Artificial graphite, its preparation method, secondary batteries containing it, and electrical devices thereof.

Abstract

This invention provides an artificial graphite, a secondary battery (5), a preparation method, and an apparatus. The artificial graphite satisfies: PD 5t / PD 0.5t ≤1.35, where PD 5t PD is the compaction density of the artificial graphite measured under 5 tons of pressure. 0.5t The compaction density of the artificial graphite was measured under a pressure of 0.5 tons.

Description

Technical Field

[0001] This application relates to the field of graphite materials, and in particular to artificial graphite, its preparation methods, secondary batteries containing it, and electrical devices thereof. Background Technology

[0002] Secondary batteries are widely used due to their outstanding features such as high energy density, no pollution, and long service life.

[0003] However, secondary batteries expand in volume during cycling, leading to increased internal stress and affecting their lifespan and safety performance. For example, with the rapid popularization of new energy vehicles, the market demands increasingly higher lifespan and safety performance from power-type secondary batteries. To enhance the market competitiveness of new energy vehicles, it is indeed necessary to provide a secondary battery that balances good electrical performance and safety performance. Summary of the Invention

[0004] This application provides an artificial graphite that can reduce the volume expansion of a secondary battery during cycling, a method for preparing the graphite, a secondary battery containing the graphite, and an electrical device thereof.

[0005] In some respects, this application provides an artificial graphite that satisfies: PD 5t / PD 0.5t ≤1.35, where PD 5t PD is the compaction density of artificial graphite measured under 5 tons of pressure. 0.5t This is the compaction density of artificial graphite measured under 0.5 tons of pressure.

[0006] This application is the first to discover that PD 5t / PD 0.5t Reflecting the sensitivity of graphite density to pressure changes, PD 5t PD is the compaction density of the artificial graphite measured under 5 tons of pressure. 0.5t The compaction density of the artificial graphite was measured under a pressure of 0.5 tons. As a negative electrode material for secondary batteries, the stress on artificial graphite changes with repeated lithium insertion / extraction processes. This application discovers that PD... 5t / PD 0.5t It can reflect the expansion changes of artificial graphite during repeated lithium insertion / extraction processes. When the PD of artificial graphite... 5t / PD 0.5t When the viscosity is ≤1.35, the expansion force during cycling is relatively small, resulting in a lower full-charge expansion rate and thus better cycle performance. Artificial graphite PD 5t / PD 0.5tMaterials with a strength ≤1.35 exhibit strong resistance to deformation. During lithium-ion battery cycling, the repeated insertion and extraction of lithium on the negative electrode leads to repeated expansion and contraction under stress. When the deformation resistance of the negative electrode is improved, its expansion during cycling is lower, its structure is more stable, and thus its cycle performance is better.

[0007] PD 5t / PD 0.5t It can effectively reflect the material's ability to resist deformation under external forces, PD 5t / PD 0.5t When the value is ≤1.35, the material has strong resistance to deformation. During battery cycling, the repeated insertion and extraction of lithium on the negative electrode leads to repeated expansion and contraction under stress. When the resistance to deformation of the negative electrode is improved, its expansion during cycling is lower, the structure is more stable, and thus the cycle performance is better.

[0008] In any implementation scheme, artificial graphite satisfies: 1.23 ≤ PD 5t / PD 0.5t ≤1.3. For example, PD 5t / PD 0.5t The values ​​can be 1.20-1.25, 1.25-1.30, or 1.30-1.35. Based on this scheme, artificial graphite is used in secondary batteries, resulting in further improvements in battery performance.

[0009] In some implementation schemes, artificial graphite satisfies: PD 5t ≥1.8g / cm 3 For example, 1.8 g / cm³ 3 ≤PD 5t ≤-1.95g / cm 3 In some other implementations, PD 5t The value is 1.8–1.85 g / cm³. 3 For example, 1.85~1.90g / cm³ 3 For example, 1.90~1.95g / cm³ 3 Based on this approach, artificial graphite is used in secondary batteries, further improving the battery's energy density performance.

[0010] In some implementation schemes, artificial graphite satisfies: PD 0.5t ≥1.4g / cm 3 For example, 1.4 g / cm³ 3 ≤PD 0.5t ≤1.5g / cm 3 In some other implementations, PD 0.5t The value is 1.4–1.45 g / cm³. 3 For example, 1.45~1.50g / cm³ 3Based on this approach, artificial graphite is used in secondary batteries, further improving the battery's energy density performance.

[0011] In some implementations, the median particle size D of the artificial graphite V 50 satisfies: D V 50 ≥ 10 μm; for example, 19 μm ≤ D V 50≤22μm. In some other embodiments, the median particle size D of the artificial graphite is... V The value of 50 is 10–13 μm, for example 13–16 μm, for example 16–19 μm, for example 19–22 μm. Based on this scheme, artificial graphite is used in secondary batteries. Reasonable control of particle size helps to prevent excessive expansion of the negative electrode material, thereby further improving the battery's kinetic and cycle performance.

[0012] In some implementations, the specific surface area (SSA) of the artificial graphite satisfies: SSA ≤ 1.5 g / m² 2 For example, 1.0g / m 2 ≤SSA≤1.4g / m 2 In some other implementations, the specific surface area (SSA) of the artificial graphite is 1.0–1.2 g / m². 2 For example, 1.2–1.4 g / m 2 For example, 1.4–1.5 g / m 2 Based on this scheme, artificial graphite is used in secondary batteries, and the negative electrode of the battery has sufficient active area for lithium intercalation, which is beneficial to further improve the battery's fast charging capability.

