Secondary battery and electronic device

Abstract

The invention provides a secondary battery and an electronic device, the secondary battery comprises a negative electrode plate and an electrolyte, the negative electrode plate comprises a negative electrode material layer, the surface density of the negative electrode material layer is rho mg / mm < 2 >, the negative electrode material layer comprises a negative electrode active material, the negative electrode active material comprises graphite with a coating layer, the graphite comprises at least one of natural graphite or artificial graphite, and the coating layer comprises at least one of lithium ion battery positive electrode and lithium ion battery negative electrode. Based on the mass of the graphite with the coating layer, the mass percentage content of the coating layer is M. The liquid retention coefficient of the electrolyte is A g / Ah, the electrolyte comprises a film-forming additive, based on the mass of the electrolyte, the mass percentage content of the film-forming additive is N, and A * N / (rho * M) is larger than or equal to 0.4 and smaller than or equal to 12. Through the arrangement, the demolding problem of the fast-charging graphite in a cathode overhang area and a non-lithium-intercalation area can be improved, and meanwhile, the low-temperature performance of the secondary battery is considered.

Description

Technical Field

[0001] The present application relates to the field of electrochemistry technology, and particularly to a secondary battery and an electronic device. Background Art

[0002] Secondary batteries represented by lithium-ion batteries have outstanding characteristics such as high energy density, long cycle life, low pollution, and no memory effect. Currently, fast-charging graphite has become the preferred negative active material in lithium-ion batteries due to its advantages of improving the charging performance and cycle life of lithium-ion batteries.

[0003] However, in a lithium-ion battery using fast-charging graphite as the negative active material, during low-temperature cycling, in the non-lithium-inserting region of the negative electrode sheet and the part of the negative electrode sheet that extends beyond the positive electrode sheet, due to slow desolvation and insufficient film formation, solvent co-insertion is likely to occur during the charge and discharge process. When the solvent co-insertion is severe, graphite debonding will occur, resulting in bumps on the appearance of the electrode assembly. Summary of the Invention

[0004] The purpose of the present application is to provide a secondary battery and an electronic device, which can improve the debonding problem of fast-charging graphite in the part of the negative electrode sheet that extends beyond the positive electrode sheet and the non-lithium-inserting region while taking into account the low-temperature performance. The specific technical solutions are as follows:

[0005] It should be noted that in the summary of the invention of the present application, a lithium-ion battery is used as an example of the secondary battery to explain the present application, but the secondary battery of the present application is not limited to lithium-ion batteries.

[0006] The first aspect of the present application provides a secondary battery, including a negative electrode sheet and an electrolyte. The negative electrode sheet includes a negative electrode material layer, and the areal density of the negative electrode material layer is ρ mg / mm 2 , the negative electrode material layer includes a negative active material, the negative active material includes graphite with a coating layer, the graphite includes at least one of natural graphite or artificial graphite, and based on the mass of the graphite with a coating layer, the mass percentage of the coating layer is M. The liquid retention coefficient of the electrolyte is A g / Ah, the electrolyte includes a film-forming additive, and based on the mass of the electrolyte, the mass percentage of the film-forming additive is N, and 0.4 ≤ A×N / (ρ×M) ≤ 12. By combining fast-charging graphite with an electrolyte added with a film-forming additive and controlling the value of A×N / (ρ×M) within the range of the present application, the amount of the coating layer on the surface of the graphite is more suitable for the film-forming additive in the electrolyte, which is beneficial to improving the quality of the SEI film. A relatively dense SEI film can be formed on the surface of the fast-charging graphite, reducing the risk of solvent co-insertion on the negative electrode sheet. In addition, it is beneficial to reduce the side reaction between the electrolyte and the active material and improve the low-temperature performance of the electrolyte. Therefore, it is beneficial to improve the debonding problem of fast-charging graphite in the overhang region and non-lithium-inserting region of the negative electrode, while taking into account the low-temperature performance of the secondary battery.

[0007] In one or more embodiments, the secondary battery satisfies at least one of the following characteristics: (1) 0.8 ≤ A × N / (ρ × M) ≤ 4.0; (2) 0.05 ≤ ρ ≤ 0.12; (3) 8% ≤ M ≤ 18%; (4) 0.1% ≤ N ≤ 2%. With the above settings, the fast-charging graphite is used in combination with the film-forming additive, which is beneficial to improving the quality of the SEI film, reducing the risk of co-insertion of solvents on the negative electrode sheet, improving the film removal problem of the fast-charging graphite in the negative electrode overhang area and the non-lithium-inserting area, and taking into account the low-temperature performance of the secondary battery.

[0008] In one or more embodiments, 2% ≤ A × N / ρ ≤ 80%. By regulating the value of A × N / ρ within the above range, the fast-charging graphite is used in combination with the film-forming additive, which is beneficial to improving the quality of the SEI film, reducing the risk of co-insertion of solvents on the negative electrode sheet, improving the film removal problem of the fast-charging graphite in the negative electrode overhang area and the non-lithium-inserting area, and taking into account the low-temperature performance of the secondary battery.

[0009] In one or more embodiments, it satisfies at least one of the following characteristics: (1) 0.2% ≤ N ≤ 1%; (2) 4% ≤ A × N / ρ ≤ 20%. With the above settings, the fast-charging graphite is used in combination with the film-forming additive, which is beneficial to improving the quality of the SEI film, reducing the risk of co-insertion of solvents on the negative electrode sheet, improving the film removal problem of the fast-charging graphite in the negative electrode overhang area and the non-lithium-inserting area, and taking into account the low-temperature performance of the secondary battery.

[0010] In one or more embodiments, the compactness of the coating layer is D, 0 ≤ D ≤ 5; optionally, 2 ≤ D ≤ 3. By regulating the value of D within the above range, it is beneficial to improving the low-temperature performance and fast-charging performance of the secondary battery. At the same time, the risk of co-insertion of solvents on the negative electrode sheet is reduced, which is beneficial to improving the film removal problem of the fast-charging graphite on the negative electrode sheet.

[0011] In one or more embodiments, the coating layer includes a coating material, and the coating material includes at least one of hard carbon, soft carbon, graphene, pitch-based, carbon nanotubes or Li3P; optionally, the coating material includes at least one of hard carbon, soft carbon, graphene, pitch-based or carbon nanotubes. Generally, the above types of coating materials are selected, which is beneficial to improving the low-temperature performance and fast-charging performance of the secondary battery.

[0012] In one or more embodiments, the film-forming additive includes at least one of 1,3-propane sultone, ethylene sulfate, 1,4-butane sultone, methylene methanedisulfonate, ethyl sulfite, diethyl sulfite, or dimethyl sulfite; optionally, the film-forming additive includes at least one of 1,3-propane sultone, ethylene sulfate, or 1,4-butane sultone. By selecting the above types of film-forming additives, it is beneficial to improve the quality of the SEI film. When combined with fast-charging graphite, it is beneficial to form a relatively dense SEI film on the surface of the fast-charging graphite, reducing the risk of co-insertion of solvents on the negative electrode sheet, and is beneficial to improving the film stripping problem of the fast-charging graphite in the negative electrode overhang area and the non-lithium-inserting area, while taking into account the low-temperature performance of the secondary battery.

[0013] The second aspect of the present application provides an electronic device, including the secondary battery in any of the foregoing embodiments. Thus, the electronic device of the present application has good performance.

[0014] Advantages of the embodiments of the present application:

[0015] The embodiments of the present application provide a secondary battery and an electronic device. By using fast-charging graphite in combination with an electrolyte added with a film-forming additive and regulating the value of A×N / (ρ×M) within the scope of the present application, the amount of the coating layer on the surface of the graphite is more adapted to the film-forming additive in the electrolyte, which is beneficial to improving the quality of the SEI film. A relatively dense SEI film can be formed on the surface of the fast-charging graphite, reducing the risk of co-insertion of solvents on the negative electrode sheet. In addition, it is beneficial to reduce the side reaction between the electrolyte and the active material and improve the low-temperature performance of the electrolyte. Thus, it is beneficial to improve the film stripping problem of the fast-charging graphite in the negative electrode overhang area and the non-lithium-inserting area, while taking into account the low-temperature performance of the secondary battery.

