Secondary battery, method for manufacturing the same, and electric device

Abstract

The application provides a secondary battery, a preparation method thereof and an electric device. The secondary battery comprises a battery cell, the battery cell comprises a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer arranged on at least one side of the negative electrode current collector, the negative electrode film layer comprises a negative electrode active material, a volume particle size distribution curve of the negative electrode active material is a bimodal curve, an abscissa of the bimodal curve is a particle size of the negative electrode active material, an ordinate is a volume percentage of the negative electrode active material, a particle size D1 of a first peak of the bimodal curve is less than a particle size D2 of a second peak of the bimodal curve; a single-side surface density of the negative electrode film layer is 80 mg / 1540.25 mm 2 -180 mg / 1540.25 mm 2 The secondary battery of the application balances the fast charging performance and the energy density.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and in particular to a secondary battery, its preparation method, and an electrical device thereof. Background Technology

[0002] In recent years, rechargeable batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace, and many other fields. With the increasing application of rechargeable batteries, higher requirements have been placed on their fast-charging performance. Summary of the Invention

[0003] This application was made in view of the aforementioned issues and aims to at least solve one of the technical problems existing in the prior art. To this end, this application provides a secondary battery, a method for manufacturing the same, and an electrical device thereof. The secondary battery of this application balances fast-charging performance and volumetric energy density.

[0004] The first aspect of this application provides a secondary battery, comprising a cell, the cell including a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector, the negative electrode film layer including a negative electrode active material, the volume particle size distribution curve of the negative electrode active material being a bimodal curve, the abscissa of the bimodal curve being the particle size of the negative electrode active material, and the ordinate being the volume percentage of the negative electrode active material, the particle size D1 of the first peak of the bimodal curve being smaller than the particle size D2 of the second peak of the bimodal curve; the one-sided density of the negative electrode film layer is 80 mg / 1540.25 mm. 2 -180mg / 1540.25mm 2 .

[0005] Liquid phase impedance, solid phase impedance, and solid-liquid interface impedance are important factors limiting the fast-charging performance of secondary batteries. This application controls the maximum single-sided density of the negative electrode film to 180 mg / 1540.25 mm². 2 This effectively improves the liquid phase diffusion resistance of the secondary battery, which is beneficial for improving the lithium intercalation consistency of active materials at different positions of the porous electrode and enhancing the fast-charging performance of the secondary battery in this application. However, while reducing the unilateral density of the negative electrode film is beneficial for improving fast-charging performance, it sacrifices some of the energy density of the secondary battery. Therefore, this application reasonably controls the minimum unilateral density of the negative electrode film to be 80 mg / 1540.25 mm. 2 While maximizing fast charging performance, it also takes into account some energy density.

[0006] Furthermore, the volumetric particle size distribution curve of the negative electrode active material in this application is a bimodal curve, where the particle size D1 of the first peak of the bimodal curve is smaller than the particle size D2 of the second peak. Since the added small-particle negative electrode active material exhibits better kinetics, the design of the negative electrode active material in this application is beneficial for improving the fast-charging performance of the secondary battery. In summary, the secondary battery of this application possesses both good fast-charging performance and good energy density.

[0007] In any embodiment, the one-sided density of the negative electrode film is 100 mg / 1540.25 mm². 2 -160mg / 1540.25mm 2 .

[0008] Further control was achieved to achieve a single-sided density of 100 mg / 1540.25 mm² for the negative electrode film. 2 -160mg / 1540.25mm 2 This allows the secondary battery in the present application embodiment to better balance fast charging performance and energy density.

[0009] In any embodiment, the range of D1 is 0.1-11.5 μm; optionally, the range of D1 is 0.1-9.5 μm; more preferably, the range of D1 is 2-4 μm; and / or,

[0010] The range of D2 is 9-25 μm, optionally, the range of D2 is 10-20 μm, and more preferably, the range of D2 is 13-15 μm.

[0011] By controlling the range of D1 and / or D2 within the aforementioned ranges, the Dv50 of both large and small particles of the negative electrode active material becomes suitable, which is beneficial for better particle gradation, further improving the compaction density of the negative electrode sheet, and thus further improving the energy density of the secondary battery of this application. It also better facilitates the fast-charging performance of the secondary battery.

[0012] In any implementation, the maximum value of the ordinate H1 of the first peak is 0.8%-3%, and / or the maximum value of the ordinate H2 of the second peak is 9%-12%.

[0013] In any implementation, the maximum value of the ordinate H1 of the first peak is 1.3%-2.5%, and / or the maximum value of the ordinate H2 of the second peak is 9.6%-10.6%.

[0014] By controlling the maximum values ​​of H1 and / or H2 within the aforementioned ranges, and ensuring an appropriate number of large and small particles, it is beneficial for better particle gradation, further increasing the compaction density of the negative electrode sheet, and thus further improving the energy density of the secondary battery of this application. It also better facilitates the fast-charging performance of the secondary battery.

[0015] In any implementation, the maximum value of H1 corresponds to a D1 of 0.5-11 μm; optionally, the maximum value of H1 corresponds to a D1 of 1-9 μm; more preferably, the maximum value of H1 corresponds to a D1 of 2-4 μm; and / or,

[0016] The maximum value of H2 corresponds to a D2 of 11-25 μm. Optionally, the maximum value of H2 corresponds to a D2 of 11-20 μm. More preferably, the maximum value of H2 corresponds to a D2 range of 13-15 μm.

[0017] By controlling the D1 corresponding to the maximum value of H1 and / or the D2 corresponding to the maximum value of H2 within the above range, the Dv50 of both large and small particles of the negative electrode active material is suitable, which is conducive to better particle gradation, further improving the compaction density of the negative electrode sheet, and thus further improving the energy density of the secondary battery of this application. It is also more conducive to balancing the fast-charging performance of the secondary battery.

[0018] In any embodiment, the negative electrode active material includes a first negative electrode active material and a second negative electrode active material, the first negative electrode active material includes secondary particles, the second negative electrode active material includes primary particles, and the Dv50 of the first negative electrode active material is greater than the Dv50 of the second negative electrode active material.

[0019] The secondary particles have uneven surfaces, and relatively small primary particles can easily embed into the uneven surfaces of relatively large secondary particles to form a rivet structure. The rivet structure is beneficial for forming better structural porosity, which is beneficial for improving the solid-liquid interface transport impedance between the negative electrode film and the electrolyte and reducing the solid-phase transport impedance inside the negative electrode film, which is beneficial for further improving the fast-charging performance of the secondary battery of this application.

[0020] In any embodiment, the Dv50 of the first negative electrode active material is 10-24 μm; and / or, the Dv50 of the second negative electrode active material is 1.5-12 μm.

[0021] In any embodiment, the Dv50 of the first negative electrode active material is 12-20 μm; and / or, the Dv50 of the second negative electrode active material is 2-10 μm.

[0022] In any embodiment, the Dv50 of the first negative electrode active material is 14-18 μm; and / or, the Dv50 of the second negative electrode active material is 4-8 μm.

[0023] Controlling the Dv50 of the first negative electrode active material and / or the second active material within the aforementioned range is beneficial for better particle gradation, further increasing the compaction density of the negative electrode sheet, and thus further improving the energy density of the secondary battery of this application. Furthermore, the particle size of the primary particles affects the electron migration path within the particles, thereby affecting fast-charging performance. Controlling the Dv50 of the second active material within the aforementioned range is beneficial for providing a suitable electron migration path, thereby further improving the fast-charging performance of the secondary battery of this application.

[0024] In any embodiment, the mass ratio of the first negative electrode active material to the second negative electrode active material is from 9.5:0.5 to 3:2.

[0025] In any embodiment, the mass ratio of the first negative electrode active material to the second negative electrode active material is 9:1 to 7:3.

[0026] Controlling the mass ratio of the first negative electrode active material and the second negative electrode active material within the above range is beneficial to forming a better particle size distribution, and also beneficial to improving the fast charging performance of the secondary battery of this application.

[0027] In any embodiment, the battery cell is a laminated battery cell, and the length of the negative electrode sheet is 300-600mm.

[0028] In any embodiment, the length of the negative electrode sheet is 500-590 mm.

[0029] The battery cell of this application adopts a stacked design and controls the length of the negative electrode. Compared with the winding structure, it further reduces the risk of lithium plating at the corner of the cell and further improves the lower limit of the overall fast charging rate of the battery. It also helps to improve the utilization rate of the cell structure, thereby helping to further improve the energy density of the secondary battery in the embodiment of this application.

[0030] In any embodiment, the conductivity of the electrolyte is 14-18 mS / cm.

[0031] Controlling the conductivity of the electrolyte within the above-mentioned range is beneficial to improving the ion conduction capacity of the electrolyte, further reducing the liquid phase impedance of the secondary battery, and thus further improving the fast charging performance of the secondary battery of this application.

[0032] In any embodiment, the negative current collector includes at least one of copper foils, and the strength of the negative current collector is 3-7 μm.

[0033] Using a high-strength negative electrode current collector helps reduce the thickness of the current collector, which can increase the thickness of the negative electrode film. It also reduces the compaction density of the negative electrode sheet while keeping the areal density constant, increases the porosity of the negative electrode film, thereby improving the electrolyte wetting rate of the negative electrode sheet, increasing the contact area between the electrolyte and the negative electrode active material, and shortening the lithium ion insertion / extraction path, which is beneficial to further improving the fast charging capability of the secondary battery.

[0034] In any embodiment, the first negative electrode active material and / or the second negative electrode active material includes at least one of graphite, carbon, or silicon-based materials.

[0035] A second aspect of this application provides a method for preparing a secondary battery, the method comprising the following steps:

[0036] A raw material comprising at least a first negative electrode active material and a second negative electrode active material is mixed to obtain a negative electrode slurry, wherein the first negative electrode active material comprises secondary particles, the second negative electrode active material comprises primary particles, and the Dv50 of the first negative electrode active material is smaller than the Dv50 of the second negative electrode active material.

