Artificial graphite negative electrode material, preparation method thereof, negative electrode sheet and secondary battery

Abstract

The application provides an artificial graphite negative electrode material, a preparation method of the artificial graphite negative electrode material, a negative electrode sheet and a secondary battery. 4 cm ‑1 ≤B≤1000×10 4 cm ‑1 ; the secondary battery adopting the application can effectively improve the compaction density of the electrode sheet, reduce the expansion phenomenon of the electrode sheet, and further improve the energy density of the battery.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to an artificial graphite anode material and its preparation method, anode sheet and secondary battery. Background Technology

[0002] In recent years, the application of lithium-ion rechargeable batteries has become increasingly widespread, with their extensive use in the new energy vehicle sector. Currently, the main commercially available anode material is graphite. However, the low compaction density and expansion issues of graphite anode sheets limit the improvement of their energy density. Therefore, addressing the compaction density and expansion problems of anode sheets is an urgent issue that needs to be resolved. Summary of the Invention

[0003] To achieve the above objectives, the first aspect of this application provides an artificial graphite anode material, wherein the product of the roughness, powder compaction density, and specific surface area of ​​the artificial graphite anode material is denoted as B, which is 370 × 10⁻⁶. 4 cm -1 ≤B≤1000×10 4 cm -1 .

[0004] This application provides an artificial graphite anode material that can effectively improve the compaction density of the electrode, reduce the electrode expansion phenomenon, and thus improve the energy density of the battery.

[0005] In any embodiment, the Ochro roughness of the artificial graphite anode material is 0.09-0.20, wherein the artificial graphite anode material undergoes micro-oxidation treatment.

[0006] In any embodiment, the powder compaction density of the artificial graphite anode material is 1.7 g / cm³. 3 -2.2g / cm 3 .

[0007] In any embodiment, the specific surface area of ​​the artificial graphite anode material is 1.8 m². 2 / g-4.5m 2 / g.

[0008] In any embodiment, the graphitization degree of the artificial graphite anode material is 91% to 98%; optionally, it is 93% to 97%.

[0009] In any embodiment, the artificial graphite material may be sintered from at least one of petroleum coke, needle coke, and pitch coke.

[0010] The second aspect of the present application provides a preparation method of artificial graphite negative material, comprising: providing coke raw material, the coke raw material is one or more selected from petroleum coke, needle coke and pitch coke, the particle size Dv10 of the coke raw material is 6.0-13.0 μm, or the Dv50 of the coke raw material is 8.0-20.0 μm, or the Dv90 of the coke raw material is 24.0-35.0 μm, the coke raw material is crushed, classified, shaped and treated to remove fine powder to obtain a first product with uniform particle size; the first product obtained in step one is added to a graphitization furnace, heated to 2800-3200 ℃, and an artificial graphite material A is obtained; a rotary kiln is heated to 600-900 ℃, the rotation speed of the furnace tube is 2-6 r / min, and the air flow rate is 1-9 m 3 / h-9 m 3 / h. The artificial graphite material A is fed into the feeding port, the material is heated in the cavity through the rotary feeder, and the artificial graphite negative material is obtained after cooling.

[0011] The third aspect of the present application provides a negative electrode sheet, comprising the artificial graphite negative material provided in the first aspect of the present application or the artificial graphite negative material prepared by the method provided in the second aspect of the present application.

[0012] In any embodiment, the compaction density of the negative electrode sheet is 1.70 g / cm 3 -2.20 g / cm 3 , and optionally 1.85 g / cm 3 -2.10 g / cm 3 .

[0013] The fourth aspect of the present application provides a preparation method of a negative electrode sheet, the artificial graphite negative material or the artificial graphite negative material prepared by the above method is fully stirred and mixed in deionized water to form a uniform negative electrode slurry; the negative electrode slurry is coated on the surface of a negative electrode current collector copper foil, and the negative electrode sheet is obtained after drying and cold pressing, the negative electrode sheet comprises a negative electrode active material layer, the negative electrode active material layer comprises the artificial graphite negative material, and the mass ratio of the artificial graphite negative material to the negative electrode active material layer is greater than 95%, and optionally 96.2-98.5%.

[0014] The fifth aspect of the present application provides a secondary battery, comprising the negative electrode sheet provided in the third aspect of the present application or the negative electrode sheet prepared by the preparation method of the negative electrode sheet provided in the fourth aspect of the present application.

[0015] The sixth aspect of the present application provides an electric device, comprising the secondary battery of the fifth aspect of the present application.

