Secondary battery and electric device comprising same

Abstract

The invention provides a secondary battery and a power utilization device comprising the same, the secondary battery comprises a negative electrode piece, the negative electrode piece comprises a negative electrode current collector and a negative electrode film layer, and the negative electrode film layer is arranged on at least one surface of the current collector and comprises a negative electrode active material and a conductive agent; the powder conductivity sigma of the negative electrode active material is greater than or equal to 80S / cm and less than or equal to 106S / cm; and the compaction density of the negative electrode film layer is 1.35 g / cm < 3 > to 1.50 g / cm < 3 >. The negative pole piece is beneficial to reducing the black spot phenomenon of the secondary battery and improving the cycle performance and the dynamic performance of the secondary battery.

Description

[0001] This application is a divisional application based on the invention with application number 2023116773901, application date December 7, 2023, applicant CATL, and invention title "Secondary Battery and Electrical Device Containing the Thereof". Technical Field

[0002] This application relates to the field of secondary battery technology, and more particularly to a secondary battery and an electrical device containing the same. Background Technology

[0003] In recent years, secondary batteries have been increasingly widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power plants, as well as in many fields such as power tools, electric bicycles, electric motorcycles, electric cars, military equipment, and aerospace. Therefore, higher requirements have been placed on the performance of secondary batteries.

[0004] During use or storage, secondary batteries often exhibit various failure phenomena due to a series of complex chemical and physical processes within the battery, such as black spots and lithium plating, which severely degrade their performance. The negative electrode active material is one of the crucial raw materials for secondary batteries and has a significant impact on their electrical performance. Failure of graphite-based negative electrode materials primarily occurs on the graphite surface, arising from the electrochemical reaction between the graphite surface and the electrolyte, forming a solid electrolyte interphase (SEI), which ultimately affects the cycle performance of the secondary battery. Therefore, it is necessary to provide a secondary battery that can improve the black spot phenomenon. Summary of the Invention

[0005] This application provides a secondary battery that has good cycle performance and kinetic performance, and can reduce the black spot phenomenon on the surface of the negative electrode of the secondary battery.

[0006] The secondary battery provided in this application includes a negative electrode sheet, wherein the negative electrode sheet comprises a negative current collector and a negative electrode film layer disposed on at least one surface of the current collector and comprising a negative electrode active material, wherein the negative electrode active material has a compaction density of 1.5 g / cm³. 3 The powder conductivity σ, measured under the specified test conditions, is greater than or equal to 80 S / cm and less than or equal to 106 S / cm; the compaction density of the negative electrode film is 1.35 g / cm³. 3 -1.50 g / cm 3 .

[0007] Adjusting the powder conductivity σ of the negative electrode active material and the compaction density of the negative electrode film can ensure good electrical contact and conductive network between the negative electrode active material particles in the negative electrode sheet. This can alleviate the gas generation lag caused by the delayed formation of the SEI film during the formation process of some active material particles, as well as the black spot defects caused by the inability of active ions to embed into the active material due to gas blockage. It can also alleviate the lithium plating problem caused by the content of active ions in the cell being greater than the acceptable amount in the negative electrode, thus helping to improve the cycle performance and kinetic performance of the secondary battery.

[0008] In any embodiment, the powder conductivity σ is 83S / cm-104S / cm, which is beneficial to further improve the conductivity of the negative electrode active material, reduce the black spot phenomenon, and improve the cycle performance of the secondary battery.

[0009] In any embodiment, the compaction density of the negative electrode film is 1.40-1.50 g / cm³. 3 This can further improve the energy density of secondary batteries.

[0010] In any embodiment, the negative electrode active material satisfies at least one of the following conditions: (1) The volume distribution particle size D of the negative electrode active material V 1 is 1.4μm-3.0μm, and can be selected as 1.7μm-2.7μm; (2) The volume distribution particle size D of the negative electrode active material V 50 is 12μm-18μm, with selectable options of 12.9μm-14.5μm; (3) Particle size distribution (D) of the negative electrode active material V 90-D V 10) / D V 50 is 1.3-1.8, and can be selected as 1.35-1.70.

[0011] Controlling the particle size D in volume distribution V 1. This can reduce excessive active sites and irreversible active ion consumption on the surface of the negative electrode active material caused by excessively high particle content; it also helps improve the conductive network between negative electrode active material particles, and helps the secondary battery to have both good cycle performance and alleviate black spot phenomenon. Controlling the volume distribution particle size D V 50 helps to obtain sufficient active sites, reduce the inhibition of active ion insertion / extraction rate, and improve the kinetic performance of secondary batteries; controlling the particle size distribution of negative electrode active materials helps to improve the particle size distribution concentration of negative electrode active materials, reduce the side reactions of excessively large and small particle sizes of negative electrode active materials in electrochemical reactions, comprehensively improve the cycle performance and kinetic performance of secondary batteries, and further reduce the black spot phenomenon.

[0012] In any embodiment, the tap density of the negative electrode active material is 1.25 g / cm³. 3 -1.45g / cm 3 The option is 1.29 g / cm³. 3 -1.41g / cm 3 Adjusting the tap density of the negative electrode active material allows for good dispersion of negative electrode active materials of different particle sizes within the negative electrode sheet. This ensures sufficient contact sites and good electrical contact between the negative electrode active material particles, enabling active ions to be well inserted and extracted between the negative electrode active materials, thus reducing the precipitation of active ions and the black spot phenomenon on the negative electrode sheet.

[0013] In any embodiment, the specific surface area of ​​the negative electrode active material is 0.8 m². 2 / g-1.4m 2 / g, optional 0.9m 2 / g-1.3m 2 / g. Adjusting the specific surface area of ​​the negative electrode active material helps to increase the contact sites and surface active sites between the negative electrode active material particles, increase the conductivity of the negative electrode active material and improve the transport performance of active ions, thereby improving the cycle performance of the secondary battery.

