Negative pole piece, secondary battery and electric device

Abstract

The invention provides a negative electrode plate, a secondary battery and a power utilization device. The negative electrode plate comprises a negative electrode current collector; the composite layer is arranged on at least one side of the negative electrode current collector, the composite layer comprises at least two active material layers and at least one active ion transmission layer which are stacked, the active material layers and the active ion transmission layers are alternately arranged, the active ion transmission layer is located between the two adjacent active material layers, and the active ion transmission layer is located between the two adjacent active material layers. Each active ion transport layer independently comprises one of an electronic insulating layer and an electronic semi-insulating layer.

Description

Negative electrode sheet, secondary battery and electrical device Technical Field

[0001] The present application belongs to the field of electrochemical technology, and in particular relates to a negative electrode plate, a secondary battery, and an electrical device. Background Art

[0002] In recent years, the application of secondary batteries, represented by lithium-ion batteries, has become increasingly widespread. They are widely used in energy storage systems such as hydropower, thermal, wind, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. With the rapid development of secondary batteries, higher requirements have been placed on their energy density, cycle performance, charging capacity, and safety performance. However, current secondary batteries, represented by traditional lithium-ion batteries, suffer from poor charging capacity and safety performance, failing to meet practical application needs.

[0003] Summary of the Invention

[0004] The purpose of this application is to provide a negative electrode plate, a secondary battery and an electrical device, which can improve the charging capacity and safety performance of the secondary battery.

[0005] In order to achieve the above-mentioned object of the invention, the first aspect of the present application provides a negative electrode sheet, comprising:

[0006] a negative electrode current collector; and

[0007] A composite layer is arranged on at least one side of the negative electrode current collector, and the composite layer includes at least two active material layers and at least one active ion transport layer stacked together, wherein the active material layers and the active ion transport layers are alternately arranged, and the active ion transport layer is located between two adjacent active material layers, and each active ion transport layer independently includes one of an electronic insulating layer and an electronic semi-insulating layer.

[0008] The negative electrode plate provided in the present application includes a negative electrode current collector and a composite layer, wherein the composite layer includes an active material layer and an active ion transport layer. After an active ion transport layer composed of an electronic insulating layer or an electronic semi-insulating layer is provided between the active material layers, the electronic insulating layer or the electronic semi-insulating layer has active ion transport characteristics, but has no electronic conductivity or the electronic conductivity is lower than the electronic conductivity of the active material layer. Therefore, the distribution of electrons in the negative electrode plate decreases from the negative electrode current collector side to the surface of the negative electrode plate, thereby forming an electric field strength that gradually decreases from the side close to the negative electrode current collector to the negative electrode surface, thereby forming a potential gradient. By regulating the potential gradient, the electron transport network of the negative electrode can be adjusted. When active ions such as lithium ions reach the surface of the negative electrode, they can be induced to embed first toward the side close to the negative electrode current collector, and then sequentially embed toward the negative electrode surface, thereby achieving orderly migration and embedding of active ions in the negative electrode, reducing the accumulation of active ions on the negative electrode surface, and prolonging the time for metallic lithium and the like to precipitate on the negative electrode surface, thereby improving the charging capacity of the secondary battery, while avoiding the formation of dendrites such as metallic lithium on the negative electrode surface as much as possible, thereby improving the safety performance of the secondary battery.

[0009] In some embodiments of the present application, the active ion transport layer satisfies at least one of the following conditions:

[0010] (1) The conductivity of the electronic insulating layer is σ1, and σ1 satisfies: 0<σ1<10 -10 S / cm, optional 10 -15 S / cm≤σ1≤10 -11 S / cm; and

[0011] (2) The conductivity of the electronic semi-insulating layer is σ2, and σ2 satisfies: 10 -10 S / cm≤σ2≤10 2 S / cm, optional 10 -6 S / cm≤σ2≤10 -3 S / cm.

[0012] The electrical conductivity of the electronic insulating layer and the electronic semi-insulating layer is within a suitable range, and an active ion transport layer with almost no electronic conductivity can be formed. By cooperating with the active material layer, it is beneficial to form an electric field gradient in the negative electrode sheet, in which the electric field strength gradually decreases from the side close to the negative electrode current collector to the negative electrode surface. This potential gradient can gradually weaken the induction ability of the negative electrode sheet to the active ions from the side close to the negative electrode current collector to the surface of the negative electrode sheet. When active ions such as lithium ions reach the negative electrode surface, the active ions can be induced to first embed toward the side close to the negative electrode current collector, and then embed toward the negative electrode surface in sequence. This achieves the orderly migration and embedding of active ions in the negative electrode, reduces the accumulation of active ions on the negative electrode surface, and prolongs the time for metal lithium and the like to precipitate on the negative electrode surface, thereby improving the charging capacity of the secondary battery, while avoiding the formation of dendrites such as metal lithium as much as possible, thereby improving the safety performance of the secondary battery.

[0013] In some embodiments of the present application, the negative electrode plate satisfies at least one of the following conditions:

[0014] (1) The conductivity of the active material layer is σ3, and σ3 satisfies: 10 -6 S / cm≤σ3≤10 5 S / cm, optional 10 -4 S / cm≤σ3≤10 3 S / cm; and

[0015] (2) The diaphragm resistance of the negative electrode plate is R, and R satisfies: 0.1mΩ≤R≤5000mΩ, and can be optionally 1mΩ≤R≤1000mΩ.

[0016] The conductivity of the active material layer and the sheet resistance of the negative electrode are within a suitable range, which is conducive to forming an electric potential gradient in the negative electrode sheet in which the electric field strength gradually decreases from the side close to the negative electrode current collector to the negative electrode surface. This potential gradient can gradually weaken the induction ability of the negative electrode sheet to active ions from the side close to the negative electrode current collector to the surface of the negative electrode sheet. When active ions such as lithium ions reach the negative electrode surface, the active ions can be induced to first embed toward the side close to the negative electrode current collector, and then sequentially embed toward the negative electrode surface. This achieves the orderly migration and embedding of active ions in the negative electrode, reduces the accumulation of active ions on the negative electrode surface, and prolongs the time for metal lithium and the like to precipitate on the negative electrode surface, thereby improving the charging capacity of the secondary battery, while avoiding the formation of dendrites such as metal lithium as much as possible, thereby improving the safety performance of the secondary battery.

[0017] In some embodiments of the present application, the electronic insulating layer comprises a first electronic insulating material, and the first electronic insulating material satisfies at least one of the following conditions:

[0018] (1) the average particle size of the particles of the first electronic insulating material is 0.1 μm to 50 μm, and optionally 1 μm to 20 μm; and

[0019] (2) The mass proportion of the first electronic insulating material in the electronic insulating layer is 70% to 100%, and can be optionally 90% to 99.9%.

[0020] The average particle size of the particles of the first electronic insulating material is controlled within a suitable range, which is beneficial to the diffusion of active ions in the electronic insulating layer and improves the charging capacity of the battery; it also ensures that the electronic insulating layer has a high compaction density.

[0021] In some embodiments of the present application, the first electronic insulating material includes a first solid electrolyte.

[0022] Optionally, the first solid electrolyte comprises a sulfide electrolyte, an oxide electrolyte, a polymer electrolyte or a combination thereof,

[0023] Further optionally, the first solid electrolyte includes LLZO, LLZTO, aluminum oxide, polyethylene oxide, lithium sulfide or a combination thereof.

[0024] The above-mentioned first solid electrolyte used in this application can ensure that the electronic insulating layer has active ion transport properties while not having electronic conductivity, so as to form an electric potential gradient with gradually decreasing electric field strength from the side close to the negative electrode current collector to the negative electrode surface after being combined with the active material layer, thereby realizing the orderly migration and embedding of active ions in the negative electrode, thereby improving the charging capacity of the secondary battery.

[0025] In some embodiments of the present application, the electronic semi-insulating layer comprises an electronic semi-insulating material and / or a combination of a second electronic insulating material and a conductive filler. Optionally, the second electronic insulating material comprises a second solid electrolyte.

[0026] The electronic semi-insulating material used in this application can ensure that the electronic semi-insulating layer has active ion transport characteristics, and at the same time the electronic conductivity is between almost no electronic conductivity and the electronic conductivity possessed by the active material layer, so that the electronic semi-insulating layer and the active material layer are combined to form an electric potential gradient in which the electric field strength gradually decreases from the side close to the negative electrode current collector to the negative electrode surface, thereby realizing the orderly migration and embedding of active ions in the negative electrode, thereby improving the charging capacity of the secondary battery.

[0027] In some embodiments of the present application, the electronic semi-insulating layer satisfies at least one of the following conditions:

[0028] (1) The electronic semi-insulating material comprises lithium titanate, silicon, sulfur, silicon oxide or a combination thereof;

[0029] (2) The average particle size of the particles of the electronic semi-insulating material is 0.1 μm to 50 μm, and can be 1 μm to 20 μm;

[0030] (3) The second solid electrolyte comprises a sulfide electrolyte, an oxide electrolyte, a polymer electrolyte or a combination thereof,

[0031] Optionally, the second solid electrolyte includes LLZO, LLZTO, aluminum oxide, polyethylene oxide, lithium sulfide or a combination thereof;

[0032] (4) the average particle size of the particles of the second electronic insulating material is 0.1 μm to 50 μm, optionally 1 μm to 20 μm; and

[0033] (5) The conductive filler includes superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, carbon nanofibers or a combination thereof,

[0034] Optionally, the conductive filler accounts for 0.1% to 50% by mass in the composition, and optionally 0.5% to 30% by mass.