[0016] The above description is only a summary of the technical solutions of the present application. In order to enable a person skilled in the art to better understand the technical means of the present application, the content of the specification can be implemented, and in order to enable the above and other purposes, features and advantages of the present application to be more obvious and easy to understand, the following specific embodiments of the present application will be described. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0018] Figure 1 is a structural schematic diagram of a battery pack provided by an embodiment of the present application;

[0019] Figure 2 is a schematic diagram of a power consumption device using a secondary battery as a power source according to an embodiment of the present application;

[0020] Figure 3 is a photo of the appearance of the pole piece after cold pressing in the process of compaction density test provided by an embodiment of the present application;

[0021] Figure 4 is a photo of the appearance of the pole piece after cold pressing in the process of compaction density test provided by another embodiment of the present application;

[0022] Figure 5 is a pressure vs compaction data curve diagram of the pole piece after cold pressing provided by an embodiment of the present application. DETAILED DESCRIPTION

[0023] Hereinafter, the embodiments of the negative pole piece, the secondary battery and the power consumption device of the present application are specifically disclosed with appropriate reference to the drawings. However, there will be cases of omitting unnecessary detailed description. For example, there will be cases of omitting detailed description of matters well known, repeated description of actually identical structures. This is to avoid the following description from becoming unnecessarily lengthy, facilitating the understanding of those skilled in the art. In addition, the drawings and the following description are provided in order for those skilled in the art to fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0024] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0025] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0026] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0027] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0028] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0029] If not specifically stated, the term "or" in this application is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following satisfy 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).

[0030] [Anode electrode sheet]

[0031] The anode electrode sheet includes an anode current collector and an anode film layer disposed on at least one surface of the anode current collector, the anode film layer including an anode active material.

[0032] As an example, the anode current collector has two surfaces opposite in the thickness direction thereof, and the anode film layer is disposed on either one or both of the two opposite surfaces of the anode current collector.

[0033] In some embodiments, the anode current collector can employ a metal foil or a composite current collector. For example, as the metal foil, a copper foil can be employed.

[0034] One embodiment of the present application provides an artificial graphite anode material, a product of three of an Occhio roughness, a powder compaction density, and a specific surface area of the artificial graphite anode material being denoted as B, 370 x 10 4 cm -1 ≤ B ≤ 1000 x 10 4 cm -1 .

[0035] The Occhio roughness of the graphite particles can be obtained by the Occhio Callisto 3D software, and the specific measurement process is as follows: after the graphite particles to be measured are dispersed, a high-contrast and high-definition picture is obtained by the Occhio Callisto 3D software to divide the specific morphology and boundary of the graphite particles, to determine the particle projection area, and to define a smooth reference by checking the largest inscribed circle of the original outline pixels contained in the corresponding pixel outline. Among them, the inscribed circle with a radius of 80% of the smooth reference radius is continuously inscribed in the particle projection area, and the total area of the inscribed circle is defined as the 80% reference. The ratio of the 80% smooth reference and the particle projection area is between 0 and 1, and the larger the ratio, the closer the surface morphology of the measured particle to smoothness; taking 80% of the largest inscribed circle radius as the reference radius can better define and quantify the final Occhio roughness value. The Occhio roughness of one embodiment of the present application refers to the ratio of 1-(80% smooth reference and particle projection area), which can indicate the sphericity parameter (surface roughness) of the particle material. The larger the Occhio roughness value, the higher the surface roughness of the material.

[0036] In the design process of lithium ion battery, the compaction density = the area density / (the thickness of the electrode sheet after rolling - the thickness of the current collector), unit: g / cm 3 ; the compaction density has a great influence on the performance of lithium ion power battery during the production process. Generally speaking, the greater the compaction density, the higher the capacity of the battery can be made, so the compaction density is also considered as one of the reference indexes of the energy density of the material. When the compaction density is too small, it is not conducive to the embedding and embedding of lithium ions, and the appropriate compaction density can increase the discharge capacity of the battery, reduce the internal resistance, reduce the polarization loss, prolong the cycle life of the battery, and improve the utilization rate of lithium ions.

[0037] The total surface area occupied by 1g of solid is the specific surface area of the substance, and generally the porous material with larger specific surface area has stronger adsorption capacity.

[0038] In an embodiment of the present application, the product of the Rauroscosity, the powder compaction density and the specific surface area of the artificial graphite negative electrode material is denoted as B; wherein the powder compaction density and the specific surface area of the graphite particles have a weak negative correlation, and the graphite particles with high specific surface area have a relatively low powder compaction density to some extent; the specific surface area of the graphite particles and the particle size are negatively correlated, and the smaller the graphite particle size, the larger the corresponding specific surface area of the graphite; and the graphite particle size and the powder compaction density are positively correlated to some extent, the smaller the graphite particle size, the more the fine powder, the greater the rebound after compaction, and the smaller the powder compaction. The artificial graphite negative electrode material provided in an embodiment of the present application has a high specific surface area and surface roughness after micro-oxidation treatment, and also has a high powder compaction density. The specific surface area represents the gas phase adsorption result of the graphite particles in three-dimensional level, the Rauroscosity represents the smoothness of the graphite particles in two-dimensional level, and the value obtained by multiplying the specific surface area, the Rauroscosity and the powder compaction density is compared with that of the graphite material without micro-oxidation treatment, which can better represent the improvement effect of the artificial graphite negative electrode material in the compaction density level. When the value of B is in the interval of 370x10 4 cm -1 ≤ B ≤ 1000x10 4 cm -1 , it is represented that the artificial graphite negative electrode material provided in an embodiment of the present application is in a certain range of Rauroscosity, powder compaction density and specific surface area, and to some extent, it indicates that the artificial graphite negative electrode material has a high powder compaction density, a low rebound degree after pressure relief, a high ultimate compaction density and a small electrode sheet rebound of the electrode sheet prepared therefrom, a high electrode sheet cohesion, an improved electrode sheet compaction density and battery energy density, and a reduced electrode sheet expansion phenomenon. At the same time, the artificial graphite negative electrode material has a high roughness, which is beneficial to improving the adhesion between the negative electrode active material layer and other film layers.