[0014] In any embodiment, the specific capacity of the negative electrode active material is 335mAh / g-350mAh / g, optionally 340.5mAh / g-347.5mAh / g, thereby improving the energy density and cycle performance of the secondary battery.

[0015] In any embodiment, the areal density of the negative electrode film layer in the negative electrode sheet is 7 mg / cm³. 2 -15mg / cm 2 This can increase the energy density of secondary batteries and improve their cycle performance.

[0016] In any embodiment, the negative electrode active material comprises artificial graphite.

[0017] A second aspect of this application provides an electrical device including a secondary battery as described in the first aspect of this application. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0019] Figure 2 yes Figure 1 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0020] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0021] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0022] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0023] Figure 6 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.

[0024] Figure 7 The cyclic curves of Embodiment 2 and Comparative Example 1 of this application are shown.

[0025] Explanation of reference numerals in the attached figures: 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Casing; 52 Electrode assembly; 53 Cover plate. Detailed Implementation

[0026] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the positive electrode active material, its manufacturing method, positive electrode sheet, secondary battery, 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.

[0027] 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.

[0028] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0029] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0030] 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.

[0031] 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.

[0032] 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).

[0033] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions (e.g., lithium ions, sodium ions) move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor for the active ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing the passage of active ions.

[0034] During the formation stage of a secondary battery, the negative electrode active material undergoes an electrochemical reaction with the electrolyte, generating a solid electrolyte interphase (SEI) accompanied by gas production. In this process, some negative electrode active material particles have poor electrical contact with surrounding particles. The electrochemical reaction between the graphite material and the electrolyte is not timely during formation, preventing the formation of a complete SEI film and resulting in delayed SEI film formation and gas generation. The gas generated by this delay cannot be discharged with the formation process and remains between the negative electrode and the separator, hindering the active ions in this area from detaching from the positive electrode, passing through the separator, and embedding into the negative electrode during the charging process, leading to black spot defects. This results in some negative electrode active materials being unable to effectively participate in the charge-discharge cycle of the secondary battery. The content of active ions in the positive electrode exceeds the maximum acceptable content of active ions in the negative electrode, causing some active ions to precipitate on the negative electrode surface and lose their electroactivity, leading to a decrease in cell capacity and rapid degradation of cycle performance.

[0035] [Rechargeable Battery] This application provides a secondary battery, including a negative electrode sheet, wherein 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, the negative electrode film layer including a negative electrode active material. The negative electrode active material has a compaction density of 1.5 g / cm³. 3 The powder conductivity σ, measured under the specified test conditions, is greater than or equal to 80 S / cm and less than or equal to 106 S / cm; and the compaction density of the negative electrode film is 1.35 g / cm³. 3 -1.50g / cm 3 .

[0036] Adjusting the powder conductivity σ of the negative electrode material and the compaction density of the negative electrode film allows for good electrical contact and a conductive network between the active material particles in the negative electrode sheet. This can mitigate the gas generation lag caused by the delayed formation of the SEI film during the formation process of some negative electrode active material particles, thereby reducing black spot defects caused by the inability of active ions to be inserted or extracted due to gas blockage and reducing lithium plating problems in secondary batteries. It also reduces the irreversible consumption of active ions and improves the cycle performance and kinetic performance of secondary batteries.

[0037] In this paper, the powder conductivity σ is the negative electrode active material at a compaction density of 1.5 g / cm³. 3 The powder conductivity σ, as determined under the test conditions, can be determined using methods known in the art, for example, using the following method: At 25℃, using the FT-8100A four-probe powder testing platform, sample preparation was performed according to the four-probe method in GB / T 30835-2014 regarding the determination of powder conductivity. 1g of the sample powder was weighed and placed in a cylindrical metal mold with a height of 25mm and a diameter of 12mm. The lower electrode of the mold was pressed down, and the sample began to be compressed when the upper electrode was pressed onto the platform. Pressure was maintained for 30s to keep the sample thickness at 0.147±0.002. Then, the conductivity of the negative electrode active material at 1.50g / cm³ was determined using the four-probe method. 3 Electrical conductivity of powder at compacted density.

[0038] In some embodiments, the negative electrode active material has a compaction density of 1.5 g / cm³. 3 The powder conductivity σ, measured under the specified test conditions, was 83 S / cm–104 S / cm. In some embodiments, the negative electrode active material was compacted to a density of 1.5 g / cm³. 3 The powder conductivity σ measured under the specified test conditions was 85 S / cm-100 S / cm, 90 S / cm-104 S / cm, 85 S / cm-104 S / cm, or 95 S / cm-100 S / cm. Adjusting the powder conductivity of the negative electrode active material helps to further improve the electrical contact between the negative electrode active material particles, improve the conductivity of the negative electrode active material, reduce the black spot phenomenon, and improve the cycle performance of the secondary battery.

[0039] In some embodiments, the compaction density of the negative electrode film is 1.40 g / cm³. 3 -1.50g / cm 3 In some embodiments, the compaction density of the negative electrode film is 1.40 g / cm³. 3 -1.43g / cm 3 1.44 g / cm 3 -1.50g / cm 3 1.41 g / cm 3-1.50g / cm 3 Or 1.40g / cm 3 -1.45g / cm 3 In some embodiments, the compaction density of the negative electrode film is 1.41 g / cm³. 3 1.42 g / cm 3 1.44 g / cm 3 1.45g / cm 3 1.46 g / cm 3 1.47 g / cm 3 1.48g / cm 3 1.49 g / cm 3 Or any range between two values. Adjusting the compaction density of the negative electrode film can further improve the energy density of the secondary battery and the diffusion channels of active ions in the secondary battery, and improve the migration performance of active ions; it also improves the rapid capacity decay caused by the precipitation of active ions on the negative electrode surface due to insufficient charge and discharge capacity in the later stages of cycling, thereby improving the cycle performance and fast charging performance of the secondary battery.

