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

Abstract

A graphite negative electrode active material and a preparation method therefor, a secondary battery, and an electric device. The degree of graphitization of the graphite negative electrode active material is 88%-93%, and the oil absorption value of the graphite negative electrode active material does not exceed 50 ml / 100 g. 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 and electrical device

[0001] Cross-references

[0002] The present disclosure refers to Chinese patent application No. 202311676609.6, filed on December 7, 2023, entitled “Graphite negative electrode active material, preparation method thereof, secondary battery and electrical device”, 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, 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] This disclosure is made in light of the above-mentioned issues, and its purpose is to provide a graphite negative electrode active material and a preparation method thereof, a secondary battery, and an electrical device, which can effectively improve the cycle life of the battery and extend the battery's service life. …

[0007] A first aspect of the present disclosure provides a graphite negative electrode active material, wherein the graphitization degree of the graphite negative electrode active material is 88%-93%, and the oil absorption value of the graphite negative electrode active material does not exceed 50 ml / 100 g.

[0008] On the one hand, the oil absorption value of the graphite negative electrode active material is controlled to be no more than 50ml / 100g, the graphite negative electrode active material has good dispersion in the negative electrode slurry, the negative electrode slurry has excellent anti-settling properties, it is easy to control the coating weight during the electrode coating process, and it is easy to prepare an electrode sheet with uniform distribution and thickness of the graphite negative electrode active material, reducing the possibility of local current density unevenness during charging and discharging, reducing the lithium precipitation phenomenon caused by electrode polarization, improving the cycle performance and storage performance of the battery, and extending the service life of the battery. On the other hand, the graphitization degree of the graphite negative electrode active material is controlled to be 88%-93%. The interlayer spacing of the graphite negative electrode active material is large, which is conducive to the rapid deintercalation of active ions. When active ions are embedded in the negative electrode, the expansion of the graphite negative electrode active material is small, which is conducive to the long cycle of the battery. At the same time, the appropriate graphitization degree is conducive to increasing the specific capacity of the graphite negative electrode active material, providing a material basis for the preparation of high energy density batteries.

[0009] In summary, graphite negative electrode active materials that meet the above requirements are conducive to improving the cycle performance and storage performance of the battery, and the battery has a high energy density.

[0010] In any embodiment, the oil absorption value of the graphite negative electrode active material is 30 ml / 100 g to 43 ml / 100 g.

[0011] In summary, the lower the oil absorption value of a graphite anode active material, the better its dispersion in the anode slurry, which facilitates the preparation of anode sheets with uniformly distributed graphite, thereby improving the battery's cycling performance. However, if the oil absorption value of a graphite anode active material is too low, high requirements are placed on the particle regularity or particle size distribution of the graphite anode active material, resulting in high costs and unfavorable for industrial promotion.

[0012] By controlling the oil absorption value of the graphite negative electrode active material within an appropriate range and meeting the requirements of long cycle performance, the cost of the graphite negative electrode active material can be reduced, which is beneficial to industrial production.

[0013] In any embodiment, the particle size distribution of the graphite negative electrode active material (Dv90-Dv10) / Dv50 is 1.2-1.6.

[0014] The particle size distribution (Dv90-Dv10) / Dv50 of the graphite negative electrode active material is within the above range. On the one hand, the oil absorption value of the graphite can be regulated to a lower value, which is beneficial to improving the uniformity of the negative electrode slurry and the uniformity of the graphite negative electrode active material in the negative electrode sheet. At the same time, it can also reduce the negative impact of large-particle graphite negative electrode active materials on the cycle performance and storage performance, thereby comprehensively improving the cycle performance and storage performance of the battery.

[0015] In any embodiment, 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 greater than or equal to 85%. In some embodiments, the number of primary particles in the graphite negative electrode active material accounts for 85%-100%.

[0016] Compared to secondary particles, primary particles have fewer gaps between particles, smaller surface angles, and a smoother particle morphology. This results in lower oil absorption for the graphite anode active material and better slurry leveling, facilitating the preparation of anode sheets with uniform distribution of graphite anode active material and improving battery cycle performance. Furthermore, compared to secondary particles, primary particles have greater structural stability and are less prone to breakage during cycling, thus improving battery cycle performance.

[0017] 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.

[0018] The graphite negative electrode active material has a low specific surface area, which is conducive to obtaining a graphite negative electrode active material with a low oil absorption value. At the same time, it also makes the graphite negative electrode active material have low surface activity, thereby reducing the consumption of active ions by SEI film formation and improving the cycle performance and storage performance of the battery.

[0019] 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.

[0020] The graphite negative electrode active material has a large volume distribution particle size Dv50, and the negative electrode film layer has a large pore size, 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.

[0021] In any embodiment, the graphite negative electrode active material satisfies at least one of the following:

[0022] (1) The powder compaction density of graphite negative electrode active material under a pressure of 49000N is less than or equal to 1.85g / cm 3 In some embodiments, the powder compaction density of the graphite negative electrode active material under a pressure of 49000N is 1.70g / cm 3 -1.85g / cm 3 ;

[0023] (2) The tap density of the graphite negative electrode active material is 1.2 g / cm 3 -1.4g / cm 3 ;

[0024] (3) 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 to 347 mAh / g.

[0025] The powder compaction density of the graphite negative electrode active material under a pressure of 49000N is within a suitable range, which can further improve the cycle performance of the battery.

[0026] When the tap density of the graphite negative electrode active material is within the above range, the compaction density of the negative electrode sheet can be improved, thereby increasing the energy density of the secondary battery; it is also beneficial to form a reasonable pore structure between the particles of the negative electrode film layer, improving the transmission performance of active ions and electrons, and improving the cycle performance and storage performance of the secondary battery.

