Graphite negative electrode active material and preparation method therefor, negative electrode plate, secondary battery, and electrical apparatus

Abstract

A graphite negative electrode active material and a preparation method therefor, a negative electrode plate, a secondary battery, and an electrical apparatus. A particle body of the graphite negative electrode active material comprises an interior area and a surface layer area at least partially surrounding the interior area, the surface layer area referring to an area formed extending a distance of 30 nm from the surface of the particle body of the graphite negative electrode active material toward the interior, and the surface layer area comprising a disordered layer. The graphite negative electrode active material can balance the dynamic performance and the cycling stability of a battery.

Description

Graphite negative electrode active material and preparation method thereof, negative electrode sheet, secondary battery and electrical device

[0001] Cross-references

[0002] This disclosure refers to Chinese patent application No. 202311675692.5, filed on December 7, 2023, entitled “Graphite negative electrode active material and preparation method thereof, negative electrode sheet, secondary battery and electrical device”, which is incorporated into this disclosure in its entirety by reference. Technical Field

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

[0004] In recent years, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields.

[0005] With the continuous expansion of secondary battery application scenarios and the continuous improvement of charge and discharge rates, higher requirements are placed on the battery's dynamic performance. However, the improvement of battery rate performance often comes at the expense of cycle life.

[0006] Summary of the Invention

[0007] The present disclosure is made in view of the above-mentioned problems, and its purpose is to provide a graphite negative electrode active material and a preparation method thereof, as well as a negative electrode sheet, a secondary battery and an electrical device containing the same, so as to take into account both the dynamic performance and cycle stability of the battery.

[0008] The first aspect of the present disclosure provides a graphite negative electrode active material, wherein the particle body of the graphite negative electrode active material includes an internal region and a surface region that at least partially surrounds the internal region, wherein the surface region refers to a region extending 30 nm from the surface of the particle body of the graphite negative electrode active material to the interior of the particle, and the surface region includes a disordered layer.

[0009] The disordered layer mainly includes amorphous carbon. The carbon atoms in the amorphous carbon structure have no regular arrangement, which makes the interaction between its molecules more complex, resulting in higher strength and hardness than the graphite crystals in the internal region. This reduces the probability of surface damage of the graphite particles due to friction between particles and between particles and the mixing tank during slurry preparation. The risk of particle cracking and exposure of new interfaces in the graphite negative electrode active material during the cold pressing of the electrode is reduced, allowing the graphite negative electrode active material to maintain higher particle integrity during the manufacturing process. Graphite negative electrode active materials with high particle integrity have fewer surface defects and a good interface with the electrolyte. They can effectively reduce side reactions between the negative electrode and the electrolyte, reduce the loss of active lithium, and are beneficial to improving battery storage stability and cycle stability. At the same time, the disordered layer on the graphite negative electrode active material also helps to improve the infiltration of the electrolyte into the negative electrode, thereby improving the battery kinetic performance.

[0010] Unlike the disordered layer coated on the surface of graphite negative electrode active materials in the prior art, the disordered layer of the graphite negative electrode active material provided in the embodiments of the present disclosure is located in the particle body of the graphite negative electrode active material. It is derived from the same raw material as the graphite negative electrode active material and is not prepared through post-processing. Therefore, compared with graphite negative electrode active materials in which the disordered layer is obtained by coating the surface of the particle body, this graphite negative electrode active material has better material consistency, resulting in a longer cycle life for the battery, achieving a balance between battery kinetic performance and cycle stability and storage stability. It is particularly suitable for energy storage batteries with extremely high requirements for cycle life and storage life.

[0011] In any embodiment, the thickness of the disordered layer is 1 nm to 20 nm; optionally 3 nm to 16 nm.

[0012] The disordered layer with a thickness within the above range is beneficial to the embedding and deintercalation of active ions, thereby improving the kinetic performance of the battery; it will not cause an excessively high degree of side reaction between the graphite negative electrode active material and the electrolyte, thereby taking into account the improvement of the battery's cycle stability and kinetic performance.

[0013] In any embodiment, the coefficient of variation of the thickness of the disordered layer is less than or equal to 50%, where the coefficient of variation refers to the ratio of the standard deviation of the thickness of the disordered layer to the average of the thickness of the disordered layer.

[0014] Different from the graphite negative electrode active material in the prior art in which the surface is coated with amorphous carbon through a post-processing process, the surface disordered layer of the graphite negative electrode active material in the embodiment of the present disclosure has higher uniformity and a low coefficient of variation of the thickness of the disordered layer, which is beneficial to improving the structural uniformity and electrochemical stability of the graphite negative electrode active material, and improving the storage stability and cycle stability of the secondary battery.

[0015] In any embodiment, the graphite negative electrode active material I D / I G is 0.05-0.10, where I D / I G is the ratio of the D peak intensity to the G peak intensity obtained from the Raman spectrum, I D Indicates that the Raman spectrum is at 1350±100cm -1 The D peak intensity at I G Indicates that the Raman spectrum is at 1580±100cm -1 The G peak intensity at .

[0016] I of graphite negative electrode active material D / I G It can be used to characterize the surface disorder of graphite negative electrode active materials. Different from the active materials with disordered layers coated on the surface of the graphite particle body, the graphite negative electrode active materials provided by the embodiments of the present disclosure have a disordered layer on the surface and have a low surface disorder. The disordered layer in the active material with disordered layers coated on the surface of the graphite particle body is usually derived from the coated organic carbon, so that the disordered layer after carbonization has a high surface disorder; while the disordered layer structure in the surface region of the graphite negative electrode active material provided by the embodiments of the present disclosure and the other parts of the graphite negative electrode active material are derived from the same precursor, and the disordered layer has high uniformity and extremely thin thickness, so that it can have a low surface disorder. On the one hand, this enables the graphite negative electrode active material to take advantage of the disordered layer and improve the kinetic performance of the battery, without causing excessive side reactions due to the excessive disorder of the surface layer of the material. It can improve the kinetic performance of the battery while taking into account the cycle stability and storage stability of the battery.

[0017] In any embodiment, the interlayer spacing of the disordered layers of the graphite negative electrode active material is recorded as d1, and the interlayer spacing of the inner region of the graphite negative electrode active material is recorded as d2, and the graphite negative electrode active material satisfies d1>d2; in some exemplary embodiments, d1 is 0.3365nm-0.3378nm; in some exemplary embodiments, d2 is 0.3358nm-0.3364nm

[0018] The interlayer spacing of the disordered layer is higher than the interlayer spacing of the internal region of the graphite negative electrode active material, which can play the role of a lithium insertion buffer layer, improve the wettability of the electrolyte to the graphite negative electrode active material, and improve the fast charging performance of the battery.

[0019] In any embodiment, the graphite negative electrode active material includes both primary particles and secondary particles. In some exemplary embodiments, the secondary particles account for less than or equal to 50% of the total number of primary particles and secondary particles in the graphite negative electrode active material.

[0020] Graphite anode active materials with a low proportion of secondary particles are beneficial for maintaining the particle integrity of the graphite anode active material during battery preparation, reducing the formation of new interfaces, reducing the consumption of active lithium during the cycle, and further improving the cycle stability of the secondary battery. At the same time, a certain number of secondary particles can reduce the expansion of the negative electrode while taking into account the kinetic performance of the secondary battery, thus ensuring that the battery cell has a kinetic window for the entire life cycle, and will not cause lithium plating due to uneven current distribution, which will lead to a sharp decline in battery capacity and a sharp deterioration in battery life, thereby comprehensively improving the battery's cycle stability.

[0021] In any embodiment, the particle size distribution of the graphite negative electrode active material is (Dv90-Dv10) / Dv50 is 1.0-1.5, and optionally 1.1-1.45.

[0022] Controlling the particle size distribution of the graphite negative electrode active material within the above range is beneficial to improving the tight packing of the graphite negative electrode active material and improving the compaction density of the negative electrode sheet. In other words, the cold pressing pressure required for the negative electrode sheet to achieve the same compaction density is smaller, thereby reducing the probability of cracking of the graphite negative electrode active material during the cold pressing process, and further improving the integrity of the graphite negative electrode active material during the processing process; and the small stress inside the graphite negative electrode active material particles is beneficial to maintaining the long-period pore structure of the electrode sheet during the cycle process, and can maintain the original pore structure of the electrode sheet during the cycle process, so that the lithium ion lithium insertion path remains unobstructed, while reducing the re-filming of the graphite negative electrode active material during the charging process, improving the kinetic performance, cycle life and storage stability. Furthermore, the particle size distribution within the above range can also improve the uniformity of lithium insertion between the graphite negative electrode active material particles, reduce polarization, avoid lithium precipitation caused by uneven current density, and help achieve long-term cycle stability. In addition, the particle size distribution within the above range can also help improve the processing performance of the electrode, and will not affect the uniformity of slurry stirring due to excessive small particles in the graphite negative electrode active material, which is beneficial to improving the uniformity and stability of the electrode quality and helping to achieve long-cycle stability.

[0023] When the particle size distribution (Dv90-Dv10) / Dv50 of the graphite negative electrode active material is 1.1-1.45, the preparation of the graphite negative electrode active material has a higher yield, which is conducive to cost reduction; at the same time, the cycle stability and storage stability of the graphite negative electrode active material are further improved.