[0016] Of course, it is not necessary for any product or method implementing the present application to achieve all the above-mentioned advantages simultaneously. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present application, and those of ordinary skill in the art can also obtain other embodiments based on these drawings.

[0018] Figure 1 It is a schematic diagram of a winding structure formed by an electrode assembly in an embodiment of the present application.

[0019] Reference numerals: electrode assembly 001; positive electrode sheet 10; positive current collector 11; positive electrode material layer 12; negative electrode sheet 20; negative current collector 21; negative electrode material layer 22; separator 30. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0020] The technical solutions in the present application will be clearly and completely described below in conjunction with the embodiments of the present application and the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on the present application belong to the scope of protection of the present application.

[0021] It should be noted that in the specific implementation manner of the present application, a lithium-ion battery is taken as an example of the secondary battery to explain the present application. However, the secondary battery of the present application is not limited to the lithium-ion battery.

[0022] When a fast-charging graphite provided with a coating layer is used to replace traditional graphite as the negative electrode active material in a lithium-ion battery, the fast-charging graphite can effectively reduce the direct contact between the graphite and the electrolyte by forming a protective film on the surface of the graphite particles, reduce the occurrence of side reactions during the cycling process, and thus improve the charging efficiency, kinetic performance, and cycle life of the secondary battery. In the prior art, in a lithium-ion battery using fast-charging graphite as the negative electrode active material, when the structure of the electrode assembly is a winding structure, it is generally required that the negative electrode material layer can wrap the positive electrode material layer to prevent the generation of lithium deposition, and the head and tail sections of the negative electrode tab exceeding the positive electrode tab are generally double-sided coated, which improves the processing efficiency while reducing the risk of powder falling off. When a fast-charging graphite provided with a coating layer is used as the negative electrode active material, during the charging process of the secondary battery at low temperature (temperature ≤ 10°C), it is easy to demold in the area where the negative electrode tab exceeds the positive electrode tab, that is, the negative overhang area, and in the head and tail non-lithiated areas of the negative electrode tab along the winding direction, that is, the area of the negative electrode tab without the opposite positive electrode tab, resulting in safety risks during the use of the secondary battery. The inventor analyzed the demolding area of the secondary battery through a scanning electron microscope and found that the graphite particles in the demolding area expanded, the interlayer structure was damaged, and solvent co-insertion occurred. In the prior art, it is generally considered that solvent co-insertion is caused by the solvent propylene carbonate (PC) in the electrolyte. The PC solvent molecules cannot stably exist after being inserted into the graphite and will continue to undergo chemical reactions in the graphite, resulting in the destruction of the graphite interlayer structure and the peeling of the graphite to cause demolding. To solve the above demolding problem, the inventor's research found that simply removing the PC solvent in the electrolyte cannot well solve the demolding problem and reduces the low-temperature performance of the secondary battery. Based on this, the present application provides a secondary battery and an electronic device, which can improve the demolding problem of fast-charging graphite in the negative overhang area and the non-lithiated area while taking into account the low-temperature performance. The specific technical solutions are as follows:

[0023] In the first aspect of the present application, a secondary battery is provided, including a negative electrode tab and an electrolyte. The negative electrode tab includes a negative electrode material layer, and the areal density of the negative electrode material layer is ρ mg / mm 2, the negative electrode material layer includes a negative electrode active material, the negative electrode active material includes graphite with a coating layer, the graphite includes at least one of natural graphite or artificial graphite, and based on the mass of the graphite with the coating layer, the mass percentage of the coating layer is M. The liquid retention coefficient of the electrolyte is A g / Ah, the electrolyte includes a film-forming additive, and based on the mass of the electrolyte, the mass percentage of the film-forming additive is N, and 0.4 ≤ A×N / (ρ×M) ≤ 12. For example, the value of A×N / (ρ×M) can be 0.4, 0.5, 0.8, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12 or a range composed of any two of these values.

[0024] Exemplarily, define the winding direction of the electrode assembly as the W direction, as Figure 1 shown, the electrode assembly 001 includes a positive electrode tab 10, a negative electrode tab 20, and a separator 30. Along the opposite direction of the winding direction (W direction) of the electrode assembly 001, the winding starting end P of the negative electrode tab 20 extends beyond the winding starting end P' of the positive electrode tab 10. Along the winding direction (W direction) of the electrode assembly 001, the winding ending end Q of the negative electrode tab 20 extends beyond the winding ending end Q' of the positive electrode tab 10. The positive electrode tab 10 includes a positive electrode current collector 11 and a positive electrode material layer 12, and the negative electrode tab 20 includes a negative electrode current collector 21 and a negative electrode material layer 22.

[0025] The inventors' research found that graphite demoulding is related not only to the PC solvent in the electrolyte but also to the film-forming quality of the solid electrolyte interface film, i.e., the SEI film. When the SEI film is formed more tightly, it is more conducive to reducing the occurrence of solvent co-insertion during the cycling of the secondary battery. When the value of A×N / (ρ×M) is too small, i.e., lower than the lower limit value of this application, in a low-temperature environment, the electrode assembly is prone to lithium deposition at a lower rate, reducing the low-temperature performance of the secondary battery. When the value of A×N / (ρ×M) is too large, i.e., higher than the upper limit value of this application, the fast-charging graphite is prone to demoulding in the negative overhang area and the non-lithium-inserted area. This application uses fast-charging graphite in combination with an electrolyte added with a film-forming additive and regulates the value of A×N / (ρ×M) within the range of this application. The amount of the coating layer on the surface of the graphite is more suitable for the film-forming additive in the electrolyte, which is conducive to improving the quality of the SEI film. A relatively dense SEI film can be formed on the surface of the fast-charging graphite, reducing the risk of solvent co-insertion on the negative electrode tab. In addition, it is conducive to reducing the side reaction between the electrolyte and the active material and improving the low-temperature performance of the electrolyte. Therefore, it is conducive to improving the demoulding problem of the fast-charging graphite in the negative overhang area and the non-lithium-inserted area, while taking into account the low-temperature performance of the secondary battery.

[0026] In the present application, the coating layer completely coats the surface of the graphite particles. At least part of the above-mentioned "complete coating" is a homogeneous layer coating, that is, at least part of the coating layer is uniformly coated on the surface of the graphite particles with a uniform thickness. The liquid retention coefficient refers to the ratio of the amount of electrolyte retained in the secondary battery to the capacity of the secondary battery.

[0027] In the present application, the areal density ρ of the negative electrode material layer can be adjusted by means known to those skilled in the art. For example, when coating the negative electrode slurry on the surface of the negative electrode current collector, on the basis that other conditions remain unchanged and the solid content of the negative electrode slurry is constant, increasing the coating amount per unit area can increase the areal density of the negative electrode material layer. The present application does not make special restrictions as long as the purpose of the present application can be achieved.

[0028] In one or more embodiments, 0.8 ≤ A × N / (ρ × M) ≤ 4.0. For example, the value of A × N / (ρ × M) can be 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4.0 or a range composed of any two of these numerical values. By adjusting the value of A × N / (ρ × M) within the above range, the amount of the coating layer on the surface of the graphite is more suitable for the film-forming additive in the electrolyte, which is beneficial to improving the quality of the SEI film, facilitating the formation of a relatively dense SEI film on the surface of the fast-charging graphite, reducing the risk of co-insertion of solvents on the negative electrode sheet. In addition, it is beneficial to reduce the side reaction between the electrolyte and the active material and improve the low-temperature performance of the electrolyte. Therefore, it is beneficial to improve the film removal problem of the fast-charging graphite in the negative electrode overhang area and the non-lithium-inserting area, while taking into account the low-temperature performance of the secondary battery.

[0029] In one or more embodiments, 0.05 ≤ ρ ≤ 0.12. For example, the value of ρ can be 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12 or a range composed of any two of these numerical values. By adjusting the value of ρ within the above range, there is more negative electrode active material on the negative electrode sheet. While the secondary battery has a higher energy density, it is beneficial to improve the quality of the SEI film, and a relatively dense SEI film can be formed on the surface of the fast-charging graphite, reducing the risk of co-insertion of solvents on the negative electrode sheet. In addition, it is beneficial to reduce the side reaction between the electrolyte and the active material and improve the low-temperature performance of the electrolyte. Therefore, it is beneficial to improve the film removal problem of the fast-charging graphite in the negative electrode overhang area and the non-lithium-inserting area, while taking into account the low-temperature performance and energy density of the secondary battery.

