Lithium ion battery, preparation method thereof and power utilization device

Abstract

The invention discloses a lithium ion battery, a preparation method thereof and an electric device. The lithium ion battery comprises a shell, a battery cell assembly and electrolyte, the battery cell assembly and the electrolyte are arranged in the shell, the battery cell assembly is located in the electrolyte, the battery cell assembly comprises a positive pole piece, a negative pole piece and a diaphragm, the diaphragm is located between the positive pole piece and the negative pole piece, the negative pole piece comprises a negative current collector and a negative membrane layer arranged on at least one side of the negative current collector, and the negative membrane layer is located between the positive pole piece and the negative pole piece. The negative electrode film layer comprises a graphite material, 70% or more of secondary particles of the graphite material are formed by compounding three or more primary particles, and the primary particles are in at least one of a sheet shape and a block shape. Through the arrangement of the graphite material, the surface of the graphite material is loose and porous, lithium embedding channels are rich, rich lithium ion transmission paths can be provided, rapid diffusion and embedding of lithium ions are facilitated, the charging process is accelerated, and the rapid charging performance is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a lithium ion battery, a preparation method thereof and an electric device. BACKGROUND

[0002] The lithium ion battery is widely applied in the fields of electronic consumer goods, energy storage and power, due to its high output voltage, large energy density, high power density, long cycle life and good environmental friendliness.

[0003] With the continuous development of the technology in the application field of the battery, the fast energy supplementing capability of the lithium ion battery is required. SUMMARY

[0004] The present application provides a lithium ion battery, a preparation method thereof and an electric device, which improves the fast energy supplementing capability of the lithium ion battery.

[0005] To solve the above technical problem, the first aspect of the present application provides a lithium ion battery, comprising: a shell, and an electrode assembly and an electrolyte arranged in the shell, the electrode assembly is located in the electrolyte, the electrode assembly comprises a positive electrode sheet, a negative electrode sheet and a separator, the separator is located between the positive electrode sheet and the negative electrode sheet, the negative electrode sheet comprises a current collector and a negative electrode film layer arranged on at least one side of the current collector, the negative electrode film layer comprises a graphite material, 70% or more of secondary particles of the graphite material are composed of three or more primary particles, and the primary particles are at least one of sheet-shaped and block-shaped.

[0006] In the embodiment of the present application, 70% or more of secondary particles of the graphite material are composed of three or more primary particles, and the primary particles are at least one of sheet-shaped and block-shaped, so that the surface of the graphite material is loose and porous, the lithium ion transmission path is rich, which is helpful for the rapid diffusion and embedding of lithium ions, thereby accelerating the charging process and improving the fast charging performance.

[0007] In an embodiment, the average particle size of the primary particles is 5-6 μm.

[0008] By setting the average particle size Dv50 of the primary particles to 5-6 μm, the particle size of the primary particles is small, which can increase the specific surface area of the material, shorten the distance of lithium ion diffusion to the inside of the negative electrode film layer, and accelerate the charging and discharging reaction speed; the particle size distribution range of the primary particles is narrow, which is conducive to forming a relatively dense negative electrode film layer, reducing the internal resistance, and improving the fast charging performance.

[0009] In an embodiment, the volume median particle size of the secondary particles is 10-20 μm.

[0010] By setting the volume median particle size Dv50 of the secondary particles of the graphite material as above, the particle size of the secondary particles is small, which can provide a shorter lithium ion diffusion path, thereby accelerating the migration speed of lithium ions in the charging and discharging process, and is beneficial to improving the fast charging capacity of the battery.

[0011] In an embodiment, the initial weight loss temperature of the graphite material is 710-745℃.

[0012] By setting the initial weight loss temperature of the graphite material as above, the initial weight loss temperature is low, indicating that the surface of the material has higher reaction activity and abundant surface active sites, and lithium ion intercalation / deintercalation is more easily carried out, which is beneficial to obtaining excellent kinetic performance.

[0013] In an embodiment, the weight loss rate of the graphite material between 35℃ and 790℃ is 60%-95%.

[0014] By setting the weight loss rate of the graphite material as above, the graphite material has high reaction activity and good kinetic performance.

[0015] In an embodiment, the oil absorption value of the graphite material is 65-90ml / 100g.

[0016] By setting the oil absorption value of the graphite material as above, the graphite material can effectively absorb and hold electrolyte, which helps to improve the permeability of electrolyte in the graphite material, and is beneficial to accelerating the transmission of lithium ions, thereby improving the fast charging performance.

[0017] In an embodiment, the specific surface area of the graphite material is 1.0-2.0m 2 / g. 2 / g.

[0018] By setting the specific surface area of the graphite material as above, it is beneficial to increase the contact area of the graphite material and the electrolyte, improve the wettability of the electrolyte to the graphite material, and is beneficial to accelerating the transmission of lithium ions; in addition, more active sites can be provided for lithium ion intercalation and deintercalation, which is beneficial to accelerating the diffusion speed of lithium ions in the graphite material, shortening the migration time of lithium ions during fast charging, and improving the fast charging capacity.

[0019] In an embodiment, the first delithiation capacity of the graphite material is 340-358mAh / g.

[0020] By setting the gram capacity of the graphite material as above, the graphite material can store more energy, which is beneficial to maintaining a high energy density of the lithium ion battery, and its kinetics can be maintained at a high level.

[0021] To solve the above technical problems, the second aspect of the present application provides a preparation method of a lithium ion battery, comprising: sequentially stacking a negative electrode sheet, a separator and a positive electrode sheet to form an electric core assembly; placing the electric core assembly in a shell; and injecting an electrolyte into the shell and sealing to form a lithium ion battery; wherein the negative electrode sheet comprises a current collector and a negative electrode film layer arranged on at least one side of the current collector, the negative electrode film layer comprises a graphite material, and the preparation method of the graphite material comprises: providing first calcined coke fine powder, the volume median particle size of the first calcined coke fine powder being 5-6 μm; granulating the first calcined coke fine powder using a binder to form a first precursor; performing graphitization treatment on the first precursor to form a graphitized product; and performing coating treatment on the graphitized product using a coating agent to form the graphite material; 70% or more of the secondary particles of the graphite material are composed of three or more primary particles, and the primary particles are at least one of a sheet shape and a block shape.

[0022] In the process of preparing the graphite material, the first calcined coke fine powder with a small volume median particle size Dv50 is used as a raw material to form the graphite material through granulation, graphitization and other treatments, so that a graphite material with small particle size can be obtained, the energy consumption is relatively low, the cost is reduced, the surface of the graphite material is kept loose and porous, the lithium ion transmission path is rich, the end group ratio is high, the lithium ions can be quickly diffused and embedded, the charging process is accelerated, and the fast charging performance is improved.

[0023] In an embodiment, the step of providing the first calcined coke fine powder specifically comprises: crushing the calcined coke to obtain calcined coke powder and second calcined coke fine powder; wherein the volume median particle size of the calcined coke powder is 7-17 μm, and the volume median particle size of the second calcined coke fine powder is 2-6 μm; and grading the second calcined coke fine powder to obtain the first calcined coke fine powder.

[0024] According to Jacob's law (broken vase theory), the material breaking process is uncontrollable and large particles and small particles can be naturally obtained; during the crushing process of the calcined coke, the calcined coke powder with a large particle size and the second calcined coke fine powder with a small particle size are naturally obtained, the calcined coke powder with a large particle size can be used as a raw material for preparing other substances, the utilization rate of the calcined coke is high, and the cost is reduced. It can also be understood that the raw material for preparing other substances is the calcined coke powder with a Dv50 of 7-17 μm, the calcined coke powder is obtained by crushing the calcined coke, the second calcined coke fine powder is a byproduct, and the byproduct is used to prepare the graphite material, thereby realizing the reuse of waste materials. Since the calcined coke is calcined, the volatile components with low molecular weight can be removed, the adhesion between particles is low, that is, the adhesion between particles of the obtained second calcined coke fine powder is low, the first calcined coke fine powder with a target particle size can be obtained by grading the second calcined coke fine powder, and the yield is high.