[0024] In any embodiment, the volume distribution particle size Dv50 of the graphite negative electrode active material is denoted as A, and the volume distribution particle size Dv50 of the graphite negative electrode active material after cold pressing under a pressure of 20,000 N is denoted as B. Then, the graphite negative electrode active material satisfies: B / A ≥ 85%. In some embodiments, the graphite negative electrode active material satisfies: B / A is 85%-98%.

[0025] The graphite negative electrode active material still maintains high particle integrity after cold pressing, which helps to improve the cycle stability.

[0026] In any embodiment, the specific surface area of ​​the graphite negative electrode active material is 1.2 m 2 / g-1.9m 2 In some embodiments, the specific surface area of ​​the graphite negative electrode active material is 1.3 m 2 / g-1.8m 2 / g.

[0027] The low specific surface area of ​​the graphite negative electrode active material helps to further reduce the degree of side reactions of the graphite negative electrode active material and improve the cycle life of the secondary battery.

[0028] In any embodiment, the volume distribution particle size Dv50 of the graphite negative electrode active material is 7.0 μm to 14.0 μm. In some embodiments, the volume distribution particle size Dv50 of the graphite negative electrode active material is 8.0 μm to 12.0 μm.

[0029] In any embodiment, the powder compaction density of the graphite negative electrode active material under a pressure of 49000N is less than or equal to 1.85g / cm 3 In some embodiments, the powder compaction density of the graphite negative electrode active material under a pressure of 49000N is 1.75g / cm 3 -1.85g / cm 3 .

[0030] Graphite negative electrode active materials with a powder compaction density within the above range are easy to maintain high particle integrity during the cold pressing process, which helps to improve the cycle life of the secondary battery.

[0031] In any embodiment, the gram capacity of the graphite negative electrode active material is 345 mAh / g to 355 mAh / g. In some embodiments, the gram capacity of the graphite negative electrode active material is 347 mAh / g to 353 mAh / g.

[0032] The graphite negative electrode active material with a gram capacity within the above range will not undergo significant lattice expansion during the charge and discharge process due to the high graphitization of the graphite negative electrode active material; nor will it be difficult to compact due to the low graphitization of the graphite negative electrode active material. In order to achieve the same electrode compaction density, a higher cold pressing pressure is required, which will cause cracks during the cold pressing process and generate new interfaces during the cycle process to consume excessive active lithium, thereby comprehensively improving the cycle life of the secondary battery.

[0033] A second aspect of the present disclosure provides a method for preparing a graphite negative electrode active material, comprising the following steps: providing raw materials; processing the raw materials to obtain an intermediate product; graphitizing the intermediate product to obtain a graphitized product; screening the graphitized product to obtain a graphite negative electrode active material; the particle body of the graphite negative electrode active material includes an internal region and a surface region that at least partially surrounds the internal region, the surface region refers to a region extending 30 nm from the surface of the particle body of the graphite negative electrode active material to the interior of the particle, and the surface region includes a disordered layer.

[0034] In any embodiment, the maximum power of the graphitization process is 70% to 90% of the rated power of the graphitization process equipment.

[0035] The maximum power of the graphitization treatment used in this disclosure needs to be lower than the rated power of the graphitization equipment to achieve uniformity in the thermal field during the graphitization process. By controlling the maximum power of the graphitization treatment, the degree of graphitization of the graphite negative electrode active material during the heat treatment can be effectively controlled. While the internal regions of the graphite negative electrode active material particles are highly graphitized, a uniform disordered layer is formed on the bulk surface, which is beneficial for improving the cycling stability of the secondary battery.

[0036] In any embodiment, the graphitization treatment is performed at maximum power for a period of 10 hours to 50 hours.

[0037] The appropriate graphitization treatment temperature and the appropriate graphitization treatment time are not likely to cause excessive rearrangement of the precursor, resulting in a high specific surface area of ​​the graphite negative electrode active material after graphitization and deterioration of high-temperature performance; it can also effectively improve the graphitization degree of the graphite negative electrode active material, thereby facilitating the simultaneous improvement of the high-temperature storage and cycle life of the secondary battery.

[0038] In any embodiment, the temperature of the graphitization treatment is 2600°C to 3000°C.

[0039] The appropriate graphitization treatment temperature and the appropriate graphitization treatment time are not likely to cause excessive rearrangement of the precursor, resulting in a high specific surface area of ​​the graphite negative electrode active material after graphitization and deterioration of high-temperature performance; it can also effectively improve the graphitization degree of the graphite negative electrode active material, thereby facilitating the simultaneous improvement of the high-temperature storage and cycle life of the secondary battery.

[0040] In any embodiment, the feedstock comprises at least one of petroleum coke, needle coke, and pitch coke. In some embodiments, the feedstock is needle coke.

[0041] Needle coke has a range of advantages, including low thermal expansion coefficient, low porosity, low sulfur, low ash, low metal content, high conductivity, and easy graphitization. The graphite anode active material after graphitization can achieve a high ultimate compaction density and a low cyclic expansion rate.

[0042] In any embodiment, based on the total area of ​​the raw material structure, the raw material fiber structure accounts for 55% or more by volume. In some embodiments, the raw material fiber structure accounts for 58% to 70% by volume.

[0043] Raw materials with a high volume fraction of fiber-type structures are beneficial for increasing the compaction density and specific capacity of graphite negative electrode active materials, allowing the graphite negative electrode active materials to retain a high degree of integrity during the compaction process, resulting in batteries with both a long cycle life and good energy density. However, an excessively high proportion of fiber-type structures will increase the cost and expansion rate of the graphite negative electrode active materials, and deteriorate the kinetic performance. Raw materials with a volume fraction of fiber-type structures within the above range have both lower costs and good specific capacity of the graphite, allowing the battery cell to have a full life cycle kinetic window, thereby comprehensively improving the long-term cycle life and electrochemical performance of the battery.

[0044] In any embodiment, processing the raw materials specifically includes the following steps: crushing, shaping and classifying the raw materials to obtain a first precursor; granulating the first precursor to obtain a second precursor; and low-temperature carbonizing the mixture of the first precursor and the second precursor to obtain an intermediate product.

[0045] In any embodiment, the first precursor has a Dv50 particle size of 6.0 μm to 10.0 μm.

[0046] In any embodiment, the particle size distribution of the first precursor is (Dv90-Dv10) / Dv50 is 1.05-1.75.

[0047] In any embodiment, the tap density of the first precursor is 0.5 g / cm 3 ~0.7g / cm 3 .

[0048] In any embodiment, the second precursor has a Dv50 particle size of 11.0 μm to 15.0 μm.

[0049] The second precursor is obtained by granulating the first precursor, and therefore, the second precursor mainly forms secondary particles in the graphite negative electrode active material.

[0050] Controlling the particle size of the first precursor and the second precursor helps to regulate the particle size and particle size distribution of the graphite negative electrode active material, thereby improving the cycle stability of the battery. A third aspect of the present disclosure provides a negative electrode plate comprising the graphite negative electrode active material of any embodiment or the graphite negative electrode active material prepared by the preparation method of any embodiment.

[0051] A fourth aspect of the present disclosure provides a secondary battery comprising the negative electrode sheet according to the third aspect of the present disclosure.

[0052] A fifth aspect of the present disclosure provides an electric device including the secondary battery according to the fourth aspect of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] To more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following briefly introduces the drawings required for use in the embodiments of the present disclosure. Obviously, the drawings described below are only some embodiments of the present disclosure, and those skilled in the art can derive other drawings based on the drawings without inventive effort.

[0054] FIG1 is a schematic diagram of a cross-sectional image of a particle of a graphite negative electrode active material disclosed herein;

[0055] FIG2 is a schematic diagram of an embodiment of a secondary battery disclosed herein;

[0056] FIG3 is an exploded schematic diagram of an embodiment of a secondary battery disclosed herein;

[0057] FIG4 is a schematic diagram of an embodiment of a battery module of the present disclosure;

[0058] FIG5 is a schematic diagram of an embodiment of a battery pack of the present disclosure;

[0059] FIG6 is an exploded schematic diagram of the embodiment of the battery pack shown in FIG5 ;

[0060] FIG7 is a schematic diagram of an embodiment of an electric device including a secondary battery of the present disclosure as a power source;

[0061] FIG8 is a transmission electron microscope image of the graphite negative electrode active material prepared in Example 1;

[0062] FIG9 is a transmission electron microscope image of the graphite negative electrode active material prepared in Comparative Example 2.

[0063] In the accompanying drawings, which are not necessarily drawn to scale, reference numerals are as follows: 1 battery pack, 2 upper housing, 3 lower housing, 4 battery module, 5 secondary battery, 51 housing, 52 electrode assembly, 53 cover plate, 100 graphite negative electrode active material, 101 surface region, 102 internal region. DETAILED DESCRIPTION

[0064] Below, the embodiments of the graphite negative electrode active material and its preparation method, secondary battery and electric device disclosed in the present invention are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate 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.

[0065] " 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.

[0066] Unless otherwise specified, all embodiments and optional embodiments of the present disclosure can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure content of the present disclosure.

