Graphite negative electrode active material and preparation method therefor, secondary battery containing same, and electric device

Abstract

A graphite negative electrode active material and a preparation method therefor, a secondary battery containing same, and an electric device. The volume distribution particle size Dv1 of the graphite negative electrode active material is 1.5 μm-3 μm, and the graphite negative electrode active material comprises primary particle morphology. The graphite negative electrode active material can improve the cycling performance of the battery and prolong the service life of the battery.

Description

Graphite negative electrode active material and preparation method thereof, secondary battery containing same and electric device

[0001] Cross-references

[0002] The present disclosure refers to Chinese patent application No. 202311679774.7 filed on December 7, 2023, entitled “Graphite negative electrode active material, preparation method thereof, secondary battery and electrical device containing the same”, which is incorporated into the present disclosure in its entirety by reference. Technical Field

[0003] The present disclosure relates to the technical field of secondary batteries, and in particular to a graphite negative electrode active material and a preparation method thereof, a secondary battery containing the same, and an electrical device. Background Art

[0004] With the introduction of carbon neutrality goals and policies, the secondary battery market for energy storage has ushered in a huge explosion. For energy storage batteries, long cycle life is a key indicator, especially for energy storage batteries used in large-scale energy storage power stations. In order to extend service life and reduce replacement frequency, it is necessary to further develop energy storage batteries with longer cycle life.

[0005] Summary of the Invention

[0006] The present disclosure is made in view of the above-mentioned problems, and its purpose is to provide a graphite negative electrode active material and a preparation method thereof, a secondary battery containing the same and an electrical device, which can effectively improve the cycle life of the battery and extend the service life of the battery.

[0007] A first aspect of the present disclosure provides a graphite negative electrode active material, wherein the volume distribution particle size Dv1 of the graphite negative electrode active material is 1.5 μm-3 μm; the graphite negative electrode active material includes a primary particle morphology.

[0008] The volume distribution particle size Dv1 of the graphite negative electrode active material is within a suitable range, and the material has a specific particle morphology, which can make the negative electrode plate have an excellent liquid absorption rate. During the battery cycle, the electrolyte can fully infiltrate the negative electrode plate during the repeated lithium insertion and extraction process of the negative electrode, reducing the possibility of local polarization, making the current of the negative electrode plate uniform during the cycle, reducing the possibility of side reactions at the negative electrode interface during the cycle, and reducing the impact of the byproducts of the side reactions clogging the pores on the battery's cycle performance. At the same time, the volume distribution particle size Dv1 within the suitable range is conducive to improving the binding force between the particles of the graphite negative electrode active material, effectively maintaining electrical contact between the particles, improving the dynamic performance of the battery, and reducing the negative impact of lithium plating on the cycle performance.

[0009] On the other hand, the graphite negative electrode active material includes primary particles, which have excellent structural stability, helping to reduce the structural fragmentation of the graphite negative electrode active material caused by expansion and contraction during the cycle, improve the structural stability of the graphite negative electrode active material, and thus improve the cycle performance of the secondary battery.

[0010] In summary, the present disclosure can effectively improve the cycle performance of the battery and extend the service life of the battery by limiting the volume distribution particle size Dv1 of the graphite negative electrode active material and the particle type of the graphite negative electrode active material.

[0011] In any embodiment, the specific surface area of ​​the graphite negative electrode active material is less than or equal to 1.4 m 2 In some embodiments, the specific surface area of ​​the graphite negative electrode active material is 0.6 m 2 / g-1.3m 2 / g.

[0012] The specific surface area of ​​the graphite negative electrode active material being within an appropriate range helps to reduce the side reactions of the graphite negative electrode active material during the cycle, reduces the loss of active lithium, and is beneficial to improving the storage stability and cycle stability of the battery.

[0013] In any embodiment, the volume distribution particle size Dv50 of the graphite negative electrode active material is 12 μm to 16 μm. In some embodiments, the volume distribution particle size Dv50 of the graphite negative electrode active material is 13 μm to 15 μm.

[0014] The graphite negative electrode active material has a large volume distribution particle size Dv50, which is conducive to the formation of a reasonable pore structure between the particles of the negative electrode film layer, which is conducive to the full infiltration of the electrolyte into the negative electrode plate, reducing the possibility of local polarization of the plate, and reducing the impact of black spots on the negative electrode on the cycle life and storage stability of the battery.

[0015] In any embodiment, the primary particles account for 80% or more of the total number of graphite anode active material particles. In some embodiments, the primary particles account for 85%-100% of the total number of graphite anode active material particles.

[0016] The primary particles within the above range help reduce the structural breakage of the graphite negative electrode active material due to expansion and contraction during the cycle, improve the structural stability of the graphite negative electrode active material, and thus improve the cycle performance and storage life of the secondary battery.

[0017] In any embodiment, the gram capacity of the graphite negative electrode active material is greater than or equal to 340 mAh / g. In some embodiments, the gram capacity of the graphite negative electrode active material is 341 mAh / g-347 mAh / g.

[0018] Graphite anode active materials have high gram capacity, providing the material foundation for high-energy-density batteries. While the gram capacity of graphite anode active materials is within the stated range, their high particle strength reduces the likelihood of particles flattening during the cold pressing of the electrode sheet, preventing the electrolyte transport path from becoming significantly longer during the cold pressing process. This helps reduce the tortuosity of the anode sheet, facilitates electrolyte circulation, and improves the battery's cycling performance and storage stability.

[0019] In any embodiment, the tap density of the graphite negative electrode active material is 1.2 g / cm 2 -1.4g / cm 2 .

[0020] When the tap density of the graphite negative electrode active material is within the above range, it is conducive to the formation of a reasonable pore structure between the particles of the negative electrode film layer, improving the wettability of the electrolyte to the negative electrode plate, and improving the cycle performance and storage stability of the secondary battery. At the same time, the appropriate tap density can also increase the compaction density of the negative electrode film layer, thereby increasing the energy density of the secondary battery.

[0021] In any embodiment, the particle size distribution of the graphite negative electrode active material (Dv90-Dv10) / Dv50 is 1.20-1.70. In some embodiments, the particle size distribution of the graphite negative electrode active material (Dv90-Dv10) / Dv50 is 1.35-1.60.

[0022] The particle size distribution of the graphite negative electrode active material meeting the above range helps to improve the concentration of the graphite negative electrode active material particle size, improve the arrangement concentration of the particles, reduce the tortuosity of the negative electrode plate, allow the electrolyte to fully infiltrate the negative electrode plate, and improve the cycle performance of the battery. At the same time, it can also reduce the uneven distribution of active ions in the graphite negative electrode active material caused by the large difference in particle size, reduce the side reaction between the smaller particle size graphite negative electrode active material and the electrolyte, and improve the cycle performance and storage stability of the secondary battery. At the same time, the particle size distribution of the graphite negative electrode active material within the above range is good, and its particle stacking performance is good, which is conducive to improving the compaction density of the negative electrode film layer, thereby further improving the energy density of the secondary battery.

[0023] The second aspect of the present disclosure provides a method for preparing a graphite negative electrode active material, comprising the following steps: providing raw materials; processing the raw materials to obtain a precursor; graphitizing the precursor to obtain an intermediate product; screening the intermediate product to obtain a graphite negative electrode active material; wherein the volume distribution particle size Dv1 of the graphite negative electrode active material is 1.5μm-3μm; and the graphite negative electrode active material includes a primary particle morphology.

