetic performance is poor. This application provides a positive electrode sheet, a battery, and an electrical device that can improve the battery kinetic performance.

[0006] In the first aspect, the present application provides a positive electrode plate, comprising a current collector and an active material layer arranged on at least one side surface of the current collector, the active material layer comprising at least one mixed active material layer; in the mixed active material layer, the positive electrode active material comprises a first positive electrode active material and a second positive electrode active material, the shrinkage rate T2 of the second positive electrode active material is greater than the shrinkage rate T1 of the first positive electrode active material, and T2-T1 ≥ 0.3%, and the proportion of the first positive electrode active material or the second positive electrode active material is 55% to 95% of the total mass of the positive electrode active material in the mixed active material layer.

[0007] In the technical solution of the embodiment of the present application, the mixed active material layer mainly contains a mixture of two different types of positive electrode active materials: one type is a positive electrode active material with a small shrinkage rate (shrinkage rate is T1), and the other type is a positive electrode active material with a large shrinkage rate (shrinkage rate is T2). There is a certain degree of shrinkage difference between the two types of positive electrode active materials in the mixed active material layer, and the mass of the positive electrode active material with a large shrinkage rate or the positive electrode active material with a small shrinkage rate accounts for a larger proportion. This reduces the problem of poor dynamic performance caused by mixing materials with large shrinkage rates and similar contents in the same layer.

[0008] In some embodiments, in the mixed active material layer, the first positive electrode active material or the second positive electrode active material accounts for 65% to 80% of the total mass of the positive electrode active material. The larger mass of the positive electrode active material with a large shrinkage rate or the positive electrode active material with a small shrinkage rate reduces the problem of poor kinetic performance caused by mixing materials with large shrinkage rates but similar content in the same layer.

[0009] In some embodiments, the value range of T1 is 0.3%-5.5%, and the value range of T2 is 1%-7%. By selecting and combining the positive electrode active materials, the shrinkage rates of the two types of positive electrode active materials can be differentially adjusted.

[0010] In some embodiments, the value range of T1 is 0.5%-4%, and the value range of T2 is 3%-6.5%.

[0011] In some embodiments, the average particle size R2 of the second positive electrode active material is greater than the average particle size R1 of the first positive electrode active material, and R2 / R1 ≥ 2, optionally, 100 ≥ R2 / R1 ≥ 5, optionally, 100 ≥ R2 / R1 ≥ 10. Mixing the second positive electrode active material with a large shrinkage rate and a large average particle size with the first positive electrode active material with a small shrinkage rate and a small average particle size to form a mixed active material layer is beneficial for improving the energy density of the battery. At the same time, compared to mixing active materials with significantly different particle sizes in similar amounts in the same layer, the solution of this embodiment can further improve the kinetic performance of the battery.

[0012] In some embodiments, the active material layer includes at least two sub-layers, wherein at least one of the sub-layers is the mixed active material layer.

[0013] In some embodiments, the two adjacent sublayers are respectively a first mixed active material layer and a second mixed active material layer. The shrinkage rate of the first positive electrode active material in the first mixed active material layer is T1, the shrinkage rate of the second positive electrode active material is T2, and T2-T1 ≥ 0.3%. The positive electrode active materials in the second mixed active material layer include a third positive electrode active material and a fourth positive electrode active material. The shrinkage rate of the third positive electrode active material is T1', the shrinkage rate of the fourth positive electrode active material is T2', and T2'-T1' ≥ 0.3%. Layered active material layers, in which at least two adjacent layers are mixed active material layers, are also embodiments that may be included in the present application and can improve the problem of poor dynamic performance.

[0014] In some embodiments, the difference between T2 and T1' is no greater than 1%, and / or the difference between T2' and T1 is no greater than 1%. If the shrinkage rate difference between the two mixed active material layers is too large, the interface contact is poor, affecting the dynamic performance.

[0015] In some embodiments, the first mixed active material layer is closer to the current collector than the second mixed active material layer, and the value of T2-T1 is smaller than the value of T2'-T1'.

[0016] In some embodiments, one of the two adjacent sublayers is a mixed active material layer, and the other is a single active material layer. The positive electrode active material of the single active material layer includes a first positive electrode active material or a second positive electrode active material. Due to the significant difference in shrinkage between the first and second positive electrode active materials, providing the first or second positive electrode active material separately can improve the kinetic performance of the entire active material layer.

[0017] In some embodiments, the single active material layer is closer to the current collector than the mixed active material layer. The single active material layer contacts the current collector, reducing the problem of poor contact between the active material layer and the current collector caused by the large difference in shrinkage between the first positive electrode active material and the second positive electrode active material.

[0018] In some embodiments, the positive electrode active material of the single active material layer includes a first positive electrode active material. This embodiment is an alternative solution that can improve the problem of poor kinetic performance.

[0019] In some embodiments, the mixed active material layer contains a linear conductive agent. Optionally, the mass proportion of the linear conductive agent with a length of 1 μm or greater in the mixed active material layer is 0.2% to 1%. Optionally, the linear conductive agent comprises at least one of carbon nanotubes, carbon fibers, and linear graphene. A certain proportion of linear conductive material is added to the mixed active material layer and dispersed around the different positive electrode active materials to reduce the deterioration of the conductive network caused by the separation of the two types of positive electrode active materials due to differential shrinkage during charge and discharge. This serves to connect and conduct the material, maintaining a stable conductive network when the contact interface between the different types of positive electrode active materials changes.

[0020] In some embodiments, the active material layer includes at least two sublayers, and among the two adjacent sublayers, the porosity of the sublayer away from the current collector is ≥30%, and the porosity of the sublayer adjacent to the current collector is ≥50%;

[0021] Optionally, the porosity of the sublayer away from the current collector is ≥50%, and the porosity of the sublayer adjacent to the current collector is ≥60%. In the active material layer, the sublayer away from the current collector has sufficient electrolyte contact, while the sublayer adjacent to the current collector has less electrolyte contact. By setting different porosities for different sublayers, the electrolyte can be fully infiltrated into each sublayer.

[0022] In a second aspect, the present application provides a battery comprising a battery cell consisting of a negative electrode sheet and the positive electrode sheet provided in the first aspect.

[0023] In a third aspect, the present application provides an electrical device comprising a battery provided according to the second aspect.

[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 structural diagram of a battery cell provided in some embodiments of the present application;

[0029] FIG4 is a schematic diagram of the exploded structure of a battery cell according to some embodiments of the present application.

[0030] Icon: 1000-vehicle; 100-battery; 10-housing; 11-accommodation space; 12-first part; 13-second part; 20-battery cell; 21-housing; 211-opening; 22-end cover assembly; 221-end cover; 222-electrode terminal; 23-electrode assembly; 24-current collecting member; 25-insulating protection member; 200-controller; 300-motor. 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 orientations or positional relationships indicated by technical terms such as "thickness", "up", "down", "front", "back", "top", "bottom", "inside", and "outside" are based on the orientations or positional relationships shown in the accompanying drawings. They 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. Therefore, they cannot be understood as limitations on the embodiments of the present application.

[0037] In the description of the embodiments of this application, unless otherwise expressly specified or limited, technical terms such as "connection" and "fixed" should be understood in a broad sense. For example, they can refer to fixed connection, detachable connection, or integration; mechanical connection or electrical connection; direct connection or indirect connection through an intermediate medium; internal communication between two components or interaction between two components. For those skilled in the art, the specific meanings of the above terms in the embodiments of this application can be understood according to specific circumstances.

[0038] 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.