[0025] In an embodiment, the first precursor has a volume median particle size of 12-16 μm.

[0026] The volume median particle size Dv50 of the first precursor formed by granulation is set as above, which can increase the specific surface area of the graphite material, thereby providing more active sites for lithium ion intercalation, and can also shorten the diffusion path of lithium ions, which is conducive to achieving fast lithium ion transmission; at the same time, the particle size distribution is relatively narrow, and the relatively uniform particle size distribution helps to maintain effective contact between the electrolyte and the graphite material, promotes uniform intercalation and deintercalation of lithium ions, and is conducive to improving the performance of the battery.

[0027] In an embodiment, the mass ratio of the binder to the first fine calcined coke is (1-2):10.

[0028] By setting the mass ratio of the binder to the first fine calcined coke as above, the first fine calcined coke is fully bonded to form a first precursor with a stable structure, and the particle size distribution of the first precursor formed by granulation is relatively uniform and the particle structure is stable.

[0029] In an embodiment, the binder includes at least one of pitch and resin.

[0030] The pitch and / or resin has adhesion, which can maintain good adhesion at different temperatures, helps the first precursor to aggregate to form particles, and can maintain a stable structure in subsequent processing. In addition, pitch has a relatively low cost, which is conducive to reducing the overall manufacturing cost.

[0031] In an embodiment, the mass ratio of the graphitized product to the coating agent is 100:(2-15).

[0032] By setting the mass ratio of the graphitized product to the coating agent as above, the additive of the coating agent is relatively appropriate, which can maintain the pores between the graphite particles while forming a coating layer on the surface of the particles, maintain the stability of the structure of the graphite material, and improve the transmission dynamics of lithium ions on the surface of the graphite particles.

[0033] In an embodiment, the coating agent includes at least one of pitch, liquid phase residual oil, and phenolic resin.

[0034] By selecting the above-mentioned materials as the coating agent, amorphous carbon is formed after carbonization, which can effectively improve the surface conductive network of the graphitized product, promote the rapid migration of lithium ions, and thereby improve the fast charging performance of the battery.

[0035] To solve the above technical problems, the third aspect of the present application provides a power utilization device including a lithium ion battery as any one of the above or a lithium ion battery prepared by the preparation method of any one of the above.

[0036] The electric device has at least the same advantages as the lithium ion battery or the lithium ion battery prepared by the preparation method of the lithium ion battery.

[0037] The above description is only a summary of the technical solutions of the present application. In order to make the technical means of the present application more clear and understandable, the content of the specification can be implemented, and in order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the following specific embodiments of the present application will be described. BRIEF DESCRIPTION OF DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings needed in the embodiment description. Obviously, the drawings in the following description are only some embodiments of the present application, and those skilled in the art can obtain other drawings according to these drawings without creative labor.

[0039] Figure 1 is a structural schematic diagram of the lithium ion battery provided by the embodiments of the present application;

[0040] Figure 2 is a decomposition structural schematic diagram of the battery monomer provided by the embodiments of the present application;

[0041] Figure 3 is an observation diagram of the graphite material provided by the embodiments of the present application under 1000X magnification of scanning electron microscope (SEM);

[0042] Figure 4 is a flowchart of the preparation method of the lithium ion battery provided by the embodiments of the present application;

[0043] Figure 5 is a flowchart of the preparation method of the graphite material in the method shown in the above; Figure 4

[0044] Figure 6 is a structural schematic diagram of the vehicle provided by the embodiments of the present application. DETAILED DESCRIPTION

[0045] In order to make the purposes, technical solutions and effects of the present application more clear and definite, the following will describe the embodiments of the technical solutions of the present application in detail with reference to the drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present application, therefore only as examples, and cannot limit the protection scope of the present application.

[0046] ​Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of this application; the use of the terms "including," "comprising," or "having" and variations thereof herein is intended to be broad and encompass the terms "consisting of" and "consisting essentially of" and variations thereof, unless otherwise noted.

[0047] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the term "a plurality of" refers to two or more (including two), and similarly, "a plurality of groups" refers to two or more groups (including two groups), and "a plurality of pieces" refers to two or more pieces (including two pieces), unless otherwise explicitly and specifically limited.

[0048] Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearances of the phrase that the phrase in the specification do not necessarily all refer to the same embodiment, nor are they necessarily mutually exclusive or alternative embodiments to one another. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0049] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the three cases of A alone, A and B together, and B alone. In addition, the character " / " in this paper generally represents that the front and rear associated objects are a "or" relationship.

[0050] Quantities, ratios, and other numerical values are presented herein in a range format. It is to be understood that such range format is used merely for the convenience of the reader and is not intended to limit the actual scope of such quantities, ratios, and other numerical values. It is to be further understood that such a range format is used merely for the convenience of the reader and is not intended to limit the actual scope of such quantities, ratios, and other numerical values, which will be encompassed by the description below.

[0051] If not otherwise specified, all steps of the present application can be carried out sequentially, randomly or in parallel, preferably sequentially. For example, the method comprises steps (a) and (b) means that the method can comprise steps (a) and (b) sequentially, steps (b) and (a) sequentially, or steps (a) and (b) in parallel. For example, the method can further comprise step (c) means that step (c) can be added to the method in any order. For example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0052] With the continuous development of the technology in the field of battery applications, the fast energy supply capability of lithium ion batteries is required. Graphite material is usually used as the negative electrode material of lithium ion batteries, and the performance of graphite material affects the fast energy supply capability of lithium ion batteries.

[0053] In view of this, the embodiments of the present application provide a lithium ion battery and a preparation method thereof and an electric device, so as to improve the fast energy supply capability of the lithium ion battery.

[0054] Please refer to Figure 1 , Figure 1 is a structural schematic diagram of a lithium ion battery provided by the embodiments of the present application.

[0055] The lithium ion battery 100 comprises a box body 10 and a battery monomer 20, and the battery monomer 20 is accommodated in the box body 10.

[0056] The box body 10 is used to provide an accommodation space for the battery monomer 20, and the box body 10 can adopt various structures. In some embodiments, the box body 10 can comprise a first part 11 and a second part 12, the first part 11 and the second part 12 are mutually covered, and the first part 11 and the second part 12 jointly define an accommodation space for accommodating the battery monomer 20. The second part 12 can be a hollow structure with one end open, and the first part 11 can be a plate-shaped structure, the first part 11 is covered on the open side of the second part 12, so that the first part 11 and the second part 12 jointly define the accommodation space; the first part 11 and the second part 12 can also be hollow structures with one side open, and the open side of the first part 11 is covered on the open side of the second part 12. Of course, the box body 10 formed by the first part 11 and the second part 12 can be various shapes, such as a cylinder, a cuboid, etc.

[0057] In the lithium ion battery 100, the battery cells 20 can be multiple, and the multiple battery cells 20 can be connected in series, in parallel, or in a mixed manner. The mixed manner means that the multiple battery cells 20 are connected in series and in parallel. The multiple battery cells 20 can be directly connected in series, in parallel, or in a mixed manner, and the whole of the multiple battery cells 20 is accommodated in the box 10. Of course, the lithium ion battery 100 can also be in the form of multiple battery cells 20 connected in series, in parallel, or in a mixed manner to form a battery module, and multiple battery modules are connected in series, in parallel, or in a mixed manner to form a whole and are accommodated in the box 10.