[0040] The compaction density of the negative electrode film has a meaning known in the art and can be determined using methods known in the art. As an example, a negative electrode sample with area S is weighed using an electronic balance, and the weight is recorded as W1. The thickness T1 of the negative electrode is measured using a micrometer. Then, the weighed electrode film is wiped off, and the weight of the negative current collector is weighed, recorded as W2. The thickness T2 of the negative current collector is measured using a micrometer. Therefore, the compaction density PD of the negative electrode film = (W1...) W2) / [(T1-T2)×S].

[0041] In some embodiments, the areal density of the negative electrode film is 7 mg / cm³. 2 -15mg / cm 2 8mg / cm 2 -15mg / cm 2 9mg / cm 2 -15mg / cm 2 7mg / cm 2 -13mg / cm 2 In some embodiments, the areal density of the negative electrode sheet is 13.0 mg / cm³. 2 12mg / cm 2 11mg / cm 2 10mg / cm 2 9mg / cm 2 8mg / cm 2 7mg / cm 2Or any value between the two. Adjusting the areal density of the negative electrode helps to improve the energy density of the secondary battery and enhance its cycle performance.

[0042] In this application, the areal density of the negative electrode film has a meaning known in the art and can be tested using methods known in the art. As an example, a cold-pressed negative electrode sheet is cut into small circular pieces with an area of ​​S1, and its weight is weighed and recorded as M1. Then, the negative electrode film layer of the weighed negative electrode sheet is wiped off, and the weight of the negative electrode current collector is weighed and recorded as M0. The areal density of the negative electrode film layer = (weight of the negative electrode sheet M1 - weight of the negative electrode current collector M0) / S1.

[0043] In some embodiments, the volume distribution particle size D of the negative electrode active material V 1 is 1.4μm-3.0μm, and can be selected as 1.7μm-2.7μm, 1.8μm-2.7μm, or 1.71μm-2.58μm. In some embodiments, the volume distribution particle size D of the negative electrode active material is... V 1 represents a range of 1.6 μm, 2.0 μm, 1.2 μm, 1.5 μm, 1.6 μm, or any two of these values. Small-particle anode active materials, due to their large specific surface area and numerous surface active sites, are more prone to forming byproducts at these sites during cycling, leading to increased consumption of active ions and deterioration of cycling performance. Adjusting the volume distribution particle size D of the anode active material... V 1. This helps reduce the content of small-particle negative electrode active materials, decreases the irreversible consumption of active ions, and improves the cycle performance of secondary batteries. Simultaneously, it adjusts the volume distribution particle size D. V 1 can further improve the diffusion channels of active ions in secondary batteries, improve the migration performance of active ions and reduce the rapid capacity decay caused by the precipitation of active ions in the later stages of cycling.

[0044] In some embodiments, the volume distribution particle size D of the negative electrode active material V The particle size distribution (Dv50) of the negative electrode active material is 12μm-18μm, and can be selected as 14μm-16.5μm, 12μm-14μm, or 12.9μm-14.5μm. In some embodiments, the particle size distribution (Dv50) of the negative electrode active material is 12.9μm, 13μm, 15μm, 16μm, 17μm, or any range between two values. The particle size distribution (Dv50) of the negative electrode active material can be adjusted. V 50 helps improve the specific surface area of ​​the negative electrode active material and provides sufficient surface active sites, and shortens the migration path of active ions, promotes the insertion and extraction of active ions, and improves the conductivity of the negative electrode active material and the power performance of the secondary battery.

[0045] In some embodiments, the particle size distribution (D) of the negative electrode active material V90-D V 10) / D V 50 is 1.3-1.8, and can be selected as 1.35-1.70 or 1.35-1.60. In some embodiments, the particle size distribution of the negative electrode active material is 1.4, 1.45, 1.5, 1.55, 1.65, 1.7, 1.75, or any two values ​​in between. Adjusting the particle size distribution of the negative electrode active material can control the content of small particles in the negative electrode active material and make the particle size distribution of the negative electrode active material more concentrated, which is beneficial to reducing irreversible active ion consumption caused by excessive small particle content; it also helps to improve the conductive network between the particles of the negative electrode active material, which can improve the cycle performance and power performance of the secondary battery.

[0046] In this application, the volume distribution particle size D of the negative electrode active material is... V 10. D V 50. D V The value 90 has a well-known meaning in the art, representing the particle size corresponding to a cumulative volumetric distribution percentage of 10%, 50%, and 90%, respectively, and can be determined using instruments and methods known in the art. For example, it can be determined using a laser particle size analyzer, referring to GB / T 19077-2016. The testing instrument can be the Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0047] In some embodiments, the tap density of the negative electrode active material is 1.25 g / cm³. 3 -1.45g / cm 3 The option is 1.25g / cm³. 3 -1.35g / cm 3 1.29g / cm 3 -1.41g / cm 3 1.25g / cm 3 -1.41g / cm 3 In some embodiments, the tap density of the negative electrode active material is 1.28 g / cm³. 3 1.30g / cm 3 1.33g / cm 3 1.40g / cm 3 1.42 g / cm 3Or any range between two values. When the tap density of the negative electrode active material is within a suitable range, smaller-diameter negative electrode active material particles can be well dispersed between larger-diameter negative electrode active material particles, filling the gaps between the larger-diameter particles and increasing the contact sites between the negative electrode active material particles. This not only improves the conductivity of the negative electrode active material particles but also facilitates the insertion and extraction of active ions in the negative electrode active material, reducing the precipitation of active ions and the black spot phenomenon on the negative electrode sheet, thereby improving the cycle performance of the secondary battery.

[0048] In this document, tap density has the meaning known in the art and can be determined using methods known in the art. For example, it can be determined using a powder tap density tester (such as Dandong Baite BT-301) in accordance with GB / T 5162-2006.