[0039] The power battery can be a lithium-ion battery. During the charging process of the lithium-ion battery, lithium ions are released from the positive electrode active material, transferred through the electrolyte, passed through the isolation membrane, and embedded in the negative electrode active material. At present, the positive electrode active material layer made based on the mixture of different positive electrode active materials has improved energy density or safety performance compared to the positive electrode active material layer of a single active material. However, the inventors found that after the positive electrode active materials with large shrinkage differences are mixed in similar amounts, the kinetic performance of the entire battery is still poor. In addition, the positive electrode sheets layered based on lithium manganese iron phosphate and ternary materials have certain optimization and improvement in kinetic performance compared to the positive electrode sheets with a single active material. However, the single layer of active material in this layered positive electrode sheet is single, and the full advantages of layered coating cannot be brought into play. Moreover, this method of distinguishing the upper and lower layers based on the type of material has a single perspective, which limits the application scope of the layered technology.

[0040] Based on the above considerations, in order to solve the problem of limited performance improvement of the mixed active material layer, a positive electrode plate is designed. By performing fine structural design on the positive electrode plate of the lithium-ion battery, clear positive electrode plate design principles and design basis are provided to improve the battery's kinetic performance and increase the battery's cycle life.

[0041] The battery cells disclosed in the embodiments of the present application can be used in, but are not limited to, electrical devices such as vehicles, ships, or aircraft.

[0042] The present invention provides an electric device that uses a battery as a power source. The electric device may be, but is not limited to, a mobile phone, a tablet, a laptop computer, an electric toy, an electric tool, a battery-powered vehicle, an electric car, a ship, a spacecraft, etc. The electric toy may include a fixed or mobile electric toy, such as a game console, an electric car toy, an electric ship toy, and an electric airplane toy, etc. The spacecraft may include an airplane, a rocket, a space shuttle, and a spacecraft, etc.

[0043] For the convenience of description, the following embodiments are described by taking a vehicle 1000 as an example of an electrical device according to an embodiment of the present application.

[0044] Please refer to Figure 1, which is a schematic diagram of the structure of a vehicle 1000 provided in some embodiments of the present application. A battery 100 is disposed within vehicle 1000. Battery 100 can be located at the bottom, front, or rear of vehicle 1000. Battery 100 can be used to power vehicle 1000, for example, as an operating power source for vehicle 1000.

[0045] The vehicle 1000 may further include a controller 200 and a motor 300 . The controller 200 is used to control the battery 100 to supply power to the motor 300 , for example, to meet the power requirements of the vehicle 1000 during startup, navigation, and driving.

[0046] 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.

[0047] FIG2 is a schematic diagram of the exploded structure of a battery 100 provided in some embodiments of the present application. Referring to FIG2 , the battery 100 includes a housing 10 and a battery cell 20 , wherein the battery cell 20 is housed in the housing 10 .

[0048] The housing 10 is used to provide a storage space 11 for the battery cells 20. In some embodiments, the housing 10 may include a first portion 12 and a second portion 13, which overlap to define the storage space 11 for accommodating the battery cells 20. Of course, the connection between the first portion 12 and the second portion 13 can be sealed by a seal (not shown), such as a sealing ring, sealant, or the like.

[0049] The first portion 12 and the second portion 13 can have various shapes, such as a rectangular parallelepiped, a cylinder, etc. The first portion 12 can be a hollow structure with an opening on one side to form a receiving cavity for accommodating the battery cell 20. The second portion 13 can also be a hollow structure with an opening on one side to form a receiving cavity for accommodating the battery cell 20. The open side of the second portion 13 covers the open side of the first portion 12, thereby forming the box 10 with the receiving space 11. Of course, as shown in Figure 2, the first portion 12 can also be a hollow structure with an opening on one side, and the second portion 13 can be a plate-like structure. The second portion 13 covers the open side of the first portion 12, thereby forming the box 10 with the receiving space 11.

[0050] In the battery 100, there can be one or more battery cells 20. If there are multiple battery cells 20, the multiple battery cells 20 can be connected in series, in parallel, or in a mixed connection. Mixed connection means that the multiple battery cells 20 are connected in series and in parallel. The multiple battery cells 20 can 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, it is also possible that the multiple battery cells 20 are first connected in series, in parallel, or in a mixed connection to form a battery module, and the multiple battery modules are then connected in series, in parallel, or in a mixed connection to form a whole, and accommodated in the box 10. The battery cell 20 can be cylindrical, flat, rectangular, or in other shapes. Figure 2 exemplifies the case where the battery cell 20 is square.

[0051] In some embodiments, the battery 100 may further include a busbar component (not shown), and the multiple battery cells 20 may be electrically connected via the busbar component to achieve series connection, parallel connection, or mixed connection of the multiple battery cells 20 .

[0052] Figure 3 is a schematic diagram of the structure of a battery cell 20 provided in some embodiments of the present application, and Figure 4 is an exploded view of a battery cell 20 provided in some embodiments of the present application. Referring to Figures 3 and 4, the battery cell 20 may include a housing 21, an end cap assembly 22, and an electrode assembly 23. The housing 21 has an opening 211, and the electrode assembly 23 is accommodated within the housing 21. The end cap assembly 22 is used to seal the opening 211.

[0053] The shape of the housing 21 can be determined according to the specific shape of the electrode assembly 23. For example, if the electrode assembly 23 is a rectangular parallelepiped structure, the housing 21 can be a rectangular parallelepiped structure. Figures 3 and 4 exemplarily show the case where the housing 21 and the electrode assembly 23 are square.

[0054] The shell 21 may be made of a variety of materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, etc., and the embodiment of the present application does not impose any special restrictions on this.

[0055] The end cap assembly 22 includes an end cap 221 and an electrode terminal 222. The end cap assembly 22 is used to seal the opening 211 of the outer shell 21 to form a sealed installation space (not shown), which is used to accommodate the electrode assembly 23. The installation space is also used to accommodate an electrolyte, such as an electrolyte. The end cap assembly 22 serves as a component for outputting the electrical energy of the electrode assembly 23. The electrode terminal 222 in the end cap assembly 22 is used to electrically connect to the electrode assembly 23, that is, the electrode terminal 222 is electrically connected to the tab of the electrode assembly 23. For example, the electrode terminal 222 is connected to the tab through the current collecting member 24 to achieve electrical connection between the electrode terminal 222 and the tab.

[0056] It should be noted that the opening 211 of the shell 21 can be one or two. If the opening 211 of the shell 21 is one, the end cap assembly 22 can also be one, and two electrode terminals 222 can be provided in the end cap assembly 22, and the two electrode terminals 222 are respectively used to electrically connect to the positive electrode tab and the negative electrode tab of the electrode assembly 23. If the opening 211 of the shell 21 is two, for example, the two openings 211 are provided on opposite sides of the shell 21, the end cap assembly 22 can also be two, and the two end cap assemblies 22 are respectively covered at the two openings 211 of the shell 21. In this case, the electrode terminal 222 in one end cap assembly 22 can be a positive electrode terminal, which is used to electrically connect to the positive electrode tab of the electrode assembly 23; and the electrode terminal 222 in the other end cap assembly 22 can be a negative electrode terminal, which is used to electrically connect to the negative electrode sheet of the electrode assembly 23.

[0057] In some embodiments, as shown in FIG4 , the battery cell 20 may further include an insulating protective member 25 secured to the periphery of the electrode assembly 23. The insulating protective member 25 is used to insulate and isolate the electrode assembly 23 from the housing 21. Exemplarily, the insulating protective member 25 is a tape adhered to the periphery of the electrode assembly 23. In some embodiments, there are multiple electrode assemblies 23, and the insulating protective member 25 is disposed around the periphery of the multiple electrode assemblies 23, forming the multiple electrode assemblies 23 into a single integrated structure to maintain structural stability.