[0035] The use of the above-mentioned second solid electrolyte in this application can ensure that the electronic semi-insulating layer has active ion transport properties while not having electronic conductivity, so that the electronic semi-insulating layer and the active material layer are combined to form an electric potential gradient in which the electric field strength gradually decreases from the side close to the negative electrode current collector to the negative electrode surface, thereby realizing the orderly migration and embedding of active ions in the negative electrode, thereby improving the charging capacity of the secondary battery.

[0036] In some embodiments of the present application, the electronic semi-insulating layer comprises an electronic semi-insulating material, and the mass proportion of the electronic semi-insulating material in the electronic semi-insulating layer is 70% to 100%, and optionally 90% to 99.9%.

[0037] The mass fraction of the electronic semi-insulating material in the electronic semi-insulating layer is within an appropriate range, and the conductivity σ2 of the electronic semi-insulating layer can be controlled within the aforementioned range provided in this application, thereby facilitating the formation of a potential gradient in the negative electrode sheet, in which the electric field intensity gradually decreases from the side close to the negative electrode current collector to the negative electrode surface. At the same time, by regulating the mass fraction of the electronic semi-insulating material in the electronic semi-insulating layer, the potential gradient can be regulated, thereby adjusting the electron transport network of the negative electrode and achieving orderly migration and embedding of active ions in the negative electrode, thereby improving the charging capacity of the secondary battery.

[0038] In some embodiments of the present application, the electronic semi-insulating layer comprises the composition, and the mass proportion of the composition in the electronic semi-insulating layer is 70% to 100%, and optionally 90% to 99.9%.

[0039] The composition's mass fraction in the electronic semi-insulating layer is within a suitable range, and the conductivity σ2 of the electronic semi-insulating layer can be controlled within the aforementioned range provided in this application, thereby facilitating the formation of a potential gradient in the negative electrode sheet, with the electric field intensity gradually decreasing from the side closest to the negative electrode current collector toward the negative electrode surface. At the same time, by regulating the composition's mass fraction in the electronic semi-insulating layer, the potential gradient can be regulated, thereby adjusting the negative electrode's electron transport network and achieving orderly migration and embedding of active ions in the negative electrode, thereby improving the rechargeability of the secondary battery.

[0040] In some embodiments of the present application, the electronic semi-insulating layer comprises an electronic semi-insulating material and the composition, and the total mass of the electronic semi-insulating material and the composition accounts for 70% to 100% of the mass of the electronic semi-insulating layer, and can optionally be 90% to 99.9%.

[0041] The total mass of the electronic semi-insulating material and the composition accounts for a proportion of the total mass of the electronic semi-insulating layer in the electronic semi-insulating layer within an appropriate range, and the electrical conductivity σ2 of the electronic semi-insulating layer can be controlled within the aforementioned range provided in the present application, thereby facilitating the formation of a potential gradient in the negative electrode sheet in which the electric field strength gradually decreases from the side close to the negative electrode current collector to the negative electrode surface.

[0042] In some embodiments of the present application, the active material layer contains a negative electrode active material, and the negative electrode active material satisfies at least one of the following conditions:

[0043] (1) The negative electrode active material includes artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material, lithium titanate or a combination thereof,

[0044] Optionally, the silicon-based material includes one or more of elemental silicon, silicon oxide compounds, silicon-carbon compounds, silicon-nitrogen compounds, and silicon alloys, and the tin-based material includes elemental tin, tin oxide compounds, tin alloys, or combinations thereof;

[0045] (2) The average particle size of the particles of the negative electrode active material is 1 μm to 100 μm, and can be 2 μm to 50 μm.

[0046] The average particle size of the negative electrode active material particles is controlled within an appropriate range, which is beneficial to the transmission of active ions and reduces the contact area between the negative electrode and the electrolyte, thereby improving the charging capacity of the battery; it also ensures that the active material layer has a high compaction density.

[0047] In some embodiments of the present application, the negative electrode plate satisfies at least one of the following conditions:

[0048] (1) The average particle size ratio of the first electronic insulating material particles to the negative electrode active material particles is (1:50) to (50:1), and can be (1:10) to (10:1);

[0049] (2) the ratio of the average particle size of the particles of the second electronic insulating material to the average particle size of the particles of the negative electrode active material is (1:50) to (50:1), and can be optionally (1:10) to (10:1); and

[0050] (3) The ratio of the average particle size of the particles of the electronic semi-insulating material to the average particle size of the particles of the negative electrode active material is (1:50) to (50:1), and can be optionally (1:10) to (10:1).

[0051] The ratio of the average particle size of the first electronic insulating material, the second electronic insulating material or the electronic semi-insulating material to the particles of the negative electrode active material is controlled within an appropriate range so that the electronic insulating layer or the electronic semi-insulating layer located between two adjacent active material layers does not affect the porosity of the active material layer located thereunder.

[0052] In some embodiments of the present application, the composite layer satisfies at least one of the following conditions:

[0053] (1) The coating weight of the active ion transport layer is 0.06 mg / cm 2 Up to 13 mg / cm 2 , optional 0.1mg / cm 2 Up to 7 mg / cm 2 ;and

[0054] (2) The coating weight of the active material layer is 0.06 mg / cm 2 Up to 65mg / cm 2 , optional 0.13mg / cm 2 Up to 26 mg / cm 2 .

[0055] In some embodiments of the present application, the coating weight ratio between the two active material layers located on opposite sides of the active ion transport layer and adjacent to the active ion transport layer is (1:99) to (99:1), and can be optionally (5:90) to (90:5).

[0056] The coating weights of the active ion transport layer and the active material layer, and the coating weight ratio between the two active material coating layers are all controlled within an appropriate range, which can form an effective potential gradient without affecting the transmission of electrons.

[0057] In some embodiments of the present application, the composite layer satisfies at least one of the following conditions:

[0058] (1) The thickness of the active ion transport layer is 0.2 μm to 50 μm, and optionally 1 μm to 20 μm; and

[0059] (2) The thickness of the active material layer is 1 μm to 500 μm, and can be optionally 10 μm to 300 μm.

[0060] The thicknesses of the active ion transport layer and the active material layer are both within a suitable range, which can not only provide a good migration channel for the active ions and facilitate the transport of active ions, but also help to form an effective potential gradient, realize the orderly migration and embedding of active ions in the negative electrode, thereby improving the charging capacity of the secondary battery.

[0061] In some embodiments of the present application, the thickness ratio of the active ion transport layer to the active material layer adjacent to the active ion transport layer is (1:3) to (1:100), and can be optionally (1:5) to (1:50).

[0062] The thickness ratio of the active ion transport layer to the active material layer adjacent to the active ion transport layer is controlled within an appropriate range, which is conducive to forming an effective potential gradient.

[0063] A second aspect of the present application provides a secondary battery, comprising the negative electrode sheet described in the first aspect of the present application.

[0064] A third aspect of the present application provides an electrical device comprising the secondary battery described in the second aspect of the present application.

[0065] The electric device of the present application includes the secondary battery provided by the present application, and thus has at least the same advantages as the secondary battery.

[0066] The details of one or more embodiments of the present application are set forth in the following drawings and description. Other features, objects, and advantages of the present application will become apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] FIG1 is a schematic diagram of an embodiment of a negative electrode sheet of the present application.

[0068] FIG. 2 is a schematic diagram of an embodiment of a secondary battery of the present application.

[0069] FIG3 is an exploded schematic diagram of an embodiment of a secondary battery of the present application.

[0070] FIG4 is a schematic diagram of another embodiment of the secondary battery of the present application.

[0071] FIG5 is a schematic diagram of another embodiment of the secondary battery of the present application.

[0072] FIG. 6 is an exploded view of FIG. 5 .

[0073] FIG. 7 is a schematic diagram of an embodiment of an electric device using a secondary battery as a power source according to the present application. DETAILED DESCRIPTION

[0074] To make the purpose, technical solutions, and advantages of this application more clear, the technical solutions of this application will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of this application, rather than all the embodiments. The relevant embodiments described herein are illustrative and are used to provide a basic understanding of this application. The embodiments of this application should not be interpreted as limiting this application.

[0075] For the sake of clarity, only some numerical ranges are specifically disclosed herein. However, any lower limit may be combined with any upper limit to form an unspecified range; and any lower limit may be combined with other lower limits to form an unspecified range, and similarly, any upper limit may be combined with any other upper limit to form an unspecified range. In addition, each individually disclosed point or single value may itself serve as a lower limit or upper limit and be combined with any other point or single value, or with other lower limits or upper limits, to form an unspecified range.

[0076] In the description herein, unless otherwise specified, “above” and “below” include the number itself.

[0077] Unless otherwise specified, the terms used in this application have the commonly understood meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of the various parameters mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application).

[0078] A list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single component or multiple components. Item B may contain a single component or multiple components. Item C may contain a single component or multiple components.

[0079] Currently, in order to improve the electron transmission performance of secondary batteries, conventional practices usually include adding a highly conductive conductive agent to the negative electrode of the secondary battery to improve the electron transmission performance of the secondary battery by improving the conductivity of the negative electrode. However, during the research process, the inventors found that for a highly conductive negative electrode, during the fast charging cycle of the secondary battery, when electron transmission is fast, due to the relatively uniform electric field strength of the negative electrode, a large number of active ions such as lithium ions will accumulate on the surface of the negative electrode, which can easily be reduced to form dendrites such as metallic lithium, which may pierce the diaphragm, thereby reducing the safety performance of the secondary battery.

[0080] To address these issues, the inventors, through extensive research, have ingeniously designed a negative electrode sheet comprising a negative current collector and a composite layer disposed on at least one side of the negative current collector. By designing and adjusting the composite layer, a controllable potential gradient can be formed within the negative electrode. By manipulating this potential gradient, the negative electrode's electron transport network can be adjusted, inducing active ions such as lithium ions to embed first near the negative current collector and then sequentially toward the negative electrode surface. This in turn prolongs the time it takes for metallic lithium and other ions to precipitate on the negative electrode surface, thereby improving the secondary battery's charging capacity and safety.