[0037] The negative electrode slurry was coated onto the surface of the negative electrode current collector, with a single-sided coating density of 80 mg / 1540.25 mm. 2 -180mg / 1540.25mm 2 The negative electrode sheet is obtained by drying.

[0038] The positive electrode, the separator, and the negative electrode are assembled to obtain the secondary battery.

[0039] The above preparation method facilitates the preparation of the secondary battery of this application. The secondary battery of this application has good fast-charging performance while also maintaining good energy density.

[0040] In any embodiment, the negative electrode slurry is coated onto the surface of the negative electrode current collector, with a single-sided coating density of 100 mg / 1540.25 mm. 2 -160mg / 1540.25mm 2 .

[0041] Further control was achieved by ensuring the density of the negative electrode slurry coating on one side was 100 mg / 1540.25 mm. 2 -160mg / 1540.25mm 2 This is beneficial for obtaining a negative electrode film layer with a suitable unilateral density. A negative electrode film layer with a suitable unilateral density is beneficial for the secondary battery of the present application embodiment to better balance fast charging performance and energy density.

[0042] In any embodiment, the mass ratio of the first negative electrode active material to the second negative electrode active material is 95:5 to 3:2, and optionally, the mass ratio of the first negative electrode active material to the second negative electrode active material is 9:1 to 7:3.

[0043] Controlling the mass ratio of the first negative electrode active material and the second negative electrode active material within the above range is beneficial to forming a better particle size distribution, and also beneficial to improving the fast charging performance of the secondary battery of this application.

[0044] In any embodiment, the first raw material is pulverized to obtain primary particles of the first raw material; the primary particles of the first raw material are granulated to obtain secondary particles of the first raw material; the secondary particles of the first raw material are then subjected to graphitization and carbonization treatments to obtain the first negative electrode active material; and / or

[0045] The second raw material is crushed to obtain primary particles of the second raw material. These primary particles are then subjected to graphitization and carbonization treatments to obtain the second negative electrode active material.

[0046] The first raw material includes at least one of needle coke, semi-calcined petroleum coke, and fully calcined petroleum coke, and / or the second raw material includes at least one of raw petroleum coke and pitch coke.

[0047] The above preparation method is advantageous for obtaining the first and second negative electrode active materials. Specifically, when the raw materials of the first negative electrode active material include at least one of needle coke, semi-calcined petroleum coke, and fully calcined petroleum coke, it is easily graphitized, which is beneficial for further improving the electron transport capability of the first negative electrode active material, bringing it close to the theoretical capacity, and thus further improving the energy density. When the raw materials of the second negative electrode active material include at least one of petroleum coke and pitch coke, it is difficult to graphitize, which is beneficial for further improving fast-charging performance.

[0048] In any embodiment, the first raw material secondary particles are subjected to graphitization, asphalt coating, and carbonization to obtain the first negative electrode active material; and / or

[0049] The second raw material particles are subjected to graphitization, asphalt coating, and carbonization to obtain the second negative electrode active material.

[0050] In any embodiment, the Dv50 of the first raw material primary particles is 6-12 μm; optionally, it is 7-9 μm; and / or

[0051] The Dv50 of the primary particles of the second raw material is 1.5-9.5μm, and optionally, it is 3-6μm.

[0052] Controlling the Dv50 of the primary particles of the first raw material and / or the primary particles of the second raw material within the above range is beneficial to preparing the first negative electrode active material and / or the second negative electrode active material of this application.

[0053] In any embodiment, the Dv50 of the secondary particles of the first raw material is 10-18 μm, and optionally, it is 13-16 μm.

[0054] Controlling the Dv50 of the secondary particles of the first raw material within the above range is beneficial for preparing the first negative electrode active material of this application.

[0055] In any embodiment, the Dv50 of the first negative electrode active material is 10-24 μm, optionally 12-20 μm, more preferably 14-18 μm; and / or, the Dv50 of the second negative electrode active material is 1.5-12 μm, optionally 2-10 μm, more preferably 4-8 μm.

[0056] Controlling the Dv50 of the first negative electrode active material and / or the second active material within the aforementioned range is beneficial for better particle gradation, further increasing the compaction density of the negative electrode sheet, and thus further improving the energy density of the secondary battery of this application. Furthermore, the particle size of the primary particles affects the electron migration path within the particles, thereby affecting fast-charging performance. Controlling the Dv50 of the second active material within the aforementioned range is beneficial for providing a suitable electron migration path, thereby further improving the fast-charging performance of the secondary battery of this application.

[0057] In any embodiment, during the asphalt coating treatment of the second raw material particles, the softening point of the asphalt is 120-180℃.

[0058] The softening point of the asphalt is within the above range, which is beneficial for the rapid softening of the asphalt during the coating process, thereby forming a more uniform and dense coating layer on the surface of the primary particles of the second raw material, which is beneficial for further improving the kinetic performance of the secondary battery of this application.

[0059] In any embodiment, the petroleum coke comprises isotropic petroleum coke.

[0060] Due to the isotropic carbon-based structure of petroleum coke, such as its high degree of carbon disorder, it is difficult to graphitize. Lower graphitization and higher carbon disorder increase the number of lithium-ion insertion / extraction sites, which helps to improve the lithium-ion insertion / extraction rate, thus contributing to further improvements in fast-charging performance.

[0061] In any embodiment, the positive electrode, the separator, and the negative electrode are stacked and assembled to obtain an electrode assembly. The electrode assembly is then placed in an outer package, and an electrolyte is added to obtain the secondary battery.

[0062] The battery cell adopts a stacked design, which is conducive to improving the utilization rate of the battery cell structure, thereby further improving the energy density of the secondary battery in the embodiments of this application.

[0063] In any embodiment, the length of the negative electrode sheet is 300-600mm, and optionally, the length of the negative electrode sheet is 500-590mm.

[0064] The battery cell of this application adopts a stacked design and controls the length of the negative electrode, which is conducive to improving the utilization rate of the battery cell structure, thereby further improving the energy density of the secondary battery in the embodiment of this application.

[0065] A third aspect of this application provides an electrical device comprising a secondary battery according to the first aspect of this application or a secondary battery obtained by the preparation method according to the second aspect of this application.

[0066] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0067] Figure 1 This is a scanning electron microscope image of the negative electrode active material according to one embodiment of this application.

[0068] Figure 2 This is a volume particle size distribution curve of the negative electrode active material according to an embodiment of this application.

[0069] Figure 3 These are volumetric particle size curves of the negative electrode active material of Comparative Example 1 of this application.

[0070] Figure 4 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0071] Figure 5 yes Figure 4 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0072] Figure 6 This is a schematic diagram of a battery module according to one embodiment of this application.

[0073] Figure 7 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0074] Figure 8 yes Figure 7 An exploded view of a battery pack according to one embodiment of this application is shown.

[0075] Figure 9 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0076] Explanation of reference numerals in the attached figures:

[0077] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0078] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the secondary battery, its preparation method, battery module, battery pack, and electrical device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0079] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0080] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0081] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0082] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0083] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0084] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0085] With the widespread application of rechargeable batteries, higher demands are being placed on their fast-charging performance. The negative electrode has a certain impact on the fast-charging capability of rechargeable batteries, such as the selection and modification of the negative electrode active material. However, how to balance fast-charging performance and energy density in rechargeable batteries is a problem that urgently needs to be solved.

[0086] [Rechargeable Battery]

[0087] Based on this, this application provides a secondary battery, which includes a cell comprising a positive electrode, a negative electrode, and an electrolyte. The negative electrode includes a negative current collector and a negative electrode film disposed on at least one side of the negative current collector. The negative electrode film includes a negative electrode active material, and the volumetric particle size distribution curve of the negative electrode active material is a bimodal curve. The horizontal axis of the bimodal curve represents the particle size of the negative electrode active material, and the vertical axis represents the volume percentage of the negative electrode active material. The particle size D1 of the first peak of the bimodal curve is smaller than the particle size D2 of the second peak. The single-sided density of the negative electrode film is 80 mg / 1540.25 mm. 2-180mg / 1540.25mm 2 .

[0088] In this paper, the term "bimodal curve" refers to a curve with two distinct peaks.

[0089] In this paper, the volumetric particle size distribution curve of the negative electrode active material can be measured using methods and equipment known in the art. Specifically, the battery is disassembled to obtain the negative electrode sheet. The negative electrode film layer of the negative electrode sheet is peeled off, and the negative electrode film layer is thoroughly washed with acetone to remove binders and other contaminants. After filtration and drying, the negative electrode active material powder is obtained. The volumetric particle size distribution curve of the negative electrode active material is measured using a laser particle size analyzer. Specifically, a clean beaker is taken, and a certain mass (e.g., greater than or equal to 3g) of the negative electrode active material to be tested is weighed. After adding a surfactant, 20ml of dispersant is added, and the sample is sonicated at 120W / 5min to ensure complete dispersion in the dispersant. The sample is poured into the injection tower and circulated with the solution to the test optical path system. Under the irradiation of the laser beam, the volumetric particle size distribution curve of the negative electrode active material is obtained by receiving and measuring the energy distribution of the scattered light. (See attached diagram.) Figure 2 The diagram shows the volumetric particle size distribution curve of a negative electrode active material according to an embodiment of this application. The curve exhibits two distinct peaks, forming a bimodal curve. From the bimodal volumetric particle size distribution curve of the negative electrode active material, the particle size range D1 of the first peak and the particle size range D2 of the second peak can be obtained. The specific ranges can be determined through visual observation.

[0090] In some embodiments, the volumetric particle size distribution curve of the negative electrode active material is the volumetric particle size distribution curve of the negative electrode active material in the initial state of the secondary battery. In some embodiments, the volumetric particle size distribution curve of the negative electrode active material is the volumetric particle size distribution curve of the negative electrode active material in the secondary battery after operation.

