Graphite negative active material, method for preparing the same, secondary battery, and electric device

Abstract

The application provides a graphite negative electrode active material, a preparation method of the graphite negative electrode active material, a secondary battery and an electric device. The graphitization degree of the graphite negative electrode active material is 88% to 93%, and the oil absorption value of the graphite negative electrode active material is not more than 50 ml / 100g. The graphite negative electrode active material can improve the cycle performance of the battery and prolong the service life of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of secondary batteries, in particular to a graphite negative electrode active material, a preparation method thereof, a secondary battery and an electric device. BACKGROUND

[0002] The market of secondary batteries for energy storage is booming. Long cycle life is a key indicator for energy storage batteries, especially for those used in large-scale energy storage power stations. In order to prolong the service life and reduce the replacement frequency, it is necessary to further develop energy storage batteries with longer cycle life. SUMMARY

[0003] The present application is made in view of the above-mentioned problems, and aims to provide a graphite negative electrode active material, a preparation method thereof, a secondary battery and an electric device, which can effectively improve the cycle life of the battery and prolong the service life of the battery.

[0004] The first aspect of the present application provides a graphite negative electrode active material, wherein the graphitization degree of the graphite negative electrode active material is 88%-93%, and the oil absorption value of the graphite negative electrode active material is not more than 50ml / 100g.

[0005] On the one hand, the oil absorption value of the graphite negative electrode active material is controlled to be not more than 50ml / 100g, the dispersibility of the graphite negative electrode active material in the negative electrode slurry is good, the negative electrode slurry has excellent anti-settling property, the coating weight in the process of coating the electrode sheet is easy to control, the electrode sheet with uniform distribution and uniform thickness of the graphite negative electrode active material is easy to prepare, the possibility of local current density unevenness in the process of charging and discharging is reduced, the lithium precipitation phenomenon caused by electrode sheet polarization is reduced, the cycle performance and storage performance of the battery are improved, and the service life of the battery is prolonged. On the other hand, the graphitization degree of the graphite negative electrode active material is controlled to be 88%-93%, the interlayer spacing of the graphite negative electrode active material is large, which is beneficial to the rapid de-intercalation of active ions, the expansion of the graphite negative electrode active material is small when the active ions are intercalated into the negative electrode, which is beneficial to the long cycle of the battery, and the appropriate graphitization degree is beneficial to improving the gram capacity of the graphite negative electrode active material, thereby providing a material basis for preparing a battery with high energy density.

[0006] In summary, the graphite negative electrode active material meeting the above requirements is beneficial to improving the cycle performance and storage performance of the battery, and the battery has high energy density.

[0007] In any embodiment, the oil absorption value of the graphite negative electrode active material is 30ml / 100g-43ml / 100g.

[0008] As described above, the oil absorption value of the graphite negative electrode active material is small, and the dispersion of the graphite negative electrode active material in the negative electrode slurry is better, which is beneficial to prepare a negative electrode sheet with uniform distribution of graphite and improve the cycle performance of the battery. However, the oil absorption value of the graphite negative electrode active material is too small, which has a higher requirement for the particle regularity or particle size distribution of the graphite negative electrode active material, and the cost of the graphite negative electrode active material is higher, which is not conducive to the industrialization.

[0009] Controlling the oil absorption value of the graphite negative electrode active material in a suitable range can reduce the cost of the graphite negative electrode active material while meeting the requirement of long cycle performance, which is conducive to industrial production.

[0010] In any embodiment, the particle size distribution (Dv90-Dv10) / Dv50 of the graphite negative electrode active material is 1.2-1.6.

[0011] The particle size distribution (Dv90-Dv10) / Dv50 of the graphite negative electrode active material in the above range can control the oil absorption value of the graphite to be lower, which is beneficial to improve the uniformity of the negative electrode slurry and the uniformity of the graphite negative electrode active material in the negative electrode sheet, and can also reduce the negative impact of large-particle-size graphite negative electrode active material on the cycle performance and storage performance, thereby comprehensively improving the cycle performance and storage performance of the battery.

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

[0013] Compared with secondary particles, primary particles have fewer gaps between particles, and the surface of primary particles has smaller edges and corners and a smoother morphology, so that the oil absorption value of the graphite negative electrode active material is smaller, the leveling performance of the slurry is better, and the graphite negative electrode active material is uniformly distributed in the negative electrode sheet, thereby improving the cycle performance of the battery. At the same time, compared with secondary particles, primary particles have better structural stability and are not easy to break during the cycle process, thereby improving the cycle performance of the battery.

[0014] In any embodiment, the specific surface area of the graphite negative electrode active material is less than or equal to 1.4 m 2 / g, which can be 0.6 m 2 / g-1.3 m 2 / g.

[0015] The graphite negative electrode active material has a low specific surface area, which is beneficial to obtain a graphite negative electrode active material with a low oil absorption value, and also makes the graphite negative electrode active material have a low surface activity, thereby reducing the consumption of active ions by SEI film formation and improving the cycle performance and storage performance of the battery.

[0016] In any embodiment, the volume distribution particle size Dv50 of the graphite anode active material is 12μm-16μm, and can be selected as 13μm-15μm.

[0017] Graphite anode active material has a large volume distribution particle size Dv50 and a large pore size in the anode film layer, which is conducive to the electrolyte fully wetting the anode sheet, reducing the possibility of local polarization of the electrode sheet, and reducing the impact of black spots on the cycle life and storage performance of the battery.

[0018] In any embodiment, the graphite anode active material satisfies at least one of the following:

[0019] (1) The compacted density of the graphite anode active material under a pressure of 49000N is less than or equal to 1.85 g / cm³. 3 The option is 1.70 g / cm³. 3 -1.85g / cm 3 ;

[0020] (2) The tap density of the graphite anode active material is 1.2 g / cm³. 3 -1.4g / cm 3 ;

[0021] (3) The specific capacity of the graphite negative electrode active material is greater than or equal to 340 mAh / g, and can be selected as 341 mAh / g-347 mAh / g.

[0022] When the powder compaction density of graphite anode active material is within a suitable range under a pressure of 49000N, the cycle performance of the battery can be further improved.

[0023] When the tap density of the graphite anode active material is within the above range, the tap density of the anode sheet can be increased, thereby improving the energy density of the secondary battery. It is also beneficial to form a reasonable pore structure between the particles of the anode film, which can improve the transport performance of active ions and electrons, and improve the cycle performance and storage performance of the secondary battery.

[0024] Graphite anode active materials possess high specific capacity, providing a material basis for high-energy-density batteries. Simultaneously, within the specified specific capacity range, graphite anode active materials exhibit relatively small lattice expansion during cycling, good crystal structure stability, and reduced irreversible consumption of active ions, thereby improving battery cycle performance and storage performance.

[0025] This application also provides a method for preparing a graphite anode active material, characterized by comprising the following steps:

[0026] Provide raw materials;

[0027] The raw materials are processed to obtain a precursor;

[0028] The precursor is subjected to graphitization treatment to obtain an intermediate product;

[0029] The intermediate product is subjected to screening treatment to obtain the graphite negative electrode active material; the graphitization degree of the graphite negative electrode active material is 88%-93%, and the oil absorption value of the graphite negative electrode active material is not more than 50 ml / 100g.

[0030] By using the above preparation method, the graphite negative electrode active material with low oil absorption value and low graphitization degree can be prepared, the cycle performance of the battery can be improved, and the service life of the battery can be prolonged.

[0031] In any embodiment, the raw material comprises at least one of petroleum coke, needle coke, pitch coke, and optionally petroleum coke.

[0032] Based on the total volume of the structure of the raw material, the volume ratio of the mosaic type and the area type structure is greater than or equal to 50%, and optionally 50%-65%.

[0033] In any embodiment, the bonding index of the raw material is less than or equal to 10, and optionally 1-9.

[0034] In any embodiment, the precursor satisfies at least one of the following conditions:

[0035] The volume distribution particle size Dv50 of the precursor is 12-18 μm; and / or,

[0036] The particle size distribution (Dv90-Dv10) / Dv50 of the precursor is 1.2-1.8.