[0081] Negative electrode

[0082] A first aspect of an embodiment of the present application provides a negative electrode plate, as shown in Figure 1, comprising: a negative electrode current collector 6; and a composite layer 7 arranged on at least one side of the negative electrode current collector, the composite layer 7 comprising at least two stacked active material layers 71 and at least one active ion transport layer 72, wherein the active material layers 71 and the active ion transport layers 72 are alternately arranged, the active ion transport layer 72 is located between two adjacent active material layers 71, and each of the active ion transport layers 72 independently includes one of an electronic insulating layer and an electronic semi-insulating layer.

[0083] It is understood that the “active ions” mentioned in the present application refer to ions, such as lithium ions, that are intercalated and deintercalated back and forth between the two electrodes of the secondary battery to ensure the normal operation of the secondary battery.

[0084] It can be understood that the "electronic insulation" mentioned in this application refers to having active ion transport properties but no electronic conductivity; the "electronic semi-insulation" mentioned herein refers to having active ion transport properties and electronic conductivity, but the electronic conductivity is between no electronic conductivity and the electronic conductivity possessed by the active material layer.

[0085] The negative electrode provided in the present application includes a negative electrode current collector and a composite layer, wherein the composite layer includes an active material layer and an active ion transport layer. Without intending to be limited by any theory, the inventors have found that after an active ion transport layer composed of an electronic insulating layer or an electronic semi-insulating layer is provided between the active material layers, since the electronic insulating layer or the electronic semi-insulating layer has active ion transport characteristics, but has no electronic conductivity or the electronic conductivity is lower than the electronic conductivity possessed by the active material layer. Therefore, the distribution of electrons in the negative electrode plate will decrease from the negative electrode current collector side to the surface of the negative electrode plate, thereby forming an electric field strength that gradually decreases from the side close to the negative electrode current collector to the negative electrode surface, thereby forming a potential gradient, which can make the negative electrode plate's ability to induce active ions gradually weaken from the side close to the negative electrode current collector to the surface of the negative electrode plate. By regulating the above-mentioned potential gradient, the electron transport network of the negative electrode can be adjusted. When active ions such as lithium ions reach the surface of the negative electrode, they can be induced to embed first toward the side close to the negative electrode current collector, and then sequentially embed toward the negative electrode surface, thereby achieving orderly migration and embedding of active ions in the negative electrode, reducing the accumulation of active ions on the negative electrode surface, and prolonging the time for metallic lithium and the like to precipitate on the negative electrode surface, thereby improving the charging capacity of the secondary battery, while avoiding the formation of dendrites such as metallic lithium on the negative electrode surface as much as possible, thereby improving the safety performance of the secondary battery.

[0086] It is understood that the composite layer of the present application may be provided with only one active ion transport layer or multiple active ion transport layers. When multiple active ion transport layers are provided in the composite layer, the two active ion transport layers adjacent to any active material layer may be the same or different; for example, the two active ion transport layers may both be electronic insulating layers, or both be electronic semi-insulating layers, or each may be an electronic insulating layer and an electronic semi-insulating layer. At the same time, when multiple active ion transport layers are provided in the composite layer, considering the process and adhesion, the preferred number of active ion transport layers may be two.

[0087] In some embodiments, the electrical conductivity of the electronic insulating layer is σ1, and σ1 satisfies: 0<σ1<10 -10 S / cm. For example, σ1 can satisfy: 0<σ1≤10 -30 S / cm, 0<σ1≤10 -25 S / cm, 0<σ1≤10 -20 S / cm, 0<σ1≤10 -15 S / cm, 0<σ1≤10 -11 S / cm, 10 -30 S / cm≤σ1≤10 -11 S / cm, 10 -25 S / cm≤σ1≤10 -11 S / cm, 10 -20S / cm≤σ1≤10 -11 S / cm, 10 -15 S / cm≤σ1≤10 -11 S / cm, 10 -30 S / cm≤σ1≤10 -15 S / cm, 10 -25 S / cm≤σ1≤10 -15 S / cm, 10 -20 S / cm≤σ1≤10 -15 S / cm or 10 -30 S / cm≤σ1≤10 -20 S / cm. Optionally, σ1 satisfies: 10 -15 S / cm≤σ1≤10 -11 S / cm. The conductivity of the electronic insulating layer is within a suitable range, and an active ion transport layer with no electronic conductivity can be formed. By cooperating with the active material layer, it is conducive to forming an electric field strength in the negative electrode sheet, in which the electric field strength gradually decreases from the side close to the negative electrode current collector to the negative electrode surface. This potential gradient can gradually weaken the induction ability of the negative electrode sheet to the active ions from the side close to the negative electrode current collector to the surface of the negative electrode sheet. When active ions such as lithium ions reach the negative electrode surface, the active ions can be induced to first be embedded in the side close to the negative electrode current collector, and then in turn embedded in the negative electrode surface. In this way, the orderly migration and embedding of active ions in the negative electrode is achieved, the accumulation of active ions on the negative electrode surface is reduced, and the time for metal lithium and the like to precipitate on the negative electrode surface is prolonged, thereby improving the charging capacity of the secondary battery, while avoiding the formation of dendrites such as metal lithium as much as possible, thereby improving the safety performance of the secondary battery.

[0088] In some embodiments, the conductivity of the electronic semi-insulating layer is σ2, and σ2 satisfies: 10 -10 S / cm≤σ2≤10 2 S / cm. For example, σ2 can satisfy, 10 -9 S / cm≤σ2≤10 2 S / cm, 10 -8 S / cm≤σ2≤10 2 S / cm, 10 -6 S / cm≤σ2≤10 2 S / cm, 10 -5 S / cm≤σ2≤10 2 S / cm, 10 -4 S / cm≤σ2≤10 2 S / cm, 10 -3 S / cm≤σ2≤10 2 S / cm, 10 -2 S / cm≤σ2≤10 2 S / cm, 10 -1S / cm≤σ2≤10 2 S / cm, 1S / cm≤σ2≤10 2 S / cm, 10S / cm≤σ2≤10 2 S / cm, 10 -10 S / cm≤σ2≤10S / cm,10 -9 S / cm≤σ2≤10S / cm,10 -8 S / cm≤σ2≤10S / cm,10 -7 S / cm≤σ2≤10S / cm,10 -6 S / cm≤σ2≤10S / cm,10 -5 S / cm≤σ2≤10S / cm,10 -4 S / cm≤σ2≤10S / cm,10 -3 S / cm≤σ2≤10S / cm,10 -2 S / cm≤σ2≤10S / cm,10 -1 S / cm≤σ2≤10S / cm, 1S / cm≤σ2≤10S / cm, 10 -10 S / cm≤σ2≤10 -1 S / cm, 10 -9 S / cm≤σ2≤10 -1 S / cm, 10 -8 S / cm≤σ2≤10 -1 S / cm, 10 -7 S / cm≤σ2≤10 -1 S / cm, 10 -6 S / cm≤σ2≤10 -1 S / cm, 10 -5 S / cm≤σ2≤10 -1 S / cm, 10 -4 S / cm≤σ2≤10 -1 S / cm, 10 -3 S / cm≤σ2≤10 -1 S / cm or 10 -2 S / cm≤σ2≤10 -1 S / cm. Optionally, σ2 satisfies: 10 -6 S / cm≤σ2≤10 -3 S / cm.

[0089] The conductivity of the electronic semi-insulating layer is within a suitable range, enabling the electronic conductivity of the active ion transport layer to be between that of no electronic conductivity and that of the active material layer. This, in conjunction with the active material layer, facilitates the formation of a potential gradient in the negative electrode sheet, where the electric field strength gradually decreases from the side closest to the negative current collector toward the negative electrode surface. This potential gradient gradually weakens the negative electrode sheet's ability to induce active ions from the side closest to the negative current collector toward the surface of the negative electrode sheet. When active ions such as lithium ions reach the negative electrode surface, they are induced to embed first toward the side closest to the negative current collector and then, sequentially, toward the negative electrode surface. This achieves orderly migration and embedding of active ions in the negative electrode, reduces the accumulation of active ions on the negative electrode surface, and prolongs the time it takes for metallic lithium and the like to precipitate on the negative electrode surface, thereby improving the secondary battery's charge capacity. This, in turn, minimizes the formation of dendrites such as metallic lithium, thereby enhancing the safety performance of the secondary battery.

[0090] In some embodiments, the conductivity of the active material layer is σ3, and σ3 satisfies: 10 -6 S / cm≤σ3≤10 5 S / cm. For example, σ3 can satisfy: 10 -5 S / cm≤σ3≤10 5 S / cm, 10 -4 S / cm≤σ3≤10 5 S / cm, 10 -3 S / cm≤σ3≤10 5 S / cm, 10 -2 S / cm≤σ3≤10 5 S / cm, 10 -1 S / cm≤σ3≤10 5 S / cm, 1S / cm≤σ3≤10 5 S / cm, 10S / cm≤σ3≤10 5 S / cm, 10 2 S / cm≤σ3≤10 5 S / cm, 10 3 S / cm≤σ3≤10 5 S / cm, 10 4 S / cm≤σ3≤10 5 S / cm, 10 -5 S / cm≤σ3≤10 4 S / cm, 10 -5 S / cm≤σ3≤10 3 S / cm, 10 -5 S / cm≤σ3≤10 2 S / cm, 10 -5 S / cm≤σ3≤10S / cm,10 -5 S / cm≤σ3≤1S / cm,10-5 S / cm≤σ3≤10 -1 S / cm, 10 -5 S / cm≤σ3≤10 -2 S / cm, 10 -5 S / cm≤σ3≤10 -3 S / cm or 10 -5 S / cm≤σ3≤10 -4 S / cm. Optionally, σ3 satisfies: 10 -4 S / cm≤σ3≤10 3 S / cm.