[0091] In this paper, the term "unilateral density" refers to the mass of the negative electrode active material per unit area of ​​a single-sided negative electrode film layer, specifically 1540.25 mm. 2 The quality of the negative electrode active material in the negative electrode film layer.

[0092] The lateral density of the negative electrode film can be measured using methods and equipment known in the art. A specific example is as follows: the battery is disassembled, the negative electrode sheet is obtained, and it is punched into a sheet with an area of ​​1540.25 mm². 2 The small round piece was weighed and recorded as M1. The area of ​​the empty copper foil was 1540.25 mm². 2 The corresponding weight is denoted as M0. In this embodiment, the empty copper foil has an area of ​​1540.25 mm². 2At that time, the weight was approximately 84 mg. Using 84 mg in the calculation, the density of the negative electrode film on one side is calculated as follows: (M1 - M0) / 2 mg / 1540.25 mm². 2 Specifically, the lateral density of the negative electrode film is (M1-84) / 2mg / 1540.25mm². 2 .

[0093] In some embodiments, the unilateral density of the negative electrode film can be 80 mg / 1540.25 mm. 2 85mg / 1540.25mm 2 90mg / 1540.25mm 2 95mg / 1540.25mm 2 100mg / 1540.25mm 2 105mg / 1540.25mm 2 110mg / 1540.25mm 2 115mg / 1540.25mm 2 120mg / 1540.25mm 2 125mg / 1540.25mm 2 130mg / 1540.25mm 2 135mg / 1540.25mm 2 140mg / 1540.25mm 2 145mg / 1540.25mm 2 150mg / 1540.25mm 2 , or the value within the single-sided density composition range or composition range of any two of the above negative electrode film layers.

[0094] Liquid phase impedance, solid phase impedance, and solid-liquid interface impedance are important factors limiting the fast-charging performance of secondary batteries. This application controls the maximum single-sided density of the negative electrode film to 180 mg / 1540.25 mm². 2 This effectively improves the liquid phase diffusion resistance of the secondary battery, which is beneficial for improving the lithium intercalation consistency of active materials at different positions of the porous electrode and enhancing the fast-charging performance of the secondary battery in this application. However, while reducing the unilateral density of the negative electrode film is beneficial for improving fast-charging performance, it sacrifices some of the energy density of the secondary battery. Therefore, this application reasonably controls the minimum unilateral density of the negative electrode film to be 80 mg / 1540.25 mm. 2 While maximizing fast charging performance, it also takes into account some energy density.

[0095] Furthermore, the volumetric particle size distribution curve of the negative electrode active material in this application is a bimodal curve, where the particle size D1 of the first peak of the bimodal curve is smaller than the particle size D2 of the second peak. Since the added small-particle negative electrode active material exhibits better kinetics, the design of the negative electrode active material in this application is beneficial for improving the fast-charging performance of the secondary battery. In summary, the secondary battery of this application possesses both good fast-charging performance and good energy density.

[0096] In some embodiments, the one-sided density of the negative electrode film is 100 mg / 1540.25 mm². 2 -160mg / 1540.25mm 2 .

[0097] Further control was achieved to achieve a single-sided density of 100 mg / 1540.25 mm² for the negative electrode film. 2 -160mg / 1540.25mm 2 This allows the secondary battery in the present application embodiment to better balance fast charging performance and energy density.

[0098] In some embodiments, D1 ranges from 0.1 to 11.5 μm. In some embodiments, D1 ranges from 0.1 to 9.5 μm. In some embodiments, D1 ranges from 2 to 4 μm.

[0099] In some implementations, D1 can be 0.1μm, 0.5μm, 0.8μm, 1μm, 1.5μm, 2μm, 2.1μm, 2.2μm, 2.3μm, 2.4μm, 2.5μm, 2.6μm, 2.625μm, 2.65μm, 2.675μm, 2.7μm, 2.725μm, 2.75μm, 2.775μm, 2.8μm, 2.825μm, 2.85μm, 2.875μm, 2.9μm, 2.925μm, 2.95μm, 2.975μm, 3μm, 3.025μm, 3.05μm, 3.075μm, 3.1μm, 3.125μm, 3.15μm. m, 3.175μm, 3.2μm, 3.225μm, 3.25μm, 3.275μm, 3.3μm, 3.325μm, 3.35μm, 3.375μm, 3.4μm, 3.425μm, 3.45μm, 3.475μm, 3.5μm, 3.525μm, 3.55μm, 3.575μm, 3.6μm, 3.625μm, 3.7μm, 3.8μm, 3.9μm, 4μm, 5.5μm, 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, or any range formed by any two of the above D1 values, or a value within the range formed by these values.

[0100] In some embodiments, D2 ranges from 9 to 25 μm. In some embodiments, D2 ranges from 10 to 20 μm. In some embodiments, D2 ranges from 13 to 15 μm.

[0101] In some implementations, D2 can be 9μm, 9.5μm, 10μm, 10.5μm, 11μm, 11.5μm, 12μm, 12.5μm, 13μm, 13.1μm, 13.2μm, 13.3μm, 13.4μm, 13.5μm, 13.6μm, 13.7μm, 13.8μm, 13.9μm, 13.95μm, 14μm, 14.05μm, 14.1μm, 14.15μm, 14.2μm, 14.25μm, 14.3μm, 14.35μm, etc. 14.4μm, 14.45μm, 14.5μm, 14.55μm, 14.6μm, 14.65μm, 14.7μm, 14.75μm, 14.8μm, 14.85μm, 14.9μm, 14.95μm, 15μm, 15.5μm, 16μm, 16.5μm, 17μm, 17.5μm, 18μm, 18.5μm, 19μm, 19.5μm, 20μm, 23μm, 25μm, or any range formed by any two of the above D2 values, or a value within that range.

[0102] By controlling the range of D1 and / or D2 within the aforementioned ranges, the Dv50 of both large and small particles of the negative electrode active material becomes suitable, which is beneficial for better particle gradation, further improving the compaction density of the negative electrode sheet, and thus further improving the energy density of the secondary battery of this application. It also better facilitates the fast-charging performance of the secondary battery.

[0103] In some implementations, the maximum value of the ordinate H1 of the first peak is 0.8%-3%.

[0104] In some implementations, the maximum value of the ordinate H1 of the first peak is 1.3%-2.5%.

[0105] In some implementations, the maximum value of H1 can be 0.8%, 0.84%, 0.9%, 0.94%, 1%, 1.04%, 1.1%, 1.14%, 1.2%, 1.24%, 1.3%, 1.34%, 1.4%, 1.44%, 1.5%, 1.54%, 1.6%, 1.64%, 1.7%, 1.74%, 1.8%, 1.84%, 1.9%, etc. 1.94%, 2%, 2.04%, 2.1%, 2.14%, 2.2%, 2.24%, 2.3%, 2.34%, 2.4%, 2.44%, 2.5%, 2.54%, 2.6%, 2.64%, 2.7%, 2.74%, 2.8%, 2.84%, 2.9%, 3%, or a range consisting of the maximum values ​​of any two of the above H1 values, or a value within that range.

[0106] In some implementations, the maximum value of the ordinate H2 of the second peak is 9%-12%.

[0107] In some implementations, the maximum value of the ordinate H2 of the second peak is 9.6%-10.6%.

[0108] In some implementations, the maximum value of H2 can be 9%, 9.1%, 9.12%, 9.2%, 9.22%, 9.3%, 9.32%, 9.4%, 9.42%, 9.5%, 9.52%, 9.6%, 9.62%, 9.7%, 9.72%, 9.82%, 9.8%, 9.92%, 10%, 10.02%, 10.1%, 10.12%, 10.2%, 10.22%, 10.32%, 10.3%, 10.4%. 2%, 10.5%, 10.52%, 10.6%, 10.62%, 10.7%, 10.72%, 10.8%, 10.82%, 10.9%, 10.92%, 11%, 11.02%, 11.1%, 11.12%, 11.3%, 11.4%, 11.5%, 11.6%, 11.7%, 11.8%, 11.9%, 12%, or a range consisting of the maximum values ​​of any two of the above H2 values, or a value within that range.

[0109] By controlling the maximum values ​​of H1 and / or H2 within the above range, the appropriate number of large and small particles is conducive to better particle gradation, further improving the compaction density of the negative electrode sheet, and thus further improving the energy density of the secondary battery of this application.

[0110] The maximum value of the ordinate H1 of the first peak and the maximum value of the ordinate H2 of the second peak can be measured using methods and equipment known in the art. A specific example is as follows: the volume particle size distribution curve of the negative electrode active material of this application is obtained according to the volume particle size distribution curve testing method of this application. The maximum value of the ordinate H1 of the first peak and the maximum value of the ordinate H2 of the second peak can then be obtained by reading the volume particle size distribution curve of the negative electrode active material. This also better balances the fast-charging performance of the secondary battery.

[0111] In some embodiments, the maximum value of H1 corresponds to a D1 of 0.5-11 μm. In some embodiments, the maximum value of H1 corresponds to a D1 of 1-9 μm. In some embodiments, the maximum value of H1 corresponds to a D1 of 2-4 μm.

