Positive pole piece, battery and electric device

Abstract

The invention provides a positive pole piece, a battery and an electric device. The positive pole piece comprises a current collector and an active layer; the active layer is arranged on at least one surface of the current collector, the active layer comprises a first active material layer and a second active material layer which are sequentially far away from the current collector in the thickness direction of the current collector, the first active material layer comprises a first material, the first material comprises a first active material, and the second active material comprises a second active material. The second active material layer comprises a second material, the second material comprises a second active material, and the structural stability of the first material is smaller than that of the second material. And the direct-current internal resistance growth rate of the battery is reduced.

Description

Technical Field

[0001] This application relates to the technical field of lithium batteries, and particularly to a positive electrode plate, a battery, and an electrical device. Background Art

[0002] Lithium-ion batteries are widely used in electric vehicles and consumer electronic products due to their advantages such as high energy density, high output power, long cycle life, and low environmental pollution. However, at present, lithium-ion batteries have the problem of a large growth rate of direct current internal resistance after multiple cycles of charge and discharge. Summary of the Invention

[0003] This application is made in view of the above problems, and its purpose is to provide a positive electrode plate, a battery, and an electrical device that can reduce the growth rate of the direct current internal resistance of the battery.

[0004] To achieve the above object, embodiments of this application provide a positive electrode plate, a battery, and an electrical device.

[0005] In a first aspect, embodiments of this application propose a positive electrode plate, including:

[0006] A current collector; and,

[0007] An active layer; disposed on at least one surface of the current collector, the active layer including a first active material layer and a second active material layer that are sequentially arranged away from the current collector in the thickness direction of the current collector,

[0008] Wherein, the first active material layer includes a first material, the first material includes a first active material, the second active material layer includes a second material, the second material includes a second active material, and the structural stability of the first material is less than that of the second material.

[0009] In embodiments of this application, the first active material layer in the positive electrode plate is relatively closer to the current collector, while the second active material layer is relatively farther from the current collector. During the charge and discharge cycle of the battery, the second material in the second active material layer (i.e., the outer layer) preferentially de-lithium ions. Therefore, embodiments of this application adopt that the structural stability of the first material in the first active layer (i.e., the inner layer) is less than that of the second material in the second active material layer (i.e., the outer layer), that is, the structural stability of the second material that preferentially de-lithium ions is stronger, so that after the charge and discharge cycle of the battery, the structure of the material in the outer layer is not easily damaged or collapsed, so that the de-inserted lithium ions can return to the raw material, and thus the growth rate of the direct current internal resistance of the battery can be reduced.

[0010] In any embodiment, the chemical formula of the first active material includes LiNi x Co y Mn 1-x-y O 2, the chemical formula of the second active material includes LiNi x Co z Mn 1-x-z O 2 , where 0 < x < 1, 0 ≤ y < 1, 0 < z < 1, and y < z. Thus, along the direction away from the current collector, the content of Co in the ternary material increases layer by layer. The increase in the content of Co is beneficial to reducing the occurrence of lithium-nickel mixing, improving the structural stability of the ternary material, and thus reducing the growth rate of the DC internal resistance of the battery.

[0011] In any embodiment, 0 ≤ y ≤ 0.1, 0.08 ≤ z ≤ 0.15; optionally, 0.05 ≤ y ≤ 0.07, 0.12 ≤ z ≤ 0.14. The values of y and z in a suitable range are beneficial to reducing the growth rate of the DC internal resistance of the battery.

[0012] In any embodiment, the chemical formula of the first active material includes LiNi x Co y Mn 1-x-y A m O 2 , the chemical formula of the second active material includes LiNi x Co y Mn 1-x-y A n O 2 , where 0 < x < 1, 0 ≤ y < 1, 0 < m < 1, 0 < n < 1, and m < n; A is a doping element, and A includes at least one of Al, Zr, B, Ti, Ce, Nb, W, and Mo. Thus, along the direction away from the current collector, the content of the doping element in the ternary material increases layer by layer. The increase in the content of the doping element is beneficial to improving the structural stability of the ternary material, and thus reducing the growth rate of the DC internal resistance of the battery.

[0013] In any embodiment, 0.0008 ≤ m ≤ 0.006, 0.003 ≤ n ≤ 0.012; optionally, 0.001 ≤ m ≤ 0.003, 0.006 ≤ n ≤ 0.008. The values of m and n in a suitable range are beneficial to reducing the growth rate of the DC internal resistance of the battery.

[0014] In any embodiment, both the first material and the second material are core-shell structures. The first material includes a first inner core and a first coating layer, the first active material is disposed in the first inner core, the second material includes a second inner core and a second coating layer, the second active material is disposed in the second inner core, and the thickness of the first coating layer is less than the thickness of the second coating layer. Thus, the second coating layer is thicker, which can inhibit the erosion of the side reaction on the material surface during the charge and discharge process of the battery and increase the structural stability of the second material. Therefore, it is beneficial to reduce the growth rate of the DC internal resistance of the battery.

[0015] In any embodiment, the thickness of the first coating layer is 1 - 150 nm, and the thickness of the second coating layer is 20 - 300 nm; optionally, the thickness of the first coating layer is 20 - 50 nm, and the thickness of the second coating layer is 60 - 80 nm. The values of the thickness of the first coating layer and the thickness of the second coating layer within a suitable range are beneficial to reducing the growth rate of the DC internal resistance of the battery.

[0016] In any embodiment, the material of the first coating layer includes Al 2 O 3 , ZrO 2 , B 2 O 3 , Ti 2 O 3 , CeO 2 , Nb 2 O 5 , WO 3 , MoO 3 and at least one of them; and / or, the material of the second coating layer includes Al 2 O 3 , ZrO 2 , B 2 O 3 , Ti 2 O 3 , CeO 2 , Nb 2 O 5 , WO 3 , MoO 3 and at least one of them. Selecting suitable materials for the first coating layer and the second coating layer is beneficial to inhibiting the erosion of the side reactions on the material surface during the charge and discharge process of the battery, thereby being beneficial to reducing the growth rate of the DC internal resistance of the battery.

[0017] In any embodiment, both the first material and the second material include single crystal particles, and the specific surface area of the single crystal particles in the first material is larger than that of the single crystal particles in the second material. Since the unstable phenomena (such as structural instability) mainly occur on the material surface, the specific surface area of the single crystal particles in the second material is relatively smaller, which is beneficial to making the structural stability of the second material relatively larger, thereby being beneficial to reducing the growth rate of the DC internal resistance of the battery.

[0018] In any embodiment, the median particle size Dv50 of the single crystal particles in the first material is smaller than the median particle size Dv50 of the single crystal particles in the second material. The larger the median particle size Dv50 of the single crystal particles, the smaller the specific surface area. The median particle size Dv50 of the single crystal particles in the second material is relatively larger, which is beneficial to making the structural stability of the second material relatively larger, thereby being beneficial to reducing the growth rate of the DC internal resistance of the battery.