[0030] In one or more embodiments, 8% ≤ M ≤ 18%. For example, the value of M can be 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18% or a range composed of any two of these values. By adjusting the value of M within the above range, it is beneficial to increase the interlayer spacing between the negative electrode active materials, improve the diffusion rate of lithium ions, and form a stable SEI film on the surface of the negative electrode sheet, reducing the occurrence of side reactions between the negative electrode active materials and the electrolyte, improving the stability of the lithium insertion region structure of the negative electrode sheet, thereby improving the low-temperature performance and fast charging performance of the secondary battery; combined with the film-forming additive in the electrolyte, it is beneficial to improve the quality of the SEI film, and it is beneficial to form a relatively dense SEI film on the surface of the fast-charging graphite, reducing the risk of co-insertion of solvents on the negative electrode sheet. In addition, it is beneficial to reduce the side reactions between the electrolyte and the active materials and improve the low-temperature performance of the electrolyte. Thus, it is beneficial to improve the film removal problem of the fast-charging graphite in the negative electrode overhang region and the non-lithium insertion region, while taking into account the low-temperature performance of the secondary battery.

[0031] In one or more embodiments, 0.1% ≤ N ≤ 2%. For example, the value of N can be 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2% or a range composed of any two of these values. By adjusting the value of N within the above range, it is beneficial to improve the quality of the SEI film. Combined with the fast-charging graphite, it is beneficial to form a relatively dense SEI film on the surface of the fast-charging graphite, reducing the risk of co-insertion of solvents on the negative electrode sheet. In addition, it is beneficial to reduce the side reactions between the electrolyte and the active materials and improve the low-temperature performance of the electrolyte. Thus, it is beneficial to improve the film removal problem of the fast-charging graphite in the negative electrode overhang region and the non-lithium insertion region, while taking into account the low-temperature performance of the secondary battery.

[0032] In one or more embodiments, 0.8 ≤ A×N / (ρ×M) ≤ 4.0; and / or, 0.05 ≤ ρ ≤ 0.12. For example, the value of A×N / (ρ×M) can be 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4.0 or a range composed of any two of these numerical values; the value of ρ can be 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12 or a range composed of any two of these numerical values. By adjusting the values of A×N / (ρ×M) and ρ within the above ranges, it is beneficial to improve the quality of the SEI film, beneficial to form a relatively dense SEI film on the surface of the fast-charging graphite, reduce the risk of co-insertion of solvents on the negative electrode sheet. In addition, it is beneficial to reduce the side reaction between the electrolyte and the active material and improve the low-temperature performance of the electrolyte. Thus, it is beneficial to improve the film stripping problem of the fast-charging graphite in the negative electrode overhang region and the non-lithium-inserting region, while taking into account the low-temperature performance and energy density of the secondary battery.

[0033] In one or more embodiments, 0.8 ≤ A×N / (ρ×M) ≤ 4.0; and / or, 8% ≤ M ≤ 18%. For example, the value of A×N / (ρ×M) can be 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4.0 or a range composed of any two of these numerical values; the value of M can be 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18% or a range composed of any two of these numerical values. By adjusting the values of A×N / (ρ×M) and M within the above ranges, it is beneficial to improve the quality of the SEI film, beneficial to form a relatively dense SEI film on the surface of the fast-charging graphite, reduce the risk of co-insertion of solvents on the negative electrode sheet. In addition, it is beneficial to reduce the side reaction between the electrolyte and the active material and improve the low-temperature performance of the electrolyte. Thus, it is beneficial to improve the film stripping problem of the fast-charging graphite in the negative electrode overhang region and the non-lithium-inserting region, while taking into account the low-temperature performance of the secondary battery.

[0034] In one or more embodiments, 0.8 ≤ A×N / (ρ×M) ≤ 4.0; and / or, 0.1% ≤ N ≤ 2%. For example, the value of A×N / (ρ×M) can be 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4.0 or a range composed of any two of these values; the value of N can be 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2% or a range composed of any two of these values. By adjusting the values of A×N / (ρ×M) and N within the above ranges, it is beneficial to improve the quality of the SEI film, beneficial to form a relatively dense SEI film on the surface of the fast-charging graphite, reduce the risk of co-insertion of solvents on the negative electrode sheet. In addition, it is beneficial to reduce the side reaction between the electrolyte and the active material and improve the low-temperature performance of the electrolyte. Thus, it is beneficial to improve the film stripping problem of the fast-charging graphite in the negative electrode overhang region and the non-lithium-inserting region, while taking into account the low-temperature performance of the secondary battery.

[0035] In one or more embodiments, 0.05 ≤ ρ ≤ 0.12; and / or, 8% ≤ M ≤ 18%. For example, the value of ρ can be 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12 or a range composed of any two of these values; the value of M can be 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18% or a range composed of any two of these values. By adjusting the values of ρ and M within the above ranges, it is beneficial to improve the quality of the SEI film, beneficial to form a relatively dense SEI film on the surface of the fast-charging graphite, reduce the risk of co-insertion of solvents on the negative electrode sheet. In addition, it is beneficial to reduce the side reaction between the electrolyte and the active material and improve the low-temperature performance of the electrolyte. Thus, it is beneficial to improve the film stripping problem of the fast-charging graphite in the negative electrode overhang region and the non-lithium-inserting region, while taking into account the low-temperature performance of the secondary battery.

[0036] In one or more embodiments, 0.05 ≤ ρ ≤ 0.12; and / or, 0.1% ≤ N ≤ 2%. For example, the value of ρ can be 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12 or a range composed of any two of these values; the value of N can be 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2% or a range composed of any two of these values. By adjusting the values of ρ and N within the above ranges, it is beneficial to improve the quality of the SEI film, beneficial to form a relatively dense SEI film on the surface of the fast-charging graphite, reduce the risk of co-insertion of solvents on the negative electrode sheet. In addition, it is beneficial to reduce the side reaction between the electrolyte and the active material and improve the low-temperature performance of the electrolyte. Thus, it is beneficial to improve the film stripping problem of the fast-charging graphite in the negative electrode overhang area and the non-lithium-inserting area, while taking into account the low-temperature performance and energy density of the secondary battery.

[0037] In one or more embodiments, 8% ≤ M ≤ 18%; and / or, 0.1% ≤ N ≤ 2%. For example, the value of M can be 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18% or a range composed of any two of these values; the value of N can be 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2% or a range composed of any two of these values. By adjusting the values of M and N within the above ranges, the fast-charging graphite and the film-forming additive act synergistically, which is beneficial to improve the quality of the SEI film, beneficial to form a relatively dense SEI film on the surface of the fast-charging graphite, reduce the risk of co-insertion of solvents on the negative electrode sheet. In addition, it is beneficial to reduce the side reaction between the electrolyte and the active material and improve the low-temperature performance of the electrolyte. Thus, it is beneficial to improve the film stripping problem of the fast-charging graphite in the negative electrode overhang area and the non-lithium-inserting area, while taking into account the low-temperature performance and energy density of the secondary battery.

[0038] In one or more embodiments, 0.8 ≤ A×N / (ρ×M) ≤ 4.0; 0.05 ≤ ρ ≤ 0.12; and / or, 8% ≤ M ≤ 18%. For example, the value of A×N / (ρ×M) can be 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4.0 or a range composed of any two of these values; the value of ρ can be 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12 or a range composed of any two of these values; the value of M can be 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18% or a range composed of any two of these values. By controlling the values of A×N / (ρ×M), ρ, and M within the above ranges, it is beneficial to improve the quality of the SEI film, beneficial to form a relatively dense SEI film on the surface of the fast-charging graphite, reduce the risk of co-insertion of solvents on the negative electrode sheet. In addition, it is beneficial to reduce the side reaction between the electrolyte and the active material and improve the low-temperature performance of the electrolyte. Thus, it is beneficial to improve the film stripping problem of the fast-charging graphite in the negative electrode overhang area and the non-lithium-inserting area, while taking into account the low-temperature performance and energy density of the secondary battery.