[0112] In some implementations, the maximum value of H1 corresponds to D1 of 0.5μm, 1μm, 1.5μm, 2μm, 2.1μm, 2.2μm, 2.3μm, 2.4μm, 2.5μm, 2.6μm, 2.625μm, 2.65μm, 2.675μm, 2.7μm, 2.725μm, 2.75μm, 2.775μm, 2.8μm, 2.825μm, 2.85μm, 2.875μm, 2.9μm, 2.925μm, 2.95μm, 2.975μm, 3μm, 3.025μm, 3.05μm, 3.075μm, 3.1μm, 3.125μm, 3.15μm, 3.17μm, 3.17μm, 3.125μm, 3.1 ... 5μm, 3.2μm, 3.225μm, 3.25μm, 3.275μm, 3.3μm, 3.325μm, 3.35μm, 3.375μm, 3.4μm, 3.425μm, 3.45μm, 3.475μm, 3.5μm, 3.525μm, 3.55μm, 3.575μm, 3.6μm, 3.625μm, 3.7μm, 3.8μm, 3.9μm, 4μm, 5.5μm, 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 10μm, 11μm, or any two of the above values ​​forming a range or values ​​within a range.

[0113] In some embodiments, the maximum value of H2 corresponds to a D2 range of 11-25 μm. In some embodiments, the maximum value of H2 corresponds to a D2 range of 11-20 μm. In some embodiments, the maximum value of H2 corresponds to a D2 range of 13-15 μm.

[0114] In some implementations, D2 can be 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.1 μm, 13.2 μm, 13.3 μm, 13.4 μm, 13.5 μm, 13.6 μm, 13.7 μm, 13.8 μm, 13.9 μm, 13.95 μm, 14 μm, 14.05 μm, 14.1 μm, 14.15 μm, 14.2 μm, 14.25 μm, 14.3 μm, 14.35 μm, 14.4 μm, 14.45 μm, or 14 μm. 5μm, 14.55μm, 14.6μm, 14.65μm, 14.7μm, 14.75μm, 14.8μm, 14.85μm, 14.9μm, 14.95μm, 15μm, 15.5μm, 16μm, 16.5μm, 17μm, 17.5μm, 18μm, 18.5μm, 19μm, 19.5μm, 20μm, 21μm, 22μm, 23μm, 24μm, 25μm, or a range of any two of the above values, or a value within a range of values.

[0115] Controlling the range of D1 and / or D2 within the aforementioned ranges is beneficial for better particle gradation, further increasing the compaction density of the negative electrode sheet, and thus further improving the energy density of the secondary battery of this application. It also better facilitates the fast-charging performance of the secondary battery.

[0116] In some embodiments, the negative electrode active material includes a first negative electrode active material and a second negative electrode active material. The first negative electrode active material includes secondary particles, and the second negative electrode active material includes primary particles. The Dv50 of the first negative electrode active material is greater than the Dv50 of the second negative electrode active material.

[0117] In this paper, the term "Dv50" refers to the particle size at which the cumulative volumetric size distribution percentage in the particle reaches 50%.

[0118] In this paper, the term "primary particle" refers to a single particle whose transmission electron microscopy image has been identified by common specialized software (e.g., SpectrumSee; Avizo 3D) and / or a single particle that can be distinguished by manual identification or manual-assisted calibration.

[0119] In this article, the term "secondary particle" refers to particles formed by the aggregation of primary particles.

[0120] The morphological characteristics of the negative electrode active material can be measured using methods and equipment known in the art. A specific example is as follows: The battery is disassembled to obtain the negative electrode sheet. The negative electrode film layer of the negative electrode sheet is peeled off, and the negative electrode film layer is thoroughly washed with acetone to remove binders, etc. After filtration and drying, the negative electrode active material powder is obtained. The morphology of the negative electrode active material is then tested using a scanning electron microscope (SEM). (See attached image.) Figure 1 The diagram shows the morphology of the negative electrode active material in Embodiment 1 of this application. Specifically, the particle size of the secondary particles is larger than that of the primary particles, and the relatively small primary particles are embedded in the uneven surface of the relatively large secondary particles to form a rivet structure.

[0121] In some embodiments, the particle size of the first negative electrode active material is mainly distributed in the D2 region.

[0122] In some embodiments, the particle size of the second negative electrode active material is mainly distributed in D1.

[0123] The secondary particles have uneven surfaces, and relatively small primary particles can easily embed into the uneven surfaces of relatively large secondary particles to form a rivet structure. The rivet structure is beneficial for forming better structural porosity, which is beneficial for improving the solid-liquid interface transport impedance between the negative electrode film and the electrolyte and reducing the solid-phase transport impedance inside the negative electrode film, which is beneficial for further improving the fast-charging performance of the secondary battery of this application.

[0124] In some embodiments, the Dv50 of the first negative electrode active material is 10-24 μm.

[0125] In some embodiments, the Dv50 of the first negative electrode active material is 12-20 μm.

[0126] In some embodiments, the Dv50 of the first negative electrode active material is 14-18 μm.

[0127] In some embodiments, the Dv50 of the first negative electrode active material can be 10μm, 11μm, 12μm, 12.5μm, 13μm, 13.5μm, 14μm, 14.5μm, 15μm, 15.5μm, 16μm, 16.5μm, 17μm, 17.5μm, 18μm, 18.5μm, 19μm, 19.5μm, 20μm, 21μm, 22μm, 23μm, 24μm, or a range of any two of the above Dv50 values, or a value within that range.

[0128] In some embodiments, the Dv50 of the second negative electrode active material is 1.5-12 μm.

[0129] In some embodiments, the Dv50 of the second negative electrode active material is 2-10 μm.

[0130] In some embodiments, the Dv50 of the second negative electrode active material is 4-8 μm.

[0131] In some embodiments, the Dv50 of the second negative electrode active material can be 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm, 10μm, 11μm, 12μm, or a range of any two of the above Dv50 values, or a value within that range.

[0132] Controlling the Dv50 of the first negative electrode active material and / or the second active material within the aforementioned range is beneficial for better particle gradation, further increasing the compaction density of the negative electrode sheet, and thus further improving the energy density of the secondary battery of this application. Furthermore, the particle size of the primary particles affects the electron migration path within the particles, thereby affecting fast-charging performance. Controlling the Dv50 of the second active material within the aforementioned range is beneficial for providing a suitable electron migration path, thereby further improving the fast-charging performance of the secondary battery of this application.

[0133] In some embodiments, the mass ratio of the first negative electrode active material to the second negative electrode active material is from 9.5:0.5 to 3:2.

[0134] In some embodiments, the mass ratio of the first negative electrode active material to the second negative electrode active material is 9:1 to 7:3.

[0135] In some embodiments, the mass ratio of the first negative electrode active material and the second negative electrode active material can be 9.5:0.5, 9.4:0.6, 9.3:0.7, 9.2:0.8, 9.1:0.9, 9:1, 17:3, 4:1, 3:1, 7:3, 13:7, 3:2, or a range of any two of the above mass ratios, or a value within that range.

[0136] Controlling the mass ratio of the first negative electrode active material and the second negative electrode active material within the above range is beneficial to forming a better particle size distribution, and also beneficial to improving the fast charging performance of the secondary battery of this application.

[0137] In some implementations, the battery cell is a laminated cell, and the length of the negative electrode is 300-600mm.

[0138] In some implementations, the length of the negative electrode sheet is 500-590 mm.

[0139] In some embodiments, the length of the negative electrode sheet can be 300mm, 350mm, 400mm, 450mm, 500mm, 510mm, 520mm, 530mm, 540mm, 550mm, 560mm, 570mm, 580mm, 590mm, 600mm, or a value within any range of two of the above lengths.

[0140] In some implementations, the length of the negative electrode is the same as the length of the positive electrode.

[0141] In some implementations, the length of the negative electrode is greater than the length of the positive electrode.

[0142] The length of the negative electrode can be measured using methods and equipment known in the art. Specifically, the battery is disassembled to obtain the negative electrode, and its length can be directly measured.

[0143] The battery cell of this application adopts a stacked design and controls the length of the negative electrode. Compared with the winding structure, it further reduces the risk of lithium plating at the corner of the cell and further improves the lower limit of the overall fast charging rate of the battery. It also helps to improve the utilization rate of the cell structure, thereby helping to further improve the energy density of the secondary battery in the embodiment of this application.

[0144] In some implementations, the electrolyte has a conductivity of 14-18 mS / cm.

[0145] The conductivity of the electrolyte can be measured using methods and equipment known in the art. A specific example is as follows: Disassemble the battery cell, take approximately 100 mL of electrolyte sample in a dry, clean, corrosion-resistant sample bottle, seal it, and place it in a constant-temperature water bath. Shake the sample occasionally, and maintain the temperature at 25°C (deviation ±0.5°C). After the sample temperature stabilizes, use a commercially available conductivity meter to test its conductivity. After thoroughly drying the conductivity meter with calibration solution, place it vertically into the liquid to be tested, click "Start Test," and record the test results after the data has stabilized for at least 10 seconds.

[0146] In some embodiments, the conductivity of the electrolyte can be 14 mS / cm, 14.2 mS / cm, 14.4 mS / cm, 14.6 mS / cm, 14.8 mS / cm, 15 mS / cm, 15.2 mS / cm, 15.4 mS / cm, 15.6 mS / cm, 15.8 mS / cm, 16 mS / cm, 16.2 mS / cm, 16.4 mS / cm, 16.6 mS / cm, 16.8 mS / cm, 17 mS / cm, 17.2 mS / cm, 17.4 mS / cm, 17.6 mS / cm, 17.8 mS / cm, 18 mS / cm, or a range of any two of the above conductivity values, or a value within that range.

[0147] In some embodiments, the electrolyte includes a liquid electrolyte, a gel electrolyte, or an all-solid electrolyte.

[0148] In some embodiments, the electrolyte includes an electrolyte salt and a solvent.

[0149] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0150] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0151] The electrolyte acts as a conductor of ions between the positive and negative electrode plates. The aforementioned electrolyte possesses superconducting properties, which enhances the ionic liquid-phase conductivity of the electrolyte, further reducing the liquid-phase impedance of the secondary battery, thereby improving the fast-charging performance of the secondary battery described in this application.

[0152] In some embodiments, the negative current collector includes at least one of copper foils, and the strength of the negative current collector is 3-7 μm.