[0039] One embodiment of the present application provides a synthetic graphite negative electrode material with an Ouchterlony roughness of 0.09-0.20, wherein the synthetic graphite negative electrode material is subjected to micro-oxidation treatment.

[0040] In one embodiment of the present application, the micro-oxidation treatment of the synthetic graphite negative electrode material refers to heating the synthetic graphite material after the raw material crushing, shaping, and fine powder removal, and high-temperature graphitization steps in a rotary kiln in an environment with a certain oxidizing atmosphere (such as air) with a temperature range set between 600°C-900°C, a gas flow rate of 1m 3 / h-9m 3 / h. In the prior art, graphite is generally heated in a nitrogen atmosphere to achieve carbonization and calcination. The micro-oxidation treatment of the material provided by the present application in an air atmosphere changes the performance of the graphite. In one embodiment of the present application, the synthetic graphite negative electrode material is subjected to the above-mentioned micro-oxidation treatment by low-temperature heating in an oxidizing gas stream in a rotary kiln. The Ouchterlony roughness of the synthetic graphite negative electrode material after the micro-oxidation treatment is generally slightly higher than that of the conventional graphite negative electrode material. After the micro-oxidation treatment, the specific surface area of the graphite increases, the powder compaction density increases, and the roughness also increases. The product of the Ouchterlony roughness, the powder compaction density, and the specific surface area of the graphite, B, is between 370x104cm -1 ≤B≤1000x104cm -1 , and the cohesion of the graphite also increases.

[0041] One embodiment of the present application provides a synthetic graphite negative electrode material with a powder compaction density of 1.7g / cm 3 -2.2g / cm 3 .

[0042] The powder compaction density of the synthetic graphite negative electrode material provided by the present application is generally slightly higher than that of the conventional graphite negative electrode material, indicating that the negative electrode sheet prepared from the material has higher capacity and energy density under the same conditions.

[0043] One embodiment of the present application provides a synthetic graphite negative electrode material with a specific surface area of 1.8m 2 / g-4.5m 2 / g.

[0044] The surface roughness of the synthetic graphite negative electrode material after the micro-oxidation treatment increases, and the specific surface area value is generally greater than 1.8m 2 / g. The synthetic graphite has a special microporous structure, a large specific surface area, an increased reaction area, and improved utilization of active materials, exhibiting high capacity and high rate performance.

[0045] One embodiment of the present application provides a synthetic graphite negative electrode material, the graphitization degree of the synthetic graphite negative electrode material is 91% to 98%; and optionally 93% to 97%.

[0046] The graphitization degree can be obtained by determining the regularity of the stacking of the carbon network, and the graphitization degree reflects the perfection of the graphite crystal structure, i.e., the regularity of the arrangement of carbon atoms in the graphite structure. The graphitization degree of the synthetic graphite negative electrode material improved by any embodiment of the present application is generally between 91% and 98%, and in practice, the synthetic graphite negative electrode material with a graphitization degree of 93% to 97% is more commonly used.

[0047] One embodiment of the present application provides a synthetic graphite negative electrode material, which can be obtained by sintering at least one of petroleum coke, needle coke and pitch coke.

[0048] Petroleum coke, needle coke and pitch coke are precursors of graphite materials, and needle coke belongs to high-capacity high-pressure dense graphite. The synthetic graphite negative electrode material prepared using needle coke as a precursor has a more obvious improvement in the compaction density; and similar effects are also achieved for non-needle coke, such as petroleum coke and pitch coke.

[0049] One embodiment of the present application provides a preparation method of a synthetic graphite negative electrode material, which includes three steps.

[0050] Step 1: providing coke raw materials, the coke raw materials are selected from one or more of petroleum coke, needle coke and pitch coke, the particle size Dv10 of the coke raw materials is 6.0 μm to 13.0 μm, or the Dv50 of the coke raw materials is 8.0 μm to 20.0 μm, or the Dv90 of the coke raw materials is equal to 24.0 μm to 35.0 μm, the coke raw materials are crushed, for example, using a mechanical mill or a roller mill to crush the coke raw materials, and the crushed coke raw materials are subjected to classification treatment, shaping and fine powder removal treatment to obtain a first product with uniform particle size;

[0051] Step 2: adding the first product obtained in Step 1 into a graphitization furnace, and heating to 2800°C to 3200°C to obtain a synthetic graphite material A;

[0052] Step 3: heating a rotary kiln to 600°C to 900°C, the rotation speed of the furnace tube is 2 r / min to 6 r / min, the air flow rate is 1 m 3 / h to 9 m 3 / h; the synthetic graphite material A is fed into the rotary feeder and then into the cavity for heating treatment, and the synthetic graphite negative electrode material is obtained after cooling.

