Battery and preparation method therefor, and electric device

Abstract

A battery and a preparation method therefor, and an electric device. The battery comprises a positive electrode sheet, a negative electrode sheet, and an isolating membrane. The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer located at least on one side of the negative electrode current collector. The negative electrode active material layer comprises a negative electrode active material, and the negative electrode active material comprises graphite. The proportion of the number of secondary particles in the negative electrode active material is greater than or equal to 65%, and the oil absorption value of the negative electrode active material is 40 mL / 100g - 65 mL / 100g. The volume distribution particle diameter Dv1 of the negative electrode active material is 4-8 μm.

Description

Batteries and their manufacturing methods, and electrical devices Technical Field

[0001] This disclosure relates to the field of battery technology, specifically to batteries and their preparation methods, and electrical devices. Background Technology

[0002] Batteries are widely used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, and electric vehicles. With the expanding application range of batteries, the market is placing higher demands on their rate performance. However, current batteries still have many shortcomings in their production and application, and their rate performance needs further improvement.

[0003] It should be noted that the above statements are only used to provide background information related to this application and do not necessarily constitute prior art.

[0004] Application content

[0005] In a first aspect, this application proposes a battery comprising a positive electrode, a negative electrode, and a separator. The negative electrode includes a negative current collector and a negative active material layer located at least on one side of the negative current collector. The negative active material layer comprises a negative active material, which includes graphite. The negative active material contains secondary particles comprising at least 65% of its content, has an oil absorption value of 40 mL / 100g-65 mL / 100g, and a volume distribution particle size Dv1 of 4 μm-8 μm. This significantly improves the rate performance and processing performance of the negative active material, thus contributing to improved battery rate performance.

[0006] In some embodiments, the negative electrode active material satisfies (Dv90-Dv10) / Dv50 of 0.8-1.2. This improves the kinetic performance of the negative electrode active material.

[0007] In some embodiments, the volumetric particle size distribution Dv10 of the negative electrode active material is 7 μm-11 μm, and / or the volumetric particle size distribution Dv90 of the negative electrode active material is 20 μm-30 μm, and / or the volumetric particle size distribution Dv50 of the negative electrode active material is 12 μm-18 μm. This can further improve the rate performance of the negative electrode active material.

[0008] In some embodiments, the graphitization degree of the negative electrode active material is 93%-95%. This improves the electronic conductivity of the negative electrode active material.

[0009] In some embodiments, the specific surface area of ​​the negative electrode active material is 2.5 m². 2 / g-3.5m 2 / g. This allows for further improvement in the processing performance of the negative electrode active material.

[0010] In some embodiments, the negative electrode active material further includes a carbon coating layer, which is located at least on a portion of the surface of the secondary particles, the secondary particles being formed by bonding at least two primary particles together, the bonding material being a carbon material. This improves the conductivity of the negative electrode active material.

[0011] In some embodiments, the porosity of the negative electrode active material layer is 18%-35%. This facilitates the wetting of the negative electrode sheet by the electrolyte.

[0012] In some embodiments, the compaction density of the negative electrode active material layer is 1.60 g / cm³. 3 -1.75g / cm 3 This facilitates the wetting of the negative electrode by the electrolyte.

[0013] In a second aspect of this application, a method for preparing the aforementioned battery is proposed, comprising: mixing primary graphite particles with a binder and subjecting them to a first heat treatment to obtain pre-bonded secondary particles; subjecting the pre-bonded secondary particles to a second heat treatment and a first classification treatment to obtain secondary particles, thereby obtaining a negative electrode active material; disposing the negative electrode active material on one side of a negative electrode current collector to obtain a negative electrode sheet; and assembling the negative electrode sheet, a separator, and a positive electrode sheet to obtain a battery. Thus, the aforementioned battery with superior rate performance can be prepared using a simple method.

[0014] In some embodiments, providing the primary graphite particles includes: subjecting the raw material to a crushing and second-grading process to obtain the primary graphite particles, wherein the raw material includes at least one of petroleum coke and needle coke; the provision of the primary graphite particles satisfies at least one of the following conditions: the volatile matter content of the raw material is 4%-7%; the true density of the raw material is 1.35 g / cm³. 3 -1.50g / cm 3 The sulfur content of the raw material is less than or equal to 2%; the feeding frequency of the crushing process is 10Hz-35Hz; and the grading frequency of the second grading process is 30Hz-50Hz. This improves the particle size uniformity of the primary graphite particles.

[0015] In some embodiments, the adhesive comprises at least one of bitumen and resin, and the adhesive satisfies at least one of the following conditions: the coking value of the adhesive is 60%-70%; the mass ratio of the adhesive to the primary graphite particles is (7-10):100; and the particle size of the adhesive is 4μm-8μm. This improves the adhesion effect of the adhesive to the primary graphite particles.

[0016] In some embodiments, the temperature of the first heat treatment is 600°C-800°C, and the duration of the first heat treatment is 1 hour-4 hours. This helps to improve the pre-bonding of the adhesive to the primary graphite particles.

[0017] In some embodiments, the temperature of the second heat treatment is 2800℃-3300℃, and the duration of the second heat treatment is 36h-72h. This helps to improve the adhesion of the adhesive to the primary graphite particles.

[0018] In some embodiments, the first grading process satisfies at least one of the following conditions: the sieve mesh size of the first grading process is 300-350 mesh; the feed frequency of the first grading process is 4Hz-10Hz; and the grading frequency of the first grading process is 30Hz-50Hz. This effectively removes fine powder from the secondary particles.

[0019] In some embodiments, obtaining the secondary particles further includes: mixing the secondary particles with a liquid-phase coating agent and subjecting them to a third heat treatment to form a carbon coating layer on a portion of the surface of the secondary particles, wherein the liquid-phase coating agent comprises at least one of asphalt and resin with a viscosity less than or equal to 500 mPa·s. This allows a carbon coating layer to be formed on the surface of the secondary particles.

[0020] In some embodiments, the mass ratio of the liquid coating agent to the secondary particles is (2-10):100, and / or the coking value of the liquid coating agent is 40%-70%. This helps the negative electrode active material to possess both superior rate performance and specific capacity.

[0021] In some embodiments, the temperature of the third heat treatment is 1000℃-1200℃, and the duration of the third heat treatment is 15h-30h. This helps to form an amorphous carbon coating layer.

[0022] In a third aspect, this application proposes an electrical device comprising the aforementioned battery, and / or a battery prepared using the aforementioned method. Thus, the electrical device possesses all the features and advantages of the aforementioned battery and preparation method, which will not be repeated here. Attached Figure Description

[0023] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0024] Figure 1 is a schematic diagram of a battery cell according to an embodiment of this application;

[0025] Figure 2 is an exploded view of a battery cell according to an embodiment of this application shown in Figure 1;

[0026] Figure 3 is a schematic diagram of a battery module according to an embodiment of this application;

[0027] Figure 4 is a schematic diagram of a battery pack according to an embodiment of this application;

[0028] Figure 5 is an exploded view of a battery pack according to an embodiment of this application shown in Figure 4;

[0029] Figure 6 is a schematic diagram of an electrical device using a battery as a power source according to an embodiment of this application;

[0030] Figure 7 is a scanning electron microscope image of the negative electrode active material according to an embodiment of this application;

[0031] Figure 8 is a scanning electron microscope image of a comparative example of the negative electrode active material of this application;

[0032] Figure 9 is a scanning electron microscope image of the negative electrode active material of one embodiment of this application.

[0033] Explanation of reference numerals in the attached diagram: 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0034] The embodiments of this application are described in detail below, with examples of these embodiments shown in the accompanying drawings. 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 to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0035] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in this application is for the purpose of describing particular embodiments only and is not intended to limit this application; unless otherwise stated, the values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0036] The terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are open-ended expressions, meaning they include what is specified in this application but do not exclude other aspects.

[0037] In the description of this application, all figures disclosed herein, whether or not the words "approximately" or "about" are used, are approximate values. Each figure may vary by less than 10% or by a difference that is considered reasonable by one of the art, such as 1%, 2%, 3%, 4%, or 5%.

[0038] 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.

[0039] In the description of this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. "First feature" and "second feature" may include one or more of the indicated feature.

[0040] In the description of this application, "A and / or B" can include any of the cases of A alone, B alone, or A and B, where A and B are merely examples and can be any technical feature connected by "and / or" in this application.

[0041] In this application, the order in which the steps are written does not imply a strict execution order and does not limit the implementation process. The specific execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps in this application can be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) can 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.