[0039] In one or more embodiments, 0.8 ≤ A×N / (ρ×M) ≤ 4.0; 0.05 ≤ ρ ≤ 0.12; and / or, 0.1% ≤ N ≤ 2%. For example, the value of A×N / (ρ×M) can be 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4.0 or a range composed of any two of these values; the value of ρ can be 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12 or a range composed of any two of these values; the value of N can be 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2% or a range composed of any two of these values. By controlling the values of A×N / (ρ×M), ρ, and N within the above ranges, it is beneficial to improve the quality of the SEI film, beneficial to form a relatively dense SEI film on the surface of the fast-charging graphite, reduce the risk of co-insertion of solvents on the negative electrode sheet. In addition, it is beneficial to reduce the side reaction between the electrolyte and the active material and improve the low-temperature performance of the electrolyte. Thus, it is beneficial to improve the film stripping problem of the fast-charging graphite in the negative electrode overhang area and the non-lithium-inserting area, while taking into account the low-temperature performance and energy density of the secondary battery.

[0040] In one or more embodiments, 0.8 ≤ A×N / (ρ×M) ≤ 4.0; 8% ≤ M ≤ 18%; and / or, 0.1% ≤ N ≤ 2%. For example, the value of A×N / (ρ×M) can be 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4.0 or a range composed of any two of these numerical values; the value of M can be 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18% or a range composed of any two of these numerical values; the value of N can be 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2% or a range composed of any two of these numerical values. By adjusting the values of A×N / (ρ×M), M, and N within the above ranges, it is beneficial to improve the quality of the SEI film, beneficial to form a relatively dense SEI film on the surface of the fast-charging graphite, reducing the risk of co-insertion of solvents on the negative electrode sheet. In addition, it is beneficial to reduce the side reactions between the electrolyte and the active material and improve the low-temperature performance of the electrolyte. Thus, it is beneficial to improve the film stripping problem of the fast-charging graphite in the negative electrode overhang region and the non-lithiated region, while taking into account the low-temperature performance and energy density of the secondary battery.

[0041] In one or more embodiments, 0.05 ≤ ρ ≤ 0.12; 8% ≤ M ≤ 18%; and / or, 0.1% ≤ N ≤ 2%. For example, the value of ρ can be 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12 or a range composed of any two of these numerical values; the value of M can be 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18% or a range composed of any two of these numerical values; the value of N can be 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2% or a range composed of any two of these numerical values. By adjusting the values of ρ, M, and N within the above ranges, it is beneficial to improve the quality of the SEI film, beneficial to form a relatively dense SEI film on the surface of the fast-charging graphite, reducing the risk of co-insertion of solvents on the negative electrode sheet. In addition, it is beneficial to reduce the side reactions between the electrolyte and the active material and improve the low-temperature performance of the electrolyte. Thus, it is beneficial to improve the film stripping problem of the fast-charging graphite in the negative electrode overhang region and the non-lithiated region, while taking into account the low-temperature performance and energy density of the secondary battery.

[0042] In one or more embodiments, 0.8 ≤ A×N / (ρ×M) ≤ 4.0; 0.05 ≤ ρ ≤ 0.12; 8% ≤ M ≤ 18%; and / or, 0.1% ≤ N ≤ 2%. For example, the value of A×N / (ρ×M) can be 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4.0 or a range composed of any two of these numerical values; the value of ρ can be 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12 or a range composed of any two of these numerical values; the value of M can be 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18% or a range composed of any two of these numerical values; the value of N can be 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2% or a range composed of any two of these numerical values. By adjusting the values of ρ, M, and N within the above ranges, it is beneficial to improve the quality of the SEI film, beneficial to form a relatively dense SEI film on the surface of fast-charging graphite, reduce the risk of co-insertion of solvents on the negative electrode sheet. In addition, it is beneficial to reduce the side reactions between the electrolyte and the active material and improve the low-temperature performance of the electrolyte. Thus, it is beneficial to improve the film removal problem of fast-charging graphite in the negative electrode overhang area and the non-lithium-inserting area, while taking into account the low-temperature performance and energy density of the secondary battery.

[0043] In one or more embodiments, 0.1 ≤ A ≤ 6, optionally, 1 ≤ A ≤ 5, and further optionally, 2.2 ≤ A ≤ 3.6. For example, the value of A can be 0.1, 0.3, 0.5, 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 5, 5.2, 5.5, 5.8, 6 or a range composed of any two of these numerical values. By controlling the value of A within the above range, the liquid retention coefficient of the electrolyte is moderate, which is beneficial to meeting the performance of the secondary battery, enabling the performance of the secondary battery to be optimized, reducing the risks of lithium deposition and capacity drop in the secondary battery, facilitating the improvement of the quality of the SEI film, facilitating the formation of a relatively dense SEI film on the surface of fast-charging graphite, reducing the risk of co-insertion of solvents on the negative electrode sheet, and in addition, facilitating the reduction of side reactions between the electrolyte and the active material and improving the low-temperature performance of the electrolyte. Thus, it is beneficial to improve the film stripping problem of fast-charging graphite in the negative electrode overhang area and the non-lithium-inserting area, while taking into account the low-temperature performance of the secondary battery. The liquid retention coefficient of the electrolyte is related to factors such as the composition of the electrolyte, the electrode sheet material, the separator, and the assembly method of the secondary battery. In this application, the liquid retention coefficient of the electrolyte can be adjusted by controlling the content and type of the film-forming additive. Exemplarily, when other conditions are constant, as the content of the film-forming additive increases and the content of the lithium salt in the electrolyte remains unchanged, the content of the organic solvent in the electrolyte decreases, and the liquid retention coefficient of the electrolyte increases; when other conditions are constant, as the content of the film-forming additive decreases and the content of the lithium salt in the electrolyte remains unchanged, the content of the organic solvent in the electrolyte increases, and the liquid retention coefficient of the electrolyte decreases.

[0044] In one or more embodiments, 2% ≤ A×N / ρ ≤ 80%. For example, the value of A×N / ρ can be 2%, 5%, 8%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80% or a range composed of any two of these numerical values. By controlling the value of A×N / ρ within the above range, the electrolyte and fast-charging graphite act synergistically, which is beneficial to improving the quality of the SEI film, facilitating the formation of a relatively dense SEI film on the surface of fast-charging graphite, reducing the risk of co-insertion of solvents on the negative electrode sheet, and in addition, facilitating the reduction of side reactions between the electrolyte and the active material and improving the low-temperature performance of the electrolyte. Thus, it is beneficial to improve the film stripping problem of fast-charging graphite in the negative electrode overhang area and the non-lithium-inserting area, while taking into account the low-temperature performance and energy density of the secondary battery.

[0045] In one or more embodiments, 0.2% ≤ N ≤ 1%. For example, the value of N can be 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or a range composed of any two of these numerical values. By controlling the value of N within the above range, it is beneficial to improve the quality of the SEI film. When combined with fast-charging graphite, it is beneficial to form a relatively dense SEI film on the surface of the fast-charging graphite, reducing the risk of co-insertion of solvents on the negative electrode sheet. In addition, it is beneficial to reduce the side reactions between the electrolyte and the active material and improve the low-temperature performance of the electrolyte. Thus, it is beneficial to improve the film removal problem of the fast-charging graphite in the negative electrode overhang region and the non-lithium-inserting region, while taking into account the low-temperature performance of the secondary battery.

[0046] In one or more embodiments, 4% ≤ A×N / ρ ≤ 20%. For example, the value of A×N / ρ can be 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or a range composed of any two of these numerical values. By controlling the value of A×N / ρ within the above range, the electrolyte and the fast-charging graphite act synergistically, which is beneficial to improve the quality of the SEI film, beneficial to form a relatively dense SEI film on the surface of the fast-charging graphite, reducing the risk of co-insertion of solvents on the negative electrode sheet. In addition, it is beneficial to reduce the side reactions between the electrolyte and the active material and improve the low-temperature performance of the electrolyte. Thus, it is beneficial to improve the film removal problem of the fast-charging graphite in the negative electrode overhang region and the non-lithium-inserting region, while taking into account the low-temperature performance and energy density of the secondary battery.