[0053] After the synthetic graphite material A is obtained by sintering one or more of petroleum coke, needle coke and pitch coke, the synthetic graphite material A is heated to 600°C to 900°C in a rotary kiln, the rotation speed of the furnace tube is 2 r / min to 6 r / min, and the air flow rate is 1 m 3 / h to 9 m 3The artificial graphite material A is heated under a higher oxidation atmosphere at h, and the temperature can be heated between 600-900°C, so that the specific surface area and roughness of the graphite surface increase after the micro-oxidation treatment, and the powder compaction density is improved, and the cohesion of the negative electrode sheet prepared from the artificial graphite material is also improved.

[0054] One embodiment of the present application provides a negative electrode sheet, comprising the artificial graphite negative electrode material provided in any of the above embodiments or the artificial graphite negative electrode material prepared by the method provided in any of the above embodiments.

[0055] One embodiment of the present application provides a negative electrode sheet, wherein the compaction density is 1.70g / cm 3 -2.20g / cm 3 , and optionally 1.85g / cm 3 -2.10g / cm 3 .

[0056] One embodiment of the present application provides a method for preparing a negative electrode sheet, wherein the artificial graphite negative electrode material provided in any of the above embodiments or the artificial graphite negative electrode material prepared by the method provided in any of the above embodiments is fully stirred and mixed in deionized water to form a uniform negative electrode slurry; the negative electrode slurry is coated on the surface of a negative electrode current collector, such as a copper foil, and after drying and cold pressing, a negative electrode sheet is obtained, the negative electrode sheet comprises a negative electrode active material layer, the negative electrode active material layer comprises the artificial graphite negative electrode material, and the mass ratio of the artificial graphite negative electrode material to the negative electrode active material layer is greater than 95%, and optionally 96.2%-98.5%.

[0057] [Positive electrode sheet]

[0058] The positive electrode sheet generally comprises a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, and the positive electrode film layer comprises a positive electrode active material.

[0059] For example, the positive electrode current collector has two opposite surfaces in the thickness direction of itself, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0060] In some embodiments, the positive electrode current collector can employ a metal foil or a composite current collector. For example, as a metal foil, an aluminum foil can be employed. 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 (e.g., a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0061] In some embodiments, the positive electrode active material can employ 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 a lithium-containing phosphate of an olivine structure, a 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 one or two or more can be used in combination. Among them, examples of the lithium transition metal oxide can include, but are not limited to, lithium cobalt oxide (e.g., LiCoO2), lithium nickel oxide (e.g., LiNiO2), lithium manganese oxide (e.g., LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (e.g., LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(also referred to simply as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2(also referred to simply as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2(also referred to simply as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2(also referred to simply as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2(also referred to simply as NCM 811 ), lithium nickel cobalt aluminum oxide (e.g., LiNi 0.85 Co 0.15 Al 0.05O2) and modified compounds thereof, etc. Examples of the lithium-containing phosphate of olivine structure can include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (which can also be referred to simply 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, a composite of lithium manganese iron phosphate and carbon.

[0062] In some embodiments, the cathode 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.

[0063] In some embodiments, the cathode 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.

[0064] In some embodiments, the cathode electrode sheet can be prepared by dispersing the above-mentioned components for preparing the cathode electrode sheet, such as the cathode active material, the conductive agent, the binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a cathode slurry; coating the cathode slurry on a cathode current collector, and after processes such as drying, cold pressing, etc., obtaining the cathode electrode sheet.

[0065] [Electrolyte]

[0066] The kind of the electrolyte is not specifically limited in the present application, and can be selected as needed. For example, the electrolyte can be liquid, gel, or all-solid.

[0067] In some embodiments, the electrolyte is liquid, and includes an electrolyte salt and a solvent.

[0068] 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 bistrifluoromethylsulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoroboric oxalate, lithium difluoroboric bisoxalate, lithium difluorophosphoric bisoxalate, and lithium tetrafluorophosphoric oxalate.

[0069] 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, butanedisulfone, methyl ethyl sulfone, and diethyl sulfone.

[0070] In some embodiments, the sodium salt and the potassium salt are also not particularly limited and can be selected according to actual needs.

[0071] In some embodiments, the electrolyte can also optionally include an additive. As an example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can also include an additive capable of improving certain performance of the battery, such as an additive capable of improving overcharge performance of the battery, an additive capable of improving high-temperature or low-temperature performance of the battery, etc.

[0072] [Separator]

[0073] 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.

[0074] 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 layers can be the same or different, and are not particularly limited.

[0075] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be made into an electrode assembly through a winding process or a stacking process.