[0027] Graphite anode active materials have high gram capacity, providing a material foundation for high-energy-density batteries. Furthermore, when the gram capacity of graphite anode active materials is within the stated range, the material undergoes relatively small lattice expansion during cycling, exhibits excellent crystal structure stability, and reduces irreversible consumption of active ions, thereby improving the battery's cycling and storage performance.

[0028] The present disclosure also provides a method for preparing a graphite negative electrode active material, which is characterized by comprising the following steps:

[0029] Provide raw materials;

[0030] processing raw materials to obtain precursors;

[0031] The precursor is graphitized to obtain an intermediate product;

[0032] The intermediate product is screened to obtain a graphite negative electrode active material; the graphitization degree of the graphite negative electrode active material is 88%-93%, and the oil absorption value of the graphite negative electrode active material does not exceed 50ml / 100g.

[0033] By adopting the above preparation method, a graphite negative electrode active material with low oil absorption value and low graphitization degree can be prepared, which can improve the cycle performance of the battery and extend the service life of the battery.

[0034] In any embodiment, the feedstock comprises at least one of petroleum coke, needle coke, and pitch coke. In some embodiments, the feedstock is petroleum coke.

[0035] Based on the total volume of the raw material structure, the volume of the mosaic and regional structures accounts for greater than or equal to 50%. In some embodiments, based on the total volume of the raw material structure, the volume of the mosaic and regional structures accounts for 50%-65%.

[0036] In any embodiment, the stock has a tackiness index of less than or equal to 10. In some embodiments, the stock has a tackiness index of 1-9.

[0037] In any embodiment, the precursor satisfies at least one of the following conditions:

[0038] The volume distribution particle size Dv50 of the precursor is 12 μm-18 μm; and / or,

[0039] The particle size distribution of the precursor (Dv90-Dv10) / Dv50 is 1.2-1.8.

[0040] Controlling the volume distribution particle size Dv50 or particle size distribution (Dv90-Dv10) / Dv50 of the precursor within a suitable range is conducive to controlling the particle size distribution (Dv90-Dv10) / Dv50 of the graphite negative electrode active material within a suitable range, thereby regulating the oil absorption value of the graphite negative electrode active material within a smaller range.

[0041] In any embodiment, the maximum power of the graphitization process is 70% to 90% of the rated power of the graphitization equipment.

[0042] In any embodiment, 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.

[0043] In any embodiment, the screening process of the intermediate product specifically comprises the following steps:

[0044] The intermediate product is screened to remove particles with a maximum particle size Dmax greater than 100 μm, thereby obtaining a graphite negative electrode active material.

[0045] Remove large particles from intermediate products to reduce the negative impact of large particle materials on battery cycle performance and storage performance.

[0046] The third aspect of the present disclosure provides a secondary battery, including a negative electrode plate, the negative electrode plate including a negative electrode collector and a negative electrode film layer formed on at least one surface of the negative electrode collector, the negative electrode film layer including the graphite negative electrode active material of the first aspect of the present disclosure or the graphite negative electrode active material prepared by the preparation method of the second aspect.

[0047] In any embodiment, the negative electrode film layer includes a conductive agent, and the mass content of the conductive agent is greater than or equal to 1.5% based on the mass of the negative electrode film layer. In some embodiments, the mass content of the conductive agent is 1.8%-2.5%.

[0048] 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

[0049] FIG. 1 is a schematic diagram of a secondary battery according to an embodiment of the present disclosure.

[0050] FIG. 2 is an exploded view of the secondary battery according to the embodiment of the present disclosure shown in FIG. 1 .

[0051] FIG3 is a schematic diagram of a battery module according to an embodiment of the present disclosure.

[0052] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present disclosure.

[0053] FIG. 5 is an exploded view of the battery pack shown in FIG. 4 according to an embodiment of the present disclosure.

[0054] 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.

[0055] Description of reference numerals:

[0056] 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

[0057] Below, the embodiments of the graphite negative electrode active material and its preparation method, secondary battery and electric device disclosed in the present invention are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by 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.

[0058] " 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.

[0059] Unless otherwise specified, all embodiments and optional embodiments of the present disclosure can be combined with each other to form new technical solutions.

[0060] Unless otherwise specified, all technical features and optional technical features disclosed herein can be combined with each other to form a new technical solution.

[0061] 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.

[0062] 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.

[0063] 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).

[0064] The negative electrode active material is the main material of the battery. The purpose of storing electricity is achieved by storing lithium in the negative electrode active material during charging. The performance of the negative electrode active material has an important influence on the cycle life of the battery. In the prior art, in order to obtain a long cycle battery, the graphitization degree of the negative electrode active material or the compaction density of the negative electrode plate are generally controlled to obtain a battery with a long cycle life. However, another factor that affects the capacity decay is the uniformity of the active material in the negative electrode plate. If the negative electrode active material is unevenly mixed with the conductive agent, binder, etc. during the preparation of the negative electrode slurry, the negative electrode slurry will precipitate or agglomerate, and the active material in the negative electrode plate formed by coating will be unevenly distributed or the plate thickness will be uneven, which can easily cause local current unevenness during the cycle. The difference in the active ion diffusion concentration will cause lithium precipitation and capacity decay, affecting the cycle performance and storage performance of the battery.

[0065] [Graphite negative electrode active material]

[0066] Based on this, the present disclosure proposes a graphite negative electrode active material, wherein the graphitization degree of the graphite negative electrode active material is 88%-93%, and the oil absorption value of the graphite negative electrode active material does not exceed 50 milliliters (ml) / 100 grams (g).

