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

Abstract

Provided are a graphite negative electrode active material and a preparation method therefor, a secondary battery containing same and an electric device. The powder compaction density of the graphite negative electrode active material under a pressure of 49,000 N is greater than or equal to 1.60 g / cm3, and the ratio Id / Ig of the peak intensity Id at 1250 cm-1 to 1500 cm-1 and the peak intensity Ig at 1500 cm-1 to 1650 cm-1 in the Raman spectrum of the graphite negative electrode active material is greater than or equal to 0.15. The graphite negative electrode active material can take both the energy density and rate capability of a battery into consideration.

Description

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

[0001] Cross-references

[0002] The present disclosure claims priority to Chinese Patent Application No. 202311679523.9, filed on December 7, 2023, entitled “Ink negative electrode active material and preparation method thereof, secondary battery and electrical device containing the same”, which is incorporated herein by reference in its entirety. Technical Field

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

[0004] With the development of electric vehicles, large-scale energy storage systems and other fields, the market has put forward increasingly higher requirements for the energy density and rate performance of energy storage devices. However, from a technical perspective, it is difficult to achieve perfect compatibility between energy density and rate performance.

[0005] Summary of the Invention

[0006] The present disclosure is made in view of the above-mentioned problems, and its purpose is to provide a graphite negative electrode active material, and a secondary battery prepared using the graphite negative electrode active material can take into account both the energy density and rate performance of the battery.

[0007] The first aspect of the present disclosure provides a graphite negative electrode active material, wherein the powder compaction density of the graphite negative electrode active material under a pressure of 49000N is greater than or equal to 1.60g / cm 3 ; 1250cm in the Raman spectrum of graphite negative electrode active material -1 Up to 1500cm -1 The peak intensity Id and 1500 cm -1 to 1650cm -1 The peak intensity Ig ratio Id / Ig is greater than or equal to 0.15.

[0008] Graphite anode active materials have a high powder compaction density under a pressure of 49,000 N, which can increase the compaction density of the anode film layer, thereby further improving the energy density of the secondary battery. The Id / Ig ratio of graphite anode active materials also indicates the degree of surface defects. When Id / Ig is within the above range, the anode material has a high number of surface defects, which can promote ion adsorption and bonding, improve the transport performance of active ions, and enhance the battery's rate performance.

[0009] In summary, by controlling the powder compaction density and Id / Ig of the graphite negative electrode active material under a pressure of 49000N within an appropriate range, the secondary battery can achieve both high energy density and excellent rate performance.

[0010] In any embodiment, the powder compaction density of the graphite negative electrode active material under a pressure of 49000N is 1.6g / cm 3 -1.80g / cm 3 , optional 1.65g / cm 3 -1.75g / cm 3 .

[0011] In any embodiment, the graphite negative electrode active material has a Raman spectrum of 1250 cm -1 Up to 1500cm -1 The peak intensity Id and 1500 cm -1 to 1650cm -1 The peak intensity Ig ratio Id / Ig is 0.2-0.35.

[0012] In any embodiment, based on the total number of particles of the graphite negative electrode active material, the number of the primary particles in the graphite negative electrode active material accounts for greater than or equal to 85%, and can be optionally 85%-100%.

[0013] The primary particles within the above range help reduce structural fragmentation of the graphite negative electrode active material due to expansion and contraction during the cycle, improve the structural stability of the graphite negative electrode active material, and thus improve the cycle performance of the secondary battery.

[0014] In any embodiment, the graphite negative electrode active material has a graphitization degree of 85%-91%.

[0015] By regulating the graphitization degree of the graphite negative electrode active material within the above range, the SP in the graphite negative electrode active material 3 The large number of bonds allows the layers of the graphite negative electrode active material to be restrained from each other, making the structure of the graphite negative electrode active material more stable. The graphite negative electrode active material has excellent stability during the cycle process, which is conducive to the cycle performance of the graphite negative electrode active material. At the same time, the graphite negative electrode active material has an appropriate degree of graphitization, a relatively regular structure, and a high specific capacity, which can improve the energy density of the battery.

[0016] In any embodiment, the volume distribution particle size Dv50 of the graphite negative electrode active material is less than or equal to 15.0 μm, and can be optionally 9.0 μm-14.0 μm.

[0017] When the volume distribution particle size Dv50 of the graphite negative electrode active material is within an appropriate range, the path of active ion embedding and de-embedding is reduced, the transmission performance of active ions and electrons is improved, and the rate performance of the battery is improved. In addition, it is also beneficial to reduce the specific surface area of ​​the graphite negative electrode active material, which helps to reduce the irreversible consumption of active ions due to side reactions between the graphite negative electrode active material and the electrolyte during the cycle, thereby improving the cycle performance and storage performance of the secondary battery.

[0018] In any embodiment, the graphite negative electrode active material comprises a core and a coating layer covering at least a surface of the core, the core is artificial graphite, and the coating layer comprises amorphous carbon.

[0019] The "core" of the graphite negative electrode active material is artificial graphite, which reduces the volume change rate during the lithium ion deintercalation and deintercalation process, reduces the side reactions caused by the breakage and reconstruction of the SEI film during the cycle, and improves the cycle performance of the battery. At the same time, the "shell" is amorphous carbon, which can effectively reduce the active ion diffusion resistance and particle surface polarization in the material, so that the Id / Ig of the material is within a suitable range, which can improve the battery's rate performance.

[0020] In any embodiment, the graphite negative electrode active material satisfies at least one of the following conditions:

[0021] (1) The tap density of the graphite negative electrode active material is 1.0 g / cm 3 -1.4g / cm 3 ;

[0022] (2) The specific surface area of ​​the graphite negative electrode active material is 0.75m 2 / g-1.75m 2 / g;

[0023] (3) The particle size distribution of the graphite negative electrode active material (Dv90-Dv10) / Dv50 is 1.30-1.80.

[0024] (4) The gram capacity of the graphite negative electrode active material is 325 mAh / g-340 mAh / g.

[0025] By regulating the tap density of the graphite negative electrode active material within the above range, the electron conduction between particles can be further improved, and the rate performance of the battery can be improved. At the same time, it is beneficial to improve the stability of the negative electrode slurry, which is beneficial to the coating of the negative electrode slurry, thereby reducing the processing difficulty, improving the appearance of the negative electrode sheet, and improving the electrical performance of the battery.

[0026] When the specific surface area of ​​the graphite negative electrode active material is within an appropriate range, the negative impact of side reactions between the graphite negative electrode active material and the electrolyte on the cycle performance can be reduced, thereby improving the cycle performance of the battery.

[0027] Regulating the volume particle size distribution in the graphite negative electrode active material within a suitable range is beneficial for the negative electrode film layer to have a suitable pore structure, thereby reducing the difficulty of ion liquid phase transmission and improving the rate performance of the secondary battery; in addition, the graphite negative electrode active material can also have good particle stacking properties, which is beneficial to improving the compaction density of the negative electrode film layer, thereby further improving the energy density of the secondary battery.

[0028] 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, and the irreversible consumption of active ions is reduced, thereby improving the cycle performance of the secondary battery.

[0029] A second aspect of the present disclosure further provides a method for preparing a graphite negative electrode active material, comprising the following steps:

[0030] Provide raw materials;

[0031] processing the raw materials to obtain a precursor;

[0032] The precursor is graphitized to obtain a graphitized product;

[0033] The graphitized product is surface treated to obtain a graphite negative electrode active material.

[0034] The powder compaction density of the graphite negative electrode active material under a pressure of 49000N is greater than or equal to 1.60g / cm 3 ;

[0035] The Raman spectrum of the graphite negative electrode active material is 1250 cm -1 Up to 1500cm -1 The peak intensity Id and 1500cm- 1 to 1650cm -1 The peak intensity Ig ratio Id / Ig is greater than or equal to 0.15.