[0042] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0043] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0044] Taking graphite as an example of anode active material, when graphite is a secondary particle, since the secondary particles are isotropic, they have more lithium-ion transport channels, which can effectively increase the lithium-ion insertion / extraction entrance of the anode active material, improve the lithium-ion interface reaction, increase the lithium-ion migration rate, and thus improve the rate performance of the anode active material. In addition, the expansion force generated during the lithium insertion process of the anode active material can be released in multiple directions, thereby reducing the thickness change of the anode sheet during charging and correspondingly reducing battery expansion.

[0045] Specifically, primary graphite particles can be bonded together to obtain secondary graphite particles. However, when primary graphite particles are bonded together with an adhesive, the surface of the secondary graphite particles develops numerous uneven structures. These structures have a strong adsorption force on dispersants, causing a large amount of dispersant from the negative electrode slurry to be adsorbed onto the surface of the secondary particles. This blocks the lithium intercalation / deintercalation channels on the graphite surface, resulting in less free dispersant in the negative electrode slurry and poor stability. Consequently, the negative electrode active material exhibits a high oil absorption value. Furthermore, filtration is required before coating the negative electrode slurry to remove impurities. The uneven structures on the surface of the secondary particles make it difficult for graphite to be completely dispersed in the negative electrode slurry, reducing its stability and preventing it from meeting filtration requirements.

[0046] To compensate for the excessive adsorption of dispersant by the negative electrode active material with a large oil absorption value and to achieve uniform dispersion of the negative electrode slurry, more dispersant needs to be added to the negative electrode slurry. However, since the dispersant itself does not have the function of lithium intercalation / deintercalation, the proportion of negative electrode active material that can provide lithium intercalation / deintercalation sites in the negative electrode slurry will decrease. Consequently, the proportion of negative electrode active material in the negative electrode active material layer formed by the negative electrode slurry coating will decrease accordingly, ultimately resulting in poor specific capacity of the negative electrode sheet.

[0047] In this application, when the proportion of secondary particles in the negative electrode active material is greater than or equal to 65%, the relatively high proportion of secondary particles in the negative electrode active material can effectively improve the rate performance of the negative electrode active material and reduce the volume expansion rate of the negative electrode active material during charge and discharge. Furthermore, during the process of graphite primary particles bonding to form graphite secondary particles, small-diameter fine powder easily forms a protruding structure on the surface of the secondary particles, resulting in an excessively high oil absorption value of the negative electrode active material. When the Dv1 particle size of the negative electrode active material is 4μm-8μm, there are very few fine powder particles with a particle size less than 3μm in the negative electrode active material, which helps to reduce the oil absorption value of the negative electrode active material. When the oil absorption value of the active material is controlled within an appropriate range, the oil absorption value of the negative electrode active material can be 40mL / 100g-65mL / 100g. The number and proportion of the uneven structure on the surface of the negative electrode active material are moderate. When the amount of binder in the negative electrode slurry is small, the negative electrode active material still has good dispersibility in the negative electrode slurry. The processing performance of the negative electrode slurry is better, and only a small amount of dispersant is needed in the negative electrode slurry. There is no need to increase the dispersant content in the negative electrode slurry, which can reduce the manufacturing cost of the negative electrode slurry, increase the proportion of negative electrode active material in the negative electrode slurry, and improve the kinetic performance of the negative electrode sheet.

[0048] As an example, the negative electrode active material can be prepared by the following method: the raw material is subjected to pulverization and second classification to obtain the graphite primary particles; the graphite primary particles are mixed with a binder and subjected to a first heat treatment to obtain pre-bonded secondary particles; the pre-bonded secondary particles are subjected to a second heat treatment and a first classification to obtain secondary particles; the secondary particles are mixed with a liquid phase coating agent and subjected to a third heat treatment to form a carbon coating layer on a portion of the surface of the secondary particles, thereby obtaining the negative electrode active material.

[0049] In some embodiments, the particle size uniformity and surface roundness of the negative electrode active material can be controlled by crushing, shaping, and grading the raw materials. For example, when the main frequency of the crushing process is moderate, the particle size of the crushed particles is moderate; when the main frequency of the shaping process is moderate, the surface morphology of the particles is relatively round and the particle size is moderate; when the frequency of the grading process is moderate, the particle size uniformity is high. Specifically, after crushing the centimeter-sized raw coke raw material into micron-sized raw material, the crushed small-particle-size raw material can be graded and screened through a second grading process to remove fine powder with excessively small particle size from the raw material, reducing the self-agglomeration of fine powder impurities due to their small size and the formation of protruding structures. Furthermore, a shaping process can be performed between the crushing process and the second grading process, thereby reducing the aspect ratio of graphite particles, increasing their sphericity, improving the particle shape, particle size distribution, and surface characteristics of the primary particle powder, and improving the particle size uniformity of the primary graphite particles.

[0050] In some implementations, the first grading process can effectively screen out and remove fine powder from the secondary particulate powder, effectively reducing the formation of protruding surfaces during subsequent surface coating, thereby reducing the oil absorption value of the negative electrode active material.

[0051] In some embodiments, the liquid phase coating agent has the advantages of good fluidity, more uniform spreading on the surface of secondary particles, fewer surface protrusions, and better coverage of the surface of secondary particles. This helps to reduce the formation of protruding surfaces during the coating process, thereby reducing the oil absorption value of the negative electrode active material.

[0052] In this application, "oil absorption value of the negative electrode active material" has a meaning known in the art and can be determined using instruments and methods known in the art. For example, the oil absorption value can be obtained based on the amount of dibutyl phthalate used when the mixture of the negative electrode active material and dibutyl phthalate changes from a free-flowing state to a semi-plastic agglomerate. Specifically, 100g of negative electrode active material is placed at the feeding port of the oil absorption value tester, and dibutyl phthalate is automatically titrated onto the negative electrode active material until the negative electrode active material becomes a semi-plastic agglomerate. The amount of dibutyl phthalate added at this time (a mL) is recorded, thereby obtaining the oil absorption value of the negative electrode active material as a mL / 100g.

[0053] In this application, "the proportion of secondary particles in the negative electrode active material" has a meaning known in the art and can be determined using instruments and methods known in the art. For example, it can be determined using a scanning electron microscope. As an example, the method for testing the proportion of secondary particles can be as follows: the negative electrode active material is laid and adhered to conductive adhesive to form a sample to be tested with a length × width of 6cm × 1.1cm; the particle morphology is tested using a scanning electron microscope (such as ZEISS Sigma 300). The test can be referred to JY / T010-1996. To ensure the accuracy of the test results, multiple (e.g., 20) different regions can be randomly selected in the sample to be tested for scanning, and at a certain magnification (e.g., 1000x), the percentage of secondary particles in each test region relative to the total number of particles is calculated, which is the proportion of secondary particles in that region. The average of the test results of multiple test regions is taken as the proportion of secondary particles in the negative electrode active material.

[0054] In some embodiments, the negative electrode active material layer on the surface of the negative electrode sheet can be removed by a scraping process, and the binder, conductive agent, dispersant, and other substances in the negative electrode active material can be removed by calcination in a muffle furnace to obtain negative electrode active material powder. Further, the proportion of secondary particles can be calculated as follows: (a) the aforementioned negative electrode active material powder is uniformly dispersed on a conductive tape substrate using a vacuum negative pressure sputtering method; (b) 50 high-speed images are taken using the mapping function of a scanning electron microscope (such as a Thermo Scientific Apreo 2 S); (c) the particles in each image are automatically labeled using AI technology to obtain the number of primary and secondary particles, and the results are statistically analyzed to calculate the proportion of secondary particles. A secondary particle is defined as two or more particles stacked together. For example, a secondary particle can be a stack of multiple particles with different diameters (see ① in Figure 9), a stack of multiple particles with similar diameters (see ② in Figure 9), or a stack of multiple smaller particles on the surface of a larger particle (see ③ in Figure 9).

[0055] In a first aspect, this application proposes a battery comprising a positive electrode, a negative electrode, and a separator. The negative electrode includes a negative current collector and a negative active material layer located at least on one side of the negative current collector. The negative active material layer comprises a negative active material, which includes graphite. The negative active material contains secondary particles comprising at least 65% of its content, has an oil absorption value of 40 mL / 100g-65 mL / 100g, and a volume distribution particle size Dv1 of 4 μm-8 μm. This significantly improves the rate performance and processing performance of the negative active material, thus contributing to improved battery rate performance.

[0056] When the proportion of secondary particles in the negative electrode active material is greater than or equal to 65%, the number of lithium ion insertion / extraction channels in the negative electrode active material can be significantly increased, thereby improving the rate performance of the negative electrode active material. When the oil absorption value of the negative electrode active material is 40mL / 100g-65mL / 100g, the surface of the negative electrode active material has fewer uneven structures, and only a small amount of dispersant is needed to achieve uniform dispersion of the negative electrode active material, resulting in better processing performance of the negative electrode active material.