[0067] In some embodiments, the degree of graphitization of the graphite negative electrode active material is any value selected from 88%, 89%, 90%, 91%, 92%, and 93%, or a range consisting of any two of these values.

[0068] In this article, the term "degree of graphitization" macroscopically characterizes the proportion of the material that reaches a complete graphite crystal structure; microscopically, it refers to the degree to which the carbon structure in different transition states approaches the ideal graphite crystal.

[0069] The degree of graphitization of graphite anode active materials reflects the integrity of the graphite crystal structure within the material, specifically the regularity of the arrangement of carbon atoms within the graphite structure. A material with a high degree of graphitization indicates a small spacing between graphite layers, smaller lattice rotation, less scattered stacking of layers, and more orderly arrangement. This results in a high specific capacity and is beneficial for achieving high-energy-density secondary batteries. A material with a low degree of graphitization indicates a large spacing between graphite layers, which facilitates rapid intercalation and deintercalation of active ions. This reduces expansion during lithium insertion, resulting in shallow charge and discharge cycles and long-term storage.

[0070] In the present disclosure, the graphitization degree of the graphite negative electrode active material can be tested using instruments and methods known in the art. For example, an X-ray diffractometer (such as Bruker D8 Discover) can be used for testing. The test can refer to JISK 0131-1996 and JB / T 4220-2011 to obtain the average interlayer spacing d of the C(002) crystal plane in the material crystal structure. 002 Then according to the formula g=(0.344-d 002 ) / (0.344-0.3354)×100% to calculate the degree of graphitization. In the above formula, d 002 It is the average interlayer spacing of the C(002) planes in the material's crystal structure expressed in nanometers (nm).

[0071] In some embodiments, the oil absorption value of the graphite negative electrode active material is no more than 30 ml / 100 g, no more than 35 ml / 100 g, no more than 40 ml / 100 g, no more than 45 ml / 100 g, or no more than 50 ml / 100 g.

[0072] As used herein, the term "oil absorption value" refers to the volume of linseed oil that can be absorbed by 100g of graphite negative electrode active material. For example, an oil absorption value of 40ml / 100g of graphite negative electrode active material means that 100g of graphite negative electrode active material can absorb 40ml of linseed oil.

[0073] The oil absorption of graphite negative electrode active materials can be tested using methods and equipment known in the art. For example, the following steps are performed: Test oil and graphite negative electrode active material samples are obtained, and a torque threshold is set for the oil absorption tester. The oil is then added to the sample in the mixing chamber of the oil absorption tester at a constant rate. As the amount of oil absorbed by the sample increases, the viscosity of the sample-oil mixture increases. When the viscosity of the mixture reaches the preset torque threshold, the tester stops and calculates the volume of oil absorbed per unit mass of the sample. This value is the oil absorption value (QI) of the sample. The test oil used is linseed oil (DBP), and the torque threshold is 1 Newton (N).

[0074] The oil absorption value of graphite anode active materials is primarily related to the material's specific surface area, surface properties, particle shape, and particle size distribution. It reflects the material's dispersibility in the anode slurry. Low oil absorption indicates excellent dispersibility in the anode slurry, resulting in excellent anti-settling and dispersibility. This makes it easier to control the coating weight during electrode coating, allowing the production of anode electrodes with uniform graphite anode active material distribution and thickness. This reduces the likelihood of localized current density unevenness during charge and discharge, mitigates lithium plating caused by electrode polarization, improves battery cycle performance, and extends both battery life and storage life.

[0075] In summary, the graphite negative electrode active material has a suitable range of graphitization degree and oil absorption value, which is beneficial to improving the cycle performance and storage performance of the battery, and the battery has a high energy density.

[0076] In some embodiments, the oil absorption value of the graphite negative electrode active material is 30 ml / 100 g to 43 ml / 100 g.

[0077] In some embodiments, the oil absorption value of the graphite negative electrode active material is any value of 30ml / 100g, 32ml / 100g, 34ml / 100g, 36ml / 100g, 38ml / 100g, 40ml / 100g, 42ml / 100g, 43ml / 100g, or a range consisting of any two of these values.

[0078] As mentioned above, the lower the oil absorption value of a graphite anode active material, the better its dispersion in the anode slurry, which facilitates the preparation of anode sheets with uniformly distributed graphite, thereby improving the battery's cycling performance. However, if the oil absorption value of a graphite anode active material is too low, high requirements are placed on the particle regularity or particle size distribution of the graphite anode active material, resulting in high costs and unfavorable for industrial promotion.

[0079] By controlling the oil absorption value of the graphite negative electrode active material within an appropriate range and meeting the requirements of long cycle performance, the cost of the graphite negative electrode active material can be reduced, which is beneficial to industrial production.

[0080] In some embodiments, the particle size distribution of the graphite negative electrode active material (Dv90-Dv10) / Dv50 is 1.2-1.6.

[0081] In some embodiments, the particle size distribution of the graphite negative electrode active material (Dv90-Dv10) / Dv50 is any value of 1.2, 1.3, 1.4, 1.5, 1.6, or a range consisting of any two values ​​thereof.