[0037] Controlling the volume distribution particle size Dv50 or the particle size distribution (Dv90-Dv10) / Dv50 of the precursor within a suitable range is conducive to controlling the particle size distribution (Dv90-Dv10) / Dv50 of the graphite negative electrode active material within a suitable range, and further adjusting the oil absorption value of the graphite negative electrode active material within a smaller range.

[0038] In any embodiment, the maximum power of the graphitization treatment is 70%-90% of the rated power of the graphitization equipment.

[0039] In any embodiment, the maximum power of the graphitization treatment is 23000-25000 W; and / or, the constant power time of the maximum power of the graphitization treatment is 10-50 h.

[0040] In any embodiment, the screening treatment of the intermediate product specifically comprises the following steps:

[0041] The intermediate product is subjected to screening treatment to remove particles with a maximum particle size Dmax greater than 100 μm in the intermediate product to obtain the graphite negative electrode active material.

[0042] Removing large size particles in the intermediate product reduces the negative impact of large particle materials on the cycle performance and storage performance of the battery.

[0043] The third aspect of the present application provides a secondary battery, comprising a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode film layer formed on at least one surface of the negative electrode current collector, the negative electrode film layer comprising the graphite negative electrode active material of the first aspect of the present application or the graphite negative electrode active material prepared by the preparation method of the second aspect of the present application.

[0044] In any embodiment, the negative electrode film layer comprises a conductive agent, the mass content of the conductive agent being greater than or equal to 1.5%, and optionally 1.8%-2.5%, based on the mass of the negative electrode film layer.

[0045] The fourth aspect of the present application provides an electric device, comprising the secondary battery of the third aspect of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0046] Figure 1 is a schematic diagram of a secondary battery according to an embodiment of the present application;

[0047] Figure 2 is a schematic diagram of a secondary battery according to an embodiment of the present application; Figure 1 is an exploded view of the secondary battery according to an embodiment of the present application shown in FIG. 1;

[0048] Figure 3 is a schematic diagram of a battery module according to an embodiment of the present application;

[0049] Figure 4 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0050] Figure 5 is a schematic diagram of a battery pack according to an embodiment of the present application; Figure 4 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG. 4;

[0051] Figure 6 is a schematic diagram of an electric device using the secondary battery according to an embodiment of the present application as a power source.

[0052] REFERENCE SIGNS:

[0053] 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 secondary battery; 51 housing; 52 electrode assembly; 53 top cover assembly. DETAILED DESCRIPTION

[0054] Hereinafter, specific embodiments of the graphite negative electrode active material and the method for manufacturing the same, the secondary battery, and the electric device of the present application will be described in detail with appropriate reference to the accompanying drawings. However, there will be cases where unnecessary detailed description is omitted. For example, there will be cases where detailed description of matters known well, repetitive description of substantially identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0055] The ranges disclosed herein are defined by their lower and upper limits. Ranges can either be inclusive or exclusive of their endpoints, and both endpoints and the exclusion of either or both endpoints are appropriately resolvable by art-recognized ranges. Unless otherwise specified, a range "a-b" is a shorthand way of disclosing each and every number and range encompassed within the range. For example, a range of 0-5 includes each and every number and range between and including 0 and 5, such as 0, 0.1, 0.2, 0.3, 0.4, 0.5, 1, 2, 3, 4, 5, etc. Also, unless otherwise specified, a range "a-b" is a shorthand way of disclosing each and every integer within the range. For example, a range of 2-8 includes each and every integer between and including 2 and 8, such as 2, 3, 4, 5, 6, 7, 8, etc.

[0056] If not particularly stated, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0057] If not particularly stated, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

[0058] If not specified otherwise, all steps of the present application can be carried out in sequence or randomly, preferably in sequence. For example, the method comprising steps (a) and (b) means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method can further comprise step (c) means that step (c) can be added to the method in any sequence, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0059] If not specified otherwise, the terms "comprising" and "including" as used in the present application are open-ended and also include the case where the listed steps / compositions are the only steps / compositions. For example, the terms "comprising" and "including" can mean that other components not listed can also be included or only the listed components can be included.

[0060] If not specified otherwise, the term "or" as used in the present application is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following is satisfied by the condition "A or B": A is true (or present) and B is false (or not present); A is false (or not present) and B is true (or present); or both A and B are true (or present).

[0061] The negative active material is the main material of the battery, and the performance of the negative active material has an important influence on the cycle life of the battery. In order to obtain a long cycle battery in the prior art, the graphitization degree of the negative active material or the compaction density of the negative electrode sheet and other parameters are generally controlled to obtain a battery with long cycle life. However, another factor affecting the capacity decay is the uniformity of the active material in the negative electrode sheet. If the negative active material is not uniformly mixed with the conductive agent and the binder during the preparation of the negative electrode slurry, the negative electrode slurry is settled or agglomerated, the active material in the negative electrode sheet formed by coating is not uniformly distributed or the thickness of the negative electrode sheet is not uniform, which can cause local current unevenness during the cycle process, and the difference in active ion diffusion concentration causes lithium precipitation, resulting in capacity decay, affecting the cycle performance and storage performance of the battery.

[0062] [Graphite negative active material]

[0063] Based on this, the present application provides a graphite negative active material, the graphitization degree of the graphite negative active material is 88%-93%, and the oil absorption value of the graphite negative active material is not more than 50 ml / 100g.

[0064] In some embodiments, the graphitization degree of the graphite negative electrode active material can be selected to be any value among 88%, 89%, 90%, 91%, 92%, 93% or a range consisting of any two values among them.

[0065] In this document, the term "graphitization degree" is macroscopically to characterize how much proportion of the material reaches the complete graphite crystal structure; microscopically, it refers to the degree to which different transition state carbon structures approach the ideal graphite crystal.

[0066] The graphitization degree of the graphite negative electrode active material reflects the completeness of the graphite crystal structure in the material, i.e. the regularity of the arrangement of carbon atoms in the graphite structure in the material. The higher the graphitization degree of the material, the smaller the interlayer spacing of the graphite, the smaller the lattice rotation, the less the accumulation of the scattered layers, the more ordered the arrangement, and the higher the gravimetric capacity of the material, which is conducive to obtaining high energy density secondary batteries. The lower the graphitization degree of the material, the larger the interlayer spacing of the graphite, which is conducive to the rapid deintercalation of active ions, the small expansion of the material when intercalating lithium, the shallow charging and discharging effect, and the long cycle and long storage.

[0067] In this application, the graphitization degree of the graphite negative electrode active material has the meaning known in the art and can be tested by instruments and methods known in the art. For example, an X-ray diffractometer (such as Bruker D8 Discover) can be used for testing, which can refer to JIS K 0131-1996, JB / T 4220-2011 to obtain the average interlayer spacing d002 of the C(002) crystal plane in the crystal structure of the material, and then calculate the graphitization degree according to the formula g=(0.344-d002) / (0.344-0.3354)×100%. In the above formula, d002 is the average interlayer spacing of the C(002) crystal plane in the crystal structure of the material, expressed in nanometers (nm).

[0068] In some embodiments, the oil absorption value of the graphite negative electrode active material can be selected to be any one of not more than 30 ml / 100g, not more than 35 ml / 100g, not more than 40 ml / 100g, not more than 45 ml / 100g, not more than 50 ml / 100g.

[0069] In this document, the term "oil absorption value" refers to the volume of linseed oil that can be absorbed by 100g of graphite negative electrode active material. For example, the oil absorption value of the graphite negative electrode active material is 40 ml / 100g, which means that 100g of the graphite negative electrode active material can absorb 40 ml of linseed oil.

[0070] The oil absorption value of the graphite negative electrode active material can be tested by using methods and devices known in the art, for example as follows: obtain a test oil and a graphite negative electrode active material sample respectively, and set a torque threshold of an oil absorption value tester; add the oil into the sample in the mixing chamber of the oil absorption value tester at a constant speed, as the oil absorption of the sample increases, the viscosity of the mixture of the sample and the oil increases continuously, when the viscosity of the mixture reaches the preset torque threshold of the oil absorption value tester, stop and calculate the volume of the oil absorbed by the sample per unit mass, which is the oil absorption value QI of the sample. The test oil is linseed oil (DBP), and the torque threshold is 1 N.