[0057] As an example, the percentage of secondary particles in the negative electrode active material can be 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100%.

[0058] It is understandable that a higher proportion of secondary particles in the negative electrode active material results in better kinetics. When the negative electrode active material consists entirely of secondary particles, its kinetic performance is optimal. In this case, the proportion of binder used to bond adjacent primary particles is relatively high. Since the binder itself can only serve as a lithium-ion intercalation / deintercalation channel and cannot act as an intercalation / deintercalation site, the negative electrode active material exhibits high kinetic performance and relatively low specific capacity. Those skilled in the art can adjust the proportion of secondary particles in the negative electrode active material according to actual conditions.

[0059] The proportion of secondary particles in the negative electrode active material is affected by the content and particle size of the binder in the negative electrode active material. Specifically, when the content of binder in the negative electrode active material is high, the bonding between the primary graphite particles is more sufficient, and the proportion of secondary particles in the negative electrode active material is higher. Furthermore, when the particle size of the binder is small, the binder can provide more adhesive surface, resulting in more effective bonding between the primary particles, and the proportion of secondary particles in the negative electrode active material is higher.

[0060] In some embodiments, the mass ratio of the adhesive to the primary graphite particles is (7-10):100. In other embodiments, the particle size of the adhesive is 4 μm-8 μm.

[0061] As an example, the oil absorption value of the negative electrode active material can be 40mL / 100g, 41mL / 100g, 42mL / 100g, 43mL / 100g, 44mL / 100g, 45mL / 100g, 46mL / 100g, 47mL / 100g, 48mL / 100g, 49mL / 100g, 50mL / 100g, 51mL / 100g, 52mL / 100g, 53mL / 100g, 54mL / 100g, 55mL / 100g, 56mL / 100g, 57mL / 100g, 58mL / 100g, 59mL / 100g, 60mL / 100g, 61mL / 100g, 62mL / 100g, 63mL / 100g, 64mL / 100g, or 65mL / 100g.

[0062] When the oil absorption value of the negative electrode active material is 40mL / 100g-65mL / 100g, the negative electrode active material has both superior kinetic performance and superior specific capacity.

[0063] In some embodiments, the negative electrode active material includes graphite, wherein the proportion of secondary particles in the graphite is greater than or equal to 65%, and the oil absorption value of the graphite is 40mL / 100g-65mL / 100g.

[0064] In some embodiments, the volume distribution particle size Dv1 of the negative electrode active material is 4μm-8μm.

[0065] During the process of forming secondary particles through primary particle bonding, fine powder with small particle size tends to form protrusions on the surface of secondary particles, resulting in excessively high oil absorption value of the negative electrode active material. When the Dv1 particle size of the negative electrode active material is 4μm-8μm, it indicates that there are very few fine powder particles with a particle size of less than 3μm in the negative electrode active material, which helps to control the oil absorption value of the negative electrode active material within an appropriate range and can further improve the processing performance of the negative electrode active material.

[0066] The aforementioned Dv1 particle size refers to the particle size corresponding to a cumulative volume distribution percentage of 1%.

[0067] In some embodiments, the negative electrode active material satisfies (Dv90-Dv10) / Dv50 of 0.8-1.2. This improves the kinetic performance of the negative electrode active material.

[0068] As an example, (Dv90-Dv10) / Dv50 can be 0.8, 0.85, 0.9, 0.95, 1, 1.05, 1.1, 1.15, or 1.2.

[0069] When the negative electrode active material satisfies (Dv90-Dv10) / Dv50 of 0.8-1.2, on the one hand, the particle size distribution of the negative electrode active material is better, the tortuosity of the lithium ion intercalation / deintercalation channel is lower, the transport path is shorter, and the negative electrode active material has better kinetic performance. On the other hand, the tap density of the negative electrode active material is also affected by the particle size distribution range. When the particle size distribution of the negative electrode active material is within the above range, there are fewer small-diameter particles in the negative electrode active material, and less agglomeration between small-diameter particles. This effectively reduces the number of large particles formed by the agglomeration of small-diameter particles, so that the negative electrode active material includes a moderate number of particles of different sizes, and the tap density is significantly improved.

[0070] The aforementioned Dv10 particle size refers to the particle size corresponding to a cumulative volume distribution percentage of 10%.

[0071] The aforementioned Dv50 particle size refers to the particle size corresponding to a cumulative volume distribution percentage of 50%.

[0072] The aforementioned Dv90 particle size refers to the particle size corresponding to a cumulative volume distribution percentage of 90%.

[0073] In some embodiments, the volumetric particle size distribution Dv10 of the negative electrode active material is 7 μm-11 μm, and / or the volumetric particle size distribution Dv90 of the negative electrode active material is 20 μm-30 μm, and / or the volumetric particle size distribution Dv50 of the negative electrode active material is 12 μm-18 μm. This can further improve the rate performance of the negative electrode active material.

[0074] As an example, the volume distribution particle size Dv10 of the negative electrode active material can be 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm or 11 μm.

[0075] As an example, the volume distribution particle size Dv50 of the negative electrode active material can be 12μm, 12.5μm, 13μm, 13.5μm, 14μm, 14.5μm, 15μm, 15.5μm, 16μm, 16.5μm, 17μm, 17.5μm or 18μm.

[0076] As an example, the volume distribution particle size Dv90 of the negative electrode active material can be 20 μm, 20.5 μm, 21 μm, 21.5 μm, 22 μm, 22.5 μm, 23 μm, 23.5 μm, 24 μm, 24.5 μm, 25 μm, 25.5 μm, 26 μm, 26.5 μm, 27 μm, 27.5 μm, 28 μm, 28.5 μm, 29 μm, 29.5 μm, or 30 μm.

[0077] The term "particle size" in this application has a meaning known in the art and can be determined using instruments and methods known in the art. For example, the particle size of the negative electrode active material can be determined using laser diffraction particle size analysis. Specifically, the particle size of the negative electrode active material can be determined using a laser particle size analyzer (e.g., Malvern Master Size 3000) in accordance with standard GB / T 19077-2016.

[0078] In some embodiments, taking graphite as an example, the OI value of the powder of the negative electrode active material can be 2-7. This can improve the lithium-ion insertion / extraction rate of the negative electrode active material.

[0079] When graphite is made into a negative electrode sheet, the orientation of the graphite layered structure has a significant impact on lithium-ion migration. Since graphite can only intercalate and deintercalate lithium ions at its end faces, ideally, the end faces of the graphite material in the negative electrode active material are perpendicular to the surface of the negative electrode sheet, which is more conducive to lithium-ion diffusion. However, in actual preparation, it is difficult to precisely control the orientation of each graphite particle. The orientation of graphite on the negative electrode sheet can be tested by XRD. When performing diffraction pattern testing on a horizontally placed negative electrode sheet sample, the diffraction signal of the (110) crystal plane can be collected from the graphite in the negative electrode active material layer that is perpendicular to the surface of the negative electrode sheet. The diffraction signals of the (002) and (004) crystal planes come from the graphite in the negative electrode active material whose structure is parallel to the surface of the electrode sheet. Therefore, the orientation of the graphite electrode can be described by the ratio of the intensity (or integrated area) of the (002) or (004) diffraction peak to the intensity (or integrated area) of the (110) diffraction peak. The formula is described as: OI = I(002) / I(110) or OI = I(004) / I(110), where OI (orientation index) is the orientation of graphite in the negative electrode active material layer.

[0080] When the OI value of the powder of the negative electrode active material is 2-7, it is beneficial to improve the volume expansion and reaction kinetics of graphite, enhance the isotropy of graphite, effectively alleviate the volume expansion effect of the negative electrode sheet during cycling, and further improve the cycle performance of the battery.

[0081] As an example, the OI value can be 2, 3, 4, 5, 6, or 7.

[0082] In some embodiments, the graphitization degree of the negative electrode active material is 93%-95%. This improves the electronic conductivity of the negative electrode active material.

[0083] The degree of graphitization refers to the extent to which carbon atoms form a close-packed hexagonal graphite crystal structure. The closer the lattice size is to the lattice parameters of ideal graphite, the higher the degree of graphitization.

[0084] The "degree of graphitization" of the negative electrode active material has a well-known meaning in the art and can be tested using methods known in the art. For example, it can be tested using an X-ray diffractometer (such as a Bruker D8 Discover). Testing can be referenced in JIS K 0131-1996 and JB / T 4220-2011 to determine d... 002 The size is then determined according to the formula G = (0.344 - d). 002 The degree of graphitization is calculated by d / (0.344-0.3354)×100%, where d 002 This refers to the interlayer spacing in the graphite crystal structure, measured in nanometers (nm). In X-ray diffraction analysis, Cu Kα rays were used as the radiation source, with the ray wavelength scanning 2θ angle range of 20°–80° and a scanning rate of 4° / min.