[0082] The volume distribution particle sizes Dv10, Dv50, and Dv90 of the graphite negative electrode active material represent the particle sizes corresponding to the 10%, 50%, and 90% cumulative volume distribution percentages of the material, respectively. These can be measured using instruments and methods known in the art. For example, they can be conveniently measured using a laser particle size analyzer, referring to the particle size distribution laser diffraction method specified in GB / T 19077-2016. The testing instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0083] The particle size distribution (Dv90-Dv10) / Dv50 of the graphite negative electrode active material will affect the material's oil absorption value. When the particle size distribution (Dv90-Dv10) / Dv50 of the graphite negative electrode active material is too large, the oil absorption value of the graphite negative electrode active material is large, and the small and large particles in the graphite negative electrode active material hinder the dispersion of the graphite negative electrode active material in the negative electrode slurry, which will adversely affect the uniformity and thickness of the electrode sheet and deteriorate the battery's cycle performance. When the particle size distribution (Dv90-Dv10) / Dv50 of the graphite negative electrode active material is too small, the preparation process of the graphite negative electrode active material is relatively complicated, the yield of the graphite negative electrode active material is significantly reduced, and the cost is significantly increased.

[0084] In summary, the particle size distribution (Dv90-Dv10) / Dv50 of the graphite negative electrode active material is within an appropriate range, the oil absorption value of the graphite negative electrode active material is low, the battery cycle performance is excellent, and at the same time, the cost of the graphite negative electrode active material can be reduced, which is conducive to industrial application.

[0085] 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 greater than or equal to 85%.

[0086] 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 85%-100%.

[0087] 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 85%, 90%, 95%, 100%, or a range consisting of any two values ​​therein.

[0088] In some embodiments, the particles in the graphite negative electrode active material include primary particles and secondary particles. Herein, "primary particles," also referred to as single particles, generally refer to non-agglomerated particles. "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).

[0089] 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. Use a scanning electron microscope; an energy spectrometer (such as ZEISS SEM (sigma300)) 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 at a certain magnification (for example, 500 times or 1000 times), the number of secondary particles and the total number of particles in the test area are counted. 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.

[0090] Compared to secondary particles, primary particles have fewer gaps between particles, smaller surface angles, and a smoother particle morphology. This results in lower oil absorption for the graphite anode active material and better slurry leveling, facilitating the preparation of anode sheets with uniform distribution of graphite anode active material and improving battery cycle performance. Furthermore, compared to secondary particles, primary particles have greater structural stability and are less prone to breakage during cycling, thus improving battery cycle performance.

[0091] 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).

[0092] 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.

[0093] As used herein, the term "specific surface area" refers to the sum of the total external surface area of ​​all particles per gram of material.

[0094] 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.

[0095] The specific surface area of ​​the graphite negative electrode active material will affect the oil absorption value of the material. A low specific surface area will result in a low oil absorption value, thereby improving the distribution uniformity of the graphite negative electrode active material in the negative electrode sheet and the uniformity of the electrode sheet thickness, and improving the battery's cycle performance and storage performance. At the same time, 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 SEI film formation and improving the battery's cycle performance and storage performance.

[0096] In some embodiments, the specific surface area of ​​the graphite negative electrode active material is 0.6 m 2 / g-1.3m 2 / g.

[0097] 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, 1.3m 2Any value in / g or a range consisting of any two values ​​in it.

[0098] As mentioned above, graphite negative electrode active materials have a small specific surface area and low oil absorption, which is beneficial to the battery's cycle life. However, too small a specific surface area can affect the electrolyte's wettability to the electrode, affecting the electrode's dynamic performance and making lithium deposition more likely to affect the battery's cycle life and storage life. An appropriate specific surface area can further improve the battery's cycle life and storage life.

[0099] In some embodiments, the volume distribution particle size Dv50 of the graphite negative electrode active material is 12 micrometers (μm) to 16 μm.

[0100] 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.

[0101] The graphite negative electrode active material has a large volume distribution particle size Dv50, and the negative electrode film layer has a large pore size, 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.

[0102] In some embodiments, the volume distribution particle size Dv50 of the graphite negative electrode active material is 13 μm-15 μm.

[0103] 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.

[0104] The graphite negative electrode active material has a suitable volume distribution particle size Dv50, and the negative electrode film layer has a suitable pore size, which facilitates the electrolyte to fully infiltrate the negative electrode plate, reducing the possibility of local polarization of the plate and reducing the impact of black spots on the battery's cycle life and storage performance. At the same time, it is conducive to improving the transmission performance of active ions and electrons. The plate has excellent kinetic performance and reduces the impact of lithium plating on the battery life.

[0105] In some embodiments, the powder compaction density of the graphite negative electrode active material under a pressure of 49000N is less than or equal to 1.85 g / cm 3 (g / cm 3 ).

[0106] In this article, the term "powder compaction density" refers to the density of the powder to be tested under a preset pressure.

[0107] The method for measuring the compacted density of the powder can be any method known in the art. For example, referring to GB / T 24533-2009, 1g of graphite negative electrode active material powder is weighed and added to a container with a bottom area of ​​1.327 cm. 2 (cm 2 ) in a mold, pressurize to a specific pressure, for example, 49000N, maintain the pressure for 30 seconds (s), then release the pressure and maintain it for 10 seconds, and measure the powder compaction density of the graphite negative electrode active material under the selected pressure by an electronic pressure testing machine (such as UTM7305 electronic pressure testing machine).

[0108] When the graphite powder compaction density of the graphite negative electrode active material under a pressure of 49000N is greater than 1.85g / cm 3 The particle strength of the graphite negative electrode active material is not enough. It is constantly squeezed during the cycle and it is difficult to maintain the original pore structure of the electrode. It will change the tortuosity of the electrode, increase the lithium ion insertion path, affect the battery's kinetic performance, and is not conducive to achieving long-term cycle stability.