[0024] By adopting the above preparation method, a graphite negative electrode active material with a volume distribution particle size Dv1 within an appropriate range and a primary particle morphology as the main component can be prepared, which can improve the cycle performance of the battery and extend the service life of the battery.

[0025] In any embodiment, processing the raw material specifically comprises the following steps:

[0026] Crushing, shaping and classifying raw materials to obtain precursors;

[0027] During the classification process, a certain proportion of fine powder is removed.

[0028] Among them, the mass proportion of the removed fine powder is 10%-35%. Based on the total mass of the raw material, the volume distribution particle size Dv50 of the fine powder is 3μm-7μm, and the (Dv90-Dv10) / Dv50 of the fine powder is greater than 1.6.

[0029] By controlling the mass proportion of the fine powder within an appropriate range, the volume distribution particle size Dv1 of the graphite negative electrode active material can be controlled within an appropriate range, which can not only make the electrode have an excellent liquid absorption rate and the electrolyte can fully infiltrate the negative electrode, but also make the graphite particles have excellent electrical contact, thereby comprehensively improving the cycle performance of the battery.

[0030] In any embodiment, the power used in the graphitization process is 70% to 90% of the rated power of the graphitization equipment.

[0031] In any embodiment, the power used in the graphitization process is 23000W-25000W.

[0032] In any embodiment, the holding time of the graphitization treatment is 10 hours to 50 hours.

[0033] In any embodiment, the precursor satisfies at least one of the following conditions:

[0034] The volume distribution particle size Dv50 of the precursor is 12 μm-18 μm; and / or,

[0035] The particle size distribution of the precursor (Dv90-Dv10) / Dv50 is 1.2-1.8.

[0036] A third aspect of the present disclosure provides a secondary battery, comprising a negative electrode plate, wherein the negative electrode plate comprises the graphite negative electrode active material of the first aspect or the graphite negative electrode active material prepared by the preparation method of the second aspect.

[0037] In any embodiment, the compaction density of the negative electrode film layer is 1.35 g / cm 3 -1.65g / cm 3 In some embodiments, the compaction density of the negative electrode film layer is 1.40 g / cm3 -1.55g / cm 3 .

[0038] The lower the compaction density of the negative electrode film, the more pores there are and the larger the pore size, making it easier for the electrolyte to enter the negative electrode pores and more easily soak into the negative electrode sheet. However, if the compaction density of the negative electrode film is too low, the energy density of the battery will decrease. It will also affect the adhesion between the active material in the negative electrode film and the current collector, as well as the adhesion between the active materials themselves, leading to active material shedding during cycling and even safety accidents.

[0039] The compaction density of the negative electrode film layer falls within the above range, which can ensure that the negative electrode film layer has abundant pores, the electrolyte can easily infiltrate the negative electrode plate, improve the cycle performance and storage stability of the battery, and at the same time the battery has a high energy density.

[0040] In any embodiment, the surface density of the negative electrode film layer is 7 mg / cm 2 -14mg / cm 2 In some embodiments, the surface density of the negative electrode film layer is 9 mg / cm 2 -12mg / cm 2 .

[0041] The surface density of the negative electrode film layer is within an appropriate range, and the thickness of the negative electrode film layer is appropriate. On the one hand, the distance for the electrolyte to laterally infiltrate the electrode sheet is relatively short, and the time required for the electrolyte to completely infiltrate the negative electrode sheet is also relatively short, reducing the possibility of local polarization and improving the cycle performance of the battery. On the other hand, the surface density within an appropriate range also ensures that the battery has a certain energy density.

[0042] A fourth aspect of the present disclosure provides an electric device including the secondary battery according to the third aspect of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] FIG. 1 is a schematic diagram of a secondary battery according to an embodiment of the present disclosure.

[0044] FIG. 2 is an exploded view of the secondary battery according to the embodiment of the present disclosure shown in FIG. 1 .

[0045] FIG3 is a schematic diagram of a battery module according to an embodiment of the present disclosure.

[0046] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present disclosure.

[0047] FIG. 5 is an exploded view of the battery pack shown in FIG. 4 according to an embodiment of the present disclosure.

[0048] FIG6 is a schematic diagram of an electric device using a secondary battery according to an embodiment of the present disclosure as a power source.

[0049] Description of reference numerals:

[0050] 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 secondary battery; 51 housing; 52 electrode assembly; 53 top cover assembly. DETAILED DESCRIPTION

[0051] Below, with appropriate reference to the accompanying drawings, the embodiments of the graphite negative electrode active material and its preparation method, the secondary battery containing the same, and the electrical device disclosed in the present invention are described in detail. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present disclosure and are not intended to limit the subject matter described in the claims.

[0052] " scope " disclosed in the present disclosure is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and selected lower limit and upper limit define the boundary of special scope.The scope that this mode limits can be to include end value or not include end value, and can be combined arbitrarily, and promptly any lower limit can form a scope with any upper limit combination.For example, if the scope of 60-120 and 80-110 is listed for specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected.In addition, if the minimum range value 1 and 2 listed, and if the maximum range value 3,4 and 5 listed, then the following scope can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5.In the present disclosure, unless otherwise specified, numerical range " ab " represents the abbreviation of any real number combination between a and b, and wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0053] Unless otherwise specified, all embodiments and optional embodiments of the present disclosure can be combined with each other to form new technical solutions.

[0054] Unless otherwise specified, all technical features and optional technical features disclosed herein can be combined with each other to form a new technical solution.

[0055] Unless otherwise specified, all steps of the present disclosure may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0056] Unless otherwise specified, the terms "include" and "comprising" mentioned in this disclosure may be open-ended or closed-ended. For example, the terms "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0057] Unless otherwise specified, the term "or" is inclusive in this disclosure. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0058] In order to improve the process efficiency of electrode coating in the prior art, the coating speed or drying speed is usually increased. However, at high coating speeds or drying speeds, the micropowder in the negative electrode active material tends to migrate to the electrode surface as the solvent evaporates (i.e., the micropowder floats up), which causes the floating micropowder to clog the pores on the surface of the negative electrode, affecting the wettability of the electrolyte to the negative electrode, and reducing the liquid absorption rate of the electrode. During the cycle, some areas of the electrode cannot absorb the electrolyte in time, which may cause the active ions to be unable to effectively embed into the negative electrode, resulting in local polarization and uneven current distribution. This causes black spots to appear on the electrode surface and is accompanied by other side reactions. The accumulation of byproducts further clogs the pores, which may cause lithium deposition on the electrode, resulting in a decrease in the battery's capacity retention rate and shortening the battery life.

[0059] [Graphite negative electrode active material]

[0060] The present disclosure provides a graphite negative electrode active material, wherein the volume distribution particle size Dv1 of the graphite negative electrode active material is 1.5 micrometers (μm) to 3 μm; and the graphite negative electrode active material includes a primary particle morphology.

[0061] In some embodiments, the volume distribution particle size Dv1 of the graphite negative electrode active material is 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2.0 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, 2.9 μm, 3 μm, or a value in the range consisting of any two of the above points.

[0062] The volume distribution particle size Dv1 of the graphite negative electrode active material represents the particle size corresponding to when the cumulative volume distribution percentage of the material reaches 1%.