[0013] In some implementations, the tap density of the artificial graphite is 0.9 g / cm³. 3 The above; for example, the tap density of artificial graphite is 1.0 g / cm³. 3 -1.4g / cm 3 In some other implementations, the tap density of the artificial graphite is 0.9–1.1 g / cm³. 3 For example, 1.1–1.3 g / cm³ 3 The use of artificial graphite based on this scheme in secondary batteries is beneficial for increasing the compaction density of the negative electrode sheet, thereby further improving the energy density of the battery.

[0014] In some implementations, the degree of graphitization of the artificial graphite is 90% or higher; for example, 92% or higher, 94% or higher, 96% or higher, 98% or higher, or 90-100%. When artificial graphite based on this scheme is used in secondary batteries, the performance of the secondary batteries is further improved. This scheme is beneficial for increasing the specific capacity of graphite and eliminating lattice defects, thus contributing to improved cell energy density and storage performance.

[0015] In some embodiments, the specific capacity of the artificial graphite is 340 mAh / g or higher; for example, 345–355 mAh / g. In still other embodiments, the specific capacity of the artificial graphite is 340–345 mAh / g, for example, 345–350 mAh / g, or even 350–355 mAh / g. When artificial graphite based on this design is used in secondary batteries, the capacity performance of the secondary batteries is further improved.

[0016] In some aspects, this application provides a method for preparing artificial graphite, comprising the following steps:

[0017] (1) Mix raw coke particles, calcined coke particles, binder and solvent;

[0018] (2) Shape the product from the previous step;

[0019] (3) Remove at least some or all of the solvent from the product of the previous step to obtain a green body;

[0020] (4) The green compact is subjected to artificial graphitization treatment to obtain a graphite compact;

[0021] (5) The graphite blank is made into powder to obtain artificial graphite;

[0022] Among them, artificial graphite satisfies: PD 5t / PD 0.5t ≤1.35, where PD 5t PD is the compaction density of artificial graphite measured under 5 tons of pressure. 0.5t This is the compaction density of artificial graphite measured under 0.5 tons of pressure.

[0023] In some implementations, step (1) includes: mechanically mixing raw coke particles, calcined coke particles, and a binder, while adding an appropriate amount of solvent, and stirring to obtain a stirred product. The stirred product is a mud-like substance or binder particles (such as binder particles in the millimeter or centimeter range).

[0024] In some implementations, step (2) includes: adding the stirred product obtained in the previous step into a forming device, extruding or pressing it to form a wet blank with a preset shape.

[0025] In some implementations, step (3) includes drying the wet blank to remove the solvent and obtain a green blank.

[0026] In some implementations, step (4) includes: placing the green blank into a graphitization furnace and graphitizing it at a temperature above 2800°C to obtain a graphite blank.

[0027] In some implementations, step (4) includes: crushing and / or grinding the graphite blank, sieving (e.g., above 200 mesh, e.g., 200-400 mesh), and demagnetizing to obtain artificial graphite powder.

[0028] In some implementations, after the graphite blank is crushed into powder, one or more of the following operations are performed: sieving, demagnetization, or a combination thereof.

[0029] In some implementations, the preparation method of artificial graphite uses a total mass of raw coke particles, calcined coke particles, and binder of 100%, with the raw coke particle content being 35% or more, for example, 35-55 wt%. Based on this approach, the amount of raw coke particles is sufficient to generate adequate bond strength, and the structural integrity of the green body can be maintained during the graphitization process. However, the artificial graphite particles obtained using this approach have relatively low bond strength and can easily deagglomerate into powder. If the content of raw coke particles is too low, the bonding effect of graphite during the high-temperature graphitization stage is weak, and the strengthening effect is insufficient, resulting in poor particle size distribution (PD). 5t / PD 0.5t Relatively large.

[0030] In some embodiments, the content of calcined coke particles in the preparation method of artificial graphite is 35 wt% or more, for example, 35-62 wt%. Based on this approach, the properties of artificial graphite are improved.

[0031] In some embodiments, the binder content in the preparation method of artificial graphite is 3 wt% or more, for example, 3-10 wt%. Based on this approach, the amount of binder is sufficient to produce adequate bond strength, and the structural integrity of the green body can be maintained during the graphitization process. Furthermore, the artificial graphite obtained based on this approach has a lower binder residual carbon content, resulting in better performance.

[0032] In some implementations, the apparent density of the green body is 1.3 g / cm³. 3 The above; for example, 1.3 g / cm³ 3 -1.5g / cm 3 1.35g / cm 3 -1.45g / cm 3 Based on this scheme, the green body possesses sufficient strength during the graphitization stage, preventing collapse and pulverization. Furthermore, the graphite green body obtained by this scheme exhibits low interparticle adhesion, easily deagglomerating into powder, resulting in graphite powder with superior performance. When this graphite powder is used in secondary batteries, the batteries demonstrate excellent cycle and storage performance. The high apparent density indicates tighter adhesion between coke particles, leading to higher stress during graphitization and thus enhancing the performance of the PD (Power Generation Device). 5t / PD 0.5t Lower costs mean better cell performance.