[0058] The lithium ion battery 100 can further include other structures, for example, the lithium ion battery 100 can further include a current collection component for realizing electrical connection between the multiple battery cells 20.

[0059] Each battery cell 20 can be a secondary battery. The battery cell 20 can be in the shape of a cylinder, a flat body, a cuboid, or other shapes.

[0060] Please refer to Figure 2 , Figure 2 is a schematic diagram of a disassembled structure of a battery cell provided by an embodiment of the present application.

[0061] The battery cell 20 refers to the smallest unit of the lithium ion battery 100. As shown in Figure 2 , the battery cell 20 includes an end cover 21, a shell 22, a cell assembly 23, and other functional components.

[0062] The end cover 21 refers to a component that covers the opening of the shell 22 to isolate the internal environment of the battery cell 20 from the external environment. Without limitation, the shape of the end cover 21 can be adapted to the shape of the shell 22 to fit the shell 22. Alternatively, the end cover 21 can be made of a material with certain hardness and strength (such as aluminum alloy), so that the end cover 21 is not easy to deform when subjected to extrusion and collision, so that the battery cell 20 can have higher structural strength, and the stability can also be improved.

[0063] The end cover 21 can be provided with functional components such as an electrode terminal 21a. The electrode terminal 21a can be used to electrically connect with the cell assembly 23 for outputting or inputting the electrical energy of the battery cell 20. In some embodiments, the end cover 21 can also be provided with a pressure relief mechanism for relieving the internal pressure of the battery cell 20 when the internal pressure or temperature of the battery cell 20 reaches a threshold value.

[0064] The material of the end cover 21 can also be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., which is not specially limited in the embodiments of the present application.

[0065] In some embodiments, an insulating member can be further provided on the inner side of the end cover 21, which can be used to isolate the electrical connection components in the shell 22 from the end cover 21 to reduce the risk of short circuit. For example, the insulating member can be made of plastic, rubber, or the like.

[0066] The shell 22 is a component used to cooperate with the end cover 21 to form an internal environment of the battery cell 20, wherein the formed internal environment can be used to accommodate the electrode assembly 23, the electrolyte, and other components. The shell 22 and the end cover 21 can be independent components, and an opening can be provided on the shell 22, and the end cover 21 is used to cover the opening to form the internal environment of the battery cell 20. Without limitation, the end cover 21 and the shell 22 can also be integrated, specifically, the end cover 21 and the shell 22 can form a common connecting surface before other components enter the shell, and when it is necessary to seal the internal environment of the shell 22, the end cover 21 is used to cover the shell 22. The shell 22 can be of various shapes and sizes, such as a cuboid, a cylinder, a hexagonal prism, etc. Specifically, the shape of the shell 22 can be determined according to the specific shape and size of the electrode assembly 23. The material of the shell 22 can be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and the present application does not make special limitations thereto.

[0067] The electrode assembly 23 is a component in which electrochemical reactions occur in the battery cell 20. One or more electrode assemblies 23 can be contained in the shell 22. The electrode assembly 23 includes a positive electrode sheet, a negative electrode sheet, and a separator, and the separator is located between the positive electrode sheet and the negative electrode sheet, and the positive electrode sheet and the negative electrode sheet are wound or stacked to form the electrode assembly 23. The positive electrode sheet and the negative electrode sheet have a portion of active material constituting the main body of the electrode assembly 23, and a portion of the positive electrode sheet and the negative electrode sheet without active material each constitutes a tab 23a. The positive and negative tabs can be located at one end of the main body or at two ends of the main body, respectively. In the charging and discharging process of the lithium ion battery 100, the positive and negative active materials react with the electrolyte, and the tab 23a is connected to the electrode terminal 21a to form a current loop.

[0068] In an embodiment, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one side of the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material.

[0069] The positive electrode current collector can be a metal foil or a composite positive electrode current collector. Optionally, aluminum foil can be used as the metal foil. Optionally, the composite positive electrode current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite positive electrode current collector can be formed by forming a metal material on the polymer material substrate; the metal material may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy; the polymer material may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0070] Positive electrode active materials include, but are not limited to, one or more of lithium transition metal oxides, lithium phosphates with olivine structures, and their respective modified compounds.

[0071] Optionally, the positive electrode active material may include materials with the general formula Li a Ni b Co c M d O e A f One or more of lithium transition metal oxides and their modified compounds. 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, M includes one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A includes one or more of N, F, S and Cl.

[0072] Optionally, the lithium transition metal oxide may include one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds.

[0073] Optionally, the lithium phosphate with an olivine structure may include one or more of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composites, and their respective modified compounds.

[0074] Optionally, the positive electrode active material may include LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 0.6 Co 0.2 Mn0.2 O2(NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.85 Co 0.15 Al 0.05 one or more of O2, LiFePO4, and LiMnPO4.

[0075] In an embodiment, the negative electrode tab includes a negative electrode current collector and a negative electrode film layer disposed on at least one side of the negative electrode current collector.

[0076] The negative electrode current collector can be a metal foil or a composite negative electrode current collector. Optionally, as the metal foil, a copper foil can be used. Optionally, the composite negative electrode 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 negative electrode current collector can be formed by forming a metal material on a polymer material base material; the metal material can include at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, and the polymer material can include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0077] Referring to Figure 3 , Figure 3 is a scanning electron microscope (SEM) observation image of the graphite material at 1000X magnification provided by an embodiment of the present application.

[0078] The negative electrode film layer includes a graphite material, 70% or more of secondary particles of the graphite material are composed of three or more primary particles, and the primary particles are at least one of a sheet shape and a block shape.

[0079] The primary particle refers to a particle directly formed in an initial stage of formation of the graphite material, without a subsequent aggregation or recombination process. The secondary particle refers to a particle restructured by interaction of the primary particles. When the morphology of the primary particle is a sheet shape, the primary particle has two dimensions (length and width) that are relatively large in size compared to a third dimension (thickness). When the morphology of the primary particle is a block shape, the primary particle has a three-dimensional shape close to an isometric shape or an irregular shape, without a clear flatness or extension direction; compared to the sheet shape, the block shape has balanced dimensions, with a small difference between the thickness and the other two dimensions. The primary particles are combined by chemical force.

[0080] The test method for the proportion of secondary particles of the graphite material composed of three or more primary particles is as follows: 1 g of graphite powder is uniformly dispersed by a gas flow dispersion device, and a scanning electron microscope is used to take a photo of the uniformly dispersed particles for observation of the morphology; AI recognition or manual recognition is performed on the secondary particles by image intelligent recognition software to obtain the number A of secondary particles (≥3 primary particles) and the total number B of particles, and A / B is the proportion of secondary particles.

[0081] The graphite material is provided as described above in the embodiments of the present application, the surface of the graphite material is loose and porous, the lithium insertion channel is rich, the lithium ion transmission path is rich, the rapid diffusion and insertion of lithium ions are facilitated, and thus the charging process is accelerated and the fast charging performance is improved.

[0082] In an embodiment, the average particle size Dv50 of the primary particles is 5-6 μm.

[0083] The test method for the average particle size of the primary particles is as follows: the negative electrode active material is tested by a scanning electron microscope, and then tested according to the standard JY / T010-1996, and the sample morphology is observed. AI recognition of the primary particles is performed by image intelligent recognition software, the particle contour, particle number, number, area, maximum caliper diameter, average number, and manual intervention are provided. The average particle size of the primary particles = the sum of all measured primary particle sizes / the sum of all measured primary particle numbers.