[0019] In any embodiment, the median particle size Dv50 of the single crystal particles in the first material is 2 - 5 μm, and the median particle size Dv50 of the single crystal particles in the second material is 3 - 6 μm; optionally, the median particle size Dv50 of the single crystal particles in the first material is 2.5 - 3.5 μm, and the median particle size Dv50 of the single crystal particles in the second material is 3.5 - 4.5 μm. The median particle size Dv50 of the single crystal particles in the first material and the median particle size Dv50 of the single crystal particles in the second material being in a suitable range is beneficial to reducing the growth rate of the DC internal resistance of the battery.

[0020] In any embodiment, both the first material and the second material include secondary particles, and the median particle size Dv50 of the secondary particles in the first material is greater than the median particle size Dv50 of the secondary particles in the second material. The median particle size Dv50 of the secondary particles in the second material is relatively smaller, which is beneficial to avoiding particle breakage, beneficial to making the structural stability of the second material relatively larger, thereby being beneficial to reducing the growth rate of the DC internal resistance of the battery.

[0021] In any embodiment, the median particle size Dv50 of the secondary particles in the first material is 5 - 13 μm, and the median particle size Dv50 of the secondary particles in the second material is 4 - 12 μm; optionally, the median particle size Dv50 of the secondary particles in the first material is 9 - 10 μm, and the median particle size Dv50 of the secondary particles in the second material is 8 - 9 μm. Selecting a suitable range for the median particle size Dv50 of the secondary particles in the first material and the median particle size Dv50 of the secondary particles in the second material is beneficial to making the structural stability of the second material relatively larger, thereby being beneficial to reducing the growth rate of the DC internal resistance of the battery.

[0022] In any embodiment, the first material includes secondary particles and the second material includes single crystal particles. Since secondary particles are relatively more likely to break, selecting suitable first and second materials is beneficial to making the structural stability of the second material relatively larger, thereby being beneficial to reducing the growth rate of the DC internal resistance of the battery.

[0023] In any embodiment, the median particle size Dv50 of the secondary particles is 4 to 13 μm, and the median particle size Dv50 of the single crystal particles is 2 to 6 μm. Selecting appropriate ranges for the median particle size Dv50 of the secondary particles in the first material and the median particle size Dv50 of the single crystal particles in the second material is beneficial to making the structural stability of the second material relatively greater, thereby facilitating the reduction of the growth rate of the DC internal resistance of the battery.

[0024] In any embodiment, both the first active material layer and the second active material layer further include a conductive agent, and the mass ratio of the conductive agent in the first active material layer is less than the mass ratio of the conductive agent in the second active material layer; and / or, the specific surface area of the conductive agent in the first active material layer is less than the specific surface area of the conductive agent in the second active material layer. Adding a conductive agent to the positive electrode sheet is beneficial to improving the conductivity of the positive electrode sheet. Using a relatively larger mass ratio or specific surface area of the conductive agent in the second active material layer is beneficial to making the conductivity of the second active material layer relatively greater, thereby facilitating the reduction of the initial DC internal resistance value and the growth rate of the DC internal resistance of the battery.

[0025] In any embodiment, the mass ratio of the conductive agent in the first active material layer is 0.01% - 2%, and the mass ratio of the conductive agent in the second active material layer is 0.02% - 3%; optionally, the mass ratio of the conductive agent in the first active material layer is 0.1% - 0.4%, and the mass ratio of the conductive agent in the second active material layer is 0.4% - 1%. The mass ratios of the conductive agent in the first active material layer and the second active material layer within appropriate ranges are beneficial to reducing the initial DC internal resistance value and the growth rate of the DC internal resistance of the battery.

[0026] In any embodiment, the specific surface area of the conductive agent in the first active material layer is 10 - 500 m 2 / g; the specific surface area of the conductive agent in the first active material layer is 300 - 1500 m 2 / g; optionally, the specific surface area of the conductive agent in the first active material layer is 50 - 300 m 2 / g; the specific surface area of the conductive agent in the first active material layer is 500 - 1000 m 2 / g. The specific surface areas of the conductive agent in the first active material layer and the second active material layer within appropriate ranges are beneficial to reducing the initial DC internal resistance value and the growth rate of the DC internal resistance of the battery.

[0027] In any embodiment, the conductive agent includes one of carbon nanotubes, graphene, and carbon black.

[0028] In any embodiment, the first active material layer and the second active material layer both further include a binder, and the mass ratio of the binder in the first active material layer is greater than that in the second active material layer. Relatively less binder in the second active material layer results in more exposed area of the active material, making it more convenient for lithium deintercalation / insertion, which is beneficial to reducing the growth rate of the DC internal resistance of the battery.

[0029] In any embodiment, the mass ratio of the binder in the first active material layer is 0.5% to 2%, and the mass ratio of the binder in the second active material layer is 0.1% to 1.2%; optionally, the mass ratio of the binder in the first active material layer is 0.8% to 1.5%, and the mass ratio of the binder in the second active material layer is 0.3% to 1%. Selecting appropriate ranges for the mass ratios of the binder in the first active material layer and the second active material layer is beneficial to reducing the growth rate of the DC internal resistance of the battery.

[0030] In any embodiment, the binder includes at least one of polyvinylidene fluoride, polyacrylamide, polyethylene oxide, polyvinylpyrrolidone, polytetrafluoroethylene, polymethyl methacrylate, polyacrylonitrile, polyimide, poly(ethylene oxide), polyvinyl alcohol, and polyacrylonitrile.

[0031] In any embodiment, the first active material layer and the second active material layer both further include an additive, and the mass ratio of the additive in the first active material layer is less than that in the second active material layer. Among them, the additive includes a siloxane compound or an alkali metal oxide. The siloxane compound is beneficial to removing hydrogen fluoride in the electrolyte, and the alkali metal oxide is beneficial to absorbing water in the electrolyte. Using relatively more additive in the second active material layer is beneficial to reducing the growth rate of the DC internal resistance of the battery.

[0032] In any embodiment, the mass ratio of the additive in the first active material layer is 0.01% to 0.05%, and the mass ratio of the additive in the second active material layer is 0.02% to 0.5%; optionally, the mass ratio of the additive in the first active material layer is 0.02% to 0.04%, and the additive content in the second active material layer is 0.1% - 0.3%. The mass ratios of the additive in the first active material layer and the second active material layer within a suitable range are beneficial to reducing the growth rate of the DC internal resistance of the battery.

[0033] In any embodiment, the siloxane compound includes at least one of hexamethyldisiloxane, polydimethylsiloxane, and dimethyldimethoxysilane; and / or, the alkali metal oxide includes CaO or MgO.

[0034] In a second aspect, an embodiment of the present application provides a battery, which includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte according to the first aspect of the present application.