[0091] The conductivity of the active material layer is within a suitable range, and it can form an electric potential gradient in the negative electrode sheet through cooperation with the active ion transport layer, in which the electric field strength gradually decreases from the side close to the negative electrode current collector to the negative electrode surface. This potential gradient can gradually weaken the negative electrode sheet's ability to induce active ions from the side close to the negative electrode current collector to the surface of the negative electrode sheet. When active ions such as lithium ions reach the negative electrode surface, they can be induced to first embed toward the side close to the negative electrode current collector, and then sequentially embed toward the negative electrode surface. This achieves the orderly migration and embedding of active ions in the negative electrode, reduces the accumulation of active ions on the negative electrode surface, and prolongs the time for metallic lithium and the like to precipitate on the negative electrode surface, thereby improving the charging capacity of the secondary battery. At the same time, the formation of dendrites such as metallic lithium is avoided as much as possible, thereby improving the safety performance of the secondary battery.

[0092] In some embodiments, the sheet resistance of the negative electrode is R, and R satisfies: 0.1mΩ≤R≤5000mΩ. For example, R can be 0.5mΩ, 1mΩ, 5mΩ, 10mΩ, 25mΩ, 50mΩ, 100mΩ, 250mΩ, 500mΩ, 750mΩ, 1000mΩ, 1500mΩ, 2000mΩ, 2500mΩ, 3000mΩ, 3500mΩ, 4000mΩ, 4500Ω or within a range consisting of any of the above values. Optionally, R satisfies: 1mΩ≤R≤1000mΩ. The sheet resistance of the negative electrode is within a suitable range,

[0093] The sheet resistance of the negative electrode is well known in the art and can be measured using instruments and methods known in the art. For example, several sheets with an area of ​​154.02 mm can be punched out. 2 The negative electrode sheet sample is tested by a diaphragm resistance tester, such as the BER1300 tester of IEST Yuanneng Technology, and the average diaphragm resistance of 10 parallel samples is used as the diaphragm resistance value of the negative electrode sheet.

[0094] The sheet resistance of the negative electrode is within an appropriate range, which is conducive to forming an electric potential gradient in the negative electrode, where the electric field strength gradually decreases from the side close to the negative electrode current collector to the negative electrode surface. This potential gradient can gradually weaken the negative electrode's ability to induce active ions from the side close to the negative electrode current collector to the surface of the negative electrode. When active ions such as lithium ions reach the negative electrode surface, they can be induced to first embed toward the side close to the negative electrode current collector, and then sequentially embed toward the negative electrode surface. This achieves the orderly migration and embedding of active ions in the negative electrode, reduces the accumulation of active ions on the negative electrode surface, and prolongs the time it takes for metallic lithium and other ions to precipitate on the negative electrode surface, thereby improving the charging capacity of the secondary battery. At the same time, it minimizes the formation of dendrites such as metallic lithium, thereby improving the safety performance of the secondary battery.

[0095] In some embodiments, the electronic insulating layer comprises a first electronic insulating material. The first electronic insulating material comprises a first solid electrolyte, which may include but is not limited to one or more of a sulfide electrolyte, an oxide electrolyte, and a polymer electrolyte.

[0096] In some embodiments, the first solid electrolyte may include, but is not limited to, one or more of LLZO, LLZTO, aluminum oxide, polyethylene oxide, and lithium sulfide. The use of the above-mentioned first solid electrolyte in this application can ensure that the electronic insulating layer has active ion transport properties while lacking electronic conductivity, so that, when combined with the active material layer, a potential gradient is formed in which the electric field intensity gradually decreases from the side close to the negative electrode current collector to the negative electrode surface, thereby achieving orderly migration and embedding of active ions in the negative electrode, thereby improving the rechargeability of the secondary battery.

[0097] It should be noted that in this application, LLZO refers to the garnet-type solid electrolyte Li7La3Zr2O 12 , and LLZTO refers to Ta-doped LLZO.

[0098] In some embodiments, the first electronic insulating material comprises 70% to 100% by weight of the electronic insulating layer. For example, the first electronic insulating material comprises 75%, 80%, 85%, 90%, 95%, 99% by weight of the electronic insulating layer, or any range thereof. Alternatively, the first electronic insulating material comprises 90% to 99.9% by weight of the electronic insulating layer.

[0099] The mass proportion of the first electronic insulating material in the electronic insulating layer is within an appropriate range, and the electrical conductivity σ1 of the electronic insulating layer can be controlled within the aforementioned range provided in this application, thereby facilitating the formation of a potential gradient in the negative electrode sheet, in which the electric field intensity gradually decreases from the side close to the negative electrode current collector to the negative electrode surface. At the same time, by regulating the mass proportion of the first electronic insulating material in the electronic insulating layer, the electrical conductivity σ1 of the electronic insulating layer can be regulated, thereby achieving the regulation of the potential gradient, thereby adjusting the electron transport network of the negative electrode, achieving the orderly migration and embedding of active ions in the negative electrode, and thus improving the charging capacity of the secondary battery.

[0100] It should be noted that, in addition to the first electronic insulating material, the electronic insulating layer of the present application may optionally include a binder to enhance the bonding strength between the electronic insulating layer and the active material layer. The binder may be a conventional binder, which may include but is not limited to polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and one or more of a fluorine-containing acrylate resin.

[0101] The average particle size of the particles of the first electronic insulating material is 0.1 μm to 50 μm. For example, the average particle size of the particles of the first electronic insulating material can be 0.5 μm, 1 μm, 5 μm, 10 μm, 20 μm, 30 μm, 40 μm, or within a range consisting of any of the above values. Optionally, the average particle size of the particles of the first electronic insulating material is 1 μm to 20 μm. Controlling the average particle size of the particles of the first electronic insulating material within a suitable range is beneficial to the diffusion of active ions in the electronic insulating layer, improving the charging capacity of the battery, and ensuring that the electronic insulating layer has a high compaction density.

[0102] In some embodiments, the electronically semi-insulating layer comprises a combination of an electronically semi-insulating material and / or a second electronically insulating material and a conductive filler.

[0103] It is understandable that the electronic semi-insulating layer may contain only the electronic semi-insulating material, only the combination of the second electronic insulating material and the conductive filler, or a combination of the electronic semi-insulating material, the second electronic insulating material and the conductive filler.

[0104] In some embodiments, the electronic semi-insulating material is not particularly limited, as long as it has active ion transport properties and its electronic conductivity is between that of no electronic conductivity and that of the active material layer. For example, the electronic semi-insulating material may include but is not limited to lithium titanate (LTO), silicon, sulfur, and silicon oxide (SiO x). The electronic semi-insulating material used in this application can ensure that the electronic semi-insulating layer has active ion transport properties, and at the same time, the electronic conductivity is between the electronic conductivity of no electronic conductivity and the electronic conductivity of the active material layer. Therefore, when the electronic semi-insulating layer and the active material layer are combined, a potential gradient is formed in which the electric field intensity gradually decreases from the side close to the negative electrode current collector to the negative electrode surface, thereby achieving orderly migration and embedding of active ions in the negative electrode, thereby improving the charging capacity of the secondary battery.

[0105] In some embodiments, the average particle size of the particles of the electronic semi-insulating material is 0.1 μm to 50 μm. For example, the average particle size of the particles of the electronic semi-insulating material can be 0.5 μm, 1 μm, 5 μm, 10 μm, 20 μm, 30 μm, 40 μm, or within a range consisting of any of the above values. Optionally, the average particle size of the particles of the electronic semi-insulating material is 1 μm to 20 μm. Controlling the average particle size of the particles of the electronic semi-insulating material within a suitable range is beneficial to the diffusion of active ions in the electronic semi-insulating layer, improving the charging capacity of the battery, and ensuring that the electronic semi-insulating layer has a high compaction density.

[0106] In some embodiments, when the electronic semi-insulating layer comprises only the electronic semi-insulating material, the electronic semi-insulating material accounts for 70% to 100% by weight of the electronic semi-insulating layer. For example, the electronic semi-insulating material accounts for 75%, 80%, 85%, 90%, 95%, 99% by weight of the electronic semi-insulating layer, or any range thereof. Alternatively, the electronic semi-insulating material accounts for 90% to 99.9% by weight of the electronic semi-insulating layer.

[0107] When the electronic semi-insulating layer contains only electronic semi-insulating material, the mass ratio of the electronic semi-insulating material in the electronic semi-insulating layer is within an appropriate range, and the conductivity σ2 of the electronic semi-insulating layer can be controlled within the aforementioned range provided in this application, thereby facilitating the formation of a potential gradient in the negative electrode sheet in which the electric field intensity gradually decreases from the side close to the negative electrode current collector to the negative electrode surface. At the same time, by regulating the mass ratio of the electronic semi-insulating material in the electronic semi-insulating layer, the conductivity σ2 of the electronic semi-insulating layer can be regulated, thereby achieving the regulation of the potential gradient, thereby adjusting the electron transport network of the negative electrode, achieving the orderly migration and embedding of active ions in the negative electrode, and thus improving the charging capacity of the secondary battery.

[0108] In some embodiments, the second electronically insulating material may include a second solid electrolyte. The second solid electrolyte may include, but is not limited to, one or more of a sulfide electrolyte, an oxide electrolyte, and a polymer electrolyte.