[0071] The oil absorption value of the graphite negative electrode active material is mainly related to the specific surface area of the material, the surface properties of the material, the particle shape of the material and the particle size distribution of the material, and the oil absorption value of the graphite negative electrode active material reflects the dispersibility of the material in the negative electrode slurry. The smaller the oil absorption value of the material, the better the dispersibility of the material in the negative electrode slurry, the better the anti-settling property and dispersibility of the negative electrode slurry, the easier to control the coating weight in the coating process of the electrode sheet, and the graphite negative electrode active material is uniformly distributed and the thickness of the negative electrode sheet is uniform, which reduces the possibility of local current density unevenness in the charging and discharging process, reduces the lithium precipitation phenomenon caused by electrode polarization, improves the cycle performance of the battery, and prolongs the service life and storage life of the battery.

[0072] In summary, the graphite negative electrode active material has a suitable range of graphitization degree and oil absorption value, which is beneficial to improve the cycle performance and storage performance of the battery, and the battery has high energy density.

[0073] In some embodiments, the oil absorption value of the graphite negative electrode active material is 30 ml / 100 g-43 ml / 100 g. In some embodiments, the oil absorption value of the graphite negative electrode active material can be selected as any value or a range consisting of any two values selected from 30 ml / 100 g, 32 ml / 100 g, 34 ml / 100 g, 36 ml / 100 g, 38 ml / 100 g, 40 ml / 100 g, 42 ml / 100 g and 43 ml / 100 g.

[0074] As described above, the smaller the oil absorption value of the graphite negative electrode active material, the better the dispersibility of the material in the negative electrode slurry, which is beneficial to prepare a negative electrode sheet with uniform distribution of graphite and improve the cycle performance of the battery. However, the oil absorption value of the graphite negative electrode active material is too small, which has a higher requirement for the particle regularity or particle size distribution of the graphite negative electrode active material, and the cost of the graphite negative electrode active material is higher, which is not conducive to the industrialization.

[0075] Controlling the oil absorption value of the graphite negative electrode active material within a suitable range can reduce the cost of the graphite negative electrode active material while meeting the requirement of long cycle performance, which is beneficial to industrial production.

[0076] In some embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the graphite negative electrode active material is 1.2-1.6. In some embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the graphite negative electrode active material can be selected as any value or a range formed by any two values in 1.2, 1.3, 1.4, 1.5, 1.6.

[0077] The volume distribution particle size Dv10, Dv50, Dv90 of the graphite negative electrode active material are meanings known in the art, which respectively represent the particle size corresponding to the cumulative volume distribution percentage of 10%, 50%, 90% of the material, which can be measured by instruments and methods known in the art. For example, GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method can be referred to for convenient measurement by using a laser particle size analyzer. The test instrument can be a Mastersizer 3000 laser particle size analyzer of Malvern Instruments Ltd., UK.

[0078] The particle size distribution (Dv90-Dv10) / Dv50 of the graphite negative electrode active material will affect the oil absorption value of the material. When the particle size distribution (Dv90-Dv10) / Dv50 of the graphite negative electrode active material is too large, the oil absorption value of the graphite negative electrode active material is large, and the small and large particle size particles in the graphite negative electrode active material hinder the dispersion of the graphite negative electrode active material in the negative electrode slurry, which will adversely affect the uniformity and thickness of the electrode sheet and deteriorate the cycle performance of the battery. When the particle size distribution (Dv90-Dv10) / Dv50 of the graphite negative electrode active material is too small, the preparation process of the graphite negative electrode active material is relatively complex, the yield of the graphite negative electrode active material is significantly reduced, and the cost is significantly increased.

[0079] In summary, when the particle size distribution (Dv90-Dv10) / Dv50 of the graphite negative electrode active material is within a suitable range, the oil absorption value of the graphite negative electrode active material is low, the cycle performance of the battery is excellent, and the cost of the graphite negative electrode active material is reduced, which is beneficial to industrial application.

[0080] In some embodiments, the proportion of the number of primary particles in the graphite negative electrode active material is greater than or equal to 85% based on the total number of particles of the graphite negative electrode active material.

[0081] In some embodiments, the proportion of the number of primary particles in the graphite negative electrode active material is 85%-100% based on the total number of particles of the graphite negative electrode active material. In some embodiments, the proportion of the number of primary particles in the graphite negative electrode active material can be selected as any value or a range formed by any two values in 85%, 90%, 95%, 100% based on the total number of particles of the graphite negative electrode active material.

[0082] In some embodiments, the particles in the graphite negative electrode active material include primary particles and secondary particles. Primary particles and secondary particles are both well known in the art. A “secondary particle” refers to an agglomerated particle formed by agglomeration between multiple primary particles or primary particles. The force of agglomeration between particles can be assisted by additional substances (e.g., a chemical substance with viscosity).

[0083] The proportion of primary particles can be determined by instruments and methods known in the art. For example, the graphite negative electrode active material is laid and adhered on conductive glue to form a sample to be tested with a length x width of 6 cm x 1.1 cm. The morphology of the particles in the sample to be tested is tested using a scanning electron microscope; energy spectrometer (e.g., ZEISS SEM (sigma300)). The test can refer to JY / T010-1996. To ensure the accuracy of the test results, multiple (e.g., 10 or 20) different areas in the sample to be tested can be randomly selected for scanning test, and the number of secondary particles and the total number of particles in the test area are counted under a certain magnification (e.g., 500x or 1000x). The ratio of the number of primary particles to the total number of particles in any test area is the proportion of the number of primary particles in that area. The average value of the test results of 10 test areas is taken as the proportion of the number of primary particles. To ensure the accuracy of the results, multiple samples to be tested (e.g., 5 or 10) can be prepared to repeat the above test, and the average value of the test results of each sample to be tested is taken as the proportion of the number of primary particles in the graphite negative electrode active material.

[0084] Compared with secondary particles, primary particles have fewer gaps between particles, smaller surface edges, smoother particle morphology, smaller oil absorption value of the graphite negative electrode active material, and better leveling performance of the slurry, which is beneficial to the preparation of a negative electrode sheet with uniform distribution of graphite negative electrode active material and improves the cycle performance of the battery. At the same time, compared with secondary particles, primary particles have better structural stability and are less likely to break during the cycle process, which improves the cycle performance of the battery.

[0085] In some embodiments, the specific surface area of the graphite negative electrode active material is less than or equal to 1.4 m 2 / g.

[0086] In some embodiments, the specific surface area of the graphite negative electrode active material can be selected from 0.4 m 2 / g, 0.5 m 2 / g, 0.6 m 2 / g, 0.7 m 2 / g, 0.75 m 2 / g, 0.85 m 2 / g, 0.85 m 2 / g, 1.05 m 2 / g, 1.15m 2 / g, 1.25m 2 / g, 1.3m 2 / g, 1.4m 2 Any value in / g or a range consisting of any two of its values.

[0087] In this paper, the term "specific surface area" refers to the sum of the total external surface areas of all particles in one gram of material.

[0088] The specific surface area of ​​graphite anode active materials can be determined using instruments and methods known in the art. For example, it can be measured using the nitrogen adsorption specific surface area analysis method according to GB / T 19587-2017, and calculated using the BET (Brunauer-Emmett-Teller) method. The nitrogen adsorption specific surface area analysis can be performed using a Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, Inc.

[0089] The specific surface area of ​​graphite anode active material affects the oil absorption value of the material. A lower specific surface area results in a lower oil absorption value. Improving the uniformity of the distribution of graphite anode active material and the uniformity of electrode thickness in the anode sheet improves the cycle performance and storage performance of the battery. At the same time, the low specific surface area of ​​graphite anode active material results in low surface activity, which can reduce the consumption of active ions by SEI film formation and improve the cycle performance and storage performance of the battery.

[0090] In some embodiments, the specific surface area of ​​the graphite anode active material is 0.6 m². 2 / g-1.3m 2 / g.