[0049] In some embodiments, the specific surface area of ​​the negative electrode active material is 0.8 m². 2 / g-1.4m 2 / g, optional 0.9m 2 / g-1.3m 2 / g, 0.95m 2 / g-1.1m 2 / g, 0.97m 2 / g-1.1m 2 / g. In some embodiments, the specific surface area of ​​the negative electrode active material is 1.0 m². 2 / g, 1.05m 2 / g, 1.1m 2 / g, 1.15m 2 / g, 1.2m 2 / g, 1.25m 2 / g, 1.30m 2 / g, 1.35m 2 / g or any range between two values. Adjusting the specific surface area of ​​the negative electrode active material is beneficial to improving the degree of overlap between negative electrode active material particles, increasing the contact sites and surface active sites of the negative electrode active material, improving the conductivity and active ion transport performance of the negative electrode active material, and improving the cycle performance and power performance of the secondary battery.

[0050] In this document, the term "specific surface area" refers to the sum of the total external surface areas of all particles per gram of material. The specific surface area of ​​graphite materials can be determined using instruments and methods known in the art. For example, the specific surface area of ​​the negative electrode active material can be measured using a specific surface area analyzer (McTriStar 3020, USA) via nitrogen adsorption / desorption, referring to GB / T 19587-2017, "Specific Surface Area Determination Method": the negative electrode active material is dried in a vacuum drying oven and then placed in a sample tube for measurement in the analyzer.

[0051] In some embodiments, the specific capacity of the negative electrode active material is 335 mAh / g to 350 mAh / g. Herein, the term "specific capacity" refers to the ratio of the electrical capacity that the graphite material can release to the mass of the graphite material. Generally, a higher specific capacity is more beneficial for improving the energy density of the secondary battery.

[0052] In some embodiments, the specific capacity of the negative electrode active material is 340.5 mAh / g to 347.5 mAh / g, such as 344.7 mAh / g, 345.5 mAh / g, 344.9 mAh / g, and 345.9 mAh / g, which helps to improve the energy density and cycle performance of the secondary battery.

[0053] The specific capacity can be measured using any method known in the art. For example, a graphite anode active material sample can be thoroughly mixed with conductive carbon black and polyvinylidene fluoride (PVDF) in a mass ratio of 91.6:1.8:6.6 in an appropriate amount of NMP solvent to form a uniform anode slurry. The anode slurry is then uniformly coated onto the surface of the copper foil anode current collector and dried and cold-pressed. Subsequently, using a lithium metal sheet as the counter electrode and a polypropylene (PP) film as the separator, an electrolyte is injected. The electrolyte formulation is as follows: dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and ethylene carbonate (EC) are mixed in a weight ratio of 1:1:1 to obtain an organic solvent. LiPF6 is then dissolved in the organic solvent to prepare an electrolyte with a concentration of 1.0 mol / L. A CR2430 coin cell is assembled in an argon-protected glove box. At 25°C, the prepared coin cell was first discharged at a constant current of 0.05C to 0.005V, then discharged at a constant current of 10μA to 0.005V, and allowed to stand for 5 minutes. The first discharge capacity of the coin cell was recorded. Subsequently, it was charged at a constant current of 0.1C to 2.0V, and the charging capacity of the coin cell was recorded. The ratio of the charging capacity of the coin cell to the mass of the graphite anode active material sample is the specific capacity of the graphite anode active material.

[0054] In this application, the negative electrode active material can be prepared using a method including the following steps: Provide raw materials; process the raw materials to obtain a precursor; perform graphitization treatment on the precursor to obtain a graphitized product; demagnetize to obtain a negative electrode active material.

[0055] In some embodiments, the raw material includes at least one of petroleum coke, needle coke, and pitch coke.

[0056] In this article, the term "petroleum coke" refers to the coke formed after petroleum residue or petroleum asphalt has undergone high-temperature carbonization.

[0057] In this article, the term "needle coke" refers to coke with needle-like textures that can be generated from coal tar pitch or petroleum pitch after liquid-phase carbonization to produce anisotropic mesophases and then undergoing high-temperature carbonization and other processes.

[0058] In this article, the term "asphalt coke" refers to the solid material generated after coal tar pitch is carbonized at high temperature.

[0059] In some embodiments, the raw material includes petroleum coke.

[0060] Petroleum coke has excellent anisotropy, which is beneficial for preparing graphite materials with low graphitization and low expansion, thus contributing to the long cycle life of batteries. At the same time, petroleum coke has high compaction density and high specific capacity, which is beneficial for improving the energy density of batteries. In addition, petroleum coke is more widely available, which is conducive to industrial production.

[0061] The aforementioned raw materials typically include at least one of mosaic, regional, and fibrous structures. Generally, based on the morphological characteristics and isochromatic area size of the coke under a polarizing microscope, isochromatic microstructures with a size less than 30 μm are classified as mosaic; isochromatic microstructures with a size greater than 30 μm are classified as regional; and anisotropic strip-shaped isochromatic areas are classified as fibrous structures.

[0062] In some embodiments of this application, based on the total volume of the raw material structure, the volume ratio of the embedded and regional structures in the raw material is greater than or equal to 60%, and can be selected as 65%-80%.

[0063] In this application, the volume ratio of mosaic and regional structures in the raw materials can be tested using methods known in the art. As an example, raw materials are taken according to GB 1997-89, and raw materials crushed to 1mm are mixed and reduced to 40g~50g. 4g~5g of 0.07mm~1.0mm grade samples are taken using a square-hole sieve for slide preparation. Powdered coke and block coke films are prepared according to MT 116.1-86. The diameter of the powdered coke film should not be less than 22mm, and the volume occupied by the cementing material should be less than 1 / 3. The sample is placed on a slide with clay, flattened, and then placed on the stage for focusing. After calibrating the microscope, the polarizer and analyzer are adjusted to make them orthogonal. A lapis lazuli test plate (1λ) is inserted to make the field of view show the interference color of first-order red. The step length of the moving scale is determined to ensure that more than 400 effective measuring points are evenly distributed, with a point spacing of 0.3~0.5mm and a row spacing of 0.5~0.8mm. Starting from one end of the sample, the type of microstructure under the crosshair intersection is determined. The volume ratio of mosaic and regional structures in the raw material is calculated by dividing the effective number of measurement points of the optical structure of mosaic and regional structures by the total number of measurement points.