[0047] In one or more embodiments, 0.2% ≤ N ≤ 1%; and / or, 4% ≤ A×N / ρ ≤ 20%. For example, the value of N can be 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or a range composed of any two of these numerical values; the value of A×N / ρ can be 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or a range composed of any two of these numerical values. By controlling the values of N and A×N / ρ within the above range, the electrolyte and the fast-charging graphite act synergistically, which is beneficial to improve the quality of the SEI film, beneficial to form a relatively dense SEI film on the surface of the fast-charging graphite, reducing the risk of co-insertion of solvents on the negative electrode sheet. In addition, it is beneficial to reduce the side reactions between the electrolyte and the active material and improve the low-temperature performance of the electrolyte. Thus, it is beneficial to improve the film removal problem of the fast-charging graphite in the negative electrode overhang region and the non-lithium-inserting region, while taking into account the low-temperature performance and energy density of the secondary battery.

[0048] In one or more embodiments, the compactness of the coating layer is D, where 0 ≤ D ≤ 5; optionally, 2 ≤ D ≤ 3. For example, the value of D can be 0, 0.2, 0.5, 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 5 or a range composed of any two of these numerical values. By adjusting the value of D within the above range, it is beneficial to increase the layer spacing between the negative active materials, improve the diffusion rate of lithium ions, form a stable SEI film on the surface of the negative electrode sheet, reduce the occurrence of side reactions between the negative active materials and the electrolyte, improve the stability of the structure of the lithium insertion region of the negative electrode sheet, thereby improving the low-temperature performance and fast-charging performance of the secondary battery. At the same time, it reduces the risk of co-insertion of solvents on the negative electrode sheet, which is beneficial to improving the film peeling problem of fast-charging graphite on the negative electrode sheet.

[0049] In the present application, the compactness of the coating layer = the porosity of the coating layer / the mass percentage content of the coating layer.

[0050] In one or more embodiments, the coating material includes at least one of hard carbon, soft carbon, graphene, pitch-based, carbon nanotubes or Li3P; optionally, the coating material includes at least one of hard carbon, soft carbon, graphene, pitch-based or carbon nanotubes. Generally, selecting the above types of coating materials is beneficial to increasing the layer spacing between the negative active materials, improving the diffusion rate of lithium ions, forming a stable SEI film on the surface of the negative electrode sheet, reducing the occurrence of side reactions between the negative active materials and the electrolyte, and improving the stability of the structure of the lithium insertion region of the negative electrode sheet, thereby improving the low-temperature performance and fast-charging performance of the secondary battery.

[0051] In one or more embodiments, the film-forming additive includes at least one of 1,3-propane sultone, ethylene sulfate, 1,4-butane sultone, methylene methanedisulfonate, ethyl sulfite, diethyl sulfite or dimethyl sulfite; optionally, the film-forming additive includes at least one of 1,3-propane sultone, ethylene sulfate or 1,4-butane sultone. By selecting the above types of film-forming additives, it is beneficial to improve the quality of the SEI film. When paired with fast-charging graphite, it is beneficial to form a relatively dense SEI film on the surface of the fast-charging graphite, reducing the risk of co-insertion of solvents on the negative electrode sheet. In addition, it is beneficial to reduce the side reactions between the electrolyte and the active materials and improve the low-temperature performance of the electrolyte. Thus, it is beneficial to improve the film peeling problem of fast-charging graphite in the overhang region and non-lithium insertion region of the negative electrode, while taking into account the low-temperature performance of the secondary battery.

[0052] In this application, the electrolyte, in addition to the film-forming additive, further includes a lithium salt and a non-aqueous solvent. There is no particular limitation on the lithium salt in this application, as long as the purpose of this application can be achieved. For example, the lithium salt may include, but is not limited to, at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalato)borate (LiBOB), or lithium difluoroborate. There is no particular limitation on the content of the lithium salt in the electrolyte in this application, as long as the purpose of this application can be achieved. For example, based on the mass of the electrolyte, the mass percentage content of the lithium salt is 8% to 15%. There is no particular limitation on the non-aqueous solvent in this application, as long as the purpose of this application can be achieved. For example, the non-aqueous solvent may include, but is not limited to, at least one of carbonate compounds, carboxylate compounds, ether compounds, or other organic solvents. The above carbonate compounds may include, but are not limited to, at least one of linear carbonate compounds, cyclic carbonate compounds, or fluorinated carbonate compounds. The above linear carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (MEC). The above cyclic carbonates may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), or vinylene ethylene carbonate (VEC). The fluorinated carbonate compounds may include, but are not limited to, at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethyl ethylene carbonate. The above carboxylate compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolide, valerolactone, or caprolactone. The above ether compounds may include, but are not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The above other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate.The content of the non-aqueous solvent in the electrolyte of the present application is not particularly limited as long as the object of the present application can be achieved.

[0053] In the present application, the negative electrode sheet further includes a negative electrode current collector, and the negative electrode material layer is disposed on at least one surface of the negative electrode current collector. The above "the negative electrode material layer is disposed on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be disposed on one surface of the negative electrode current collector along its thickness direction, or can be disposed on two surfaces of the negative electrode current collector along its thickness direction. It should be noted that the "surface" here can be the entire area of the surface of the negative electrode current collector or a partial area of the surface of the negative electrode current collector, and the present application has no particular limitation as long as the object of the present application can be achieved. The present application has no particular limitation on the negative electrode current collector as long as the object of the present application can be achieved. For example, it can include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam or composite current collector. Exemplarily, the composite current collector can be a lithium-copper composite current collector, a carbon-copper composite current collector, a nickel-copper composite current collector, a titanium-copper composite current collector, etc. In the present application, the negative electrode material layer may further include a conductive agent and a binder. The present application has no particular limitation on the type of the conductive agent in the negative electrode material layer as long as the object of the present application can be achieved. For example, the conductive agent can include but is not limited to at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fiber, flake graphite, graphene, metal material or conductive polymer. The conductive carbon black can include but is not limited to at least one of acetylene black or Ketjen black. The above carbon nanotubes can include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above carbon fiber can include but is not limited to vapor-grown carbon fiber (VGCF) and / or nanofiber. The above metal material can include but is not limited to metal powder and / or metal fiber. Specifically, the metal can include but is not limited to at least one of copper, nickel, aluminum or silver. The above conductive polymer can include but is not limited to at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene or polypyrrole. The present application has no particular limitation on the type of the binder in the negative electrode material layer as long as the object of the present application can be achieved. For example, the binder can include but is not limited to at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyimide, polyamideimide, styrene-butadiene rubber or polyvinylidene fluoride. Optionally, the negative electrode material layer further includes a thickening agent. The present application has no particular limitation on the type of the thickening agent as long as the object of the present application can be achieved. For example, the thickening agent can include at least one of carboxymethyl cellulose or sodium carboxymethyl cellulose. The present application has no particular limitation on the mass ratio of the negative electrode active material, conductive agent, binder and thickening agent in the negative electrode material layer, and those skilled in the art can select according to actual needs as long as the object of the present application can be achieved.

[0054] The present application does not particularly limit the preparation method of the negative electrode active material, as long as the purpose of the present application can be achieved. For example, the preparation method of the negative electrode active material may include, but is not limited to, the following steps: mixing graphite with a coating material, followed by ball milling, and then putting the mixture into a protective atmosphere for sintering to obtain graphite with a coating layer, that is, the negative electrode active material.

[0055] The present application does not particularly limit the protective atmosphere, as long as the purpose of the present application can be achieved. For example, the protective atmosphere can be argon (Ar). The present application does not particularly limit the mixing and stirring step, as long as the purpose of the present application can be achieved. For example, the mixing and stirring time can be 1 h to 24 h, and the mixing and stirring speed can be 500 rpm to 3000 rpm. The present application does not particularly limit the ball milling time, as long as the purpose of the present application can be achieved. For example, the ball milling time can be 16 h to 24 h. The present application does not particularly limit the sintering step, as long as the purpose of the present application can be achieved. For example, the sintering temperature can be 900 °C to 1200 °C, and the sintering time can be 2 h to 6 h.

[0056] In the present application, the mass percentage content of the coating layer can be adjusted by controlling the mass ratio of graphite to the coating material added. In the present application, the compactness of the coating layer can be adjusted by controlling the ball milling time. For example, the longer the ball milling time, the greater the compactness of the coating layer, and the shorter the ball milling time, the smaller the compactness of the coating layer.