[0091] In some embodiments, the specific surface area of ​​the graphite anode active material may be selected as 0.6 m². 2 / g, 0.7m 2 / g, 0.75m 2 / g, 0.85m 2 / g, 0.85m 2 / g, 1.05m 2 / g, 1.15m 2 / g, 1.25m 2 / g, 1.3m 2 Any value in / g or a range consisting of any two of its values.

[0092] As described above, the graphite negative electrode active material has a small specific surface area, and the graphite negative electrode active material has a low oil absorption value, which is beneficial to the cycle life of the battery. However, if the specific surface area is too small, the wettability of the electrolyte to the pole piece will be affected, the kinetic performance of the pole piece will be affected, and the lithium precipitation phenomenon will occur, which will affect the cycle life and storage life of the battery. The specific surface area in a suitable range can further improve the cycle life and storage life of the battery.

[0093] In some embodiments, the volume distribution particle size Dv50 of the graphite negative electrode active material is 12 μm-16 μm.

[0094] In some embodiments, the volume distribution particle size Dv50 of the graphite negative electrode active material can be selected as any value or a range formed by any two values in 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm, 15.5 μm, 16 μm.

[0095] The graphite negative electrode active material has a large volume distribution particle size Dv50, and the negative electrode film layer has a large pore size, which is beneficial to the full wettability of the electrolyte to the negative electrode pole piece, reduces the possibility of local polarization of the pole piece, and reduces the influence of the black spot phenomenon of the negative electrode on the cycle life and storage performance of the battery.

[0096] In some embodiments, the volume distribution particle size Dv50 of the graphite negative electrode active material is 13 μm-15 μm.

[0097] In some embodiments, the volume distribution particle size Dv50 of the graphite negative electrode active material can be selected as any value or a range formed by any two values in 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm.

[0098] The graphite negative electrode active material has a suitable volume distribution particle size Dv50, and the negative electrode film layer has a suitable pore size, which is beneficial to the full wettability of the electrolyte to the negative electrode pole piece, reduces the possibility of local polarization of the pole piece, and reduces the influence of the black spot phenomenon of the negative electrode on the cycle life and storage performance of the battery. At the same time, it is beneficial to improve the transmission performance of active ions and electrons, the pole piece has excellent kinetic performance, and the influence of lithium precipitation on the service life of the battery is reduced.

[0099] In some embodiments, the powder compaction density of the graphite negative electrode active material under a pressure of 49,000 N is less than or equal to 1.85 g / cm 3 .

[0100] In this paper, the term "powder compaction density" refers to the density of the powder to be tested under a predetermined pressure.

[0101] The method for measuring the powder compaction density can use any known method in the art, for example, refer to GB / T24533-2009, weigh 1 g of the graphite negative electrode active material powder, add into a mold with a bottom area of 1.327 cm 2 , press to a specific pressure, for example, 49000 N, keep the pressure for 30 s, then release the pressure, keep for 10 s, and then measure the powder compaction density of the graphite negative electrode active material at the selected pressure by an electronic pressure testing machine (for example, UTM7305 type electronic pressure testing machine).

[0102] When the powder compaction density of the graphite in the graphite negative electrode active material at 49000 N pressure is greater than 1.85 g / cm 3 , the particle strength of the graphite negative electrode active material is not enough, and the original pore structure of the electrode sheet is difficult to maintain during the compression in the cycle process, which changes the tortuosity of the electrode sheet, increases the lithium ion intercalation path, and affects the kinetic performance of the battery, which is not conducive to realizing the long cycle stability.

[0103] In some embodiments, the powder compaction density of the graphite negative electrode active material at 49000 N pressure is 1.70 g / cm 3 -1.85 g / cm 3 . In some embodiments, the powder compaction density of the graphite negative electrode active material at 49000 N pressure can be selected as any value in 1.70 g / cm 3 , 1.72 g / cm 3 , 1.74 g / cm 3 , 1.76 g / cm 3 , 1.78 g / cm 3 , 1.80 g / cm 3 , 182 g / cm 3 , 1.84 g / cm 3 , 1.85 g / cm 3 , or a range composed of any two values thereof.

[0104] As described above, the powder compaction density of the graphite negative electrode active material at 49000 N pressure is less than or equal to 1.85 g / cm 3 , which is conducive to improving the cycle performance of the battery. At the same time, the powder compaction density of the graphite negative electrode active material at 49000 N pressure also affects the energy density of the battery, and the higher the powder compaction density, the greater the compaction density of the negative electrode film layer, which is more conducive to increasing the energy density of the secondary battery.

[0105] Controlling the powder compaction density of the graphite negative electrode active material at 49000 N pressure within a suitable range can improve the cycle life of the battery while also taking into account the high energy density of the battery.

[0106] In some embodiments, the tap density of the graphite negative electrode active material is 1.2 g / cm 3 -1.4 g / cm 3 In some embodiments, the tap density of the graphite negative electrode active material can be selected from any value or range defined by any two values among 1.2 g / cm 3 , 1.25 g / cm 3 , 1.30 g / cm 3 , 1.35 g / cm 3 , 1.4 g / cm 3 .

[0107] In the present disclosure, the term “tap density” refers to the density of a powder material after vibration compression under certain conditions.

[0108] The tap density can be measured by any method known in the art. For example, the tap density can be measured by using a powder tap density tester according to GB / T 5162-2006. The tester can be BT-301 from Dandong Baiter.

[0109] When the tap density of the graphite negative electrode active material is within the above range, the tap density of the negative electrode sheet can be improved, and thus the energy density of the secondary battery can be improved. In addition, the tap density of the graphite negative electrode active material can help to form a reasonable pore structure among the particles of the negative electrode film layer, and thus the transport performance of active ions and electrons can be improved, and the cycle performance and storage performance of the secondary battery can be improved.

[0110] In some embodiments, the graphite negative electrode active material has a gravimetric capacity of 340 mAh / g or more. In some embodiments, the gravimetric capacity of the graphite negative electrode active material can be selected from any value or range defined by any two values among 340 mAh / g, 341 mAh / g, 342 mAh / g, 343 mAh / g, 344 mAh / g, 345 mAh / g, 346 mAh / g, 347 mAh / g, 349 mAh / g, 350 mAh / g, 351 mAh / g, 352 mAh / g.

[0111] The method for measuring the gram capacity can use any method known in the art. For example, a graphite negative electrode active material sample can be mixed with a 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 uniformly coated on the surface of a negative electrode current collector copper foil and dried and cold-pressed. Then, a metal lithium sheet is used as a counter electrode, a polypropylene (PP) film is used as a separator film, and an electrolyte is injected, wherein the electrolyte formulation used is as follows: dimethyl carbonate (DMC), methyl ethyl 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. A CR2430 type button cell is assembled in an argon glove box. At 25°C, the button cell prepared above is first discharged at a current of 0.05C to 0.005V, and then discharged at a constant current of 10μA to 0.005V, and then left for 5min, and the first cycle discharge capacity of the button cell is recorded. Then, the button cell is charged at a current of 0.1C to 2.0V, and the charge capacity of the button cell is 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.

[0112] The graphite negative electrode active material has excellent gram capacity, which can improve the energy density of the secondary battery.

[0113] In some embodiments, the gram capacity of the graphite negative electrode active material is 341mAh / g-347mAh / g. In some embodiments, the gram capacity of the graphite negative electrode active material can be selected as any value or a range consisting of any two values in 341mAh / g, 342mAh / g, 343mAh / g, 344mAh / g, 345mAh / g, 346mAh / g, and 347mAh / g.

[0114] The gram capacity of the graphite negative electrode active material is within the range, the lattice expansion during the material cycle is relatively small, the crystal structure stability is good, the irreversible consumption of active ions is reduced, and the cycle performance and storage performance of the battery are improved.

[0115] In the embodiments of the present application, a preparation method of a graphite negative electrode active material is also provided, characterized in that it comprises the following steps:

[0116] providing raw materials;

[0117] processing the raw materials to obtain a precursor;

[0118] subjecting the precursor to graphitization treatment to obtain an intermediate product;

[0119] The intermediate product is subjected to a screening process to obtain the graphite negative electrode active material; the graphitization degree of the graphite negative electrode active material is 88%-93%, and the oil absorption value of the graphite negative electrode active material is not more than 50ml / 100g.