[0064] In some implementations, crushing is the process of reducing the particle size of raw materials, which can be achieved by any mechanical device such as a crusher or a mechanical mill.

[0065] Grading is a process of adjusting the particle size distribution of raw materials to obtain precursors that meet particle size requirements. The particle size and particle size distribution of the precursors can be controlled by adjusting the grading frequency and the air intake. In some implementations, the grading frequency is 40Hz-50Hz, and the damper opening is 20%-70%.

[0066] In some embodiments, the precursor D V The particle size of 50 particles ranges from 10.0 μm to 25.0 μm.

[0067] In some embodiments, the precursor D V 50 Particle sizes are 10.0 μm, 13.0 μm, 15.0 μm, 17.0 μm, 20.0 μm, 23.0 μm, 25.0 μm or any value between two of these.

[0068] In some embodiments, the particle size distribution (D) of the drive body V 90-D V 10) / D V 50 is 1.05-1.75.

[0069] In some embodiments, the particle size distribution (D) of the precursor V 90-D V 10) / D V50 is a value range of 1.05, 1.15, 1.25, 1.35, 1.45, 1.55, 1.65, 1.75, or any two of these values.

[0070] In some embodiments, the tap density of the precursor is 0.5 g / cm³. 3 ~2g / cm 3 .

[0071] In some embodiments, the tap density of the precursor is 0.5 g / cm³. 3 0.8g / cm 3 1.0g / cm 3 1.2g / cm 3 1.5g / cm 3 1.8g / cm 3 Or the range of values ​​between any two.

[0072] In some embodiments, a low-temperature carbonization treatment can be performed before graphitization. In some embodiments, the low-temperature carbonization temperature is 900℃-1300℃, and the low-temperature carbonization time is 24h-240h.

[0073] In some embodiments, the temperature for low-temperature carbonization can be selected as 900°C, 1000°C, 1100°C, 1200°C, 1300°C, or any value range between the two.

[0074] In some implementations, the low-temperature carbonization time can be selected as 24h, 50h, 75h, 100h, 150h, 200h, 240h or any range between the two.

[0075] In this article, the term "graphitization treatment" refers to the heat treatment process of carbon materials, in which carbon materials undergo "microcrystal" growth to transform from a two-dimensional carbon network structure to a three-dimensional ordered structure.

[0076] In some implementations, the maximum power of the graphitization process is 70%-90% of the rated power of the graphitization process equipment.

[0077] In some implementations, the maximum power for graphitization is 70%, 75%, 80%, 85%, 90%, or any range between two of the rated power of the graphitization equipment. It is understood that graphitization equipment refers to any device capable of performing graphitization, including but not limited to Atchison furnaces, box furnaces, internal furnaces, continuous graphitization, electric forging furnaces, medium-frequency furnaces, and tube furnaces. The rated power of graphitization equipment produced by different manufacturers may vary; the appropriate device can be selected based on the specific circumstances.

[0078] In some embodiments, the graphitization equipment is an internal furnace with a rated power of 25,000-32,000W. The graphitization time can be 10-30 hours, or optionally 15-25 hours.

[0079] In some embodiments, the graphitization equipment is an Atchison furnace with a rated power of 28,000-30,000 W. The graphitization time can be 30-50 hours, and optionally 40-50 hours.

[0080] The maximum power of the graphitization process used in this application needs to be lower than the rated power of the graphitization equipment in order to achieve uniformity of the thermal field during the graphitization process.

[0081] In some implementations, the maximum power of the graphitization process can be 20,000W-25,000W.

[0082] In some implementations, the maximum power for graphitization can be selected as 20000W, 21000W, 22000W, 22500W, 23000W, 23500W, 24000W, 25000W, or any value range between the two.

[0083] By controlling the maximum power of graphitization treatment, the degree of graphitization of graphite materials during heat treatment can be effectively controlled. While the internal region of graphite particles is highly graphitized, a uniform disordered layer is formed on the surface of the material, which is beneficial to improving the cycle stability of secondary batteries.

[0084] In some embodiments, the constant power at maximum power is maintained for 10-50 hours during the graphitization process. In some embodiments, the constant power at maximum power is maintained for 10 hours, 13 hours, 16 hours, 19 hours, 22 hours, 25 hours, 28 hours, 31 hours, 33 hours, 36 hours, 39 hours, 42 hours, 45 hours, 48 ​​hours, 50 hours, or any value between the two.

[0085] In some embodiments, the graphitization temperature is 2600°C to 3000°C.

[0086] In some embodiments, the graphitization temperature is 2600°C, 2700°C, 2800°C, 2900°C, 3000°C, or any value between two of these.

[0087] Appropriate graphitization temperature and time can prevent excessive rearrangement of the precursor, which would result in a high specific surface area and deterioration of high-temperature performance in the graphitized material. At the same time, they can effectively improve the degree of graphitization of the graphite material, thereby facilitating the simultaneous improvement of high-temperature storage and cycle life of secondary batteries.

[0088] [Negative electrode plate] As an example of a negative electrode sheet, the negative 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 current collector.

[0089] In some embodiments, the negative electrode film layer comprises the graphite material prepared by the method described in the first aspect of this application, thereby enabling the secondary battery to achieve both good cycle performance and kinetic performance.

[0090] In some embodiments, the negative electrode active material includes one of artificial graphite, natural graphite, soft carbon, hard carbon, and mesophase carbon microspheres. In some embodiments, the negative electrode active material includes artificial graphite.