[0067] Unless otherwise specified, all technical features and optional technical features of the present disclosure can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure content of the present disclosure.

[0068] 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.

[0069] 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.

[0070] 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).

[0071] Unless otherwise specified, the terms used in the present disclosure have the common meanings that are generally understood by those skilled in the art.

[0072] Unless otherwise specified, the numerical values ​​of the parameters mentioned in the present disclosure can be measured using various test methods commonly used in the art, for example, they can be measured according to the test methods given in the present disclosure.

[0073] Unless otherwise specified, in the present disclosure, the term "active ions" refers to ions that can be intercalated and extracted back and forth between the positive electrode and the negative electrode of a secondary battery, including but not limited to lithium ions.

[0074] In the present disclosure, the terms "plurality" and "multiplicity" refer to two or more.

[0075] Negative electrode active materials are a crucial component of secondary batteries, critically impacting their capacity, energy density, cycle stability, and kinetic performance. The primary approach to improving battery kinetic performance is to increase the wettability between the negative electrode active material and the electrolyte. This inevitably leads to a corresponding increase in the degree of side reactions between the negative electrode active material and the electrolyte, increasing the loss of active lithium and reducing the battery's cycle stability. This means that improvements in secondary battery kinetic performance often come at the expense of cycle life.

[0076] Based on this, the present disclosure provides a graphite negative electrode active material, wherein the particle body of the graphite negative electrode active material includes an internal region and a surface region that at least partially surrounds the internal region, wherein the surface region refers to a region extending 30 nanometers (nm) from the surface of the particle body of the graphite negative electrode active material to the interior of the particle, and the surface region includes a disordered layer.

[0077] Figure 1 is a schematic diagram of a cross-sectional image of a particle of the graphite negative electrode active material 100 disclosed herein. As shown in Figure 1 , the region extending 30 nm inward from the surface of the particle of graphite negative electrode active material 100 is surface region 101, and the region within surface region 101 is interior region 102. Surface region 101 includes a disordered layer.

[0078] The carbon material in the disordered layer can be characterized using transmission electron microscopy (TEM). Using a focused ion beam (FIB) microscope, thin slices approximately 100 nm thick are cut from the center of the graphite anode active material particles. TEM analysis of the slices reveals a disordered layer with long-range disorder and short-range order in the surface region, including lattice fringes. The electron diffraction pattern in the disordered layer exhibits a halo-like pattern.

[0079] The disordered layer mainly includes amorphous carbon. The carbon atoms in the amorphous carbon structure have no regular arrangement, which makes the interaction between its molecules more complex, resulting in higher strength and hardness than the graphite crystals in the internal region. This reduces the probability of surface damage of the graphite particles due to friction between particles and between particles and the mixing tank during slurry preparation. The risk of particle cracking and exposure of new interfaces in the graphite negative electrode active material during the cold pressing of the electrode is reduced, allowing the graphite negative electrode active material to maintain higher particle integrity during the manufacturing process. Graphite negative electrode active materials with high particle integrity have fewer surface defects and a good interface with the electrolyte. They can effectively reduce side reactions between the negative electrode and the electrolyte, reduce the loss of active lithium, and are beneficial to improving battery storage stability and cycle stability. At the same time, the disordered layer on the graphite negative electrode active material also helps to improve the infiltration of the electrolyte into the negative electrode, thereby improving the battery kinetic performance.

[0080] Unlike the disordered layer coated on the surface of graphite negative electrode active materials in the prior art, the disordered layer of the graphite negative electrode active material provided in the embodiments of the present disclosure is located within the particle body of the graphite negative electrode active material. It is derived from the same raw material as the graphite negative electrode active material and is not prepared through post-processing. Therefore, compared with graphite negative electrode active materials with disordered layers obtained through surface coating treatment, this graphite negative electrode active material has better material consistency, resulting in a longer cycle life for the battery, achieving a balance between battery kinetic performance and cycle stability and storage stability. It is particularly suitable for energy storage batteries with extremely high requirements for cycle life and storage life.

[0081] In some embodiments, the disordered layer has a thickness of 1 nm to 20 nm. In some embodiments, the disordered layer has a thickness of 3 nm to 16 nm.

[0082] In the present disclosure, the thickness of the disordered layer can be tested by methods known in the art. As an example, it can be obtained by transmission electron microscopy (TEM) testing. A thin slice with a thickness of about 20nm to 50nm is cut from the middle of the graphite negative electrode active material particle body by a focused ion beam (FIB), and then the thin slice is subjected to TEM testing to obtain the original TEM test image. The original image obtained by the above TEM test is opened in the Digital Micrograph software, and the disordered layer is identified by diffraction stripes or lattice spacing, and its thickness is measured. Normally, the disordered layer has no diffraction stripes, and the lattice spacing is larger than that of the ordered layer.

[0083] In some embodiments, the thickness of the disordered layer is 1 nm, 4 nm, 5 nm, 8 nm, 10 nm, 12 nm, 15 nm, 16 nm, 20 nm, or any range therebetween.

[0084] The disordered layer with a thickness within the above range is beneficial to the embedding and deintercalation of active ions, thereby improving the kinetic performance of the battery; it will not cause an excessively high degree of side reaction between the graphite negative electrode active material and the electrolyte, thereby taking into account the improvement of the battery's cycle stability and kinetic performance.

[0085] In some embodiments, the coefficient of variation of the thickness of the disordered layer is less than or equal to 50%, where the coefficient of variation refers to the ratio of the standard deviation of the thickness of the disordered layer to the average of the thickness of the disordered layer.

[0086] In some embodiments, the coefficient of variation of the thickness of the disordered layer is 10%, 20%, 30%, 40%, 50%, or any range therebetween.

[0087] As used herein, the term "coefficient of variation" refers to the ratio of the standard deviation to the mean.

[0088] In the present disclosure, the coefficient of variation of the thickness of the disordered layer can be tested using methods known in the art. As an example, the coefficient of variation (cov) of the thickness of the disordered layer is calculated by the formula cov = σ / u × 100%, where σ represents the standard deviation of the thickness of the disordered layer, and u represents the average value of the thickness of the disordered layer, and the two are calculated by the following formulas respectively.

[0089] Among them, X i is the thickness of the disordered layer, n is the total number of particles counted. During the statistical process, at least 10 particles were taken for each sample, and at least five different sites were measured for each particle.

[0090] Different from the graphite negative electrode active material in the prior art in which the surface is coated with amorphous carbon through a post-processing process, the surface disordered layer of the graphite negative electrode active material in the embodiment of the present disclosure has higher uniformity and a low coefficient of variation of the thickness of the disordered layer, which is beneficial to improving the structural uniformity and electrochemical stability of the graphite negative electrode active material, and improving the storage stability and cycle stability of the secondary battery.

[0091] In some embodiments, the graphite negative electrode active material is D / I G is 0.05-0.10, where I D / I G is the ratio of the D peak intensity to the G peak intensity obtained from the Raman spectrum, I D The Raman spectrum is at 1350 ± 100 cm -1 (cm -1 ) at the D peak intensity, I G Indicates that the Raman spectrum is at 1580±100cm -1 The G peak intensity at .

[0092] In the present disclosure, the graphite negative electrode active material I D / I G Any known mode of Raman spectroscopy can be used for testing. As an example, referring to GB / T 40219-2021, an InVia Qontor (Reflex) Raman spectrometer is used for testing; a solid-state laser with a wavelength of 532 nm is used as the light source, 100 points are sampled in an area of ​​100 microns (μm) × 100 μm, and I is taken. D / I G The median I of graphite as anode active material D / I G , the median is the collected I arranged in order of size D / I G The middle number in the data.

[0093] In some embodiments, the graphite negative electrode active material is D / I G 0.05, 0.06, 0.07, 0.08, 0.09, 0.10 or any numerical range therebetween.

[0094] I of graphite negative electrode active material D / I G It can be used to characterize the surface disorder of graphite negative electrode active materials. Different from the active materials with disordered layers coated on the surface of the graphite particle body, the graphite negative electrode active materials provided by the embodiments of the present disclosure have a disordered layer on the surface and have a low surface disorder. The disordered layer in the active material with disordered layers coated on the surface of the graphite particle body is usually derived from the coated organic carbon, so that the disordered layer after carbonization has a high surface disorder; while the disordered layer structure in the surface region of the graphite negative electrode active material provided by the embodiments of the present disclosure and the other parts of the graphite negative electrode active material are derived from the same precursor, and the disordered layer has high uniformity and extremely thin thickness, so that it can have a low surface disorder. On the one hand, this enables the graphite negative electrode active material to take advantage of the disordered layer and improve the kinetic performance of the battery, without causing excessive side reactions due to the excessive disorder of the surface layer of the material. It can improve the kinetic performance of the battery while taking into account the cycle stability and storage stability of the battery.

[0095] In some embodiments, the interlayer spacing of the disordered layers of the graphite negative electrode active material is denoted as d1, and the interlayer spacing of the inner region of the graphite negative electrode active material is denoted as d2, and the graphite negative electrode active material satisfies d1>d2. In some embodiments, 0.3365nm≤d1≤0.3378nm. In some embodiments, 0.3358nm≤d2≤0.3364nm.