[0035] In a third aspect, an embodiment of the present application provides an electrical device, which includes the battery according to the second aspect of the present application. Description of the Drawings

[0036] Figure 1 is a schematic structural view of a positive electrode sheet according to an embodiment of the present application;

[0037] Figure 2 is a schematic view of a secondary battery according to an embodiment of the present application;

[0038] Figure 3 is Figure 2 an exploded view of the secondary battery according to an embodiment of the present application shown in ;

[0039] Figure 4 is a schematic view of a battery module according to an embodiment of the present application;

[0040] Figure 5 is a schematic view of a battery pack according to an embodiment of the present application;

[0041] Figure 6 is Figure 5 an exploded view of the battery pack according to an embodiment of the present application shown in ;

[0042] Figure 7 is a schematic view of an electrical device using the secondary battery according to an embodiment of the present application as a power source.

[0043] Description of the Reference Numerals:

[0044] 1 battery pack; 2 upper box body; 3 lower box body; 4 battery module; 5 secondary battery; 51 housing; 52 electrode assembly; 521 positive electrode sheet; 5211 current collector; 5212 active layer; 5212-1 first active material layer; 5212-2 second active material layer; 53 top cover assembly. Detailed Embodiments

[0045] Hereinafter, embodiments of the positive electrode sheet, battery, battery module, battery pack, and electrical device of the present application will be specifically disclosed in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter recited in the claims.

[0046] The "ranges" disclosed in this application are defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower and upper limits define the boundaries of the particular range. The ranges defined in this way can include the end values or not include the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 - 120 and 80 - 110 are listed for a specific parameter, ranges of 60 - 110 and 80 - 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4, and 2 - 5. In this application, unless otherwise stated, the numerical range "a - b" represents an abbreviated representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0 - 5" means that all real numbers between "0 - 5" are fully listed herein, and "0 - 5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0047] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined with each other to form new technical solutions.

[0048] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form new technical solutions.

[0049] Unless otherwise specified, all steps of this application can be carried out sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out sequentially, or can also include steps (b) and (a) carried out sequentially. For example, when it is mentioned that the method may further include step (c), it means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b), and (c), or can also include steps (a), (c), and (b), or can also include steps (c), (a), and (b), etc.

[0050] Unless otherwise specified, the "including" and "comprising" mentioned in this application mean open-ended or can also be closed-ended. For example, the "including" and "comprising" can mean that other components not listed can also be included or comprised, or can also mean only including or comprising the listed components.

[0051] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) while B is true (or exists); or both A and B are true (or exist).

[0052] Lithium-ion batteries are widely used in electric vehicles and consumer electronic products due to their advantages such as high energy density, high output power, long cycle life, and low environmental pollution. However, at present, lithium-ion batteries have the problem of a relatively large growth rate of direct current internal resistance after multiple cycles of charge and discharge.

[0053] Based on this, referring to Figure 1 , a first aspect of the present application provides a positive electrode plate 521, including a current collector 5211 and an active layer 5212; the active layer 5212 is disposed on at least one surface of the current collector 5211, and the active layer 5212 includes a first active material layer 5212-1 and a second active material layer 5212-2 that are sequentially arranged away from the current collector 5211 in the thickness direction of the current collector 5211. Among them, the first active material layer 5212-1 includes a first material, the first material includes a first active material, the second active material layer 5212-2 includes a second material, the second material includes a second active material, and the structural stability of the first material is less than the structural stability of the second material.

[0054] Exemplarily, the current collector 5211 includes two opposite surfaces in its own thickness direction. The active layer 5212 can be disposed on any one of the two opposite surfaces of the current collector 5211, or the active layer 5212 can be disposed on the two opposite surfaces of the current collector 5211 respectively.

[0055] It should be noted that in this article, "structural stability" can refer to the structural stability of the positive electrode active material. The structural stability of the positive electrode active material can refer to the ability of the positive electrode active material not to be damaged after the battery is cycled for charge and discharge. For example, after experiencing n charge and discharge cycles, the degree of lithium-nickel mixing in the crystals of the positive electrode active material does not increase significantly; the crystals in the positive electrode active material do not undergo irreversible phase changes or the proportion of irreversible phase changes is low. Irreversible phase changes of crystals include, for example, a change from a layered structure to a spinel structure, etc.; the shell structure of the positive electrode active material does not crack; the particles of the positive electrode active material do not break, etc.

[0056] In the embodiments of the present application, the first active material layer 5212-1 in the positive electrode plate 521 is relatively closer to the current collector 5211, while the second active material layer 5212-2 is relatively farther from the current collector 5211. During the charge and discharge cycles of the battery, the second material in the second active material layer 5212-2 (i.e., the outer layer) preferentially de-lithiates. Thus, in the embodiments of the present application, the structural stability of the first material in the first active layer 5212 (i.e., the inner layer) is less than that of the second material in the second active material layer 5212-2 (i.e., the outer layer), that is, the structural stability of the second material that preferentially de-lithiates is stronger, so that after the charge and discharge cycles of the battery, the structure of the material in the outer layer is not easily damaged or collapsed, enabling the de-inserted and inserted lithium ions to return to the raw material, and thus reducing the growth rate of the DC internal resistance of the battery.

[0057] In any embodiment, the chemical formula of the first active material includes LiNi x Co y Mn 1-x-y O 2 , and the chemical formula of the second active material includes LiNi x Co z Mn 1-x-z O 2 , where 0 < x < 1, 0 ≤ y < 1, 0 < z < 1, and y < z. Thus, along the direction away from the current collector, the content of Co in the ternary material increases layer by layer. The increase in the content of Co is beneficial to reducing the occurrence of lithium-nickel mixing, improving the structural stability of the ternary material, and thus reducing the growth rate of the DC internal resistance of the battery.

[0058] In any embodiment, 0 ≤ y ≤ 0.1, 0.08 ≤ z ≤ 0.15; the values of y and z within this appropriate range are beneficial to reducing the growth rate of the DC internal resistance of the battery. 0.05 ≤ y ≤ 0.07, 0.12 ≤ z ≤ 0.14. Within this range, it is more beneficial to reduce the growth rate of the DC internal resistance of the battery. The chemical formula of the first active material can be LiNi 0.55 Mn 0.45 O 2 , LiNi 0.55 Co 0.03 Mn 0.42 O 2 , LiNi 0.55 Co 0.05 Mn 0.4 O 2 , LiNi 0.55 Co 0.07 Mn 0.38 O 2 , LiNi 0.55 Co 0.1 Mn 0.35 O 2; The chemical formula of the second active material can be LiNi 0.55 Co 0.08 Mn 0.37 O 2 、LiNi 0.55 Co 0.1 Mn 0.35 O 2 、LiNi 0.55 Co 0.12 Mn 0.33 O 2 、LiNi 0.55 Co 0.15 Mn 0.3 O 2 。

[0059] In any embodiment, the chemical formula of the first active material includes LiNi x Co y Mn 1-x-y A m O 2 ,and the chemical formula of the second active material includes LiNi x Co y Mn 1-x-y A n O 2 where 0 < x < 1, 0 ≤ y < 1, 0 < m < 1, 0 < n < 1, and m < n; A is a doping element, and A includes at least one of Al, Zr, B, Ti, Ce, Nb, W, and Mo. Thus, along the direction away from the current collector, the content of the doping element in the ternary material increases layer by layer, and the increase in the content of the doping element is beneficial to improving the structural stability of the ternary material, thereby being beneficial to reducing the growth rate of the DC internal resistance of the battery.