[0063] The Dv1 of the graphite negative electrode active material can be tested using methods known in the art. For example, GB / T 19077-2016 can be used for characterization testing using a Malvern laser particle size analyzer, such as a Malvern Mastersizer-3000.

[0064] The graphite negative electrode active material has a large volume distribution particle size Dv1 and a relatively low content of fine powder in the graphite negative electrode active material. This can effectively reduce the phenomenon of fine powder floating during coating or drying, increase the liquid absorption rate of the negative electrode plate, and improve the wettability of the electrolyte to the negative electrode plate, allowing the electrolyte to fully penetrate the negative electrode plate during the lithium insertion and extraction process, reducing the possibility of local polarization, ensuring uniform current distribution in the negative electrode plate during the cycle, reducing the possibility of side reactions at the negative electrode interface during the cycle, and reducing the impact of side reactions on the battery's cycle performance due to the clogging of pores by byproducts. If the volume distribution particle size Dv1 of the graphite negative electrode active material is too large, the fine powder content between particles will be too low, and effective electrical contact between particles cannot be maintained, affecting the battery's kinetic performance, leading to the occurrence of lithium plating, and further affecting the battery's cycle performance.

[0065] Herein, "primary particles" are also referred to as single particles, and generally refer to non-agglomerated particles. Primary particles can be confirmed by scanning electron microscopy (SEM).

[0066] The graphite negative electrode active material contains primary particles, which have excellent structural stability, helping to reduce the structural fragmentation of the graphite negative electrode active material due to expansion and contraction during the cycle, thereby improving the structural stability of the graphite negative electrode active material and improving the cycle performance of the secondary battery.

[0067] In summary, the present disclosure can effectively improve the cycle performance of the battery and extend the service life of the battery by limiting the volume distribution particle size Dv1 of the graphite negative electrode active material and the particle type of the graphite negative electrode active material.

[0068] In some embodiments, the specific surface area of ​​the graphite negative electrode active material is less than or equal to 1.4 m 2 / g(m 2 / g).

[0069] In some embodiments, the specific surface area of ​​the graphite negative electrode active material is 0.4 m 2 / g, 0.5m 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.75m 2 / g, 0.85m 2 / g, 0.85m 2 / g, 1.05m 2 / g, 1.15m 2 / g, 1.25m 2 / g, 1.3m 2 / g, 1.4m 2 Any value in / g or a range consisting of any two values ​​in it.

[0070] The specific surface area of ​​the graphite negative electrode active material can be measured using instruments and methods known in the art. For example, the specific surface area can be measured using the nitrogen adsorption specific surface area analysis method according to GB / T 19587-2017 and calculated using the BET (Brunauer Emmett Teller) method. The nitrogen adsorption specific surface area analysis can be performed using a Micromeritics Tri-Star 3020 specific surface area pore size analyzer.

[0071] The graphite negative electrode active material has a low specific surface area, which makes the material have low surface activity, thereby reducing the consumption of active ions by the side reactions between the graphite negative electrode active material and the electrolyte, and improving the cycle performance and storage stability of the battery.

[0072] In some embodiments, the specific surface area of ​​the graphite negative electrode active material is 0.6 m 2 / g-1.3m 2 / g.

[0073] In some embodiments, the specific surface area of ​​the graphite negative electrode active material is 0.6 m 2 / g, 0.7m 2 / g, 0.75m 2 / g, 0.85m 2 / g, 0.85m 2 / g, 1.05m 2 / g, 1.15m 2 / g, 1.25m 2 / g, 1.3m2 Any value in / g or a range consisting of any two values ​​in it.

[0074] As mentioned above, graphite negative electrode active materials have a small specific surface area, which can reduce the consumption of active ions in the side reactions between the graphite negative electrode active material and the electrolyte, thereby improving the battery's cycle performance and storage stability. However, if the specific surface area is too small, it will affect the electrolyte's wettability to the electrode, affecting the electrode's dynamic performance and easily causing lithium deposition, which will affect the battery's cycle life and storage performance. A suitable specific surface area range can further improve the battery's cycle life and storage performance.

[0075] In some embodiments, the volume distribution particle size Dv50 of the graphite negative electrode active material is 12 μm-16 μm.

[0076] In some embodiments, the volume distribution particle size Dv50 of the graphite negative electrode active material is any value of 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm, 15.5 μm, 16 μm, or a range consisting of any two values ​​thereof.

[0077] The volume distribution particle size Dv50 of the graphite negative electrode active material represents the particle size corresponding to 50% of the cumulative volume distribution percentage of the material, and can be measured using instruments and methods known in the art. For example, characterization testing can be performed using a Malvern laser particle size analyzer, such as the Malvern Mastersizer-3000, in accordance with GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method.

[0078] The graphite negative electrode active material has a large volume distribution particle size Dv50, which is conducive to the formation of a reasonable pore structure between the particles of the negative electrode film layer, which is conducive to the full infiltration of the electrolyte into the negative electrode plate, reducing the possibility of local polarization of the plate, and reducing the impact of black spots on the negative electrode on the cycle life and storage performance of the battery.

[0079] In some embodiments, the volume distribution particle size Dv50 of the graphite negative electrode active material is 13 μm-15 μm.

[0080] In some embodiments, the volume distribution particle size Dv50 of the graphite negative electrode active material is any value selected from the group consisting of 13 μm, 13.5 μm, 14 μm, 14.5 μm, and 15 μm, or a range consisting of any two of these values.

[0081] The graphite negative electrode active material has a suitable volume distribution particle size Dv50, which is conducive to the formation of a reasonable pore structure between the particles in the negative electrode film layer, which facilitates the full infiltration of the electrolyte into the negative electrode plate, reduces the possibility of local polarization of the plate, and reduces the impact of black spots on the battery's cycle life and storage performance. It also helps to improve the transmission performance of active ions and electrons. The plate has excellent kinetic properties and reduces the impact of lithium plating on the battery's life and storage performance.

[0082] In some embodiments, based on the total number of particles of the graphite negative electrode active material, the number of the primary particles accounts for greater than or equal to 80%.

[0083] In some embodiments, based on the total amount of the graphite negative electrode active material, the amount of primary particles in the graphite negative electrode active material accounts for 85%-100%.

[0084] In some embodiments, based on the total number of particles of the graphite negative electrode active material, the number of primary particles in the graphite negative electrode active material accounts for any value among 80%, 85%, 90%, 95%, 100% or a range consisting of any two values ​​therein.

[0085] In some embodiments, the particles in the graphite negative electrode active material include primary particles and secondary particles. Herein, "secondary particles" refer to agglomerated particles formed by agglomeration of multiple primary particles or primary particles. The force that causes the particles to agglomerate may be assisted by another substance (e.g., a sticky chemical).