[0036] The graphite negative electrode active material prepared by the method has a relatively high powder compaction density and Id / Ig, which can take into account both the energy density and charge and discharge capacity of the battery. The secondary battery prepared using the material has both high energy density and excellent rate performance.

[0037] In any embodiment, the graphitized product is subjected to a fusion treatment to obtain an intermediate, wherein the frequency of the fusion treatment is 20-40 Hz, and / or the time of the fusion treatment is 5-15 min;

[0038] The intermediate is mixed with asphalt at room temperature and then carbonized to obtain a graphite negative electrode active material.

[0039] The present invention first performs a fusion treatment on the graphitized product and then performs an asphalt coating treatment. The fusion treatment can achieve the purpose of spheroidization and de-edge corners. On the one hand, the intermediate obtained by fusion spheroidization has a relatively regular structure, which can increase the powder compaction density of the intermediate. On the other hand, the small particles of graphite produced by de-edge corners can fill the voids in the intermediate material, further increasing the intermediate powder compaction density, providing a basis for obtaining a graphite negative electrode active material with a high powder compaction density.

[0040] In any embodiment, the mass ratio of the intermediate to the asphalt is 1:99-10:90, and can be optionally 2:98-5:95.

[0041] When the mass ratio of the intermediate to the asphalt is within an appropriate range, the purpose of coating modification can be achieved, so that the graphite negative electrode active material has amorphous carbon of appropriate thickness, and the graphite negative electrode active material has a high Id / Ig value, while avoiding excessive negative effects of excessive amorphous carbon on the powder compaction density of the material, so that the material has both high energy density and excellent kinetic properties.

[0042] In any embodiment, the raw material comprises one or more of petroleum coke, needle coke, and pitch coke, and petroleum coke may be selected.

[0043] Based on the total volume of the raw material structure, the volume proportion of the mosaic structure and the regional structure is greater than or equal to 60%, and can be optionally 65%-80%.

[0044] By controlling the volume ratio of the mosaic and regional structures within an appropriate range, the highly isotropic raw materials provide the basis for obtaining highly isotropic graphite anode active materials. During the battery's charge and discharge processes, the graphite anode active materials can embed active ions in multiple directions, resulting in more uniform stress and relatively small expansion, which is beneficial for improving the battery's cycle life. Furthermore, highly isotropic graphite anode active materials have more active ion transport channels and shorter transmission paths, which is beneficial for improving rate performance.

[0045] In any embodiment, the maximum power of the graphitization process is 70%-90% of the rated power of the graphitization process equipment.

[0046] In any embodiment, the maximum power of the graphitization treatment is 21000W-26000W; and / or the constant power time of the graphitization treatment at the maximum power is 8h-40h.

[0047] The maximum power of the appropriate graphitization treatment and / or the constant power time at the maximum power, the powder compaction density and defectivity of the graphitized product are within a suitable range. After the graphitized product is surface treated, a graphite negative electrode active material with excellent high powder compaction density and defectivity can be obtained.

[0048] In any embodiment, the graphitized product has a gram capacity of 325-340 mAh / g.

[0049] The gram capacity of the graphitized product is within a suitable range, and the powder compaction density and defectivity of the graphitized product are within a suitable range. After the graphitized product is surface treated, a graphite negative electrode active material with relatively high powder compaction density and high defectivity can be obtained.

[0050] In any embodiment, the processing of the raw material specifically comprises the following steps:

[0051] The raw materials are crushed, shaped, and graded, and fine powder is removed to obtain secondary raw materials;

[0052] Carbonizing the secondary raw material to obtain a precursor,

[0053] The volume distribution particle size Dv50 of the secondary raw material is 8.0-16.0 μm, and / or the particle size distribution (Dv90-Dv10) / Dv50 of the secondary raw material is 1.30-1.70.

[0054] Controlling the Dv50 of secondary raw materials within a suitable range is beneficial to controlling the Dv50 of graphite negative electrode active materials within a suitable range, reducing the paths of active ion embedding and de-embedding, improving the transmission performance of active ions and electrons, improving the rate performance of the battery, and helping to reduce the side reactions of graphite negative electrode active materials and the irreversible consumption of active ions during the cycle process, thereby improving the cycle performance and storage performance of the secondary battery.

[0055] Controlling the particle size distribution (Dv90-Dv10) / Dv50 of the secondary raw materials within a suitable range is beneficial to controlling the particle size distribution (Dv90-Dv10) / Dv50 of the graphite negative electrode active material within a suitable range, which is beneficial for the negative electrode film layer to have a suitable pore structure, thereby reducing the difficulty of ion liquid phase transmission and improving the rate performance of the secondary battery; in addition, the graphite negative electrode active material can also have good particle stacking properties, which is beneficial to improving the compaction density of the negative electrode film layer, thereby further improving the energy density of the secondary battery.

[0056] A third aspect of the present disclosure provides a secondary battery, comprising a negative electrode plate, wherein the negative electrode plate is 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.

[0057] A fourth aspect of the present disclosure provides an electrical device comprising the secondary battery according to the third aspect of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] FIG. 1 is a schematic diagram of a secondary battery according to an embodiment of the present disclosure.

[0059] FIG. 2 is an exploded view of the secondary battery according to the embodiment of the present disclosure shown in FIG. 1 .

[0060] FIG3 is a schematic diagram of a battery module according to an embodiment of the present disclosure.

[0061] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present disclosure.

[0062] FIG. 5 is an exploded view of the battery pack shown in FIG. 4 according to an embodiment of the present disclosure.

[0063] 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.

[0064] Explanation of reference numerals: 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 secondary battery; 51 housing; 52 electrode assembly; 53 cover plate. DETAILED DESCRIPTION

[0065] Below, with appropriate reference to the accompanying drawings, the embodiments of the graphite negative electrode active material and its preparation method, the secondary battery containing the same, and the electrical device disclosed in the present invention are described in detail. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present disclosure and are not intended to limit the subject matter described in the claims.

[0066] " 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.

[0067] Unless otherwise specified, all embodiments and optional embodiments of the present disclosure can be combined with each other to form new technical solutions.

[0068] Unless otherwise specified, all technical features and optional technical features disclosed herein can be combined with each other to form a new technical solution.

[0069] 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.

[0070] 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.

[0071] 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).

[0072] Graphite negative electrode active material is one of the important raw materials for negative electrode sheets and has a significant impact on the electrical performance of negative electrode sheets and secondary batteries. In the prior art, in order to improve the rate performance of graphite negative electrode active materials, the graphite negative electrode active material is mixed evenly with a coating agent (such as asphalt, polymer compounds, etc.) and then heat-treated to coat the surface of the graphite negative electrode active material with an amorphous carbon layer. However, the traditional coating treatment will cause the powder compaction density of the graphite negative electrode active material to be significantly reduced, affecting the compaction density of the negative electrode film layer and reducing the energy density of the secondary battery. The existing technology is difficult to achieve a perfect balance between high energy density and excellent rate performance.

[0073] [Graphite negative electrode active material]

[0074] The present disclosure provides a graphite negative electrode active material, wherein the powder compaction density of the graphite negative electrode active material under a pressure of 49000N is greater than or equal to 1.60g / cm 3 , 1250cm in the Raman spectrum of graphite negative electrode active material -1 Up to 1500cm - 1 The peak intensity Id and 1500 cm -1 to 1650cm -1 The peak intensity Ig ratio Id / Ig is greater than or equal to 0.15.