[0060] In any embodiment, 0.0008 ≤ m ≤ 0.006, 0.003 ≤ n ≤ 0.012; the values of m and n in this appropriate range are beneficial to reducing the growth rate of the DC internal resistance of the battery. 0.001 ≤ m ≤ 0.003, 0.006 ≤ n ≤ 0.008. Within this range, it is more beneficial to reduce the growth rate of the DC internal resistance of the battery. The chemical formula of the first active material can be LiNi 0.55 Co 0.05 Mn 0.4 Zr0.0008O 2 、LiNi 0.55 Co 0.05 Mn 0.4 Zr0.001O 2 、LiNi 0.55 Co 0.05 Mn 0.4 Zr0.0015O 2 、LiNi 0.55Co 0.05 Mn 0.4 Zr0.002O 2 、LiNi 0.55 Co 0.05 Mn 0.4 Zr0.0025O 2 、LiNi 0.55 Co 0.05 Mn 0.4 Zr0.003O 2 ; The chemical formula of the second active material can be LiNi 0.55 Co 0.05 Mn 0.4 Zr0.003O 2 、LiNi 0.55 Co 0.05 Mn 0.4 Zr0.004O 2 、LiNi 0.55 Co 0.05 Mn 0.4 Zr0.005O 2 、LiNi 0.55 Co 0.05 Mn 0.4 Zr0.006O 2 、LiNi 0.55 Co 0.05 Mn 0.4 Zr0.007O 2 、LiNi 0.55 Co 0.05 Mn 0.4 Zr0.008O 2 、LiNi 0.55 Co 0.05 Mn 0.4 Zr0.009O 2 、LiNi 0.55 Co 0.05 Mn 0.4 Zr0.010O 2 、LiNi 0.55 Co 0.05 Mn 0.4 Zr0.011O 2 、LiNi 0.55 Co 0.05 Mn 0.4 Zr0.012O 2 。

[0061] In any embodiment, both the first material and the second material are core-shell structures. The first material includes a first inner core and a first coating layer, and the first active material is disposed in the first inner core. The second material includes a second inner core and a second coating layer, and the second active material is disposed in the second inner core. The thickness of the first coating layer is less than that of the second coating layer. Thus, the thicker second coating layer can inhibit the erosion of the material surface by side reactions during the charge and discharge of the battery, increasing the structural stability of the second material. This is conducive to reducing the growth rate of the DC internal resistance of the battery.

[0062] In any embodiment, the thickness of the first coating layer is 1-150 nm, and the thickness of the second coating layer is 20-300 nm. When the thicknesses of the first coating layer and the second coating layer are within this appropriate range, it is conducive to reducing the growth rate of the DC internal resistance of the battery. The thickness of the first coating layer is 20-50 nm, and the thickness of the second coating layer is 60-80 nm. Within this range, it is more conducive to reducing the growth rate of the DC internal resistance of the battery. The thickness of the first coating layer can be 1 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm; the thickness of the second coating layer can be 20 nm, 40 nm, 60 nm, 80 nm, 100 nm, 120 nm, 140 nm, 160 nm, 180 nm, 200 nm, 220 nm, 240 nm, 260 nm, 280 nm, 300 nm.

[0063] In any embodiment, the material of the first coating layer includes Al 2 O 3 、ZrO 2 、B 2 O 3 、Ti 2 O 3 、CeO 2 、Nb 2 O 5 、WO 3 、MoO 3 and at least one of the following; and / or, the material of the second coating layer includes Al 2 O 3 、ZrO 2 、B 2 O 3 、Ti 2 O 3 、CeO 2 、Nb 2 O 5 、WO 3 、MoO 3At least one of them. Selecting the materials for the above-mentioned suitable first coating layer and the second coating layer is beneficial to inhibiting the erosion of the material surface by side reactions during the charge and discharge process of the battery, thereby being beneficial to reducing the growth rate of the DC internal resistance of the battery.

[0064] In any embodiment, both the first material and the second material include single crystal particles, and the specific surface area of the single crystal particles in the first material is larger than that of the single crystal particles in the second material. Since unstable phenomena (such as structural instability) mainly occur on the material surface, the relatively smaller specific surface area of the single crystal particles in the second material is beneficial to making the structural stability of the second material relatively larger, thereby being beneficial to reducing the growth rate of the DC internal resistance of the battery.

[0065] In any embodiment, the median particle size Dv50 of the single crystal particles in the first material is smaller than the median particle size Dv50 of the single crystal particles in the second material. The larger the median particle size Dv50 of the single crystal particles, the smaller the specific surface area. The relatively larger median particle size Dv50 of the single crystal particles in the second material is beneficial to making the structural stability of the second material relatively larger, thereby being beneficial to reducing the growth rate of the DC internal resistance of the battery.

[0066] In any embodiment, the median particle size Dv50 of the single crystal particles in the first material is 2 - 5 μm, and the median particle size Dv50 of the single crystal particles in the second material is 3 - 6 μm; the median particle size Dv50 of the single crystal particles in the first material and the median particle size Dv50 of the single crystal particles in the second material being in this suitable range is beneficial to reducing the growth rate of the DC internal resistance of the battery. The median particle size Dv50 of the single crystal particles in the first material is 2.5 - 3.5 μm, and the median particle size Dv50 of the single crystal particles in the second material is 3.5 - 4.5 μm. Within this range, it is more beneficial to reducing the growth rate of the DC internal resistance of the battery. The median particle size Dv50 of the single crystal particles in the first material can be 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm; the median particle size Dv50 of the single crystal particles in the second material can be 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm.

[0067] In any embodiment, both the first material and the second material include secondary particles, and the median particle size Dv50 of the secondary particles in the first material is larger than the median particle size Dv50 of the secondary particles in the second material. The relatively smaller median particle size Dv50 of the secondary particles in the second material is beneficial to avoiding particle breakage, beneficial to making the structural stability of the second material relatively larger, thereby being beneficial to reducing the growth rate of the DC internal resistance of the battery.