[0058] According to some embodiments of the present application, the positive electrode plate includes a current collector and an active material layer arranged on at least one side surface of the current collector, the active material layer includes at least one mixed active material layer; in the mixed active material layer, the positive electrode active material includes a first positive electrode active material and a second positive electrode active material, the shrinkage rate T2 of the second positive electrode active material is greater than the shrinkage rate T1 of the first positive electrode active material, and T2-T1≥0.3%, the first positive electrode active material or the second positive electrode active material accounts for 55% to 95% of the total mass of the positive electrode active material in the mixed active material layer, and accordingly, the second positive electrode active material or the first positive electrode active material accounts for 5% to 45% of the total mass of the positive electrode active material.

[0059] The shrinkage rate (expansion rate) in this application refers to the degree of volumetric expansion change of the positive electrode active material during the charge and discharge process. The shrinkage rate test method for the positive electrode active material is as follows: a certain positive electrode active material is used as the sole positive electrode active material to form a fresh electrode sheet, wherein the active material layer is formed by mixing the positive electrode active material, the binder PVDF, and the conductive agent in a mass ratio of 97wt%:1.5wt%:1.5wt%. The cross-section of the active material layer in the fully charged and fully discharged states of the battery is photographed using a scanning electron microscope (the active material layer is cut perpendicular to the current collector surface and the cross-section is photographed using a scanning electron microscope). The particle size of the positive electrode material in the fully charged state is calculated as L1 and the particle size in the fully discharged state is calculated as L2. The shrinkage rate of the positive electrode material is calculated as L1-L2 / L2. The particle size L1 or L2 is calculated by measuring the particle size of 20 particles in the image and taking the average value, which is the particle size value.

[0060] The shrinkage rate of the positive electrode active material is a property of the material itself. By specifically selecting the composition of the positive electrode active material, a positive electrode active material with a specific shrinkage rate can be obtained.

[0061] In some embodiments of the present application, other layers, such as an adhesive layer, may be provided between the current collector and the active material layer.

[0062] According to some embodiments of the present application, in the mixed active material layer, the first positive electrode active material or the second positive electrode active material accounts for 65% to 80% of the total mass of the positive electrode active material, and the second positive electrode active material or the first positive electrode active material accounts for 20% to 35% of the total mass of the positive electrode active material. As an example, the second positive electrode active material may account for 65%, 70%, 75%, or 80% of the total mass of the positive electrode active material, or any value within the above two numerical ranges; the first positive electrode active material may account for 20%, 25%, 30%, or 35% of the total mass of the positive electrode active material, or any value within the above two numerical ranges. Alternatively, the first positive electrode active material may account for 65%, 70%, 75%, or 80% of the total mass of the positive electrode active material, or any value within the above two numerical ranges; the second positive electrode active material may account for 20%, 25%, 30%, or 35% of the total mass of the positive electrode active material, or any value within the above two numerical ranges.

[0063] According to some embodiments of the present application, the value range of T1 is 0.3%-5.5%, and the value range of T2 is 1%-7%.

[0064] According to some embodiments of the present application, the value range of T1 is 0.5%-4%, the value range of T2 is 3%-6.5%, and optionally, T2-T1≥1%.

[0065] Exemplarily, T1 can be 0.3%, 0.5%, 1%, 2%, 3%, 4%, 4.5% or 5.5%, or any value between the above two values; T2 can be 1%, 2%, 3%, 4%, 5%, 6%, 2.5%, 6.5% or 7%, or any value between the above two values.

[0066] The first positive electrode active material can be a single positive electrode active material, or it can include two or even more positive electrode active materials with different shrinkage rates. The shrinkage rate of each positive electrode active material meets the shrinkage rate difference requirement with the second positive electrode active material. The shrinkage rate difference between the positive electrode active materials in the first positive electrode active material is 0 to 0.5%. Exemplarily, the shrinkage rate difference between the first positive electrode active materials can be 0, 0.1%, 0.2%, 0.3%, 0.4% or 0.5%.

[0067] Similarly, the second positive electrode active material can be a positive electrode active material, or it can include two or even more positive electrode active materials with different shrinkage rates. The shrinkage rate of each positive electrode active material meets the shrinkage rate difference requirement with the second positive electrode active material. The shrinkage rate difference between the positive electrode active materials in the second positive electrode active material is 0 to 1%. Exemplarily, the shrinkage rate difference between the second positive electrode active materials can be 0, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8% or 1%.

[0068] In one embodiment, the first positive electrode active material includes a positive electrode active material with a shrinkage rate of T1a and a positive electrode active material with a shrinkage rate of T1b, and the second positive electrode active material includes a positive electrode active material with a shrinkage rate of T2a and a positive electrode active material with a shrinkage rate of T2b, wherein T2b ≥ T2a > T1b ≥ T1a, and T2a - T1b ≥ 0.3%. The difference between T1b and T1a is 0 to 0.5%, and the difference between T2b and T2a is 0 to 1%. Optionally, the first positive electrode active material is a single positive electrode active material, T1a = T1b, and the shrinkage rate of the first positive electrode active material can be considered a unique value. The second positive electrode active material is a single positive electrode active material, T2a = T2b, and the shrinkage rate of the second positive electrode active material can be considered a unique value.

[0069] According to some embodiments of the present application, in the mixed active material layer, the sum of the mass of the first positive electrode active material and the second positive electrode active material is 90% to 100% of the total mass of the positive electrode active material; alternatively, the sum of the mass of the first positive electrode active material and the second positive electrode active material is 95% to 100% of the total mass of the positive electrode active material; alternatively, in the mixed active material layer, the sum of the mass of the first positive electrode active material and the second positive electrode active material is 98% to 100% of the total mass of the positive electrode active material. Exemplarily, the sum of the mass of the first positive electrode active material and the second positive electrode active material can be 90%, 92%, 95%, 96%, 97%, 98%, 99% or 100% of the total mass of the positive electrode active material, or any value within the above two numerical ranges.

[0070] In the mixed active material layer, the proportion of the first positive electrode active material (T1) with a small shrinkage rate or the second positive electrode active material (T2) with a large shrinkage rate is more than 55%, and the total proportion of these two types of positive electrode active materials reaches more than 90%. A small amount of positive electrode active material with a shrinkage rate between T1 and T2 can be allowed to exist.

[0071] According to some embodiments of the present application, the average particle size R2 of the second positive electrode active material is greater than the average particle size R1 of the first positive electrode active material, and R2 / R1≥2, which can be optionally 100≥R2 / R1≥5, or optionally 100≥R2 / R1≥10, R1 can be any value between 0.1μm and 0.4μm, and R2 can be any value between 1μm and 20μm.

[0072] According to some embodiments of the present application, the active material layer includes at least two sub-layers, wherein at least one sub-layer is a mixed active material layer.

[0073] By structurally designing the positive electrode sheets of lithium-ion batteries, we can obtain layered and optimized positive electrode sheets. Positive electrode active materials with different shrinkage rates are matched in a certain mass ratio, which is beneficial to improving the dynamics and life of the sheet.

[0074] In some embodiments of the present application, the two adjacent sub-layers are respectively a first mixed active material layer and a second mixed active material layer, the shrinkage rate of the first positive electrode active material in the first mixed active material layer is T1, the shrinkage rate of the second positive electrode active material is T2, T2-T1≥0.3%, the positive electrode active material in the second mixed active material layer includes a third positive electrode active material and a fourth positive electrode active material, the shrinkage rate of the third positive electrode active material is T1', the shrinkage rate of the fourth positive electrode active material is T2', T2'-T1'≥0.3%.