[0153] In some embodiments, the strength of the negative electrode current collector can be 3Um, 3.25Um, 3.5Um, 3.75Um, 4Um, 4.25Um, 4.5Um, 4.75Um, 5Um, 5.25Um, 5.5Um, 5.75Um, 6Um, 6.25Um, 6.5Um, 6.75Um, 7Um, or a range of the above strengths or a value within the range.

[0154] Using a high-strength negative electrode current collector helps reduce the thickness of the current collector, which can increase the thickness of the negative electrode film. It also reduces the compaction density of the negative electrode sheet while keeping the areal density constant, increases the porosity of the negative electrode film, thereby improving the electrolyte wetting rate of the negative electrode sheet, increasing the contact area between the electrolyte and the negative electrode active material, and shortening the lithium ion insertion / extraction path, which is beneficial to further improving the fast charging capability of the secondary battery.

[0155] In some embodiments, the first negative electrode active material and / or the second negative electrode active material includes at least one of graphite, carbon, or silicon-based materials.

[0156] In some embodiments, the negative electrode film layer may optionally 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).

[0157] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0158] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0159] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 4 This is an example of a square-structured secondary battery 5.

[0160] In some implementations, refer to Figure 5 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0161] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0162] Figure 6 This is battery module 4, used as an example. (See reference...) Figure 6 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0163] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0164] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0165] Figure 7 and Figure 8 This is battery pack 1 as an example. (See reference...) Figure 7 and Figure 8 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0166] [Preparation methods for secondary batteries]

[0167] This application provides a method for preparing a secondary battery, the method comprising the following steps:

[0168] A raw material comprising at least a first negative electrode active material and a second negative electrode active material is mixed to obtain a negative electrode slurry, wherein the first negative electrode active material comprises secondary particles, the second negative electrode active material comprises primary particles, and the Dv50 of the first negative electrode active material is smaller than the Dv50 of the second negative electrode active material.

[0169] The negative electrode slurry was coated onto the surface of the negative electrode current collector, with a single-sided coating density of 80 mg / 1540.25 mm. 2 -180mg / 1540.25mm 2 The negative electrode sheet is obtained by drying.

[0170] By assembling the positive electrode, separator, and negative electrode, a secondary battery is obtained.

[0171] In some embodiments, the unilateral density of the negative electrode film can be 80 mg / 1540.25 mm. 2 85mg / 1540.25mm 2 90mg / 1540.25mm 2 95mg / 1540.25mm 2 100mg / 1540.25mm 2 105mg / 1540.25mm 2 110mg / 1540.25mm 2 115mg / 1540.25mm 2 120mg / 1540.25mm 2 125mg / 1540.25mm 2 130mg / 1540.25mm2 135mg / 1540.25mm 2 140mg / 1540.25mm 2 145mg / 1540.25mm 2 150mg / 1540.25mm 2 , or the value within the single-sided density composition range or composition range of any two of the above negative electrode film layers.

[0172] The above preparation method facilitates the preparation of the secondary battery of this application. The secondary battery of this application has good fast-charging performance while also maintaining good energy density.

[0173] In some embodiments, the negative electrode slurry is coated onto the surface of the negative electrode current collector, with a single-sided density of 100 mg / 1540.25 mm. 2 -160mg / 1540.25mm 2 .

[0174] Further control was achieved by ensuring the density of the negative electrode slurry coating on one side was 100 mg / 1540.25 mm. 2 -160mg / 1540.25mm 2 This is beneficial for obtaining a negative electrode film layer with a suitable unilateral density. A negative electrode film layer with a suitable unilateral density is beneficial for the secondary battery of the present application embodiment to better balance fast charging performance and energy density.

[0175] In some embodiments, the mass ratio of the first negative electrode active material to the second negative electrode active material is 95:5 to 3:2.

[0176] In some embodiments, the mass ratio of the first negative electrode active material to the second negative electrode active material is 9:1 to 7:3.

[0177] In some embodiments, the mass ratio of the first negative electrode active material and the second negative electrode active material can be 95:5, 94:6, 93:7, 92:8, 91:9, 9:1, 17:3, 4:1, 3:1, 7:3, 13:7, 3:2, or any range of two of the above mass ratios, or a value within that range.

[0178] Controlling the mass ratio of the first negative electrode active material and the second negative electrode active material within the above range is beneficial to forming a better particle size distribution, and also beneficial to improving the fast charging performance of the secondary battery of this application.

[0179] In some embodiments, a first raw material is pulverized to obtain primary particles of the first raw material; the primary particles of the first raw material are granulated to obtain secondary particles of the first raw material; and the secondary particles of the first raw material are subjected to graphitization and carbonization treatments to obtain a first negative electrode active material; and / or

[0180] The second raw material is crushed to obtain primary particles of the second raw material. These primary particles are then subjected to graphitization and carbonization treatments to obtain the second negative electrode active material.

[0181] The first raw material includes at least one of needle coke, semi-calcined petroleum coke, and fully calcined petroleum coke, and / or the second raw material includes at least one of petroleum green coke and pitch coke.

[0182] In some implementations, the graphitization process may include two stages. Specifically, the first stage has a temperature range of 1000-1800°C, during which the carbon material begins to undergo a graphitization reaction, its internal crystalline particles begin to grow, and the structure gradually transforms into graphite crystals. The second stage has a temperature range of 1800-3000°C, during which, as the temperature increases, the interlayer spacing of the graphite gradually decreases, and the degree of graphitization continuously improves. When the temperature reaches 3000°C, the graphitization process gradually slows down until it is complete. The graphitization temperature may vary depending on the specific graphitization process and equipment.

[0183] In some implementations, the graphitization treatment time ranges from 96 to 168 hours. The graphitization treatment time varies depending on the specific graphitization temperature and the graphitization equipment. Generally speaking, increasing the graphitization temperature may shorten the graphitization treatment time, while decreasing the graphitization temperature may increase the graphitization treatment time.

[0184] In some embodiments, the carbonization treatment is carried out at a temperature of 900-1350°C for 6-12 hours.

[0185] The above preparation method is beneficial for obtaining the first and second negative electrode active materials. When the raw materials of the first negative electrode active material include at least one of needle coke, semi-calcined petroleum coke, and fully calcined petroleum coke, these materials are easily graphitized, which is beneficial for further improving the electron transport capability of the first negative electrode active material, bringing it close to its theoretical capacity, and thus further increasing the energy density. When the raw materials of the second negative electrode active material include at least one of petroleum green coke and pitch coke, these materials are difficult to graphitize, which is beneficial for further improving fast-charging performance.

[0186] In some embodiments, the secondary particles of the first raw material are subjected to graphitization, asphalt coating, and carbonization to obtain the first negative electrode active material; and / or

[0187] The primary particles of the second raw material are subjected to graphitization, asphalt coating, and carbonization treatments to obtain the second negative electrode active material.

[0188] In some embodiments, during the asphalt coating treatment of the secondary particles of the first raw material, the softening point of the asphalt is 200-280℃.

[0189] In some embodiments, the asphalt coating treatment of the secondary particles of the first raw material includes the following steps: mixing asphalt and graphitized secondary particles of the first raw material at a mass ratio of 4:96 to 5:95, adding the mixture to a reaction vessel, heating it to 550°C-650°C, and stirring thoroughly to obtain secondary particles of the first raw material with a coating layer.

[0190] In some embodiments, the asphalt coating treatment of the primary particles of the second raw material includes the following steps: mixing asphalt and graphitized primary particles of the second raw material at a mass ratio of 3:97 to 4:96, and stirring thoroughly at room temperature to obtain primary particles of the second raw material with a coating layer.

[0191] In this article, the term "room temperature" refers to indoor temperature, which is generally 20℃-25℃.

[0192] In some implementations, the Dv50 of the primary particles of the first raw material is 6-12 μm.

[0193] In some implementations, the Dv50 of the primary particles of the first raw material is 7-9 μm.

[0194] In some embodiments, the Dv50 of the primary particles of the first raw material can be 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm, 10μm, 11μm, 12μm, or a range of any two of the above Dv50s or a value within the range.

[0195] In some embodiments, the Dv50 of the primary particles of the second raw material is 1.5-9.5 μm.

[0196] In some implementations, the Dv50 of the primary particles of the second raw material is 3-6 μm.

[0197] In some embodiments, the Dv50 of the primary particles of the second raw material can be 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm, or a range of any two of the above Dv50 values, or a value within that range.

[0198] The Dv50 of particles can be measured using methods and equipment known in this application. For example, it can be determined using a laser particle size analyzer (Malvern Master Size 3000) with reference to GB / T19077.1-2016. The testing instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0199] Controlling the Dv50 of the primary particles of the first raw material and / or the primary particles of the second raw material within the above range is beneficial to preparing the first negative electrode active material and / or the second negative electrode active material of this application.

[0200] In some embodiments, the Dv50 of the secondary particles of the first raw material is 10-18 μm.

[0201] In some embodiments, the Dv50 of the secondary particles of the first raw material is 13-16 μm.

[0202] In some embodiments, the Dv50 of the secondary particles of the first raw material can be 10μm, 10.5μm, 11μm, 11.5μm, 12μm, 12.5μm, 13μm, 13.5μm, 14μm, 14.5μm, 15μm, 15.5μm, 16μm, 16.5μm, 17μm, 17.5μm, 18μm, or a range of any two of the above Dv50s, or a value within the range.

[0203] Controlling the Dv50 of the secondary particles of the first raw material within the above range is beneficial for preparing the first negative electrode active material of this application.

[0204] In some embodiments, the Dv50 of the first negative electrode active material is 10-24 μm.

[0205] In some embodiments, the Dv50 of the first negative electrode active material is 12-20 μm.

[0206] In some embodiments, the Dv50 of the first negative electrode active material is 14-18 μm.