[0096] As used herein, the term "interlayer spacing" refers to the shortest distance between two adjacent carbon atoms in the same carbon layer in graphite.

[0097] In the present disclosure, the interlayer spacing between different regions of the graphite negative electrode active material can be measured using instruments and methods known in the art. For example, a high-resolution transmission electron microscope (HRTEM) can be used for measurement. The measurement instrument can be a Thermo Fisher Scientific Spectra S / TEM scanning transmission electron microscope.

[0098] In some embodiments, the interlayer spacing d1 of the disordered layers of the graphite negative electrode active material is 0.3365 nm, 0.3367 nm, 0.3369 nm, 0.3371 nm, 0.3372 nm, 0.3373 nm, 0.3375 nm, 0.3378 nm, or any range therebetween. In some embodiments, the interlayer spacing d2 of the inner region of the graphite negative electrode active material is 0.3358 nm, 0.3359 nm, 0.3361 nm, 0.3363 nm, 0.3364 nm, or any range therebetween.

[0099] The interlayer spacing of the disordered layer is higher than the interlayer spacing of the internal region of the graphite negative electrode active material, which can play the role of a lithium insertion buffer layer, improve the wettability of the electrolyte to the graphite negative electrode active material, and improve the fast charging performance of the battery.

[0100] In some embodiments, the graphite negative electrode active material includes both primary particles and secondary particles. In some embodiments, the secondary particles account for less than or equal to 50% of the total number of primary particles and secondary particles in the graphite negative electrode active material.

[0101] As used herein, the term "primary particles" refers to particles in a non-agglomerated state.

[0102] As used herein, the term "secondary particles" refers to particles in an agglomerated state formed by the aggregation of two or more primary particles.

[0103] Primary particles and secondary particles can be distinguished by observing the particle cross-section of the graphite negative electrode active material using a scanning electron microscope (SEM). In the present disclosure, the proportion of the number of secondary particles in the graphite negative electrode active material can be tested by methods known in the art. As an example, a cross-section polisher (such as the IB-09010CP argon ion cross-section polisher of Japan's JEOL company) can be used to prepare the cross-section of the negative electrode sheet; then, referring to JY / T010-1996, a scanning electron microscope (such as the Sigma 300 scanning electron microscope of Germany's ZEISS company) is used to scan the cross-section of the negative electrode sheet, and multiple test areas are randomly selected in the test sample. Images of the multiple test areas are obtained using a scanning electron microscope, and the number of graphite negative electrode active materials with secondary particle morphology in each image is counted as the ratio of the total number of graphite negative electrode active material particles. The average value of the multiple statistical results is the number proportion of secondary particles in the graphite negative electrode active material.

[0104] In some embodiments, based on the total number of primary particles and secondary particles in the graphite negative active material, the number of secondary particles accounts for 50%, 40%, 30%, 20%, 10% or any range therebetween.

[0105] Graphite anode active materials with a low proportion of secondary particles are beneficial for maintaining the particle integrity of the graphite anode active material during battery preparation, reducing the formation of new interfaces, reducing the consumption of active lithium during the cycle, and further improving the cycle stability of the secondary battery. At the same time, a certain number of secondary particles can reduce the expansion of the negative electrode while taking into account the kinetic performance of the secondary battery, thus ensuring that the battery cell has a kinetic window for the entire life cycle, and will not cause lithium plating due to uneven current distribution, which will lead to a sharp decline in battery capacity and a sharp deterioration in battery life, thereby comprehensively improving the battery's cycle stability.

[0106] In some embodiments, the particle size distribution of the graphite negative electrode active material (Dv90-Dv10) / Dv50 is 1.0-1.5. In some embodiments, the particle size distribution of the graphite negative electrode active material (Dv90-Dv10) / Dv50 is 1.1-1.45.

[0107] In this article, the terms "Dv90" and "Dv10" refer to the particle sizes corresponding to when the cumulative volume distribution number of particles reaches 90% and 10% in the particle size distribution curve, respectively.

[0108] In the present disclosure, the volume distribution particle size Dv90 and Dv10 of the graphite negative electrode active material can be measured using methods known in the art. As an example, referring to GB / T 19077-2016, they can be measured using a laser particle size analyzer. The testing instrument can be a Mastersizer 3000 laser particle size analyzer manufactured by Malvern Instruments Ltd., UK.

[0109] In some embodiments, the particle size distribution of the graphite negative active material (Dv90-Dv10) / Dv50 is 1.0, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, or any range therebetween.

[0110] Controlling the particle size distribution of the graphite negative electrode active material within the above range is beneficial to improving the tight packing of the graphite negative electrode active material and improving the compaction density of the negative electrode sheet. In other words, the cold pressing pressure required for the negative electrode sheet to achieve the same compaction density is smaller, thereby reducing the probability of cracking of the graphite negative electrode active material during the cold pressing process, and further improving the integrity of the graphite negative electrode active material during the processing process; and the small stress inside the graphite negative electrode active material particles is beneficial to maintaining the long-period pore structure of the electrode sheet during the cycle process, and can maintain the original pore structure of the electrode sheet during the cycle process, so that the lithium ion lithium insertion path remains unobstructed, while reducing the re-filming of the graphite negative electrode active material during the charging process, improving the kinetic performance, cycle life and storage stability. Furthermore, the particle size distribution within the above range can also improve the uniformity of lithium insertion between the graphite negative electrode active material particles, reduce polarization, avoid lithium precipitation caused by uneven current density, and help achieve long-term cycle stability. In addition, the particle size distribution within the above range can also help improve the processing performance of the electrode, and will not affect the uniformity of slurry stirring due to excessive small particles in the graphite negative electrode active material, which is beneficial to improving the uniformity and stability of the electrode quality and helping to achieve long-cycle stability.

[0111] When the particle size distribution (Dv90-Dv10) / Dv50 of the graphite negative electrode active material is 1.1-1.45, the preparation of the graphite negative electrode active material has a higher yield, which is conducive to cost reduction; at the same time, the cycle stability and storage stability of the graphite negative electrode active material are further improved.

[0112] In some embodiments, the volume distribution particle size Dv50 of the graphite negative electrode active material is denoted as A, and the volume distribution particle size Dv50 of the graphite negative electrode active material after cold pressing under a pressure of 20,000 Newtons (N) is denoted as B. Then, the graphite negative electrode active material satisfies: B / A ≥ 85%. In some embodiments, the graphite negative electrode active material satisfies: B / A is 85%-98%.

[0113] As used herein, the term "volume distribution particle size Dv50" refers to the particle size corresponding to when the cumulative volume distribution number of particles reaches 50% in the particle size distribution curve.

[0114] In the present disclosure, the volume distribution particle size (Dv50) of the active material can be measured using methods known in the art. For example, it can be measured using a laser particle size analyzer, referring to GB / T 19077-2016. The testing instrument can be a Mastersizer 3000 laser particle size analyzer manufactured by Malvern Instruments Ltd., UK. The Dv50 ratio of the powder before and after cold pressing can be calculated by comparing the Dv50 of the powder to the Dv50 measured by scraping the electrode after cold pressing.

[0115] In some embodiments, A / B is 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 100% or any range therebetween.

[0116] The graphite negative electrode active material still maintains high particle integrity after cold pressing, which helps to improve the cycle stability.

[0117] In some embodiments, the specific surface area of ​​the graphite negative electrode active material is 1.2 m 2 / g(m 2 / g)-1.9m 2 In some embodiments, the specific surface area of ​​the graphite negative electrode active material is 1.3 m 2 / g-1.8m 2 / g.

[0118] In the present disclosure, the specific surface area of ​​the graphite negative electrode active material can be measured using methods known in the art. As an example, the specific surface area of ​​the graphite negative electrode active material 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 testing instrument can be a Tri-Star 3020 specific surface area pore size analyzer available from Micromeritics, Inc., USA.

[0119] In some embodiments, the specific surface area of ​​the graphite negative electrode active material is 1.2 m 2 / g, 1.3m 2 / g, 1.4m 2 / g, 1.5m 2 / g, 1.6m 2 / g, 1.7m 2 / g, 1.8m 2 / g, 1.9m 2 / g or any range of values ​​between them.

[0120] The low specific surface area of ​​the graphite negative electrode active material helps to further reduce the degree of side reactions of the graphite negative electrode active material and improve the cycle life of the secondary battery.

[0121] In some embodiments, the volume distribution particle size Dv50 of the graphite negative electrode active material is 7.0 μm to 14.0 μm. In some embodiments, the volume distribution particle size Dv50 of the graphite negative electrode active material is 8.0 μm to 12.0 μm.

[0122] In some embodiments, the volume distribution particle size Dv50 of the graphite negative electrode active material is 7.0 μm, 8.0 μm, 9.0 μm, 10.0 μm, 11.0 μm, 12.0 μm, or any range therebetween.

[0123] In some embodiments, the powder compaction density of the graphite negative electrode active material under a pressure of 49000N is less than or equal to 1.85 g / cm 3 (g / cm 3 In some embodiments, the powder compaction density of the graphite negative electrode active material under a pressure of 49000N is 1.75g / cm 3 -1.85g / cm 3 .