[0120] By using the preparation method, the graphite negative electrode active material with low oil absorption value and low graphitization degree can be prepared, and the cycle performance of the battery can be further improved, and the service life of the battery is prolonged.

[0121] In some embodiments, the raw material includes at least one of petroleum coke, needle coke, and pitch coke.

[0122] In this document, the term "petroleum coke" refers to coke formed after petroleum residue or petroleum pitch is subjected to high-temperature carbonization.

[0123] In this document, the term "needle coke" refers to coke with needle-like texture formed after coal tar pitch or petroleum pitch is subjected to liquid-phase carbonization to form an anisotropic mesophase and then subjected to high-temperature carbonization and other processes.

[0124] In this document, the term "pitch coke" refers to solid material formed after coal tar pitch is subjected to high-temperature carbonization.

[0125] In some embodiments, the raw material includes petroleum coke.

[0126] Petroleum coke has excellent anisotropy, which is beneficial to the preparation of graphite negative electrode active material with low graphitization degree and low expansion, and is beneficial to the long cycle life of the battery. In addition, petroleum coke has high compaction density and high gram capacity, which is beneficial to improving the energy density of the battery. In addition, the source of petroleum coke is more extensive, which is beneficial to industrialized production.

[0127] Based on the total volume of the structure of the raw material, the volume ratio of the mosaic type and the regional type is greater than or equal to 50%.

[0128] According to the morphological characteristics and isochromatic zone size of the coke material under a polarizing microscope, the microstructure can be divided into mosaic type, regional type and fiber type. Generally, the microstructure of the isochromatic zone with a size less than 30μm is determined as the mosaic type; the microstructure of the isochromatic zone with a size greater than 30μm is determined as the regional type, and the anisotropic strip-shaped isochromatic zone is determined as the fiber type structure.

[0129] In the present application, the volume fraction of mosaic and regional structure in the raw material can be tested by methods known in the art. As an example, the raw material is taken according to GB 1997-89, the raw material crushed to 1 mm is mixed, 40 g to 50 g is divided, and 4 g to 5 g of 0.07 mm to 1.0 mm grade sample is taken by square hole sieve for tablet preparation; the powder coke and block coke optical film is prepared according to MT 116.1-86, the diameter of the powder coke optical film should not be less than 22 mm, and the volume of the cement should be less than 1 / 3; the sample is placed on the slide with cement, flattened, placed on the stage, and focused; the polarizer, analyzer, and microscope are adjusted to be orthogonal. Insert the cyanine detection plate (1λ), and make the visual field present the first-order red interference color; determine the step length of the moving ruler to ensure that more than 400 effective measuring points are evenly distributed, and the point distance is preferably 0.3-0.5 mm, and the line distance is preferably 0.5-0.8 mm. Starting from one end of the sample, determine the microstructure category at the intersection of the crosshairs, and the volume fraction of mosaic and regional structure in the raw material is calculated by dividing the number of effective measuring points of the optical organization of mosaic and regional structure by the total number of test points.

[0130] In some embodiments, the volume fraction of mosaic and regional structure is 50%-65% based on the total volume of the raw material structure. In some embodiments, the volume fraction of mosaic and regional structure can be selected as any value or a range consisting of any two values in 50%, 55%, 60%, 65% based on the total volume of the raw material structure.

[0131] As described above, a high volume fraction of mosaic and regional structure is beneficial to obtain a graphite negative electrode active material with low oil absorption value, but a too high volume fraction of mosaic and regional structure will affect the specific capacity of the graphite negative electrode active material and the energy density of the battery.

[0132] In some embodiments, the caking index of the raw material is less than or equal to 10. In some embodiments, the caking index of the raw material can be selected as any value or a range consisting of any two values in 1, 2, 3, 4, 5, 6, 7, 8, 9, 10.

[0133] In some embodiments, the caking index of the raw material is less than or equal to 1-9. In some embodiments, the caking index of the raw material can be selected as any value or a range consisting of any two values in 1, 2, 3, 4, 5, 6, 7, 8, 9.

[0134] In this paper, the term "caking index" is used to characterize the caking property of the raw material, which refers to the formation of a plastic colloid during high-temperature heating, which can bind itself or external inert substances and has a certain strength. It is a manifestation of the combined action of surface bonding and internal force (adhesion and cohesion) of colloid-like substances.

[0135] In the present application, the bonding index of the raw material can be tested by a method known in the art, for example, referring to GB / T5447-2014 / ISO 15585:2006, using TX-600 to test the bonding index. First, take 200g of the sample and place it in a 100℃ drying oven for 1 hour; sieve the dried sample through a set of sieves with a pore size of 200μm+100μm, and take the sample under the 200μm sieve and the sample above the 100μm sieve; then, take 3.00±0.001g of special anthracite coal, and take 3.00±0.001g of the test sample and place them into a crucible, and mix them evenly; use tweezers to clamp the briquette and place it in the center of the crucible, and then place it under a pressure device, and gently lower the pressure rod, and press for 30s; quickly place the crucible into a preheated muffle furnace (850℃), and heat for 15min; the temperature of the muffle furnace is maintained at 850℃±10℃ during the heating process; after the crucible is taken out of the furnace and cooled, measure the total weight of the sample as m, and then place the sample into a rotating drum device for a rotating drum test; sieve the sample after the rotating drum test with a 1mm round hole sieve, and measure the weight of the sieve residue as m1; place the sieve residue into a rotating drum for a second rotating drum test, sieve and measure the sieve residue m2; and calculate the bonding index G according to the formula G=(30*m1+70*m2) / (5*m).

[0136] If the bonding index of the raw material is too high, the material is prone to bonding during the heat treatment process, and secondary particles are easily formed, so that the graphite negative active material has a relatively irregular morphology, and the graphite negative active material has a large oil absorption value, which is not conducive to the dispersion of the negative electrode slurry, and affects the cycle performance and storage performance of the battery.

[0137] In some embodiments, the processing of the raw material specifically includes the following steps:

[0138] crushing, shaping and grading the raw material to obtain a secondary raw material;

[0139] removing part of the fine powder in the secondary raw material to obtain a precursor.

[0140] In some embodiments, in the step of crushing the raw material, a crusher such as a jaw crusher can be used to crush the raw material. For example, the raw material can be crushed to a set particle size before sieving.

[0141] In some embodiments, in the step of shaping the raw material, a shaper can be used to shape the crushed raw material. Shaping can reduce burrs on the surface of the crushed raw material, which is beneficial to obtaining a round graphite negative active material and a graphite negative active material with a low oil absorption value.

[0142] In some embodiments, the raw material is classified in step (S3), and the classified raw material is classified by using an air flow classifier. Optionally, the air flow frequency can be greater than or equal to 20 Hz, and the classification frequency can be greater than or equal to 65 Hz. The classification can reduce the content of large particles and small particles in the precursor.

[0143] In some embodiments, the volume distribution particle size Dv50 of the precursor is 12 μm-18 μm. In some embodiments, the volume distribution particle size Dv50 of the precursor can be any value selected from 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, or a range formed by any two of the values.

[0144] In some embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the precursor is 1.2-1.8. In some embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the precursor can be any value selected from 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, or a range formed by any two of the values.

[0145] Controlling the volume distribution particle size Dv50 or the particle size distribution (Dv90-Dv10) / Dv50 of the precursor within a suitable range is conducive to controlling the particle size distribution (Dv90-Dv10) / Dv50 of the graphite negative electrode active material within a suitable range, and further regulating the oil absorption value of the graphite negative electrode active material within a smaller range.

[0146] In this document, the term "graphitization treatment" refers to a heat treatment process of carbon materials, in which the carbon materials are transformed from a two-dimensional structure of carbon network to a three-dimensional ordered structure through the growth of "microcrystals" under the action of high temperature.

[0147] In some embodiments, the maximum power of the graphitization treatment is 70%-90% of the rated power of the graphitization treatment equipment.