[0109] In some embodiments, the second solid electrolyte may include, but is not limited to, one or more of LLZO, LLZTO, aluminum oxide, ethylene oxide, and lithium sulfide. The use of the aforementioned second solid electrolyte in this application can ensure that the electronic semi-insulating layer has active ion transport properties while lacking electronic conductivity, so that the electronic semi-insulating layer and the active material layer form a potential gradient with a gradually decreasing electric field intensity from the side close to the negative electrode current collector toward the negative electrode surface, thereby achieving orderly migration and embedding of active ions in the negative electrode, thereby improving the rechargeability of the secondary battery.

[0110] In some embodiments, when the electronic semi-insulating layer comprises only a composition of the second electronic insulating material and the conductive filler, the composition comprises 70% to 100% by weight of the electronic semi-insulating layer. For example, the composition may comprise 75%, 80%, 85%, 90%, 95%, 99% by weight of the electronic semi-insulating layer, or any range thereof. Alternatively, the composition may comprise 90% to 99.9% by weight of the electronic semi-insulating layer.

[0111] When the electronic semi-insulating layer only contains a composition of a second electronic insulating material and a conductive filler, the mass proportion of the composition in the electronic semi-insulating layer is within an appropriate range, and the conductivity σ2 of the electronic semi-insulating layer can be controlled within the aforementioned range provided in this application, thereby facilitating the formation of a potential gradient in the negative electrode sheet in which the electric field intensity gradually decreases from the side close to the negative electrode current collector to the negative electrode surface. At the same time, by regulating the mass proportion of the composition in the electronic semi-insulating layer, the conductivity σ2 of the electronic semi-insulating layer can be regulated, thereby achieving the regulation of the potential gradient, thereby adjusting the electron transport network of the negative electrode, achieving the orderly migration and embedding of active ions in the negative electrode, and thus improving the charging capacity of the secondary battery.

[0112] In some embodiments, the average particle size of the particles of the second electronic insulating material in the composition is 0.1 μm to 50 μm. For example, the average particle size of the particles of the second electronic insulating material in the composition can be 0.5 μm, 1 μm, 5 μm, 10 μm, 20 μm, 30 μm, 40 μm or within a range consisting of any of the above values. Optionally, the average particle size of the particles of the second electronic insulating material in the composition is 1 μm to 20 μm. The average particle size of the particles of the second electronic insulating material is controlled within a suitable range, which is beneficial to the diffusion of active ions in the electronic semi-insulating layer and improves the charging capacity of the battery; it can also ensure that the electronic semi-insulating layer has a high compaction density.

[0113] In some embodiments, when the electronic semi-insulating layer comprises both an electronic semi-insulating material and a composition of a second electronic insulating material and a conductive filler, the total mass of the electronic semi-insulating material and the composition accounts for 70% to 100% of the mass of the electronic semi-insulating layer. For example, the total mass of the electronic semi-insulating material and the composition may account for 75%, 80%, 85%, 90%, 95%, 99% or any range thereof. Alternatively, the total mass of the electronic semi-insulating material and the composition accounts for 90% to 99.9% of the mass of the electronic semi-insulating layer.

[0114] When the electronic semi-insulating layer contains both an electronic semi-insulating material and a composition of a second electronic insulating material and a conductive filler, the mass ratio of the total mass of the electronic semi-insulating material and the composition in the electronic semi-insulating layer is within a suitable range, and the conductivity σ2 of the electronic semi-insulating layer can be controlled within the aforementioned range provided in this application, thereby facilitating the formation of a potential gradient in the negative electrode sheet in which the electric field intensity gradually decreases from the side close to the negative electrode current collector to the negative electrode surface. At the same time, by regulating the mass ratio of the total mass of the electronic semi-insulating material and the composition in the electronic semi-insulating layer, the conductivity σ2 of the electronic semi-insulating layer can be regulated, thereby achieving the regulation of the potential gradient, thereby adjusting the electron transport network of the negative electrode, achieving the orderly migration and embedding of active ions in the negative electrode, and thus improving the charging capacity of the secondary battery.

[0115] In some embodiments, the conductive filler may be a conventional conductive agent in the art. For example, the conductive filler may include, but is not limited to, one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0116] In some embodiments, the conductive filler accounts for 0.1% to 50% by mass in the composition. For example, the conductive filler accounts for 0.5%, 1%, 5%, 10%, 20%, 30%, 40% or is within the range of any of the above values. Optionally, the conductive filler accounts for 0.5% to 30% by mass in the composition. The mass proportion of the conductive filler in the composition is within a suitable range, which can regulate the electronic conductivity of the composition and control the conductivity σ2 of the electronic semi-insulating layer within the aforementioned range provided in this application, thereby facilitating the formation of a potential gradient in the negative electrode sheet in which the electric field strength gradually decreases from the side close to the negative electrode current collector to the negative electrode surface, and the regulation of the potential gradient can be achieved, thereby adjusting the electron transport network of the negative electrode and achieving orderly migration and embedding of active ions in the negative electrode, thereby improving the charging capacity of the secondary battery.

[0117] In some embodiments, the active material layer contains a negative electrode active material. The negative electrode active material can be a negative electrode active material for a secondary battery 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 material, tin-based material, lithium titanate, etc. The silicon-based material can be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material 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 traditional materials that can be used as negative electrode active materials for batteries can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0118] Alternatively, the negative electrode active material may include, but is not limited to, one or more of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. Further, optionally, the silicon-based material includes one or more of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys, and the tin-based material includes one or more of elemental tin, tin oxides, and tin alloys.

[0119] In some embodiments, the average particle size of the particles of the negative electrode active material is 1 μm to 100 μm. For example, the average particle size of the particles of the negative electrode active material can be 5 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm or within a range consisting of any of the above values. Optionally, the average particle size of the particles of the negative electrode active material is 2 μm to 50 μm. The average particle size of the particles of the negative electrode active material is controlled within a suitable range, which is beneficial to the transmission of active ions and reduces the contact area between the negative electrode and the electrolyte, thereby improving the charging capacity of the battery; it can also ensure that the active material layer has a high compaction density.

[0120] In this application, the average particle size of the particles of the negative electrode active material, the average particle size of the particles of the first electronically insulating material, the average particle size of the particles of the electronically semi-insulating material, and the average particle size of the particles of the second electronically insulating material are all well-known in the art and can be measured using instruments and methods well-known in the art. For example, they can be conveniently measured using a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK, with reference to GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method.

[0121] In some embodiments, the ratio of the average particle size of the particles of the first electronic insulating material to the particles of the negative electrode active material is (1:50) to (50:1). For example, the ratio of the average particle size of the particles of the first electronic insulating material to the particles of the negative electrode active material can be 1:40, 1:30, 1:20, 1:10, 1:1, 5:1, 10:1, 20:1, 30:1, 40:1, or within a range consisting of any of the above values. Alternatively, the ratio of the average particle size of the particles of the first electronic insulating material to the particles of the negative electrode active material is (1:10) to (10:1).

[0122] In some embodiments, the ratio of the average particle size of the particles of the second electronic insulating material to the particles of the negative electrode active material is (1:50) to (50:1). For example, the ratio of the average particle size of the particles of the second electronic insulating material to the particles of the negative electrode active material can be 1:40, 1:30, 1:20, 1:10, 1:1, 5:1, 10:1, 20:1, 30:1, 40:1, or within a range consisting of any of the above values. Alternatively, the ratio of the average particle size of the particles of the second electronic insulating material to the particles of the negative electrode active material is (1:10) to (10:1).

[0123] In some embodiments, the ratio of the average particle size of the particles of the electronic semi-insulating material to the particles of the negative electrode active material is (1:50) to (50:1). For example, the ratio of the average particle size of the particles of the electronic semi-insulating material to the particles of the negative electrode active material can be 1:40, 1:30, 1:20, 1:10, 1:1, 5:1, 10:1, 20:1, 30:1, 40:1, or any range thereof. Alternatively, the ratio of the average particle size of the particles of the electronic semi-insulating material to the particles of the negative electrode active material is (1:10) to (10:1).

[0124] In the present application, the ratio of the average particle size of the particles of the first electronic insulating material, the second electronic insulating material or the electronic semi-insulating material to the negative electrode active material is controlled within the corresponding ranges described above to ensure that the electronic insulating layer or the electronic semi-insulating layer located between two adjacent active material layers does not affect the porosity of the active material layer located therebelow. If the ratio of the average particle sizes of the particles is relatively small, the particles of the electronic insulating layer or the electronic semi-insulating layer located in the middle may penetrate into the active material layer below, filling the pores of the active material layer below, which may in turn affect the infiltration of the electrolyte into the active material and the transport of active ions. If the ratio of the average particle sizes of the particles is relatively large, it may affect the overall compaction density of the negative electrode.

[0125] In some embodiments, the coating weight of the active ion transport layer is 0.06 mg / cm 2 Up to 13 mg / cm2 For example, the coating weight of the active ion transport layer can be 0.1 mg / cm 2 , 0.5mg / cm 2 , 1mg / cm 2 , 5mg / cm 2 , 10mg / cm 2 , 12mg / cm 2 Alternatively, the coating weight of the active ion transport layer is 0.1 mg / cm 2 Up to 7 mg / cm 2 .

[0126] In some embodiments, the coating weight of the active material layer is 0.06 mg / cm 2 Up to 65mg / cm 2 For example, the coating weight of the active material layer can be 0.1 mg / cm 2 , 0.5mg / cm 2 , 1mg / cm 2 , 5mg / cm 2 , 10mg / cm 2 , 20mg / cm 2 , 30mg / cm 2 , 40mg / cm 2 , 50mg / cm 2 , 60mg / cm 2 Or within the range of any of the above values. Optionally, the coating weight of the active material layer is 0.13 mg / cm 2 Up to 26 mg / cm 2 .