[0068] In any embodiment, the median particle size Dv50 of the secondary particles in the first material is 5 to 13 μm, and the median particle size Dv50 of the secondary particles in the second material is 4 to 12 μm; selecting the appropriate range for the median particle size Dv50 of the secondary particles in the first material and the median particle size Dv50 of the secondary particles in the second material is beneficial to making the structural stability of the second material relatively greater, thereby being beneficial to reducing the growth rate of the DC internal resistance of the battery. The median particle size Dv50 of the secondary particles in the first material is 9 to 10 μm, and the median particle size Dv50 of the secondary particles in the second material is 8 to 9 μm. Within this range, it is more beneficial to reduce the growth rate of the DC internal resistance of the battery. The median particle size Dv50 of the secondary particles in the first material can be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm; the median particle size Dv50 of the secondary particles in the second material can be 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm.

[0069] In any embodiment, the first material includes secondary particles, and the second material includes single crystal particles. Since the secondary particles are relatively more prone to breakage, selecting appropriate first and second materials is beneficial to making the structural stability of the second material relatively greater, thereby being beneficial to reducing the growth rate of the DC internal resistance of the battery.

[0070] In any embodiment, the median particle size Dv50 of the secondary particles is 4 to 13 μm, and the median particle size Dv50 of the single crystal particles is 2 to 6 μm. Selecting the appropriate range for the median particle size Dv50 of the secondary particles in the first material and the median particle size Dv50 of the single crystal particles in the second material is beneficial to making the structural stability of the second material relatively greater, thereby being beneficial to reducing the growth rate of the DC internal resistance of the battery. The median particle size Dv50 of the secondary particles can be 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm. The median particle size Dv50 of the single crystal particles can be 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm.

[0071] In any embodiment, both the first active material layer and the second active material layer further include a conductive agent, and the mass ratio of the conductive agent in the first active material layer is less than the mass ratio of the conductive agent in the second active material layer; and / or, the specific surface area of the conductive agent in the first active material layer is less than the specific surface area of the conductive agent in the second active material layer. Adding a conductive agent to the positive electrode sheet is beneficial to improving the conductivity of the positive electrode sheet. Using a relatively larger mass ratio or specific surface area of the conductive agent in the second active material layer is beneficial to making the conductivity of the second active material layer relatively greater, thereby being beneficial to reducing the initial DC internal resistance value and the growth rate of the DC internal resistance of the battery.

[0072] It should be noted that the BET specific surface area has a well-known meaning in the art and can be measured by instruments and methods well-known in the art. For example, reference can be made to the national standard GB / T 19587-2017 "Determination of Specific Surface Area of Solid Substances by Gas Adsorption BET Method".

[0073] In any embodiment, the mass ratio of the conductive agent in the first active material layer is 0.01%-2%, and the mass ratio of the conductive agent in the second active material layer is 0.02%-3%. The mass ratio of the conductive agent in the first active material layer and the second active material layer within this appropriate range is beneficial to reducing the initial DC internal resistance value and the growth rate of the DC internal resistance of the battery. The mass ratio of the conductive agent in the first active material layer is 0.1%-0.4%, and the mass ratio of the conductive agent in the second active material layer is 0.4%-1%. Within this range, it is more beneficial to reduce the initial DC internal resistance value and the growth rate of the DC internal resistance of the battery. The mass ratio of the conductive agent in the first active material layer can be 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.10%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, 0.17%, 0.18%, 0.19%, 0.2%; the mass ratio of the conductive agent in the second active material layer can be 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.10%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, 0.17%, 0.18%, 0.19%, 0.2%, 0.21%, 0.22%, 0.23%, 0.24%, 0.25%, 0.26%, 0.27%, 0.28%, 0.29%, 0.3%.

[0074] In any embodiment, the specific surface area of the conductive agent in the first active material layer is 10-500m 2 / g; the specific surface area of the conductive agent in the first active material layer is 300-1500m 2 / g; the specific surface area of the conductive agent in the first active material layer and the second active material layer within a suitable range is beneficial to reducing the initial DC internal resistance value and the growth rate of the DC internal resistance of the battery. The specific surface area of the conductive agent in the first active material layer is 50-300m 2 / g; the specific surface area of the conductive agent in the first active material layer is 500-1000m 2 / g. It is more beneficial to reduce the initial DC internal resistance value and the growth rate of the DC internal resistance of the battery. The specific surface area of the conductive agent in the first active material layer can be 10m 2 / g, 50m 2 / g, 100m2 / g, 150 m 2 / g, 200 m 2 / g, 250 m 2 / g, 300 m 2 / g, 350 m 2 / g, 400 m 2 / g, 450 m 2 / g, 500 m 2 / g; The specific surface area of the conductive agent in the second active material layer can be 300 m 2 / g, 400 m 2 / g, 500 m 2 / g, 600 m 2 / g, 700 m 2 / g, 800 m 2 / g, 900 m 2 / g, 1000 m 2 / g, 1100 m 2 / g, 1200 m 2 / g, 1300 m 2 / g, 1400 m 2 / g, 1500 m 2 / g.

[0075] In any embodiment, the conductive agent includes one of carbon nanotubes, graphene, and carbon black.

[0076] In any embodiment, both the first active material layer and the second active material layer further include a binder, and the mass ratio of the binder in the first active material layer is greater than the mass ratio of the binder in the second active material layer. The binder in the second active material layer is relatively less, the exposed area of its active material is more, and it is more convenient to deintercalate and intercalate lithium. This is beneficial to reducing the growth rate of the DC internal resistance of the battery.

[0077] In any embodiment, the mass ratio of the binder in the first active material layer is 0.5 to 2%, and the mass ratio of the binder in the second active material layer is 0.1 to 1.2%; selecting the appropriate range for the mass ratio of the binder in the first active material layer and the second active material layer is beneficial to reducing the growth rate of the DC internal resistance of the battery. The mass ratio of the binder in the first active material layer is 0.8 to 1.5%, and the mass ratio of the binder in the second active material layer is 0.3 to 1%. Within this range, it is more beneficial to reduce the growth rate of the DC internal resistance of the battery. The mass ratio of the binder in the first active material layer can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%; the mass ratio of the binder in the first active material layer can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%.

[0078] In any embodiment, the binder includes at least one of polyvinylidene fluoride, polyacrylamide, polyethylene oxide, polyvinylpyrrolidone, polytetrafluoroethylene, polymethyl methacrylate, polyacrylonitrile, polyimide, poly(ethylene oxide), polyvinyl alcohol, polyacrylonitrile.

[0079] In any embodiment, both the first active material layer and the second active material layer further include an additive, and the mass ratio of the additive in the first active material layer is less than the mass ratio of the additive in the second active material layer. Among them, the additive includes a siloxane compound or an alkali metal oxide. The siloxane compound is beneficial to removing hydrogen fluoride in the electrolyte, and the alkali metal oxide is beneficial to absorbing water in the electrolyte. Using relatively more additives in the second active material layer is beneficial to reducing the growth rate of the DC internal resistance of the battery.