[0075] In some embodiments, the powder compaction density of the graphite negative electrode active material under a pressure of 49000N may be 1.60g / cm 3 , 1.61g / cm 3 , 1.62g / cm 3 , 1.63g / cm 3 , 1.64g / cm 3 , 1.65g / cm 3 , 1.66g / cm3, 1.67g / cm 3 、1.68g / cm 3 , 1.69g / cm 3 , 1.70g / cm 3 , 1.71g / cm 3 , 1.72g / cm 3 , 1.73g / cm 3 , 1.74g / cm3 , 1.75g / cm 3 , 1.76g / cm 3 , 1.77g / cm 3 , 1.78g / cm 3 , 1.79g / cm 3 , 1.80g / cm 3 、1.81g / cm 3 , 1.82g / cm 3 , 1.83g / cm 3 、1.84g / cm 3 , 1.85g / cm 3 , or the range between any two of the above values.

[0076] In this article, the term "powder compaction density" refers to the density of the powder under a preset pressure. A higher powder compaction density indicates a higher mass per unit volume. For graphite anode active materials, a higher powder compaction density increases the compaction density of the anode film, which contributes to higher energy density in secondary batteries.

[0077] The graphite negative electrode active material disclosed in the present invention has a high powder compaction density, and the negative electrode film layer has a high compaction density, providing a material basis for preparing high energy density batteries.

[0078] The method for measuring the compacted density of the powder can be any method known in the art. For example, referring to GB / T24533-2009, 1g of graphite negative electrode active material powder is weighed and added to a bottom area of ​​1.327cm 2 The mold is pressurized to a specific pressure, for example, 49000N, and the pressure is maintained for 30 seconds, then the pressure is released and maintained for 10 seconds. The powder compaction density of the graphite negative electrode active material under the selected pressure is measured by an electronic pressure testing machine (such as UTM7305 electronic pressure testing machine).

[0079] The Raman spectrum of graphite anode active material is 1250 cm -1 Up to 1500cm -1 The peak intensity Id and 1500 cm -1 to 1650cm -1 The peak intensity Ig ratio (Id / Ig) can characterize the ratio of surface defects to crystalline regions in a graphite negative electrode active material. A larger Id / Ig indicates a greater proportion of surface defects in the graphite negative electrode active material. A high defectivity can increase the deintercalation and deintercalation channels for active ions and increase the deintercalation and deintercalation rate of active ions, thereby improving the rate performance of the graphite negative electrode active material. The graphite negative electrode active material disclosed herein has a high Id / Ig ratio. The high surface defectivity of the graphite negative electrode active material can effectively improve the rate performance of the battery.

[0080] In some embodiments, the Raman spectrum of the graphite negative electrode active material is 1250 cm -1 Up to 1500cm -1 The peak intensity Id and 1500 cm -1 to 1650cm -1 The peak intensity Ig ratio Id / Ig can be selected as 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, 0.25, 0.30, 0.35, 0.40, 0.45 or 0.50, or a range between any two of the above values.

[0081] The Raman spectrum of graphite anode active material is 1250 cm -1 Up to 1500cm -1 The peak intensity Id and 1500 cm - 1 to 1650cm -1 The peak intensity Ig ratio Id / Ig can be measured using any method known in the art. For example, an InVia Qontor (Reflex) laser microscope Raman spectrometer is used for testing, wherein a solid laser with a wavelength of 523 nm is used as a light source, 100 points are sampled in an area of ​​100 μm × 100 μm, and the peak intensity Ig ratio of each point at 1250 cm is calculated. - 1 Up to 1500cm -1 The peak intensity Id and 1500 cm -1 to 1650cm -1 The ratio of Id / Ig to the peak intensity Ig is taken as the median of the Id / Ig values ​​of 100 points as the peak intensity of 1250cm in the Raman spectrum of the graphite negative electrode active material. -1 Up to 1500cm -1 The peak intensity Id and 1500 cm -1 to 1650cm -1 The peak intensity Ig ratio is Id / Ig.

[0082] In summary, the graphite negative electrode active material disclosed in the present invention has both high powder compaction density and Id / Ig, and the secondary battery prepared using the graphite negative electrode active material can have both energy density and rate performance.

[0083] In some embodiments, the powder compaction density of the graphite negative electrode active material under a pressure of 49000N is 1.60g / cm 3 -1.80g / cm 3 .

[0084] In some embodiments, the powder compaction density of the graphite negative electrode active material under a pressure of 49000N may be 1.60g / cm 3 , 1.65g / cm 3 , 1.66g / cm 3 , 1.67g / cm 3 、1.68g / cm 3 , 1.69g / cm 3 , 1.70g / cm 3 , 1.71g / cm 3 , 1.72g / cm 3 , 1.73g / cm 3 , 1.74g / cm 3 , 1.75g / cm 3 , 1.76g / cm 3 , 1.77g / cm 3 , 1.78g / cm 3 , 1.79g / cm 3 or 1.80g / cm 3 , or the range between any two of the above values.

[0085] In some embodiments, the powder compaction density of the graphite negative electrode active material under a pressure of 49000N is 1.65g / cm 3 -1.75g / cm 3 .

[0086] In some embodiments, the powder compaction density of the graphite negative electrode active material under a pressure of 49000N may be 1.65g / cm 3 , 1.66g / cm 3 , 1.67g / cm 3 、1.68g / cm 3 , 1.69g / cm 3 , 1.70g / cm 3 , 1.71g / cm 3 , 1.72g / cm 3 , 1.73g / cm 3 , 1.74g / cm 3 or 1.75g / cm 3 , or the range between any two of the above values.

[0087] By controlling the powder compaction density of the graphite negative electrode active material under a pressure of 49000N within an appropriate range, the negative electrode film layer has a high compaction density, which can improve the energy density of the secondary battery; it is also beneficial for the negative electrode film layer to have a suitable pore structure, reduce the difficulty of ion liquid phase transmission, improve the ion and electron transmission performance, and improve the wetting and retention characteristics of the negative electrode film layer to the electrolyte, thereby further improving the rate performance and cycle performance of the secondary battery.

[0088] In some embodiments, the Raman spectrum of the graphite negative electrode active material is 1250 cm -1 Up to 1500cm -1 The peak intensity Id and 1500 cm -1 to 1650cm -1 The peak intensity Ig ratio Id / Ig is 0.2-0.35.

[0089] In some embodiments, Id / Ig is 0.2-0.33. In some embodiments, Id / Ig can be 0.20, 0.21, 0.22, 0.23, 0.24, 0.25, 0.30 or 0.35, or a range between any two of the above values.

[0090] If Id / Ig is too large and there are too many defects on the graphite surface, it will affect the thickness of the solid electrolyte interface (SEI) film formed during the first cycle of the secondary battery, resulting in irreversible capacity loss and affecting the energy density and cycle performance of the battery.

[0091] When Id / Ig is within the above range, the negative electrode material surface has an appropriate number of defects, which can promote ion adsorption and binding, while reducing the irreversible capacity loss caused by high defect levels. This allows the negative electrode film layer to have high compaction while also improving the battery's cycling performance.

[0092] In some embodiments, based on the total number of particles of the graphite negative electrode active material, the number of the primary particles accounts for greater than or equal to 85%.

[0093] In some embodiments, the primary particles account for 85% to 100% of the total number of particles of the graphite negative electrode active material. In some embodiments, the primary particles account for 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or 100% of the total number of particles of the graphite negative electrode active material, or a range between any two of the above values, based on the total number of the primary particles and the secondary particles.

[0094] Herein, "primary particles" are also referred to as single particles, and generally refer to non-agglomerated particles. Primary particles can be confirmed by using a scanning electron microscope (SEM) image.