[0057] In the present application, the secondary battery further includes a positive electrode tab, which includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector. The above-mentioned "positive electrode material layer disposed on at least one surface of the positive current collector" means that the positive electrode material layer can be disposed on one surface of the positive current collector along its own thickness direction, or can be disposed on both surfaces of the positive current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of the surface of the positive current collector, or a partial area of the surface of the positive current collector. There is no special limitation in the present application, as long as the purpose of the present application can be achieved. There is no special limitation on the positive current collector in the present application, as long as the purpose of the present application can be achieved. For example, it can include aluminum foil, aluminum alloy foil or composite current collector (such as aluminum-carbon composite current collector), etc. The positive electrode material layer includes positive electrode active materials. There is no special limitation on the positive electrode active materials in the present application, as long as the purpose of the present application can be achieved. For example, the positive electrode active materials can include, but are not limited to, lithium nickel cobalt manganese oxide (such as NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminate, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate or lithium titanate, etc. There is no special limitation on the thickness of the positive current collector and the positive electrode material layer in the present application, as long as the purpose of the present application can be achieved. The positive electrode material layer may further include a conductive agent and a binder. There is no special limitation on the type of binder in the positive electrode material layer in the present application, as long as the purpose of the present application can be achieved. For example, the binder can be the same as the binder in the above-mentioned negative electrode material layer. There is no special limitation on the type of conductive agent in the positive electrode material layer in the present application, as long as the purpose of the present application can be achieved. For example, the conductive agent can be the same as the conductive agent in the above-mentioned negative electrode material layer. There is no special limitation on the mass ratio of the positive electrode active materials, conductive agent and binder in the positive electrode material layer, and those skilled in the art can select according to actual needs, as long as the purpose of the present application can be achieved.

[0058] Optionally, the positive electrode tab may further include a conductive layer, which is located between the positive current collector and the positive electrode material layer. The composition of the conductive layer is not particularly limited and can be a commonly used conductive layer in the art. The conductive layer includes a conductive agent and a binder.

[0059] There is no special limitation on the type of binder in the conductive layer in the present application, as long as the purpose of the present application can be achieved. For example, the binder can be the same as the binder in the above-mentioned negative electrode material layer. There is no special limitation on the type of conductive agent in the conductive layer in the present application, as long as the purpose of the present application can be achieved. For example, the conductive agent can be the same as the conductive agent in the above-mentioned negative electrode material layer.

[0060] In the present application, the secondary battery further includes a separator. There is no particular limitation on the separator in the present application, as long as it can achieve the purpose of the present application. For example, the material of the separator may include, but is not limited to, at least one of polyolefins (PO) mainly composed of polyethylene (PE) and polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The type of the separator may include at least one of a woven film, a non-woven film, a microporous film, a composite film, a rolled film, or a spun film. In some embodiments of the present application, the separator may include a substrate layer and a surface treatment layer. The substrate layer may be a non-woven fabric film or a composite film having a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film may be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer may be a polymer layer, an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance. In some embodiments of the present application, the inorganic layer includes inorganic particles and a binder. There is no particular limitation on the inorganic particles in the present application. For example, the inorganic particles may include at least one of alumina, silica, magnesia, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. There is no particular limitation on the binder in the present application. For example, the binder may be at least one of the above-mentioned binders. In some embodiments of the present application, the polymer layer includes a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene ether, polyvinylidene fluoride, or poly(vinylidene fluoride-hexafluoropropylene). In the present application, there is no particular limitation on the thickness of the separator, as long as it can achieve the purpose of the present application. For example, the thickness of the separator may be 3 μm to 30 μm.

[0061] The secondary battery further includes a housing for accommodating the positive electrode plate, the separator, the negative electrode plate, and the electrolyte, as well as other components known in the field of secondary batteries. The present application does not limit the above-mentioned other components. There is no particular limitation on the housing in the present application, and it may be a housing well-known in the art, as long as it can achieve the purpose of the present application. For example, the housing may be a hard shell housing or a flexible housing. The material of the hard shell housing may be a metal. The present application does not limit the type of the metal, and a metal hard shell housing known in the art may be used, as long as it can achieve the purpose of the present application. The flexible housing may be a metal plastic film, such as an aluminum plastic film, a steel plastic film, etc.

[0062] The preparation process of the secondary battery of the present application is well-known to those skilled in the art, and there is no special limitation in the present application. For example, the preparation process of the secondary battery may include but is not limited to the following steps: stacking a separator, a negative electrode sheet, a separator, and a positive electrode sheet in sequence, and winding, folding, etc. as needed to obtain a wound electrode assembly, placing the electrode assembly in a housing, injecting an electrolyte into the housing and sealing it to obtain a secondary battery.

[0063] The second aspect of the present application provides an electronic device including the secondary battery in any of the foregoing embodiments. Thus, the electronic device of the present application has good performance in use.

[0064] The present application does not particularly limit the type of the electronic device, and it can be any electronic device known in the prior art. In some embodiments of the present application, the electronic device may include but is not limited to 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, a liquid crystal TV, a hand-held cleaner, a portable CD player, a minidisc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, a moped, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor, etc.

[0065] Examples

[0066] Hereinafter, examples and comparative examples are given to more specifically illustrate the embodiments of the present application. Various tests and evaluations are carried out according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0067] Test method and device:

[0068] Measurement of the areal density ρ of the negative electrode material layer:

[0069] At an ambient temperature of 25 °C, disassemble the lithium-ion battery to obtain a wound electrode assembly, take out the negative electrode sheet, soak it in dimethyl carbonate (DMC) for 20 min, and then place the negative electrode sheet in an oven and dry it at 80 °C for 12 h to obtain a test sample of the negative electrode sheet.

[0070] Punch the negative electrode sheet sample with a double-sided coated negative electrode material layer into 4 small circular pieces with a radius of 22.14 mm (area: 1540.25 mm 2 ), weigh them in sequence and take the average value, denoted as a; wipe off the negative electrode material layer on the two surfaces of the small circular pieces with deionized water, weigh them in sequence and take the average value, denoted as b, then,

[0071] The areal density ρ of the negative electrode material layer = (a - b) / (2×1540.25).

[0072] Test of the mass percentage content M of the coating layer:

[0073] Under an air atmosphere, tests are carried out using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The weight loss rate of the graphite sample with the coating layer between 200°C and 600°C is the mass percentage content of the coating layer.

[0074] Test of the liquid retention coefficient A of the electrolyte:

[0075] In an environment with a temperature of 25°C, the lithium-ion battery is weighed, then washed with dimethyl carbonate (DMC), placed in a vacuum oven for drying, and taken out and weighed again.

[0076] The liquid retention coefficient A of the electrolyte = (weight of the lithium-ion battery before drying - weight of the lithium-ion battery after drying) / rated capacity of the lithium-ion battery. In this application, the rated capacity of the lithium-ion battery is 2800 mAh.

[0077] Test of the components of the electrolyte:

[0078] The components of the electrolyte are tested using a gas chromatography-mass spectrometry (GC-MS, model: Agilent GC 7890A), and the test is carried out in combination with the external standard method. The mass percentage contents of each component in the electrolyte are measured respectively, and the mass percentage content N of the film-forming additive is measured.

[0079] Test of the porosity of the coating layer:

[0080] The porosity of the coating layer is measured using the BET specific surface area measurement method.

[0081] Low-temperature cycle demoulding and lithium plating test:

[0082] The test temperature is maintained at -10°C. The lithium-ion batteries in the examples and comparative examples are charged at a constant current of 0.1C to 4.25V, then charged at a constant voltage of 4.25V until the current ≤ 0.05C, left standing for 30 min, discharged at a constant current of 0.5C to 2.4V, and left standing for 30 min. The above steps are recorded as 1 cycle, and each group of lithium-ion batteries is cycled 10 times. After the cycle is completed, each group of lithium-ion batteries is disassembled, the negative electrode plate is taken out, and the states of the non-lithium-inserted area and the overhang area of each group of negative electrode plates are observed and recorded.

[0083] The criteria for judging the degree of demolding of lithium-ion batteries are as follows: a demolding area of 0% means no demolding, i.e., no demolding; a demolding area greater than 0 and less than or equal to 2% means slight demolding, i.e., slight demolding; a demolding area greater than 2% and less than or equal to 20% means moderate demolding, i.e., moderate demolding; a demolding area greater than 20% and less than or equal to 100% means severe demolding, i.e., severe demolding, wherein the percentage of the demolding area is calculated based on the total area of the non-lithium embedded area and the overhang area of the negative electrode.