[0080] In any embodiment, the mass ratio of the additive in the first active material layer is 0.01% to 0.05%, and the mass ratio of the additive in the second active material layer is 0.02% to 0.5%. When the mass ratios of the additives in the first active material layer and the second active material layer are within this appropriate range, it is beneficial to reduce the growth rate of the DC internal resistance of the battery. The mass ratio of the additive in the first active material layer is 0.02% to 0.04%, and the additive content in the second active material layer is 0.1% - 0.3%. Within this range, it is more beneficial to reduce the growth rate of the DC internal resistance of the battery. The mass ratio of the additive in the first active material layer can be 0.01%, 0.02%, 0.03%, 0.04%, 0.05%; the mass ratio of the additive in the second active material layer can be 0.02%, 0.04%, 0.06%, 0.08%, 0.1%, 0.12%, 0.14%, 0.16%, 0.18%, 0.2%, 0.22%, 0.24%, 0.26%, 0.28%, 0.3%, 0.32%, 0.34%, 0.36%, 0.38%, 0.4%, 0.42%, 0.44%, 0.46%, 0.48%, 0.5%.

[0081] In any embodiment, the siloxane compound includes at least one of hexamethyldisiloxane, polydimethylsiloxane, and dimethyldimethoxysilane; and / or, the alkali metal oxide includes CaO or MgO.

[0082] In a second aspect, an embodiment of the present application provides a battery, including the positive electrode sheet, negative electrode sheet, separator, and electrolyte of the first aspect of the present application.

[0083] In a third aspect, an embodiment of the present application provides an electrical device, including the battery of the second aspect of the present application.

[0084] In any embodiment, the battery includes a lithium-ion battery or a sodium-ion battery.

[0085] In addition, the secondary battery, battery module, battery pack, and electrical device of the present application will be described below with appropriate reference to the drawings.

[0086] In an embodiment of the present application, a secondary battery is provided.

[0087] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the charge and discharge process of the battery, active ions are embedded and extracted back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet, mainly playing a role in preventing short circuit between the positive and negative electrodes, and at the same time allowing ions to pass through.

[0088] The positive electrode tab includes the positive electrode tab of the first aspect of the present application.

[0089] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be formed by forming a metal material (such as 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.).

[0090] In some embodiments, when the secondary battery is a lithium-ion battery, the positive electrode active material may be a positive electrode active material for lithium-ion batteries well known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as the positive electrode active material of the battery may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO 2 ), lithium nickel oxide (such as LiNiO 2 ), lithium manganese oxide (such as LiMnO 2 , LiMn 2 O 4 ), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 (which can also be abbreviated as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (which can also be abbreviated as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O 2 (which can also be abbreviated as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (which can also be abbreviated as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O 2(which can also be abbreviated as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O 2 ), and at least one of its modified compounds, etc. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, lithium iron phosphate (such as LiFePO 4 (which can also be abbreviated as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO 4 ), a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and at least one of a composite material of lithium manganese iron phosphate and carbon.

[0091] In some embodiments, the positive electrode sheet can be prepared by the following method: dispersing the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode sheet can be obtained.

[0092] 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, and the negative electrode film layer includes a negative electrode active material.

[0093] As an example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode film layer is provided on any one or both of the two opposite surfaces of the negative electrode current collector.

[0094] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (such as copper, copper 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.).

[0095] In some embodiments, the negative electrode active material can be the negative electrode active material for batteries known in the art. As an example, the negative electrode active material can 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, etc. The silicon-based materials can be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based materials can 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 conventional materials that can be used as the negative electrode active material of the battery can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0096] In some embodiments, the negative electrode film layer may further optionally include a binder. The binder can 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).

[0097] In some embodiments, the negative electrode film layer may further optionally include a conductive agent. The conductive agent can be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0098] In some embodiments, the negative electrode film layer may further optionally include other additives, such as thickeners (such as sodium carboxymethyl cellulose (CMC-Na)), etc.

[0099] In some embodiments, the negative electrode plate can be prepared in the following manner: Dispersing the components for preparing the negative electrode plate, such as the negative electrode active material, the conductive agent, the binder, and any other components, in a solvent (such as deionized water) to form a negative electrode slurry; Coating the negative electrode slurry on the negative electrode current collector, and after processes such as drying and cold pressing, the negative electrode plate can be obtained.

[0100] The electrolyte plays a role in conducting ions between the positive electrode plate and the negative electrode plate. The present application has no specific limitation on the type of the electrolyte, and it can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or all-solid.

[0101] In some embodiments, the electrolyte uses an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0102] In some embodiments, the electrolyte salt can 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 difluorooxalate borate, lithium bis(oxalato)borate, lithium difluoro bis(oxalato)phosphate, and lithium tetrafluorooxalate phosphate.

[0103] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl 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, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0104] In some embodiments, the electrolyte may further optionally include additives. For example, the additives may include anode film-forming additives, cathode film-forming additives, and may also include additives that can improve certain battery performances, such as additives for improving the overcharge performance of the battery, additives for improving the high-temperature or low-temperature performance of the battery, and the like.

[0105] In some embodiments, the secondary battery further includes a separator. The present application does not particularly limit the type of the separator, and any well-known porous separator with good chemical stability and mechanical stability can be selected.

[0106] In some embodiments, the material of the separator may be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may 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 may be the same or different, without particular limitation.

[0107] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be made into an electrode assembly by a winding process or a stacking process.

[0108] In some embodiments, the secondary battery may include an outer package. The outer package can be used to encapsulate the above electrode assembly and electrolyte.

[0109] In some embodiments, the outer package of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0110] The present application does not particularly limit the shape of the secondary battery, and it can be cylindrical, square, or any other arbitrary shape. For example, Figure 2 is a secondary battery 5 with a square structure as an example.

[0111] In some embodiments, refer to Figure 3, the outer package may include a housing 51 and a cover plate 53. Among them, the housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose to form a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the separator can be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. The number of electrode assemblies 52 included in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0112] In some embodiments, the secondary battery can be assembled into a battery module. The number of secondary batteries included in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0113] Figure 4 is a battery module 4 as an example. Refer to Figure 4 , in the battery module 4, a plurality of secondary batteries 5 can be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other way. Further, the plurality of secondary batteries 5 can be fixed by fasteners.

[0114] Optionally, the battery module 4 may further include a housing having a receiving space, and a plurality of secondary batteries 5 are received in the receiving space.

[0115] In some embodiments, the above battery module can be further assembled into a battery pack. The number of battery modules included in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0116] Figure 5 and Figure 6 is a battery pack 1 as an example. Refer to Figure 5 and Figure 6 , in the battery pack 1, it may include a battery box and a plurality of battery modules 4 arranged in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can be covered on the lower box body 3 to form a closed space for receiving the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any way.

[0117] In addition, the present application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided by the present application. The secondary battery, battery module, or battery pack can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device can include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc., but is not limited thereto.

[0118] As the electrical device, the secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0119] Figure 7 is an electrical device as an example. The electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the electrical device for the secondary battery, a battery pack or a battery module can be adopted.

[0120] Another example of the device can be a mobile phone, a tablet computer, a laptop computer, etc. This device usually requires being thin and light, and a secondary battery can be used as the power source.