[0095] The number ratio of primary particles can be determined by instruments and methods known in the art. An example is as follows: a graphite negative electrode active material is laid and adhered to a conductive adhesive to form a sample to be tested with a length × width = 6 cm × 1.1 cm. A scanning electron microscope; an energy spectrometer (such as ZEISS SEM (sigma300)) is used to test the morphology of the particles in the sample to be tested. The test can refer to JY / T010-1996. In order to ensure the accuracy of the test results, a plurality of (for example, 10 or 20) different areas can be randomly selected from the sample to be tested for scanning testing, and at a certain magnification (for example, 500 times or 1000 times), the number of primary 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. In order 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 the number of primary particles.

[0096] During cycling, graphite anode active materials undergo repeated expansion and contraction deformation, which causes particle breakage and reduces the mechanical integrity of the graphite anode active material particles. At the same time, these broken particles increase electrolyte penetration and side reactions, increasing the irreversible consumption of active ions and negatively impacting the battery's cycling performance. Primary particles have excellent structural stability, which helps reduce particle breakage caused by expansion and contraction during cycling, improves the chemical-mechanical stability of the graphite anode active material, reduces irreversible consumption of active ions, and ultimately enhances the cycling performance of secondary batteries.

[0097] In some embodiments, the graphite negative electrode active material has a degree of graphitization of 85% to 91%. In some embodiments, the graphitization degree of the graphite negative electrode active material can be 85%, 86%, 87%, 88%, 89%, 90% or 91%, or a range between any two of the above values.

[0098] In the present disclosure, the degree of graphitization of the graphite negative electrode active material can be tested using instruments and methods known in the art. For example, an X-ray diffractometer (e.g., a 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 d002 of the C(002) plane in the material's crystal structure. The degree of graphitization is then calculated using the formula g = (0.344-d002) / (0.344-0.3354) × 100%. In the above formula, d002 is the average interlayer spacing of the C(002) plane in the material's crystal structure expressed in nanometers (nm).

[0099] The degree of graphitization reflects the completeness of the graphite crystal structure in the material, that is, the regularity of the arrangement of carbon atoms in the graphite structure of the material. A material with a high degree of graphitization indicates that the distance between graphite layers is small, the smaller the lattice rotation, the less scattered stacking of the layers, the more orderly the arrangement, and the higher the specific capacity of the material. A material with a low degree of graphitization indicates that the distance between graphite layers is large, which is conducive to the rapid intercalation and deintercalation of active ions and is conducive to improving the rate performance of the battery. In addition, the large distance between graphite layers means that the material expands less when lithium is inserted, which has the effect of shallow charge and shallow discharge. At the same time, the material has a low degree of graphitization, and the SP in the graphite negative electrode active material is low. 3 There are more bonds, which makes the layers of the graphite negative electrode active material restrain each other, thereby making the structure of the graphite negative electrode active material more stable. The graphite negative electrode active material has excellent stability during the cycle and is conducive to long-term circulation.

[0100] By regulating the graphitization degree of the graphite negative electrode active material within the above range, the cycle stability, gram capacity and active ion transport performance of the material can be taken into account, which is conducive to obtaining a battery with high energy density, long cycle and high rate performance.

[0101] In some embodiments, the volume distribution particle size Dv50 of the graphite negative electrode active material is less than or equal to 15.0 μm.

[0102] In some embodiments, the volume distribution particle size Dv50 of the graphite negative electrode active material can be selected to be less than or equal to 15.0 μm, less than or equal to 14.0 μm, less than or equal to 13.0 μm, less than or equal to 12.0 μm, less than or equal to 11.0 μm, less than or equal to 10.0 μm or less than or equal to 9.0 μm.

[0103] In the present disclosure, the volume distribution particle size Dv50 of the carbon-based negative electrode material represents the particle size corresponding to the cumulative volume distribution percentage of the material reaching 50%, and can be measured using instruments and methods known in the art. For example, it can be measured using a laser particle size analyzer in accordance with GB / T 19077-2016. The testing instrument can be a Mastersizer 3000 laser particle size analyzer manufactured by Malvern Instruments Ltd. in the United Kingdom.

[0104] The graphite negative electrode active material has a small volume distribution particle size Dv50, and the path for active ion embedding and extraction is short, which can improve the transmission performance of active ions and electrons and improve the rate performance of the material.

[0105] In some embodiments, the volume distribution particle size Dv50 of the graphite negative electrode active material is 9.0 μm-14.0 μm.

[0106] In some embodiments, the volume distribution particle size Dv50 of the graphite negative electrode active material can be selected as 9.0 μm, 9.5 μm, 10.0 μm, 10.5 μm, 11.0 μm, 11.5 μm, 12.0 μm, 12.5 μm, 13.0 μm, 13.5 μm, 14.0 μm or a range between any two of the above values.

[0107] When the volume distribution particle size Dv50 of the graphite negative electrode active material is within an appropriate range, the path of active ion embedding and de-embedding is reduced, the transmission performance of active ions and electrons is improved, and the rate performance of the battery is improved. In addition, it is also beneficial to reduce the specific surface area of ​​the graphite negative electrode active material, which helps to reduce the side reactions of the graphite negative electrode active material and the irreversible consumption of active ions during the cycle process, thereby improving the cycle performance and storage performance of the secondary battery.

[0108] In some embodiments, the graphite negative electrode active material comprises a core and a coating layer covering at least a surface of the core, the core is artificial graphite, and the coating layer comprises amorphous carbon.

[0109] In this article, the term "artificial graphite" refers to carbon materials obtained by high-temperature graphitization treatment.

[0110] In this article, the term "amorphous carbon" refers to a carbon material with a low degree of graphitization and crystallization and a disordered and irregular microstructure.

[0111] The "core" of the graphite negative electrode active material is artificial graphite, which reduces the volume change rate during the lithium ion deintercalation and deintercalation process, reduces the side reactions caused by the breakage and reconstruction of the SEI film during the cycle, and improves the cycle performance of the battery. At the same time, the "shell" is amorphous carbon, which can effectively reduce the active ion diffusion resistance and particle surface polarization in the material, so that the Id / Ig of the material is within a suitable range, which can improve the battery's rate performance.

[0112] In some embodiments, the tap density of the graphite negative electrode active material is 1.0 g / cm 3 -1.4g / cm 3 In some embodiments, the tap density of the graphite negative electrode active material may be 1.0 g / cm 3 , 1.05g / cm 3 , 1.1g / cm 3 , 1.15g / cm 3 , 1.20g / cm 3 , 1.25g / cm 3 , 1.3g / cm 3 or 1.4 g / cm 3 , or the range between any two of the above values.

[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 of the graphite negative electrode active material can be measured using instruments and methods known in the art. For example, it can be measured using a powder tap density tester in accordance with GB / T 5162-2006. A Dandong Better BT-301 tester can be used. Test parameters are as follows: vibration frequency 250 ± 15 times / minute, amplitude 3 ± 0.2 mm, number of vibrations 5000 times, and a 25 mL graduated cylinder.

[0115] By regulating the tap density of the graphite negative electrode active material within the above range, the electron conduction between particles can be further improved, and the rate performance of the battery can be improved. At the same time, it is beneficial to improve the stability of the negative electrode slurry, which is beneficial to the coating of the negative electrode slurry, thereby reducing the processing difficulty, improving the appearance of the negative electrode sheet, and improving the electrical performance of the battery.

[0116] In some embodiments, the specific surface area of ​​the graphite negative electrode active material is 0.75 m 2 / g-1.75m 2 In some embodiments, the specific surface area of ​​the graphite negative electrode active material can be 0.75m 2 / g, 0.85m 2 / g, 0.95m 2 / g, 1.05m 2 / g, 1.15m 2 / g, 1.25m 2 / g, 1.35m 2 / g, 1.45m 2 / g, 1.55m 2 / g, 1.65m 2 / g or 1.75m2 / g, or the range between any two of the above values.

[0117] 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.