[0084] By setting the average particle size of the primary particles to 5-6 μm, the particle size of the primary particles is small, the specific surface area of the material is increased, the distance of lithium ion diffusion into the negative electrode film layer is shortened, and the charging and discharging reaction speed is accelerated; the particle size distribution range of the primary particles is narrow, which is conducive to forming a relatively dense negative electrode film layer, reducing the internal resistance, and improving the fast charging performance.

[0085] The average particle size of the primary particles can be 5 μm, 5.1 μm, 5.2 μm, 5.3 μm, 5.4 μm, 5.5 μm, 5.6 μm, 5.7 μm, 5.8 μm, 5.9 μm, 6 μm, etc., or a range formed by any two of the above values, for example, 5-5.8 μm, 5.1-5.9 μm, etc.

[0086] In an embodiment, the volume median particle size Dv50 of the secondary particles is 10-20 μm.

[0087] The volume median particle size Dv50 represents the particle size at which the cumulative volume distribution reaches 50%. By setting the volume median particle size Dv50 of the secondary particles of the graphite material as described above, the particle size of the secondary particles is small, which can provide a shorter lithium ion diffusion path, thereby accelerating the migration speed of lithium ions during charging and discharging, and is beneficial to improving the fast charging capability of the battery. The volume median particle size Dv50 of the secondary particles of the graphite material can be 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, etc., or a range of any two of the above values, such as 10 μm-15 μm, 14 μm-19 μm, etc.

[0088] In an embodiment, the initial weight loss temperature of the graphite material is 710-745 °C.

[0089] The initial weight loss temperature is the temperature corresponding to the intersection of the tangent at the horizontal before the step of the thermogravimetric analysis curve and the tangent at the maximum weight loss rate. That is, the initial weight loss temperature of the graphite material is obtained according to the thermogravimetric analysis curve of the graphite material. Optionally, the thermal gravimetric analysis test of the carbon material can be carried out according to JY / T 014-1996. Optionally, the test method of the thermogravimetric analysis curve: 10±0.05 mg of the graphite negative electrode active material is weighed and placed in a flat-bottomed crucible, shaken uniformly, opened, the sweeping gas is air, and the airflow rate is 60 mL / min, the temperature rising rate is 5 °C / min, and the differential scanning thermal gravimetric analysis is carried out in the range of 35-950 °C to obtain the thermogravimetric (TG) analysis curve of the graphite negative electrode active material; wherein the test instrument can be a NETZSCH STA449F3 type synchronous thermal analyzer of NETZSCH Instruments GmbH, Germany.

[0090] By setting the initial weight loss temperature of the graphite material as described above, the graphite material has high reactivity and good kinetic performance; a lower initial weight loss temperature indicates that the material surface has higher reactivity and rich surface active sites, and lithium ion intercalation / deintercalation is more easily carried out, which is beneficial to obtaining excellent kinetic performance.

[0091] The initial weight loss temperature of the graphite material can be 710 °C, 715 °C, 720 °C, 725 °C, 730 °C, 735 °C, 740 °C, 745 °C, etc., or a range of any two of the above values, such as 710-730 °C, 720-740 °C, etc.

[0092] In an embodiment, the weight loss rate of the graphite material between 35-790 °C is 60-95%.

[0093] The weight loss rate of the graphite material at a certain temperature refers to the proportion of the loss of the graphite sample at a certain temperature point compared to the initial mass in the thermal gravimetric analysis experiment. The weight loss rate of the graphite material at a certain temperature is obtained from the thermal gravimetric analysis curve of the graphite material. By setting the weight loss rate of the graphite material as described above, the graphite material has high reactivity and good kinetic performance.

[0094] The weight loss rate of the graphite material between 35°C and 790°C can be 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, etc., or a range composed of any two of the above values, for example, 60%-75%, 70%-85%, etc.

[0095] In an embodiment, the oil absorption value of the graphite material is 65ml / 100g-90ml / 100g.

[0096] The oil absorption value refers to the volume of liquid that can be absorbed and retained by unit mass of graphite material, and is a comprehensive index reflecting particle size distribution, surface morphology, and specific surface area. By setting the oil absorption value of the graphite material as described above, the graphite material can effectively absorb and retain electrolyte, which helps to improve the permeability of electrolyte in the graphite material and accelerate the transmission of lithium ions, thereby improving the fast charging performance. The oil absorption value of the graphite material can be 65ml / 100g, 70ml / 100g, 75ml / 100g, 80ml / 100g, 85ml / 100g, 90ml / 100g, etc., or a range composed of any two of the above values, for example, 65ml / 100g-75ml / 100g, 65ml / 100g-90ml / 100g, etc.

[0097] The test method for the oil absorption value can refer to GB / T 3780.2-2017. Alternatively, the test method for the oil absorption value is as follows: a certain mass of graphite material is placed in a mixing cabin, paraffin oil is dropped into the material through a titrator, the torque of the rotor is tested synchronously during the titration process, a torque-oil absorption value curve is obtained, and the oil absorption value corresponding to 70% of the maximum torque value is taken as the test value.

[0098] In an embodiment, the specific surface area of the graphite material is 1.0m 2 / g-2.0m 2 / g.

[0099] Specific surface area refers to the total surface area per unit mass of graphite material. By adjusting the specific surface area of ​​the graphite material as described above, it is beneficial to increase the contact area between the graphite material and the electrolyte, improve the wettability of the electrolyte on the graphite material, and accelerate lithium-ion transport. Furthermore, it provides more active sites for lithium-ion insertion and extraction, which helps to accelerate the diffusion rate of lithium ions in the graphite material, shorten the lithium-ion migration time during fast charging, and improve fast charging capability. The specific surface area of ​​the graphite material can be 1.0 m². 2 / g, 1.1m 2 / g, 1.2m 2 / g, 1.3m 2 / g, 1.4m 2 / g, 1.5m 2 / g, 1.6m 2 / g, 1.7m 2 / g, 1.8m 2 / g, 1.9m 2 / g, 2.0m 2 / g, etc., can also be a range consisting of any two of the above values, for example, 1.0m. 2 / g-1.5m 2 / g, 1.2m 2 / g-1.9m 2 / g etc.

[0100] In one embodiment, the initial delithiation capacity of the graphite material is 340 mAh / g to 358 mAh / g.

[0101] Specific capacity refers to the number of lithium ions that can be intercalated or deintercalated from a unit mass of graphite material. By setting the specific capacity of graphite material as described above, graphite can store more energy, which is beneficial for maintaining a high energy density in lithium-ion batteries and keeping their kinetics at a high level. The larger interlayer spacing of graphite material is conducive to the solid-phase diffusion of lithium ions, thereby promoting the improvement of fast charging capability. The specific capacity of graphite material can be 340mAh / g, 342mAh / g, 344mAh / g, 346mAh / g, 348mAh / g, 350mAh / g, 352mAh / g, 354mAh / g, 356mAh / g, 358mAh / g, etc., or it can be a range of any two of the above values, such as 340mAh / g-350mAh / g, 342mAh / g-354mAh / g, etc.

[0102] Please see Figure 4 and Figure 5 , Figure 4 This is a schematic flowchart of the method for preparing a lithium-ion battery according to an embodiment of this application. Figure 5 yes Figure 4A flowchart of a preparation method of a graphite material in the method shown.

[0103] The application further provides a preparation method of a lithium ion battery, which can be used to prepare the lithium ion battery provided in the above embodiments. The preparation method of the lithium ion battery provided in the application specifically comprises:

[0104] Step S01: sequentially stack the negative electrode sheet, the separator and the positive electrode sheet to form an electric core assembly.