[0127] The coating weight of the active material layer is well known in the art and can be measured using methods known in the art. For example, a dried negative electrode sheet coated with active material is cut into five sheets of equal area. The thickness of each negative electrode sheet is measured using a micrometer, recorded as d0 cm. The active material layer is scraped off the negative electrode sheet using a scraper, and the mass of the active material layer is weighed using a balance, recorded as m (mg). The coating weight of the active material layer can be obtained by dividing m by d0.

[0128] In some embodiments, the coating weight ratio between the upper and lower active material layers located on opposite sides of the active ion transport layer and adjacent to the active ion transport layer is (1:99) to (99:1). For example, the coating weight ratio between the upper and lower active material layers can be 1:90, 1:80, 1:70, 1:60, 1:50, 1:40, 1:30, 1:10, 1:90, 1:5, 1:1, 5:1, 10:1, 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, 80:1, 90:1, or within a range consisting of any of the above values. Alternatively, the coating weight ratio between the upper and lower active material layers is (5:90) to (90:5).

[0129] In the present application, the range control of the coating weight ratio between the upper and lower layers of active material coatings is designed based on the potential distribution of the negative electrode plate in the present application. Taking the composite layer in the negative electrode plate as an example, which is three layers (that is, the composite layer includes two active material layers and one active ion transport layer, and the active ion transport layer is located between the two active material layers), if the coating weight ratio of the upper and lower active material layers is relatively high, it may affect the electron transport of the active material layer located on the upper layer, which may increase the charge transfer resistance, slow down the electrochemical kinetic process, and the electronic conductivity of the plate close to the electrolyte side is low, and the charge transfer electrons increase. The kinetic process may be relatively slow during fast charging; if the coating weight ratio of the upper and lower active material layers is relatively low, the electronic conductivity of the active material layer located on the upper layer may change little, and thus the effect of inducing active ions such as lithium ions to migrate from the surface of the negative electrode plate to the interior by the potential gradient may not be achieved.

[0130] In some embodiments, the active ion transport layer has a thickness of 0.2 μm to 50 μm. For example, the thickness of the active ion transport layer can be 0.5 μm, 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, or a range thereof. Alternatively, the thickness of the active ion transport layer is 1 μm to 20 μm.

[0131] The thickness of the active ion transport layer refers to the thickness of the active ion transport layer after cold pressing, and also includes the thickness measured after the electrode is installed in the battery and subjected to charge and discharge cycles. It can be tested using methods known in the art. For example, a micrometer (such as Mitutoyo 293-100, with an accuracy of 0.1 μm) can be used for testing.

[0132] In some embodiments, the thickness of the active material layer is 1 μm to 500 μm. For example, the thickness of the active material layer can be 1 μm, 5 μm, 10 μm, 25 μm, 50 μm, 75 μm, 100 μm, 150 μm, 200 μm, 250 μm, 300 μm, 350 μm, 400 μm, 450 μm, 500 μm, or a range thereof. Optionally, the thickness of the active material layer is 10 μm to 300 μm.

[0133] The thickness of the active material layer refers to the thickness of the active material layer after cold pressing, and also includes the thickness measured after the electrode is installed in the battery and subjected to charge and discharge cycles. It can be tested using methods known in the art. For example, a micrometer (such as Mitutoyo 293-100, with an accuracy of 0.1 μm) can be used to test the active material layer.

[0134] In the present application, the thicknesses of the active ion transport layer and the active material layer are both within an appropriate range, which can not only provide a good migration channel for the active ions and facilitate the transport of active ions, but also help to form an effective potential gradient, realize the orderly migration and embedding of active ions in the negative electrode, thereby improving the charging capacity of the secondary battery.

[0135] In some embodiments, the thickness ratio of the active ion transport layer to the active material layer adjacent to the active ion transport layer is from (1:3) to (1:100). For example, the thickness ratio can be 1:5, 1:10, 1:20, 1:30, 1:40, 1:50, 1:60, 1:70, 1:80, 1:90, or any range thereof. Alternatively, the thickness ratio is from (1:5) to (1:50).

[0136] In the present application, the thickness ratio of the active ion transport layer and the active material layer adjacent to the active ion transport layer is controlled within a suitable range, which is conducive to the formation of an effective potential gradient. If the thickness ratio of the two is relatively small, the thickness of the active ion transport layer may be thinner than the thickness of the active material layer, and an effective potential gradient may not be formed in the negative electrode sheet. When active ions such as lithium ions reach the surface of the negative electrode, it is not easy for the active ions to migrate and embed in the negative electrode in an orderly manner, and it is not easy to effectively improve the charging capacity of the secondary battery. If the thickness ratio of the two is relatively large, the thickness of the active ion transport layer may be thicker than the thickness of the active material layer, which may easily lead to a longer migration path for the active ions to be transmitted, which may affect the charging capacity of the battery.

[0137] In some embodiments, the negative electrode current collector has two opposite surfaces 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.

[0138] 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 material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material on a polymer material substrate. Among them, the metal material includes but is not limited to copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver and silver alloys, etc., and the polymer material substrate includes but is not limited to polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE) and other substrates.

[0139] 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).

[0140] In some embodiments, the active material 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.

[0141] In some embodiments, the active material layer may optionally further include other auxiliary agents, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0142] In some embodiments, the negative electrode plate can be prepared by the following method: the components for preparing the active material layer, 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 an active material slurry; the first electronic insulating material and the binder are dispersed in the solvent to form an electronic insulating slurry; the second electronic insulating material and the conductive filler are dispersed in the solvent, or the electronic semi-insulating material is dispersed in the solvent to form an electronic semi-insulating slurry; the active material slurry is coated on the negative electrode current collector and dried, and then the electronic insulating slurry or the electronic semi-insulating slurry is coated and dried, and finally the active material slurry is coated again. After drying, cold pressing and other processes, the negative electrode plate can be obtained.

[0143] The negative electrode sheet of the present application does not exclude other additional functional layers in addition to the composite layer. For example, in some embodiments, the negative electrode sheet of the present application may further include a conductive primer layer (e.g., composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the composite layer and disposed on the surface of the negative electrode current collector. In other embodiments, the negative electrode sheet of the present application may further include a protective layer covering the surface of the composite layer.

[0144] secondary batteries

[0145] A third aspect of the embodiments of the present application provides a secondary battery, including any device in which an electrochemical reaction occurs to convert chemical energy into electrical energy, for example, a sodium ion secondary battery.

[0146] In some embodiments, the secondary battery of the present application includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. During the battery's charge and discharge process, active ions are intercalated and released back and forth between the positive and negative electrode sheets. The electrolyte conducts ions between the positive and negative electrode sheets. The separator is disposed between the positive and negative electrode sheets, primarily preventing a short circuit between the positive and negative electrodes while allowing ions to pass through.

[0147] [Positive electrode]

[0148] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector. The positive electrode film layer includes a positive electrode active material. For example, the positive electrode current collector has two opposing surfaces in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposing surfaces of the positive electrode current collector.

[0149] 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 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 on a polymer material substrate. Among them, the metal material includes but is not limited to aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc. Polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0150] In some embodiments, the positive electrode active material may adopt the positive electrode active material for batteries that is 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 traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3Mn 1 / 3 O2 (also referred to as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0151] In some embodiments, the positive electrode active material may also include at least one of the following materials: a sodium transition metal oxide, a polyanionic compound, and a Prussian blue compound. However, this application is not limited to these materials; other conventional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more.

[0152] As an optional technical solution of the present application, in the sodium transition metal oxide, the transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. Sodium transition metal oxide is, for example, Na x MO2, wherein M includes one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0<x≤1.

[0153] As an optional technical solution of the present application, the polyanionic compound can be a compound having sodium ions, transition metal ions and tetrahedral (YO4) n- A class of compounds with anionic units. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce; Y can be at least one of P, S and Si; n represents (YO4) n- valence.

[0154] Polyanionic compounds can also be sodium ions, transition metal ions, tetrahedral (YO4) n- A class of compounds containing anion units and halogen anions. The transition metal includes at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y includes at least one of P, S, and Si, and n represents (YO4) n- valence state; the halogen includes at least one of F, Cl and Br.

[0155] Polyanionic compounds can also be sodium ions, tetrahedral (YO4) n- Anion unit, polyhedron unit (ZO y ) m+ and an optional halogen anion. Y includes at least one of P, S and Si, and n represents (YO4) n- valence state; Z represents a transition metal, including at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce, m represents (ZO y ) m+ valence state; the halogen includes at least one of F, Cl and Br.

[0156] Polyanionic compounds include NaFePO4, Na3V2(PO4)3 (sodium vanadium phosphate, abbreviated as NVP), Na4Fe3(PO4)2(P2O7), NaM'PO4F (M' includes one or more of V, Fe, Mn and Ni) and Na3(VOy)2(PO4)2F3- 2y At least one of (0≤y≤1).

[0157] Prussian blue compounds can be sodium ions, transition metal ions and cyanide ions (CN - ). The transition metal includes at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. Prussian blue compounds are, for example, Na a Me b Me' c (CN)6, wherein Me and Me' each independently include at least one of Ni, Cu, Fe, Mn, Co and Zn, 0<a≤2, 0<b<1, 0<c<1.

[0158] In some embodiments, the positive electrode film layer may further optionally include a conductive agent. 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.

[0159] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0160] The positive electrode sheets herein can be prepared according to conventional methods in the art. For example, the positive electrode film layer is typically formed by coating a positive electrode slurry onto a positive electrode current collector, drying, and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring them uniformly. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP).