[0033] In some implementations, the bulk density of the green body is 0.85 g / cm³. 3 Below, for example, 0.45-0.85 g / cm³ 3 In some other implementations, the bulk density of the green body is 0.45–0.55 g / cm³. 3 For example, 0.55~0.65g / cm³ 3 For example, 0.65–0.75 g / cm³ 3 For example, 0.75–0.85 g / cm³ 3 Based on this method, the artificial graphite exhibits a high degree of graphitization and fewer defects, resulting in secondary batteries with better cycle performance and longer storage life. This is particularly relevant when the bulk density of the green compact is in the range of 0.45-0.85 g / cm³. 3 At this stage, the performance and production efficiency of artificial graphite are well balanced. If the bulk density is too high, the resistivity will be low. According to Joule's law, the heat generated in the graphitization furnace will decrease, resulting in a lower graphitization temperature. A lower temperature leads to a weaker strengthening effect of the coke particles, thus causing PD (photovoltaic particle size distribution). 5t / PD 0.5t Too large. (The strengthening effect is mainly affected by the adhesion and temperature.)

[0034] In some embodiments, the green body has a size ≥1cm in at least one direction, for example 1-10cm, 1-3cm, 3-5cm, 5-7cm, or 7-9cm.

[0035] In some implementations, the green body has a size ≥1cm in at least two mutually perpendicular directions, for example, 1-10cm, 1-3cm, 3-5cm, 5-7cm, or 7-9cm.

[0036] In some implementations, the green body has a size ≥1cm in three mutually perpendicular directions, for example, 1-10cm, 1-3cm, 3-5cm, 5-7cm, or 7-9cm.

[0037] In some embodiments, the shape of the green body is selected from one or more of the following: columnar, spherical, ellipsoidal, and blocky.

[0038] In some implementations, the volatile matter content of the coke particles is ≥6 wt%, for example, ≥8 wt%, or 8 wt%-12 wt%. Based on this approach, the coke particles can generate volatile matter with a binding effect above 1000°C, thereby maintaining the structural integrity of the green body. If the volatile matter content of the coke particles is too low, the bonding effect of graphite during the high-temperature graphitization stage is weak, and the strengthening effect is low, thus affecting the PD (Polymerization Process). 5t / PD 0.5tRelatively large.

[0039] In some implementations, the median particle size Dv50 of the green coke particles is smaller than that of the calcined coke particles. Based on this design, the green coke particles can better fill the gaps between the calcined coke particles, thus better exerting a bonding effect and better maintaining the structural integrity of the billet during graphitization. The Dv50 of the green coke... V 50% lower than the D of the calcined coke V At a concentration of 50, the coke is more easily and evenly dispersed in the precursor, resulting in a more uniform adhesion effect. This helps maintain a more uniform compressive stress, leading to a more uniform strengthening effect and thus improving PD performance. 5t / PD 0.5t Lower.

[0040] In some implementations, the median particle size Dv50 of the green coke particles is below 15 μm, for example, 8-14 μm. Based on this approach, the green coke particles can better perform their adhesive function and better maintain the structural integrity of the billet during graphitization.

[0041] In some implementations, the median particle size Dv50 of the calcined coke particles is below 20 μm, for example, 15-17 μm. Based on this approach, the green coke particles can better perform their binding function and better maintain the structural integrity of the billet during graphitization.

[0042] In some implementations, the binder is evaporable or decomposed above 1000°C. Based on this approach, the coke particles in the green body primarily act as binders at high temperatures above 1000°C, while the binder component mainly acts as a binder at low temperatures below 1000°C. The green body is effectively bound throughout the entire graphitization temperature range, maintaining the structural integrity of the green block. If the binder content is too low, the bonding between coke particles is insufficient, compressive stress is difficult to maintain, and the strengthening effect is inadequate, leading to poor particle size distribution (PD). 5t / PD 0.5t Too large.

[0043] In some implementations, the adhesive is a polymer adhesive.

[0044] In some embodiments, the polymer binder includes water-soluble polymer binders, non-water-soluble polymer binders, or combinations thereof.

[0045] In some embodiments, the water-soluble polymer binder is selected from polyvinyl alcohol, starch, cellulose, or combinations thereof.

[0046] In some embodiments, the non-water-soluble polymer binder is selected from: rubber binders, thermosetting resin binders, or combinations thereof.

[0047] In some aspects, this application provides a secondary battery comprising artificial graphite of any of the above-mentioned types or comprising artificial graphite prepared using the methods described in any of the above-mentioned types.

[0048] In some respects, this application provides an electrical device including the aforementioned secondary battery. Attached Figure Description

[0049] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0050] Figure 1 (a) and (b) are scanning electron microscope images of artificial graphite, respectively, from an embodiment of this application and a pair of proportions.

[0051] Figure 2 This is a schematic diagram of a secondary battery provided in an embodiment of this application.

[0052] Figure 3 This is a schematic diagram of a battery module provided in an embodiment of this application.

[0053] Figure 4 This is a schematic diagram of a battery pack provided in an embodiment of this application.

[0054] Figure 5 yes Figure 4 An exploded view of the battery pack.

[0055] Figure 6 This is a schematic diagram of an apparatus provided in an embodiment of this application.

[0056] The accompanying drawings are not drawn to scale. Detailed Implementation

[0057] The embodiments of this application will be described in further detail below with reference to the accompanying drawings and examples. The detailed description of the following embodiments and the accompanying drawings are used to illustrate the principles of this application by way of example, but should not be used to limit the scope of this application, that is, this application is not limited to the described embodiments.

[0058] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the negative electrode active material, its manufacturing method, secondary battery, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0059] 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.