[0207] In some embodiments, the Dv50 of the first negative electrode active material can be 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm, 22μm, 23μm, 24μm, or a range composed of any two of the above Dv50 or a value within that range.

[0208] In some embodiments, the Dv50 of the second negative electrode active material is 1.5-12 μm.

[0209] In some embodiments, the Dv50 of the second negative electrode active material is 2-10 μm.

[0210] In some embodiments, the Dv50 of the second negative electrode active material is 4-8 μm.

[0211] In some embodiments, the Dv50 of the second negative electrode active material can be 1.5μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, or a range composed of any two of the above Dv50 or a value within the range.

[0212] Controlling the Dv50 of the first negative electrode active material and / or the second active material within the aforementioned range is beneficial for better particle gradation, further increasing the compaction density of the negative electrode sheet, and thus further improving the energy density of the secondary battery of this application. Furthermore, the particle size of the primary particles affects the electron migration path within the particles, thereby affecting fast-charging performance. Controlling the Dv50 of the second active material within the aforementioned range is beneficial for providing a suitable electron migration path, thereby further improving the fast-charging performance of the secondary battery of this application.

[0213] In some embodiments, during the asphalt coating treatment of the primary particles of the second raw material, the softening point of the asphalt is 120-180°C.

[0214] In some embodiments, during the asphalt coating treatment of the second raw material particles, the softening point of the asphalt can be 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, or a range of any two of the above softening points, or a value within that range.

[0215] The softening point of the asphalt is within the above range, which is beneficial for the rapid softening of the asphalt during the coating process, thereby forming a more uniform and dense coating layer on the surface of the primary particles of the second raw material, which is beneficial for further improving the kinetic performance of the secondary battery of this application.

[0216] In some implementations, petroleum coke includes isotropic petroleum coke.

[0217] Due to the isotropic carbon-based structure of petroleum coke, such as its high degree of carbon disorder, it is difficult to graphitize. Lower graphitization and higher carbon disorder increase the number of lithium-ion insertion / extraction sites, which helps to improve the lithium-ion insertion / extraction rate, thus contributing to further improvements in fast-charging performance.

[0218] In some embodiments, the positive electrode, the separator, and the negative electrode are stacked and assembled to obtain an electrode assembly. The electrode assembly is then placed in an outer package and injected with electrolyte to obtain a secondary battery.

[0219] The battery cell adopts a stacked design, which is conducive to improving the utilization rate of the battery cell structure, thereby further improving the energy density of the secondary battery in the embodiments of this application.

[0220] In some implementations, the length of the negative electrode sheet is 300-600 mm.

[0221] In some implementations, the length of the negative electrode sheet is 500-590 mm.

[0222] In some embodiments, the length of the negative electrode sheet can be 300mm, 350mm, 400mm, 450mm, 500mm, 510mm, 520mm, 530mm, 540mm, 550mm, 560mm, 570mm, 580mm, 590mm, 600mm, or a value within any range of two of the above lengths.

[0223] The battery cell of this application adopts a stacked design and controls the length of the negative electrode, which is conducive to improving the utilization rate of the battery cell structure, thereby further improving the energy density of the secondary battery in the embodiment of this application.

[0224] In some implementations, the electrolyte has a conductivity of 14-18 mS / cm.

[0225] In some embodiments, the conductivity of the electrolyte can be 14 mS / cm, 14.2 mS / cm, 14.4 mS / cm, 14.6 mS / cm, 14.8 mS / cm, 15 mS / cm, 15.2 mS / cm, 15.4 mS / cm, 15.6 mS / cm, 15.8 mS / cm, 16 mS / cm, 16.2 mS / cm, 16.4 mS / cm, 16.6 mS / cm, 16.8 mS / cm, 17 mS / cm, 17.2 mS / cm, 17.4 mS / cm, 17.6 mS / cm, 17.8 mS / cm, 18 mS / cm, or a range of any two of the above conductivity values, or a value within that range.

[0226] Controlling the conductivity of the electrolyte within the above-mentioned range is beneficial to improving the ionic liquid phase conduction capability of the electrolyte, further reducing the liquid phase impedance of the secondary battery, and thus further improving the fast charging performance of the secondary battery of this application.

[0227] In some embodiments, the negative current collector comprises copper foil, and the strength of the negative current collector is 3-7 μm.

[0228] In some embodiments, the strength of the negative electrode current collector is 3Um, 3.25Um, 3.5Um, 3.75Um, 4Um, 4.25Um, 4.5Um, 4.75Um, 5Um, 5.25Um, 5.5Um, 5.75Um, 6Um, 6.25Um, 6.5Um, 6.75Um, 7Um, or a range of the above strengths or a value within the range.

[0229] Using a high-strength negative electrode current collector helps reduce the thickness of the current collector, which can increase the thickness of the negative electrode film. It also reduces the compaction density of the negative electrode sheet while keeping the areal density constant, increases the porosity of the negative electrode film, thereby improving the electrolyte wetting rate of the negative electrode sheet, increasing the contact area between the electrolyte and the negative electrode active material, and shortening the lithium ion insertion / extraction path, which is beneficial to further improving the fast charging capability of the secondary battery.

[0230] [Positive electrode plate]

[0231] This application provides a positive electrode sheet, including a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector.

[0232] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0233] In some embodiments, the positive 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 substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0234] In some embodiments, the positive electrode film layer includes a positive electrode active material, which may be a known positive electrode active material for batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and 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. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0235] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0236] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0237] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0238] [Negative electrode plate]

[0239] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, wherein the negative electrode film layer includes the negative electrode active material of this application.

[0240] As an example, the negative electrode current collector has two surfaces opposite each other in its own 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.

[0241] In some embodiments, the negative electrode film layer may optionally 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).

[0242] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0243] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0244] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0245] [Isolation membrane]

[0246] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0247] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0248] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0249] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0250] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0251] [Electrical appliances]

[0252] This application also provides an electrical device, which includes a secondary battery according to the first aspect of this application or a secondary battery obtained by the preparation method according to the second aspect of this application.

[0253] In some embodiments, the electrical device of this application may further include at least one of a battery module or a battery pack. A secondary battery, battery module, or battery pack can be used as the power source for the electrical device or as the energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0254] As an electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0255] Figure 9 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0256] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0257] Example

[0258] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0259] Example 1

[0260] 1) Preparation of positive electrode sheet

[0261] Lithium iron phosphate, conductive carbon black, and polyvinylidene fluoride (PVDF) were added to N-methylpyrrolidone solvent at a mass ratio of 97.5:0.4:2.1 and stirred until homogeneous to obtain the positive electrode slurry.

[0262] Then, using a double-sided coating device, the coating concentration is 0.285 mg / 1540.25 cm⁻¹. 2 The single-sided weight coating is applied to the aluminum foil. After double-sided coating is completed, the foil is dried, cold-pressed, and cut to obtain the positive electrode sheet.

[0263] 2) Preparation of negative electrode active materials

[0264] Needle coke was pulverized to obtain primary needle coke particles, with a Dv50 controlled at 8 μm. The primary needle coke particles were granulated to obtain secondary needle coke particles, with a Dv50 controlled at 12.5 μm. The secondary needle coke particles were then graphitized. Pitch (softening point 205℃) and the graphitized secondary needle coke particles were mixed at a mass ratio of 4.5:95.5 and added to a reaction vessel. The mixture was heated to 600℃ and thoroughly stirred to obtain coated secondary needle coke particles. These coated particles were then transferred to a static high-temperature furnace for carbonization at 1150℃ to obtain the first negative electrode active material with a Dv50 of 14.5 μm.

[0265] Isotropic petroleum coke was pulverized to obtain primary petroleum coke particles, with a Dv50 controlled at 4 μm. The primary petroleum coke particles were then graphitized. Pitch (softening point 135℃) and graphitized primary petroleum coke particles were mixed at a mass ratio of 3:97 and thoroughly stirred at room temperature to obtain coated primary petroleum coke particles. These coated particles were then transferred to a static high-temperature furnace for carbonization at 1150℃ to obtain the second negative electrode active material with a Dv50 of 4.5 μm.

[0266] The first negative electrode active material and the second negative electrode active material are mixed and stirred evenly at a mass ratio of 4:1 to obtain the negative electrode active material.

[0267] 3) Preparation of negative electrode sheet

[0268] The above-mentioned negative electrode active material, conductive carbon black (Super P), binder styrene-butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC) are mixed evenly in deionized water at a mass ratio of 97.8:0.7:0.8:0.7 to obtain a second negative electrode slurry; the above-mentioned negative electrode active material, conductive carbon black (Super P), binder styrene-butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC) are mixed evenly in deionized water at a mass ratio of 96.4:0.4:2.5:0.7 to obtain the first negative electrode slurry. The mixture is then added to deionized water and stirred evenly to obtain a negative electrode slurry.

[0269] Then, it is coated using a double-sided coating machine at a rate of 130mg / 1540.25mm. 2 The negative electrode slurry is coated onto the copper foil using a single-sided density method. After double-sided coating, the negative electrode sheet is dried, cold-pressed, and slit to obtain the negative electrode sheet.

[0270] 4) Preparation of the separating membrane

[0271] A 5μm polypropylene membrane was used as the separator.

[0272] 5) Preparation of electrolyte

[0273] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate (EC) and dimethyl carbonate (DMC) organic solvents were mixed evenly at a volume ratio of 1 / 1. Lithium salt LiPF6 was added and dissolved in the organic solvent. The concentration of LiPF6 in the solution was 1 mol / L. The mixture was stirred evenly to obtain the electrolyte.

[0274] 6) Battery manufacturing

[0275] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The negative electrode is 580 mm long, thus obtaining the electrode assembly. The electrode assembly is placed in an outer packaging, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, the secondary battery of Example 1 is obtained.