[0121] Hereinafter, embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application and should not be construed as a limitation to the present application. For those not specified in the embodiments regarding specific technologies or conditions, they shall be carried out according to the technologies or conditions described in the literature in the field or according to the product specifications. For the reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0122] The parameters of the positive electrode sheets in Embodiments 1 to 18 and Comparative Examples 1 to 3 of the present application refer to the parameters in Table 1.

[0123] In Embodiment 1, the first active material layer includes a first material, conductive agent carbon black, and binder polyvinylidene fluoride, and the second active material layer includes a second material, conductive agent carbon black, and binder polyvinylidene fluoride. Among them, the mass ratio of the conductive agent carbon black in the first active material layer and the second active material layer is 0.1% each, and the specific surface area of the conductive agent carbon black in the first active material layer and the second active material layer is 500m 2 / g. The mass ratio of the binder polyvinylidene fluoride in the first active material layer and the second active material layer is 0.5% each.

[0124] Embodiments 19 - 33 use the same first material and second material as Embodiment 1. The differences between Embodiments 19 - 33 and Embodiment 1 refer to the parameters in Table 2.

[0125]

[0126]

[0127] Testing method

[0128] Testing method for DCR growth rate:

[0129] At 25 °C, adjust the secondary battery to 50% SOC with a 1C current, and record the voltage U1. Then discharge at a 4C current for 30 seconds, and record the voltage U2. DCR = (U1 - U2) / 4C. Then perform 0.5C / 0.5C charge and discharge cycles on the battery for 1000 weeks, record the DCR at the 1000th week, divide the DCR at the 1000th week by the DCR at the first week and multiply by 100% to obtain the DCR growth rate at the 1000th week. See Table 3 for test results.

[0130] Table 3 Performance test results of Examples 1-33 and Comparative Examples 1-3

[0131]

[0132] As can be seen from Table 3, through Examples 1 to 7 and Comparative Example 1, it can be seen that by making the Co content in the second active material greater than the Co content in the first active material, or making the content of the doping element in the second active material greater than the content of the doping element in the first active material, the DCR growth rate of the battery can be reduced. As can be seen from the comparison between Examples 8-11 and Comparative Example 3, by making the thickness of the second coating layer in the second material greater than the thickness of the first coating layer in the first material, the DCR growth rate of the battery can be reduced. As can be seen from the comparison between Examples 12-14 and Comparative Example 1, by making the Dv50 of the single crystal particles of the second active material in the second material greater than the Dv50 of the single crystal particles of the first active material in the first material, the DCR growth rate of the battery can be reduced. As can be seen from the comparison between Examples 15-18 and Comparative Example 2, by making the Dv50 of the secondary particles of the second active material in the second material less than the Dv50 of the secondary particles of the first active material in the first material, the DCR growth rate of the battery can be reduced.

[0133] As can be seen from Example 20 and Example 1, on the basis of making the Co content in the second active material greater than the Co content in the first active material, further making the mass ratio of the conductive agent in the second active material layer greater than the mass ratio of the conductive agent in the first active material layer can further reduce the DCR growth rate of the battery.

[0134] As can be seen from Example 24 and Example 1, on the basis that the Co content in the second active material is greater than that in the first active material, further making the specific surface area of the conductive agent in the second active material layer greater than that in the first active material layer can further reduce the DCR growth rate of the battery.

[0135] As can be seen from Example 26 and Example 1, on the basis that the Co content in the second active material is greater than that in the first active material, further making the mass proportion of the binder in the second active material layer less than that in the first active material layer can further reduce the DCR growth rate of the battery.

[0136] As can be seen from Examples 30 - 33 and Example 1, on the basis that the Co content in the second active material is greater than that in the first active material, adding additives to the first active material layer and the second active material layer, and further making the mass proportion of the additives in the second active material layer greater than that in the first active material layer can further reduce the DCR growth rate of the battery.

[0137] As can be seen from Examples 19 - 21, on the basis that the Co content in the second active material is greater than that in the first active material, the mass proportion of the conductive agent in the first active material layer and the second active material layer affects the DCR growth rate of the battery. When the mass proportion of the conductive agent in the first active material layer is 0.1 - 2 and the mass proportion of the conductive agent in the second active material layer is 0.4 - 3, the DCR growth rate of the battery is lower.

[0138] As can be seen from Examples 22 - 25, on the basis that the Co content in the second active material is greater than that in the first active material, the specific surface area of the conductive agent in the first active material layer and the second active material layer affects the DCR growth rate of the battery. When the specific surface areas of the conductive agents in the first active material layer and the second active material layer both increase, the DCR growth rate of the battery is lower.

[0139] As can be seen from Examples 26 - 29, on the basis that the Co content in the second active material is greater than that in the first active material, the mass proportion of the binder in the first active material layer and the second active material layer affects the DCR growth rate of the battery. When the mass proportions of the binders in the first active material layer and the second active material layer both decrease, the DCR growth rate of the battery is lower.

[0140] As can be seen from Examples 15 - 18 and Comparative Examples 1 - 2, the particle types of the active materials in the first active material layer and the second active material layer affect the initial DCR value of the battery. Using secondary particles can reduce the initial DC internal resistance value of the battery.

[0141] As can be seen from Examples 19-24, the content of the conductive agent and the specific surface area of the conductive agent in the first active material layer and the second active material layer affect the initial DCR value of the battery. When the content of the conductive agent in both the first active material layer and the second active material layer increases, or the specific surface area of the conductive agent in both the first active material layer and the second active material layer increases, the initial DC internal resistance value of the battery can be reduced.

[0142] It should be noted that the present application is not limited to the above embodiments. The above embodiments are only examples, and embodiments having the same structure and the same effect as the technical idea within the technical solution scope of the present application are included in the technical scope of the present application. In addition, within the scope of not departing from the gist of the present application, various modifications that can be conceived by those skilled in the art to the embodiments and other modes constructed by combining some constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A positive electrode sheet, characterized in that: include: current collector; as well as, An active layer is disposed on at least one surface of the current collector, wherein the active layer includes a first active material layer and a second active material layer disposed sequentially away from the current collector in the thickness direction of the current collector, The first active material layer includes a first material, the first material includes a first active material, the second active material layer includes a second material, the second material includes a second active material, and the structural stability of the first material is less than the structural stability of the second material.

2. The positive electrode sheet according to claim 1, characterized in that: The chemical formula of the first active material includes LiNi x Co y Mn 1-x-y O2, the chemical formula of the second active material includes LiNi x Co z Mn 1-x-z O2, wherein 0<x<1, 0≤y<1, 0<z<1, and y<z.

3. The positive electrode sheet according to claim 2, characterized in that: 0≤y≤0.1,0.08≤z≤0.15; Optionally, 0.05≤y≤0.07, 0.12≤z≤0.

14.