[0075] The active material layer in this application has a layered structure, which means that the active material layer includes two or more sublayers with a clear dividing line. The dividing line refers to the difference in composition between two adjacent sublayers, forming a dividing line at the contact position. The contact position of the two adjacent layers may intersect, i.e., forming a transition layer. For example, the two sublayers contain different positive electrode active materials, for example, the second positive electrode active material with a larger shrinkage rate in the two adjacent sublayers is a different substance, and the first positive electrode active material with a smaller shrinkage rate in the two adjacent sublayers is a different substance; or, the proportions of the positive electrode active materials in the two sublayers are different, for example, the proportions of the second positive electrode active material with a larger shrinkage rate in the two adjacent sublayers are different.

[0076] The first mixed active material layer on one side of the dividing line contains a first positive electrode active material (T1) with a small shrinkage rate during charging and discharging and a second positive electrode active material (T2) with a large shrinkage rate, T2-T1≥0.3%, and the mass of the first positive electrode active material (T1) with a small shrinkage rate or the second positive electrode active material (T2) with a large shrinkage rate accounts for a large proportion, accounting for 55% to 95% of the total mass of the positive electrode active materials in the first mixed active material layer; the second mixed active material layer on the other side of the dividing line also contains a third positive electrode active material (T1') with a small shrinkage rate during charging and discharging and a fourth positive electrode active material (T2') with a large shrinkage rate, T2'-T1'≥0.3%, and the mass of the third positive electrode active material (T1') with a small shrinkage rate or the fourth positive electrode active material (T2') with a large shrinkage rate accounts for a large proportion, accounting for 55% to 95% of the total mass of the positive electrode active materials in the second mixed active material layer.

[0077] The second positive electrode active material with a large shrinkage rate in the two mixed active material layers can be the same substance or different substances, and the first positive electrode active material with a small shrinkage rate in the two mixed active material layers can be the same substance or different substances.

[0078] It can be adjusted according to performance design requirements to give full play to the advantages of layered design.

[0079] In some embodiments of the present application, the difference between T2 and T1' is no greater than 1%, and / or the difference between T2' and T1 is no greater than 1%.As an alternative, the shrinkage difference of the positive electrode active materials in the two mixed active material layers is small.

[0080] In some embodiments of the present application, the first hybrid active material layer is closer to the current collector than the second hybrid active material layer, and the value of T2-T1 is less than the value of T2'-T1'. Optionally, the difference between T2 and T1 of the hybrid active material layers on the same side gradually increases from the direction adjacent to the current collector to the direction away from the current collector. By setting the difference between T2 and T1 of the hybrid active material layers at different locations to be different, the advantages of the layered design can be fully utilized.

[0081] In some embodiments of the present application, the two adjacent sub-layers are a mixed active material layer and a single active material layer, respectively. The positive electrode active material of the single active material layer includes a first positive electrode active material or a second positive electrode active material, and the mass of the first positive electrode active material or the second positive electrode active material is 90% to 100% of the total mass of the positive electrode active material.

[0082] The mixed active material layer on one side of the dividing line contains a first positive electrode active material (T1) with a small shrinkage rate and a second positive electrode active material (T2) with a large shrinkage rate during the charge and discharge process, and the mass of the first positive electrode active material (T1) with a small shrinkage rate or the second positive electrode active material (T2) with a large shrinkage rate accounts for a relatively large proportion; the positive electrode active material of the single active material layer on the other side of the dividing line contains the first positive electrode active material or the second positive electrode active material (T1 or T2), which can be adjusted according to performance design requirements to give full play to the advantages of the layered design.

[0083] In some embodiments of the present application, in a single active material layer, the mass of the first positive electrode active material or the second positive electrode active material is 95% to 100% of the total mass of the positive electrode active material; alternatively, the mass of the first positive electrode active material or the second positive electrode active material is 98% to 100% of the total mass of the positive electrode active material. For example, the sum of the masses of the first positive electrode active material or the second positive electrode active material in a single active material layer can be 95%, 96%, 97%, 98%, 99%, or 100% of the total mass of the positive electrode active material, or any value within the above two numerical ranges.

[0084] In some embodiments of the present application, the single active material layer is closer to the current collector than the mixed active material layer.

[0085] In some embodiments of the present application, the positive electrode active material of the single active material layer includes a first positive electrode active material.

[0086] In some embodiments of the present application, active material layers are disposed on both sides of the current collector; optionally, the active material layers on both sides of the current collector are symmetrical with respect to the current collector. All sublayers are symmetrically disposed with respect to the current collector, and the two symmetrical sublayers are made of the same material and thickness.

[0087] In some embodiments, the positive electrode active material is selected from lithium nickel cobalt manganese oxide (NCM), lithium nickel cobalt aluminum oxide (NCA), quaternary material (NCMA), lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP), modified and doped lithium manganese iron phosphate, lithium cobalt oxide (LCO), lithium manganese oxide (LMO), lithium-rich cathode material (Li-rich cathode) and lithium nickel manganese oxide, as well as at least one of the doped or coated materials of the above materials.

[0088] In some embodiments of the present application, the first positive electrode active material includes at least one of a spinel structure positive electrode material or an olivine structure positive electrode material.

[0089] The first positive electrode active material includes at least one of a spinel structure positive electrode material and an olivine structure positive electrode material, which makes it easy to obtain a positive electrode active material layer with a small shrinkage rate.

[0090] In some embodiments of the present application, the first positive electrode active material includes Li 1+x Mn 1-y A y P 1-z R z O4, wherein x is any value in the range of -0.100 to 0.100, y is any value in the range of 0.001 to 0.500, z is any value in the range of 0.001 to 0.100, A includes one or more elements selected from the group consisting of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and R includes one or more elements selected from the group consisting of B, S, Si and N.

[0091] Compound Li 1+x Mn 1-y A y P 1-z R z O4 can be purchased from the market or prepared according to the following preparation method: 1+x Mn 1-y A y P 1-z R z The preparation method of O4 may include the following steps:

[0092] (1) dissolving a manganese source, a source of element A to be doped at the manganese position, and an acid in a solvent and stirring to generate a suspension of a manganese salt doped with element A, filtering the suspension and drying the filter cake to obtain a manganese salt doped with element A;

[0093] (2) adding a lithium source, a phosphorus source, an element R source, a solvent, and the manganese salt doped with element A obtained in step (1) into a reaction vessel, grinding and mixing to obtain a slurry;

[0094] (3) transferring the slurry obtained in step (2) to a spray drying device for spray drying and granulation to obtain granules;

[0095] (4) Sintering the particles obtained in step (3) to obtain a positive electrode active material.

[0096] In any embodiment, the manganese source may be a manganese-containing substance known in the art that can be used to prepare lithium manganese phosphate. For example, the manganese source may be selected from elemental manganese, manganese dioxide, manganese phosphate, manganese oxalate, manganese carbonate, or a combination thereof.

[0097] The acid is selected from one or more of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and organic acids such as oxalic acid, and may be, for example, oxalic acid. The source of element R is selected from at least one of sulfates, borates, nitrates, and silicates of element R. The source of element A is selected from at least one of a simple substance, oxide, phosphate, oxalate, carbonate, and sulfate of A.

[0098] Furthermore, in some embodiments of the present application, the first positive electrode active material includes Li a A e Mn 1-f B f P 1-g C g O 4-n D n ;

[0099] wherein A comprises one or more elements selected from the group consisting of Zn, Al, Na, K, Mg, Nb, Mo, and W;

[0100] B includes one or more elements selected from the group consisting of Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge;

[0101] C includes one or more elements selected from B, S, Si and N;

[0102] D includes one or more elements selected from the group consisting of S, F, Cl, and Br;

[0103] a is selected from the range of 0.9 to 1.1, e is selected from the range of 0.001 to 0.1, f is selected from the range of 0.001 to 0.5, g is selected from the range of 0.001 to 0.1, n is selected from the range of 0.001 to 0.1, and the first positive active material is electrically neutral.