[0060] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0061] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0062] 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.

[0063] 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.

[0064] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0065] In the description of this application, it should be noted that, unless otherwise stated, "a plurality of" means two or more; the terms "upper," "lower," "left," "right," "inner," and "outer," etc., indicating orientation or positional relationships, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application. Furthermore, the terms "first," "second," and "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance. "Vertical" is not vertical in the strict sense, but within the allowable tolerance range. "Parallel" is not parallel in the strict sense, but within the allowable tolerance range.

[0066] Secondary batteries

[0067] In some embodiments, this application provides a secondary battery.

[0068] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0069] [Negative electrode plate]

[0070] A negative electrode typically includes a negative current collector and a negative electrode film disposed on at least one surface of the negative current collector.

[0071] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film is laminated on either or both of the two opposite surfaces of the negative electrode current collector.

[0072] The negative electrode current collector can be made of a material with good conductivity and mechanical strength, serving both as a conductor and a current collector. In some embodiments, the negative electrode current collector can be made of copper foil.

[0073] The negative electrode membrane includes the negative electrode active material.

[0074] In some embodiments, this application provides an artificial graphite anode active material, wherein the artificial graphite satisfies PD... 5t / PD 0.5t When the value is ≤1.35, the material has a stronger resistance to deformation. During the cycling process of lithium-ion batteries, the repeated insertion and extraction of lithium on the negative electrode leads to repeated expansion and contraction under stress. When the deformation resistance of the negative electrode is improved, its expansion during cycling is lower, the structure is more stable, and thus the cycle performance is better.

[0075] This application is the first to discover that PD 5t / PD 0.5t It can reflect the sensitivity of artificial graphite to pressure changes, among which PD 5t PD is the compacted density of the artificial graphite measured under a pressure of 5 tons (49000N). 0.5t The compaction density of the artificial graphite was measured under a pressure of 0.5 tons (4900 N). As a negative electrode material for secondary batteries, the stress on artificial graphite changes with repeated lithium insertion / extraction processes. This application discovers that PD... 5t / PD 0.5t It can reflect the expansion changes of artificial graphite during repeated lithium insertion / extraction processes. When the PD of artificial graphite... 5t / PD 0.5t When the specific gravity is ≤1.35, the expansion force during cycling is small, resulting in a lower full-charge expansion rate. Optionally, the battery also exhibits one or more of the following advantages: higher specific capacity, higher first-cycle efficiency, better cycle performance, and longer storage life.

[0076] In some implementations, artificial graphite satisfies: 1.23 ≤ PD 5t / PD 0.5t ≤1.3. For example, PD 5t / PD 0.5tThe values ​​can be 1.20-1.25, 1.25-1.30, or 1.30-1.35. When artificial graphite meets this condition, the cycle performance of the battery is further improved.

[0077] In some implementation schemes, artificial graphite satisfies: PD 5t ≥1.8g / cm 3 For example, it could be 1.8 g / cm³. 3 ≤PD 5t ≤-1.95g / cm 3 1.8g / cm 3 ≤PD 5t ≤-1.85g / cm 3 1.85g / cm 3 ≤PD 5t ≤-1.90g / cm 3 1.90 g / cm 3 ≤PD 5t ≤-1.95g / cm 3 Based on this approach, artificial graphite is used in secondary batteries, further improving the battery's energy density performance.

[0078] In some implementation schemes, artificial graphite satisfies: PD 0.5t ≥1.4g / cm 3 For example, 1.4 g / cm³ 3 ≤PD 0.5t ≤1.5g / cm 3 In some other implementations, PD 0.5t The value is 1.4-1.45 g / cm³. 3 For example, 1.45-1.50 g / cm³ 3 Based on this scheme, artificial graphite is used in secondary batteries, which further improves the energy density of the secondary batteries.

[0079] The compaction density of artificial graphite under a specific pressure is a well-known concept in the art and can be tested using methods known in the art. For example, it can be tested using an electronic pressure testing machine (such as UTM7305) according to GB / T 24533-2019: Place a sample of artificial graphite powder of a preset mass M on a compaction mold (bottom area S), set different pressures (for example, 4900N and 49000N in this application), hold the pressure for 30s, release the pressure, wait for 10s, read the thickness H of the powder after compaction under that pressure on the equipment, and calculate the compaction density under that pressure. The compaction density of the negative electrode active material under this pressure = M / (H*S).

[0080] In some implementations, the median particle size D of the artificial graphite V 50 satisfies: D V50 ≥ 10 μm; for example, 19 μm ≤ D V 50 ≤ 22 μm. For example, 19 μm ≤ D V 50≤22μm. In some other embodiments, the median particle size D of the artificial graphite is... V The value of 50 is 10-13 μm, for example 13-16 μm, for example 16-19 μm, for example 19-22 μm. Based on this scheme, artificial graphite is used in secondary batteries. Reasonable control of particle size helps to prevent the expansion of the negative electrode material from being too large, thereby helping to further improve the kinetic performance and cycle performance of the battery.

[0081] Dv50 is the particle size corresponding to a cumulative volume distribution percentage of 50% for the artificial graphite, and can be tested using methods known in the art. For example, it can be determined using laser diffraction particle size analysis. It can be determined using a laser particle size analyzer (e.g., Malvern Master Size 3000) with reference to standard GB / T 19077-2016.