[0276] The preparation methods of the secondary batteries in Examples 2-5 are basically the same as those in Example 1, except that the density of the negative electrode slurry coating on one side is different, as shown in Table 1.

[0277] The secondary batteries in Examples 6-9 are prepared in basically the same way as those in Example 1, except that the Dv50 of the first negative electrode active material and the second negative electrode active material are different, as shown in Table 1.

[0278] The secondary battery in Example 10 is prepared in a basically the same way as that in Example 1, except that the assembly method of the positive electrode, separator, and negative electrode is different, and the stacking process is replaced by the winding process, as detailed below:

[0279] The positive electrode, separator, and negative electrode are stacked in sequence and wound to obtain a battery cell. The battery cell is then placed in an outer packaging, and the electrolyte mentioned above is added. After processes such as encapsulation, settling, formation, and aging, a secondary battery is obtained.

[0280] The secondary batteries in Examples 11-12 are prepared in basically the same way as those in Example 1, except that the length of the negative electrode sheet is different, as shown in Table 1.

[0281] The preparation method of the secondary battery in Example 13 is basically the same as that in Example 1, except that the raw material of the first negative electrode active material is petroleum coke, and the raw material of the second negative electrode active material is semi-forged needle coke, as shown in Table 1.

[0282] The preparation method of the secondary battery in Example 14 is basically the same as that in Example 1. The difference lies in the preparation method of the first negative electrode active material. Specifically, the primary particles are directly subjected to graphitization, asphalt coating and carbonization treatment to obtain the first negative electrode active material as primary particles with a Dv50 of 14.5 μm, as shown in Table 1.

[0283] The preparation method of the secondary battery in Comparative Example 1 is basically the same as that in Example 1, except that the negative electrode active material is different and the single-sided coating density of the negative electrode slurry is different, as detailed below:

[0284] Needle coke was crushed, ground, and shaped to obtain primary needle coke particles with a Dv50 of 9.5 μm. These primary particles were then granulated to obtain secondary needle coke particles with a Dv50 of 11.3 μm. The secondary needle coke particles were then graphitized. Pitch (softening point 205℃) and the graphitized secondary needle coke particles were mixed at a mass ratio of 3:97 and then carbonized in a static high-temperature furnace at 1150℃ to obtain the negative electrode active material with a Dv50 of 11.8 μm.

[0285] The above-mentioned negative electrode active material, conductive carbon black (Super P), styrene-butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC) were mixed evenly in deionized water at a mass ratio of 96.4:0.4:2.5:0.7 to obtain the second negative electrode slurry;

[0286] Then, it is coated with a double-sided coating machine at a concentration of 60mg / 1540.25m. 2 The negative electrode slurry is coated onto the copper foil using a single-sided density method. After double-sided coating, the coating is dried, cold-pressed, and slit to obtain the negative electrode sheet.

[0287] The preparation method of the secondary battery in Comparative Example 2 is basically the same as that in Comparative Example 1, except that the surface density of the negative electrode slurry coating on one side is different, as shown in Table 1.

[0288] The secondary battery of Comparative Example 3 was prepared using a method basically the same as that of Example 1, except that the surface density of the negative electrode slurry coated on one side was different, being 200 mg / 1540.25 mm. 2 See Table 1 for details.

[0289] II. Battery Performance Testing

[0290] 1. Performance testing of negative electrode active materials and negative electrode sheets

[0291] 1) Volumetric particle size distribution curve test

[0292] The battery is disassembled to obtain the negative electrode sheet. The negative electrode film layer of the negative electrode sheet is peeled off, and the negative electrode film layer is thoroughly washed with acetone to remove the binders and other substances in the negative electrode film layer. After filtration and drying, the negative electrode active material powder is obtained.

[0293] The volumetric particle size distribution curve of the negative electrode active material was measured using a laser particle size analyzer. The specific procedure is as follows: A clean beaker was used, and 3g of the negative electrode active material to be tested was weighed. A surfactant was added, followed by 20ml of dispersant. The sample was sonicated at 120W / 5min to ensure complete dispersion in the dispersant. The sample was then poured into the injection tower and circulated with the solution to the test optical path system. Under laser beam irradiation, the volumetric particle size distribution curve of the negative electrode active material was obtained by receiving and measuring the energy distribution of the scattered light. Based on the obtained volumetric particle size distribution curve, the ranges of D1 and D2 values ​​were statistically analyzed, along with the maximum D1 value corresponding to the maximum H1 value, the maximum D2 value corresponding to the maximum H2 value, the maximum value of H1, and the maximum value of H2.

[0294] 2) Morphology testing of negative electrode active materials

[0295] The battery was disassembled to obtain the negative electrode sheet. The negative electrode film layer of the negative electrode sheet was peeled off, and the negative electrode film layer was thoroughly washed with acetone to remove binders and other substances. After filtration and drying, the negative electrode active material powder was obtained. The morphology of the negative electrode active material was tested using a scanning electron microscope (SEM). Specifically, a small amount of negative electrode active material powder was picked up using a round dot with conductive adhesive. Samples with poor conductivity needed to be sputter-coated with gold. The parameters were set as follows: mode: In-lens, voltage: 10KV, aperture: 30um, working distance: 4.5mm. The test procedure was as follows: the sample was moved at about 100x magnification. After confirming that there were no obvious abnormalities in the sample as a whole, two fields of view were randomly selected for the anode and the particle surface was focused. The anode was set to 10K, 5K, 3K, 1K, and 500 pixels, and the cathode was set to 30K, 10K, 5K, 3K, 1K, and 500 pixels. The magnification was 30-50000 magnification measured with a field emission scanning electron microscope (Zeiss Sigma300). The resolution was 20nm with a field emission scanning electron microscope (Zeiss Sigma300).

[0296] 3) Single-sided density test of negative electrode film

[0297] Negative electrode film: After disassembling the battery, the negative electrode sheet is obtained and punched into a sheet with an area of ​​1540.25 mm². 2 The small round piece was weighed and recorded as M1. The area of ​​the empty copper foil was 1540.25 mm². 2 The corresponding weight is denoted as M0. In this embodiment, the empty copper foil has an area of ​​1540.25 mm². 2 At that time, the weight was approximately 84 mg. Using 84 mg in the calculation, the density of the negative electrode film on one side is calculated as follows: (M1 - M0) / 2 mg / 1540.25 mm². 2 Specifically, the lateral density of the negative electrode film is (M1-84) / 2mg / 1540.25mm². 2 .

[0298] 2. Battery performance testing

[0299] 1) Fast charging capability test

[0300] The secondary battery was charged and discharged for the first time at a current of 1C (i.e., the current value at which the theoretical capacity is completely discharged within 1 hour). Specifically, at 35°C, the secondary battery was charged at a constant current rate of 1C to a voltage of 4.4V, then charged at a constant voltage rate to a current ≤0.05C, left to stand for 5 minutes, and then discharged at a constant current rate of 0.33C to a voltage of 2.8V. Its actual capacity was recorded as C0. Then, the battery was sequentially charged at constant current rates of 1.0C0, 1.3C0, 1.5C0, 1.8C0, 2.0C0, 2.3C0, 2.5C0, 3.0C0, 3.5C0, 4C0, 4.5C0, and 5C0 until the full battery charging cutoff voltage of 4.4V or the negative terminal cutoff potential of 0V (whichever comes first). After each charging, the battery was discharged at 1C0 until the full battery discharge cutoff voltage of 2.8V. The state of charge (SOC) was recorded at different charging rates until 10%, 20%, 30%, ..., 80%. Charge, or State of Charge, refers to the negative electrode potential at which the battery is fully discharged (SOC = 0) and fully charged (SOC = 100%). Charging rate-negative electrode potential curves are plotted for different SOC states. Linear fitting yields the charging rate corresponding to a negative electrode potential of 0V at each SOC state. This charging rate is the charging window for that SOC state, denoted as C10%SOC, C20%SOC, C30%SOC, and C40%SOC. For batteries with SOC values ​​of C50%, C60%, C70%, and C80%, the charging time T from 10% SOC to 80% SOC can be calculated using the formula (60 / C20% SOC + 60 / C30% SOC + 60 / C40% SOC + 60 / C50% SOC + 60 / C60% SOC + 60 / C70% SOC + 60 / C80% SOC) × 10%, in minutes. The equivalent charging rate is calculated as 0.7 × 60 / T. Fast charging capability is characterized by the equivalent charging rate; a higher equivalent charging rate indicates better fast charging performance.

[0301] 2) Volumetric energy density test

[0302] At 25°C, the secondary battery was fully charged and fully discharged at a rate of 0.33C three times, and the actual discharge energy C0 was recorded at this time. Under the same temperature conditions, the volume of the secondary battery was measured using an electronic balance. The ratio of the actual discharge energy C0 of the secondary battery at 0.33C to the volume V of the lithium-ion battery is the actual volumetric energy density of the lithium-ion battery.

[0303] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0304] Batteries for each embodiment and comparative example were prepared according to the above method, and various performance parameters were measured. The parameters of the negative electrode active material are shown in Table 1, the results of the bimodal curves are shown in Table 2, and the performance test results are shown in Table 3.

[0305] Table 1

[0306]

[0307]

[0308] Continued from Table 1

[0309]

[0310] Table 2

[0311]

[0312]

[0313] Table 3

[0314]

[0315] Examples 1-14 provide a secondary battery, which includes a cell, a positive electrode, a negative electrode, and an electrolyte. The negative electrode includes a negative current collector and a negative electrode film disposed on at least one side of the negative current collector. The negative electrode film includes a negative active material, and the volumetric particle size distribution curve of the negative active material is a bimodal curve. The particle size D1 of the first peak of the bimodal curve is smaller than the particle size D2 of the second peak of the bimodal curve. The abscissa of the bimodal curve represents the particle size of the negative active material. The one-sided density of the negative electrode film is 80 mg / 1540.25 mm. 2 -180mg / 1540.25mm 2 This approach helps improve the battery's fast-charging performance while maintaining energy density. The secondary battery of this application exhibits good fast-charging performance while also maintaining a good energy density.