[0104] It should be noted that Li a A x Mn 1-y B y P 1-z C z O 4-n D n The compound is actually a specific LiMPO4 material, and its preparation method can refer to Li 1+x Mn 1-y A y P 1-z R z O4, no limitation here.

[0105] The second positive electrode active material includes a layered structure positive electrode material, which makes it easy to obtain a positive electrode active material layer with a large shrinkage rate.

[0106] Furthermore, in some embodiments of the present application, the second positive electrode active material includes at least one of a ternary material of lithium nickel cobalt manganese oxide, a ternary material of lithium nickel cobalt aluminum oxide, or a doped modified ternary material.

[0107] Furthermore, in some embodiments of the present application, the chemical formula of the above-mentioned doped modified ternary material includes LiNi mCo i Mn k A 1-m-i-k O2, where 0.5≤m≤0.98, 0.02≤i≤0.18, 0≤k≤0.35.

[0108] In some embodiments, the mixed active material layer contains a linear conductive agent (having an aspect ratio greater than 1). Optionally, the weight percentage of the linear conductive agent with a length of 1 μm or greater in the mixed active material layer is 0.2% to 1%. Optionally, the linear conductive agent comprises at least one of carbon nanotubes, carbon fibers, and linear graphene. The mixed active material layer contains a certain proportion of the linear conductive material to maintain the stability of the conductive network.

[0109] In some embodiments, the active material layer includes at least two sublayers, and among the two adjacent sublayers, the porosity of the sublayer away from the current collector is ≥30%, and the porosity of the sublayer adjacent to the current collector is ≥50%; optionally, the porosity of the sublayer away from the current collector is ≥50%, and the porosity of the sublayer adjacent to the current collector is ≥60%.

[0110] Porosity refers to the proportion of pore volume existing in the active material layer before it is charged and discharged. According to the embodiments of the present application, the porosity can be determined by the gas replacement method. Specifically, according to the embodiments of the present application, it can be determined by referring to GB / T 24586-2009 through the following steps: immerse the electrode in dimethyl carbonate (DMC), clean and dry it. If it is a fresh electrode, it does not need to be cleaned. Put the sample into the sample cup, record the number of samples to calculate the apparent volume, place the sample in a true density tester, and measure the true volume using the gas replacement method. The electrode porosity is the percentage of the pore volume in the electrode to the total volume of the electrode. The calculation formula is: Porosity = (V-V0) / V×100%, where V0 is the true volume and V is the apparent volume; Apparent volume V = S*H*A, S is the surface area of ​​the electrode, H is the thickness of the electrode, and A is the number of electrode samples.

[0111] Optionally, in two adjacent sublayers, the porosity of the sublayer away from the current collector can be 30%, 40%, 50%, 60% or 70%, and the porosity of the sublayer adjacent to the current collector can be 50%, 55%, 60%, 65%, 70% or 75%.

[0112] In some embodiments, the mass ratio of the positive electrode active material in the sub-layer is 89.0% to 98.0%.

[0113] In some embodiments, the sublayers of the positive electrode sheet are prepared by a positive electrode slurry including the positive electrode active material, the conductive agent and the binder that comply with the above-mentioned design principles. The positive electrode active material in the sublayer accounts for 89.0% to 98.0% of the total mass of the sublayer, the conductive agent accounts for 0.4% to 5.0% of the total mass of the positive electrode sheet, and the binder accounts for 0.6%-7.0% of the total mass of the positive electrode sheet.

[0114] As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0115] As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0116] To meet actual production needs, the coating area of ​​each sub-layer is 1540.25mm 2 The minimum coating weight is 50 mg, generally 50-200 mg.

[0117] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0118] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0119] According to some embodiments of the present application, the present application further provides a battery comprising a cell consisting of a negative electrode sheet, a separator, and the above-mentioned positive electrode sheet. The battery includes any form of a single cell, a battery module, or a battery pack.

[0120] [Negative electrode]

[0121] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0122] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0123] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0124] In some embodiments, the negative electrode active material may be a negative electrode active material for a battery that is well known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0125] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0126] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0127] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0128] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0129] [Isolation film]

[0130] The present application has no particular limitation on the type of isolation membrane, and any known isolation membrane with a porous structure having good chemical stability and mechanical stability can be selected.

[0131] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0132] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0133] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0134] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0135] [Electrolytes]

[0136] The battery cell also includes an electrolyte, which conducts ions between the positive and negative electrodes. The electrolyte can be in liquid or gel form.

[0137] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0138] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0139] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0140] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0141] According to some embodiments of the present application, the present application provides an electrical device, including the battery cell provided above or the battery provided above.

[0142] Next, one or more embodiments will be described in more detail with reference to the following examples. Of course, these examples do not limit the scope of one or more embodiments.

[0143] Among the positive electrode active materials used in the experiment, the first material is LiMn 1-y1-y2 Fe y1 Ti y2 P 1-z Si z O4, where y1+y2 is any value in the range of 0.001 to 0.500, z is any value in the range of 0.001 to 0.100, and the material composition of different shrinkage rates is slightly different; the second material is Li 1.00 Ni m Co i Mn k O2, where 0.5≤m≤0.98, 0.02≤i≤0.18, 0≤k≤0.35,

[0144] m+i+k=1, and the material compositions of different shrinkage rates are slightly different.

[0145] The following lists some preparation methods and sources of positive electrode active materials to better illustrate this application.

[0146]

First Material

[0147] A. Compound LiMn 0.22 Fe 0.78 The preparation method of PO4 includes:

[0148] Step S1: Preparation of Fe-doped manganese oxalate

[0149] 252.9g of manganese carbonate and 903.7g of ferrous carbonate were added to a mixer and thoroughly mixed for 6 hours. The resulting mixture was then transferred to a reactor, and 5L of deionized water and 1260.6g of oxalic acid dihydrate were added. The mixture was heated to 80°C and stirred at 500 rpm for 6 hours, mixing until the reaction terminated and no bubbles were generated, resulting in an Fe-doped manganese oxalate suspension. The suspension was then filtered, dried at 120°C, and sand-milled to obtain ferromanganese oxalate particles.

[0150] Step S2: Preparation of LiMn 0.22 Fe 0.78 PO4

[0151] Take the manganese oxalate iron (C2O4Mn 0.22 Fe 0.78 1791.4 g of 2H2O (calculated as 2H2O), 369.4 g of lithium carbonate, and 1150.1 g of ammonium dihydrogen phosphate were added to 20 L of deionized water, stirred thoroughly, and uniformly mixed at 80°C for 10 hours to obtain a slurry. The slurry was transferred to a spray dryer for spray drying and granulation, and then dried at 250°C to obtain a powder. The powder was sintered in a roller kiln at 700°C for 4 hours in a protective atmosphere (90% nitrogen and 10% hydrogen).

[0152] Carbon-coated LiMn 0.22 Fe 0.78 The preparation method of PO4 includes:

[0153] Take the manganese oxalate iron (C2O4Mn 0.22 Fe 0.78 1791.4 g of 1% nitric acid (based on 2H2O), 369.4 g of lithium carbonate, 1150.1 g of ammonium dihydrogen phosphate, and 0.005 mol of sucrose were added to 20 L of deionized water, stirred thoroughly, and uniformly mixed at 80°C for 10 hours to obtain a slurry. The slurry was transferred to a spray dryer for spray drying and granulation, and then dried at 250°C to obtain a powder. The powder was sintered in a roller kiln at 700°C for 4 hours in a protective atmosphere (90% nitrogen and 10% hydrogen).

[0154] The preparation steps of other undoped lithium manganese iron phosphate materials are the same as those of the aforementioned compound A, with the only difference being that the contents of manganese carbonate and ferrous carbonate are changed to satisfy the molar ratio of manganese to iron in the chemical formula of the corresponding compound.

[0155] You can also buy it directly from the market.