[0082] In some implementations, the specific surface area (SSA) of the artificial graphite satisfies: SSA ≤ 1.5 g / m² 2 For example, 1.0g / m 2 ≤SSA≤1.4g / m 2 In some other implementations, the specific surface area (SSA) of the artificial graphite is 1.0-1.2 g / m². 2 For example, 1.2-1.4 g / m 2 For example, 1.4-1.5 g / m 2 Based on this scheme, artificial graphite is used in secondary batteries, and the negative electrode has sufficient active area for lithium intercalation, which is beneficial to further improve the battery's fast charging capability.

[0083] The specific surface area (SSA) of artificial graphite is a well-known concept in the art and can be tested using methods known in the field. For example, it can be tested using the nitrogen adsorption specific surface area analysis method according to GB / T 19587-2017, and calculated using the BET (Brunauer-Emmett-Teller) method. The nitrogen adsorption specific surface area analysis can be performed using a Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, Inc.

[0084] In some implementations, the tap density of the artificial graphite is 0.9 g / cm³. 3 The above; for example, the tap density of artificial graphite is 1.0 g / cm³. 3 -1.4g / cm 3 In some other implementations, the tap density of the artificial graphite is 0.9-1.1 g / cm³.3 For example, 1.1-1.3 g / cm³ 3 The use of artificial graphite based on this scheme in secondary batteries is beneficial for increasing the compaction density of the negative electrode sheet, thereby further improving the energy density of the battery.

[0085] The tap density of artificial graphite is a well-known concept in the art and can be tested using methods known in the field. For example, it can be determined using a powder tap density tester, referring to standard GB / T 5162-2006. If using the FZS4-4B tap density tester from the Beijing Iron and Steel Research Institute, the test parameters are as follows: vibration frequency: 250±15 times / minute, amplitude: 3±0.2mm, number of vibrations: 5000 times, measuring cylinder: 25mL.

[0086] In some implementations, the degree of graphitization of the artificial graphite is 90% or higher; for example, 92% or higher, 94% or higher, 96% or higher, 98% or higher, or 90-100%. When artificial graphite based on this scheme is used in secondary batteries, the performance of the secondary batteries is further improved. This scheme is beneficial for increasing the specific capacity of graphite and eliminating lattice defects, thus contributing to improved cell energy density and storage performance.

[0087] The degree of graphitization of artificial graphite is a well-known concept in the art and can be tested using methods known in the field. For example, an X-ray diffractometer (e.g., Bruker D8 Discover) can be used, and the test can be performed according to JIS K 0131-1996 and JB / T4220-2011. The size of d002 is measured, and then the degree of graphitization is calculated using the formula G = (0.344 - d002) / (0.344 - 0.3354) × 100%, where d002 is the interlayer spacing in the graphite crystal structure expressed in nanometers (nm). In X-ray diffraction analysis, a copper target can be used as the anode target, with CuKα rays as the radiation source, and the wavelength of the rays is... The scanning 2θ angle range is 20° to 80°, and the scanning rate can be 4° / min.

[0088] In some embodiments, the specific capacity of the artificial graphite is above 340 mAh / g; for example, 345-355 mAh / g. In still other embodiments, the specific capacity of the artificial graphite is 340-345 mAh / g, for example, 345-350 mAh / g, or even 350-355 mAh / g. Artificial graphite based on this design, when used in secondary batteries, further improves the performance of the secondary batteries.

[0089] The specific capacity of artificial graphite has a well-known meaning in the art and can be tested using methods known in the art. As an example, it can be tested as follows: The prepared artificial graphite, conductive agent Super P, binder (SBR), and thickener (CMC) are thoroughly mixed in an appropriate amount of deionized water at a mass ratio of 96.2:0.8:1.8:1.2 to form a slurry. The prepared slurry is coated onto a copper foil current collector and dried in an oven for later use. A lithium metal sheet is used as the counter electrode. A polyethylene (PE) film is used as the separator. Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1. Then, LiPF6 is uniformly dissolved in the above solution to obtain an electrolyte, wherein the concentration of LiPF6 is 1 mol / L. The above components are assembled into a CR2430 coin cell in an argon-protected glove box. After the obtained button cells were left to stand for 12 hours, they were discharged at a constant current of 0.05C to 0.005V, left to stand for 10 minutes, and then discharged at a constant current of 50μA to 0.005V. They were then charged at a constant current of 0.1C to 2V, and the charging capacity was recorded. The ratio of the charging capacity to the mass of the artificial graphite is the specific capacity of the artificial graphite.

[0090] In some embodiments, this application provides a method for preparing artificial graphite, comprising the following steps:

[0091] (1) Prepare a mixture of raw coke particles, calcined coke particles, binder and solvent;

[0092] (2) Shape the mixture to obtain an intermediate;

[0093] (3) Remove at least some or all of the solvent from the intermediate to obtain a green compact;

[0094] (4) The green blank is graphitized to obtain a graphite blank;

[0095] (5) The graphite blank is made into powder to obtain artificial graphite;

[0096] Among them, artificial graphite satisfies: PD 5t / PD 0.5t ≤1.35, where PD 5t PD is the compaction density of artificial graphite measured under 5 tons of pressure. 0.5t This is the compaction density of artificial graphite measured under 0.5 tons of pressure.

[0097] In some implementations, step (1) includes: mechanically mixing raw coke particles, calcined coke particles, and a binder, while adding an appropriate amount of solvent, and stirring to obtain a stirred product. The stirred product is a mud-like substance or binder particles (such as binder particles in the millimeter or centimeter range).