[0118] The specific surface area of ​​the graphite negative electrode active material is within an appropriate range, and the material has appropriate adsorption sites, which can promote the adsorption of active ions and improve the rate performance of the secondary battery. At the same time, it can avoid excessive side reactions between the graphite negative electrode active material and the electrolyte, which have a negative impact on the cycle performance, and take into account both the cycle performance and rate performance of the battery.

[0119] In some embodiments, the volume particle size distribution (Dv90-Dv10) / Dv50 of the graphite negative electrode active material is 1.30-1.80. In some embodiments, the volume particle size distribution (Dv90-Dv10) / Dv50 of the graphite negative electrode active material can be 1.30, 1.35, 1.40, 1.45, 1.50, 1.60, 1.70 or 1.80, or a range between any two of the above values.

[0120] The volume distribution particle sizes Dv10, Dv50, and Dv90 of the graphite negative electrode active material represent the particle sizes corresponding to the cumulative volume distribution percentages of the material reaching 10%, 50%, and 90%, respectively, and can be measured using instruments and methods known in the art. For example, characterization testing can be performed using a Malvern laser particle size analyzer, such as the Malvern Mastersizer-3000, in accordance with GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method.

[0121] Regulating the volume particle size distribution in the graphite negative electrode active material within a suitable range is beneficial for the negative electrode film layer to have a suitable pore structure, thereby reducing the difficulty of ion liquid phase transmission and improving the rate performance of the secondary battery; in addition, the graphite negative electrode active material can also have good particle stacking properties, which is beneficial to improving the compaction density of the negative electrode film layer, thereby further improving the energy density of the secondary battery.

[0122] In some embodiments, the gram capacity of the graphite negative electrode active material is 325 mAh / g-340 mAh / g.

[0123] Herein, the term "gram capacity" refers to the ratio of the amount of electricity released by the graphite negative electrode active material to the mass of the graphite negative electrode active material. Generally speaking, a higher gram capacity is more conducive to improving the energy density of the secondary battery.

[0124] In some embodiments, the gram capacity of the graphite negative electrode active material is 325 mAh / g, 328 mAh / g, 329 mAh / g, 330 mAh / g, 331 mAh / g, 332 mAh / g, 333 mAh / g, 334 mAh / g, 335 mAh / g, 336 mAh / g, 337 mAh / g or 340 mAh / g, or a range between any two of the above values.

[0125] The gram capacity can be measured using any method known in the art. For example, a graphite anode active material sample can be thoroughly stirred and 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°C, the prepared button cell was first discharged at a constant current of 0.05C to 0.005V, then discharged at a constant current of 10μA to 0.005V. The cell was allowed to rest for 5 minutes, and the first-cycle discharge capacity was recorded. The cell was then charged at a constant current of 0.1C to 2.0V, and the charge capacity was recorded. The ratio of the charge capacity of the button cell to the mass of the graphite anode active material sample is the gram capacity of the graphite anode active material.

[0126] The gram capacity of the graphite negative electrode active material is within the above range, the lattice expansion during the material cycle is relatively small, the crystal structure stability is good, the irreversible consumption of active ions is reduced, and the cycle performance of the battery is improved; at the same time, the graphite negative electrode active material has excellent capacitance and can improve the energy density of the secondary battery.

[0127] [Method for preparing graphite negative electrode active material]

[0128] The present disclosure also provides a method for preparing a graphite negative electrode active material, comprising the following steps:

[0129] Provide raw materials;

[0130] processing the raw materials to obtain a precursor;

[0131] The precursor is graphitized to obtain a graphitized product;

[0132] The graphitized product is surface treated to obtain a graphite negative electrode active material.

[0133] The powder compaction density of the graphite negative electrode active material under a pressure of 49000N is greater than or equal to 1.60g / cm 3 ;

[0134] The Raman spectrum of the graphite negative electrode active material is 1250 cm -1 Up to 1500cm -1 The peak intensity Id and 1500 cm - 1 to 1650cm -1 The peak intensity Ig ratio Id / Ig is greater than or equal to 0.15.

[0135] The graphite negative electrode active material prepared by the method has high energy density and excellent charge and discharge capacity, and the secondary battery prepared using the material has both high energy density and excellent rate performance.

[0136] In some embodiments, the surface treatment is to perform a fusion treatment on the graphitized product to obtain an intermediate, wherein the frequency of the fusion treatment is 20-40 Hz, and / or the time of the fusion treatment is 5-15 minutes;

[0137] The intermediate is mixed with asphalt at room temperature and then carbonized to obtain a graphite negative electrode active material.

[0138] Existing technology involves directly coating graphitized products with asphalt to increase the surface defectivity of graphite negative electrode active materials, thereby improving the material's rate performance. However, direct coating of graphitized products can significantly reduce the material's powder compaction density, lowering the compaction density of the negative electrode film layer and, in turn, affecting the energy density of the secondary battery.

[0139] The present invention discloses a fusion treatment of the graphitized product under specific process conditions before the asphalt coating treatment, which can achieve the purpose of spheroidization and de-edgeing. On the one hand, the intermediate obtained by the fusion spheroidization has a relatively regular structure, which can improve the powder compaction density of the intermediate. On the other hand, the small particles of graphite produced by the de-edgeing can fill the voids in the intermediate material, further improving the powder compaction density of the intermediate. The fusion treatment can effectively compensate for the adverse effects of the asphalt coating treatment on the powder compaction density of the material, which is conducive to obtaining a negative electrode film layer with a high compaction density, and is conducive to obtaining a graphite negative electrode active material with high energy density and excellent rate performance.

[0140] In some embodiments, the frequency of the fusion process may be selected to be 20 Hz, 25 Hz, 30 Hz, 35 Hz, or 40 Hz, or a range between any two of the above values.

[0141] The frequency of fusion treatment affects the powder compaction density and specific surface area of ​​graphite negative electrode active materials. A high fusion treatment frequency can increase the powder compaction density of graphite negative electrode active materials, while also avoiding damage to processing equipment caused by an excessively high fusion treatment frequency.

[0142] In some embodiments, the fusion treatment time is 5-15 minutes. In some embodiments, the fusion treatment time can be selected from 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes, 11 minutes, 12 minutes, 13 minutes, 14 minutes or 15 minutes, or a range between any two of the above values.

[0143] The fusion treatment time affects the powder compaction density, specific surface area, and Id / Ig of the graphite anode active material. Longer fusion treatment times can increase the powder compaction density and Id / Ig of the graphite anode active material, resulting in a higher compaction density anode film and higher battery energy density.

[0144] In some embodiments, the carbonization treatment is performed at a temperature of 950°C to 1350°C.

[0145] In some embodiments, the treatment temperature of the carbonization treatment may be selected as 950° C., 1000° C., 1100° C., 1200° C., 1300° C., or 1350° C., or a range between any two of the above values.

[0146] The carbonization temperature affects the Id / Ig ratio of the graphite anode active material. If the carbonization temperature is too high, the asphalt coating is high, and the coating layer of the graphite anode active material is highly intact, which reduces the Id / Ig ratio of the graphite anode active material and is not conducive to improving the battery's rate performance. If the carbonization temperature is too low, the functional groups on the asphalt surface may not be completely removed, causing side reactions during the cycle and affecting the battery's cycle performance.

[0147] In some embodiments, the feedstock comprises one or more of petroleum coke, needle coke, and pitch coke.

[0148] As used herein, the term "petroleum coke" refers to coke formed by carbonizing petroleum residue or petroleum asphalt at high temperatures.

[0149] 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.

[0150] As used herein, the term "pitch coke" refers to the solid material produced by carbonizing coal tar pitch at high temperatures.

[0151] In some embodiments, the feedstock comprises petroleum coke.