[0124] In this article, the term "powder compaction density" refers to the mass of powder particles per unit volume under a certain pressure.

[0125] In the present disclosure, the powder compaction density of the graphite negative electrode active material under a pressure of 49000N can be tested by methods known in the art. As an example, referring to GB / T 24533-2009, 1g of graphite negative electrode active material powder is weighed and added to a bottom area of ​​1.327 cm 2 (cm 2 ) in a mold, pressurize to 4900 kilograms (kg) (equivalent to 49000N), maintain the pressure for 30 seconds (s), then release the pressure and maintain it for 10 seconds, and measure the powder compaction density of the graphite negative electrode active material under a pressure of 49000N by an electronic pressure testing machine (such as UTM7305 electronic pressure testing machine).

[0126] In some embodiments, the powder compaction density of the graphite negative electrode active material under a pressure of 49000N is 1.69g / cm 3 , 1.72g / cm 3 , 1.75g / cm 3 , 1.78g / cm 3 , 1.82g / cm 3 , 1.85g / cm 3 or any range of values ​​between them.

[0127] Graphite negative electrode active materials with a powder compaction density within the above range are easy to maintain high particle integrity during the cold pressing process, which helps to improve the cycle life of the secondary battery.

[0128] In some embodiments, the graphite negative electrode active material has a gram capacity of 345 milliampere hours per gram (mAh / g) to 355 mAh / g. In some embodiments, the graphite negative electrode active material has a gram capacity of 347 mAh / g to 353 mAh / g.

[0129] As used herein, the term "gram capacity" refers to the ratio of the amount of electricity that an active material can release to the mass of the active material.

[0130] In the present disclosure, the gram capacity of the graphite negative electrode active material can be tested using methods known in the art. As an example, the graphite negative electrode active material is thoroughly stirred and mixed with the conductive agent carbon black and polyvinylidene fluoride (PVDF) in a mass ratio of 91.6:1.8:6.6 in an appropriate amount of solvent NMP to form a uniform negative electrode slurry; the negative electrode slurry is evenly coated on the surface of the negative electrode current collector copper foil and dried and cold pressed; then, a metal lithium sheet is used as the counter electrode and a polypropylene (PP) film is used as the separator, and an electrolyte is injected. The electrolyte formula 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 obtain an organic solvent, and then LiPF6 is dissolved in the above organic solvent to prepare an electrolyte with a concentration of 1.0 mol / L. CR2430 button cells are assembled in an argon-protected glove box. At 25 degrees Celsius (°C), the prepared button cell was first discharged at a constant current of 0.05 coulombs (C) to 0.005 volts (V). It was then discharged at a constant current of 10 microamperes (μA) to 0.005 V and allowed to rest for 5 minutes. The first-cycle discharge capacity of the button cell was recorded. The button cell was then charged at a constant current of 0.1 C to 2.0 V, and the charge capacity of the button cell was recorded. The ratio of the charge capacity of the button cell to the mass of the graphite negative electrode active material sample is the gram capacity of the graphite negative electrode active material.

[0131] In some embodiments, the gram capacity of the graphite negative electrode active material is 345 mAh / g, 346 mAh / g, 347 mAh / g, 348 mAh / g, 349 mAh / g, 350 mAh / g, 351 mAh / g, 352 mAh / g, 353 mAh / g, 354 mAh / g, 355 mAh / g, or any range therebetween.

[0132] The graphite negative electrode active material with a gram capacity within the above range will not undergo significant lattice expansion during the charge and discharge process due to the high graphitization of the graphite negative electrode active material; nor will it be difficult to compact due to the low graphitization of the graphite negative electrode active material. In order to achieve the same electrode compaction density, a higher cold pressing pressure is required, which will cause cracks during the cold pressing process and generate new interfaces during the cycle process to consume excessive active lithium, thereby comprehensively improving the cycle life of the secondary battery.

[0133] A second aspect of the present disclosure provides a method for preparing a graphite negative electrode active material, comprising the following steps: providing raw materials; processing the raw materials to obtain an intermediate product; graphitizing the intermediate product to obtain a graphitized product; screening the graphitized product to obtain a graphite negative electrode active material; the particle body of the graphite negative electrode active material includes an internal region and a surface region that at least partially surrounds the internal region, the surface region refers to a region extending 30 nm from the surface of the particle body of the graphite negative electrode active material to the interior of the particle, and the surface region includes a disordered layer.

[0134] In this article, the term "graphitization" refers to the heat treatment process of carbon materials. Under high temperature, the carbon material transforms from a two-dimensional carbon network structure to a three-dimensional ordered structure through "microcrystal growth".

[0135] In some embodiments, the maximum power of the graphitization process is 70% to 90% of the rated power of the graphitization process equipment.

[0136] In some embodiments, the maximum power of the graphitization treatment is 70%, 75%, 80%, 85%, 90% or any numerical range therebetween of the rated power of the graphitization treatment equipment. It is understood that the graphitization treatment device refers to any device capable of performing graphitization treatment, including but not limited to Acheson furnace, box furnace, internal string furnace, continuous graphitization, electric calcining furnace, medium frequency furnace, tubular furnace and other devices. Among them, the rated power of graphitization treatment equipment produced by different manufacturers may be different, and can be selected according to actual conditions. The maximum power of the graphitization treatment adopted in the present disclosure needs to be lower than the rated power of the graphitization treatment device to achieve uniformity of the thermal field during the graphitization treatment process.

[0137] In some embodiments, the graphitization treatment equipment is an internal string furnace, and the rated power of the internal string furnace is 25,000 watts (W) to 32,000W.

[0138] In some embodiments, the graphitization treatment equipment is an Acheson furnace, and the rated power of the Acheson furnace is 28,000W-30,000W.

[0139] In some embodiments, the graphitization process is performed at maximum power for a period of 10 hours (h) to 50 hours.

[0140] In some embodiments, the graphitization treatment is performed at maximum power for 10 h, 13 h, 16 h, 19 h, 22 h, 25 h, 28 h, 31 h, 33 h, 36 h, 39 h, 42 h, 45 h, 48 h, 50 h, or any range therebetween.

[0141] In some embodiments, the graphitization treatment equipment is an internal series furnace, and the graphitization treatment time at maximum power is 10 hours to 30 hours.

[0142] In some embodiments, the graphitization treatment equipment is an Acheson furnace, and the graphitization treatment time at maximum power is 30 hours to 50 hours.

[0143] In some embodiments, the temperature of the graphitization treatment is 2600°C to 3000°C.

[0144] In some embodiments, the temperature of the graphitization treatment is 2600° C., 2700° C., 2800° C., 2900° C., 3000° C., or any range therebetween.

[0145] The appropriate graphitization treatment temperature and the appropriate graphitization treatment time are not likely to cause excessive rearrangement of the precursor, resulting in a high specific surface area of ​​the graphite negative electrode active material after graphitization and deterioration of high-temperature performance; it can also effectively improve the graphitization degree of the graphite negative electrode active material, thereby facilitating the simultaneous improvement of the high-temperature storage and cycle life of the secondary battery.

[0146] In some embodiments, the feedstock comprises at least one of petroleum coke, needle coke, and pitch coke. In some embodiments, the feedstock is needle coke.

[0147] In this article, the term "petroleum coke" refers to the coke formed by high-temperature carbonization of petroleum residue or petroleum asphalt.

[0148] 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.

[0149] As used herein, the term "pitch coke" refers to the solid material produced by carbonizing coal tar pitch at high temperatures.

[0150] Needle coke has a range of advantages, including low thermal expansion coefficient, low porosity, low sulfur, low ash, low metal content, high conductivity, and easy graphitization. The graphite anode active material after graphitization can achieve a high ultimate compaction density and a low cyclic expansion rate.

[0151] In some embodiments, based on the total volume of the raw material structure, the volume proportion of the fiber-type structure in the raw material is greater than or equal to 55%. In some embodiments, the volume proportion of the fiber-type structure in the raw material is 58%-70%.

[0152] In this article, "fibrous structure" is also called streamlined structure, which refers to the structure of the raw material with obvious fibrous texture observed under a microscope.

[0153] Generally, the microstructure of the raw material can be divided into mosaic, regional, and fibrous types based on its morphological characteristics and the size of the isochromatic zones under a polarizing microscope. Generally, isochromatic zones with a size less than 30 μm are classified as mosaic, those with a size greater than 30 μm are classified as regional, and anisotropic banded isochromatic zones are classified as fibrous.

[0154] In the present disclosure, the volume percentage of the fiber structure in the raw material can be tested using methods known in the art. As an example, according to the provisions of GB 1997-89, the raw material is crushed to 1 mm and mixed, and 40 grams (g) to 50 grams are separated. A square hole sieve is used to take 4g to 5g of a 0.07mm to 1.0mm grade sample for film making; according to the provisions of MT 116.1-86, powder coke and block coke optical films are prepared. The diameter of the powder coke optical film shall not be less than 22mm, and the volume occupied by the cement shall be less than 1 / 3; the sample is placed on a slide with clay, flattened, and then placed on the stage for focusing. After calibrating the microscope, the polarizer and analyzer are adjusted to make them orthogonal. Insert a sapphire 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 0.3mm to 0.5mm and a line spacing of 0.5mm to 0.8mm. Starting from one end of the sample, determine the microstructure category at the intersection of the crosshairs, and divide the number of effective measurement points of the fiber-type optical structure by the total number of test points as the volume proportion of the fiber-type structure in the raw material.