[0161] The positive electrode sheet of the present application does not exclude other additional functional layers in addition to the positive electrode film layer. For example, in some embodiments, the positive electrode sheet of the present application further includes a conductive primer layer (e.g., composed of a conductive agent and a binder) sandwiched between the positive electrode current collector and the positive electrode film layer and disposed on the surface of the positive electrode current collector. In other embodiments, the positive electrode sheet of the present application further includes a protective layer covering the surface of the positive electrode film layer.

[0162] [Negative electrode]

[0163] The negative electrode plate may adopt the negative electrode plate of the first aspect of the present application.

[0164] [Electrolyte]

[0165] The electrolyte plays a role in conducting active ions between the positive electrode and the negative electrode. The electrolyte that can be used in the secondary battery of the present application can be an electrolyte known in the prior art.

[0166] In some embodiments, the electrolyte includes an organic solvent, an electrolyte salt, and optional additives. The types of the organic solvent, electrolyte salt, and additives are not particularly limited and can be selected according to needs.

[0167] In some embodiments, as an example, the electrolyte salt may be a lithium salt, including at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonyl imide (LiFSI, LiN(FSO2)2), lithium bistrifluoromethanesulfonyl imide (LiN(CF3SO2)2), lithium trifluoromethanesulfonate (CF3SO3Li), lithium difluorophosphate (LiPO2F2), lithium difluorooxalatoborate (LiDFOB, LiBC2O4F2), lithium dioxalatoborate (LiBOB, LiB(C2O4)2), lithium difluorodioxalatophosphate (LiDODFP, Li(C2O4)2PF2) and lithium tetrafluorooxalatophosphate (LiOTFP, LiC2O4PF4).

[0168] In some embodiments, as an example, the electrolyte salt may be a sodium salt, including but not limited to at least one of NaPF6, NaClO4, NaBCl4, NaSO3CF3, and Na(CH3)C6H4SO3. One of the sodium salts may be used alone, or two or more may be used simultaneously.

[0169] In some embodiments, as an example, the organic solvent includes but is not limited to at least one of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS) and diethyl sulfone (ESE). The above organic solvents can be used alone or in combination. Alternatively, two or more organic solvents are used in combination.

[0170] In some embodiments, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0171] As an example, the additive includes but is not limited to at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), diethylene sulfate (DTD), propylene sulfate, vinyl sulfite (ES), 1,3-propane sultone (PS), 1,3-propene sultone (PST), sulfonate cyclic quaternary ammonium salt, succinic anhydride, succinonitrile (SN), adiponitrile (AND), tris(trimethylsilyl) phosphate (TMSP), and tris(trimethylsilyl) borate (TMSB).

[0172] The electrolyte solution can be prepared according to conventional methods in the art. For example, an organic solvent, an electrolyte salt, and optional additives can be uniformly mixed to obtain the electrolyte solution. The order in which the materials are added is not particularly limited. For example, the electrolyte salt and optional additives can be added to the organic solvent and mixed uniformly to obtain the electrolyte solution; alternatively, the electrolyte salt can be first added to the organic solvent, and then the optional additives can be added to the organic solvent and mixed uniformly to obtain the electrolyte solution.

[0173] [Isolation film]

[0174] The separator is placed between the positive and negative electrodes to prevent short circuits between the positive and negative electrodes while allowing active ions to pass through. This application does not impose any particular restrictions on the type of separator; any known porous separator with good chemical and mechanical stability can be used.

[0175] In some embodiments, the material of the isolation membrane can be selected from one or more of, but not limited to, glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different. In some embodiments, the isolation membrane can also be provided with an organic / inorganic composite coating, including a ceramic particle coating or a metal oxide coating.

[0176] 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.

[0177] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0178] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc. The present application has no particular restrictions on the shape of the secondary battery cell, which can be cylindrical, square or other arbitrary shapes. Figure 2 shows a secondary battery 5 with a square structure as an example.

[0179] In some embodiments, referring to FIG3 , the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 is used to cover the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the separator may be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 may be one or more, which can be adjusted according to demand.

[0180] In some embodiments, the secondary battery may also be a battery module assembled from a plurality of battery cells. The battery module may contain multiple secondary battery cells, and the specific number may be adjusted according to the application and capacity of the battery module.

[0181] Figure 4 shows an example battery module 4. Referring to Figure 4 , within the battery module 4, multiple secondary battery cells 5 may be arranged sequentially along the length of the battery module 4. Of course, they may also be arranged in any other manner. Furthermore, the multiple secondary battery cells 5 may be secured together using fasteners.

[0182] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of secondary battery cells 5 are accommodated in the accommodation space.

[0183] In some embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0184] In some embodiments, the battery cells mentioned above may also be directly assembled into a battery pack, and the number of battery cells contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0185] Figures 5 and 6 illustrate an example battery pack 1. Referring to Figures 5 and 6 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 covers the lower case 3 and forms an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 may be arranged in any manner within the battery box.

[0186] Electrical devices

[0187] The fifth aspect of the embodiment of the present application provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack of the present application. The secondary battery, battery module, or battery pack can be used as a power source for the device, and can also be used as an energy storage unit for the device. The device can be, but is not limited to, a mobile device, an electric vehicle, an electric train, a ship and a satellite, an energy storage system, etc. For example, it can be a laptop computer, a pen-input computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD TV, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery, etc.

[0188] The device can select a secondary battery, a battery module or a battery pack according to its usage requirements.

[0189] Figure 7 shows an example device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0190] Example

[0191] The following examples describe the present disclosure in more detail and are intended to be illustrative only, as various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and used directly without further processing, and all instruments used in the examples are commercially available.

[0192] Example 1

[0193] Preparation of negative electrode sheet

[0194] Graphite (the negative electrode active material), conductive carbon (the conductive agent), sodium carboxymethyl cellulose (CMC) (the thickener), and styrene-butadiene rubber (SBR) (the binder) were added to water in a 96:2:1:1 mass ratio and mixed evenly to form an active material slurry. Al2O3 and conductive carbon black were mixed evenly in a 98:2 mass ratio to form an active ion transport slurry. The active material slurry was evenly coated on the negative electrode current collector copper foil and dried at 85°C. The active ion transport slurry was then applied and dried at 85°C. Finally, a layer of active material slurry was applied and dried at 85°C. The negative electrode sheet was then cold-pressed to form the negative electrode.

[0195] Preparation of positive electrode

[0196] The positive electrode active material ternary material nickel cobalt manganese oxide (NCM811), conductive agent conductive carbon black, and binder polyvinylidene fluoride (PVDF) are mixed evenly in a mass ratio of 97:2:1 and added to the solvent NMP to prepare a positive electrode slurry; the positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil, dried at 85°C and cold pressed, and then die-cut and slit to make positive electrode sheets.

[0197] Preparation of electrolyte

[0198] Lithium hexafluorophosphate was dissolved in a mixed solvent of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate to prepare an electrolyte with a lithium hexafluorophosphate concentration of 1 mol / L, wherein the volume ratio of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate was 1:2:1.

[0199] Preparation of isolation membrane

[0200] A polyethylene microporous film is used as a porous isolation membrane substrate, and inorganic alumina powder, polyvinylpyrrolidone, and acetone solvent are evenly mixed in a weight ratio of 3:1.5:5.5 to form a slurry, which is then coated on one side of the substrate and dried to obtain an isolation membrane.

[0201] Preparation of conventional lithium-ion batteries

[0202] The positive electrode sheets, negative electrode sheets and separators are stacked to obtain a battery cell, which is then packaged, injected, formed, vented and other processes to produce a conventional lithium-ion battery. The battery has a designed charging N / P of 1.05, where N is the capacity of the negative electrode during charging and P is the capacity of the positive electrode in the charged state. It is necessary to ensure that N / P>1 to ensure that the negative electrode has sufficient active sites to accommodate lithium ions released from the positive electrode, thereby reducing the risk of metallic lithium precipitation. The battery cell has a designed capacity of 146mAh.

[0203] Preparation of three-electrode lithium-ion batteries

[0204] Prepare copper wire and attach it to a separator. Stack the positive electrode sheet, copper wire-attached separator, separator, negative electrode sheet, separator, and positive electrode sheet in this order to create a three-electrode cell. This is then packaged, filled, formed, and vented to create a three-electrode lithium-ion battery. Solder the copper wire to a nickel sheet and charge at a constant current of 30μA for 2 hours to obtain a lithium-plated copper wire. This lithium-plated copper wire serves as the third electrode.

[0205] Examples 2 to 32

[0206] The preparation methods of conventional lithium-ion batteries and three-electrode lithium-ion batteries are similar to those in Example 1, except that the negative electrode sheet and related parameters in the preparation process are adjusted. The specific parameters are detailed in Table 1 below. Wherein, “ / ” indicates that the corresponding parameter does not exist.

[0207] Among them, in Example 28, the mass ratio of PEO to Li2S is 6:4; in Example 31, the mass ratio of LTO to Si is 2:8; in Example 32, the mass ratio of LLZO to Al2O3 is 5:5.

[0208] Comparative Example 1

[0209] Comparative Example 1 is similar to Example 1, except that the active ion transport layer is removed from the negative electrode plate.

[0210] Comparative Example 2

[0211] Comparative Example 2 is similar to Example 1, except that the active ion transport layer is removed from the negative electrode plate, and the active material layer is only one layer.