[0085] When the degree of graphitization of the negative electrode active material is within the aforementioned range, the structure of the negative electrode active material is regular, there are fewer defects such as stacking faults and dislocations in the crystal, the resistance to electron migration is small, and the dynamic performance of the negative electrode active material is improved.

[0086] As an example, the degree of graphitization of the negative electrode active material can be 93%, 93.5%, 94%, 94.5%, or 95%.

[0087] In some embodiments, the specific surface area of ​​the negative electrode active material is 2.5 m². 2 / g-3.5m 2 / g. This allows for further improvement in the processing performance of the negative electrode active material.

[0088] Specific surface area refers to the surface area of ​​a unit mass of material. The smaller the particle size of the negative electrode active material, the larger the specific surface area. Correspondingly, there are more channels and shorter paths for lithium ion migration, resulting in better rate performance. However, this also requires more dispersant for dispersion; that is, the larger the specific surface area of ​​the negative electrode active material, the greater its oil absorption value. When the specific surface area of ​​the negative electrode active material is within the aforementioned range, the negative electrode active material has both excellent rate performance and relatively low oil absorption value, eliminating the need for excessive addition of dispersant during the preparation of the negative electrode slurry.

[0089] It is understandable that the specific surface area is affected by the particle size distribution of the material. When the particle size of the negative electrode active material meets the aforementioned limit, the specific surface area within the above range can be obtained.

[0090] The "specific surface area" of negative electrode active materials is a well-known concept in the art and can be tested using methods known in the art. For example, a Gemini VII 2390 multi-station fully automated specific surface area and porosity analyzer can be used. Approximately 7g of the negative electrode active material sample can be placed in a 9cc long tube with a bulb, degassed at 150°C for 15 minutes, and then placed in the main unit for testing to obtain BET data.

[0091] In some embodiments, the negative electrode active material further includes a carbon coating layer, which is located at least on a portion of the surface of the secondary particles, the secondary particles being formed by bonding at least two primary particles together, the bonding material being a carbon material. This improves the conductivity of the negative electrode active material.

[0092] The carbon coating layer can cover the active sites on the surface of the graphite secondary particles, reduce the occurrence of irreversible side reactions, reduce the specific surface area of ​​the negative electrode active material, isolate the graphite secondary particles from the electrolyte, reduce the direct contact between the secondary particles in the negative electrode active material and the electrolyte, and also restrict and buffer the volume expansion of graphite, thereby increasing the stability of the cycle.

[0093] As an example, the carbon coating layer can include amorphous carbon. Amorphous carbon coating layers have a larger interlayer spacing, which helps to improve the diffusion rate of lithium ions within the negative electrode active material, enhances the high-current charge and discharge capability, and improves the battery performance at high rates.

[0094] In some embodiments, the tap density of the negative electrode active material is 0.9 g / cm³. 3 -1.15g / cm 3 This can improve the processing performance of the negative electrode active material.

[0095] Tapped density refers to the mass per unit volume of powder in a container after it has been tapped under specified conditions, and is expressed in g / cm³. 3It is measured by a specialized tap density instrument.

[0096] When the tap density of the negative electrode active material is within the aforementioned range, the porosity in the negative electrode active material is appropriate, which is conducive to electrolyte wetting, thereby making it easier for lithium ions to embed inside the negative electrode active material and improving the rate performance.

[0097] Tap density can reflect the oil absorption value of negative electrode active material to a certain extent. When there are fewer uneven structures on the surface of negative electrode active material, the negative electrode active material can be more tightly attached. At this time, the tap density of negative electrode active material is larger, and the oil absorption value of negative electrode active material will also be lower due to fewer uneven structures.

[0098] It is understandable that tap density is affected by the particle size of the material. When the particle size of the negative electrode active material meets the aforementioned limit, the tap density within the above range can be obtained.

[0099] In some embodiments, the compaction density of the negative electrode active material at a pressure of 50,000 N is 1.75 g / cm³. 3 -1.85g / cm 3 This can increase the energy density of the negative electrode active material layer containing this negative electrode active material.

[0100] Secondary particles are formed by bonding primary particles together. Because the binder does not have lithium insertion / extraction sites, the specific capacity of secondary particles is slightly lower than that of primary particles, while their compaction density is higher. Generally, the higher the compaction density of the negative electrode active material, the higher the energy density of the battery. When the compaction density of the negative electrode active material with the aforementioned secondary particle ratio is within the aforementioned range under 50,000 N pressure, the thickness of the negative electrode sheet after rolling is smaller, the volumetric energy density of the battery is higher, and the porosity in the negative electrode sheet is preserved, which is beneficial for lithium ion insertion / extraction.

[0101] In some embodiments, the specific capacity of the negative electrode active material is 355 mAh / g-360.5 mAh / g. Therefore, the negative electrode active material has a high specific capacity.

[0102] Secondary particles are formed by bonding primary particles together. Since the binder does not have lithium insertion / extraction sites, it cannot contribute to the specific capacity. Therefore, the specific capacity of secondary particles is slightly lower than that of primary particles. When the specific capacity of the negative electrode active material is 355mAh / g-360.5mAh / g, the proportion of binder used to bond primary particles in the negative electrode active material is relatively small, and the negative electrode active material still has a high specific capacity.

[0103] In some embodiments, when the surface of the negative electrode active material has a carbon coating layer, the Id / Ig peak intensity ratio of the Raman spectrum of the negative electrode active material is 0.20-0.40.

[0104] In the Raman scattering analysis of the negative electrode active material, at a Raman shift of 1320 cm⁻¹ -1 -1410cm -1 and 1550cm -1 -1650cm -1 The positions of these positions exhibit scattering peaks. Specifically, in the Raman spectrum of the negative electrode active material, at a Raman shift of 1320 cm⁻¹, there are scattering peaks. -1 -1410cm -1 The position has a carbon D-band scattering peak (referred to as the D peak), at a Raman shift of 1550 cm⁻¹. -1 -1650cm -1 The position of the peak is the scattering peak of carbon in the G band (referred to as the G peak). The ratio of the peak intensity Id of the D peak to the peak intensity Ig of the G peak can reflect the degree of defects in the negative electrode active material. When the Id / Ig peak intensity ratio of the Raman spectrum of the negative electrode active material is within the aforementioned range, there are more defect sites on the surface of the negative electrode active material, which helps to improve the performance of the battery at high rates.

[0105] In some embodiments, the porosity of the negative electrode active material layer is 18%-35%. This facilitates the wetting of the negative electrode sheet by the electrolyte.

[0106] As an example, the porosity of the negative electrode active material layer can be 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, or 35%.

[0107] When the porosity of the negative electrode active material layer is within the aforementioned range, the negative electrode active material layer has more pores, which is beneficial for the electrolyte to wet the negative electrode sheet, exhibiting good ion transport characteristics, and the energy density of the negative electrode slurry is also higher.

[0108] In some embodiments, the compaction density of the negative electrode active material layer is 1.60 g / cm³. 3 -1.75g / cm 3 This facilitates the wetting of the negative electrode by the electrolyte.

[0109] As an example, the compaction density of the negative electrode active material layer can be 1.60 g / cm³. 3 1.61 g / cm 3 1.62g / cm 3 1.63g / cm 3 1.64 g / cm 3 1.65g / cm 3 1.66 g / cm 3 1.67 g / cm 31.68g / cm 3 1.69 g / cm 3 1.70g / cm 3 1.71g / cm 3 1.72g / cm 3 1.73g / cm 3 1.74 g / cm 3 Or 1.75g / cm 3 .

[0110] The compaction density of the negative electrode active material layer is related to the porosity of the negative electrode active material layer. When the compaction density of the negative electrode active material layer is within the aforementioned range, the porosity of the negative electrode active material layer can meet the aforementioned requirements.

[0111] In some embodiments, the areal density of the negative electrode active material layer is 5 mg / cm³. 2 -10mg / cm 2 .

[0112] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0113] 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.).

[0114] In some embodiments, in addition to the aforementioned negative electrode active material, the negative electrode active material layer may also contain negative electrode active materials known in the art for use in batteries.

[0115] As an example, the negative electrode active material may also include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. Silicon-based materials include at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials include at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0116] In some embodiments, the negative electrode active material layer may optionally include a binder. The binder includes at least one selected from 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).