[0155] In some embodiments, based on the total volume of the raw material structure, the volume proportion of the fibrous structure in the raw material is 55%, 58%, 60%, 65%, 70% or any range therebetween.

[0156] Raw materials with a high volume fraction of fiber-type structures are beneficial for increasing the compaction density and specific capacity of graphite negative electrode active materials, allowing the graphite negative electrode active materials to retain a high degree of integrity during the compaction process, resulting in batteries with both a long cycle life and good energy density. However, an excessively high proportion of fiber-type structures will increase the cost and expansion rate of the graphite negative electrode active materials, and deteriorate the kinetic performance. Raw materials with a volume fraction of fiber-type structures within the above range have both lower costs and good specific capacity of the graphite, allowing the battery cell to have a full life cycle kinetic window, thereby comprehensively improving the long-term cycle life and electrochemical performance of the battery.

[0157] In some embodiments, the maximum gram capacity that can be achieved by the raw material is greater than the gram capacity of the graphite negative electrode active material.

[0158] By using high-grade raw materials and controlling the degree of graphitization so that the maximum gram capacity that the raw materials can achieve is not fully utilized, a graphite negative electrode active material including a disordered layer in the surface area is obtained, achieving a balance between battery cycle life and kinetic performance.

[0159] In some embodiments, the processing of raw materials specifically includes: crushing, shaping, and grading the raw materials to obtain a first precursor; granulating the first precursor to obtain a second precursor; and low-temperature carbonizing a mixture of the first precursor and the second precursor to obtain the intermediate product.

[0160] Crushing is the process of reducing the particle size of raw materials. The raw materials can be crushed by any mechanical device such as crusher, mechanical mill, etc.

[0161] Shaping is the process of adjusting the curvature and particle size of the raw materials.

[0162] Classification is the process of adjusting the particle size distribution of the raw materials to obtain a first precursor that meets the particle size requirements. The particle size and particle size distribution of the first precursor can be controlled by adjusting the classification frequency and air flow rate.

[0163] It can be understood that low-temperature carbonization of the first precursor and the second precursor to obtain the intermediate product includes low-temperature carbonization of a mixture of the first precursor and the second precursor to obtain the intermediate product; it also includes low-temperature carbonization of the first precursor and the second precursor separately to obtain the first intermediate product and the second intermediate product respectively.

[0164] In some embodiments, the Dv50 particle size of the first precursor is 6.0 μm to 10.0 μm.

[0165] In some embodiments, the Dv50 particle size of the first precursor is 6.0 μm, 7.0 μm, 8.0 μm, 9.0 μm, 10.0 μm, or any range therebetween.

[0166] In some embodiments, the particle size distribution of the first precursor (Dv90-Dv10) / Dv50 is 1.05-1.75.

[0167] In some embodiments, the particle size distribution of the first precursor (Dv90-Dv10) / Dv50 is 1.05, 1.15, 1.25, 1.35, 1.45, 1.55, 1.65, 1.75, or any range therebetween.

[0168] In some embodiments, the tap density of the first precursor is 0.5 g / cm 3 ~0.7g / cm 3 .

[0169] As used herein, the term "tap density" refers to the mass per unit volume of powder in a container measured after being tapped under specified conditions.

[0170] In the present disclosure, the tap density of the first precursor can be tested using methods known in the art. For example, it can be measured using a powder tap density tester in accordance with GB / T 5162-2006. The test instrument can be a Dandong Better BT-301, with the following test parameters: vibration frequency of 250±15 times / minute, amplitude of 3±0.2 mm, number of vibrations of 5000 times, and a 25 milliliter (mL) graduated cylinder.

[0171] In some embodiments, the tap density of the first precursor is 0.5 g / cm 3 , 0.55g / cm 3 , 0.6g / cm 3 , 0.65g / cm 3 , 0.7g / cm 3 or any range of values ​​between them.

[0172] In some embodiments, the Dv50 particle size of the second precursor is 11.0 μm to 15.0 μm.

[0173] In some embodiments, the Dv50 particle size of the second precursor is 11.0 μm, 12.0 μm, 13.0 μm, 14.0 μm, 15.0 μm, or any range therebetween.

[0174] The second precursor is obtained by granulating the first precursor, and therefore, the second precursor mainly forms secondary particles in the graphite negative electrode active material.

[0175] Controlling the particle sizes of the first precursor and the second precursor helps to regulate the particle size and particle size distribution of the graphite negative electrode active material and improve the cycle stability of the battery.

[0176] In some embodiments, the crushing, shaping, and grading of the raw materials to obtain the first precursor includes: crushing, shaping, and grading the raw materials to obtain secondary raw materials; removing fine powder accounting for 10%-35% of the total mass of the secondary raw materials to obtain the first precursor; the Dv50 of the fine powder is 3μm-7μm and Dv99 is less than or equal to 30μm, and the particle size distribution of the fine powder (Dv90-Dv10) / Dv50 is greater than 1.6.

[0177] In some embodiments, the temperature of low-temperature carbonization is 900° C.-1300° C., and the time of low-temperature carbonization is 24 hours-240 hours.

[0178] In some embodiments, the temperature of the low temperature carbonization is 900° C., 1000° C., 1100° C., 1200° C., 1300° C., or any range therebetween.

[0179] In some embodiments, the low-temperature carbonization time is 24 h, 50 h, 75 h, 100 h, 150 h, 200 h, 240 h, or any range therebetween.

[0180] [Negative electrode]

[0181] In some embodiments, the negative electrode plate includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector. For example, the negative electrode current collector has two surfaces that are opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposing surfaces of the negative electrode current collector.

[0182] In some embodiments, the negative electrode film layer includes the graphite negative electrode active material of the first aspect of the embodiment of the present disclosure or the graphite negative electrode active material prepared by the method described in the second aspect of the embodiment of the present disclosure. This enables the secondary battery to have high initial coulombic efficiency, high energy density, and good cycle performance.

[0183] 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.

[0184] In some embodiments, the negative electrode film layer further includes a negative electrode conductive agent. The present disclosure does not particularly limit the type of the negative electrode conductive agent. As an example, the negative electrode conductive agent may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0185] In some embodiments, the negative electrode film layer further includes a negative electrode binder. The present disclosure does not particularly limit the type of the negative electrode binder. As an example, the negative electrode binder may include one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0186] In some embodiments, the negative electrode film layer further comprises other additives, for example, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, and the like.

[0187] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. As an example, the polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS) and polyethylene (PE).

[0188] In some embodiments, the negative electrode film layer is typically formed by coating a negative electrode slurry onto a negative electrode current collector, drying, and cold pressing. The negative electrode slurry is typically formed by dispersing a negative electrode active material, an optional conductive agent, an optional binder, and other optional additives in a solvent and stirring until uniformly mixed. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP) or deionized water.

[0189] The negative electrode plate does not exclude other additional functional layers in addition to the negative electrode film layer. For example, in some embodiments, the negative electrode plate described in the present disclosure further includes a conductive primer layer (e.g., composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector; in some embodiments, the negative electrode plate described in the present disclosure further includes a protective layer covering the surface of the negative electrode film layer.

[0190] [Positive electrode]

[0191] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector. For example, the positive electrode current collector has two surfaces that are opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposing surfaces of the positive electrode current collector.

[0192] The positive electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0193] In some embodiments, the positive electrode film layer generally comprises a positive electrode active material, an optional binder and an optional conductive agent. The positive electrode film layer is generally formed by coating a positive electrode slurry on the positive electrode current collector, drying and cold pressing. The positive electrode slurry is generally formed by dispersing a positive electrode active material, an optional conductive agent, an optional binder and any other components in a solvent and stirring evenly. The solvent may be N-methylpyrrolidone (NMP), but is not limited thereto. As an example, the binder for the positive electrode film layer may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin. As an example, the conductive agent for the positive electrode film layer includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0194] The positive electrode active material may be a positive electrode active material for a secondary battery known in the art.

[0195] When the secondary battery of the present disclosure is a lithium-ion battery, the positive electrode active material may include, but is not limited to, one or more of a lithium-containing transition metal oxide, a lithium-containing phosphate, and their respective modified compounds. Examples of the lithium transition metal oxide may include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds.

[0196] In some embodiments, the positive electrode active material includes a lithium-containing phosphate. Examples of the lithium-containing phosphate may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, a composite material of lithium iron manganese phosphate and carbon, and modified compounds thereof.

[0197] In the present disclosure, the modified compounds of the above-mentioned positive electrode active materials may be the ones subjected to doping modification and / or surface coating modification on the positive electrode active materials.

[0198] [Electrolytes]

[0199] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0200] The type of the electrolyte salt is not particularly limited and can be selected according to actual needs.

[0201] When the secondary battery of the present disclosure is a lithium ion battery, as an example, the electrolyte salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobisoxalatophosphate (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0202] The type of the solvent is not specifically limited and can be selected according to actual needs. In some embodiments, for example, the solvent may include ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS) and diethyl sulfone (ESE). One or more.