[0091] In some embodiments, the negative electrode film layer may further include other negative electrode active materials besides the graphite material described above. In some embodiments, the other negative electrode active materials include, but are not limited to, one or more of conventional natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based materials may include one or more of elemental silicon, silicon oxide, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based materials may include one or more of elemental tin, tin oxide, and tin alloys.

[0092] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer 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 (copper, copper 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.).

[0093] In some embodiments, the negative electrode film layer may optionally include an adhesive. The adhesive 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).

[0094] In some embodiments, the negative electrode also includes a conductive agent. The conductive agent includes one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0095] In some embodiments, the conductive agent includes carbon black. In some embodiments, the conductive agent includes carbon nanotubes. In some embodiments, the conductive agent includes both carbon black and carbon nanotubes. The conductive agent is widely available, has excellent conductivity, and is beneficial for controlling the manufacturing cost of secondary batteries and improving the conductivity of the negative electrode.

[0096] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0097] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as 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 a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0098] [Positive electrode plate] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0099] 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.

[0100] 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.).

[0101] In some embodiments, the positive electrode active material may be a known battery positive electrode active material. 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 battery positive electrode active materials 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.

[0102] 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.

[0103] 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.

[0104] 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.

[0105] [Electrolytes] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0106] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0107] 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.

[0108] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0109] 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.

[0110] [Isolation membrane] 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.

[0111] 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.

[0112] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0113] 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.

[0114] 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.

[0115] In addition, the secondary battery, battery module, battery pack and power device of this application will be described below with appropriate reference to the accompanying drawings.

[0116] In one embodiment of this application, a secondary battery is provided.

[0117] 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 1 This is an example of a square-structured secondary battery 5.

[0118] In some implementations, refer to Figure 2 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.

[0119] 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.

[0120] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 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.

[0121] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0122] 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.

[0123] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 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.

[0124] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for 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.

[0125] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0126] Figure 6 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.

[0127] 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.

[0128] Example 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.

[0129] I. Testing Methods 1. Particle size testing of powder Measurement method: Particle size distribution was determined using laser diffraction, as per GB / T 19077-2016, and a Master Size 3000 laser particle size analyzer (e.g., Malvern Instruments Ltd., UK). The volumetric particle size distribution D was obtained. V 10. D V 50. D V 90 and D V 1.

[0130] 2. Powder conductivity test At 25℃, using the FT-8100A four-probe powder testing platform, sample preparation was performed according to the four-probe method in GB / T 30835-2014 regarding the determination of powder conductivity. 1g of the sample powder was weighed and placed in a cylindrical metal mold with a height of 25mm and a diameter of 12mm. The lower electrode of the mold was pressed down, and the sample began to be compressed when the upper electrode was pressed onto the platform. Pressure was maintained for 30s to keep the sample thickness at 0.147±0.002. Then, the carbon material's conductivity at 1.50 g / cm³ was determined using the four-probe method. 3 Powder conductivity under compaction.

[0131] 3. Specific surface area test of powder According to GB / T 19587-2017, the specific surface area of ​​the negative electrode active material was measured by nitrogen adsorption / desorption using a specific surface area analyzer (American Microt TriStar 3020): the negative electrode active material was dried in a vacuum drying oven and then placed in a sample tube for measurement in the analyzer.

[0132] 4. Powder tap density test Referring to GB / T 5162-2006 and GB / T 24533-2009, the tap density was determined using a powder tap density tester (such as Dandong Baite BT-301) with the following parameters: vibration frequency 250±15 times / minute, amplitude 3±0.2mm, number of vibrations 5000 times, and measuring cylinder 25 mL.

[0133] 5. Specific capacity testing of negative electrode active materials The specific capacity can be measured using any method known in the art. For example, a graphite anode active material sample can be thoroughly mixed with conductive carbon black and polyvinylidene fluoride (PVDF) in a mass ratio of 91.6:1.8:6.6 in an appropriate amount of NMP solvent to form a uniform anode slurry. The anode slurry is then uniformly coated onto the surface of the copper foil anode current collector and dried and cold-pressed. Subsequently, using a lithium metal sheet as the counter electrode and a polypropylene (PP) film as the separator, an electrolyte is injected. The electrolyte formulation is as follows: dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and ethylene carbonate (EC) are mixed in a weight ratio of 1:1:1 to obtain an organic solvent. LiPF6 is then dissolved in the organic solvent to prepare an electrolyte with a concentration of 1.0 mol / L. A CR2430 coin cell is assembled in an argon-protected glove box. At 25°C, the prepared coin cell was first discharged at a constant current of 0.05C to 0.005V, then discharged at a constant current of 10μA to 0.005V, and allowed to stand for 5 minutes. The first discharge capacity of the coin cell was recorded. Subsequently, it was charged at a constant current of 0.1C to 2.0V, and the charging capacity of the coin cell was recorded. The ratio of the charging capacity of the coin cell to the mass of the graphite anode active material sample is the specific capacity of the graphite anode active material.

[0134] 6. Compaction density test of negative electrode film layer The negative electrode sample with area S was weighed using an electronic balance, and the weight was recorded as W1. The thickness T1 of the negative electrode was measured using a micrometer. Then, the electrode film was wiped off, and the weight of the negative current collector was measured, recorded as W2. The thickness T2 of the negative current collector was measured using a micrometer. The compaction density PD of the negative electrode film is then calculated as follows: (W1...) W2) / [(T1-T2)×S].

[0135] 7. High-temperature cycling performance test At 60°C, the batteries of the above embodiments and comparative examples were charged at a constant current of 1C to a voltage of 3.65V, then charged at a constant voltage of 3.65V until the current was ≤0.05C. The batteries were then discharged at a constant current of 1C to a voltage of 2.5V. This constitutes one charge-discharge cycle, and the discharge capacity C1 of the first cycle was recorded. This charge-discharge cycle was repeated until the battery capacity decreased to 80% of the initial capacity C1. The test was then stopped, and the number of test cycles was recorded.