[0098] The term "raw coke" has a meaning known in the art. Raw coke, for example, conforms to the requirements of NBSHT 0527-2019 Petroleum Coke (raw coke).

[0099] In some implementations, the volatile matter content of the coke particles is ≥6 wt%, for example, ≥8 wt%, or 8 wt%-12 wt%. Based on this approach, the coke particles can generate volatile matter with a binding effect above 1000°C, thereby maintaining the structural integrity of the green body. If the volatile matter content of the coke particles is too low, the bonding effect of graphite during the high-temperature graphitization stage is weak, and the strengthening effect is low, thus affecting the PD (Polymerization Process). 5t / PD 0.5t Relatively large.

[0100] The volatile matter content of raw coke was tested according to "SHT0026-1990 - Determination of Volatile Matter in Petroleum Coke".

[0101] In some implementation schemes, the total mass of raw coke particles, calcined coke particles, and binder is 100%, with the raw coke particle content being 35 wt% or higher, for example, 35 wt%-55 wt%. Based on this scheme, the amount of raw coke particles is sufficient to produce moderate adhesive strength, maintaining the structural integrity of the green body during graphitization. Simultaneously, the artificial graphite particles obtained using this scheme exhibit lower adhesive strength and are more easily deagglomerated into powder. If the raw coke particle content is too low, the adhesive effect of graphite during the high-temperature graphitization stage is weak, and the strengthening effect is insufficient, resulting in PD (Potentially Differential Particles)... 5t / PD 0.5t Relatively large.

[0102] In some implementations, the median particle size Dv50 of the green coke particles is smaller than that of the calcined coke particles. Based on this design, the green coke particles can better fill the gaps between the calcined coke particles, thus better exerting a bonding effect and better maintaining the structural integrity of the billet during graphitization. The Dv50 of the green coke... V 50% lower than the D of the calcined coke V At a concentration of 50, the coke is more easily and evenly dispersed in the precursor, resulting in a more uniform adhesion effect. This helps maintain a more uniform compressive stress, leading to a more uniform strengthening effect and thus improving PD performance. 5t / PD 0.5t Lower.

[0103] In some implementations, the median particle size Dv50 of the green coke particles is below 15 μm, for example, 8-14 μm. Based on this approach, the green coke particles can better perform their adhesive function and better maintain the structural integrity of the billet during graphitization.

[0104] The term "calcined coke" has the meaning known in the art. Calcined coke, for example, is calcined petroleum coke conforming to YS T 625-2012 for prebaked anodes.

[0105] In some implementations, the median particle size Dv50 of the calcined coke particles is below 20 μm, for example, 15-17 μm. Based on this approach, the green coke particles can better perform their binding function and better maintain the structural integrity of the billet during graphitization.

[0106] In some implementations, the content of calcined coke particles is above 35 wt%, for example, it can be 35 wt% to 62 wt%. Based on this approach, the properties of artificial graphite are improved.

[0107] In some implementations, the binder is evaporable or decomposed above 1000°C. Based on this approach, the coke particles in the green body mainly act as binders at high temperatures above 1000°C, while the binder components mainly act as binders at low temperatures below 1000°C. The green body is effectively bound throughout the entire graphitization temperature range, thus maintaining the structural integrity of the green body.

[0108] In some embodiments, the adhesive is a polymeric adhesive. The polymeric adhesive may include water-soluble polymeric adhesives, non-water-soluble polymeric adhesives, or combinations thereof.

[0109] In some embodiments, the water-soluble polymer binder may include: polyvinyl alcohol, starch, cellulose, or combinations thereof.

[0110] In some embodiments, the non-water-soluble polymer binder is selected from: rubber binders, thermosetting resin binders, or combinations thereof.

[0111] In some implementations, the binder content is above 2 wt%, for example, 3 wt%-10 wt%, or ≤6%, or 2%-4%. Based on this approach, the amount of binder is sufficient to generate adequate bond strength, and the structural integrity of the green body can be maintained during graphitization. Furthermore, the artificial graphite obtained using this approach has a lower binder residual carbon content, resulting in better performance. The carbonization and decomposition residue of the binder (residual carbon) is hard carbon, difficult to graphitize. When the amount of residual carbon in artificial graphite is high, it increases the specific surface area of ​​the artificial graphite, thereby reducing its capacity and initial coulombic efficiency, and consequently reducing the energy density and cycle performance of the battery. If the binder content is low, the adhesion between coke particles is insufficient, compressive stress is difficult to maintain, and the strengthening effect is insufficient, leading to poor performance of the PD. 5t / PD 0.5t Too large.

[0112] In some implementations, step (2) includes: adding the mixture obtained in the previous step to a molding device, extruding or pressing it to obtain an intermediate with a preset shape, which may also be referred to as a wet blank.

[0113] In some implementations, step (3) includes drying the wet blank to remove the solvent and obtain a green blank.

[0114] In some implementations, the apparent density of the green body is 1.3 g / cm³. 3 The above; for example, 1.3 g / cm³ 3 -1.5g / cm 3 1.35g / cm 3 -1.45g / cm 3 Based on this scheme, the green body possesses sufficient strength during the graphitization stage, preventing collapse and pulverization. Furthermore, the graphite green body obtained by this scheme exhibits low interparticle adhesion, easily deagglomerating into powder, resulting in graphite powder with superior performance. When this graphite powder is used in a secondary battery, the battery demonstrates excellent cycle and storage performance.