[0203] In some embodiments, the electrolyte further includes additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, or additives capable of improving certain properties of the secondary battery, such as additives that improve the overcharge performance of the secondary battery, additives that improve the high-temperature performance of the secondary battery, and additives that improve the low-temperature power performance of the secondary battery.

[0204] [Isolation film]

[0205] The present disclosure has no particular limitation on the type of the isolation membrane, and any known isolation membrane with a porous structure having good chemical stability and mechanical stability can be selected.

[0206] In some embodiments, the material of the isolation membrane may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The isolation membrane may be a single-layer film or a multi-layer composite film. When the isolation membrane is a multi-layer composite film, the materials of each layer may be the same or different.

[0207] In some embodiments, the positive electrode sheet, the separator, and the negative electrode sheet can be formed into an electrode assembly through a winding process or a lamination process.

[0208] secondary batteries

[0209] A fourth aspect of the embodiments of the present disclosure provides a secondary battery.

[0210] The present disclosure has no particular restrictions on the types of secondary batteries. For example, the secondary battery can be a lithium-ion battery, etc. In general, a secondary battery includes a positive electrode plate, a negative electrode plate, and an electrolyte, etc. During the charge and discharge process of the secondary battery, active ions are embedded and extracted back and forth between the positive electrode plate and the negative electrode plate, and the electrolyte plays a role in conducting active ions between the positive electrode plate and the negative electrode plate. The present disclosure has no particular restrictions on the type of the electrolyte, and it can be selected according to actual needs. For example, the electrolyte can be selected from at least one of a solid electrolyte and a liquid electrolyte (i.e., an electrolyte). Secondary batteries using electrolytes and some secondary batteries using solid electrolytes can also include an isolation membrane, which is arranged between the positive electrode plate and the negative electrode plate to play an isolation role.

[0211] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0212] In some embodiments, the outer packaging can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0213] The present disclosure has no particular limitation on the shape of the secondary battery, which can be cylindrical, square, or any other shape. FIG2 shows a secondary battery 5 with a square structure as an example.

[0214] In some embodiments, as shown in FIG3 , 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 is used to cover the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation film 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 impregnated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, which can be adjusted according to demand.

[0215] The preparation method of the secondary battery disclosed herein is well known. In some embodiments, a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte can be assembled to form a secondary battery. As an example, the positive electrode sheet, separator, and negative electrode sheet can be wound or laminated to form an electrode assembly. The electrode assembly is then placed in an outer packaging, dried, and then injected with electrolyte. The secondary battery is then vacuum packaged, allowed to stand, formed, and shaped to obtain the secondary battery.

[0216] In some embodiments of the present disclosure, the secondary batteries according to the present disclosure may be assembled into a battery module. The battery module may contain multiple secondary batteries, and the specific number may be adjusted according to the application and capacity of the battery module.

[0217] Figure 4 is a schematic diagram of an exemplary battery module 4. As shown in Figure 4 , 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 using fasteners.

[0218] In some embodiments, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 may be received in the receiving space.

[0219] In some embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0220] Figures 5 and 6 are schematic diagrams of an exemplary battery pack 1. As shown in Figures 5 and 6, 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 covers the lower case 3 and forms an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 may be arranged in any manner within the battery box.

[0221] Electrical devices

[0222] The present disclosure also provides an electric device, which includes at least one of the secondary battery, battery module, or battery pack of 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 can be, but is not limited to, a mobile device (such as a mobile phone, a tablet computer, a laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship, a satellite, an energy storage system, etc.

[0223] The electrical device may select a secondary battery, a battery module or a battery pack according to its usage requirements.

[0224] Figure 7 is a schematic diagram of an exemplary 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 this device, a battery pack or battery module may be used.

[0225] As another example, the electric device may be a mobile phone, a tablet computer, a laptop computer, etc. Such an electric device is usually required to be lightweight and thin, and may use a secondary battery as a power source.

[0226] Example

[0227] The following examples describe the present disclosure in more detail. These examples are intended to be illustrative only, as various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing, and all instruments used in the examples are commercially available.

[0228] Preparation method

[0229] Example 1

[0230] (1) Preparation of graphite negative electrode active materials

[0231] The needle coke with a fiber structure of 62.3% was crushed; the crushed material was shaped to remove fine powder to obtain the first precursor. The mass of the removed fine powder accounted for 21% of the total mass of the crushed material. The Dv50 of the fine powder was 3-7μm and Dv99 was less than or equal to 30μm. The particle size distribution of the fine powder (Dv90-Dv10) / Dv50 was greater than 1.6. Among them, the Dv50 particle size of the first precursor was 9.2μm, the particle size distribution (Dv90-Dv10) / Dv50 was 1.37, and the tap density of the first precursor was 0.67g / cm 3 .

[0232] The first precursor is granulated and shaped in a reactor to obtain a second precursor with a particle size Dv50 of 14.3 μm;

[0233] The first precursor and the second precursor were placed in a kiln for carbonization at a temperature of 1100°C and a high temperature zone time of 24 hours to obtain a first intermediate product and a second intermediate product. The tap density of the first intermediate product was 0.99 g / cm 3 The tap density of the second intermediate product is 0.93g / cm 3 ;

[0234] The first intermediate product and the second intermediate product are respectively graphitized in an inner series furnace at a temperature of 2800°C. The graphitization treatment device is an inner series furnace with a rated power of 28000W. The maximum power of the graphitization treatment is 22400W, the maximum power / rated power = 80%, and the time for maintaining the maximum power is 24 hours to obtain primary particles and secondary particles respectively.

[0235] The primary particles and secondary particles are evenly mixed in a mass ratio of 1:1, and the final graphite negative electrode active material is obtained after sieving.

[0236] The thickness of the disordered layer of the graphite negative electrode active material is 11.2 nm, and the coefficient of variation of the disordered layer thickness is 34.1%. D / I G The interlayer spacing d1 of the disordered layer is 0.3368 nm, the interlayer spacing d2 of the inner region is 0.3361 nm, the particle size distribution (Dv90-Dv10) / Dv50 is 1.28, the B / A value is 93.4%, and the specific surface area is 1.65 m 2 / g, the volume distribution particle size Dv50 is 10.2μm, and the powder compaction density under a pressure of 49000N is 1.81g / cm 3 , the gram capacity is 350.8mAh / g.

[0237] (2) Preparation of negative electrode sheet

[0238] The graphite negative electrode active material prepared above, the conductive agent Super P, the thickener sodium carboxymethyl cellulose, and the binder styrene-butadiene rubber (SBR) were mixed in a dry material mass ratio of 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, and the negative electrode sheets were obtained after drying, cold pressing, and slitting. The compacted density of the negative electrode film layer was 1.60 g / cm 3 , with a surface density of 9.2 mg / cm 2 .

[0239] (3) Preparation of positive electrode sheet

[0240] The positive electrode active material lithium iron phosphate (LFP), the conductive agent Super P, and the binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 97:1:2, and the solvent N-methylpyrrolidone (NMP) was added. The mixture was stirred in 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 compacted density of the positive electrode film layer is 2.50g / cm 3 , with a surface density of 19.7 mg / cm 2 .

[0241] (4) Preparation of electrolyte

[0242] 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.

[0243] (5) Preparation of isolation membrane

[0244] Polypropylene film is used as the isolation film.

[0245] (6) Preparation of lithium-ion batteries

[0246] 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 packaging shell, dried, and then injected with electrolyte, and after vacuum packaging, standing, forming, shaping and other processes, a lithium-ion battery is obtained.

[0247] The preparation method of Example 2-3 is basically the same as that of Example 1, except that the ton consumption during the graphitization treatment is kept unchanged, and the ratio of maximum power to rated power and the duration at maximum power are adjusted accordingly, as shown in Table 1.

[0248] The preparation methods of Examples 4-5 are basically the same as those of Example 1, except that the volume ratio of the raw material fiber structure is adjusted, and the raw materials are directly purchased, as shown in Table 1.

[0249] The preparation methods of Examples 6-8 are basically the same as those of Example 1, except that the ratio of fine powder removed from the raw materials is adjusted, as shown in Table 1.

[0250] Table 1

[0251] The preparation method of Comparative Example 1 is basically the same as that of Example 1, except that the maximum power is the rated power of the equipment and the time at the maximum power is 35 hours, and the surface area of ​​the prepared graphite negative electrode active material body particles has no disordered layer.

[0252] The specific preparation method of Comparative Example 2 is as follows:

[0253] The graphite negative electrode active material obtained in Comparative Example 1 was mixed with the carbonaceous precursor pitch in a mixer at a mass ratio of 100:3 for 2 hours. The mixture was then placed in a high-temperature furnace for heat treatment in a nitrogen atmosphere. After the reaction, the mixture was cooled and sieved to obtain a carbon-coated negative electrode active material. The mixer speed was 200 r / min, the high-temperature furnace heating rate was 5°C / min, and the temperature was raised to 1100°C and then heat treated at this constant temperature for 2 hours.

[0254] In Comparative Example 2, the coating layer of graphite is not located in the surface region of the particle body, but is coated on the surface of the graphite particle body. The coating layer thickness is 12.1 nm, and the coefficient of variation of the coating layer thickness is 64.3%.