[0105] Specifically, the step of forming the electric core assembly specifically comprises: sequentially preparing the positive electrode sheet and the negative electrode sheet, alternately stacking the positive electrode sheet and the negative electrode sheet, and arranging the separator between the positive electrode sheet and the negative electrode sheet to play a role of isolation, so as to obtain the electric core assembly, which can also be obtained after winding.

[0106] In the embodiment, the negative electrode sheet comprises a current collector and a negative electrode film layer arranged on at least one side of the current collector, the negative electrode film layer comprises a graphite material, and the preparation method of the graphite material comprises:

[0107] Step S011: providing first calcined fine coke, and the volume median particle size Dv50 of the first calcined fine coke is 5-6 μm.

[0108] Step S012: granulating the first calcined fine coke by using a binder to form a first precursor.

[0109] Step S013: graphitizing the first precursor to form a graphitized product.

[0110] Step S014: coating the graphitized product by using a coating agent to form a graphite material; 70% or more of secondary particles of the graphite material are composed of three or more primary particles, and the primary particles are at least one of a sheet shape and a block shape.

[0111] Step S02: placing the electric core assembly in a shell.

[0112] Specifically, the shell is a component for forming an internal environment, and the formed internal environment can be used to accommodate the electric core assembly. The shape of the shell can be determined according to the specific shape and size of the electric core assembly. The material of the shell can be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and the application does not specially limit this.

[0113] Step S03: injecting an electrolyte into the shell and sealing to form a lithium ion battery.

[0114] Specifically, the internal environment formed by the shell is also used to accommodate electrolyte, which affects the performance of the lithium ion battery. The electrolyte provides a path for lithium ions to move between the positive and negative electrode plates, facilitating the charging and discharging process of the battery. The specific composition of the electrolyte is designed as needed.

[0115] The electrolyte is injected into the shell, and the seal is sealed to obtain a battery monomer. After integrating a plurality of battery monomers, a battery module is formed, which can provide higher voltage and capacity, and has a specific function output; then the battery module is installed in the battery box, and a battery management system and the like are usually added to form a battery pack, which is usually a product provided to the user. Alternatively, a plurality of battery monomers can also be directly installed in the box to form a battery pack.

[0116] In the preparation process of the graphite material, the first calcined fine powder with a smaller volume median particle size Dv50 is used as a raw material to form a graphite material through granulation, graphitization and other treatments. The graphite material with smaller particle size can be obtained, which has lower energy consumption, is conducive to reducing cost, maintains the loose and porous surface of the graphite material, and provides rich lithium ion transmission paths. The high end group ratio is helpful for the rapid diffusion and embedding of lithium ions, thereby accelerating the charging process and improving the fast charging performance. In the embodiment of the application, the volume median particle size Dv50 of the first calcined fine powder is 5-6 μm, and the particle size distribution is narrow, which is conducive to forming a graphite material with uniform particle size distribution, improving material performance, and improving consistency and stability.

[0117] The volume median particle size Dv50 of the first calcined fine powder can be 5 μm, 5.1 μm, 5.2 μm, 5.3 μm, 5.4 μm, 5.5 μm, 5.6 μm, 5.7 μm, 5.8 μm, 5.9 μm, 6 μm, or a range formed by any two of the above values, for example, 5-5.8 μm, 5.1-5.9 μm, etc.

[0118] In an embodiment, in step S011, the step of providing the first calcined fine powder specifically includes: crushing the calcined coke to obtain calcined coke powder and second calcined fine powder; wherein the volume median particle size Dv50 of the calcined coke powder is 7-17 μm, and the volume median particle size Dv50 of the second calcined fine powder is 2-6 μm; and the second calcined fine powder is classified to obtain the first calcined fine powder.

[0119] Calcined coke is the product of green coke after calcination process; specifically, green coke is calcined at high temperature in an air-tight environment. Calcined coke can be the product of coal-based green coke calcination, or the product of oil-based green coke calcination. Calcined coke can be semi-calcined, or fully calcined; alternatively, semi-calcined is the product of green coke calcination at 700-900°C, and fully calcined is the product of green coke calcination at about 1300°C. According to Jacob's law (cracked vase theory), the breaking process of materials is uncontrollable, and large and small particles will be naturally obtained; during the crushing process of calcined coke, large-particle calcined coke powder and second calcined coke fine powder of small particle size are naturally obtained, the large-particle calcined coke powder can be used as raw material for preparing other substances, and the utilization rate of calcined coke is high, which is conducive to reducing costs. It can also be understood that the raw material for preparing other substances is calcined coke powder with a Dv50 of 7-17 μm, the calcined coke powder is obtained by crushing the calcined coke, and the second calcined coke fine powder is a byproduct, which is used to prepare graphite materials, realizing the reuse of waste materials. Since the calcined coke is calcined, low-molecular-weight volatile matter can be removed, and the adhesion between particles is low, i.e., the adhesion between particles of the obtained second calcined coke fine powder is low, and the first calcined coke fine powder of target particle size can be obtained by classifying the second calcined coke fine powder, and the yield is high.

[0120] At present, graphite materials are mainly prepared by crushing centimeter-sized coke into smaller aggregate, and then using the smaller aggregate for subsequent granulation, graphitization, coating, etc. to improve the end group ratio and enrich the lithium intercalation channel through granulation to achieve fast lithium deintercalation. However, the existing crushing equipment needs high energy consumption and high cost to crush the coke into aggregate with a particle size of 8-9 μm or less. The present application adopts crushing of calcined coke to obtain calcined coke powder and second calcined coke fine powder, and classifying the second calcined coke fine powder to obtain first calcined coke fine powder with a particle size of 5-6 μm, which has relatively low energy consumption.

[0121] The volume median particle size Dv50 of the calcined coke powder can be 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, etc., or a range formed by any two of the above values, for example, 7-15 μm, 7-10 μm, etc.

[0122] The volume median particle size Dv50 of the second calcined coke fine powder can be 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, etc., or a range formed by any two of the above values, for example, 3-6 μm, 4-6 μm, etc.

[0123] Optionally, the second calcined fine coke accounts for 20%-30% of the mass of the material obtained by crushing the calcined coke. The second calcined fine coke obtained by crushing the calcined coke can account for 20%, 22%, 24%, 26%, 28%, 30%, etc. of the mass, or a range formed by any two of the above values, for example, 24%-30%, 22%-28%, etc.

[0124] Optionally, the second calcined fine coke is classified by a classifier to obtain the first calcined fine coke.

[0125] In an embodiment, the first precursor has a volume median particle size Dv50 of 12-16 μm.

[0126] The volume median particle size Dv50 of the first precursor formed by granulation is set as above, which can increase the specific surface area of the graphite material, thereby providing more active sites for lithium ion intercalation, and can also shorten the diffusion path of lithium ions, which is conducive to achieving fast lithium ion transmission; at the same time, the particle size distribution is relatively narrow, and a relatively uniform particle size distribution helps to maintain effective contact between the electrolyte and the graphite material, promotes uniform intercalation and extraction of lithium ions, and is conducive to improving the performance of the battery. The volume median particle size Dv50 of the first precursor can be 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, etc., or a range formed by any two of the above values, for example, 12-15 μm, 14-16 μm, etc.

[0127] In an embodiment, in step S012, the mass ratio of the binder to the first calcined fine coke is (1-2):10.

[0128] By setting the mass ratio of the binder to the first calcined fine coke as above, the first calcined fine coals are fully bonded to form a first precursor with a stable structure, and the particle size distribution of the first precursor formed by granulation is relatively uniform, and the particle structure is stable.