[0086] The number ratio of primary particles can be determined by instruments and methods known in the art. An example is as follows: a graphite negative electrode active material is laid and adhered to a conductive adhesive to form a sample to be tested with a length × width = 6 cm × 1.1 cm. A scanning electron microscope; an energy spectrometer (such as ZEISS SEM (sigma300)) is used to test the morphology of the particles in the sample to be tested. The test can refer to JY / T010-1996. In order to ensure the accuracy of the test results, a plurality of (for example, 10 or 20) different areas can be randomly selected from the sample to be tested for scanning testing, and the number of primary particles and the total number of particles in the test area can be counted at a certain magnification (for example, 500 times or 1000 times). The ratio of the number of primary particles to the total number of particles in any test area is the number ratio of primary particles in the area, and the average value of the test results of the 10 test areas is taken as the number ratio of primary particles. To ensure the accuracy of the results, multiple test samples (eg, 5 or 10) may be prepared to repeat the above test, and the average value of the test results of each test sample may be taken as the percentage of primary particles in the graphite negative electrode active material.

[0087] The primary particles within the above range help reduce the structural fragmentation of the graphite negative electrode active material due to expansion and contraction during the cycle, improve the structural stability of the graphite negative electrode active material, and thus improve the cycle stability and storage stability of the secondary battery.

[0088] In some embodiments, the graphite negative electrode active material has a gram capacity of greater than or equal to 340 milliampere hours per gram (mAh / g).

[0089] In some embodiments, the gram capacity of the graphite negative electrode active material is any value of 340mAh / g, 341mAh / g, 342mAh / g, 343mAh / g, 344mAh / g, 345mAh / g, 346mAh / g, 347mAh / g, 349mAh / g, 350mAh / g, 351mAh / g, 352mAh / g, or a range consisting of any two of these values.

[0090] The gram capacity can be measured using any method known in the art. For example, a graphite anode active material sample can be thoroughly mixed with the conductive agent carbon black and polyvinylidene fluoride (PVDF) in a suitable amount of NMP solvent at a mass ratio of 91.6:1.8:6.6 to form a uniform anode slurry. The anode slurry is evenly coated on the surface of the anode current collector copper foil and dried and cold-pressed. An electrolyte is then injected using a lithium metal sheet as the counter electrode and a polypropylene (PP) film as the separator. The electrolyte formulation used is as follows: dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and ethylene carbonate (EC) are mixed in a weight ratio of 1:1:1 to form an organic solvent, and LiPF6 is dissolved in the organic solvent to prepare an electrolyte solution with a concentration of 1.0 mol / L. CR2430 button cells are assembled in an argon-protected glove box. At 25 degrees Celsius (°C), the prepared button cell was first discharged at a constant current of 0.05 coulombs (C) to 0.005 volts (V). The cell was then discharged at a constant current of 10 microamperes (μA) to 0.005 V and allowed to rest for 5 minutes. The first-cycle discharge capacity of the button cell was recorded. The cell was then charged at a constant current of 0.1 C to 2.0 V, and the charge capacity of the button cell was recorded. The ratio of the charge capacity of the button cell to the mass of the graphite negative electrode active material sample is the gram capacity of the graphite negative electrode active material.

[0091] Graphite negative electrode active materials have high gram capacity and provide the material basis for high energy density batteries.

[0092] In some embodiments, the gram capacity of the graphite negative electrode active material is 341 mAh / g to 347 mAh / g. In some embodiments, the gram capacity of the graphite negative electrode active material is any value of 341 mAh / g, 342 mAh / g, 343 mAh / g, 344 mAh / g, 345 mAh / g, 346 mAh / g, 347 mAh / g, or a range consisting of any two of these values.

[0093] The gram capacity of the graphite negative electrode active material is within an appropriate range, which can improve the energy density of the battery. At the same time, when the gram capacity of the graphite negative electrode active material is within the above range, its particle strength is high, which reduces the possibility of the particles tending to be flat during the cold pressing process of the electrode, avoids the electrolyte transmission path from becoming significantly longer during the cold pressing process, is beneficial to reducing the tortuosity of the negative electrode, is beneficial to the circulation of the electrolyte, improves the wetting effect of the electrolyte on the electrode, and improves the cycle performance and storage performance of the battery.

[0094] In some embodiments, the tap density of the graphite negative electrode active material is 1.2 g / cm 3 (g / cm 3 )-1.4g / cm 3 .

[0095] In some embodiments, the tap density of the graphite negative electrode active material is 1.2 g / cm 3 , 1.25g / cm 3 , 1.3g / cm 3 , 1.35g / cm 3 , 1.4g / cm 3 Or a value within the range formed by any two of the above points.

[0096] In this article, the term "tap density" refers to the density of a powder material after vibration compression under certain conditions.

[0097] The tap density can be measured using any method known in the art. For example, it can be measured using a powder tap density tester in accordance with GB / T 5162-2006. The test instrument can be a Dandong Better BT-301. The test parameters are as follows: vibration frequency 250 ± 15 times / minute, amplitude 3 ± 0.2 millimeters (mm), number of vibrations 5000 times, and a 25 milliliter (mL) graduated cylinder.

[0098] When the tap density of the graphite negative electrode active material is within the above range, it is conducive to the formation of a reasonable pore structure between the particles of the negative electrode film layer, improving the wettability of the electrolyte to the negative electrode plate, and improving the cycle performance and storage performance of the secondary battery. At the same time, the appropriate tap density can also increase the compaction density of the negative electrode film layer, thereby increasing the energy density of the secondary battery.

[0099] In some embodiments, the particle size distribution of the graphite negative electrode active material (Dv90-Dv10) / Dv50 is 1.20-1.70. In some embodiments, the (Dv90-Dv10) / Dv50 of the graphite negative electrode active material is any value selected from 1.20, 1.30, 1.40, 1.50, 1.60, and 1.70, or a range consisting of any two of these values.

[0100] In some embodiments, the particle size distribution of the graphite negative electrode active material (Dv90-Dv10) / Dv50 is 1.35-1.60. In some embodiments, the (Dv90-Dv10) / Dv50 of the graphite negative electrode active material is any value selected from 1.35, 1.45, 1.55, and 1.60, or a range consisting of any two of these values.

[0101] The volume distribution particle sizes Dv10, Dv50, and Dv90 of the graphite negative electrode active material represent the particle sizes corresponding to the cumulative volume distribution percentages of the material reaching 10%, 50%, and 90%, respectively. These can be measured using methods known in the art. For example, characterization testing can be performed using a Malvern laser particle size analyzer, such as the Malvern Mastersizer-3000, with reference to GB / T19077-2016.

[0102] The particle size distribution of the graphite negative electrode active material meeting the above range helps to improve the concentration of the graphite negative electrode active material particle size, improve the arrangement concentration of the particles, reduce the tortuosity of the negative electrode plate, reduce the transmission path of the electrolyte, allow the electrolyte to fully infiltrate the negative electrode plate, and improve the cycle performance of the battery. At the same time, it can also reduce the uneven distribution of active ions in the graphite negative electrode active material caused by the large difference in particle size, reduce the side reaction between the smaller particle size graphite negative electrode active material and the electrolyte, and improve the cycle performance and storage performance of the secondary battery. At the same time, the particle size distribution of the graphite negative electrode active material is within the above range, and its particle stacking performance is good, which is conducive to improving the compaction density of the negative electrode film layer, thereby further improving the energy density of the secondary battery.

[0103] The present disclosure also provides a method for preparing a graphite negative electrode active material, comprising the following steps: providing raw materials; processing the raw materials to obtain a precursor; graphitizing the precursor to obtain an intermediate product; screening the intermediate product to obtain a graphite negative electrode active material; wherein the volume distribution particle size Dv1 of the graphite negative electrode active material is 1.5 μm-3 μm; and the graphite negative electrode active material includes a primary particle morphology.