[0136] 8. Dark Spot Test At 25°C, the batteries of the above embodiments and comparative examples were charged at a constant current of 0.33C to a voltage of 3.65V, and then disassembled in a drying room to observe whether there were black spots on the surface of the negative electrode. (1) The total area of ​​black spots / the total area of ​​negative electrode plates ≤ 1%, and the area of ​​black spots in a single electrode plate / the area of ​​a single electrode plate ≤ 8% is defined as a first-level black spot; (2) 1% < total area of ​​black spots / total area of ​​negative electrode ≤ 3%, or 8% < area of ​​black spots in a single electrode / area of ​​a single electrode ≤ 15% is defined as a secondary black spot; (3) If the total area of ​​black spots / the total area of ​​negative electrode is greater than 3%, or if the area of ​​black spots in a single electrode / the area of ​​a single electrode is greater than 15%, it is defined as a third-degree black spot.

[0137] 9. Dynamic performance testing At 25°C, the secondary battery was charged at a constant current of 0.33C to 3.65V, then charged at a constant voltage to a current of 0.05C. After standing for 5 minutes, the secondary battery was discharged at a constant current of 0.33C to 2.50V, and its actual capacity was recorded as C0.

[0138] Then, the secondary battery was sequentially charged at constant currents of 1.0 C0, 1.3 C0, 1.5 C0, 1.8 C0, 2.0 C0, 2.3 C0, 2.5 C0, and 3.0 C0 until it reached a negative electrode cutoff potential of 3.5 V or 0 V (whichever comes first). After each charge, it was discharged to 2.5 V at 1 C0. The negative electrode potentials corresponding to 10%, 20%, 30%, ..., 80% SOC (State of Charge) were recorded at different charging rates. The charging rate-negative electrode potential curves under different SOC states were plotted. After linear fitting, the charging rate corresponding to a negative electrode potential of 0 V under different SOC states was obtained. This charging rate is the charging window under that SOC state, denoted as C. 10%SOC C 20%SOC C 30%SOC C 40%SOC C 50%SOC C 60%SOC C 70%SOC C 80%SOC According to the formula (60 / C) 10%SOC +60 / C 20%SOC + 60 / C 30%SOC + 60 / C 40%SOC + 60 / C 50%SOC + 60 / C 60%SOC + 60 / C 70%SOC + 60 / C 80%SOC The charging time T (assuming no lithium plating) from 10% SOC to 80% SOC is calculated by multiplying the value by 10%. The unit is minutes. The shorter the charging time, the better the fast-charging performance of the secondary battery.

[0139] II. Preparation methods of negative electrode active materials 1. Preparation of negative electrode active material H1 Petroleum coke, comprising 67% of the material with an embedded and zoned structure, was coarsely crushed. The coarsely crushed material was then further crushed and sieved. The sieved material was then shaped and classified. During the classification process, the induced draft frequency of the classifier was controlled to remove fine powder (particles with a volumetric particle size distribution Dv50 of 3μm-7μm) accounting for 25% of the total mass of the petroleum coke raw material, thus obtaining the precursor. The precursor had a volumetric particle size distribution Dv50 of 15.2μm and a particle size distribution (Dv90-Dv10) / Dv50 ratio of 1.45.

[0140] The precursor was graphitized in an Atchison furnace at a temperature of 2800°C and a maximum power of 21000W. After maintaining the maximum power for 48 hours, the surface temperature of the graphite crucible in the Atchison furnace was cooled to 250°C to obtain the intermediate product. The obtained intermediate product was sieved and demagnetized to obtain the negative electrode active material graphite H1.

[0141] 2. Preparation of negative electrode active material H2 The preparation process of the negative electrode active material H2 is similar to that of H1, with the following differences: Using the same raw materials, the material undergoes crushing, shaping, and grading processes, without removing fine powder during grading. After the same graphitization and sieving demagnetization processes, the negative electrode active material H2 is obtained.

[0142] 3. Preparation of negative electrode active material H3 The preparation process of the negative electrode active material H3 is similar to that of H1, with the following differences: During the grading process, 16% of the fine powder, which accounts for 16% of the total mass of the petroleum coke raw material, is removed. After the same graphitization and sieving demagnetization process, the negative electrode active material H3 is obtained.

[0143] 4. Preparation of negative electrode active material H4 The preparation process of the negative electrode active material H4 is similar to that of H1, with the following differences: During the grading process, 20% of the fine powder, which accounts for 20% of the total mass of the petroleum coke raw material, is removed. After the same graphitization and sieving demagnetization process, the active material H4 is obtained.

[0144] 5. Preparation of negative electrode active material H5 The preparation process of the negative electrode active material H5 is similar to that of H1, with the following differences: During the grading process, fine powder accounting for 35% of the total mass of petroleum coke raw material is removed. After undergoing the same graphitization and sieving demagnetization processes, active material H5 is obtained.

[0145] The above method was used to test the negative electrode active materials H1-H5, and the parameter test results are shown in Table 1: Table 1

[0146] III. Preparation of Secondary Batteries Example 1 1) Preparation of negative electrode sheet The prepared negative electrode active material, conductive agent carbon black Super P, thickener sodium carboxymethyl cellulose, and binder styrene-butadiene rubber were mixed at a mass ratio of 96:1:1.2:1.8. Deionized water was added as a solvent, and the mixture was stirred under vacuum until homogeneous to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated onto a copper foil current collector, and after drying, cold pressing, and slitting, negative electrode sheets were obtained. The compacted density of the negative electrode sheets was 1.50 g / cm³. 3 The areal density is 9.50 mg / cm³. 2 .