[0316] As can be seen from Examples 1-14 and Comparative Example 1, the lower limit of the unilateral density of the negative electrode film is 80 mg / 1540.25 mm. 2 This approach is beneficial for improving the fast-charging performance of secondary batteries while maintaining energy density.

[0317] As can be seen from Examples 1-14 and Comparative Example 3, the upper limit of the single-sided density of the negative electrode film is 180 mg / 1540.25 mm. 2 This approach helps to balance the fast-charging performance and energy density of secondary batteries.

[0318] As can be seen from Examples 1, 6-7, 9-14 and Comparative Example 2, the volume particle size distribution curve of the negative electrode active material is a bimodal curve. The particle size D1 of the first peak of the bimodal curve is smaller than the particle size D2 of the second peak of the bimodal curve, which is beneficial to improving the fast charging performance of the secondary battery.

[0319] A comparison of Examples 1, 4-5, and 2-3 shows that the single-sided density of the negative electrode film is 100 mg / 1540.25 mm². 2 -160mg / 1540.25mm 2 This helps to better balance the battery's fast charging performance and energy density.

[0320] As can be seen from the comparison of Examples 1 and Examples 6-9, reasonable control of the range of D1, the range of D2, the maximum value of H1, the maximum value of H2, the D1 value corresponding to the maximum value of H1 and / or the D1 value corresponding to the maximum value of H2 is beneficial to better balance the battery's fast charging performance and energy density.

[0321] A comparison of Example 1 and Example 10 shows that the cell is a stacked cell, which is beneficial to further improve the battery energy density.

[0322] A comparison of Examples 1, 11, and 12 shows that a negative electrode length of 300-600 mm is beneficial for further improving the energy density of the battery.

[0323] A comparison of Examples 1 and 13 shows that when the first raw material includes at least one of needle coke, semi-calcined petroleum coke, and fully calcined petroleum coke, and the second raw material includes at least one of petroleum raw coke and pitch coke, it is beneficial to further improve the fast charging performance of the battery.

[0324] A comparison of Examples 1 and 14 shows that when the first negative electrode material includes secondary particles, it helps to further improve the fast charging performance of the battery.

[0325] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A secondary battery, characterized in that, The secondary battery includes a cell, which includes a positive electrode, a negative electrode, and an electrolyte. The negative electrode includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector. The negative electrode film layer includes a negative electrode active material. The volume particle size distribution curve of the negative electrode active material is a bimodal curve. The horizontal axis of the bimodal curve represents the particle size of the negative electrode active material, and the vertical axis represents the volume percentage of the negative electrode active material. The particle size D1 of the first peak of the bimodal curve is smaller than the particle size D2 of the second peak of the bimodal curve. The single-sided density of the negative electrode film is 80 mg / 1540.25 mm. 2 -180mg / 1540.25mm 2 .

2. The secondary battery according to claim 1, characterized in that, The single-sided density of the negative electrode film is 100 mg / 1540.25 mm². 2 -160mg / 1540.25mm 2 .

3. The secondary battery according to claim 1 or 2, characterized in that, The range of D1 is 0.1-11.5 μm, optionally, the range of D1 is 0.1-9.5 μm, more preferably, the range of D1 is 2-4 μm; and / or, The range of D2 is 9-25 μm, optionally, the range of D2 is 10-20 μm, and more preferably, the range of D2 is 13-15 μm.

4. The secondary battery according to any one of claims 1-3, characterized in that, The maximum value of the ordinate H1 of the first peak is 0.8%-3%, optionally, the maximum value of the ordinate H1 of the first peak is 1.3%-2.5%; and / or, The maximum value of the ordinate H2 of the second peak is 9%-12%, and optionally, the maximum value of the ordinate height H2 of the second peak is 9.6%-10.6%.

5. The secondary battery according to any one of claims 1-4, characterized in that, The maximum value of H1 corresponds to a D1 of 0.5-11 μm; optionally, the maximum value of H1 corresponds to a D1 of 1-9 μm; more preferably, the maximum value of H1 corresponds to a D1 of 2-4 μm; and / or, The maximum value of H2 corresponds to D2 of 11-25 μm. Optionally, the maximum value of H2 corresponds to D2 of 11-20 μm. More preferably, the maximum value of H2 corresponds to D2 of 11-25 μm. The range of D2 is 13-15 μm.

6. The secondary battery according to any one of claims 1-5, characterized in that, The negative electrode active material includes a first negative electrode active material and a second negative electrode active material. The first negative electrode active material includes secondary particles, and the second negative electrode active material includes primary particles. The Dv50 of the first negative electrode active material is greater than the Dv50 of the second negative electrode active material.

7. The secondary battery according to claim 6, characterized in that, The first negative electrode active material has a Dv50 of 10-24 μm; and / or, the second negative electrode active material has a Dv50 of 1.5-12 μm; optionally, the first negative electrode active material has a Dv50 of 12-20 μm; and / or, the second negative electrode active material has a Dv50 of 2-10 μm; more preferably, the first negative electrode active material has a Dv50 of 14-18 μm; and / or, the second negative electrode active material has a Dv50 of 4-8 μm.

8. The secondary battery according to any one of claims 6 or 7, characterized in that, The mass ratio of the secondary particles to the primary particles is from 9.5:0.5 to 3:

2.

9. The secondary battery according to any one of claims 6-8, characterized in that, The mass ratio of the secondary particles to the primary particles is 9:1 to 7:

3.

10. The secondary battery according to any one of claims 1-9, characterized in that, The battery cell is a laminated cell, and the length of the negative electrode is 300-600mm.

11. The secondary battery according to any one of claims 1-10, characterized in that, The length of the negative electrode sheet is 500-590mm.

12. The secondary battery according to any one of claims 1-11, characterized in that, The conductivity of the electrolyte is 14-18 mS / cm.

13. The secondary battery according to any one of claims 1-12, characterized in that, The negative electrode current collector includes copper foil, and the strength of the negative electrode current collector is 3-7 μm.

14. The secondary battery according to any one of claims 1-13, characterized in that, The first negative electrode active material and / or the second negative electrode active material include at least one of graphite, carbon or silicon-based materials and their modified materials.

15. A method for preparing a secondary battery, characterized in that, The preparation method includes the following steps: A raw material comprising at least a first negative electrode active material and a second negative electrode active material is mixed to obtain a negative electrode slurry, wherein the first negative electrode active material comprises secondary particles, the second negative electrode active material comprises primary particles, and the Dv50 of the first negative electrode active material is smaller than the Dv50 of the second negative electrode active material. The negative electrode slurry was coated onto the surface of the negative electrode current collector, with a single-sided coating density of 80 mg / 1540.25 mm. 2 -180mg / 1540.25mm 2 The negative electrode sheet is obtained by drying; optionally, the density of the coating on one side is 100mg / 1540.25mm. 2 -160mg / 1540.25mm 2 ; The positive electrode, the separator, and the negative electrode are assembled to obtain the secondary battery.

16. The preparation method according to claim 15, characterized in that, The mass ratio of the first negative electrode active material to the second negative electrode active material is 95:5 to 3:2, and optionally, the mass ratio of the first negative electrode active material to the second negative electrode active material is 9:1 to 7:

3.

17. The preparation method according to any one of claims 15 or 16, characterized in that, The first raw material is crushed to obtain primary particles of the first raw material; the primary particles of the first raw material are granulated to obtain secondary particles of the first raw material; the secondary particles of the first raw material are then subjected to graphitization and carbonization treatments to obtain the first negative electrode active material; and / or The second raw material is crushed to obtain primary particles of the second raw material. These primary particles are then subjected to graphitization and carbonization treatments to obtain the second negative electrode active material. The first raw material includes at least one of needle coke, semi-calcined petroleum coke, and fully calcined petroleum coke, and / or the second raw material includes at least one of petroleum raw coke and pitch coke.

18. The preparation method according to claim 17, characterized in that, The first raw material secondary particles are subjected to graphitization, asphalt coating, and carbonization treatments to obtain the first negative electrode active material; and / or The second raw material particles are subjected to graphitization, asphalt coating, and carbonization to obtain the second negative electrode active material.

19. The preparation method according to claim 17 or 18, characterized in that, The first raw material primary particles have a Dv50 of 6-12 μm, optionally 7-9 μm; and / or The Dv50 of the primary particles of the second raw material is 1.5-9.5μm, and optionally 3-6μm.

20. The preparation method according to any one of claims 17-19, characterized in that, The Dv50 of the secondary particles of the first raw material is 10-18 μm, and optionally 13-16 μm.

21. The preparation method according to any one of claims 15-20, characterized in that, The first negative electrode active material has a Dv50 of 10-24 μm, optionally 12-20 μm, and more preferably 14-18 μm; and / or, the second negative electrode active material has a Dv50 of 1.5-12 μm, optionally 2-10 μm, and more preferably 4-8 μm.

22. The preparation method according to any one of claims 18-21, characterized in that, In the asphalt coating treatment of the second raw material particles, the softening point of the asphalt is 120-180℃.

23. The preparation method according to any one of claims 17-22, characterized in that, The petroleum coke includes isotropic petroleum coke.

24. The preparation method according to any one of claims 15-23, characterized in that, The positive electrode, the separator, and the negative electrode are stacked and assembled to obtain an electrode assembly. The electrode assembly is placed in an outer package, and an electrolyte is added to obtain the secondary battery. Optionally, the length of the negative electrode is 300-600 mm, and more preferably, the length of the negative electrode is 500-590 mm.

25. An electrical appliance, characterized in that, The electrical device includes a secondary battery according to any one of claims 1-14 or a secondary battery obtained by the preparation method according to any one of claims 15-24.

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