[0117] In some embodiments, the negative electrode active material layer may optionally include a conductive agent. The conductive agent includes at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0118] In some embodiments, the negative electrode active material layer may optionally include a dispersant, such as sodium carboxymethyl cellulose (CMC-Na), polyacrylic acid, etc.

[0119] In a second aspect, this application proposes a method for preparing the aforementioned battery, thereby enabling the simple fabrication of a battery with superior rate performance. Specifically, the method for preparing the negative electrode active material includes:

[0120] S100: Graphite particles are mixed with a binder and subjected to a first heat treatment.

[0121] In some embodiments, the primary graphite particles are mixed with a binder in this step and subjected to a first heat treatment to obtain pre-bonded secondary particles.

[0122] As an example, primary graphite particles can be mixed with a binder and stirred and heated in a high-temperature reactor. After cooling, pre-bonded secondary particles are obtained. Furthermore, the pre-bonded secondary particles can be shaped to break up weakly bonded particles, reducing cracking and breakage during subsequent rolling processes.

[0123] In some embodiments, the method of obtaining primary graphite particles is not particularly limited. For example, providing the primary graphite particles may include: subjecting a raw material to a crushing process and a second classification process to obtain the primary graphite particles, wherein the raw material includes at least one of petroleum coke and needle coke.

[0124] The crushing process breaks down centimeter-sized raw materials into micron-sized raw materials. The second classification process further classifies and sieves the small-diameter raw materials to remove excessively small fine powder. Furthermore, a shaping process can be performed between the crushing and second classification processes, which can significantly reduce the aspect ratio of graphite particles and increase their sphericity. This enhances the mechanical properties and volume utilization of graphite, improves the particle shape, size distribution, and surface characteristics of primary graphite powder, and increases the uniformity of primary graphite particle size.

[0125] As an example, the second grading process may specifically include grading steps and screening steps.

[0126] As an example, the crushing, shaping, and second grading of raw materials can be carried out in a continuous process.

[0127] When the shaping process is performed at a moderate frequency, it can make the surface morphology of primary graphite particles more rounded and the primary graphite particles of appropriate size.

[0128] In some embodiments, the feeding frequency of the pulverizing process is 10Hz-35Hz; the grading frequency of the second grading process is 30Hz-50Hz.

[0129] When the raw material crushing and second classification processes are carried out in a continuous process, the fine powder content in the primary graphite particles can be effectively controlled by controlling the feeding frequency of the crushing process and the classification frequency of the second classification process. When the feeding frequency of the crushing process and the classification frequency of the second classification process are within the aforementioned range, the feeding frequency is moderate, the raw material particles can be fully crushed, and the generated fine powder can be effectively removed in the subsequent second classification process. At the same time, the overall particle size of the primary graphite particles will not be too large, thus affecting the kinetic performance of the negative electrode active material.

[0130] In some embodiments, the true density of the raw material is 1.35 g / cm³. 3 -1.50g / cm 3 .

[0131] When the true density of the raw material is 1.35 g / cm³ 3 -1.50g / cm 3 At that time, the bulk phase of the raw material is relatively compact with fewer pores, and the secondary graphite particles obtained after the second heat treatment process have a higher specific gravity.

[0132] In some embodiments, the volatile matter content of the raw material is 4%-7%. The sulfur content of the raw material is less than or equal to 2%.

[0133] When the volatile matter and sulfur content of the raw material are within the aforementioned range, the volatile matter content in the raw material is moderate, the sulfur content is low, the impurity components in the raw material are few, the crystal development is biased towards anisotropy, and the specific capacity is better.

[0134] In some embodiments, the adhesive may be a solid adhesive, for example, the adhesive may include at least one of bitumen and resin. Solid adhesives facilitate blending with primary particles, readily bond with primary particles, and have strong adhesive properties, thereby improving the adhesive effect on graphite primary particles.

[0135] In some embodiments, the coking value of the adhesive is 60%-70%.

[0136] The primary particles are mainly bonded together by the binder to form secondary particles. When the coking value of the binder is within the aforementioned range, the amount of carbon residue left by the binder during the first heat treatment is appropriate, the secondary particle structure is relatively dense, the oil absorption value is moderate, and only a small amount of binder needs to be added to increase the proportion of secondary particles.

[0137] In some embodiments, the mass ratio of the adhesive to the primary graphite particles is (7-10):100.

[0138] When the mass ratio of the binder to the primary graphite particles is within the aforementioned range, the bonding between the primary graphite particles is relatively sufficient, the proportion of secondary particles in the negative electrode active material is relatively high, the structure of the pre-bonded secondary particles is relatively dense, and the compaction density of the final negative electrode active material is relatively high.

[0139] In some embodiments, the particle size of the adhesive is 4μm-8μm.

[0140] When the particle size of the binder is within the aforementioned range, the particle size of the binder is moderate, and the binder can provide a large amount of adhesive surface, resulting in more effective bonding between primary particles. The number of secondary particles in the negative electrode active material is relatively high, and the binder itself is not easy to agglomerate and thus cannot disperse, thereby failing to play a bonding role. Its own steric hindrance is small, and it can effectively contact and form a bond with the primary graphite particles.

[0141] In some embodiments, the temperature of the first heat treatment is 600°C-800°C, and the duration of the first heat treatment is 1 hour-4 hours. This helps to improve the pre-bonding of the adhesive to the primary graphite particles.

[0142] The first heat treatment can bind the primary particles together with an adhesive. The adhesive at the bonding point will undergo a pyrolysis reaction at the temperature of the first heat treatment to form carbon. This can alleviate the volume shrinkage stress caused by the thermal decomposition of the primary particles during the subsequent second heat treatment, thereby reducing the collapse of the graphite secondary particle structure caused by the volume shrinkage stress.

[0143] When the time and temperature of the first heat treatment meet the aforementioned range, the amount of carbon residue volatiles formed at the bonding site by the adhesive is less, the bonding between primary particles is more stable, and the first heat treatment takes less time and consumes less energy.

[0144] S200: Perform a second heat treatment and a first grading treatment on the pre-bonded secondary particles.

[0145] In some embodiments, secondary particles are obtained by subjecting the pre-bonded secondary particles to a second heat treatment and a first grading treatment.

[0146] As an example, pre-bonded secondary particles can undergo a second heat treatment in an Atchison graphitization furnace, followed by cooling and a first classification process to sieve and control the fine powder content, thereby obtaining graphitized secondary particles.

[0147] In some embodiments, the temperature of the second heat treatment is 2800℃-3300℃, and the duration of the second heat treatment is 36h-72h. This helps to improve the adhesion of the adhesive to the primary graphite particles.

[0148] When the time and temperature of the second heat treatment are within the aforementioned range, the heat treatment time is moderate, the energy consumption is low, and the heat capacity is high, which helps the adhesive to be fully graphitized.

[0149] In related technologies, a negative electrode active material with a surface carbon coating is obtained by mixing, carbonizing, and sieving graphite secondary particles with a solid-phase coating agent. However, solid-phase mixing only ensures that the secondary particles and coating agent are uniformly dispersed after mixing. The material needs to be transferred from the mixing equipment to the carbonization line. During the transportation and transfer process, the coating agent and graphite secondary particles will have differences in density, particle size, etc., resulting in uneven dispersion. This leads to irregular particle surface morphology after carbonization, producing a large number of uneven structures, and the resulting negative electrode active material has an excessively high oil absorption value. Furthermore, since the carbonization process after mixing graphite secondary particles and coating agent is static, the fine powder impurities in the secondary particles will tend to agglomerate due to their small size, forming a raised structure on the surface of the secondary particles. Subsequently, in the coating process, the agglomerated fine powder will adhere to the surface of the secondary particles through the coating agent, forming protrusions again. This results in poor surface morphology regularity of the secondary particles, an increased oil absorption value of the negative electrode active material, and the need for more dispersant for dispersion.

[0150] In some implementations, the first grading process can screen out and remove fine powder from the secondary particulate powder, effectively reducing the formation of raised surfaces during subsequent surface coating.

[0151] In some implementations, when the first classification process is carried out in a continuous process, the fine powder content in the secondary graphite particles can be effectively controlled by controlling the feed frequency and classification frequency of the first classification process.

[0152] In some implementations, the feed frequency for the first stage is 4Hz-10Hz. This moderate feed frequency allows for effective removal of fine powder, thereby improving the processing performance of the negative electrode active material.

[0153] As an example, the feed frequency for the first stage processing can be 4Hz, 5Hz, 6Hz, 7Hz, 8Hz, 9Hz, or 10Hz.

[0154] In some embodiments, the grading frequency of the first grading process is 30Hz-50Hz, thereby effectively removing fine powder, improving the processing performance of the negative electrode active material, and preventing the overall particle size of the graphite secondary particles from being too large, thus affecting the kinetic performance of the negative electrode active material.