[0104] By adopting the above preparation method, a graphite negative electrode active material having a volume distribution particle size Dv1 within a suitable range and containing primary particles can be prepared, which can further improve the cycle performance of the battery and extend the service life of the battery.

[0105] In some embodiments, the feedstock includes at least one of petroleum coke, needle coke, and pitch coke.

[0106] As used herein, the term "petroleum coke" refers to coke formed by carbonizing petroleum residue or petroleum asphalt at high temperatures.

[0107] In this article, the term "needle coke" refers to coal tar pitch or petroleum pitch, which, after undergoing liquid phase carbonization to generate an anisotropic mesophase, can produce coke with a needle-like texture through processes such as high-temperature carbonization.

[0108] As used herein, the term "pitch coke" refers to the solid material produced by carbonizing coal tar pitch at high temperatures.

[0109] In some embodiments, the feedstock comprises petroleum coke.

[0110] Petroleum coke has excellent anisotropy, which is conducive to the preparation of low-graphitization and low-expansion graphite materials, which is conducive to the long cycle life of the battery. At the same time, petroleum coke has high compaction density and high gram capacity, which is conducive to improving the energy density of the battery. In addition, the source of petroleum coke is more extensive, which is conducive to industrial production.

[0111] The above-mentioned raw materials generally include at least one of mosaic, regional, and fibrous structures. Generally, based on the morphological characteristics and isochromatic zone size of the char material under a polarizing microscope, isochromatic zones with a size less than 30 μm are classified as mosaic; isochromatic zones with a size greater than 30 μm are classified as regional; and anisotropic banded isochromatic zones are classified as fibrous.

[0112] In some embodiments of the present disclosure, the volume of the mosaic and regional structures in the raw material accounts for greater than or equal to 60% based on the total volume of the raw material structure. In some embodiments, the volume of the mosaic and regional structures in the raw material accounts for 65%-80% based on the total volume of the raw material structure.

[0113] In the present disclosure, the volume proportion of mosaic and regional structures in the raw materials can be tested using methods known in the art. As an example, according to the provisions of GB 1997-89, the raw materials are crushed to 1mm and mixed, and 40 grams (g) to 50 grams are separated. A square hole sieve is used to take 4g to 5g of a 0.07mm to 1.0mm grade sample for film making; according to the provisions of MT 116.1-86, powder coke and block coke optical films are prepared. The diameter of the powder coke optical film shall not be less than 22mm, and the volume occupied by the cement shall be less than 1 / 3; the sample is placed on a slide with clay, flattened, and then placed on the stage for focusing. After calibrating the microscope, the polarizer and analyzer are adjusted to make them orthogonal. Insert the azurite inspection plate (1λ) so that the field of view shows the interference color of the first order red; determine the step length of the moving ruler to ensure that more than 400 effective measuring points are evenly distributed, with a point spacing of 0.3mm to 0.5mm and a line spacing of 0.5mm to 0.8mm. Starting from one end of the sample, determine the microstructure category under the intersection of the crosshairs, and divide the number of effective measuring points of the mosaic-type and regional-type optical tissues by the total number of statistical testing points as the volume proportion of the mosaic-type and regional-type structures in the raw material.

[0114] In some embodiments, the processing of the raw material specifically comprises the following steps:

[0115] crushing, shaping and classifying the raw materials to obtain a precursor;

[0116] During the classification process, a certain proportion of fine powder is removed.

[0117] Among them, the mass proportion of the removed fine powder is 10%-35%. Based on the total mass of the raw material, the volume distribution particle size Dv50 of the fine powder is 3μm-7μm, and the (Dv90-Dv10) / Dv50 of the fine powder is greater than 1.6.

[0118] In some embodiments, based on the total mass of the raw material, the mass percentage of the removed fine powder is any value among 10%, 15%, 20%, 25%, 30%, 35%, or a range consisting of any two values ​​therein.

[0119] By controlling the mass ratio of removed fine powder within an appropriate range, the volume distribution particle size Dv1 of the graphite negative electrode active material can be controlled within an appropriate range, which can not only make the electrode have an excellent liquid absorption rate and the electrolyte can fully infiltrate the negative electrode, but also make the graphite particles have excellent electrical contact, thereby comprehensively improving the cycle performance of the battery.

[0120] In some embodiments, in the step of crushing the raw material, a crusher, such as a jaw crusher, can be used to crush the raw material. For example, the raw material can be crushed to a set particle size before screening.

[0121] In some embodiments, during the step of shaping the raw material, a shaping machine can be used to shape the crushed raw material. This shaping process can reduce burrs on the surface of the crushed raw material, facilitate obtaining a rounded graphite negative electrode active material, and facilitate increasing the compaction density of the negative electrode film layer.

[0122] In some embodiments, during the step of classifying the raw materials, an air classifier can be used to classify the shaped raw materials. In some embodiments, the induced air frequency can be greater than or equal to 20 Hz, and the classification frequency can be greater than or equal to 65 Hz. Classification can reduce the content of large and small particles in the precursor.

[0123] In some embodiments, the maximum power of the graphitization process is 70% to 90% of the rated power of the graphitization process equipment.

[0124] In some embodiments, the maximum power of the graphitization process is 70%, 75%, 80%, 85%, 90%, or any range therebetween, of the rated power of the graphitization process equipment. It is understood that the graphitization process equipment refers to any device capable of performing graphitization, including but not limited to Acheson furnaces, box furnaces, internal furnaces, continuous graphitization furnaces, electric calcining furnaces, medium-frequency furnaces, and tubular furnaces. The rated power of graphitization process equipment produced by different manufacturers may vary, and the rated power can be selected based on actual conditions.

[0125] The maximum power of the graphitization process used in this disclosure needs to be lower than the rated power of the graphitization equipment to achieve uniformity of the temperature field during the graphitization process, ensure the consistency of the material's gram capacity, and help improve the cycle life of the battery.

[0126] In some embodiments, the graphitization treatment equipment is an internal string furnace, and the rated power of the internal string furnace is 25,000 watts (W) to 32,000W.

[0127] In some embodiments, the graphitization treatment equipment is an Acheson furnace, and the rated power of the Acheson furnace is 28,000W-30,000W.

[0128] In some embodiments, the maximum power of the graphitization process is 23,000 W to 25,000 W. For example, it can be 23,000 W, 23,500 W, 24,000 W, 24,500 W, 25,000 W, or any range therebetween.

[0129] In some embodiments, the graphitization treatment is performed at a maximum power constant power time of 10 hours (h) to 50 hours.

[0130] In some embodiments, the graphitization treatment is performed at a constant power time of maximum power of 10 h, 13 h, 16 h, 19 h, 22 h, 25 h, 28 h, 31 h, 33 h, 36 h, 39 h, 42 h, 45 h, 48 h, 50 h, or any range therebetween.

[0131] In some embodiments, the graphitization treatment equipment is an internal series furnace, and the graphitization treatment is performed at a constant power of maximum power for 10 hours to 30 hours.

[0132] In some embodiments, the graphitization treatment equipment is an Acheson furnace, and the graphitization treatment is performed at a constant power time of maximum power for 30 hours to 50 hours.