[0156] B. Compound Li 1.001 Mn 0.999 Fe0.001 P 0.999 Si 0.001 The preparation method of O4 includes:

[0157] Step S1: Preparation of Fe-doped manganese oxalate

[0158] 1148.2g of manganese carbonate and 1.2g of ferrous carbonate were added to a mixer and thoroughly mixed for 6 hours. The resulting mixture was then transferred to a reactor, and 5L of deionized water and 1260.6g of oxalic acid dihydrate were added. The mixture was heated to 80°C and stirred at 500 rpm for 6 hours, mixing until the reaction terminated and no bubbles were generated, resulting in an Fe-doped manganese oxalate suspension. The suspension was then filtered, dried at 120°C, and sand-milled to obtain ferromanganese oxalate particles.

[0159] Step S2: Preparation of Li 1.001 Mn 0.999 Fe 0.001 P 0.999 Si 0.001 O4

[0160] Take the manganese oxalate iron (C2O4Mn 0.999 Fe 0.001 1789.6 g of 2H2O (calculated as 2H2O), 369.8 g of lithium carbonate, 1148.9 g of ammonium dihydrogen phosphate, and 0.8 g of silicic acid were added to 20 L of deionized water, stirred thoroughly, and uniformly mixed at 80°C for 10 hours to obtain a slurry. The slurry was transferred to a spray dryer for spray drying and granulation, and then dried at 250°C to obtain a powder. The powder was sintered in a roller kiln at 700°C for 4 hours in a protective atmosphere (90% nitrogen and 10% hydrogen).

[0161] The preparation steps of lithium manganese iron phosphate materials doped with other elements (such as Ti) are the same as the preparation steps of the aforementioned compound B. The only difference is that silicic acid is replaced as the source of the corresponding element (such as titanium tetrachloride) and the raw material ratio is adjusted to meet the molar ratio in the chemical formula of the corresponding compound.

[0162] It can also be purchased directly from the market.

[0163]

Second material

[0164] The layered structure positive electrode material was purchased from the market.

[0165] Example 1

[0166] (1) Preparation of positive electrode sheet

[0167] The positive electrode active material, the binder PVDF, and the conductive agent carbon black are mixed in a mass ratio of 97wt%:1.5wt%:1.5wt% and dispersed in N-methylpyrrolidone. The positive electrode active material is divided into a first material and a second material. The average particle size of the first material is 0.2μm, the average particle size of the second material is 1μm, and the first material is Li 1.00 Mn 0.36 Fe 0.64 PO4, whose shrinkage rate T1 is 2.5%, and the second material is Li 1.00 Ni 0.59 Co 0.14 Mn 0.27 O2, its shrinkage rate T2 is 3%, and the mass ratio of the first material to the second material is 35%:65%, and the positive electrode active material slurry A1 is prepared.

[0168] The positive electrode active material slurry A1 was coated on both sides of the aluminum foil with a coating weight of 200 mg / 1540.25 mm 2 , and obtain the positive electrode.

[0169] (2) Preparation of lithium-ion secondary batteries

[0170] Lithium-ion secondary batteries are composed of a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, along with mechanical components such as an aluminum casing and a top cover. The positive electrode sheet has a compression ratio of 2.35 and a thickness of 213μm. The negative electrode material comprises the following components: 96.5% graphite, 1.3% SBR, 1.1% CMC, and 0.4% SP, with a compression ratio of 1.65 and a thickness of 142μm. The electrolyte comprises the following components: a mixture of ethylene carbonate, dimethyl carbonate, and 1,2-propylene glycol carbonate in a volume ratio of 1:1:1, followed by a uniform dissolution of LiPF6 in the solution to produce an electrolyte. The LiPF6 concentration in this electrolyte is 1 mol / L. Specifically, the positive electrode sheet, negative electrode sheet and separator are formed into a bare battery cell, the bare battery cell is insulated and then placed in an aluminum shell, and the top cover is welded to obtain a dry battery cell; the dry battery cell is baked and injected with electrolyte, and is subjected to formation and aging to obtain a hard shell battery.

[0171] Example 2

[0172] (1) Preparation of positive electrode sheet

[0173] The positive electrode active material, the binder PVDF, and the conductive agent carbon black are mixed in a mass ratio of 97wt%:1.5wt%:1.5wt% and dispersed in N-methylpyrrolidone. The positive electrode active material is divided into a first material and a second material. The average particle size of the first material is 0.2μm, the average particle size of the second material is 1μm, and the first material is Li 1.00 Mn 0.36Fe 0.64 PO4, whose shrinkage rate T1 is 2.5%, and the second material is Li 1.00 Ni 0.59 Co 0.14 Mn 0.27 O2, its shrinkage rate T2 is 3%, and the mass ratio of the first material to the second material is 35%:65%, and the positive electrode active material slurry A1 is prepared.

[0174] The positive electrode active material, the binder PVDF, and the conductive agent carbon black are mixed in a mass ratio of 97wt%:1.5wt%:1.5wt% and dispersed in N-methylpyrrolidone. The positive electrode active material is divided into a first material and a second material. The average particle size of the first material is 0.2μm, the average particle size of the second material is 1μm, and the first material is Li 1.00 1Mn 0.999 Fe 0.001 P 0.999 Si 0.001 O4, its shrinkage rate T1' is 3.2%, and the second material is Li 1.00 Ni 0.82 Co 0.12 Mn 0.06 O2, its shrinkage rate T2' is 5%, and the mass ratio of the first material to the second material is 35%:65%, and the positive electrode active material slurry A2 is prepared.

[0175] The positive electrode active material slurry A1 was coated on both sides of the aluminum foil with a coating weight of 100 mg / 1540.25 mm 2 , the positive electrode active material slurry A2 is coated on the positive electrode surface coated with the positive electrode active material slurry A1, and the coating weight is 100 mg / 1540.25 mm 2 , and obtain the positive electrode.

[0176] (2) Preparation of lithium-ion secondary batteries

[0177] Lithium-ion secondary batteries are composed of a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, along with mechanical components such as an aluminum casing and a top cover. The positive electrode sheet has a compression ratio of 2.35 and a thickness of 213μm. The negative electrode material comprises the following components: 96.5% graphite, 1.3% SBR, 1.1% CMC, and 0.4% SP, with a compression ratio of 1.65 and a thickness of 142μm. The electrolyte comprises the following components: a mixture of ethylene carbonate, dimethyl carbonate, and 1,2-propylene glycol carbonate in a volume ratio of 1:1:1, followed by a uniform dissolution of LiPF6 in the solution to produce an electrolyte. The LiPF6 concentration in this electrolyte is 1 mol / L. Specifically, the positive electrode sheet, negative electrode sheet and separator are formed into a bare battery cell, the bare battery cell is insulated and then placed in an aluminum shell, and the top cover is welded to obtain a dry battery cell; the dry battery cell is baked and injected with electrolyte, and is subjected to formation and aging to obtain a hard shell battery.

[0178] Example 3

[0179] Except that the mass ratio of the first material to the second material in forming the positive electrode active material slurry A1 in step (1) is 5%:95%, and the mass ratio of the first material to the second material in forming the positive electrode active material slurry A2 is 5%:95%, the rest is the same as in Example 2.

[0180] Example 4

[0181] Except that the mass ratio of the first material and the second material in forming the positive electrode active material slurry A1 in step (1) is 35%:65%, and the mass ratio of the first material and the second material in forming the positive electrode active material slurry A2 is 5%:95%, the rest is the same as in Example 2.

[0182] Example 5

[0183] Except that the first material of the positive electrode active material slurry A2 in step (1) is Li 1.00 Mn 0.36 Fe 0.64 PO4, its shrinkage rate T1' is 2.5%, and the second material is Li 1.00 Ni 0.59 Co 0.14 Mn 0.27 O2, its shrinkage rate T2' is 3% (the first material and the second material are the same as those in the positive electrode active material slurry A1), but the mass ratio of the first material and the second material is 20%:80%, and the rest is the same as Example 2.