[0109] In some embodiments, the powder compaction density of the graphite negative electrode active material under a pressure of 49000N is 1.70g / cm 3 -1.85g / cm 3 In some embodiments, the powder compaction density of the graphite negative electrode active material under a pressure of 49000N is 1.70g / cm 3 , 1.72g / cm 3 , 1.74g / cm 3 , 1.76g / cm 3 , 1.78g / cm 3 , 1.80g / cm 3 、182g / cm 3 、1.84g / cm 3 , 1.85g / cm 3 Any value in , or a range of any two values ​​in .

[0110] As mentioned above, the powder compaction density of the graphite negative electrode active material under a pressure of 49000N is less than or equal to 1.85g / cm 3 , which is beneficial to improving the battery's cycle performance. At the same time, the powder compaction density of the graphite negative electrode active material under a pressure of 49000N will also affect the battery's energy density. The higher the powder compaction density, the greater the compaction density of the negative electrode film layer, which is more conducive to increasing the energy density of the secondary battery.

[0111] By controlling the powder compaction density of the graphite negative electrode active material under a pressure of 49000N within an appropriate range, the cycle life of the battery can be improved while also taking into account the high energy density of the battery.

[0112] In some embodiments, the tap density of the graphite negative electrode active material is 1.2 g / cm 3 -1.4g / cm 3 In some embodiments, the tap density of the graphite negative electrode active material is 1.2 g / cm 3 , 1.25g / cm 3 , 1.30g / cm 3 , 1.35g / cm 3 , 1.4g / cm 3 Any value in , or a range of any two values ​​in .

[0113] In this article, the term "tap density" refers to the density of a powder material after vibration compression under certain conditions.

[0114] The tap density can be measured using any method known in the art. For example, GB / T 5162-2006 can be used to measure the tap density of a powder. The testing instrument can be Dandong Better BT-301.

[0115] When the tap density of the graphite negative electrode active material is within the above range, the compaction density of the negative electrode sheet can be improved, thereby increasing the energy density of the secondary battery; it is also beneficial to form a reasonable pore structure between the particles of the negative electrode film layer, improving the transmission performance of active ions and electrons, and improving the cycle performance and storage performance of the secondary battery.

[0116] In some embodiments, the gram capacity of the graphite negative electrode active material is greater than or equal to 340 milliampere hours / gram (mAh / g). 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.

[0117] 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.

[0118] Graphite negative electrode active materials have excellent gram capacity and can improve the energy density of secondary batteries.

[0119] 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.

[0120] The gram capacity of the graphite negative electrode active material is within the above range, the lattice expansion of the material during cycling is relatively small, the crystal structure stability is good, the irreversible consumption of active ions is reduced, and the cycle performance and storage performance of the battery are improved.

[0121] The present disclosure also provides a method for preparing a graphite negative electrode active material, which comprises the following steps:

[0122] Provide raw materials;

[0123] processing the raw materials to obtain a precursor;

[0124] The precursor is graphitized to obtain an intermediate product;

[0125] The intermediate product is subjected to screening treatment to obtain a graphite negative electrode active material; the graphitization degree of the graphite negative electrode active material is 88%-93%, and the oil absorption value of the graphite negative electrode active material does not exceed 50ml / 100g.

[0126] By adopting the above preparation method, a graphite negative electrode active material with low oil absorption value and low graphitization degree can be prepared, which can further improve the cycle performance of the battery and extend the service life of the battery.

[0127] In some embodiments, the feedstock includes at least one of petroleum coke, needle coke, and pitch coke.

[0128] As used herein, the term "petroleum coke" refers to coke formed by carbonizing petroleum residue or petroleum asphalt at high temperatures.

[0129] 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.

[0130] As used herein, the term "pitch coke" refers to the solid material produced by carbonizing coal tar pitch at high temperatures.

[0131] In some embodiments, the feedstock comprises petroleum coke.

[0132] Petroleum coke has excellent anisotropy, which is conducive to the preparation of low-graphitization, low-expansion graphite negative electrode active 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.

[0133] Based on the total volume of the raw material structure, the volume of the mosaic-type and regional-type structures accounts for greater than or equal to 50%.

[0134] Based on the morphological characteristics and isochromatic zone size under a polarizing microscope, the microstructure of the char material can be divided into mosaic, regional, and fibrous types. Generally, isochromatic zone microstructures with a size less than 30 μm are classified as mosaic, isochromatic zone microstructures with a size greater than 30 μm are classified as regional, and anisotropic striped isochromatic zones are classified as fibrous.

[0135] In the present disclosure, the volume proportion of mosaic and regional structures in the raw material can be tested using methods known in the art. As an example, according to GB 1997-89, the raw material is crushed to 1 mm and mixed, and 40g to 50g is separated. A square hole sieve is used to take 4g to 5g of a 0.07mm to 1.0mm grade sample for slice making. According to MT 116.1-86, powder coke and block coke optical slices are prepared. The diameter of the powder coke optical slice 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. A 1λ azurite inspection plate is inserted to make the field of view show the interference color of first-order red. The step length of the moving ruler is determined 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.

[0136] In some embodiments, the volume of the mosaic and domain-type structures accounts for 50%-65% based on the total volume of the raw material structure. In some embodiments, the volume of the mosaic and domain-type structures accounts for any value among 50%, 55%, 60%, 65%, or a range consisting of any two of these values ​​based on the total volume of the raw material structure.

[0137] As mentioned above, a high volume proportion of mosaic and regional structures is conducive to obtaining graphite negative electrode active materials with low oil absorption values. However, if the volume proportion of mosaic and regional structures is too high, it will affect the gram capacity of the graphite negative electrode active material and the energy density of the battery.