[0076] [Secondary battery]

[0077] A secondary battery, also referred to as a rechargeable battery or a storage battery, refers to a battery that can continue to be used by activating the active material through charging after the battery is discharged. Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. During the charging and discharging process of the battery, active ions (e.g., lithium ions) are inserted and extracted between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet, and mainly functions to prevent short circuiting of the positive and negative electrodes, while allowing the active ions to pass through. The electrolyte is between the positive electrode sheet and the negative electrode sheet, and mainly functions to conduct the active ions.

[0078] One embodiment of the present application provides a secondary battery including the negative electrode sheet and the artificial graphite negative electrode material of some embodiments of the present application.

[0079] In some embodiments, the secondary battery can include an outer package. The outer package can be used to encapsulate the electrode assembly and the electrolyte described above.

[0080] In some embodiments, the outer package of the secondary battery can be a hard case, such as a hard plastic case, an aluminum case, a steel case, or the like. 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, polybutylene succinate, and the like can be listed.

[0081] The shape of the secondary battery according to the present application is not particularly limited, and it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 is a square structure of a secondary battery as an example.

[0082] In addition, the present application also provides an electric device including the secondary battery provided by the present application. The secondary battery can be used as a power source of the electric device, or can be used as an energy storage unit of the electric device. The electric 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.

[0083] As the electric device, the secondary battery, the battery module, or the battery pack can be selected according to the use requirement thereof.

[0084] Figure 2 is an electric device as an example. The electric 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 electric device, a battery pack can be used.

[0085] [Embodiment]

[0086] Hereinafter, an embodiment of the present application will be described. The embodiment described below is exemplary and is for the purpose of explanation of the present application only, and should not be construed as a limitation of the present application. In the embodiment, the specific technique or condition not mentioned is performed according to the technique or condition described in the literature in the art or according to the product manual. The reagent or instrument not mentioned the manufacturer is a conventional product that can be obtained by purchase in the market.

[0087] Preparation of the embodiment

[0088] Example 1

[0089] (1) Preparation of artificial graphite

[0090] S1: The needle-shaped green coke raw material is fed into a jaw crusher through a vibrating feeder for coarse crushing, and then the qualified material is fed into a mechanical mill for fine crushing, and is subjected to classification and shaping treatment to obtain a precursor with a Dv50 of 11 μm;

[0091] S2: The precursor obtained in step S1 is added to a reaction kettle, and 10% of a binder pitch (Dv50 of 7 μm) relative to the weight of the precursor for granulation is added for granulation, the stirring speed is 1200 r / min, the temperature is raised to 560℃ at a rate of 10℃ / min at room temperature, and then the temperature is kept constant for 8 hours, the granulation is to Dv50 of 18 μm, and intermediate 1 is obtained;

[0092] S3: The intermediate 1 obtained in step S2 is added to a graphitization furnace, the temperature is raised to 3000℃ for graphitization treatment, and a 200-mesh screen is used for screening to obtain intermediate 2;

[0093] S4: The rotary kiln is heated to 700℃ for heating and micro-oxidation, the furnace tube speed is 4 r / min, and the air flow rate is 4 m 3 / h. The graphitized material is fed from the feeding port, the material enters the cavity at a uniform speed through the rotary feeder. After the micro-oxidation treatment in the cavity, the material falls into the discharge bag after cooling from the discharge port, and the micro-oxidized artificial graphite is obtained.

[0094] (2) Preparation of negative electrode sheet

[0095] The above-prepared artificial graphite, conductive agent (conductive carbon black (Super P)), binder (styrene-butadiene rubber (SBR)), and thickening agent (carboxymethyl cellulose-sodium (CMC-Na)) are fully stirred and mixed in a proper amount of deionized water in a mass ratio of 96.2:0.8:1.8:1.2 to form a uniform negative electrode slurry; the negative electrode slurry is coated on the surface of the negative electrode current collector copper foil, and after drying and cold pressing, a negative electrode sheet is obtained. The compaction density of the negative electrode sheet is 1.70 g / cm 3 , and the area density is 11.4 mg / cm 2 .

[0096] (3) Preparation of positive electrode sheet

[0097] The positive electrode active material LiNi 0.5 Co 0.2 Mn 0.3O2 (large single-crystal lithium nickel cobalt manganese oxide (NCM523)), conductive agent (Super P), binder (polyvinylidene fluoride (PVDF)) were mixed in a weight ratio of 96.2:2.7:1.1 in an appropriate amount of N-methyl pyrrolidone (NMP) to form a uniform positive electrode slurry; the positive electrode slurry was coated on the surface of a positive electrode current collector aluminum foil, and after drying and cold pressing, a positive electrode sheet was obtained. The compaction density of the positive electrode sheet was 3.45 g / cm 3 , and the area density was 18.8 mg / cm 2 .

[0098] (4) Preparation of electrolyte

[0099] Ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1, and then LiPF6 was uniformly dissolved in the above solution to obtain an electrolyte, wherein the concentration of LiPF6 was 1 mol / L.

[0100] (5) Separator

[0101] A polyethylene (PE) film was used.