[0133] Appropriate graphitization treatment at the constant power time of maximum power is not likely to cause excessive rearrangement of the precursor, resulting in a high specific surface area of ​​the graphite material after graphitization and deterioration of the cycle performance; it can also effectively increase the gram capacity of the graphite material, thereby facilitating the simultaneous improvement of the energy density and cycle life of the secondary battery.

[0134] In some embodiments, the volume distribution particle size Dv50 of the precursor is 12 μm-18 μm. In some embodiments, the volume distribution particle size Dv50 of the precursor is 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, or any range therebetween.

[0135] In some embodiments, the particle size distribution of the precursor (Dv90-Dv10) / Dv50 is 1.2-1.8. In some embodiments, the particle size distribution of the precursor (Dv90-Dv10) / Dv50 is 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8 or any range therebetween.

[0136] Regulating the volume distribution particle size Dv50 or particle size distribution of the precursor within a suitable range is beneficial to the volume distribution particle size Dv50 and specific surface area of ​​the graphite negative electrode active material within a suitable range, obtaining a graphite negative electrode active material with excellent cycle stability and storage stability, which is beneficial to improving the cycle life and storage performance of the battery.

[0137] In addition, the secondary battery, battery module, battery pack, and electric device of the present disclosure will be described below with reference to the drawings as appropriate.

[0138] In one embodiment of the present disclosure, a secondary battery is provided.

[0139] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0140] [Negative electrode]

[0141] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes the graphite negative electrode active material in any embodiment or prepared by the preparation method in any embodiment.

[0142] In some embodiments, the compaction density of the negative electrode film layer is 1.35 g / cm 3 -1.65g / cm 3 In some embodiments, the compaction density of the negative electrode film layer is 1.35 g / cm 3 , 1.40g / cm 3 , 1.45g / cm 3 , 1.50g / cm 3 , 1.55g / cm 3 , 1.60g / cm 3 , 1.65g / cm 3 or any range of values ​​between them.

[0143] In the present disclosure, the compaction density of the negative electrode film layer can be tested using methods known in the art. As an example, an electronic balance is used to weigh a negative electrode sheet test sample with an area of ​​S, and the weight is recorded as W1. The thickness of the negative electrode sheet T1 is measured using a caliper. The weighed electrode sheet film layer is then wiped off, the weight of the negative electrode current collector is weighed, recorded as W2, and the thickness of the negative electrode current collector T2 is measured using a caliper. The compaction density of the negative electrode film layer PD = (W1-W2) / [(T1-T2)×S].

[0144] A high compaction density of the negative electrode film can increase the battery's energy density. However, this high compaction density results in smaller pores in the negative electrode sheet, which can be blocked by graphite powder, affecting the electrolyte's wettability. The present disclosure effectively compensates for the effect of high compaction density on the sheet's wettability by controlling the volume distribution particle size Dv1 of the graphite negative electrode active material. This improves the sheet's wettability and increases the battery's cycle life, while maintaining a high energy density.

[0145] In some embodiments, the compaction density of the negative electrode film layer is 1.40 g / cm 3 -1.55g / cm3 In some embodiments, the compaction density of the negative electrode film layer is 1.40 g / cm 3 , 1.45g / cm 3 , 1.50g / cm 3 , 1.55g / cm 3 or any range of values ​​between them.

[0146] The compaction density of the negative electrode film layer is within an appropriate range, so that the negative electrode film layer has an appropriate number of pores, the electrolyte has good wettability to the negative electrode plate, reducing the possibility of local polarization, and improving the battery's cycle performance and storage performance. On the other hand, the compaction density in the appropriate range also ensures that the battery has a certain energy density.

[0147] In some embodiments, the surface density of the negative electrode film layer is 7 mg / cm 2 (mg / cm 2 )-14mg / cm 2 In some embodiments, the surface density of the negative electrode film layer is 7 mg / cm 2 , 8mg / cm 2 , 9mg / cm 2 、10mg / cm 2 、11mg / cm 2 , 12mg / cm 2 、13mg / cm 2 , 14mg / cm 2 or any range of values ​​between them.

[0148] In some embodiments, the surface density of the negative electrode film layer is 9 mg / cm 2 -12mg / cm 2 In some embodiments, the surface density of the negative electrode film layer is 9 mg / cm 2 、10mg / cm 2 、11mg / cm 2 , 12mg / cm 2 or any range of values ​​between them.

[0149] The areal density of the negative electrode film layer can be measured using any method and equipment known in the art. As an example, take a cold-pressed negative electrode sheet and punch it into small discs with an area of ​​S1. Weigh this disc and record its weight as M1. Then, wipe off the negative electrode film layer from the weighed negative electrode sheet and weigh the negative electrode current collector, recording it as M0. The areal density of the negative electrode film layer = (weight of the negative electrode sheet M1 - weight of the negative electrode current collector M0) / S1.

[0150] The surface density of the negative electrode film layer is within an appropriate range, and the thickness of the negative electrode plate is appropriate. On the one hand, the distance for the electrolyte to laterally infiltrate the plate is relatively short, the tortuosity of the plate is small, and the time required for the electrolyte to completely infiltrate the negative electrode plate is also relatively short, reducing the possibility of local polarization and improving the cycle performance of the battery. On the other hand, the surface density within an appropriate range also ensures that the battery has a certain energy density.

[0151] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0152] 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 base layer and a metal layer formed on at least one surface of the polymer base material. 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 base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0153] In some embodiments, the negative electrode film layer may further include other negative electrode active materials in addition to the above-mentioned graphite negative electrode active material. In some embodiments, the other negative electrode active materials include, but are not limited to, one or more of conventional natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based materials may include one or more of elemental silicon, silicon oxide, silicon-carbon composites, silicon-nitrogen composites, and silicon alloy materials. The tin-based materials may include one or more of elemental tin, tin oxide, and tin alloy materials.

[0154] In some embodiments, the negative electrode film layer further includes a binder, wherein the binder is at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0155] In some embodiments, the negative electrode film layer further includes a conductive agent, which is at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0156] In some embodiments, the negative electrode film layer further includes other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0157] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as graphite negative electrode active material, conductive agent, binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0158] [Positive electrode]

[0159] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes the positive electrode active material according to the first aspect of the present disclosure.

[0160] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0161] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. 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 material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0162] In some embodiments, the positive electrode active material may adopt the positive electrode active material for batteries that is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present disclosure is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0163] In some embodiments, the positive electrode film layer further includes a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0164] In some embodiments, the positive electrode film layer further includes a conductive agent, which may include, for example, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0165] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0166] [Electrolytes]

[0167] The electrolyte conducts ions between the positive and negative electrodes. This disclosure does not specifically limit the type of electrolyte, and the electrolyte can be selected based on needs. For example, the electrolyte can be liquid, gel, or solid.

[0168] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0169] In some embodiments, the electrolyte salt is at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethanesulfonyl imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0170] In some embodiments, the solvent is at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0171] In some embodiments, the electrolyte further includes additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives capable of improving certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0172] [Isolation film]

[0173] In some embodiments, the secondary battery further includes a separator. The present disclosure has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0174] In some embodiments, the separator is made of at least one of fiberglass, non-woven 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.

[0175] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0176] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0177] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0178] The present disclosure has no particular limitation on the shape of the secondary battery, which may be cylindrical, square, or any other shape. For example, FIG1 shows a secondary battery 5 having a square structure as an example.