[0148] In some embodiments, the maximum power of the graphitization treatment can be selected as 70%, 75%, 80%, 85%, 90% of the rated power of the graphitization treatment equipment, or a numerical range between any two of the values. It can be understood that the graphitization treatment equipment 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, pipe furnace, etc. The rated power of the graphitization treatment equipment produced by different manufacturers can be different, and can be selected according to the actual situation.

[0149] The maximum power of the graphitization adopted in this application needs to be lower than the rated power of the graphitization treatment equipment, in order to achieve the uniformity of the temperature field in the graphitization treatment process. Ensuring the consistency of the material capacity is conducive to improving the cycle life of the battery.

[0150] In some embodiments, the graphitization treatment device is an inner string furnace, and the rated power of the inner string furnace is 25000W-32000W.

[0151] In some embodiments, the graphitization treatment device is an Acheson furnace, and the rated power of the Acheson furnace is 28000W-30000W.

[0152] In some embodiments, the maximum power of the graphitization treatment is 23000W-25000W.

[0153] For example, the maximum power of the graphitization treatment can be selected as 23000W, 23500W, 24000W, 24500W, 25000W, or any numerical range between any two of them.

[0154] By controlling the maximum power of the graphitization treatment, the graphitization degree of the graphite negative electrode active material during the heat treatment process can be effectively controlled, which is beneficial to improve the cycle life of the battery.

[0155] In some embodiments, the constant power time of the graphitization treatment at the maximum power is 10h-50h.

[0156] In some embodiments, the constant power time of the graphitization treatment at the maximum power is 10h, 13h, 16h, 19h, 22h, 25h, 28h, 31h, 33h, 36h, 39h, 42h, 45h, 48h, 50h, or any numerical range between any two of them.

[0157] In some embodiments, the graphitization treatment device is an inner string furnace, and the constant power time of the graphitization treatment at the maximum power is 10h-30h.

[0158] In some embodiments, the graphitization treatment device is an Acheson furnace, and the constant power time of the graphitization treatment at the maximum power is 30h-50h.

[0159] The constant power time of the suitable maximum power neither easily causes excessive rearrangement of the precursor, nor effectively reduces the specific surface area of the graphite negative electrode active material, thereby improving the cycle performance of the battery; nor effectively improves the gram capacity of the graphite negative electrode active material, thereby benefiting the energy density of the secondary battery.

[0160] In some embodiments, the screening treatment of the intermediate product specifically comprises the following steps:

[0161] The screening treatment of the intermediate product removes the particles with a maximum particle size Dmax greater than 100μm in the intermediate product, thereby obtaining the graphite negative electrode active material.

[0162] The removal of the large particle size particles in the intermediate product reduces the negative impact of the large particle materials on the cycle performance and storage performance of the battery.

[0163] In addition, the secondary battery, the battery module, the battery pack, and the power consuming device of the present application are described below with appropriate reference to the accompanying drawings.

[0164] [Anode electrode sheet]

[0165] The anode electrode sheet comprises an anode current collector and an anode film layer disposed on at least one surface of the anode current collector, wherein the anode film layer comprises the graphite anode active material of the first aspect of the embodiments of the present application or the graphite anode active material prepared by the method of the second aspect of the embodiments of the present application.

[0166] In some embodiments, the anode film layer comprises a conductive agent, and the mass content of the conductive agent is greater than or equal to 1.5% based on the mass of the anode film layer.

[0167] In some embodiments, the mass content of the conductive agent is 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 3.0%, 3.1%, 3.2%, 3.2%, 3.3%, or any numerical range between any two of them, based on the total mass of the anode film layer.

[0168] During the battery cycle process, active ions continuously embed and extract in the graphite anode active material lattice, and the graphite anode active material is prone to produce particle "isolation", thereby losing electrochemical activity, causing local current unevenness, producing polarization, accelerating capacity decay, and leading to a "dive" in battery performance. In order to solve the above problems, a relatively high content of conductive agent is usually added in the anode film layer to effectively enhance the electrical contact between the graphite anode active materials and improve the cycle stability of the battery. However, adding a high content of conductive agent in the anode slurry will affect the dispersibility of the anode slurry. The low oil absorption value graphite anode active material of the present application has excellent dispersibility in the anode slurry, which can make up for the influence of high content of conductive agent on the dispersibility of the anode slurry.

[0169] The high content of conductive agent is matched with the low oil absorption value graphite anode active material, the anode slurry has good dispersibility, the electrode sheet has excellent uniformity, and the graphite anode active material has good electrical contact, thereby comprehensively improving the cycle performance of the battery.

[0170] In some embodiments, the mass content of the conductive agent is 1.8%-2.5% based on the mass of the anode film layer. In some embodiments, the mass content of the conductive agent is 1.8%, 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, or any numerical range between any two of them, based on the total mass of the anode film layer.

[0171] The mass percentage of the conductive agent is within a suitable range, which enhances the electrical contact between the graphite negative electrode active material while not causing a loss in the energy density of the battery due to the inclusion of too much active conductive agent in the negative electrode film layer.

[0172] As an example, the negative electrode current collector has two surfaces opposite in the thickness direction thereof, and the negative electrode film layer is provided on either one or both of the two surfaces of the negative electrode current collector.

[0173] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, a copper foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base layer such as a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0174] In some embodiments, the negative electrode film layer can further include other negative electrode active materials in addition to the above-described graphite negative electrode active material. In some embodiments, the other negative electrode active materials include, but are not limited to, one or more of conventional natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based materials can include one or more of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy materials. The tin-based materials can include one or more of elemental tin, tin oxide, and tin alloy materials.

[0175] In some embodiments, the conductive agent can be selected from at least one of super-p, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0176] In some embodiments, the negative electrode film layer can further optionally include a binder. The binder can be selected from at least one of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0177] In some embodiments, the negative electrode film layer can further optionally include other auxiliary agents, such as a thickening agent (e.g., sodium carboxymethyl cellulose (CMC-Na)) and the like.

[0178] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry on a negative electrode current collector, and after processes such as drying, cold pressing, etc., obtaining the negative electrode sheet.

[0179] [Positive electrode sheet]

[0180] 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, the positive electrode film layer including the positive electrode active material of the first aspect of the present application.

[0181] As an example, the positive electrode current collector has two surfaces opposite in the thickness direction thereof, and the positive electrode film layer is disposed on either one or both of the two opposite surfaces of the positive electrode current collector.

[0182] In some embodiments, the positive electrode current collector can adopt a metal foil or a composite current collector. For example, as the metal foil, an aluminum foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0183] In some embodiments, the positive electrode active material can adopt a positive electrode active material for a battery known in the art. As an example, the positive electrode active material can include at least one of the following materials: lithium-containing phosphate of olivine structure, lithium transition metal oxide, and a modified compound of each thereof. However, the present application is not limited to these materials, and other conventional materials that can be used as a positive electrode active material for a battery can also be used. These positive electrode active materials can be used alone only or in combination of two or more. Among them, examples of the lithium transition metal oxide can include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (which can also be referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (which can also be referred to as NCM 523 ), LiNi 0.5Co 0.25 Mn 0.25 O2(also can be referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2(also can be referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2(also can be referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2), and modified compounds thereof. Examples of lithium-containing phosphates of olivine structure can include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4(also can be referred to as LFP)), a composite of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite of lithium manganese iron phosphate and carbon.

[0184] In some embodiments, the positive electrode film layer further optionally includes a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene-fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene-fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0185] In some embodiments, the positive electrode film layer further optionally includes a conductive agent. As an example, the conductive agent can include at least one of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0186] In some embodiments, the positive electrode tab can be prepared by dispersing the above-mentioned components for preparing the positive electrode tab, such as the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on a positive electrode current collector, and after processes such as drying, cold pressing, and the like, obtaining the positive electrode tab.

[0187] [Electrolyte]

[0188] The electrolyte plays a role of conducting ions between the positive electrode tab and the negative electrode tab. The type of the electrolyte is not specifically limited in the present application and can be selected as needed. For example, the electrolyte can be in a liquid state, a gel state, or a full solid state.