[0102] (6) Preparation of secondary battery

[0103] The positive electrode sheet, the separator, and the negative electrode sheet were stacked in order, and after winding, an electric core was obtained. The electric core was placed in an outer package, the above electrolyte was added, and after packaging, standing, formation, aging, and other processes, a secondary battery was obtained. The outer package selected a hard shell shell with length* width* height = 148 mm*28.5 mm*97.5 mm.

[0104] Example 2

[0105] Example 2 was generally similar to Example 1, except that the raw material was petroleum coke.

[0106] Example 3

[0107] Example 3 was generally similar to Example 1, except that the raw material was pitch coke.

[0108] Example 4

[0109] Example 4 was generally similar to Example 1, except that the degree of crushing and sizing was increased.

[0110] Example 5

[0111] Example 5 was generally similar to Example 1, except that the degree of crushing and sizing was reduced.

[0112] Example 6

[0113] Example 6 was generally similar to Example 1, except that the granulation was to Dv50 of 12 μm.

[0114] Example 7

[0115] Example 7 is substantially similar to Example 1, except that granulation is to Dv50 of 25 μm.

[0116] Example 8

[0117] Example 8 is substantially similar to Example 1, except that the graphitization temperature is 3200℃, and the graphitization furnace discharge time is extended.

[0118] Example 9

[0119] Example 9 is substantially similar to Example 1, except that the graphitization temperature is 2800℃, and the graphitization furnace discharge time is shortened.

[0120] Comparative Example 1

[0121] (1) Preparation of the negative electrode material

[0122] S1: The needle-shaped green coke raw material is fed into a jaw crusher through a vibrating feeder for coarse crushing, and then the qualified material is fed into a mechanical mill for fine crushing, and is subjected to classification and shaping treatment to obtain a precursor with Dv50 of 11 μm;

[0123] S2: The precursor obtained in step S1 is added to a reaction kettle, and 10% of a binder pitch (Dv50 of 7 μm) relative to the weight of the precursor used for granulation is added for granulation, the stirring speed is 1200 r / min, the temperature is raised to 560℃ at a rate of 10℃ / min at room temperature, and then the temperature is kept constant for 8 hours, the granulation is to Dv50 of 18 μm, and intermediate 1 is obtained;

[0124] S3: The intermediate 1 obtained in step S2 is added to a graphitization furnace, and is subjected to graphitization treatment at a temperature of 3000℃, and is sieved with a 200 mesh screen to obtain a finished product of graphite;

[0125] (2) Preparation of the negative electrode sheet

[0126] The above-mentioned artificial graphite, conductive agent (Super P), binder (SBR), thickening agent (CMC-Na) are fully stirred and mixed in a proper amount of deionized water in a mass ratio of 96.2:0.8:1.8:1.2 to form a uniform negative electrode slurry; the negative electrode slurry is coated on the surface of the negative electrode current collector copper foil, and after drying and cold pressing, a negative electrode sheet is obtained. The compaction density of the negative electrode sheet is 1.65 g / cm 3 , and the area density is 11.4 mg / cm 2 .

[0127] (3) Preparation of the positive electrode sheet

[0128] LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), conductive agent (Super P), binder PVDF were mixed in a weight ratio of 96.2:2.7:1.1 in an appropriate amount of NMP to form a uniform positive electrode slurry; the positive electrode slurry was coated on the surface of the positive electrode current collector aluminum foil, and after drying and cold pressing, a positive electrode tab was obtained. The compaction density of the positive electrode tab was 3.45 g / cm 3 , the area density was 18.8 mg / cm 2 .

[0129] (4) Preparation of electrolyte

[0130] Ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1, and then LiPF6was uniformly dissolved in the above solution to obtain an electrolyte, wherein the concentration of LiPF6was 1 mol / L.

[0131] (5) Separating film

[0132] A polyethylene (PE) film was used.

[0133] (6) Preparation of secondary battery

[0134] The positive electrode tab, the separating film, and the negative electrode tab were stacked in order, and after winding, an electric core was obtained, which was put into an outer package, and the above electrolyte was added, and after packaging, standing, formation, aging, and other processes, a secondary battery was obtained. The outer package selected a hard shell shell with length* width* height = 148 mm*28.5 mm*97.5 mm.

[0135] Comparative Example 2

[0136] Comparative Example 2 was basically the same as Comparative Example 1, except that the raw material was petroleum coke.

[0137] Comparative Example 3

[0138] Comparative Example 3 was basically the same as Comparative Example 1, except that the raw material was pitch coke.

[0139] Table 1: The parameters of the related examples and comparative examples are shown in the following table:

[0140]

[0141] Test method

[0142] 1. Test method of specific surface area:

[0143] The specific surface area (SSA) of the artificial graphite can be tested by methods known in the art. For example, it can be tested by nitrogen adsorption specific surface area analysis test method according to GB / T 19587-2017, and calculated by BET (Brunauer Emmett Teller) method, wherein the nitrogen adsorption specific surface area analysis test can be performed by a Tri-Star 3020 specific surface area pore size analyzer of the American Micromeritics company.