[0129] The mass ratio of the binder to the first fine calcined coke powder is selected from the above range, the amount of the binder is appropriate, the first fine calcined coke powder is firmly bonded, the bonding is effective in subsequent cell manufacturing and cell application, and the lithium consumption is reduced; and the first precursor formed by bonding the first fine calcined coke powder has appropriate particle size, and does not need to be depolymerized to control the target particle size of 12-16 μm, thereby reducing the problems of increased surface defects of the material particles and increased surface side reaction active sites caused by the depolymerization process. The mass ratio of the binder to the first fine calcined coke powder can be 1:10, 1.1:10, 1.2:10, 1.3:10, 1.4:10, 1.5:10, 1.6:10, 1.7:10, 1.8:10, 1.9:10, 2:10, or a range between any two of the above values, for example, 1:10-1.5:10 or 1.3:10-2:10.

[0130] In an embodiment, in step S012, the binder includes at least one of pitch and resin.

[0131] The pitch and / or resin has viscosity and can maintain good adhesive properties at different temperatures, which helps the first precursor to aggregate to form particles and maintain structural stability in subsequent processing.

[0132] Optionally, in step S012, the softening point of the pitch is 150-250 °C, which is conducive to forming particles with uniform particle size. The softening point of the pitch can be 150 °C, 160 °C, 170 °C, 180 °C, 190 °C, 200 °C, 210 °C, 220 °C, 230 °C, 240 °C, 240 °C, or a range between any two of the above values, for example, 150-210 °C or 170-240 °C.

[0133] Optionally, in step S012, the granulation temperature is 500-700 °C, which is conducive to forming particles with uniform particle size. The granulation temperature can be 500 °C, 520 °C, 540 °C, 560 °C, 580 °C, 600 °C, 620 °C, 640 °C, 660 °C, 680 °C, 700 °C, or a range between any two of the above values, for example, 500-640 °C or 540-680 °C.

[0134] In an embodiment, in step S013, the graphitization of the first precursor includes: graphitizing the second precursor at a temperature of 3000 °C or higher, and performing screening and magnetic removal to form a graphitized product.

[0135] Optionally, the screening is performed using a 200 mesh+325 mesh screen.

[0136] In an embodiment, in step S014, the mass ratio of the graphitized product to the coating agent is 100:(2-15).

[0137] The mass ratio of the graphitized product to the coating agent is set as above, the additive of the coating agent is more appropriate, the pores between the graphite particles are maintained, and the coating agent can form a coating layer on the surface of the particles, maintain the stability of the structure of the graphite material, and improve the transmission dynamics of lithium ions on the surface of the graphite particles.

[0138] The mass ratio of the graphitized product to the coating agent is selected in the above range, the amount of the coating agent is appropriate, the amorphous carbon formed on the surface of the graphitized product is appropriate, the loss of the first coulomb efficiency caused by too much amorphous carbon is reduced, and the particle size of the graphitized product is appropriate, the depolymerization is not ordered, and the problems such as the increase of the surface defect of the particles caused by the depolymerization introduced by the adhesion of the graphitized product, and the increase of the surface side reaction active site are reduced; in addition, the coating layer formed by the coating agent on the surface of the graphite particles is uniform and continuous, which is beneficial to realize high dynamics. The mass ratio of the graphitized product to the coating agent can be 100:2, 100:3, 100:4, 100:5, 100:6, 100:7, 100:8, 100:9, 100:10, 100:11, 100:12, 100:13, 100:14, 100:15, etc., or a range between any two of the above values, for example, 100:(3-10), 100:(5-15), etc.

[0139] In an embodiment, in step S014, the coating agent includes at least one of pitch, liquid phase residual oil, and resin.

[0140] By selecting the above materials as the coating agent, the surface conductive network of the graphitized product can be effectively improved after carbonization, and the rapid migration of lithium ions is promoted, thereby improving the fast charging performance of the battery.

[0141] Optionally, the resin includes phenolic resin.

[0142] Optionally, the residual carbon value of the liquid phase residual oil is 10%-20%. The residual carbon value of the liquid phase residual oil refers to the percentage content of the non-volatile solid carbon remaining after the residual oil is heated, evaporated, and cracked. The residual carbon value of the liquid phase residual oil can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, etc., or a range between any two of the above values, for example, 13%-17%, 15%-20%, etc.

[0143] Optionally, the carbon residue value of the resin is 40%-50%. The carbon residue value of the resin refers to the percentage of non-volatile solid carbon remaining after thermal decomposition of the resin. The carbon residue value of the resin can be 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, etc., or a range formed by any two of the above values, for example, 43%-48%, 42%-45%, etc.

[0144] Optionally, the asphalt includes at least one of solid-phase asphalt and liquid-phase asphalt. The carbon residue value of the solid-phase asphalt is 30%-70%, and the carbon residue value of the solid-phase asphalt refers to the percentage of non-volatile solid carbon remaining after thermal decomposition of the solid-phase asphalt. The carbon residue value of the solid-phase asphalt can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, etc., or a range formed by any two of the above values, for example, 30%-55%, 45%-65%, etc. The carbon residue value of the liquid-phase asphalt is 10%-20%, and the carbon residue value of the liquid-phase asphalt refers to the percentage of non-volatile solid carbon remaining after thermal decomposition of the liquid-phase asphalt. The carbon residue value of the liquid-phase asphalt can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, etc., or a range formed by any two of the above values, for example, 13%-17%, 15%-20%, etc.

[0145] In an embodiment, in step S014, the graphitized product is coated with a coating agent, and after carbonization, a high-kinetic graphite material is obtained. Optionally, the carbonization temperature is 1100°C-1200°C, and the carbonization time is 1h-4h. The carbonization temperature can be 1110°C, 1120°C, 1130°C, 1140°C, 1150°C, 1160°C, 1170°C, 1180°C, 1190°C, 1200°C, etc., or a range formed by any two of the above values, for example, 1120°C-1200°C, 1110°C-1180°C, etc. The carbonization time can be 1h, 2h, 3h, 4h, etc., or a range formed by any two of the above values, for example, 1h-3h, 2h-4h, etc.

[0146] In an embodiment, after step S012, the method further includes: performing shaping treatment on the first precursor to make the surface of the material smooth and improve the compactness of the material accumulation, i.e., improve the vibration, which is beneficial to the uniform distribution of the particle size of the graphite material; and then performing step S013. The shaping treatment refers to changing the shape of the first precursor to the desired geometric shape by strengthening the friction between particles and particles, and particles and the edge wall through the high-speed impact force generated by the high-speed rotation of the grinding block, thereby ensuring the uniformity of the particles.

[0147] In a specific embodiment, the method for preparing a graphite material includes:

[0148] 1) Calcined coke is crushed to obtain a calcined coke powder with Dv50 = 7 μm-17 μm and a second calcined coke fine powder with Dv50 = 2 μm-6 μm.

[0149] 2) The second calcined coke fine powder is separated into a first calcined coke fine powder by a classifier, to obtain a first calcined coke fine powder with Dv50 = 5 μm-6 μm.

[0150] 3) The first calcined coke fine powder is granulated by using pitch, wherein the pitch: the first calcined coke fine powder = 10-20: 100 (mass ratio), to obtain a first precursor with Dv50 = 12 μm-16 μm.

[0151] 4) The first precursor is subjected to high-temperature graphitization treatment, and then is screened and de-magnetized to obtain a graphitized product.

[0152] 5) The graphitized product is mixed with a coating agent, which can be pitch, liquid phase residual oil, phenolic resin, etc., and the liquid phase residual oil (with a carbon residue of 15%) is selected here, wherein the graphitized product: the coating agent = 100: 2-15, and a high-kinetic graphite material is obtained after carbonization.