[0147] 2) Preparation of positive electrode sheet Lithium iron phosphate (LFP) as the positive electrode active material, Super P as the conductive agent, and polyvinylidene fluoride as the binder were mixed at a mass ratio of 97:1:2. N-methylpyrrolidone as the solvent was added, and the mixture was stirred under vacuum until homogeneous to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated onto an aluminum foil current collector, and then dried, cold-pressed, and slit to obtain the positive electrode sheet. The compacted density of the positive electrode sheet was 2.5 g / cm³. 3 Its surface density is 19.5 mg / cm³. 2 .

[0148] 4) Preparation of electrolyte In an argon atmosphere glove box with a water content of <10 ppm, 8% lithium hexafluorophosphate (LiPF6), 2% vinylene carbonate (VC), 30% ethylene carbonate (EC), 30% ethyl methyl carbonate (EMC), and the remainder is supplemented with diethyl carbonate (DEC) to 100% by mass percentage of the electrolyte to obtain the corresponding electrolyte.

[0149] 5) Separating membrane Polypropylene film was selected as the separator.

[0150] 6) Preparation of secondary batteries 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 cells are then wound to obtain a bare cell. The bare cell is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a lithium-ion battery is obtained.

[0151] Examples 2-6 and Comparative Examples 1-4 The preparation methods of the secondary batteries in Examples 2-6 and Comparative Examples 1-4 are similar to those in Example 1, but the negative electrode active material and the secondary battery preparation parameters were adjusted. The results of testing the secondary batteries prepared in Examples 1-6 and Comparative Examples 1-4 using the above methods are shown in Table 2 below: Table 2

[0152] As shown in Examples 1-6, the powder conductivity σ of the negative electrode active material is greater than or equal to 80 S / cm and less than or equal to 106 S / cm, and the compaction density of the negative electrode film is 1.35 g / cm³. 3 -1.50g / cm 3 At the same time, it effectively improved the black spot phenomenon, and the secondary battery also has a good cycle count and charging time.

[0153] Examples 1-2 and Comparative Example 1 show that the compaction density of the negative electrode film is less than 1.35 g / cm³. 3 At this time, the electrical contact between the negative electrode active material particles deteriorates and the energy density of the secondary battery is low, resulting in a reduction in the number of cycles of the secondary battery and an aggravation of the black spot phenomenon. Figure 7 Cycling curves for Example 2 and Comparative Example 1 are shown. It can be seen that the cycling performance of the secondary battery in Example 2 is significantly better than that in Comparative Example 1.

[0154] Examples 1-2 and Comparative Example 2 show that the compaction density of the negative electrode film is higher than 1.50 g / cm³. 3 When the electrical contact between the active materials in the negative electrode film is improved, the black spot phenomenon can be improved; however, the increased compaction density leads to a significant deterioration in kinetics, a significant increase in charging time, and consequently, rapid decay in the later stages of cycling, which reduces the cycle performance of the secondary battery.

[0155] As can be seen from Examples 1-6 and Comparative Example 3, the negative electrode active material in Comparative Example 3 contains a large amount of fine powder, resulting in a powder conductivity σ of less than or equal to 80 S / cm. Although the fine powder in the active material can improve the electrical contact between the active materials, too much fine powder will block the channels, significantly prolong the charging time, and thus lead to rapid decay in the later stage of the cycle, affecting the cycle performance of the secondary battery.

[0156] As can be seen from Examples 1-6 and Comparative Example 4, the negative electrode active material in Comparative Example 4 has a lower content of fine powder, resulting in a powder conductivity σ greater than 106 S / cm. This leads to poorer electrical contact and conductive network between negative electrode active materials, increased irreversible consumption of active ions in the secondary battery, and affects the charge-discharge performance and capacity of the secondary battery. Consequently, the number of cycles is significantly reduced, and severe black spot phenomenon occurs.

[0157] 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 comprising a negative electrode sheet including a negative electrode current collector and a negative electrode film layer provided on at least one surface of the current collector and including a negative electrode active material, characterized in that, The negative active material has a powder conductivity σ of 80 S / cm to 106 S / cm measured under the test conditions of a compaction density of 1.5 g / cm 3 ; and the negative electrode film layer has a compaction density of 1.35 g / cm 3 -1.50 g / cm 3 .

2. The secondary battery according to claim 1, characterized by the powder conductivity σ is 83 S / cm to 104 S / cm.

3. The secondary battery according to claim 1 or 2, characterized by The compaction density of the negative electrode film layer is 1.40 g / cm 3 -1.50 g / cm 3 .

4. The secondary battery according to any one of claims 1 to 3, characterized by the negative electrode active material satisfies at least one of the following conditions: (1) the volume distribution particle diameter Dv of the negative electrode active material V 1 is 1.4 μm to 3.0 μm, and can be selected from 1.7 μm to 2.7 μm; (2) the volume distribution particle diameter D of the negative electrode active material V 50 is 12 μm - 18 μm, optionally 12.9 μm - 14.5 μm; (3) the particle size distribution (D V 90-D V 10) / D V 50 is 1.3-1.8, optionally 1.35-1.

70.

5. The secondary battery according to any one of claims 1 to 4, characterized by tap density of the negative active material is 1.25 g / cm 3 -1.45 g / cm 3 , optionally 1.29 g / cm 3 -1.41 g / cm 3 .

6. The secondary battery according to any one of claims 1 to 5, characterized by The negative active material has a specific surface area of 0.8 m 2 / g-1.4 m 2 / g, optionally 0.9 m 2 / g-1.3 m 2 / g.

7. The secondary battery according to any one of claims 1 to 6, characterized by, the gravimetric capacity of the negative electrode active material is 335 mAh / g to 350 mAh / g, optionally 340.5 mAh / g to 347.5 mAh / g.

8. The secondary battery according to any one of claims 1 to 7, characterized by, The areal density of the negative electrode sheet is 7 mg / cm 2 - 15 mg / cm 2 .

9. The secondary battery according to any one of claims 1 to 8, characterized by, the negative electrode active material includes artificial graphite.

10. An electrical device, characterized by a secondary battery including the negative electrode sheet according to any one of claims 1 to 9.

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