[0084] The test temperature was maintained at -10°C, and the lithium-ion batteries in the examples and comparative examples were charged to 4.25V at a constant current of 0.1C, then charged to a current of 0.05C at a constant voltage of 4.25V, left to stand for 30 minutes, and discharged to 2.4V at a constant current of 0.5C, left to stand for 30 minutes. The above steps were recorded as 1 cycle, and each group of lithium-ion batteries cycled 10 times. After that, the lithium-ion battery was placed in an environment of 25°C, and then charged to 4.3V at a constant current of 0.5C, and then charged to 0.05C at a constant voltage of 4.3V, left to stand for 15 minutes, and the lithium-ion battery was disassembled to observe the lithium deposition state on the surface of the lithium-embedded area of the negative electrode. The non-lithium deposition area on the surface of the lithium-embedded area of the negative electrode was golden yellow, and the lithium deposition area was off-white. The boundary value of the lithium deposition rate of the lithium-embedded area of the negative electrode shall be based on the result of measuring the minimum lithium deposition rate.

[0085] If there is no lithium deposition on the surface of the lithium embedded area of the negative electrode, the lithium-ion battery prepared in the same way is placed at a test temperature of -10°C, and the charge rate is increased by 0.1C. The other charge and discharge parameters are the same as the above charge and discharge steps for charge and discharge cycles. After 10 cycles, the lithium-ion battery is placed in an environment of 25°C, and then charged to 4.3V at a constant current rate of 0.5C, and charged to 0.05C at a constant voltage of 4.3V. After standing for 15 minutes, the lithium-ion battery is disassembled to observe the lithium deposition state on the surface of the lithium embedded area of the negative electrode. The charge rate is increased by 0.1C each time until the lithium deposition in the lithium embedded area of the negative electrode is completed, and the lithium deposition rate boundary value of the lithium embedded area of the negative electrode is recorded. Among them, the higher the lithium deposition rate boundary value of the lithium embedded area of the negative electrode, the better the low temperature performance of the lithium-ion battery.

[0086] In this application, those skilled in the art will understand that "C" refers to the rated capacity of the finished lithium-ion battery when it leaves the factory. "1C" is the current value that fully discharges the capacity of the lithium-ion battery within 1 hour, "0.1C" is the current value that fully discharges the capacity of the lithium-ion battery within 10 hours, and other multiples are similar.

[0087] Example 1

[0088] <Preparation of negative electrode active material>

[0089] Artificial graphite and asphalt base are added to a mixing device in a mass ratio of 88:12 for mixing and stirring, the mixing and stirring time is 8 hours, and the mixing and stirring speed is 2500rpm; then the mixture is ball milled for 20 hours; then sintered under Ar protective atmosphere, the sintering temperature is 1100℃, the sintering time is 4 hours, and the sintered powder is sieved to obtain artificial graphite coated with carbon nanotubes as a negative electrode active material. Among them, based on the mass of graphite, the mass percentage M of the coating layer is 12%, the porosity of the coating layer is 30%, and the compactness D of the coating layer is 2.5.

[0090] <Preparation of negative electrode sheet>

[0091] The negative electrode active material, conductive carbon black (Super P), and styrene-butadiene rubber (SBR) prepared above are mixed in a weight ratio of 97:1.5:1.5, and deionized water is added as a solvent to prepare a negative electrode slurry with a solid content of 57wt%, and stirred evenly. The negative electrode slurry is evenly coated on a negative electrode current collector copper foil with a thickness of 10μm, and dried at 110°C to complete the single-sided coating of the negative electrode pole piece. After that, the above steps are repeated on the other surface of the negative electrode current collector copper foil to obtain a negative electrode pole piece with a double-sided coating of a negative electrode material layer. Then, after cold pressing, cutting, and striping, it is dried under vacuum conditions at 105°C for 4h to obtain a negative electrode pole piece with a specification of 1742mm×67mm for standby use. Among them, the surface density of the negative electrode material layer is 0.08mg / mm 2 The compaction density of the negative electrode material layer is 1.55g / cm 3 .

[0092] <Preparation of positive electrode sheet>

[0093] The positive electrode active material lithium manganese iron phosphate (LMFP), the positive electrode binder polyvinylidene fluoride (PVDF) and the conductive carbon black are dispersed in N-methylpyrrolidone (NMP) solvent in a mass ratio of 94.8:2.8:2.4, and the mixture is fully stirred to obtain a positive electrode slurry with a solid content of 72wt%. The positive electrode slurry is evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 13μm, and dried at 105°C to obtain a positive electrode sheet coated with a single-sided positive electrode material layer. After that, the above steps are repeated on the other surface of the positive electrode current collector aluminum foil to obtain a positive electrode sheet coated with a double-sided positive electrode material layer. Then, after cold pressing, cutting and slitting, it is dried under vacuum conditions at 105°C for 4h to obtain a positive electrode sheet with a specification of 1600mm×64mm for standby use. Among them, the surface density of the positive electrode material layer is 250mg / 1540.25mm 2 The compaction density of the positive electrode material layer is 2.7g / cm 3 .

[0094] <Diaphragm>

[0095] A polyethylene (PE) film with a thickness of 12 μm is used as the separator.

[0096] <Preparation of electrolyte>

[0097] In a dry argon atmosphere, first, the organic solvents ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a mass ratio of EC:EMC:DEC = 30:50:20 to obtain a base solvent. Then, the film-forming additive 1,3-propane sultone and the lithium salt lithium hexafluorophosphate (LiPF6) are added to the base solvent and dissolved and mixed evenly to obtain the electrolyte. Among them, based on the mass of the electrolyte, the mass percentage of the lithium salt is 12%, the mass percentage of the film-forming additive is 0.6%, and the balance is the base solvent.

[0098] <Preparation of lithium-ion battery>

[0099] The separator, negative electrode sheet, separator, and positive electrode sheet prepared above are stacked in sequence, and pre-wound first to ensure that the separator is between the negative electrode sheet and the positive electrode sheet. Then, after winding, flattening, current collector welding, casing, bottom penetration welding, inkjet printing, vacuum drying, electrolyte injection, sealing, and high-temperature standing, formation and capacity are carried out, and then the lithium-ion battery can be obtained. Among them, the upper limit voltage of formation is 4.3 V, and the formation temperature is 75 °C.

[0100] Examples 2 to 24

[0101] Except for adjusting the relevant preparation parameters according to Table 1, the rest are the same as in Example 1. Among them, when the value of M changes, the mass ratio of the addition of artificial graphite and pitch-based is adjusted so that the mass percentage of the coating layer is as shown in Table 1. When the value of ρ changes, the coating amount per unit area is adjusted so that the surface density of the negative electrode material layer is as shown in Table 1. When the mass percentage of the film-forming additive in the electrolyte changes, the mass percentage of the base solvent changes accordingly, the proportion of each component in the base solvent remains unchanged, and the mass percentage of the lithium salt remains unchanged. When the value of D changes, the ball milling time is adjusted so that the compactness of the coating layer is as shown in Table 1.

[0102] Comparative Example 1

[0103] Except that the electrolyte is prepared according to the following steps, the rest are the same as in Example 1.

[0104] <Preparation of electrolyte>

[0105] In a dry argon atmosphere, first, the organic solvents ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a mass ratio of EC:EMC:DEC = 30:50:20 to obtain a base solvent. Then, propylene carbonate (PC) and lithium hexafluorophosphate (LiPF6) were added to the base solvent and dissolved and mixed evenly to obtain an electrolyte. Among them, based on the mass of the electrolyte, the mass percentage of the lithium salt was 12%, the mass percentage of PC was 0.6%, and the balance was the base solvent.

[0106] Comparative Example 2

[0107] Except that the electrolyte was prepared according to the following steps, the rest was the same as in Example 1. Among them, when the value of D changed, the ball milling time was adjusted so that the compactness of the coating layer was as shown in Table 1.

[0108] <Preparation of Electrolyte>

[0109] In a dry argon atmosphere, first, the organic solvents ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a mass ratio of EC:EMC:DEC = 30:50:20 to obtain a base solvent. Then, lithium hexafluorophosphate (LiPF6) was added to the base solvent and dissolved and mixed evenly to obtain an electrolyte. Among them, based on the mass of the electrolyte, the mass percentage of the lithium salt was 12%, and the balance was the base solvent.