[0153] The lithium ion battery and the preparation method of the lithium ion battery disclosed in the embodiments of the present application can be used in an electric device using the battery as a power source or various energy storage systems using the battery as an energy storage element. The electric device includes the lithium ion battery provided in the above embodiments or the lithium ion battery prepared by the preparation method of the lithium ion battery provided in the above embodiments. The electric device can be, but is not limited to, a mobile phone, a tablet, a notebook computer, an electric toy, an electric tool, an electric vehicle, an electric car, a ship, a spacecraft, etc. The electric toy can include a fixed or mobile electric toy, such as a game console, an electric car toy, an electric ship toy, an electric plane toy, etc., and the spacecraft can include an airplane, a rocket, a space shuttle, a spacecraft, etc.

[0154] The following embodiments are described by taking a vehicle 1000 as an example for convenience of description. Please refer to Figure 6 , Figure 6 The vehicle provided in the embodiments of the present application is shown in the structure diagram.

[0155] The vehicle 1000 can be a fuel automobile, a gas automobile, or a new energy automobile, and the new energy automobile can be a pure electric automobile, a hybrid automobile, or a range extended automobile, etc. The vehicle 1000 is internally provided with a lithium ion battery 100, which can be arranged at the bottom, head, or tail of the vehicle 1000. The lithium ion battery 100 can be used for power supply of the vehicle 1000, for example, the lithium ion battery 100 can be used as an operating power supply of the vehicle 1000. The vehicle 1000 can further include a controller 200 and a motor 300, and the controller 200 is used to control the lithium ion battery 100 to supply power to the motor 300, for example, to meet the power demand of the vehicle 1000 during starting, navigation, and driving.

[0156] In some embodiments of the present application, the lithium ion battery 100 can not only be used as an operating power supply of the vehicle 1000, but also be used as a driving power supply of the vehicle 1000, to replace or partially replace fuel or natural gas to provide driving power for the vehicle 1000.

[0157] The present application also studies the performance of the lithium ion battery prepared by the preparation method of the lithium ion battery provided by the embodiments of the present application.

[0158] The preparation process of Example 1 is as follows:

[0159] (1) Preparation of graphite material:

[0160] (a) The calcined coke is crushed to obtain a calcined coke powder with Dv50=12 μm and a second calcined coke fine powder with Dv50=3.5 μm.

[0161] (b) The second calcined coke fine powder is separated from the first calcined coke fine powder by a classifier to obtain a first calcined coke fine powder with Dv50=5.0 μm.

[0162] (c) The first calcined coke fine powder is granulated by using pitch, wherein the mass ratio of pitch to the first calcined coke fine powder is 1.5:10, to obtain a first precursor with Dv50=14.5 μm.

[0163] (d) The first precursor is graphitized at a temperature of 3000°C, and is screened by using a 200 mesh+325 mesh screen to obtain a graphitized product after magnetic removal.

[0164] (e) The graphitized product is mixed with a coating agent, and the coating agent is a liquid pitch, and the mass ratio of the graphitized product to the coating agent is 100:6. When carbonized at a temperature of 1150°C for 2 hours, a high-kinetic graphite material is obtained.

[0165] (2) Preparation of negative electrode sheet:

[0166] (a) A negative electrode current collector copper foil with a thickness of 8 μm is obtained.

[0167] (b) The negative active material graphite material, the conductive agent carbon black (Super P), the thickening agent sodium carboxymethyl cellulose, and the binder styrene-butadiene rubber were mixed in a ratio of 96.4:1:1.2:1.4 by weight percentage in the solvent water, and were stirred to prepare a negative active slurry. The negative active slurry was coated on the negative current collector copper foil to form a negative active material layer with a thickness of 75 μm.

[0168] (c) After drying and cold pressing, a negative electrode sheet was obtained.

[0169] (3) Preparation of a positive electrode sheet:

[0170] (a) A positive current collector aluminum foil with a thickness of 13 μm was obtained.

[0171] (b) The positive active material lithium iron phosphate, the conductive agent carbon black, and the binder polyvinylidene fluoride (PVDF) were stirred and dispersed in the dispersant N-methyl pyrrolidone in a ratio of 96:2:2 by mass percentage, and were stirred uniformly to prepare a positive active slurry. The positive active slurry was coated on both surfaces of the positive current collector aluminum foil to form a positive active material layer with a thickness of 90 μm.

[0172] (c) After drying and cold pressing, a negative electrode sheet was obtained.

[0173] (4) Preparation of an electrolyte:

[0174] Ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent, and then LiPF6 was dissolved in the organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0175] (5) Separator:

[0176] A 12 μm polyethylene film was used as the separator.

[0177] (6) Assembly:

[0178] The prepared negative electrode sheet and the positive electrode sheet were stacked in order, with the separator between the positive electrode sheet and the negative electrode sheet to play a separating role, and were wound to obtain a bare cell. Then, the bare cell was inserted into a battery shell, electrolyte was injected after drying, and a lithium ion battery (secondary battery) was obtained through processes such as vacuum packaging, standing, formation, and shaping.

[0179] It should be noted that the SEM image of the graphite material prepared in Example 1 is shown in FIG. 1. Figure 3

[0180] ​The difference between Example 2 to Example 5 and Example 1 is that the ratio of pitch to the first fine calcined coke powder in the granulation step, and the ratio of graphitization product to coating agent in the coating step.

[0181] The difference between Example 6 and Example 7 and Example 1 is that the particle size of the calcined coke powder, the particle size of the second fine calcined coke powder, and the particle size of the first fine calcined coke powder are different.

[0182] The difference between Example 8 and Example 1 is that step (3) of preparing the positive electrode sheet is not performed. Specifically, the negative electrode sheet is dried in a vacuum drying box for standby; using a lithium metal sheet as the counter electrode, a 12 μm polyethylene (PE) film as the separator, and the electrolyte prepared above, a CR2430 type button cell is assembled in an argon glove box.

[0183] The difference between Comparative Example 1 and Example 1 is that in the preparation of the graphite material, step (b) is not performed, and in step (c), the second fine calcined coke powder is granulated with pitch, i.e., the first fine calcined coke powder in step (c) is replaced with the second fine calcined coke powder; and the amount of pitch added is different.

[0184] The difference between Comparative Example 2 and Example 8 is that in the preparation of the graphite material, step (b) is not performed, and in step (c), the second fine calcined coke powder is granulated with pitch, i.e., the first fine calcined coke powder in step (c) is replaced with the second fine calcined coke powder.

[0185] The relevant parameters of each example and each comparative example are tested as follows:

[0186] 1. Specific surface area test.

[0187] According to GB / T 19587-2017, the nitrogen adsorption specific surface area analysis test method is used for testing, and the BET (Brunauer Emmett Teller) method is used for calculation, wherein the nitrogen adsorption specific surface area analysis test can be performed by a Tri-Star 3020 type specific surface area and pore size analyzer of the United States Micromeritics Company.

[0188] 2. Dv50 test.

[0189] According to GB / T 19077-2016 particle size distribution laser diffraction method, a laser particle size analyzer is used for convenient determination. The testing instrument can be a Mastersizer 3000 type laser particle size analyzer of the United Kingdom Malvern Instruments Limited.

[0190] 3. Test method of oil absorption value:

[0191] A certain mass of graphite material is placed in a mixing cabin, and paraffin oil is dropped into the material through a titrator. The torque of the rotor is tested synchronously during the titration process, and a torque-oil absorption value curve is obtained. The oil absorption value corresponding to 70% of the maximum torque value is taken as the test value.

[0192] 4. Test method of thermogravimetric analysis curve.