[0189] In some embodiments, the electrolyte employs an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0190] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorobisoxalate borate, lithium bisoxalate borate, lithium difluorobisoxalate phosphate, and lithium tetrafluorobisoxalate phosphate.

[0191] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclobutane sulfone, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0192] In some embodiments, the electrolyte solution can further optionally include an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can further include an additive capable of improving certain performance of the battery, such as an additive for improving overcharge performance of the battery, an additive for improving high-temperature or low-temperature performance of the battery, etc.

[0193] [Separator]

[0194] In some embodiments, the secondary battery further includes a separator. The type of the separator is not particularly limited in the present application, and any known porous structure separator having good chemical stability and mechanical stability can be used.

[0195] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single layer film or a multi-layer composite film, and is not particularly limited. When the separator is a multi-layer composite film, the materials of the respective layers can be the same or different, and are not particularly limited.

[0196] In some embodiments, the positive electrode tab, the negative electrode tab, and the separator can be made into an electrode assembly through a winding process or a stacking process.

[0197] In some embodiments, the secondary battery can include an outer package. The outer package can be used to package the above-mentioned electrode assembly and the electrolyte.

[0198] In some embodiments, the outer package of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic, and as plastic, polypropylene, polybutylene terephthalate, and polybutylene succinate, etc. can be listed.

[0199] The shape of the secondary battery is not particularly limited, and can be cylindrical, square, or any other shape. For example, Figure 1 is a square structure as an example of a secondary battery 5.

[0200] In some embodiments, referring to Figure 2 , the outer package can include a housing 51 and a cover plate 53. The housing 51 can 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 housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be provided on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator can form an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is packaged 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, and the skilled person can select according to the specific actual needs.

[0201] In some embodiments, the secondary battery can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, and the specific number can be selected by the skilled person according to the application and capacity of the battery module.

[0202] Figure 3 is a battery module 4 as an example. Referring to Figure 3 , in the battery module 4, a plurality of secondary batteries 5 can be arranged in sequence along the length direction of the battery module 4. Of course, it can also be arranged in any other way. Further, the plurality of secondary batteries 5 can be fixed by fasteners.

[0203] Optionally, the battery module 4 can also include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0204] In some embodiments, the above-mentioned battery module can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by the skilled person according to the application and capacity of the battery pack.

[0205] Figure 4 and Figure 5 is a battery pack 1 as an example. Referring to Figure 4 and Figure 5 , the battery pack 1 can include a battery box and a plurality of battery modules 4 arranged in the battery box. The battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be provided on the lower box body 3 to form a closed space for receiving the battery module 4. The plurality of battery modules 4 can be arranged in the battery box in any way.

[0206] In addition, the application also provides a power utilization device, which comprises at least one of the secondary battery, the battery module, or the battery pack provided by the application. The secondary battery, the battery module, or the battery pack can be used as a power supply of the power utilization device, and can also be used as an energy storage unit of the power utilization device. The power utilization device can include a mobile device (such as a mobile phone, a notebook 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 and a satellite, an energy storage system, etc., but is not limited thereto.

[0207] As the power utilization device, the secondary battery, the battery module, or the battery pack can be selected according to the use requirement thereof.

[0208] Figure 6 The power utilization device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirement of high power and high energy density of the secondary battery for the power utilization device, the battery pack or the battery module can be used.

[0209] The device as another example can be a mobile phone, a tablet computer, a notebook computer, etc. The device usually requires thinning, and the secondary battery can be used as a power supply.

[0210] Embodiment

[0211] Hereinafter, the embodiments of the application are described. The embodiments described below are exemplary and are only used to explain the application, and cannot be understood as a limitation of the application. If the specific technology or condition is not indicated in the embodiments, the technology or condition described in the literature in the art or according to the product instruction is used. If the reagent or instrument used is not indicated by the manufacturer, it is a conventional product that can be obtained by market purchase.

[0212] Embodiment 1

[0213] (1) Preparation of graphite negative electrode active material

[0214] The petroleum coke with a volume ratio of 57.3% of the embedded type and the area type structure and a bonding index of 6.2 is coarsely crushed, and then the coarsely crushed material is crushed and sieved. The sieved material is shaped and classified, and a certain content of fine powder is removed in the classification process to obtain a precursor, wherein the fine powder refers to particles with a volume distribution particle size Dv50 of 3-7 μm and a particle size distribution (Dv90-Dv10) / Dv50>1.6, the volume distribution particle size Dv50 of the precursor is 16.2 μm, and the particle size distribution (Dv90-Dv10) / Dv50 of the precursor is 1.78;

[0215] The precursor is graphitized by using an Acheson furnace, the graphitization temperature is 2800 DEG C, the maximum power used in the graphitization is 23000 W (herein, it refers to the actual power used in the Acheson furnace, about 85% of the rated power of the Acheson furnace), the power is kept unchanged for 40 h, then the surface temperature of the graphite crucible of the Acheson furnace is cooled to 200 DEG C, and an intermediate product is obtained;

[0216] The obtained intermediate product is screened and de-magnetized to obtain the graphite negative electrode active material. The graphitization degree of the graphite negative electrode active material is 88%, the oil absorption value is 43 ml / 100g, the specific surface area is 0.92 m 2 / g, and the Dv50 is 14.8 µm.

[0217] (2) Preparation of the negative electrode sheet

[0218] The graphite negative electrode active material prepared above, the conductive agent Super P, the thickening agent carboxymethyl cellulose CMC, and the binder styrene-butadiene rubber SBR are mixed in a dry material mass ratio of 96:1:1.2:1.8, then a solvent deionized water is added, and the system is stirred to be uniform under the action of a vacuum stirrer, so that a negative electrode slurry is obtained; the negative electrode slurry is uniformly coated on a negative electrode current collector copper foil, and then dried, cold-pressed, and cut to obtain a negative electrode sheet. The compaction density of the negative electrode sheet is 1.50 g / cm 3 , and the area density is 9.6 mg / cm 2 .

[0219] (3) Preparation of the positive electrode sheet

[0220] The positive electrode active material lithium iron phosphate (LFP), the conductive agent Super P, and the binder polyvinylidene fluoride are mixed in a mass ratio of 97:1:2, a solvent N-methyl pyrrolidone is added, and the system is stirred to be uniform under the action of a vacuum stirrer, so that a positive electrode slurry is obtained; the positive electrode slurry is uniformly coated on a positive electrode current collector aluminum foil, and then dried, cold-pressed, and cut to obtain a positive electrode sheet. The compaction density of the positive electrode sheet is 2.50 g / cm 3 , and the area density is 19.7 mg / cm 2 .

[0221] (4) Preparation of the electrolyte

[0222] In an argon atmosphere glove box with water content <10 ppm, ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain an organic solvent, then a fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L, and vinylene carbonate is added to the above solution, and the mass content of the vinylene carbonate in the electrolyte is 2%.

[0223] (5) Preparation of the separator film

[0224] A polypropylene film is used as the separator film.

[0225] (6) Preparation of the lithium ion battery

[0226] The positive electrode sheet, the separator film, and the negative electrode sheet are stacked in order with the separator film between the positive electrode sheet and the negative electrode sheet to play a separating role, and then the electrode assembly is obtained by winding. The electrode assembly is placed in an outer package, electrolyte is injected after drying, and the lithium ion battery is obtained after processes such as vacuum packaging, standing, formation, and shaping.

[0227] Example 2-3 is basically the same as Example 1, except that the volume ratio of mosaic and regional structures in the raw material, the bonding index of the raw material, the maximum power of graphitization treatment, and the particle size distribution (Dv90-Dv10) / Dv50 of the precursor are adjusted, as shown in Table 1.

[0228] Comparative Example 1-3 is basically the same as Example 1, except that the volume ratio of mosaic and regional structures in the raw material, the bonding index of the raw material, the maximum power of graphitization treatment, and the particle size distribution (Dv90-Dv10) / Dv50 of the precursor are adjusted, as shown in Table 1.