[0179] In some embodiments, referring to Figure 2, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0180] In some embodiments, secondary batteries can be assembled into a battery module. The number of secondary batteries contained in the battery module can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0181] Figure 3 shows an example battery module 4. Referring to Figure 3 , within the battery module 4, multiple secondary batteries 5 may be arranged sequentially along the length of the battery module 4. Of course, any other arrangement is also possible. Furthermore, the multiple secondary batteries 5 may be secured together using fasteners.

[0182] In some embodiments, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 may be received in the receiving space.

[0183] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0184] Figures 4 and 5 illustrate an example battery pack 1. 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 comprises an upper case 2 and a lower case 3. The upper case 2 can be placed over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0185] In addition, the present disclosure further provides an electric device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present disclosure. The secondary battery, battery module, or battery pack can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device may include 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., but is not limited thereto.

[0186] As the electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0187] Figure 6 shows an example of an electric 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 the secondary battery, a battery pack or battery module can be used.

[0188] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0189] Example

[0190] The following examples are provided. The examples described below are illustrative and are intended only to explain the present disclosure and are not to be construed as limiting the present disclosure. Where specific techniques or conditions are not specified in the examples, the methods were performed according to those described in the literature in the art or according to the product specifications. Reagents or instruments used without manufacturer's indication are all commercially available conventional products.

[0191] 1. Preparation method

[0192] Example 1

[0193] (1) Preparation of graphite negative electrode active materials

[0194] A petroleum coke raw material having a mosaic and regional structure volume accounting for 60% is coarsely crushed, and the coarsely crushed material is then crushed and sieved. The sieved material is shaped and graded, and a certain amount of fine powder is removed during the grading process to obtain a precursor, wherein the mass of the removed fine powder accounts for 21% of the total mass of the petroleum coke raw material, and the volume distribution particle size Dv50 of the precursor is 15.5 μm, and the particle size distribution (Dv90-Dv10) / Dv50 is 1.50, wherein the fine powder refers to particles with a Dv50 particle size of 3 μm to 7 μm and a particle size distribution (Dv90-Dv10) / Dv50 greater than 1.6;

[0195] The precursor is graphitized in an Acheson furnace at a temperature of 2800° C. and a maximum power of 24,000 W (this refers to the actual power used by the Acheson furnace, which is approximately 85% of the rated power of the Acheson furnace). After the power is maintained constant for 40 hours, the surface temperature of the graphite crucible in the Acheson furnace is cooled to 300° C. to obtain an intermediate product.

[0196] The intermediate product is screened and demagnetized to obtain graphite negative electrode active material. The graphite negative electrode active material is mainly composed of primary particles, which account for more than 85% of the material. The Dv1 of the graphite negative electrode active material is 2.0μm, Dv50 is 14.3μm, and BET is 1.1m. 2 / g.

[0197] (2) Preparation of negative electrode sheet

[0198] The graphite negative electrode active material prepared above, the conductive agent Super P, the thickener sodium carboxymethyl cellulose, and the binder styrene-butadiene rubber (SBR) were mixed in a dry material mass ratio of 95.4:1.6:1.2:1.8, and deionized water was added as a solvent. The mixture was stirred in a vacuum mixer until the system became uniform to obtain a negative electrode slurry. The negative electrode slurry was evenly coated on the negative electrode current collector copper foil, and the negative electrode sheet was obtained after drying, cold pressing, and slitting. The compacted density of the negative electrode film layer was 1.40 g / cm 3 , with a surface density of 9.6 mg / cm 2 .

[0199] (2) Preparation of positive electrode sheet

[0200] The positive electrode active material lithium iron phosphate (LFP), the conductive agent Super P, and the binder polyvinylidene fluoride were mixed in a mass ratio of 97:1:2, and the solvent N-methylpyrrolidone was added. The mixture was stirred in a vacuum mixer until the system was uniform to obtain a positive electrode slurry. The positive electrode slurry was evenly coated on the positive electrode current collector aluminum foil, and the positive electrode sheet was obtained after drying, cold pressing, and slitting. The compacted density of the positive electrode sheet is 2.50g / cm 3 , with a surface density of 19.7 mg / cm 2 .

[0201] 4) Preparation of electrolyte

[0202] In an argon atmosphere glove box with a water content of less than 10 ppm, diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and ethylene carbonate (EC) were mixed in a weight ratio of 1:1:1 to obtain an organic solvent. LiPF6 was then dissolved in the organic solvent to prepare an electrolyte with a concentration of 1.0 mol / L. Vinylene carbonate (VC) was then added, and the VC content was 2% of the total mass of the electrolyte.

[0203] 5) Isolation film

[0204] Polypropylene film is used as the isolation film.

[0205] 6) Preparation of secondary batteries

[0206] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive and negative electrode sheets to serve as an isolation, and then wound to obtain an electrode assembly; the electrode assembly is placed in an outer package, dried, and then injected with electrolyte, and after vacuum packaging, standing, forming, shaping and other processes, a lithium-ion battery is obtained.

[0207] The preparation methods of Examples 2-3 are basically the same as those of Example 1, except that the mass proportion of the removed fine powder is different, as shown in Table 1.

[0208] Table 1

[0209] The preparation methods of Examples 4-6 are basically the same as those of Example 1, except that the volume distribution particle size Dv50 of the precursor, the particle size distribution (Dv90-Dv10) / Dv50 of the precursor, and the constant power time of the graphitization treatment at maximum power are regulated, as shown in Table 2.

[0210] Table 2

[0211] The preparation method of Comparative Example 1-2 is basically the same as that of Example 1, except that the mass ratio of the removed fine powder is as shown in Table 1.

[0212] The preparation method of the graphite negative electrode active material in Comparative Example 3 is as follows:

[0213] S1: crushing the needle-shaped raw coke, shaping it, classifying it, removing fine powder, and obtaining a precursor with a Dv50 of 11 μm;

[0214] S2: The precursor obtained in step S1 was added to a reactor, and 10% of the mass of the precursor relative to the binder asphalt (the Dv50 of the asphalt was 5 μm-8 μm) was added for granulation. The temperature was raised to 560°C at a rate of 10°C / min at room temperature, and then kept at this temperature for 8 hours to obtain intermediate 1. The Dv50 of intermediate 1 was 18 μm.

[0215] S3: The intermediate 1 obtained in step S2 is added to a graphitization furnace, and the temperature is raised to 3000°C for graphitization treatment. The power of the graphitization treatment adopts the rated power of the equipment 29000W, and the obtained intermediate product is sieved and demagnetized to obtain a graphite negative electrode active material; the graphite negative electrode active material is mainly in the form of secondary particles, the content of the secondary particle morphology is about 70% or more, Dv1 is 2.3μm, Dv50 is 14μm, and the gram capacity is 357mAh / g.

[0216] 2. Performance Testing

[0217] 1. Secondary battery black spot test

[0218] At 25° C., the batteries of the above embodiments and comparative examples were charged at a constant current of 0.33C to a voltage of 3.65V, and then disassembled in a dry room to observe whether there were black spots on the surface of the negative electrode.

[0219] (1) The total area of ​​black spots / total area of ​​the negative electrode is ≤1%, and the area of ​​black spots in a single electrode is ≤8% of the area of ​​a single electrode.