[0115] In the above scheme, apparent density affects the stability and internal stress of the green body; apparent density is 1.3 g / cm³. 3 The above; for example, 1.3 g / cm³ 3 -1.5g / cm 3 1.35g / cm 3 -1.45g / cm 3 During graphitization, graphite particles are strengthened by stress, meaning their resistance to deformation is enhanced, thus resulting in the PD (polydimer) of artificial graphite. 5t / PD 0.5t The value is ≤1.35. A high apparent density indicates a tighter bond between coke particles, resulting in higher stress during graphitization and thus higher PD. 5t / PD 0.5t Lower costs mean better cell performance.

[0116] The apparent density of the green body is tested using the displacement method. An exemplary test method includes: weighing a bonded block precursor, mass m1; adding an appropriate amount of water to a beaker and weighing it, mass m2; suspending the precursor in the water using a thin copper wire (diameter <0.05mm) of negligible volume, ensuring the water level slightly covers the precursor without it contacting the bottom of the beaker; and weighing the total mass of the beaker, water, and the precursor suspended in the water, mass m3. The density of water is approximately 1 g / cm³. 3 The density of the precursor is then m1 / (m3-m2) g / cm³. 3 Take 10 samples, measure them, and take the average value to obtain the apparent density of the green body.

[0117] In some implementations, the bulk density of the green body is 0.85 g / cm³. 3 Below, for example, 0.45-0.85 g / cm³ 3 In some other implementations, the bulk density of the green body is 0.45–0.55 g / cm³. 3 For example, 0.55~0.65g / cm³ 3 For example, 0.65–0.75 g / cm³ 3 For example, 0.75–0.85 g / cm³ 3 Based on this method, the artificial graphite exhibits a high degree of graphitization and fewer defects, resulting in secondary batteries with better cycle performance and storage life. This is particularly relevant when the bulk density of the green compact is in the range of 0.45-0.85 g / cm³. 3 At this stage, the performance and production efficiency of artificial graphite are well balanced. If the bulk density is too high, the resistivity will be low. According to Joule's law, the heat generated in the graphitization furnace will decrease, resulting in a lower graphitization temperature. A lower temperature leads to a weaker strengthening effect of the coke particles, thus causing PD (photovoltaic particle size distribution). 5t / PD 0.5t Too large. (The strengthening effect is mainly affected by the bonding effect and temperature).

[0118] The packing density test of green blocks shall refer to GB / T 14685-2011 Construction Pebbles and Crushed Stones, Section 7.13 Packing Density and Porosity (Loose Packing Density).

[0119] In some embodiments, the green body has a size ≥1cm in at least one direction, for example 1-10cm, 1-3cm, 3-5cm, 5-7cm, or 7-9cm.

[0120] In some implementations, the green body has a size ≥1cm in at least two mutually perpendicular directions, for example, 1-10cm, 1-3cm, 3-5cm, 5-7cm, or 7-9cm.

[0121] In some implementations, the green body has a size ≥1cm in three mutually perpendicular directions, for example, 1-10cm, 1-3cm, 3-5cm, 5-7cm, or 7-9cm.

[0122] In some embodiments, the shape of the green body is selected from one or more of columnar, spherical, ellipsoidal, and blocky shapes. Columnar, spherical, ellipsoidal, and blocky shapes should be understood to include quasi-columnar, quasi-spherical, quasi-ellipsoidal, and quasi-blocky shapes.

[0123] In some implementations, step (4) includes: placing the green blank into a graphitization furnace and graphitizing it at a temperature above 2800°C to obtain a graphite blank.

[0124] In some implementations, step (4) includes: crushing and / or grinding the graphite blank, sieving (e.g., above 200 mesh, e.g., 200-400 mesh), and demagnetizing to obtain artificial graphite powder.

[0125] In some implementations, after the graphite blank is crushed into powder, one or more of the following operations are performed: sieving, demagnetization, or a combination thereof.

[0126] Applying the artificial graphite prepared above to the negative electrode film can effectively improve the cycle performance of the battery.

[0127] In some embodiments, the negative electrode film may optionally include other negative electrode active materials that can be used as the negative electrode of a secondary battery. Other negative electrode active materials may be one or more of other graphite materials (e.g., other artificial graphite, natural graphite), mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon-based materials, and tin-based materials.

[0128] In some embodiments, the negative electrode membrane may further include an adhesive. As an example, the adhesive may be selected from one or more of polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), styrene-butadiene rubber (SBR), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0129] In some embodiments, the negative electrode membrane may optionally include a thickener. As an example, the thickener may be sodium carboxymethyl cellulose (CMC-Na).

[0130] In some embodiments, the negative electrode membrane may optionally include a conductive agent. As an example, the conductive agent used for the negative electrode membrane may be selected from one or more of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0131] [Positive electrode plate]

[0132] The positive electrode includes a positive current collector and a positive electrode film disposed on at least one surface of the positive current collector. As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film is laminated and disposed on either or both of the two opposite surfaces of the positive current collector.

[0133] The positive current collector can be made of a material with good conductivity and mechanical strength. In some embodiments, the positive current collector can be aluminum foil.

[0134] The positive electrode film includes a positive electrode active material. This application does not impose specific limitations on the specific type of positive electrode active material; materials known in the art that can be used as positive electrodes for secondary batteries can be used, and those skilled in the art can select according to actual needs.