[0144] 2. Test method of the compacted density:

[0145] The powder compacted density of the artificial graphite can be tested by methods known in the art. For example, it can be tested by using an electronic pressure testing machine (such as UTM7305) according to GB / T 24533-2009: a certain amount of powder is placed on a special mold for compaction, different pressures are set, and the thickness of the powder under different pressures can be read on the equipment, and the compacted density under different pressures can be calculated.

[0146] 3. Test method of the limit compacted density:

[0147] 1) Confirm the test pressure gradient of the negative electrode material (0.05 g / cc), such as (1.55 1.60 1.65 1.70 1.75), and fill in the table in the appendix;

[0148] 2) Calculate the target thickness (±0.003 mm) after cold pressing according to the actual coating weight of the electrode sheet before cold pressing and the pressure gradient;

[0149] 3) Cold pressing window verification: adjust the left and right gaps and the tonnage of the pressure roller of the cold press according to the design pressure adjustment of the project; after adjusting the roller gap, only adjust the cold pressing pressure to achieve the required pressure value, and ensure that the thickness of the electrode sheet on both sides is consistent (lateral consistency) after cold pressing. Remark: (When adjusting the consistency of the electrode sheet on both sides, it needs to be adjusted under low pressure conditions);

[0150] 4) First, adjust the cold pressing pressure at low speed, and when it approaches the required cold pressing thickness value, increase the speed to ≥35 m / min, keep the machine running, and run at high speed for 1-2 min to confirm whether the appearance of the electrode sheet is OK, whether there are edge overpressure, belt breakage, roller sticking, wrinkling and other phenomena, and take pictures for preservation; the thickness of the electrode sheet after cold pressing needs to be measured by using a micrometer and recorded; record the actual cold pressing parameters and fill in the table in the appendix Remark: (The thickness of the electrode sheet at low speed is significantly different from that at high speed, and the actual thickness of the electrode sheet is the thickness of the electrode sheet after high cold pressing);

[0151] 5) Adjust the cold pressing pressure without changing the roller gap, complete the cold pressing of the compaction of each group, and measure the thickness of the electrode sheet after cold pressing by using a micrometer to confirm the actual compaction;

[0152] 6) Record the transverse thickness of the electrode sheet and take a photo within 2 minutes after each compaction; record the cold pressing pressure, electrode sheet appearance, and cold pressing thickness corresponding to each compaction; carefully observe the appearance of the cold pressing roller and the electrode sheet, such as... Figure 3 , 4 ; Figure 3 The results showed that the appearance was normal, with a pressure of 43T and a compaction density of 1.67g / cc. Figure 4 The results showed that the edges were over-compressed and the appearance was unacceptable. The pressure was 85T and the compaction density was 1.73g / cc.

[0153] 7) Summarize the appearance photos of the cold-pressed electrode sheets and the pressure vs. compaction data, and provide the corresponding powder batch information for compaction window verification;

[0154] 8) For backup materials, the compaction window verification needs to be compared with the original main material, and the batch number of powder materials in the comparison verification compaction window should be provided.

[0155] 4. Cohesive strength test method:

[0156] Apply double-sided tape to both sides of a 2cm wide stainless steel plate. Evenly attach the electrode to be tested onto the tape, ensuring it is of uniform length and width. Evenly apply copper foil tape to the electrode surface (ensuring a smooth, wrinkle-free surface after application), leaving a small section of copper foil tape attached to a piece of paper (the copper foil and paper should be in a straight line). Set the tensile testing machine parameters and place the electrode vertically in the center of the machine's slot, ensuring it is perfectly aligned vertically. Click "Start Test" on the computer to obtain the cohesive force data.

[0157] 5. Occio roughness test method:

[0158] The Occhio roughness can be obtained by Occhio Callisto 3D software, and the specific calculation process is as follows: the measured graphite particles are dispersed, and high-contrast and high-definition pictures are obtained by Occhio Callisto 3D software to divide the specific morphology and boundary of the graphite particles, to determine the particle projection area, and to define a smooth reference by checking the maximum inscribed circle of the original outline pixel contained in the corresponding pixel contour. Among them, the inscribed circle with a radius of 80% of the smooth reference radius is continuously inscribed in the particle projection area, and the total area of the inscribed circle is defined as the 80% reference. The ratio of 80% smooth reference and particle projection area is between 0-1, and the larger the ratio, the closer the surface morphology of the measured particle to smooth. Taking 80% of the maximum inscribed circle radius as the reference radius can better define and quantify the final Occhio roughness value. The Occhio roughness of one embodiment of the present application refers to the ratio of 1-(80% smooth reference and particle projection area), which can indicate the sphericity parameter (surface roughness) of the particle material. The larger the Occhio roughness value, the higher the surface roughness of the material.