[0155] As an example, the feed frequency for the first stage can be 30Hz, 35Hz, 40Hz, 45Hz or 50Hz.

[0156] When the feed frequency and classification frequency of the first classification process are within the aforementioned range, the first classification process can remove fine powder from the powder, resulting in a moderate overall particle size and superior kinetic performance of the secondary particles in the negative electrode active material. Consequently, the content of fine powder in the negative electrode active material decreases, the Dv1 particle size slightly increases, the Dv50 particle size becomes moderate, the adhesion between primary particles in the negative electrode active material is more uniform, the number of secondary particles in the negative electrode active material is greater, and the kinetics of the negative electrode active material are superior.

[0157] In some implementations, the first grading process may specifically include a grading step and a sieving step, wherein the mesh size of the sieve in the sieving step may be 300-350 mesh.

[0158] When the mesh size of the sieve is within the aforementioned range, the secondary particles obtained after sieving have a moderate particle size, which not only has a high weight capacity but also reduces the occurrence of coating scratches during processing.

[0159] In some embodiments, the method for preparing the negative electrode active material further includes:

[0160] S300: The secondary particles are mixed with a liquid coating agent and subjected to a third heat treatment.

[0161] In some embodiments, the negative electrode active material with the desired particle size can be obtained by stirring the secondary particles and liquid phase coating agent in a mechanical fusion machine, carbonizing them at high temperature and cooling them to room temperature, and then sieving them.

[0162] The carbon coating layer can cover the active sites on the surface of the graphite secondary particles, reduce the occurrence of irreversible side reactions, reduce the specific surface area of ​​the negative electrode active material, isolate the graphite secondary particles from the electrolyte, reduce the direct contact between the secondary particles in the negative electrode active material and the electrolyte, and also restrict and buffer the volume expansion of graphite, thereby increasing the stability of the cycle.

[0163] Compared to solid-phase coating agents, liquid-phase coating agents have advantages such as better fluidity, more uniform spreading on the surface of secondary particles, fewer surface protrusions, and better coverage of the secondary particle surface. Furthermore, the mixing of secondary particles and liquid-phase coating agents with the third heat treatment is usually carried out using different equipment. During the transportation and transfer of materials, the liquid-phase coating agent can stably coat the surface of graphite secondary particles with high dispersion uniformity.

[0164] In some embodiments, the liquid-phase coating agent comprises at least one of asphalt and resin with a viscosity less than or equal to 500 mPa·s. Therefore, the liquid-phase coating agent exhibits good coating effect on secondary particles.

[0165] The lower the viscosity of the liquid phase coating agent, the better its fluidity, the more sufficient the contact between the graphite secondary particles and the liquid phase coating agent, the fewer surface protrusions formed after coating, and the better the processing performance of the negative electrode active material.

[0166] It is understandable that the viscosity of a liquid coating agent is related to its molecular weight. Specifically, when the viscosity of a liquid coating agent is too low, its molecular weight is too small, resulting in a low coking value.

[0167] In some embodiments, the mass ratio of the liquid coating agent to the secondary particles is (2-10):100.

[0168] The main function of surface coating is to cover the active sites on the surface of secondary particles, reducing irreversible side reactions. This allows the secondary particles in the modified negative electrode active material to retain the advantages of high capacity and low potential of graphite-based materials. The carbon coating layer on the graphite surface has good electrolyte compatibility, effectively suppressing adverse effects such as graphite exfoliation, pulverization, and volume expansion caused by solvation. However, the surface carbon coating layer has limited effect on improving the specific capacity of the negative electrode active material; an excessively thick surface carbon coating layer will significantly reduce the specific capacity. When the mass ratio of the liquid-phase coating agent to the secondary particles is (2-10):100, the negative electrode active material exhibits superior electrolyte resistance and higher specific capacity.

[0169] In some embodiments, the coking value of the liquid phase coating agent is 40%-70%.

[0170] When the coking value of the liquid phase coating agent is within the aforementioned range, and the carbonization amount of the liquid phase coating agent remains unchanged after heat treatment, the proportion of liquid phase coating agent added is more suitable, there are more contact points between it and the secondary particles, the surface coating of the secondary particles is more complete, and the liquid phase coating agent needs to release less volatile matter during the carbonization process, which greatly reduces the possibility of the carbonization furnace exhaust port reacting with air and causing risks.

[0171] In some embodiments, the temperature of the third heat treatment is 1000℃-1200℃, and the duration of the third heat treatment is 15h-30h. This helps to form an amorphous carbon coating layer.

[0172] When the temperature and time of the third heat treatment are within the above range, the heat treatment time is moderate, the thermal field uniformity in the carbonization furnace is high, which is conducive to improving the uniformity of the formed carbon coating layer. Moreover, the carbon coating layer has a high degree of disorder in crystal structure, which is close to amorphous carbon, which is conducive to improving the kinetic performance of the negative electrode active material.

[0173] 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, dispersant 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.

[0174] In some embodiments, the mass fraction of the dispersant in the negative electrode slurry is 0.8%-1.2%.

[0175] Typically, a battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active metal ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits between them while allowing active metal ions to pass through.

[0176] In some implementations, the active metal ion can be a lithium ion, and the battery can be a lithium-ion battery.

[0177] In some implementations, the active metal ion can be a sodium ion, and the battery can be a sodium-ion battery.

[0178] [Positive electrode plate]

[0179] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0180] 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.).

[0181] In some embodiments, when the battery is a lithium-ion battery, the positive electrode active material may be a positive electrode active material known in the art for lithium-ion batteries.

[0182] 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 may 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) 0.8 Co 0.15 Al 0.05At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure may include, but are not limited to, at least one of 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. The modified compounds of the above materials may be for doping modification and / or surface coating modification of the materials.

[0183] During the charging and discharging process of a battery, lithium (Li) undergoes insertion / extraction and consumption, resulting in varying molar Li content at different discharge states. In the examples of positive electrode active materials in this application, the molar Li content refers to the initial state of the material, i.e., before feeding. After charge-discharge cycles, the molar Li content changes when the positive electrode active material is applied to the battery system.

[0184] In the examples of positive electrode active materials in this application, the molar content of O is only a theoretical value. Oxygen release from the crystal lattice will cause changes in the molar content of oxygen, and the actual molar content of O will fluctuate.

[0185] In some embodiments, when the battery is a sodium-ion battery, the positive electrode active material may be a positive electrode active material known in the art for sodium-ion batteries.

[0186] As an example, the positive electrode active material may include at least one of the following materials: sodium transition metal oxides, polyanionic compounds, and Prussian blue sodium compounds, 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. The modified compounds of the above materials may be for doping modification and / or surface coating modification of the materials.

[0187] In some embodiments, the transition metal in the sodium transition metal oxide can be at least one selected from Ti, V, Mn, Co, Ni, Fe, Zn, V, Zr, Ce, Cr, and Cu. The chemical formula of the sodium transition metal oxide can satisfy Na x MO2, wherein M includes at least one of Ti, V, Mn, Co, Ni, Fe, Zn, V, Zr, Ce, Cr, and Cu, and 0 < x ≤ 1.

[0188] In some embodiments, the polyanionic compound may be a sodium ion, a transition metal ion, or a tetrahedral (YO4) compound. n- A class of compounds with anionic units. The transition metal may include at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y may include at least one of P, S, and Si; n represents (YO4). n- The price state.

[0189] In some embodiments, the polyanionic compound may also have sodium ions, transition metal ions, or a tetrahedral (YO4) structure. n- A class of compounds containing anionic units and halide anions. Transition metals may include at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y may include at least one of P, S, and Si, where n represents (YO4). n- The valence state of halogens can include at least one of F, Cl, and Br.

[0190] In some embodiments, the polyanionic compound may also be a tetrahedral compound containing sodium ions (YO4). n- Anionic unit, polyhedral unit (ZO) y ) m+ And a class of compounds with optional halide anions. M may include at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce, Y may include at least one of P, S and Si, and n represents (YO4). n- The valence state, Z represents transition metal, m represents (ZO) y ) m+ The valence state of halogens can include at least one of F, Cl, and Br.

[0191] As an example, polyanionic compounds can satisfy the chemical formulas NaFePO4, Na3V2(PO4)3 (sodium vanadium phosphate, abbreviated as NVP), Na4Fe3(PO4)2(P2O7), NaM'PO4F (M' includes at least one of V, Fe, Mn and Ni), and Na3(VO y )2(PO4)2F 3-2y At least one of (0≤y≤1).