[0138] In some embodiments, the bonding index of the raw material is less than or equal to 10. In some embodiments, the bonding index of the raw material is any value of 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or a range consisting of any two values ​​therein.

[0139] In some embodiments, the bonding index of the raw material is less than or equal to 1 to 9. In some embodiments, the bonding index of the raw material is any value of 1, 2, 3, 4, 5, 6, 7, 8, 9, or a range consisting of any two values ​​thereof.

[0140] In this article, the term "bonding index" is used to characterize the cohesiveness of a material. It refers to the ability of a material to form a plastic, colloid-like structure during high-temperature heating, which bonds itself or an inert material with a certain strength. It reflects the combined effects of surface bonding and internal forces (adhesion and cohesion) within the colloid.

[0141] In the present disclosure, the adhesion index of the raw materials can be tested by methods known in the art. As an example, the adhesion index test is performed using TX-600 with reference to GB / T5447-2014 / ISO 15585:2006. First, take 200g of sample and place it in a drying oven at 100℃ for 1 hour; pass the dried sample through a sieve with an aperture of 200μm+100μm, and take samples below the 200μm sieve and above the 100μm sieve; then weigh 3.00±0.001g of special anthracite, and then weigh 3.00±0.001g of test sample and put it into the crucible, stir and mix evenly; use tweezers to clamp the block and place it in the center of the crucible, then place it under the press, gently lower the pressure rod, and press for 30s; quickly put the crucible into the preheated muffle The crucible was taken out of the furnace and cooled, and the total weight of the sample was measured as m. The sample was then placed in a rotary drum device for a rotary drum test. The sample after the rotary drum was sieved with a 1 mm round hole sieve, and the weight of the material on the sieve was weighed and recorded as m1. The material on the sieve was placed in a rotary drum for a second rotary drum test, and then the material on the sieve was sieved and weighed as m2. The bonding index G was calculated according to the formula G = (30*m1+70*m2) / (5*m).

[0142] If the bonding index of the raw material is too high, the material is likely to bond during the heat treatment process and to form secondary particles, which makes the graphite negative electrode active material have a relatively irregular morphology. The graphite negative electrode active material has a large oil absorption value, which is not conducive to the dispersion of the negative electrode slurry and affects the cycle performance and storage performance of the battery.

[0143] In some embodiments, the processing of the raw material specifically comprises the following steps:

[0144] Crushing, shaping and classifying the raw materials to obtain secondary raw materials;

[0145] Part of the fine powder in the secondary raw material is removed to obtain a precursor.

[0146] 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.

[0147] 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, thereby facilitating the production of a rounded graphite negative electrode active material and a graphite negative electrode active material with low oil absorption.

[0148] 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.

[0149] 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 any value among 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, or a range consisting of any two values ​​therein.

[0150] In some embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the precursor is 1.2-1.8. In some embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the precursor is any value of 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, or a range consisting of any two values ​​thereof.

[0151] Controlling the volume distribution particle size Dv50 or particle size distribution (Dv90-Dv10) / Dv50 of the precursor within a suitable range is conducive to controlling the particle size distribution (Dv90-Dv10) / Dv50 of the graphite negative electrode active material within a suitable range, thereby regulating the oil absorption value of the graphite negative electrode active material within a smaller range.

[0152] In this article, the term "graphitization treatment" refers to the heat treatment process of carbon materials. Under the action of high temperature, the carbon material transforms from a two-dimensional carbon network structure to a three-dimensional ordered structure through "microcrystal" growth.

[0153] In some embodiments, the maximum power of the graphitization process is 70% to 90% of the rated power of the graphitization process equipment.

[0154] 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 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.

[0155] The maximum power of graphitization used in the present 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.

[0156] 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.

[0157] In some embodiments, the graphitization treatment equipment is an Acheson furnace, and the rated power of the Acheson furnace is 28,000W-30,000W.

[0158] In some embodiments, the maximum power of the graphitization process is 23,000W-25,000W.

[0159] For example, the maximum power of the graphitization treatment is 23000 W, 23500 W, 24000 W, 24500 W, 25000 W, or any range therebetween.

[0160] By controlling the maximum power of the graphitization treatment, the graphitization degree of the graphite negative electrode active material during the heat treatment process can be effectively controlled, which is beneficial to improving the cycle life of the battery.

[0161] In some embodiments, the graphitization treatment is performed at a constant power time of 10 hours (h) to 50 hours at the maximum power.

[0162] 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.

[0163] 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.

[0164] 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.

[0165] The appropriate constant power time of maximum power is not likely to cause excessive rearrangement of the precursor, and can effectively reduce the specific surface area of ​​the graphite negative electrode active material, thereby improving the cycle performance of the battery; it can also effectively increase the gram capacity of the graphite negative electrode active material, which is beneficial to the energy density of the secondary battery.

[0166] In some embodiments, the screening process of the intermediate product specifically comprises the following steps:

[0167] The intermediate product is screened to remove particles with a maximum particle size Dmax greater than 100 μm, thereby obtaining a graphite negative electrode active material.

[0168] Remove large particles from intermediate products to reduce the negative impact of large particle materials on battery cycle performance and storage performance.

[0169] 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.

[0170] [Negative electrode]

[0171] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes the graphite negative electrode active material of the first aspect of the embodiment of the present disclosure or the graphite negative electrode active material prepared by the method described in the second aspect of the embodiment of the present disclosure.

[0172] In some embodiments, the negative electrode film layer includes a conductive agent, and the mass content of the conductive agent is greater than or equal to 1.5% based on the mass of the negative electrode film layer.