[0152] Petroleum coke has excellent anisotropy, which is conducive to the preparation of low-graphitization, low-expansion graphite negative electrode active materials, which is beneficial to the long cycle life of the battery. In addition, the source of petroleum coke is more extensive, which is conducive to industrial production.

[0153] The above-mentioned raw materials generally include at least one of mosaic, regional, and fibrous structures. Generally, based on the morphological characteristics and isochromatic zone size of the char material under a polarizing microscope, isochromatic zones with a size less than 30 μm are classified as mosaic; isochromatic zones with a size greater than 30 μm are classified as regional; and anisotropic banded isochromatic zones are classified as fibrous.

[0154] In some embodiments of the present disclosure, based on the total volume of the raw material structure, the volume proportion of the mosaic and regional structures in the raw material is greater than or equal to 60%, and can be optionally 65%-80%.

[0155] In some embodiments, based on the total volume of the raw material structure, the volume proportion of the mosaic structure and the regional structure can be selected as 60%, 65%, 70%, 75%, 80%, 85% or 90%, or a range between any two of the above values.

[0156] In the present disclosure, the volume proportion of mosaic and regional structures in the raw materials can be tested using methods known in the art. As an example, according to the provisions of GB 1997-89, the raw materials are crushed to 1mm and mixed, and 40g to 50g of them are separated. 4g to 5g of 0.07mm to 1.0mm grade samples are taken through a square hole sieve for slice making. According to the provisions of MT 116.1-86, powder coke and block coke films are prepared. The diameter of the powder coke film shall not be less than 22mm, and the volume occupied by the cement shall be less than 1 / 3. The sample is placed on a slide with clay, flattened, and then placed on the stage for focusing. After calibrating the microscope, the polarizer and analyzer are adjusted to make them orthogonal. Insert the azurite inspection plate (1λ) so that the field of view shows the interference color of first-order red. Determine the step length of the moving ruler to ensure that more than 400 effective measuring points are evenly distributed, with a point spacing of 0.3 to 0.5mm and a line spacing of 0.5 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.

[0157] Raw materials with many mosaic structures and regional structures have excellent isotropy, which is beneficial to reducing the graphitization degree of the graphite negative electrode active material, making the expansion of the graphite negative electrode active material relatively small during the cycle, which is beneficial to improving the cycle stability of the material.

[0158] In some embodiments, based on the total volume of the raw material structure, the volume proportion of the mosaic structure and the regional structure can be selected to be 65%, 70%, 75% or 80%, or a range between any two of the above values.

[0159] An excessively high volume ratio of the mosaic structure and the regional structure will reduce the powder compaction density and gram capacity of the graphite negative electrode active material, affecting the energy density of the battery. Controlling the volume ratio of the mosaic structure and the regional structure can take into account both the energy density and cycle performance of the battery.

[0160] In some embodiments, the maximum power of the graphitization process is 70% to 90% of the rated power of the graphitization process equipment.

[0161] In some embodiments, the maximum power of the graphitization process can be selected as 70%, 75%, 80%, 85%, 90%, or any range therebetween, of the rated power of the graphitization process equipment. It is understood that the graphitization process equipment refers to any device capable of performing graphitization, including but not limited to Acheson furnaces, box furnaces, internal series 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.

[0162] In some embodiments, the graphitization treatment equipment is an inner string furnace, and the rated power of the inner string furnace is 25000-32000W.

[0163] In some embodiments, the graphitization treatment equipment is an Acheson furnace, and the rated power of the Acheson furnace is 28,000-30,000W.

[0164] The maximum power of the graphitization process used in this disclosure needs to be lower than the rated power of the graphitization equipment to achieve uniformity of the temperature field during the graphitization process, ensure the consistency of the material's gram capacity, and help improve the cycle life of the battery.

[0165] In some embodiments, the maximum power of the graphitization treatment is 21000 W to 26000 W. In some embodiments, the maximum power of the graphitization treatment can be 21000 W, 23000 W, 23500 W, 24000 W, 26000 W, or any range therebetween.

[0166] In some embodiments, the graphitization treatment is performed at a constant power time of 8 hours to 40 hours at the maximum power.

[0167] In some embodiments, the graphitization treatment is performed at a constant power time of maximum power of 8 h, 13 h, 16 h, 19 h, 22 h, 25 h, 28 h, 31 h, 33 h, 36 h, 39 h, 40 h, or any range therebetween.

[0168] In some embodiments, the graphitization treatment equipment is an internal series furnace, and the graphitization treatment is performed at a constant power of 8 hours to 20 hours at maximum power, and optionally 9 hours to 16 hours. For example, the graphitization treatment at a constant power of 8 hours, 15 hours, 20 hours, or any range therebetween.

[0169] In some embodiments, the graphitization treatment apparatus is an Acheson furnace, and the graphitization treatment is performed at a constant power time of 20 hours to 40 hours at maximum power. For example, the graphitization treatment is performed at a constant power time of 20 hours, 30 hours, 35 hours, 40 hours, or any range therebetween.

[0170] The maximum power of the appropriate graphitization treatment and / or the constant power time at the maximum power, the powder compaction density and defectivity of the graphitized product are within a suitable range. After the graphitized product is surface treated, a graphite negative electrode active material with excellent powder compaction density and defectivity can be obtained.

[0171] In some embodiments, the gram capacity of the graphitized product is 325-340 mAh / g. In some embodiments, the gram capacity of the graphitized product can be 325 mAh / g, 330 mAh / g, 335 mAh / g, or 340 mAh / g, or a range between any two of the above values.

[0172] The gram capacity of the graphitized product is within an appropriate range, and the compaction density and defectivity of the graphitized product are within an appropriate range. After the graphitized product is surface treated, a graphite negative electrode active material with excellent powder compaction density and defectivity can be obtained.

[0173] In some embodiments, the processing of the raw material specifically comprises the following steps:

[0174] The raw materials are crushed, shaped, and graded, and fine powder is removed to obtain secondary raw materials;

[0175] Carbonizing the secondary raw material to obtain a precursor,

[0176] The volume distribution particle size Dv50 of the secondary raw material is 8.0-16.0 μm, and / or the particle size distribution (Dv90-Dv10) / Dv50 of the secondary raw material is 1.30-1.70.

[0177] In some embodiments, during the step of crushing the raw materials, a crusher, such as a jaw crusher, can be used to crush the coke raw materials. For example, the raw materials can be crushed to a predetermined particle size before being screened.

[0178] In some embodiments, in the step of shaping the raw material, a shaping machine can be used to shape the crushed raw material. The shaping process can reduce burrs on the surface of the crushed raw material.

[0179] In some embodiments, during the step of classifying the raw materials, an air classifier can be used to classify the shaped raw materials. Optionally, 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 particles and fine powder in the resulting precursor.

[0180] In some embodiments, the volume distribution particle size Dv50 of the secondary raw material can be selected as 8.0 μm, 9.0 μm, 10.0 μm, 11.0 μm, 12.0 μm, 13.0 μm, 14.0 μm, 15.0 μm or 16.0 μm, or a range between any two of the above values.

[0181] Controlling the Dv50 of secondary raw materials within a suitable range is beneficial to controlling the Dv50 of graphite negative electrode active materials within a suitable range, reducing the paths of active ion embedding and de-embedding, improving the transmission performance of active ions and electrons, improving the rate performance of the battery, and helping to reduce the side reactions of graphite negative electrode active materials and the irreversible consumption of active ions during the cycle process, thereby improving the cycle performance and storage performance of the secondary battery.

[0182] In some embodiments, the particle size distribution of the secondary raw material (Dv90-Dv10) / Dv50 can be selected as 1.30, 1.40, 1.50, 1.60 or 1.70, or a range between any two of the above values.