[0192] In some embodiments, Prussian blue compounds may contain sodium ions, transition metal ions, and cyanide ions (CN). - A class of compounds. Transition metals may include at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce.

[0193] As an example, Prussian blue compounds can satisfy the chemical formula Na a Me b Me' c (CN)6, wherein Me and Me' each independently include at least one of Ni, Cu, Fe, Mn, Co, and Zn, 0 < a ≤ 2, 0 < b < 1, and 0 < c < 1.

[0194] During the charging and discharging process of a battery, sodium (Na) undergoes insertion / extraction and consumption, resulting in varying molar Na content at different discharge states. In the examples of positive electrode active materials in this application, the molar Na content refers to the initial state of the material, i.e., before feeding. After charge-discharge cycles, the molar Na content changes when the positive electrode active material is applied to the battery system.

[0195] In the examples of positive electrode active materials for sodium-ion batteries in this application, the molar content of O is only a theoretical value. Oxygen release from the crystal lattice will cause changes in the molar content of oxygen, and the actual molar content of O will fluctuate.

[0196] In some embodiments, the positive electrode active material layer may optionally include a binder.

[0197] As an example, the adhesive may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0198] In some embodiments, the positive electrode active material layer may optionally include a conductive agent.

[0199] As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0200] 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.

[0201] [Electrolytes]

[0202] 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.

[0203] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0204] In some embodiments, the electrolyte salt includes 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.

[0205] In some embodiments, the solvent includes at least one selected from 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.

[0206] 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.

[0207] In some embodiments, the 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.

[0208] [Isolation membrane]

[0209] In some embodiments, the material of the separator includes at least one selected from 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.

[0210] The batteries of this application include battery cells, battery modules, and battery packs. The battery cells, battery modules, and battery packs of this application will be described below with appropriate reference to the accompanying drawings.

[0211] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0212] In some embodiments, the battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0213] In some embodiments, the battery's outer packaging can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The battery's outer packaging can also be a soft pack, such as a pouch-type soft pack. The soft pack can be made of plastic, for example, polypropylene, polybutylene terephthalate, or polybutylene succinate.

[0214] This application does not impose any particular limitation on the shape of the battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 shows a square battery cell 5 as an example.

[0215] In some embodiments, referring to FIG2, the outer packaging may include a housing 51 and a top cover assembly 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 top cover assembly 53 can cover the opening to close the receiving cavity. The positive electrode sheet, negative electrode sheet, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in a single battery cell may be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0216] In some implementations, the batteries can be assembled into battery modules, and the number of batteries contained in a 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.

[0217] Figure 3 shows a battery module 4 as an example. Referring to Figure 3, in the battery module 4, multiple battery cells 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other manner. Furthermore, the multiple battery cells 5 can be fixed in place using fasteners.

[0218] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0219] 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.

[0220] Figures 4 and 5 show a battery pack 1 as an example. Referring to Figures 4 and 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 box 2 and a lower box 3, with the upper box 2 covering the lower box 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.

[0221] In a third aspect, this application proposes an electrical device comprising the aforementioned battery, and / or a battery prepared using the aforementioned method. Thus, the electrical device possesses all the features and advantages of the aforementioned battery and preparation method, which will not be repeated here.

[0222] Batteries, battery modules, and battery packs can be used as power sources for electrical devices or as energy storage units for electrical devices. Electrical devices can include, but are not limited to, mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0223] As an electrical device, batteries, battery modules, or battery packs can be selected according to their usage requirements.

[0224] Figure 6 shows an example of an electrical device. This device is 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 this device, a battery pack or battery module can be used.

[0225] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can be powered by a battery.

[0226] The following specific embodiments illustrate the solution of this application. It should be noted that these embodiments are for illustrative purposes only and should not be considered as limiting the scope of 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 whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0227] Example 1

[0228] Preparation of negative electrode active materials:

[0229] The selected volatile matter content is 4.5%, and the true density is 1.40 g / cm³. 3 Needle coke with a sulfur content of 0.1% is used as raw material. Fine powder is removed through crushing, shaping and second grading to obtain primary graphite particles. The feeding frequency of crushing is 10Hz and the grading frequency of second grading is 40Hz.

[0230] Solid asphalt with a coking value of 67% was selected as the binder. The aforementioned primary graphite particles were mixed with solid asphalt at a mass ratio of 7:100 and then stirred and heated at 650°C for 2 hours in a high-temperature reactor. After cooling, the particles were shaped to obtain pre-bonded secondary particles.

[0231] The aforementioned pre-bonded secondary particles were heated at 3000°C for 48 hours in an Atchison graphitization furnace. After cooling, they underwent a first grading process to obtain secondary particles. The feeding frequency of the first grading process was 10Hz, the grading frequency was 45Hz, and the sieve mesh size was 300 mesh.

[0232] A resin with a coking value of 60% and a viscosity of 500 mPa·s was selected as the liquid phase coating agent. The aforementioned secondary particles and the liquid phase coating agent were placed in a mechanical fusion machine at a mass ratio of 3:100 and stirred. After carbonization at 1100℃ for 15 hours, a carbon coating layer was formed. After cooling to room temperature, the negative electrode active material was obtained by sieving.

[0233] Assembling the aforementioned negative electrode active materials into a battery specifically includes:

[0234] Negative electrode sheet: The negative electrode active material, conductive carbon, sodium carboxymethyl cellulose stabilizer, and SBR binder are dispersed in deionized water at a mass ratio of 96.8:0.7:1.2:1.3 to form a negative electrode slurry. The negative electrode slurry is then uniformly coated on both sides of the copper foil of the negative electrode current collector, with a coating weight of 0.160g / 1540mm. 2 The material is dried and then compacted using a cold press to achieve a compaction density of 1.60 g / cm³ for the negative electrode film. 3 .

[0235] Positive electrode sheet: LiNi is used as the positive electrode active material. 0.8 Co 0.1 Mn 0.1 O2, conductive agent Super-P, and binder polyvinylidene fluoride were dispersed in N-methylpyrrolidone at a mass ratio of 97.4:1.5:1.1 to prepare a positive electrode slurry. This slurry was then coated onto the positive electrode current collector aluminum foil, with a coating weight of 0.238 g / 1540 mm. 2 After being compacted by a cold press, the positive electrode sheet is cut to obtain a compacted density of 3.5 g / cm³. 3 .

[0236] Separating membrane: A 12μm thick porous polyethylene membrane was selected.

[0237] Electrolyte: Ethyl carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed at a volume ratio of 1:1:1 at 25°C to obtain a mixed solvent. LiPF6 is then dissolved in the mixed solvent to obtain the electrolyte, wherein the concentration of LiPF6 is 1 mol / L.

[0238] Battery assembly: The prepared negative electrode sheet, separator, and positive electrode sheet are stacked in sequence, with the separator in the middle of the positive and negative electrode sheets to provide isolation. The cells are then wound to obtain bare cells, which are then inserted into the battery casing. The battery is obtained through processes such as baking, electrolyte injection, settling, encapsulation, formation, and capacity testing.

[0239] Example 2

[0240] Example 2 is the same as Example 1, except that the feeding frequency of the first stage is 5Hz.

[0241] Example 3

[0242] Example 3 is the same as Example 2, except that the grading frequency of the first grading process is 30Hz.

[0243] Example 4

[0244] Example 4 is the same as Example 3, except that the coking value of the liquid phase coating agent is 45%.

[0245] Example 5

[0246] Example 5 is the same as Example 4, except that the viscosity of the liquid phase coating agent is 225 mPa·s.

[0247] Comparative Example 1

[0248] Comparative Example 1 is the same as Example 1, except that the first grading process is not performed.

[0249] Comparative Example 2

[0250] Comparative Example 2 is the same as Example 1, except that the first grading treatment is not performed, and asphalt is used as a solid coating agent to form a carbon coating layer. The solid coating agent has a coking value of 60% and a softening point of 200°C.

[0251] Comparative Example 3

[0252] Comparative Example 3 is the same as Example 3, except that the solid coating agent in Comparative Example 2 is used to form the carbon coating layer in Comparative Example 3.

[0253] The negative electrode active materials in the aforementioned embodiments and comparative examples were tested as follows, and the test results are shown in Table 1:

[0254] Oil absorption value: Place 100g of negative electrode active material at the feeding port of the oil absorption value tester, and automatically titrate dibutyl phthalate to the negative electrode active material until the negative electrode active material becomes a semi-plastic agglomerate. Record the amount of dibutyl phthalate added at this time (a mL), and thus obtain the oil absorption value of the negative electrode active material as a mL / 100g.