4. The positive electrode sheet according to any one of claims 1 to 3, characterized in that: The chemical formula of the first active material includes LiNi x Co y Mn 1-x-y A m O2, the chemical formula of the second active material includes LiNi x Co y Mn 1-x-y A n O2, wherein 0<x<1, 0≤y<1, 0<m<1, 0<n<1, and m<n; A is a doping element, and A includes at least one of Al, Zr, B, Ti, Ce, Nb, W, and Mo.

5. The positive electrode sheet according to claim 4, characterized in that: 0.0008≤m≤0.006, 0.003≤n≤0.012; Optionally, 0.001≤m≤0.003, 0.006≤n≤0.

008.

6. The positive electrode sheet according to any one of claims 1 to 5, characterized in that: The first material and the second material are both core-shell structures, the first material includes a first core and a first coating layer, the first active material is arranged in the first core, the second material includes a second core and a second coating layer, the second active material is arranged in the second core, and the thickness of the first coating layer is less than the thickness of the second coating layer.

7. The positive electrode sheet according to claim 6, characterized in that: The thickness of the first coating layer is 1-150 nm, and the thickness of the second coating layer is 20-300 nm; Optionally, the thickness of the first cladding layer is 20-50 nm, and the thickness of the second cladding layer is 60-80 nm.

8. The positive electrode sheet according to claim 6 or 7, characterized in that: The material of the first coating layer includes at least one of Al2O3, ZrO2, B2O3, Ti2O3, CeO2, Nb2O5, WO3, and MoO3; and / or, The material of the second coating layer includes at least one of Al2O3, ZrO2, B2O3, Ti2O3, CeO2, Nb2O5, WO3, and MoO3.

9. The positive electrode sheet according to any one of claims 1 to 8, characterized in that: The first material and the second material both include single crystal particles, and the specific surface area of ​​the single crystal particles in the first material is greater than the specific surface area of ​​the single crystal particles in the second material.

10. The positive electrode sheet according to claim 9, characterized in that: The median particle size Dv50 of the single crystal particles in the first material is smaller than the median particle size Dv50 of the single crystal particles in the second material.

11. The positive electrode sheet according to claim 9 or 10, characterized in that: The median particle size Dv50 of the single crystal particles in the first material is 2 to 5 μm, and the median particle size Dv50 of the single crystal particles in the second material is 3 to 6 μm; Optionally, the median particle size Dv50 of the single crystal particles in the first material is 2.5-3.5 μm, and the median particle size Dv50 of the single crystal particles in the second material is 3.5-4.5 μm.

12. The positive electrode sheet according to any one of claims 1 to 8, characterized in that: The first material and the second material both include secondary particles, and a median particle size Dv50 of the secondary particles in the first material is greater than a median particle size Dv50 of the secondary particles in the second material.

13. The positive electrode sheet according to claim 12, characterized in that: The median particle size Dv50 of the secondary particles in the first material is 5 to 13 μm, and the median particle size Dv50 of the secondary particles in the second material is 4 to 12 μm; Optionally, the median particle size Dv50 of the secondary particles in the first material is 9 to 10 μm, and the median particle size Dv50 of the secondary particles in the second material is 8 to 9 μm.

14. The positive electrode sheet according to any one of claims 1 to 8, characterized in that: The first material includes secondary particles and the second material includes single crystal particles.

15. The positive electrode sheet according to claim 14, characterized in that: The median particle size Dv50 of the secondary particles is 4 to 13 μm, and the median particle size Dv50 of the single crystal particles is 2 to 6 μm.

16. The positive electrode sheet according to any one of claims 1 to 15, characterized in that: The first active material layer and the second active material layer both further include a conductive agent, and the mass proportion of the conductive agent in the first active material layer is smaller than the mass proportion of the conductive agent in the second active material layer; and / or, The specific surface area of ​​the conductive agent in the first active material layer is smaller than the specific surface area of ​​the conductive agent in the second active material layer.

17. The positive electrode sheet according to claim 16, characterized in that: The mass proportion of the conductive agent in the first active material layer is 0.01%-2%, and the mass proportion of the conductive agent in the second active material layer is 0.02%-3%; Optionally, the mass proportion of the conductive agent in the first active material layer is 0.1%-0.4%, and the mass proportion of the conductive agent in the second active material layer is 0.4%-1%.

18. The positive electrode sheet according to claim 16 or 17, characterized in that: The specific surface area of ​​the conductive agent in the first active material layer is 10 to 500 m 2 / g; the specific surface area of ​​the conductive agent in the first active material layer is 300 to 1500 m 2 / g; Optionally, the specific surface area of ​​the conductive agent in the first active material layer is 50 to 300 m 2 / g; the specific surface area of ​​the conductive agent in the first active material layer is 500 to 1000 m 2 / g.

19. The positive electrode sheet according to any one of claims 16 to 18, characterized in that: The conductive agent includes one of carbon nanotubes, graphene and carbon black.

20. The positive electrode sheet according to any one of claims 1 to 19, characterized in that: The first active material layer and the second active material layer both further include a binder, and the mass proportion of the binder in the first active material layer is greater than the mass proportion of the binder in the second active material layer.

21. The positive electrode sheet according to claim 20, characterized in that: The mass proportion of the binder in the first active material layer is 0.5-2%, and the mass proportion of the binder in the second active material layer is 0.1-1.2%; Optionally, the mass proportion of the binder in the first active material layer is 0.8-1.5%, and the mass proportion of the binder in the second active material layer is 0.3-1%.

22. The positive electrode sheet according to claim 20 or 21, characterized in that: The adhesive includes at least one of polyvinylidene fluoride, polyacrylamide, polyethylene oxide, polyvinyl pyrrolidone, polytetrafluoroethylene, polymethyl methacrylate, polyacrylonitrile, polyimide, polyethylene oxide, polyvinyl alcohol, and polyacrylonitrile.

23. The positive electrode sheet according to any one of claims 1 to 22, characterized in that: The first active material layer and the second active material layer both further include additives, wherein the mass proportion of the additives in the first active material layer is smaller than the mass proportion of the additives in the second active material layer, wherein the additives include siloxane compounds or alkali metal oxides.

24. The positive electrode sheet according to claim 23, characterized in that: The mass proportion of the additive in the first active material layer is 0.01% to 0.05%, and the mass proportion of the additive in the second active material layer is 0.02% to 0.5%; Optionally, the mass proportion of the additive in the first active material layer is 0.02% to 0.04%, and the mass proportion of the additive in the second active material layer is 0.1% to 0.3%.

25. The positive electrode sheet according to claim 23 or 24, characterized in that: The siloxane compound includes at least one of hexamethyldisiloxane, polydimethylsiloxane, and dimethyldimethoxysilane; and / or the alkali metal oxide includes CaO or MgO.

26. A battery, characterized in that: It comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte as described in any one of claims 1 to 25.

27. An electrical device, characterized in that: The electrical device comprises the battery as claimed in claim 26.

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