[0184] Example 6

[0185] Except that the first material of the positive electrode active material slurry A1 in step (1) is Li 1.00 Mn0.36 Fe 0.64 PO4, whose shrinkage rate T1 is 2.5%, and the second material is Li 1.00 Ni 0.59 Co 0.14 Mn 0.27 O2, its shrinkage rate T2 is 3%, and the first material forming the positive electrode active material slurry A2 is Li 1.00 Mn 0.36 Fe 0.64 PO4, its shrinkage rate T1' is 2.5%, and the second material is Li 1.00 Ni 0.82 Co 0.12 Mn 0.06 O2, its shrinkage rate T2' is 5%, and the others are the same as those in Example 2.

[0186] Example 7

[0187] Except that the first material of the positive electrode active material slurry A1 in step (1) is Li 1.00 Mn 0.77 Fe 0.20 Ti 0.03 PO4, whose shrinkage rate T1 is 4.5%, and the second material is Li 1.00 Ni 0.89 Co 0.07 Mn 0.04 O2, its shrinkage rate T2 is 6.5%, and the first material forming the positive electrode active material slurry A2 is Li 1.00 Mn 0.22 Fe 0.78 PO4, its shrinkage rate T1' is 0.3%, and the second material is Li 1.00 Ni 0.89 Co 0.07 Mn 0.04 O2, its shrinkage rate T2' is 6.5%, and the others are the same as those in Example 2.

[0188] Example 8

[0189] Except that in step (1), the mass ratio of the first material and the second material in forming the positive electrode active material slurry A2 is 65%:35%, the rest is the same as in Example 2.

[0190] Example 9

[0191] In addition to coating the positive electrode active material slurry A2 on both sides of the aluminum foil in step (1), the positive electrode active material slurry A1 is coated on the surface of the positive electrode that has been coated with the positive electrode active material slurry A2, that is, A1 in this embodiment is A2 in Example 1, and A2 in this embodiment is A2 in Example 1, to obtain a positive electrode sheet, and the rest is the same as Example 2.

[0192] Example 10

[0193] In addition to step (1), the positive electrode active material, the binder PVDF, and the conductive agent carbon black are mixed in a mass ratio of 97wt%:1.5wt%:1.5wt% and dispersed in N-methylpyrrolidone. The positive electrode active material is divided into a first material and a second material. The first material is Li 1.00 Mn 0.36 Fe 0.64 PO4, its shrinkage rate T1* is 2.5%, and the second material is Li 1.00 Ni 0.82 Co 0.12 Mn 0.06 O2, its shrinkage rate T2* is 5%, and the mass ratio of the first material to the second material is 35%:65%, and the positive electrode active material slurry A3 is prepared.

[0194] The positive electrode active material slurry A1 was coated on both sides of the aluminum foil with a coating weight of 70 mg / 1540.25 mm 2 , the positive electrode active material slurry A2 is coated on the positive electrode surface coated with the positive electrode active material slurry A1, and the coating weight is 70mg / 1540.25mm 2 , the positive electrode active material slurry A3 is coated on the positive electrode surface coated with the positive electrode active material slurry A2, and the coating weight is 60mg / 1540.25mm 2 , and obtain the positive electrode.

[0195] The rest is the same as Example 2.

[0196] Example 11

[0197] In addition to step (1), the first material for forming the positive electrode active material slurry A1 is Li 1.00 Mn 0.36 Fe 0.64 PO4, its shrinkage rate T1 is 2.5%, the second material is divided into second material a and second material b, the second material a is Li 1.00 Ni 0.59 Co 0.14 Mn 0.27 O2, its shrinkage rate T2a is 3%, and the second material b is Li 1.00 Ni 0.82 Co 0.12 Mn 0.06 O2, whose shrinkage rate T2b is 5%, and the mass ratio of the first material to the second material is 35%: (30% + 35%);

[0198] The positive electrode active material slurry A2 is formed using the same materials as the above-mentioned positive electrode active material slurry A2, but the mass ratio of the first material to the second material is 40%: (40%+20%).

[0199] The rest is the same as Example 2.

[0200] Example 12

[0201] Except that the positive electrode active material used to form the positive electrode active material slurry A2 in step (1) is the first material used to form the positive electrode active material slurry A1, the rest is the same as that of Example 2.

[0202] Example 13

[0203] Except that the positive electrode active material used to form the positive electrode active material slurry A2 in step (1) is the second material used to form the positive electrode active material slurry A1, the rest is the same as that of Example 2.

[0204] Example 14

[0205] Except that the mass ratio of the first material and the second material in forming the positive electrode active material slurry A1 in step (1) is 65%:35%, the rest is the same as in Example 1.

[0206] Example 15

[0207] Except that the mass ratio of the first material to the second material in forming the positive electrode active material slurry A1 in step (1) is 65%:35%, and the mass ratio of the first material to the second material in forming the positive electrode active material slurry A2 is 65%:35%, the rest is the same as in Example 2.

[0208] Example 16

[0209] The process was the same as that of Example 1 except that the average particle size of the first material and the average particle size of the second material in forming the positive electrode active material slurry A1 in step (1) was 0.5 μm and 1 μm, respectively.

[0210] Example 17

[0211] The process was the same as that of Example 1 except that the average particle size of the first material and the average particle size of the second material in forming the positive electrode active material slurry A1 in step (1) was 0.2 μm and 2 μm, respectively.

[0212] Comparative Example 1

[0213] Except that in step (1), the mass ratio of the first material and the second material to form the positive electrode active material slurry A1 is 50%:50%, and the mass ratio of the first material and the second material to form the positive electrode active material slurry A2 is 50%:50%, the rest is the same as Example 2.

[0214] Comparative Example 2

[0215] Except that in step (1), the mass ratio of the first material and the second material in forming the positive electrode active material slurry A1 is 50%:50%, the rest is the same as in Example 1.

[0216] In order to demonstrate the effect of expansion rate on battery performance, the average particle size of all first materials used in Examples 1 to 15 and Comparative Examples 1 to 2 was 0.2 μm, and the average particle size of all second materials was 1 μm. The hard-shell batteries obtained in Examples 1 to 13 and Comparative Examples 1 to 2 were subjected to cycle testing:

[0217] At a constant temperature of 25°C, charge the full battery at 1C to 4.3V, then charge at a constant voltage at 4.3V until the current is less than or equal to 0.05mA. Let it rest for 5 minutes, then discharge it at 1C to 2.5V. Record the discharge capacity at this point as D0 and the impedance as X0. Repeat the above charge and discharge cycle for 500 cycles, recording the final discharge capacity as D1 and the impedance as X1. Calculate the capacity retention as D1 / D0 × 100%, and the impedance growth rate as (D1-D0) / D0 × 100%.

[0218] The performance of the battery tested is shown in Table 1:

[0219] Table 1 Battery performance

[0220] Combined with the results in Table 1, we can see that:

[0221] Compared with Comparative Examples 1 to 2, the active material layer of the positive electrode sheets of Examples 1 to 15 contains at least one layer of positive electrode active materials with a large shrinkage rate and a small shrinkage rate, and a mixed positive electrode material layer formed by a large mass proportion of the large shrinkage rate material or the small shrinkage rate material. This can effectively improve the kinetic performance of the battery, and after the battery is cycled multiple times, it can increase the capacity retention rate of the battery and reduce the impedance growth of the battery, that is, improve the kinetic performance of the battery.