[0220] (2) 1% < total area of ​​black spots / total area of ​​negative electrode ≤ 3%, or 8% < area of ​​black spots in a single electrode / area of ​​a single electrode ≤ 15% is defined as secondary black spots;

[0221] (3) The total area of ​​black spots / total area of ​​the negative electrode is greater than 3%, or the area of ​​black spots in a single electrode / area of ​​a single electrode is greater than 15%, which is defined as level 3 black spots.

[0222] 2. Cycle performance test of secondary batteries

[0223] At 60°C, the batteries of the above examples and comparative examples were charged at a constant current of 1C to a voltage of 3.65V. They were then charged at a constant voltage of 3.65V to a current ≤ 0.05C. The batteries were then discharged at a constant current of 1C to a voltage of 2.5V. This constituted one charge and discharge cycle, and the discharge capacity (C1) of the first cycle was recorded. This charge and discharge cycle was repeated until the battery capacity decayed to 80% of the initial capacity (C1). The test was then stopped, and the number of test cycles was recorded.

[0224] 3. Storage performance test of secondary batteries

[0225] In an environment of 25°C, a charge and discharge test is carried out. The battery is charged at a constant current of 1C to a voltage of 3.65V, and then charged at a constant voltage of 3.65V to a current of ≤0.05C. The battery is then discharged at a constant current of 1C to a voltage of 2.5V. This is a charge and discharge process. The discharge capacity of the first cycle is recorded, which is the initial discharge capacity, recorded as C0. The battery cell is then fully charged and placed in an environment of 60°C for different periods of time. Every 30 days, it is taken out and tested at 25°C for the remaining capacity C1. This is a storage cycle, and the discharge capacity this time is the discharge capacity after the first storage. Subsequently, the first storage test process is repeated, the discharge capacity value during the storage process is recorded, and the 120-day cycle capacity retention rate is recorded.

[0226] 3. Results

[0227] As shown in Table 3, the volume distribution particle size Dv1 of the graphite negative electrode active materials provided in Examples 1-3 of the present disclosure ranges from 1.5 μm to 3 μm, and the graphite negative electrode active materials are primarily primary particles. Comparing Examples 1-3 with Comparative Examples 1-3 demonstrates that the graphite negative electrode active materials disclosed herein can reduce the likelihood of black spots on the electrode sheet, increase the number of battery cycles, and improve the cycle life and service life of the battery.

[0228] Table 3

[0229] As shown in Table 4, the volume distribution particle size Dv50 of the graphite negative electrode active material is 12μm-16μm, which can effectively balance the cycle life and storage stability of the battery. The volume distribution particle size Dv50 of the graphite negative electrode active material is 13μm-15μm, which can further improve the cycle life and storage stability of the battery.

[0230] As shown in Table 4, the specific surface area of ​​the graphite negative electrode active material is less than or equal to 1.4m 2 / g, which can effectively balance the cycle life and storage stability of the battery. The specific surface area of ​​the graphite negative electrode active material is 0.6m 2 / g-1.3m 2 / g, which can further improve the cycle life and storage stability of the battery.

[0231] Table 4

[0232] It should be noted that the present disclosure is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and within the scope of the technical solution of the present disclosure, embodiments having substantially the same structure as the technical concept and exerting the same effects are all included in the technical scope of the present disclosure. In addition, within the scope of the present disclosure, various modifications that can be imagined by those skilled in the art to the embodiments, and other methods constructed by combining some of the constituent elements of the embodiments are also included in the scope of the present disclosure.

Claims

1. A graphite negative electrode active material, characterized in that: The volume distribution particle size Dv1 of the graphite negative electrode active material is 1.5 μm-3 μm; the graphite negative electrode active material includes a primary particle morphology.

2. The graphite negative electrode active material according to claim 1, characterized in that: The specific surface area of ​​the graphite negative electrode active material is less than or equal to 1.4 m 2 / g, optional 0.6m 2 / g-1.3m 2 / g.

3. The graphite negative electrode active material according to claim 1 or 2, characterized in that: The volume distribution particle size Dv50 of the graphite negative electrode active material is 12 μm-16 μm, and can be optionally 13 μm-15 μm.

4. The graphite negative electrode active material according to any one of claims 1 to 3, characterized in that Based on the total number of particles of the negative graphite negative electrode active material, the number of the primary particles accounts for greater than or equal to 80%, and can be optionally 85%-100%.

5. The graphite negative electrode active material according to any one of claims 1 to 4, characterized in that The gram capacity of the graphite negative electrode active material is greater than or equal to 340 mAh / g, and can be optionally 341 mAh / g-347 mAh / g.

6. The graphite negative electrode active material according to any one of claims 1 to 5, characterized in that The tap density of the graphite negative electrode active material is 1.2 g / cm 3 -1.4g / cm 3 .

7. The graphite negative electrode active material according to any one of claims 1 to 6, characterized in that The particle size distribution of the graphite negative electrode active material is (Dv90-Dv10) / Dv50 is 1.20-1.70, and can be optionally 1.35-1.

60.

8. A method for preparing a graphite negative electrode active material, characterized in that: The steps include: Provide raw materials; Processing the raw material to obtain a precursor; The precursor is graphitized to obtain an intermediate product; The intermediate product is subjected to screening treatment to obtain a graphite negative electrode active material; The volume distribution particle size Dv1 of the graphite negative electrode active material is 1.5 μm-3 μm; and the graphite negative electrode active material includes a primary particle morphology.

9. The preparation method according to claim 8, characterized in that: The processing of raw materials specifically comprises the following steps: crushing, shaping and classifying the raw materials to obtain a precursor; During the classification process, a certain proportion of fine powder is removed. Among them, the mass proportion of the removed fine powder is 10%-35%, based on the total mass of the raw material; the volume distribution particle size Dv50 of the fine powder is 3μm-7μm, and the (Dv90-Dv10) / Dv50 of the fine powder is greater than 1.

6.

10. The preparation method according to claim 8 or 9, characterized in that: The maximum power of the graphitization treatment is 70%-90% of the rated power of the graphitization equipment.

11. The preparation method according to claim 10, characterized in that: The maximum power of the graphitization treatment is 23000W-25000W; and / or the constant power time of the graphitization treatment at the maximum power is 10h-50h.

12. The preparation method according to any one of claims 8 to 11, characterized in that: The precursor satisfies at least one of the following conditions: The volume distribution particle size Dv50 of the precursor is 12 μm-18 μm; and / or, The particle size distribution of the precursor (Dv90-Dv10) / Dv50 is 1.2-1.

8.

13. A secondary battery, comprising a negative electrode plate, characterized in that: The negative electrode sheet comprises the graphite negative electrode active material according to any one of claims 1 to 7 or the graphite negative electrode active material prepared by the preparation method according to any one of claims 8 to 12.

14. The secondary battery according to claim 13, characterized in that: The compaction density of the negative electrode film layer is 1.35 g / cm 3 -1.65g / cm 3 , optional 1.40g / cm 3 -1.55g / cm 3 .

15. The secondary battery according to claim 13 or 14, characterized in that: The surface density of the negative electrode film layer is 7 mg / cm 2 -14mg / cm 2 , optional 9mg / cm 2 -12mg / cm 2 .

16. An electrical device, characterized in that: A secondary battery comprising the secondary battery according to any one of claims 13 to 15.

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