[0173] In some embodiments, based on the total mass of the negative electrode film layer, the mass proportion of the conductive agent is 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 3.0%, 3.1%, 3.2%, 3.2%, 3.3% or any numerical range therebetween.

[0174] During the battery cycle, active ions are continuously embedded in and out of the graphite negative electrode active material lattice, and the graphite negative electrode active material is prone to "isolated" particles, thereby losing electrochemical activity, causing local current unevenness, generating polarization, accelerating capacity decay, and causing the battery performance to "dive". In order to solve the above problems, a relatively high content of conductive agent is usually added to the negative electrode film layer to effectively enhance the electrical contact between the graphite negative electrode active materials and improve the cycle stability of the battery. However, adding a high content of conductive agent to the negative electrode slurry will affect the dispersibility of the negative electrode slurry. The low oil absorption value of the graphite negative electrode active material disclosed in the present invention has excellent dispersibility in the negative electrode slurry, which can make up for the effect of high content of conductive agent on the dispersibility of the negative electrode slurry.

[0175] The high content of conductive agent is combined with the graphite negative electrode active material with low oil absorption value. The negative electrode slurry has good dispersibility and the electrode has excellent uniformity. At the same time, the graphite negative electrode active material has good electrical contact, which comprehensively improves the cycle performance of the battery.

[0176] In some embodiments, the weight content of the conductive agent is 1.8%-2.5% based on the weight of the negative electrode film layer. In some embodiments, the weight content of the conductive agent is 1.8%, 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, or any range therebetween, based on the total weight of the negative electrode film layer.

[0177] The mass proportion of the conductive agent is within an appropriate range, which can enhance the electrical contact between the graphite negative electrode active materials while not causing loss of the battery's energy density due to excessive active conductive agent contained in the negative electrode film layer.

[0178] 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.

[0179] 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.).

[0180] 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 material may include one or more of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy material. The tin-based material may include one or more of elemental tin, tin oxide, and tin alloy material.

[0181] In some embodiments, the conductive agent includes at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0182] In some embodiments, the negative electrode film layer further comprises a binder. In some embodiments, 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).

[0183] In some embodiments, the negative electrode film layer further includes other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0184] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the 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 current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0185] [Positive electrode]

[0186] 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.

[0187] 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.

[0188] 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.).

[0189] 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 0.5Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 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.

[0190] 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.

[0191] 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.

[0192] 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.

[0193] [Electrolytes]

[0194] 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.

[0195] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0196] 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.

[0197] 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.

[0198] 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.

[0199] [Isolation film]

[0200] 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.

[0201] 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.

[0202] 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.

[0203] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0204] 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.

[0205] 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.

[0206] 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.

[0207] 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.

[0208] 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.

[0209] 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.

[0210] 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.

[0211] 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.

[0212] In addition, the present disclosure further provides an electrical 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 electrical device, and can also be used as an energy storage unit for the electrical device. The electrical 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.

[0213] As the electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0214] 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.

[0215] 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.

[0216] Example

[0217] 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.

[0218] Example 1

[0219] (1) Preparation of graphite negative electrode active materials

[0220] Petroleum coke having a volume proportion of 57.3% of mosaic and regional structures and a bonding index of 6.2 is coarsely crushed, the coarsely crushed material is 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 fine powder refers to particles with a volume distribution particle size Dv50 of 3-7 μm and a particle size distribution (Dv90-Dv10) / Dv50>1.6, the volume distribution particle size Dv50 of the precursor is 16.2 μm, and the particle size distribution (Dv90-Dv10) / Dv50 of the precursor is 1.78;

[0221] The precursor is graphitized in an Acheson furnace at a temperature of 2800° C. and a maximum power of 23000 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 200° C. to obtain an intermediate product.

[0222] The intermediate product was sieved and demagnetized to obtain a graphite negative electrode active material. The graphitization degree of the graphite negative electrode active material was 88%, the oil absorption value was 43ml / 100g, and the specific surface area was 0.92m 2 / g, Dv50 is 14.8μm.

[0223] (2) Preparation of negative electrode sheet

[0224] The graphite negative electrode active material prepared above, the conductive agent Super P, the thickener carboxymethyl cellulose CMC, and the binder styrene butadiene rubber SBR were mixed in a dry material mass ratio of 96:1:1.2:1.8, and deionized water was added as a solvent. The mixture was stirred in a vacuum mixer until the system was 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 sheet is 1.50g / cm 3 , with a surface density of 9.6 mg / cm 2 .

[0225] (3) Preparation of positive electrode sheet

[0226] 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 .

[0227] (4) Preparation of electrolyte

[0228] In an argon atmosphere glove box with a water content of less than 10 ppm, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, sufficiently dried lithium salt LiPF6 is dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L. To the above solution, vinylene carbonate is added, and the mass content of vinylene carbonate is 2% of the total mass of the electrolyte.

[0229] (5) Preparation of isolation membrane

[0230] Polypropylene film is used as the isolation film.

[0231] (6) Preparation of lithium-ion batteries

[0232] 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. After vacuum packaging, standing, forming, shaping and other processes, a lithium-ion battery is obtained.

[0233] Examples 2-3 are basically the same as Example 1, except that the bonding index of the raw materials, the maximum power of the graphitization treatment, and the particle size distribution (Dv90-Dv10) / Dv50 of the precursor are adjusted, as shown in Table 1.