[0193] The graphite negative active material is weighed and placed in a flat-bottomed crucible, shaken uniformly, and opened to the air. The gas flow rate is 60 mL / min, the heating rate is 5 ℃ / min, and differential scanning thermal gravimetric analysis is performed in the range of 35-950 ℃ to obtain the thermogravimetric (TG) analysis curve and the thermogravimetric differential (DTG) curve of the graphite negative active material.

[0194] 5. Test of first coulomb efficiency of secondary battery.

[0195] The above-prepared secondary battery is formed at 45 ℃, and charged at 0.02 C constant current for 10 h (the charge capacity C0 at this time is recorded). The secondary battery is discharged at 0.2 C constant current to 2.0 V at 25 ℃, and the discharge capacity D0 at this time is recorded. Then it is charged at 0.33 C constant current to 3.8 V, and then charged at constant voltage to a current of 0.05 C, and the charge capacity C1 at this time is recorded. It is discharged at 0.33 C constant current to 2.5 V, and then discharged at 0.33 C constant current to 2.0 V after 5 min of standing, and then discharged at 0.1 C constant current to 2.0 V, and the discharge capacity D1 at this time is recorded. The first coulomb efficiency of the secondary battery (%) = D1 / (C0-D0+C1).

[0196] 6. Test of fast charging performance (charging time) of secondary battery.

[0197] The secondary battery was charged at 0.33C to 3.65V at 25°C, and then charged at a constant voltage to a current of 0.05C, and after standing for 5 min, the secondary battery was discharged at 0.33C to 2.0V, and the actual capacity was recorded as C0. Then the secondary battery was charged at 0.5C0, 1.0C0, 1.5C0, 2.0C0, 3.0C0, 4.0C0, 5.0C0, 7.0C0, and 9.0C0 in turn to 3.65V or 0V negative electrode cut-off potential (whichever is reached first), and after each charging was completed, it was discharged to 2.0V at 1C0, and the negative electrode potential corresponding to 20%, 30%, …, 80% SOC (State of Charge) was recorded at different charging rates, and the charging rate corresponding to the negative electrode potential of 0V at different SOC states was obtained by linear fitting of the charging rate-negative electrode potential curve at different SOC states, which was the charging window at the SOC state, and was recorded as C20% SOC, C30% SOC, C40% SOC, C50% SOC, C60% SOC, C70% SOC, and C80% SOC, respectively. The charging time T of the secondary battery from 20% SOC to 80% SOC was calculated according to the formula (60 / C20% SOC+60 / C30% SOC+60 / C40% SOC+60 / C50% SOC+60 / C60% SOC+60 / C70% SOC+60 / C80% SOC) x 10%, and the unit was min.

[0198] 7. Gravimetric capacity test.

[0199] At 25°C, the prepared button cell was first discharged at a current of 0.15mA to 0.005V, and then discharged at a constant current of 10μA to 0.005V, and the first circle discharge capacity of the button cell was recorded. Then the button cell was charged at a current of 0.3mA to 2.0V, and the first circle charge capacity of the button cell was recorded, and the ratio of the charge capacity to the sample mass was the gravimetric capacity of the material.

[0200]

[0201]

[0202] As can be seen from Comparative Examples 1 to 7 and Comparative Example 1, the graphite material prepared by the preparation method of the graphite material provided in the examples is used to prepare a secondary battery, which is beneficial to improve the fast charging performance, requires shorter charging time, and is also beneficial to improve the initial efficiency of the battery.

[0203] It can be seen by comparing Example 8 with Comparative Example 2 that the graphite material prepared by the preparation method provided in the examples of the present application is used to prepare a button cell, which is beneficial to improve the gram capacity and the performance of the battery.

[0204] The above merely illustrates the embodiments of the present application, and does not limit the patent scope of the present application, and any equivalent structure or equivalent process conversion using the content of the specification and drawings, or direct or indirect application in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A lithium-ion battery, characterized in that, include: The battery includes a housing, a battery cell assembly disposed within the housing, and an electrolyte. The battery cell assembly is located in the electrolyte. The battery cell assembly includes a positive electrode, a negative electrode, and a separator. The separator is located between the positive and negative electrode. The negative electrode includes a current collector and a negative electrode film layer disposed on at least one side of the current collector. The negative electrode film layer includes graphite material. 70% or more of the secondary particles of the graphite material are composed of three or more primary particles. The primary particles are at least one of sheet-like or block-like shapes.

2. The lithium-ion battery according to claim 1, characterized in that, The average particle size of the primary particles is 5μm-6μm.

3. The lithium-ion battery according to claim 1 or 2, characterized in that, The median volumetric particle size of the secondary particles is 10μm-20μm.

4. The lithium-ion battery according to any one of claims 1 to 3, characterized in that, The initial weight loss temperature of the graphite material is 710℃-745℃.

5. The lithium-ion battery according to any one of claims 1 to 4, characterized in that, The weight loss rate of the graphite material is 60%-95% between 35℃ and 790℃.

6. The lithium-ion battery according to any one of claims 1 to 5, characterized in that, The oil absorption value of the graphite material is 65ml / 100g-90ml / 100g.

7. The lithium-ion battery according to any one of claims 1 to 6, characterized in that, The specific surface area of ​​the graphite material is 1.0 m². 2 / g-2.0m 2 / g.

8. The lithium-ion battery according to any one of claims 1 to 7, characterized in that, The initial delithiation capacity of the graphite material is 340 mAh / g-358 mAh / g.

9. A method for preparing a lithium-ion battery, characterized in that, include: A battery cell assembly is formed by sequentially stacking negative electrode plates, a separator, and positive electrode plates; The battery cell assembly is placed inside the housing; as well as An electrolyte is injected into the casing and sealed to form a lithium-ion battery; The negative electrode sheet includes a current collector and a negative electrode film layer disposed on at least one side of the current collector. The negative electrode film layer includes a graphite material, and the preparation method of the graphite material includes: Provide a first calcined coke fine powder, wherein the median particle size of the first calcined coke fine powder is 5μm-6μm; The first calcined coke powder is granulated using a binder to form a first precursor; The first precursor is graphitized to form a graphitized product; The graphitized product is coated with a coating agent to form the graphite material; 70% or more of the secondary particles of the graphite material are composed of three or more primary particles, and the primary particles are at least one of the following: flakes and blocks.

10. The method for preparing a lithium-ion battery according to claim 9, characterized in that, The step of providing the first calcined coke fine powder specifically includes: The calcined coke is pulverized to obtain calcined coke powder and second calcined coke fine powder; wherein the median volume particle size of the calcined coke powder is 7μm-17μm, and the median volume particle size of the second calcined coke fine powder is 2μm-6μm. The second calcined coke fine powder is classified to obtain the first calcined coke fine powder.

11. The method for preparing a lithium-ion battery according to claim 9 or 10, characterized in that, The median particle size of the first precursor is 12 μm-16 μm.

12. The method for preparing a lithium-ion battery according to any one of claims 9 to 11, characterized in that, The mass ratio of the binder to the first calcined coke powder is (1-2):

10.

13. The method for preparing a lithium-ion battery according to any one of claims 9 to 12, characterized in that, The adhesive includes at least one of asphalt and resin.

14. The method for preparing a lithium-ion battery according to any one of claims 9 to 13, characterized in that, The mass ratio of the graphitized product to the coating agent is 100:(2-15).

15. The method for preparing a lithium-ion battery according to any one of claims 9 to 14, characterized in that, The coating agent includes at least one of asphalt, liquid phase residue oil, and phenolic resin.

16. An electrical appliance, characterized in that, The lithium-ion battery includes the lithium-ion battery as described in any one of claims 1 to 8 or the lithium-ion battery prepared by any one of claims 9 to 15.

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