[0222] Compared with Comparative Example 2, the positive electrode sheet active material layer of Example 1 is a mixed positive electrode material layer composed of positive electrode active materials with high and low shrinkage rates at a high and low mass ratio, which can significantly improve the battery's dynamic performance. The active material layer of Example 14 is a mixed positive electrode material layer composed of positive electrode active materials with low and high shrinkage rates at a high and low mass ratio, which can also improve the battery's dynamic performance.

[0223] Compared to the layered structure of the active material layer in the positive electrode sheet of Comparative Example 1, the positive electrode sheet of Example 8 has one layer that meets the shrinkage difference requirements for the positive electrode active materials with large and small shrinkage rates, and the positive electrode active material with large shrinkage rate accounts for a large proportion, which can improve the battery's kinetic performance. The positive electrode sheet of Example 2 has two layers that meet the shrinkage difference requirements for the positive electrode active materials with large and small shrinkage rates, and the positive electrode active material with large shrinkage rate accounts for a large proportion, which can significantly improve the battery's kinetic performance. The active material layers of the positive electrode sheet of Example 15 are arranged in layers, and each layer is a mixed positive electrode material layer formed by the positive electrode active materials with small and large shrinkage rates in a high and low mass ratio, which can also improve the battery's kinetic performance.

[0224] Compared with Comparative Example 1, the positive electrode sheets of Examples 2 to 5 are provided with two layers of mixed positive electrode material layers, and the mass proportion of the positive electrode active material with a large shrinkage rate in the positive electrode active material of the mixed positive electrode material layer is 55% to 95%, which can be optionally 65% ​​to 80%. After the battery is cycled multiple times, the capacity retention rate of the battery can be improved and the impedance growth of the battery can be reduced.

[0225] Compared with Example 9, the difference in shrinkage rates between the positive electrode active materials with large shrinkage rates and small shrinkage rates in the mixed active material layer adjacent to the current collector side of the positive electrode plate of Example 2 is smaller than the difference in shrinkage rates on the side away from the current collector, which can improve the capacity retention rate of the battery and reduce the impedance growth of the battery.

[0226] Compared with Comparative Example 1, the positive electrode plate of Example 10 adopts multiple layers of mixed positive electrode material layers, and each layer of the mixed positive electrode material layer of the positive electrode plate of Example 11 adopts multiple positive electrode active materials, and the positive electrode active materials with large shrinkage rates account for a large proportion, both of which can improve the capacity retention rate of the battery and reduce the impedance growth of the battery.

[0227] Compared with Comparative Example 1, the positive electrode sheets of Examples 12 to 13 are provided with adjacent mixed active material layers and single active material layers containing only one type of positive electrode active material. The positive electrode active material of the single active material layer is a type of positive electrode active material in the mixed active material layer, which can improve the capacity retention rate of the battery and reduce the impedance growth of the battery after the battery is cycled multiple times, that is, improve the kinetic performance of the battery.

[0228] All first materials used in Example 1, Examples 16-17, and Comparative Example 2 were identical, with a shrinkage of 2.5%. All second materials were identical, with a shrinkage of 3%. The differences were that the average particle size R1 of the first material and the average particle size R2 of the second material were not identical, or that the mass ratio of the first material to the second material was different. Cycling tests were performed on the hard-shell batteries obtained in Examples 16-17 using the same method as described above. The performance of the batteries obtained is shown in Table 2:

[0229] Table 2 Battery performance

[0230] Combined with the results in Table 2, we can see that:

[0231] The positive electrode active material in the mixed active layer is a second material with a large shrinkage rate and a first material with a small shrinkage rate, and the average particle size (R2) of the second material and the average particle size (R1) of the first material are mixed according to R2 / R1≥2, R2 / R1≥5 and R2 / R1≥10 can be selected. After the battery is recycled for many times, the capacity retention rate of the battery can be improved and the impedance growth of the battery can be reduced, that is, the dynamic performance of the battery can be improved.

[0232] The embodiments described above are part of the embodiments of the present application, rather than all of the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

Claims

1. A positive electrode sheet, characterized in that: It includes a current collector and an active material layer arranged on at least one side surface of the current collector, the active material layer includes at least one mixed active material layer; in the mixed active material layer, the positive electrode active material includes a first positive electrode active material and a second positive electrode active material, the shrinkage rate T2 of the second positive electrode active material is greater than the shrinkage rate T1 of the first positive electrode active material, and T2-T1≥0.3%, and the proportion of the first positive electrode active material or the second positive electrode active material is 55% to 95% of the total mass of the positive electrode active material in the mixed active material layer.

2. The positive electrode sheet according to claim 1, characterized in that: In the mixed active material layer, the first positive electrode active material or the second positive electrode active material accounts for 65% to 80% of the total mass of the positive electrode active material.

3. The positive electrode sheet according to claim 1 or 2, characterized in that: The value range of T1 is 0.3%-5.5%, and the value range of T2 is 1%-7%.

4. The positive electrode sheet according to any one of claims 1 to 3, characterized in that: The value range of T1 is 0.5%-4%, and the value range of T2 is 3%-6.5%.

5. The positive electrode sheet according to any one of claims 1 to 4, characterized in that: The average particle size R2 of the second positive electrode active material is greater than the average particle size R1 of the first positive electrode active material, and R2 / R1≥2, optionally, 100≥R2 / R1≥5, optionally, 100≥R2 / R1≥10.

6. The positive electrode sheet according to any one of claims 1 to 5, characterized in that: The active material layer includes at least two sub-layers, wherein at least one of the sub-layers is the mixed active material layer.

7. The positive electrode sheet according to claim 6, characterized in that: The two adjacent sublayers are respectively a first mixed active material layer and a second mixed active material layer, the shrinkage rate of the first positive electrode active material in the first mixed active material layer is T1, the shrinkage rate of the second positive electrode active material is T2, T2-T1≥0.3%, the positive electrode active material in the second mixed active material layer includes a third positive electrode active material and a fourth positive electrode active material, the shrinkage rate of the third positive electrode active material is T1', the shrinkage rate of the fourth positive electrode active material is T2', T2'-T1'≥0.3%.

8. The positive electrode sheet according to claim 7, characterized in that: The difference between T2 and T1' is not greater than 1%, and / or the difference between T2' and T1 is not greater than 1%.

9. The positive electrode sheet according to claim 7, characterized in that: The first mixed active material layer is closer to the current collector than the second mixed active material layer, and the value of T2-T1 is smaller than the value of T2'-T1'.

10. The positive electrode sheet according to claim 6, characterized in that: One of the two adjacent sublayers is the mixed active material layer, and the other is a single active material layer. The positive electrode active material of the single active material layer includes the first positive electrode active material or the second positive electrode active material.

11. The positive electrode sheet according to claim 10, characterized in that: The single active material layer is closer to the current collector than the mixed active material layer.

12. The positive electrode sheet according to claim 10, characterized in that: The positive electrode active material of the single active material layer includes the first positive electrode active material.

13. The positive electrode sheet according to claim 6, characterized in that: The mixed active material layer contains a linear conductive agent; optionally, in the mixed active material layer, the mass proportion of the linear conductive agent with a length ≥1 μm is 0.2% to 1%; optionally, the linear conductive agent includes at least one of carbon nanotubes, carbon fibers and linear graphene.

14. The positive electrode sheet according to claim 6, characterized in that: Among the two adjacent sub-layers, the porosity of the sub-layer on the side away from the current collector is ≥30%, and the porosity of the sub-layer on the side adjacent to the current collector is ≥50%; Optionally, the porosity of the sublayer on a side away from the current collector is ≥50%, and the porosity of the sublayer on a side adjacent to the current collector is ≥60%.

15. A battery, characterized in that: A battery cell comprising the positive electrode sheet as claimed in any one of claims 1 to 14.

16. An electrical device, characterized in that: Comprising a battery according to claim 15.

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