[0110] Comparative Examples 3 to 4

[0111] Except that the relevant preparation parameters were adjusted according to Table 1, the rest was the same as in Example 1. Among them, when the value of M changed, the mass ratio of artificial graphite and pitch-based materials added was adjusted so that the mass percentage of the coating layer was as shown in Table 1. When the value of ρ changed, the coating amount per unit area was adjusted so that the surface density of the negative electrode material layer was as shown in Table 1. When the mass percentage of the film-forming additive in the electrolyte changed, the mass percentage of the base solvent changed accordingly, and the ratio of each component in the base solvent remained unchanged, and the mass percentage of the lithium salt remained unchanged.

[0112] The preparation parameters and performance parameters of each example and comparative example are shown in Table 1.

[0113]

[0114] As can be seen from Examples 1 to 24 and Comparative Examples 1 to 4, by using fast-charging graphite in combination with an electrolyte added with a film-forming additive and regulating the value of A×N / (ρ×M) within the scope of the present application, the degree of demolding and lithium deposition in the overhang region and non-lithium-inserting region of the negative electrode tab is relatively light, indicating that the problem of demolding of fast-charging graphite in the overhang region and non-lithium-inserting region of the negative electrode is improved, while taking into account the low-temperature performance of the secondary battery. In Comparative Example 1, the fast-charging graphite lithium-ion battery is combined with an electrolyte containing PC; in Comparative Example 2, the fast-charging graphite lithium-ion battery is combined with an electrolyte that does not contain PC and does not contain the film-forming additive of the present application; in Comparative Examples 3 to 4, the value of A×N / (ρ×M) is not within the scope of the present application. In Comparative Examples 1 to 4, the degree of demolding and / or lithium deposition in the overhang region and non-lithium-inserting region of the negative electrode tab is relatively heavy, indicating that the lithium-ion batteries in the comparative examples cannot take into account the improvement of the demolding problem and the low-temperature performance. While in Examples 1 to 24, the degree of demolding and lithium deposition in the overhang region and non-lithium-inserting region of the negative electrode tab during low-temperature cycling is relatively light, indicating that the problem of demolding of fast-charging graphite in the overhang region and non-lithium-inserting region of the negative electrode is improved, while taking into account the low-temperature performance of the lithium-ion battery.

[0115] The value of ρ usually affects the demolding and lithium deposition in the overhang region and non-lithium-inserting region of the negative electrode in a lithium-ion battery. As can be seen from Examples 1 to 5 and Examples 10 to 14, when the value of ρ is within the scope of the present application, the degree of demolding and lithium deposition in the overhang region and non-lithium-inserting region of the negative electrode tab is relatively light, indicating that the lithium-ion battery of the present application improves the problem of demolding of fast-charging graphite in the overhang region and non-lithium-inserting region of the negative electrode, while taking into account the low-temperature performance.

[0116] The value of M usually affects the demolding and lithium deposition in the overhang region and non-lithium-inserting region of the negative electrode in a lithium-ion battery. As can be seen from Example 1 and Examples 6 to 14, when the value of M is within the scope of the present application, the degree of demolding and lithium deposition in the overhang region and non-lithium-inserting region of the negative electrode tab is relatively light, indicating that the lithium-ion battery of the present application improves the problem of demolding of fast-charging graphite in the overhang region and non-lithium-inserting region of the negative electrode, while taking into account the low-temperature performance.

[0117] The value of N usually affects the demolding and lithium deposition in the overhang region and non-lithium-inserting region of the negative electrode in a lithium-ion battery. As can be seen from Example 1 and Examples 10 to 14, when the value of N is within the scope of the present application, the degree of demolding and lithium deposition in the overhang region and non-lithium-inserting region of the negative electrode tab is relatively light, indicating that the lithium-ion battery of the present application improves the problem of demolding of fast-charging graphite in the overhang region and non-lithium-inserting region of the negative electrode, while taking into account the low-temperature performance.

[0118] The value of D usually affects the demolding and lithium deposition in the overhang area of the negative electrode and the non-lithium-inserted area in a lithium-ion battery. It can be seen from Example 1, Example 15 to Example 18 that when the value of D is within the scope of this application, the degree of demolding and lithium deposition in the overhang area of the negative electrode sheet and the non-lithium-inserted area are relatively light, indicating that the lithium-ion battery of this application improves the demolding problem of fast-charging graphite in the overhang area of the negative electrode and the non-lithium-inserted area, and at the same time takes into account the low-temperature performance.

[0119] The type of coating material usually affects the demolding and lithium deposition in the overhang area of the negative electrode and the non-lithium-inserted area in a lithium-ion battery. It can be seen from Example 1, Example 19 to Example 21 that when the type of coating material is within the scope of this application, the degree of demolding and lithium deposition in the overhang area of the negative electrode sheet and the non-lithium-inserted area are relatively light, indicating that the lithium-ion battery of this application improves the demolding problem of fast-charging graphite in the overhang area of the negative electrode and the non-lithium-inserted area, and at the same time takes into account the low-temperature performance.

[0120] The type of film-forming additive usually affects the demolding and lithium deposition in the overhang area of the negative electrode and the non-lithium-inserted area in a lithium-ion battery. It can be seen from Example 1, Example 22 to Example 24 that when the type of film-forming additive is within the scope of this application, the degree of demolding and lithium deposition in the overhang area of the negative electrode sheet and the non-lithium-inserted area are relatively light, indicating that the lithium-ion battery of this application improves the demolding problem of fast-charging graphite in the overhang area of the negative electrode and the non-lithium-inserted area, and at the same time takes into account the low-temperature performance.

[0121] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method or article including a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method or article.

[0122] Each embodiment in this specification is described in a related manner. For the same or similar parts between each embodiment, reference can be made to each other. The key point of each embodiment is to illustrate the differences from other embodiments.

[0123] The above are only the preferred embodiments of this application, and are not intended to limit this application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of this application shall be included within the scope of protection of this application.

Claims

1. A secondary battery, comprising a negative electrode plate and an electrolyte, wherein the negative electrode plate comprises a negative electrode material layer, and the areal density of the negative electrode material layer is ρ mg / mm 2 , the negative electrode material layer comprises a negative electrode active material, the negative electrode active material comprises graphite with a coating layer, the graphite comprises at least one of natural graphite or artificial graphite, and based on the mass of the graphite with the coating layer, the mass percentage content of the coating layer is M; The liquid retention coefficient of the electrolyte is A g / Ah. The electrolyte includes a film-forming additive. Based on the mass of the electrolyte, the mass percentage content of the film-forming additive is N, and 0.4 ≤ A×N / (ρ×M) ≤ 12.

2. The secondary battery according to claim 1, which satisfies at least one of the following characteristics: (1) 0.8 ≤ A×N / (ρ×M) ≤ 4.0; (2) 0.05 ≤ ρ ≤ 0.12; (3)8％≤M≤18％； (4)0.1％≤N≤2％。 3. The secondary battery according to claim 2, wherein, 2% ≤ A×N / ρ ≤ 80%.

4. The secondary battery according to claim 2, which satisfies at least one of the following characteristics: (1)0.2％≤N≤1％； (2) 4% ≤ A×N / ρ ≤ 20%.

5. The secondary battery according to any one of claims 1 to 4, wherein, The compactness of the coating layer is D, and 0 ≤ D ≤ 5.

6. The secondary battery according to claim 5, wherein, 2≤D≤3。 7. The secondary battery according to any one of claims 1 to 6, wherein, The coating layer includes a coating material, and the coating material includes at least one of hard carbon, soft carbon, graphene, pitch-based, carbon nanotubes or Li3P.

8. The secondary battery according to claim 7, wherein, The coating material includes at least one of hard carbon, soft carbon, graphene, pitch-based or carbon nanotubes.

9. The secondary battery according to any one of claims 1 to 8, wherein, The film-forming additive includes at least one of 1,3-propane sultone, ethylene sulfate, 1,4-butane sultone, methylene methanedisulfonate, ethyl sulfite, diethyl sulfite or dimethyl sulfite.

10. The secondary battery according to claim 9, wherein, The film-forming additive includes at least one of 1,3-propane sultone, ethylene sulfate or 1,4-butane sultone.

11. An electronic device, comprising the secondary battery according to any one of claims 1 to 10.

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