[0234] Comparative Examples 1-3 are basically the same as Example 1, except that the volume proportion of the mosaic and regional structures in the raw materials, the bonding index of the raw materials, the maximum power of the graphitization treatment, and the particle size distribution (Dv90-Dv10) / Dv50 of the precursor are adjusted, as shown in Table 1.

[0235] Table 1

[0236] Performance Testing

[0237] 1. Filtration time of negative electrode slurry

[0238] First, determine the filter mesh size: 200. Cut the filter mesh into 25cm x 25cm pieces with scissors. Find a clean 500ml beaker and make sure it is clean. Fold the 150-mesh filter mesh into a triangle. Pour 500ml of the slurry into the filter mesh over the top, pouring it all at once. Start recording the time when the slurry begins to flow from the tip of the filter mesh into the beaker. Record the time it takes to filter 300ml.

[0239] 2. Cycle performance test of secondary batteries at 60°C

[0240] 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.

[0241] 3. Storage performance of secondary batteries at room temperature

[0242] 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.

[0243] 3. Results

[0244] As can be seen from Table 2, the graphite negative electrode active materials provided in Examples 1-3 of the present disclosure have a graphitization degree of 88%-93%, and the oil absorption value of the graphite negative electrode active materials does not exceed 50ml / 100g. As can be seen from the comparison of Examples 1-3 with Comparative Example 1, controlling the oil absorption value of the graphite negative electrode active materials to no more than 50ml / 100g can improve the dispersibility and filterability of the negative electrode slurry, and improve the cycle life and storage performance of the battery. As can be seen from the comparison of Examples 1-3 with Comparative Examples 2-3, controlling the graphitization degree of the graphite negative electrode active materials to 88%-93% can take into account both the gram capacity and cycle performance of the graphite negative electrode active materials, and the battery has both high energy density and long cycle life, while also improving the storage performance of the battery.

[0245] From Examples 1-3, it can be seen that the specific surface area of ​​the graphite negative electrode active material is less than or equal to 1.4 m 2 / g, the negative electrode slurry has excellent dispersibility and filterability, the graphite negative electrode active material has a high gram capacity, and the secondary battery has excellent cycle stability and storage stability.

[0246] It can be seen from Examples 1-3 that the volume distribution particle size Dv50 of the graphite negative electrode active material is 12-16 μm, the negative electrode slurry has excellent dispersibility and filterability, the graphite negative electrode active material has a high gram capacity, and the secondary battery has excellent cycle stability and storage stability.

[0247] Table 2

[0248] 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 graphitization degree of the graphite negative electrode active material is 88%-93%, and the oil absorption value of the graphite negative electrode active material does not exceed 50ml / 100g.

2. The graphite negative electrode active material according to claim 1, characterized in that: The oil absorption value of the graphite negative electrode active material is 30 ml / 100 g to 43 ml / 100 g.

3. The graphite negative electrode active material according to claim 1 or 2, characterized in that: The particle size distribution of the graphite negative electrode active material (Dv90-Dv10) / Dv50 is 1.2-1.

6.

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 graphite negative electrode active material, the number of primary particles in the graphite negative electrode active material accounts for greater than or equal to 85%, 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 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.

6. The graphite negative electrode active material according to any one of claims 1 to 5, 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.

7. The graphite negative electrode active material according to any one of claims 1 to 6, characterized in that The graphite negative electrode active material satisfies at least one of the following: (1) The powder compaction density of the graphite negative electrode active material under a pressure of 49000N is less than or equal to 1.85g / cm 3 , optional 1.70g / cm 3 -1.85g / cm 3 ; (2) The tap density of the graphite negative electrode active material is 1.2 g / cm 3 -1.4g / cm 3 ; (3) The gram capacity of the graphite negative electrode active material is greater than or equal to 340 mAh / g, optional It is 341mAh / g-347mAh / g.

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 graphitization degree of the graphite negative electrode active material is 88%-93%, and the oil absorption value of the graphite negative electrode active material does not exceed 50ml / 100g.

9. The preparation method according to claim 8, characterized in that: The raw material includes at least one of petroleum coke, needle coke and pitch coke, and petroleum coke can be selected.

10. The preparation method according to claim 8 or 9, characterized in that: Based on the total volume of the raw material structure, the volume proportion of the mosaic type and regional type structure is greater than or equal to 50%, and can be optionally 50%-65%.

11. The preparation method according to any one of claims 8 to 10, characterized in that: The bonding index of the raw material is less than or equal to 10, and can be selected from 1 to 9.

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. The preparation method according to any one of claims 8 to 12, characterized in that: The maximum power of the graphitization treatment is 70%-90% of the rated power of the graphitization equipment.

14. The preparation method according to claim 13, 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.

15. The preparation method according to any one of claims 8 to 14, characterized in that: The screening process of the intermediate product specifically comprises the following steps: The intermediate product is sieved to remove particles with a maximum particle size Dmax greater than 100 μm, thereby obtaining a graphite negative electrode active material.

16. A secondary battery, comprising a negative electrode plate, characterized in that: The negative electrode plate includes a negative electrode current collector and a negative electrode film layer formed on at least one surface of the negative electrode current collector, characterized in that the negative electrode film layer includes the graphite negative electrode active material described in any one of claims 1 to 7 or the graphite negative electrode active material prepared by the preparation method described in any one of claims 8 to 15.

17. The secondary battery according to claim 16, characterized in that: The negative electrode film layer includes a conductive agent. Based on the mass of the negative electrode film layer, the mass content of the conductive agent is greater than or equal to 1.5%, and can be optionally 1.8%-2.5%.

18. An electrical device, characterized in that: A secondary battery comprising the secondary battery according to claim 16 or 17.

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