[0255] Battery performance test

[0256] (1) Maximum charge rate test of secondary batteries

[0257] At 25°C, charge the secondary battery at a constant current of x C to a voltage of 3.65V. Then, charge it at a constant voltage of 3.65V until the current is <0.05C, and discharge it at 1C to a voltage of 2.5V. Repeat this 10 times. Then, charge the battery at a constant current of x C to a voltage of 3.65V. Then, remove the negative electrode and observe the lithium deposition on the surface of the negative electrode. If no lithium deposition occurs on the negative electrode surface, increase the charge rate x C by 0.1C and test again until lithium deposition occurs on the negative electrode surface. Stop testing. The charge rate at this point is (x - 0.1) C, which is the maximum charge rate of the battery.

[0258] (2) Cycle performance test of secondary batteries

[0259] 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-discharge cycle, and the discharge capacity (C0) of the first cycle was recorded. This charge and discharge cycle was repeated until the battery capacity decayed to 80% of the initial capacity (C0). The test was then stopped, and the number of cycles tested was recorded.

[0260] (3) 90-day storage performance test of secondary batteries

[0261] In an environment of 25°C, the batteries of the above-mentioned embodiments and comparative examples are charged at a constant current of 1C to a voltage of 3.65V, and then charged at a constant voltage of 3.65V to a current ≤ 0.05C. The batteries are then discharged at a constant current of 1C to a voltage of 2.5V. This is a charge and discharge process, and the discharge capacity C1 of the first cycle is recorded. The fully charged battery cells are then placed in an environment of 60°C for different periods of time. Every 30 days, they are taken out and tested for the remaining capacity at 25°C. This is a storage cycle, and the discharge capacity this time is the discharge capacity after the first storage. Subsequently, the first storage test process is repeated, and the discharge capacity value during the storage process is recorded. It is divided by the discharge capacity C1 of the first cycle as the cycle capacity retention rate of the battery after 90 days.

[0262] result

[0263] As can be seen from Table 2, the graphite negative electrode active material provided by the embodiments of the present disclosure includes a disordered layer in the surface region of the particle body, so that the secondary battery has good kinetic performance, cycle life and storage stability.

[0264] Table 2

[0265] As can be seen from Table 3, disordered layers with a thickness of 3nm-20nm can effectively take into account the battery's dynamic performance, cycle life and storage stability.

[0266] Table 3

[0267] As can be seen from Table 4, when the particle size distribution (Dv90-Dv10) / Dv50 of the graphite negative electrode active material is 1.0-1.5, the secondary battery has good kinetic performance, cycle life and storage stability.

[0268] Table 4

[0269] Figure 8 is a transmission electron micrograph of the graphite negative electrode active material prepared in Example 1. Figure 9 is a transmission electron micrograph of the graphite negative electrode active material prepared in Comparative Example 2. A comparison of Figures 8 and 9 shows that the graphite negative electrode active material provided by the embodiments of the present disclosure has a thin and uniform disordered layer thickness and a low coefficient of variation in disordered layer thickness.

[0270] It should be noted that the present disclosure is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and within the scope of the technical solution of the present disclosure, embodiments having substantially the same structure as the technical concept and exerting the same effects are all included in the technical scope of the present disclosure. In addition, within the scope of the present disclosure, various modifications that can be imagined by those skilled in the art to the embodiments, and other methods constructed by combining some of the constituent elements of the embodiments are also included in the scope of the present disclosure.

Claims

1. A graphite negative electrode active material, characterized in that: The particle body of the graphite negative electrode active material includes an internal region and a surface region that at least partially surrounds the internal region. The surface region refers to a region extending 30 nm from the particle body surface of the graphite negative electrode active material to the interior of the particle. The surface region includes a disordered layer.

2. The graphite negative electrode active material according to claim 1, characterized in that: The thickness of the disordered layer is 1 nm-20 nm, and can be optionally 3 nm-16 nm.

3. The graphite negative electrode active material according to claim 1 or 2, characterized in that: The coefficient of variation of the thickness of the disordered layer is less than or equal to 50%, and the coefficient of variation refers to the ratio of the standard deviation of the thickness of the disordered layer to the average of the thickness of the disordered layer.

4. The graphite negative electrode active material according to any one of claims 1 to 3, characterized in that The graphite negative electrode active material I D / I G is 0.05-0.10, among which I D / I G is the ratio of the D peak intensity to the G peak intensity obtained from the Raman spectrum, I D Indicates that the Raman spectrum is at 1350±100cm -1 The D peak intensity at I G Indicates that the Raman spectrum is at 1580±100cm -1 The G peak intensity at .

5. The graphite negative electrode active material according to any one of claims 1 to 4, characterized in that The interlayer spacing of the disordered layers of the graphite negative electrode active material is recorded as d1, the interlayer spacing of the internal region of the graphite negative electrode active material is recorded as d2, and the graphite negative electrode active material satisfies d1>d2; optionally, 0.3365nm≤d1≤0.3378nm; optionally, 0.3358nm≤d2≤0.3364nm.

6. The graphite negative electrode active material according to any one of claims 1 to 5, characterized in that The graphite negative electrode active material includes both primary particles and secondary particles; optionally, based on the total number of primary particles and secondary particles in the graphite negative electrode active material, the number of the secondary particles accounts for less than or equal to 50%.

7. The graphite negative electrode active material according to any one of claims 1 to 6, characterized in that The particle size distribution of the graphite negative electrode active material is (Dv90-Dv10) / Dv50 is 1.0-1.5, and can be optionally 1.1-1.

45.

8. The graphite negative electrode active material according to any one of claims 1 to 7, characterized in that The volume distribution particle size Dv50 of the graphite negative electrode active material is recorded as A, and the volume distribution particle size Dv50 of the graphite negative electrode active material after cold pressing under a pressure of 20000N is recorded as B. Then the graphite negative electrode active material satisfies: B / A≥85%, which can be optionally 85%-98%.

9. The graphite negative electrode active material according to any one of claims 1 to 8, characterized in that The graphite negative electrode active material satisfies at least one of the following: (1) The specific surface area of ​​the graphite negative electrode active material is 1.2 m 2 / g-1.9m 2 / g, optional 1.3m 2 / g-1.8m 2 / g; (2) The volume distribution particle size Dv50 of the graphite negative electrode active material is 7.0 μm-14.0 μm, and can be optionally 8.0 μm-12.0 μm; (3) The powder compaction density of the graphite negative electrode active material under a pressure of 49000N is less than or equal to 1.85g / cm 3 , optional 1.75g / cm 3 -1.85g / cm 3 ; (4) The gram capacity of the graphite negative electrode active material is 345 mAh / g-355 mAh / g, and can be optionally 347 mAh / g-353 mAh / g.

10. A method for preparing a graphite negative electrode active material, characterized in that: The following steps are involved: Provide raw materials; Processing the raw materials to obtain intermediate products; performing graphitization treatment on the intermediate product to obtain a graphitized product; The graphitized product is screened to obtain a graphite negative electrode active material; the particle body of the graphite negative electrode active material includes an internal region and a surface region that at least partially surrounds the internal region, the surface region refers to a region extending 30 nm from the surface of the particle body of the graphite negative electrode active material to the interior of the particle, and the surface region includes a disordered layer.

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

12. The preparation method according to claim 10 or 11, characterized in that: The graphitization treatment satisfies at least one of the following conditions: (1) The graphitization treatment time at the maximum power is 10h-50h; (2) The temperature of the graphitization treatment is 2600°C to 3000°C.

13. The preparation method according to any one of claims 10 to 12, characterized in that: The raw material includes at least one of petroleum coke, needle coke and asphalt coke, and needle coke can be selected.

14. The preparation method according to any one of claims 10 to 13, characterized in that: Based on the total volume of the raw material structure, the volume proportion of the fiber-type structure in the raw material is greater than or equal to 55%, and can be optionally 58%-70%.

15. The preparation method according to any one of claims 10 to 14, characterized in that: The processing of raw materials to obtain intermediate products specifically includes: crushing, shaping and classifying the raw materials to obtain a first precursor; Granulating the first precursor to obtain a second precursor; The first precursor and the second precursor are carbonized at low temperature to obtain the intermediate product.

16. The preparation method according to claim 15, characterized in that: The first precursor satisfies at least one of the following conditions: (1) The Dv50 particle size of the first precursor is 6.0 μm to 10.0 μm; (2) the particle size distribution of the first precursor (Dv90-Dv10) / Dv50 is 1.05-1.75; (3) The tap density of the first precursor is 0.5 g / cm 3 ~0.7g / cm 3 .

17. The preparation method according to claim 15 or 16, characterized in that: The Dv50 particle size of the second precursor is 11.0 μm to 15.0 μm.

18. A negative electrode plate, characterized in that: The negative electrode sheet comprises the graphite negative electrode active material according to any one of claims 1 to 9 or the graphite negative electrode active material prepared by the preparation method according to any one of claims 10 to 17.

19. A secondary battery, characterized in that: Including the negative electrode sheet as described in claim 18.

20. An electrical device, characterized in that: Includes the secondary battery as claimed in claim 19.

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