[0255] Secondary particle proportion: The negative electrode active material is laid and adhered to conductive adhesive to form a test sample with dimensions of 6cm x 1.1cm. The particle morphology is tested using a scanning electron microscope (such as ZEISS Sigma 300). The test can be referenced in JY / T010-1996. To ensure the accuracy of the test results, multiple (e.g., 20) different regions can be randomly selected from the test sample for scanning tests. At a certain magnification (e.g., 1000x), the percentage of secondary particles in each test region relative to the total number of particles is calculated. This percentage is the proportion of secondary particles in that region. The average of the test results from multiple test regions is taken as the proportion of secondary particles in the negative electrode active material.

[0256] Processing performance: The negative electrode active material, conductive carbon, sodium carboxymethyl cellulose stabilizer, and SBR binder were dispersed in deionized water at a mass ratio of 96.8:0.7:1.2:1.3 to form a negative electrode slurry. 500 mL of the negative electrode slurry was filtered through a 150-mesh stainless steel screen. The time required to filter to obtain 300 mL of slurry was recorded. The shorter the time, the easier the slurry was to filter, and the better the processing performance.

[0257] The batteries in the aforementioned embodiments and comparative examples were tested as follows, and the test results are shown in Table 1:

[0258] 25℃ Fast Charging Capability Test: The prepared battery was placed at room temperature (25℃) and charged to 4.25V using a constant current rate of 0.33C. Then, it was charged to 0.05C using a constant voltage rate, allowed to rest for 5 minutes, and then discharged to 2.5V using a constant current rate of 0.33C. The constant current discharge capacity was recorded as the initial capacity C0. The battery was then sequentially charged at constant current rates of 0.5C0, 1C0, 1.5C0, 2C0, 2.5C0, 3C0, and 3.5C0 until the full cell potential of 4.25V or the negative electrode cutoff potential of 0mV (reaching either condition indicates completion of charging). After each charging, it was discharged to 2.5V using a constant current rate of 0.33C0. At 10% SOC intervals (from 10% SOC to 80% SOC), the corresponding negative electrode potential at different charging rates was recorded. Rate-negative electrode potential curves were plotted for different SOCs. After linear fitting, the charging rate corresponding to a negative electrode potential of 0mV at different SOCs was obtained, denoted as C. x (x = 2 - 8). Using the formula (1 / C2 + 1 / C3 + 1 / C4 + 1 / C5 + 1 / C6 + 1 / C7 + 1 / C8) × 0.1 × 60, the charging time T (min) for the battery to charge from 10% SOC to 80% SOC is calculated. The shorter this time, the better the battery's fast charging performance.

[0259] Cycle performance (45°C 1C / 1C, 1000 cycles, capacity retention): At 45°C, the battery was charged at a constant current of 0.33C to the charging cutoff voltage of 4.25V, then charged at a constant voltage to a current of 0.05C, allowed to rest for 5 minutes, and then discharged at a constant current of 0.33C to the discharge cutoff voltage of 2.5V. The initial capacity was recorded as C0. Then, the battery was charged and discharged at a 1C0 rate, and the discharge capacity C of each cycle was recorded. n (n is the number of cycles, n = 1 - 1000), until 1000 cycles are completed, then calculate the cycle capacity retention rate (i.e., C). 1000 / C0×100%). A higher cycle retention rate indicates a better lifespan.

[0260] Table 1

[0261] The scanning electron microscope (SEM) image of the negative electrode active material in Example 1 is shown in Figure 7. In Comparative Example 1, the negative electrode active material has fewer surface irregularities and a lower oil absorption value. The SEM image of the negative electrode active material in Comparative Example 1 is shown in Figure 8. In Comparative Example 1, the negative electrode active material has more surface irregularities and a higher oil absorption value.

[0262] Test results show that in the preparation process of the negative electrode active material in Examples 1-5, the first stage treatment effectively removes fine powder from the powder. After liquid phase coating, the negative electrode active material has a low oil absorption value. The negative electrode active material has both a high proportion of secondary particles and a low oil absorption value, thus significantly improving the rate performance and processing performance of the negative electrode active material. Furthermore, compared with solid phase coating agents, liquid phase coating agents have better fluidity, spread more evenly on the surface of secondary particles, and have a better coating effect. They can restrict and buffer the volume expansion of graphite, increasing the cycle stability of the negative electrode active material.

[0263] 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 battery, wherein, The device includes a positive electrode, a negative electrode, and a separator. The negative electrode includes a negative current collector and a negative active material layer located at least on one side of the negative current collector. The negative active material layer includes a negative active material, which includes graphite. The negative active material contains secondary particles accounting for more than or equal to 65%, and the oil absorption value of the negative active material is 40mL / 100g-65mL / 100g. The volume distribution particle size Dv1 of the negative active material is 4μm-8μm.

2. The battery according to claim 1, wherein, The negative electrode active material satisfies (Dv90-Dv10) / Dv50 of 0.8-1.

2.

3. The battery according to claim 2, wherein, The volume distribution particle size Dv10 of the negative electrode active material is 7μm-11μm, and / or the volume distribution particle size Dv90 of the negative electrode active material is 20μm-30μm, and / or the volume distribution particle size Dv50 of the negative electrode active material is 12μm-18μm.

4. The battery according to any one of claims 1-3, wherein, The graphitization degree of the negative electrode active material is 93%-95%.

5. The battery according to any one of claims 1-3, wherein, The specific surface area of ​​the negative electrode active material is 2.5 m². 2 / g-3.5m 2 / g.

6. The battery according to any one of claims 1-3, wherein, The negative electrode active material further includes a carbon coating layer, which is located at least on a portion of the surface of the secondary particles. The secondary particles are formed by bonding at least two primary particles together, and the bonding material includes carbon material.

7. The battery according to any one of claims 1-3, wherein, The porosity of the negative electrode active material layer is 18%-35%.

8. The battery according to any one of claims 1-3, wherein, The compaction density of the negative electrode active material layer is 1.60 g / cm³. 3 -1.75g / cm 3 .

9. A method for preparing the battery according to any one of claims 1-8, wherein, include: Primary graphite particles are mixed with an adhesive and subjected to a first heat treatment to obtain pre-bonded secondary particles. The pre-bonded secondary particles are subjected to a second heat treatment and a first classification treatment to obtain secondary particles, thereby obtaining a negative electrode active material. The negative electrode active material is placed on one side of the negative electrode current collector to obtain a negative electrode sheet. The negative electrode sheet, separator, and positive electrode sheet are assembled to obtain a battery.

10. The method according to claim 9, wherein, Providing the primary graphite particles includes: pulverizing and second classifying the raw material to obtain the primary graphite particles, wherein the raw material includes at least one of petroleum coke and needle coke. The provided primary graphite particles satisfy at least one of the following conditions: The volatile matter content in the raw material is 4%-7%; The true density of the raw material is 1.35 g / cm³. 3 -1.50g / cm 3 ; The sulfur content of the raw material is less than or equal to 2%; The feeding frequency for the pulverizing process is 10Hz-35Hz; The grading frequency of the second grading process is 30Hz-50Hz.

11. The method according to claim 9 or 10, wherein, The adhesive comprises at least one of asphalt and resin, and the adhesive satisfies at least one of the following conditions: The coking value of the adhesive is 60%-70%; The mass ratio of the adhesive to the primary graphite particles is (7-10):100; The adhesive has a particle size of 4μm-8μm.

12. The method according to claim 9 or 10, wherein, The temperature of the first heat treatment is 600℃-800℃, and the time of the first heat treatment is 1h-4h.

13. The method according to claim 9, wherein, The temperature of the second heat treatment is 2800℃-3300℃, and the time of the second heat treatment is 36h-72h.

14. The method according to claim 9, wherein, The first hierarchical processing satisfies at least one of the following conditions: The mesh size of the sieve used in the first grading process is 300-350 mesh; The feeding frequency for the first staged process is 4Hz-10Hz; The first graded processing frequency is 30Hz-50Hz.

15. The method according to claim 9, wherein, After obtaining the secondary particles, the process further includes: The secondary particles are mixed with a liquid coating agent and subjected to a third heat treatment to form a carbon coating layer on a portion of the surface of the secondary particles, wherein the liquid coating agent comprises at least one of asphalt and resin with a viscosity of less than or equal to 500 mPa·s.

16. The method according to claim 15, wherein, The mass ratio of the liquid coating agent to the secondary particles is (2-10):100, and / or the coking value of the liquid coating agent is 40%-70%.

17. The method according to claim 15 or 16, wherein, The temperature of the third heat treatment is 1000℃-1200℃, and the time of the third heat treatment is 15h-30h.

18. An electrical appliance, wherein, Includes the battery according to any one of claims 1-8, or a battery prepared by the method according to any one of claims 9-17.

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