[0183] Controlling the particle size distribution (Dv90-Dv10) / Dv50 of the secondary raw materials within a suitable range is beneficial to controlling the particle size distribution (Dv90-Dv10) / Dv50 of the graphite negative electrode active material within a suitable range, which is beneficial for the negative electrode film layer to have a suitable pore structure, thereby reducing the difficulty of ion liquid phase transmission and improving the rate performance of the secondary battery; in addition, the graphite negative electrode active material can also have good particle stacking properties, which is beneficial to improving the compaction density of the negative electrode film layer, thereby further improving the energy density of the secondary battery.

[0184] 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.

[0185] In one embodiment of the present disclosure, a secondary battery is provided.

[0186] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0187] [Positive electrode]

[0188] 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.

[0189] 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.

[0190] 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.).

[0191] In some embodiments, the positive electrode active material may adopt the positive electrode active material for batteries that is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present disclosure is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co0.2 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.

[0192] In some embodiments, the positive electrode film layer may further optionally include 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.

[0193] In some embodiments, the positive electrode film layer may further include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0194] 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.

[0195] [Negative electrode]

[0196] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes the graphite negative electrode active material in any embodiment.

[0197] 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.

[0198] 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, other 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.

[0199] 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.).

[0200] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0201] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0202] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0203] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as graphite negative electrode active material, conductive agent, binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0204] [Electrolytes]

[0205] 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.

[0206] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0207] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0208] In some embodiments, the solvent can be selected from 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.

[0209] In some embodiments, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0210] [Isolation film]

[0211] 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.

[0212] In some embodiments, the material of the separator can be selected from at least one of glass fiber, 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.

[0213] 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.

[0214] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0215] 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.

[0216] 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.

[0217] 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.

[0218] 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.

[0219] 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.

[0220] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0221] 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.

[0222] 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.

[0223] In addition, the present disclosure further provides an electric device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present disclosure. The secondary battery, battery module, or battery pack can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0224] As the electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0225] 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.

[0226] 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.

[0227] Example

[0228] 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.

[0229] 1. Preparation method

[0230] Example 1

[0231] (1) Preparation of graphite negative electrode active materials

[0232] The petroleum coke raw material with a volume proportion of 65% of mosaic and regional structures is coarsely crushed, and then the coarsely crushed material is crushed and sieved. The sieved material is shaped, graded, and finely powdered to obtain a secondary raw material with a Dv50 particle size of 12.0 μm and a particle size distribution of (Dv90-Dv10) / Dv50 of 1.61;

[0233] The secondary raw materials were placed in a kiln for pre-carbonization at a temperature of 1000°C and a high temperature zone time of 24 hours to obtain a precursor with a tap density of 0.99 g / cm 3 ;

[0234] The precursor was graphitized in an inner furnace at a temperature of 2850°C and a maximum power of 25000W (this refers to the actual power used by the inner furnace, which is about 85% of the rated power of the inner furnace). The power was kept constant for 9.5 hours, and the surface temperature of the graphite crucible in the inner furnace was cooled to 300°C to obtain a graphitized product.

[0235] The graphitized product was fused in a high-speed fusion machine to obtain an intermediate. The fusion frequency was 40 Hz and the fusion time was 10 min. The intermediate was mixed with asphalt in a mass ratio of 98% to 2% and then carbonized at 1150 ° C for 2 h. After the finished product was demagnetized and mixed, a graphite negative electrode active material was obtained. The powder compaction density under a pressure of 49000 N was 1.70 g / cm 3 The ratio of the peak intensity Id from 1250 cm-1 to 1500 cm-1 to the peak intensity Ig from 1500 cm-1 to 1650 cm-1 in its Raman spectrum is 0.27, and the degree of graphitization is 89.1%.

[0236] (2) Preparation of secondary batteries

[0237] The prepared negative electrode active material, conductive agent carbon black Super P, thickener sodium carboxymethyl cellulose, and binder styrene-butadiene rubber were mixed in a 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 became uniform to obtain a negative electrode slurry. The negative electrode slurry was evenly coated on the negative electrode current collector copper foil to form a negative electrode film layer. After drying, cold pressing, and slitting, the negative electrode sheets were obtained. The surface density of the negative electrode film layer was 0.99 mg / cm 2 The cold pressing roller gap of the cold pressing treatment is -199, and the cold pressing pressure is 50T.

[0238] 2) Preparation of positive electrode sheet

[0239] 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 under the action of a vacuum mixer until the system became 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 sheets were obtained after drying, cold pressing, and slitting. The compaction density of the positive electrode film layer was 2.50 g / cm 3 , with a surface density of 19.7 mg / cm 2 .

[0240] 3) Preparation of electrolyte

[0241] In an argon atmosphere glove box with a water content of less than 10 ppm, diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and ethylene carbonate (EC) were mixed in a weight ratio of 1:1:1 to obtain an organic solvent. LiPF6 was then dissolved in the organic solvent to prepare an electrolyte with a concentration of 1.0 mol / L. Vinylene carbonate (VC) was then added, and the VC content was 2% of the total mass of the electrolyte.

[0242] 5) Isolation film

[0243] Polypropylene film is used as the isolation film.

[0244] 6) Preparation of secondary batteries

[0245] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive and negative electrode sheets to serve as an isolation, and then wound to obtain an electrode assembly; the electrode assembly is placed in an outer package, dried, and then injected with electrolyte, and after vacuum packaging, standing, forming, shaping and other processes, a lithium-ion battery is obtained.

[0246] The preparation methods of Examples 2-5 are basically the same as those of Example 1, except that the gram capacity of the graphitized product is adjusted by adjusting the volume ratio of the mosaic structure and the regional structure in the raw material, the maximum power of the graphitization treatment, or the constant power time of the graphitization treatment at the maximum power, as shown in Table 1.

[0247] The preparation method of Example 6 is basically the same as that of Example 1, except that the gram capacity of the graphitized product is adjusted by adjusting the volume ratio of the mosaic structure and the regional structure in the raw material, the maximum power of the graphitization treatment or the constant power time of the graphitization treatment at the maximum power, and the fusion frequency and fusion time of the fusion treatment are adjusted, as shown in Table 1.

[0248] Table 1

[0249] The preparation method of Comparative Example 1 is substantially the same as that of Example 1, except that the fusion treatment and the asphalt coating treatment are not performed during the preparation of the graphite negative electrode active material.

[0250] The preparation method of Comparative Example 2 is substantially the same as that of Example 2, except that the graphite negative electrode active material is directly coated without undergoing fusion treatment during preparation.

[0251] 2. Performance Testing

[0252] Cycle performance test of secondary batteries

[0253] 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.

[0254] 2. Charging time of secondary batteries

[0255] At 25°C, the secondary battery was charged to 3.65V at a constant current of 0.33C, then charged to a current of 0.05C at a constant voltage. After standing for 5 minutes, the secondary battery was discharged to 2.50V at a constant current of 0.33C, and its actual capacity was recorded as C0.