[0229] Table 1

[0230]

[0231] Performance test

[0232] 1. Filtration time of the negative electrode slurry

[0233] First, determine the filtration screen of 200 meshes, and cut the filtration screen into 25 cm*25 cm with scissors. Find a clean 500 ml beaker and determine that the beaker is clean. Fold the 150 mesh filtration screen into a triangle, pour 500 ml of slurry from above the filtration screen, pour it all at once, and start recording the time when the slurry starts to flow from the tip of the filter screen into the beaker. Record the filtration time of 300 ml.

[0234] 2. Cycle performance test of the secondary battery at 60°C

[0235] At 60°C, charge the batteries of each of the above examples and comparative examples at 1C constant current to a voltage of 3.65V, then charge at 3.65V constant voltage until the current is ≤0.05C, then discharge the battery at 1C constant current to a voltage of 2.5V, which is one charge and discharge process, and record the discharge capacity C1 of the first cycle. Repeat the charging and discharging cycles until the battery capacity decays to 80% of the initial capacity C1, stop the test, and record the number of cycles.

[0236] 3. Storage performance of the secondary battery at room temperature

[0237] The charge-discharge test was carried out in an environment of 25°C, charged at 1C constant current to 3.65V, then charged at 3.65V constant voltage to current≤0.05C, and then discharged the battery at 1C constant current to 2.5V, which was one charge-discharge process, and the discharge capacity of the first cycle was recorded, that is, the initial discharge capacity, denoted as C0. Then the battery was placed in an environment of 60°C for different times, and the residual capacity C1 was tested every 30 days at 25°C, which was one storage period, and the discharge capacity after the first storage was recorded. Subsequently, the first storage test process was repeated, and the discharge capacity value during storage was recorded, and the cycle capacity retention rate after 120 days was recorded.

[0238] III. Results

[0239] As can be seen from Table 2, the graphitization degree of the graphite negative electrode active material provided by the embodiments 1-3 is 88%-93%, and the oil absorption value of the graphite negative electrode active material is not more than 50ml / 100g. As can be seen from the comparison of the embodiments 1-3 and the comparative example 1, controlling the oil absorption value of the graphite negative electrode active material to be not more than 50ml / 100g can improve the dispersibility and filterability of the negative electrode slurry, and improve the cycle life and storage performance of the battery. As can be seen from the comparison of the embodiments 1-3 and the comparative examples 2-3, controlling the graphitization degree of the graphite negative electrode active material to be 88%-93% can balance the gram capacity and cycle performance of the graphite negative electrode active material, and the battery balances high energy density and long cycle life, and also can improve the storage performance of the battery.

[0240] As can be seen from the embodiments 1-3, the specific surface area of the graphite negative electrode active material is less than or equal to 1.4m 2 / g, the negative electrode slurry has excellent dispersibility and filterability, the graphite negative electrode active material has high gram capacity, and the secondary battery has excellent cycle stability and storage stability.

[0241] As can be seen from the embodiments 1-3, the volume distribution particle size Dv50 of the graphite negative electrode active material is 12-16μm, the negative electrode slurry has excellent dispersibility and filterability, the graphite negative electrode active material has high gram capacity, and the secondary battery has excellent cycle stability and storage stability.

[0242] Table 2

[0243]

[0244] Note that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and embodiments having substantially the same configuration, function, and effect as the technical idea of the present application are included in the technical scope of the present application. Furthermore, other modes constructed by applying various modifications to the embodiments, or by combining part of the configurations of the embodiments, which can be conceived by those skilled in the art, without departing from the spirit of the present application, are also included in the scope of the present application.

Claims

1. A graphite anode active material, characterized in that, The graphite anode active material has a graphitization degree of 88%-93%, and the oil absorption value of the graphite anode active material does not exceed 50ml / 100g. Based on the total number of particles in the graphite anode active material, the proportion of primary particles in the graphite anode active material is greater than or equal to 85%.

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

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

6.

4. The graphite anode active material according to claim 1, characterized in that, Based on the total number of particles in the graphite anode active material, the proportion of primary particles in the graphite anode active material is 85%-100%.

5. The graphite anode active material according to claim 1, characterized in that, The specific surface area of ​​the graphite anode active material is less than or equal to 1.4 m². 2 / g.

6. The graphite anode active material according to claim 1, characterized in that, The specific surface area of ​​the graphite anode active material is 0.6 m². 2 / g-1.3m 2 / g.

7. The graphite anode active material according to claim 1, characterized in that, The volume distribution particle size Dv50 of the graphite anode active material is 12-16 μm.

8. The graphite anode active material according to claim 1, characterized in that, The volume distribution particle size Dv50 of the graphite anode active material is 13-15 μm.

9. The graphite anode active material according to any one of claims 1 to 8, characterized in that, The graphite anode active material satisfies at least one of the following: (1) The compacted density of the graphite anode active material under a pressure of 49000N is less than or equal to 1.85 g / cm³. 3 ; (2) The tap density of the graphite anode active material is 1.2 g / cm³. 3 -1.4g / cm 3 ; (3) The specific capacity of the graphite negative electrode active material is greater than or equal to 340 mAh / g.

10. The graphite anode active material according to any one of claims 1 to 8, characterized in that, The graphite anode active material satisfies at least one of the following: (1) The compacted density of the graphite anode active material under a pressure of 49000N is 1.70 g / cm³. 3 -1.85g / cm 3 ; (2) The specific capacity of the graphite negative electrode active material is 341mAh / g-347mAh / g.

11. A method for preparing a graphite anode active material, characterized in that, Includes the following steps: Provide raw materials; The raw materials are processed to obtain a precursor; The precursor is graphitized to obtain an intermediate product; The intermediate product is subjected to sieving to obtain a graphite anode active material; the graphitization degree of the graphite anode active material is 88%-93%, and the oil absorption value of the graphite anode active material does not exceed 50ml / 100g. Based on the total volume of the raw material structure, the volume ratio of the mosaic and regional structures is greater than or equal to 50%; The adhesiveness index of the raw material is less than or equal to 10.

12. The preparation method according to claim 11, characterized in that, The raw materials include at least one of petroleum coke and pitch coke.

13. The preparation method according to claim 11, characterized in that, The raw material is petroleum coke.

14. The preparation method according to claim 11, characterized in that, The raw material is needle coke.

15. The preparation method according to claim 11, characterized in that, Based on the total volume of the raw material structure, the volume ratio of the mosaic and regional structures is 50%-65%.

16. The preparation method according to claim 11, characterized in that, The adhesiveness index of the raw material is 1-9.

17. The preparation method according to any one of claims 11 to 16, characterized in that, The precursor satisfies at least one of the following conditions: The precursor has a volumetric particle size distribution (Dv50) of 12 μm-18 μm; and / or, The particle size distribution (Dv90-Dv10) / Dv50 of the precursor is 1.2-1.

8.

18. The preparation method according to any one of claims 11 to 16, characterized in that, The maximum power of the graphitization process is 70%-90% of the rated power of the graphitization equipment.

19. The preparation method according to claim 18, characterized in that, The maximum power of the graphitization treatment is 23000W-25000W; and / or, the constant power time of the graphitization treatment at the maximum power is 10h-50h.

20. The preparation method according to any one of claims 11 to 16, characterized in that, The screening process for the intermediate product specifically includes the following steps: The intermediate product is sieved to remove particles with a maximum particle size Dmax greater than 100 μm, thus obtaining the graphite anode active material.

21. A secondary battery, comprising a negative electrode, characterized in that, The negative electrode sheet includes a negative current collector and a negative electrode film layer formed on at least one surface of the negative current collector, characterized in that the negative electrode film layer includes a graphite negative electrode active material according to any one of claims 1 to 10 or a graphite negative electrode active material prepared by the preparation method according to any one of claims 11 to 20.

22. The secondary battery according to claim 21, characterized in that, The negative electrode film layer includes a conductive agent, and based on the mass of the negative electrode film layer, the mass content of the conductive agent is greater than or equal to 1.5%.

23. The secondary battery according to claim 21, characterized in that, The negative electrode film layer includes a conductive agent, and the mass content of the conductive agent is 1.8%-2.5% based on the mass of the negative electrode film layer.

24. An electrical appliance, characterized in that, The secondary battery includes any one of claims 21 to 23.

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