[0212] Table 1

[0213] Test section

[0214] (1) Lithium-ion battery charging capacity test

[0215] The test sample is a three-electrode lithium-ion battery; the test temperature is 25°C; the charge and discharge voltage range is 2.5V to 4.25V; and the protection voltage range is 2.45V to 4.3V. The test process is as follows: first, the capacity is calibrated; based on the calibrated capacity, each test sample is tested at different charge rates to obtain its charging curve. The charging cut-off voltage is 4.25V, and the negative electrode potential is monitored (charging can be terminated in advance when the negative electrode potential is lower than -10mV). The tested charge rates are 0.33C, 0.5C, 1C, 1.5C, 2C, 2.5C, and 3C, respectively, to obtain the maximum achievable charge rate curve of each test sample at different SOCs; based on the curve, the time required for the battery to charge in the range of 10% SOC to 80% SOC is calculated, thereby evaluating the charging capacity of each sample. Generally, the shorter the time required for charging, the stronger the charging capacity.

[0216] (2) Lithium-ion battery safety performance test

[0217] The test sample is a conventional lithium-ion battery, the test temperature is 10℃, the charge and discharge voltage range is 2.5V to 4.25V, the protection voltage range is 2.45V to 4.3V, and the charge and discharge rate is 1C. In situ optical microscopy is used to observe the insertion / extraction process of active ions in the negative electrode and the precipitation of metallic lithium during the charge and discharge process, and the safety of the battery is judged by the precipitation time of metallic lithium.

[0218] The positive electrode and negative electrode sheets were respectively attached to the two opposite sides of the cuvette, and the electrolyte was injected into the cuvette. The amount of electrolyte injected needed to cover the positive and negative electrode sheets. The positive and negative electrode sheets were led out through silver wires, covered with lids and sealed, and the positive and negative electrodes were connected to the electrochemical testing system (Wuhan Land Electric, model Land CT2001A). A charging test was performed under the above conditions, and the time of metallic lithium precipitation on the negative electrode side was observed in real time under an optical microscope.

[0219] Table 2 shows the performance test results of Examples 1 to 32 and Comparative Examples 1 to 2.

[0220] Table 2

[0221] A comparative analysis of Examples 1 to 32 and Comparative Examples 1 to 2 shows that, compared with Comparative Examples 1 and 2 in which the negative electrode plates are not provided with an active ion transport layer, the 10% SOC to 80% SOC charging time of Examples 1 to 32 is significantly lower, indicating that the negative electrode plates provided with an active ion transport layer provided in the present application can improve the charging capacity of the battery; in addition, compared with Comparative Examples 1 and 2, the precipitation time of metallic lithium in Examples 1 to 32 is also significantly prolonged, indicating that the negative electrode plates provided with an active ion transport layer provided in the present application can simultaneously improve the safety performance of the battery.

[0222] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0223] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and such modifications or substitutions should be included in the scope of protection of this application. Therefore, the scope of protection of this application should be based on the scope of protection of the claims, and the description and drawings can be used to interpret the scope of protection of the claims.

Claims

1. A negative electrode sheet, comprising: Anode current collector; and A composite layer is arranged on at least one side of the negative electrode current collector, the composite layer includes at least two active material layers and at least one active ion transport layer stacked, wherein the active material layers and the active ion transport layers are alternately arranged, the active ion transport layer is located between two adjacent active material layers, and each of the active ion transport layers independently includes one of an electronic insulating layer and an electronic semi-insulating layer.

2. The negative electrode sheet according to claim 1, wherein: The active ion transport layer satisfies at least one of the following conditions: (1) The conductivity of the electronic insulating layer is σ1, and σ1 satisfies: 0<σ1<10 -10 S / cm, optional 10 -15 S / cm≤σ1≤10 -11 S / cm; and (2) The conductivity of the electronic semi-insulating layer is σ2, and σ2 satisfies: 10 -10 S / cm≤σ2≤10 2 S / cm, optional 10 -6 S / cm≤σ2≤10 -3 S / cm.

3. The negative electrode sheet according to claim 1 or 2, wherein: The negative electrode sheet satisfies at least one of the following conditions: (1) The conductivity of the active material layer is σ3, and σ3 satisfies: 10 -6 S / cm≤σ3≤10 5 S / cm, optional 10 -4 S / cm≤σ3≤10 3 S / cm; and (2) The membrane resistance of the negative electrode plate is R, and R satisfies: 0.1mΩ≤R≤5000mΩ, and can be optionally 1mΩ≤R≤1000mΩ.

4. The negative electrode sheet according to any one of claims 1 to 3, wherein: The electronic insulating layer includes a first electronic insulating material, and the first electronic insulating material satisfies at least one of the following conditions: (1) The average particle size of the particles of the first electronic insulating material is 0.1 μm to 50 μm, and can be 1 μm to 20 μm; and (2) The mass proportion of the first electronic insulating material in the electronic insulating layer is 70% to 100%, and can be optionally 90% to 99.9%.

5. The negative electrode sheet according to claim 4, wherein: The first electronic insulating material comprises a first solid electrolyte, Optionally, the first solid electrolyte comprises a sulfide electrolyte, an oxide electrolyte, a polymer electrolyte or a combination thereof, Further optionally, the first solid electrolyte includes LLZO, LLZTO, aluminum oxide, polyethylene oxide, lithium sulfide or a combination thereof.

6. The negative electrode sheet according to any one of claims 1 to 5, wherein: The electronic semi-insulating layer comprises an electronic semi-insulating material and / or a combination of a second electronic insulating material and a conductive filler. Optionally, the second electronic insulating material comprises a second solid electrolyte.

7. The negative electrode sheet according to claim 6, wherein: The electronic semi-insulating layer satisfies at least one of the following conditions: (1) The electronic semi-insulating material comprises lithium titanate, silicon, sulfur, silicon oxide or a combination thereof; (2) The average particle size of the particles of the electronic semi-insulating material is 0.1 μm to 50 μm, and can be 1 μm to 20 μm; (3) The second solid electrolyte comprises a sulfide electrolyte, an oxide electrolyte, a polymer electrolyte or a combination thereof, Optionally, the second solid electrolyte includes LLZO, LLZTO, aluminum oxide, polyethylene oxide, lithium sulfide or a combination thereof; (4) The average particle size of the particles of the second electronic insulating material is 0.1 μm to 50 μm, and can be 1 μm to 20 μm; and (5) The conductive filler comprises superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, carbon nanofibers or a combination thereof, Optionally, the conductive filler accounts for 0.1% to 50% by mass in the composition, and optionally 0.5% to 30% by mass.

8. The negative electrode sheet according to claim 6 or 7, wherein: The electronic semi-insulating layer contains electronic semi-insulating material, and the mass proportion of the electronic semi-insulating material in the electronic semi-insulating layer is 70% to 100%, and can be 90% to 99.9%.

9. The negative electrode sheet according to claim 6 or 7, wherein: The electronic semi-insulating layer comprises the composition, and the mass proportion of the composition in the electronic semi-insulating layer is 70% to 100%, and optionally 90% to 99.9%.

10. The negative electrode sheet according to claim 6 or 7, wherein: The electronic semi-insulating layer comprises the electronic semi-insulating material and the composition, and the total mass of the electronic semi-insulating material and the composition accounts for 70% to 100% of the mass of the electronic semi-insulating layer, and can be optionally 90% to 99.9%.

11. The negative electrode sheet according to any one of claims 1 to 10, wherein: The active material layer contains a negative electrode active material, and the negative electrode active material satisfies at least one of the following conditions: (1) The negative electrode active material comprises artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material, lithium titanate or a combination thereof, Optionally, the silicon-based material includes one or more of elemental silicon, silicon oxide compounds, silicon-carbon compounds, silicon-nitrogen compounds and silicon alloys, and the tin-based material includes elemental tin, tin oxide compounds, tin alloys or combinations thereof; (2) The average particle size of the negative electrode active material particles is 1 μm to 100 μm, and can be 2 μm to 50 μm.

12. The negative electrode sheet according to claim 11, wherein: The negative electrode sheet satisfies at least one of the following conditions: (1) The average particle size ratio of the first electronic insulating material particles to the negative electrode active material particles is (1:50) to (50:1), and may be (1:10) to (10:1); (2) The average particle size ratio of the particles of the second electronic insulating material to the particles of the negative electrode active material is (1:50) to (50:1), and can be (1:10) to (10:1); and (3) The ratio of the average particle size of the particles of the electronic semi-insulating material to the average particle size of the particles of the negative electrode active material is (1:50) to (50:1), and can be optionally (1:10) to (10:1).

13. The negative electrode sheet according to any one of claims 1 to 12, wherein: The composite layer satisfies at least one of the following conditions: (1) The coating weight of the active ion transport layer is 0.06 mg / cm 2 Up to 13mg / cm 2 , optional 0.1mg / cm 2 Up to 7mg / cm 2 ;and (2) The coating weight of the active material layer is 0.06 mg / cm 2 Up to 65mg / cm 2 , optional 0.13mg / cm 2 Up to 26mg / cm 2 .

14. The negative electrode sheet according to any one of claims 1 to 13, wherein: The coating weight ratio between the two active material layers located on opposite sides of the active ion transport layer and adjacent to the active ion transport layer is (1:99) to (99:1), and can be optionally (5:90) to (90:5).

15. The negative electrode sheet according to any one of claims 1 to 14, wherein: The composite layer satisfies at least one of the following conditions: (1) The thickness of the active ion transport layer is 0.2 μm to 50 μm, and can be 1 μm to 20 μm; and (2) The thickness of the active material layer is 1 μm to 500 μm, and can be 10 μm to 300 μm.

16. The negative electrode sheet according to any one of claims 1 to 15, wherein: The thickness ratio of the active ion transport layer to the active material layer adjacent to the active ion transport layer is (1:3) to (1:100), and can be (1:5) to (1:50). 17 . A secondary battery comprising the negative electrode sheet according to claim 1 .

18. An electrical device comprising the secondary battery according to claim 17.

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