[0159] Table 2: The results of the relevant performance tests are shown in the following table:

[0160]

[0161] According to Table 1 and Table 2, the most important difference between the examples and the comparative examples is whether heat treatment is performed, the examples all undergo heat treatment, Example 1 (Comparative Example 1), Example 2 (Comparative Example 2), and Example 3 (Comparative Example 3) respectively use needle coke, petroleum coke, and pitch coke as the precursor, and through the test results, it can be known that the B value, the Ouchiro roughness value, the compaction density value, and the specific surface area of the same precursor after heat treatment are obviously higher than those of the comparative examples without heat treatment, and at the same time, it also has higher pole piece cohesion and pole piece limit compaction; compared with Example 2 and Example 3, Example 1 also has higher compaction density, pole piece cohesion, and pole piece limit compaction, which reflects the advantage of needle coke as high-capacity high-compaction graphite in improving the compaction level. Example 4 and Example 1 both use needle coke as the precursor, the difference is that the crushing and shaping degree is increased in Example 4, and the calculated Ouchiro roughness is smaller than that of Example 1; on the contrary, the main difference between Example 5 and Example 1 is that the crushing and shaping degree is reduced, and the Ouchiro roughness is larger than that of Example 1; the difference between Example 6 and Example 1 is that the granulation is to Dv50 of 12 μm, and the powder compaction density is smaller than that of Example 1; the difference between Example 7 and Example 1 is that the granulation is to Dv50 of 25 μm, and the powder compaction density is larger than that of Example 1. The main difference between Example 8 and Example 1 is that the graphitization temperature of Example 1 is 3000 ℃, and the graphitization temperature of Example 8 is 3200 ℃, which is higher than that of Example 1, and the specific surface area is smaller than that of Example 1. The difference between Example 9 and Example 1 is that the graphitization temperature is 2800 ℃, which shortens the graphitization discharge time, and the specific surface area is larger than that of Example 1.

[0162] It should be noted that the present application is not limited to the above-described embodiments. The above-described embodiments are only examples, and embodiments having the same technical idea and playing the same role and effect within the scope of the technical solutions of the present application are all included in the technical scope of the present application. In addition, within the scope of the main idea of the present application, various modifications that can be thought of by those skilled in the art, and other ways constructed by combining part of the components of the embodiments are also included in the scope of the present application.

Claims

1. Artificial graphite negative electrode material, characterized by, The artificial graphite negative electrode material has an Ouchyao roughness of 0.09-0.20, a powder compaction density of 1.7 g / cm 3 -2.2 g / cm 3 , and a specific surface area of 1.8 m 2 / g-4.5 m 2 / g.

2. The artificial graphite negative electrode material according to claim 1, characterized by, The artificial graphite negative electrode material is subjected to micro-oxidation treatment.

3. The artificial graphite negative material according to any one of claims 1-2, characterized in that, The product of the Ouchy roughness, the powder compaction density and the specific surface area of the artificial graphite negative electrode material is denoted as B, 370x10 4 cm -1 ≤B≤1000x10 4 cm -1 .

4. The artificial graphite negative electrode material according to any one of claims 1 to 3, characterized by, The artificial graphite negative electrode material has a graphitization degree of 91% to 98%.

5. The artificial graphite negative material according to any one of claims 1-4, characterized in that, The artificial graphite material can be sintered from at least one of petroleum coke, needle coke and pitch coke.

6. A method for producing an artificial graphite negative electrode material, characterized by, The method comprises: providing a coke raw material selected from one or more of petroleum coke, needle coke and pitch coke, the coke raw material having a particle size Dv10 of 6.0 to 13.0 microns, or a Dv50 of 8.0 to 20.0 microns, or a Dv90 of 24.0 to 35.0 microns, the coke raw material being subjected to crushing and classification treatment, shaping and fine powder removal treatment to obtain a first product with uniform particle size; adding the first product obtained by the treatment into a graphitization furnace and heating to 2800 to 3200 degrees Celsius to obtain an artificial graphite material A; The rotary kiln is heated to 600-900 DEG C, the speed of the furnace tube is 2-6 r / min, the air flow is 1 m 3 / h -9m 3 / h; the artificial graphite material A is put into the feeding port, the material is put into the cavity through the rotary feeder for heating treatment, and the artificial graphite negative electrode material is obtained after cooling.

7. A negative electrode sheet characterized by comprising: The artificial graphite negative electrode material according to any one of claims 1 to 5 or prepared by the method according to claim 6.

8. The negative electrode sheet according to claim 7, characterized by The compacted density of the negative electrode sheet is 1.70 g / cm 3 - 2.20 g / cm 3 .

9. The method of producing a negative electrode sheet according to claim 7 or 8, characterized by, The artificial graphite negative electrode material according to any one of claims 1 to 5 or prepared by the method according to claim 6 is fully stirred and mixed in deionized water to form a uniform negative electrode slurry, the negative electrode slurry is coated on the surface of a negative electrode current collector, and after drying and cold pressing, a negative electrode sheet is obtained, the negative electrode sheet comprising a negative electrode active material layer, the negative electrode active material layer comprising the artificial graphite negative electrode material, and the mass ratio of the artificial graphite negative electrode material to the negative electrode active material layer being greater than 95%.

10. A secondary battery characterized by comprising: The negative electrode sheet according to any one of claims 7 to 8 or prepared by the method for preparing a negative electrode sheet according to claim 9.

11. An electrical device, characterized by The secondary battery according to claim 10.

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