[0256] Then the secondary battery is charged with a constant current of 1.0C0, 1.3C0, 1.5C0, 1.8C0, 2.0C0, 2.3C0, 2.5C0, 3.0C0 in sequence to a negative electrode cutoff potential of 3.5V or 0V (whichever is reached first). After each charging is completed, it is discharged to 2.5V at 1C0. The negative electrode potential corresponding to charging to 10%, 20%, 30%, ..., 80% SOC (State of Charge) at different charging rates is recorded, and the charging rate-negative electrode potential curve under different SOC states is drawn. After linear fitting, the charging rate corresponding to the negative electrode potential of 0V under different SOC states is obtained. The charging rate is the charging window under the SOC state, which is recorded as C10% SOC, C20% SOC, C30% SOC, C40% SOC, C50% SOC, C60% SOC, C70% SOC, C80% SOC, C90% SOC, ...110% SOC, C120% SOC, C130% SOC, C140% SOC, C150% SOC, C160% SOC, C170% SOC, C180% SOC, C190% SOC, C20% SOC, C210% SOC, C220% SOC, C230% SOC, C240% SOC, C250% SOC, C260% SOC, C270% SOC, C300% SOC, C310% SOC, C320% SOC, C330% At 80% SOC, the charging time T (in minutes) required for the secondary battery to charge from 10% SOC to 80% SOC (assuming lithium deposition does not occur in the secondary battery) is calculated using the formula (60 / C10% SOC + 60 / C20% SOC + 60 / C30% SOC + 60 / C40% SOC + 60 / C50% SOC + 60 / C60% SOC + 60 / C70% SOC + 60 / C80% SOC) × 10%. The shorter the charging time, the better the fast charging performance of the secondary battery.

[0257] 3. Compaction density of negative electrode film layer

[0258] The compaction density of the negative electrode film layer can be tested using methods known in the art. As an example, a negative electrode sheet test sample with an area of ​​S is weighed using an electronic balance, with the weight recorded as W1. The thickness of the negative electrode sheet is measured using a caliper to obtain the thickness T1 of the negative electrode sheet. The weighed electrode sheet film layer is then wiped off, the weight of the negative electrode current collector is weighed as W2, and the thickness of the negative electrode current collector is measured using a caliper to obtain the thickness T2 of the negative electrode current collector. The compaction density of the negative electrode film layer is then calculated as PD = (W1-W2) / [(T1-T2)×S].

[0259] 3. Results

[0260] As shown in Table 2, the powder compaction density of the graphite negative electrode active material provided by the embodiment of the present disclosure is greater than or equal to 1.60 g / cm 3 , and the Raman spectrum of the graphite negative electrode active material is 1250cm -1 Up to 1500cm -1 The peak intensity Id and 1500 cm -1 to 1650cm -1The peak intensity Ig ratio Id / Ig is greater than or equal to 0.15. As can be seen from the comparison of Examples 1-6 with Comparative Examples 1-2, the graphite negative electrode active material disclosed herein combines high powder compaction density and Id / Ig. On the premise that the negative electrode film layer has a high compaction density, the charging time of the battery from 10% SOC to 80% SOC can be shortened. This allows the secondary battery to effectively improve its rate performance while having a relatively high energy density, while also increasing the number of cycles and improving the battery's cycling performance.

[0261] As can be seen from Table 2, the graphitization degree of the graphite negative electrode active material is between 85% and 91%, the negative electrode film layer has a high compaction density, and the battery has a short charging time from 10% SOC to 80% SOC and a large number of cycles. The secondary battery has high energy density, excellent cycle performance and rate performance.

[0262] Table 2

[0263] 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, wherein: The powder compaction density of the graphite negative electrode active material under a pressure of 49000N is greater than or equal to 1.60g / cm 3 In the Raman spectrum of the graphite negative electrode active material, 1250 cm -1 Up to 1500cm -1 The peak intensity Id and 1500cm -1 Up to 1650cm -1 The peak intensity Ig ratio Id / Ig is greater than or equal to 0.

15.

2. The graphite negative electrode active material according to claim 1, wherein The powder compaction density of the graphite negative electrode active material under a pressure of 49000N is 1.60g / cm 3 -1.80g / cm 3 , optional 1.65g / cm 3 -1.75g / cm 3 .

3. The graphite negative electrode active material according to claim 1 or 2, wherein: In the Raman spectrum of the graphite negative electrode active material, 1250 cm -1 Up to 1500cm -1 The peak intensity Id and 1500cm -1 Up to 1650cm -1 The peak intensity Ig ratio Id / Ig is 0.2-0.

35.

4. The graphite negative electrode active material according to any one of claims 1 to 3, wherein 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, wherein The graphitization degree of the graphite negative electrode active material is 85%-91%.

6. The graphite negative electrode active material according to any one of claims 1 to 5, wherein The volume distribution particle size Dv50 of the graphite negative electrode active material is less than or equal to 15.0 μm, and can be optionally 9.0 μm-14.0 μm.

7. The graphite negative electrode active material according to any one of claims 1 to 6, wherein The graphite negative electrode active material comprises a core and a coating layer at least covering the surface of the core, the core is artificial graphite, and the coating layer comprises amorphous carbon.

8. The graphite negative electrode active material according to any one of claims 1 to 7, wherein The graphite negative electrode active material satisfies at least one of the following conditions: (1) The tap density of the graphite negative electrode active material is 1.0 g / cm 3 -1.4g / cm 3 ; (2) The specific surface area of ​​the graphite negative electrode active material is 0.75 m 2 / g-1.75m 2 / g; (3) The particle size distribution of the graphite negative electrode active material (Dv90-Dv10) / Dv50 is 1.30-1.80; (4) The gram capacity of the graphite negative electrode active material is 325 mAh / g-340 mAh / g.

9. A method for preparing a graphite negative electrode active material, wherein: The steps include: Provide raw materials; Processing the raw material to obtain a precursor; The precursor is graphitized to obtain a graphitized product; The graphitized product is subjected to surface treatment to obtain a graphite negative electrode active material. The powder compaction density of the graphite negative electrode active material under a pressure of 49000N is greater than or equal to 1.60g / cm 3 ; In the Raman spectrum of the graphite negative electrode active material, 1250 cm -1 Up to 1500cm -1 The peak intensity Id and 1500cm -1 Up to 1650cm -1 The peak intensity Ig ratio Id / Ig is greater than or equal to 0.

15.

10. The preparation method according to claim 9, wherein: The surface treatment specifically comprises the following steps: The graphitized product is subjected to a fusion treatment to obtain an intermediate, wherein the frequency of the fusion treatment is 20-40 Hz, and / or the time of the fusion treatment is 5-15 min; The intermediate is mixed with asphalt at room temperature and then carbonized to obtain a graphite negative electrode active material.

11. The preparation method according to claim 10, wherein: The mass ratio of the intermediate to asphalt is 1:99-10:90, and can be optionally 2:98-5:

95.

12. The preparation method according to any one of claims 9 to 11, wherein The raw material comprises one or more of petroleum coke, needle coke, and pitch coke, and petroleum coke can be selected.

13. The preparation method according to claim 12, wherein: Based on the total volume of the raw material structure, the volume proportion of the mosaic structure and the regional structure is greater than or equal to 60%, and can be optionally 65%-80%.

14. The preparation method according to any one of claims 9 to 13, wherein The maximum power of the graphitization treatment is 70%-90% of the rated power of the graphitization treatment equipment.

15. The preparation method according to any one of claims 9 to 14, wherein The maximum power of the graphitization treatment is 21000W-26000W; and / or the constant power time of the graphitization treatment at the maximum power is 8h-40h.

16. The preparation method according to any one of claims 9 to 15, wherein The gram capacity of the graphitized product is 325-340 mAh / g.

17. The preparation method according to any one of claims 9 to 16, wherein The processing of raw materials specifically comprises the following steps: The raw materials are crushed, shaped, and graded, and fine powder after crushing is removed to obtain secondary raw materials; Carbonizing the secondary raw material to obtain a precursor, Wherein, the volume distribution particle size Dv50 of the secondary raw material is 8.0-16.0 μm, and / or the particle size distribution (Dv90-Dv10) / Dv50 of the secondary raw material is 1.30-1.

70.

18. A secondary battery, comprising a negative electrode plate, wherein: The negative electrode sheet comprises the graphite negative electrode active material according to any one of claims 1 to 8 or the graphite negative electrode active material prepared by the preparation method according to any one of claims 9 to 17.

19. An electrical device comprising the secondary battery according to claim 18.

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