[0135] In some embodiments, the secondary battery may be a lithium-ion secondary battery. The positive electrode active material may be selected from lithium transition metal oxides and their modified materials, wherein the modified material may be a lithium transition metal oxide that has undergone doping modification and / or coating modification. For example, the lithium transition metal oxide may be selected from one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium phosphates with an olivine structure.

[0136] As an example, the positive electrode active material can be selected from LiCoO2, LiNiO2, LiMnO2, LiMn2O4, and LiNi. 1 / 3 Co 1 / 3 Mn 1 / 3O2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 0.6 Co 0.2 Mn 0.2 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 (LFP), and LiMnPO4.

[0137] In some embodiments, the positive electrode membrane may optionally include an adhesive. There is no specific limitation on the type of adhesive, and those skilled in the art can select one according to actual needs. As an example, the adhesive used for the positive electrode membrane may include one or more of polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE).

[0138] In some embodiments, the positive electrode membrane may optionally include a conductive agent. There is no specific limitation on the type of conductive agent, and those skilled in the art can select it according to actual needs. As an example, the conductive agent used for the positive electrode membrane may include one or more of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0139] [Electrolytes]

[0140] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be selected from at least one of solid electrolytes and liquid electrolytes (i.e., electrolyte solutions).

[0141] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0142] In some embodiments, the electrolyte salt may be selected from one or more of LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiClO4 (lithium perchlorate), LiAsF6 (lithium hexafluoroarsenate), LiFSI (lithium bis(fluorosulfonyl)imide), LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalate borate), LiBOB (lithium dioxalate borate), LiPO2F2 (lithium difluorophosphate), LiDFOP (lithium difluorodioxalate phosphate), and LiTFOP (lithium tetrafluorooxalate phosphate).

[0143] In some embodiments, the solvent may be selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0144] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, additives that improve battery low-temperature performance, etc.

[0145] [Isolation membrane]

[0146] Secondary batteries using electrolytes, and some secondary batteries using solid electrolytes, also include a separator. The separator is positioned between the positive and negative electrodes to provide isolation. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected. In some embodiments, the separator material can be selected from one or more 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. When the separator is a multi-layer composite film, the materials of each layer can be the same or different.

[0147] [Outer Packaging]

[0148] In some embodiments, the secondary battery may include an outer packaging for encapsulating a positive electrode, a negative electrode, and an electrolyte. As an example, the positive electrode, negative electrode, and separator may be stacked or wound to form a stacked or wound battery cell, with the cell encapsulated within the outer packaging; the electrolyte may be a liquid electrolyte that wets the cell. The number of cells in the secondary battery may be one or more, adjustable as needed.

[0149] In some embodiments, the outer packaging of the secondary battery can be a soft pack, such as a pouch. The soft pack can be made of plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS). The outer packaging of the secondary battery can also be a hard shell, such as an aluminum shell.

[0150] [Preparation methods for secondary batteries]

[0151] A method for preparing a secondary battery, including the step of preparing a negative electrode sheet using the artificial graphite of this application.

[0152] In some embodiments, the step of preparing a negative electrode sheet using artificial graphite of the first aspect of this application may include: dispersing the negative electrode active material including artificial graphite of the first aspect of this application with a binder, and optionally a thickener and a conductive agent in a solvent, the solvent being deionized water, to form a uniform negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and obtaining a negative electrode sheet after processes such as drying and cold pressing.

[0153] The preparation method of a secondary battery may also include the step of preparing a positive electrode sheet. In some embodiments, the positive electrode active material, conductive agent and binder can be dispersed in a solvent (e.g., N-methylpyrrolidone, abbreviated as NMP) to form a uniform positive electrode slurry; the positive electrode slurry is coated on a positive electrode current collector, and after drying, cold pressing and other processes, a positive electrode sheet is obtained.

[0154] The method for preparing a secondary battery also includes the step of assembling a negative electrode, a positive electrode, and an electrolyte to form a secondary battery. In some embodiments, the positive electrode, the separator, and the negative electrode can be wound or stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation, thus obtaining a battery cell; the battery cell is placed in an outer package, electrolyte is injected, and the package is sealed to obtain the secondary battery of this application.

[0155] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. Figure 2 A square-structured secondary battery 5 is shown as an example.

[0156] In some embodiments, secondary batteries can be assembled into battery modules, and the number of secondary batteries contained in a battery module can be multiple, the specific number of which can be adjusted according to the application and capacity of the battery module.

[0157] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0158] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0159] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0160] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0161] Electrical appliances

[0162] In some embodiments, this application provides an electrical device. The electrical device includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0163] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0164] Figure 6 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0165] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0166] Although this application has been described with reference to preferred embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

[0167] Example

[0168] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0169] I. Preparation of Artificial Graphite

[0170] Examples 1-7

[0171] Examples 1-7 show the preparation of artificial graphite using a graphitization furnace. The preparation method includes the following steps:

[0172] (1) Preparation of green body

[0173] Prepare a precursor composition according to the precursor formulation shown in Table 2, add water and stir until a mud is formed, then extrude the mud for granulation and molding, and dry until the moisture content is less than 3%, to obtain a green compact. The shape of a single green compact is cylindrical, with a size of Φ15mm×4mm. The apparent density and bulk density of the green compact are shown in Table 2.

[0174] (2) Artificial graphitization treatment

[0175] Graphitization treatment is performed on the green compact prepared in the previous step. The peak temperature of the graphitization treatment reaches 2800°C. Graphitization is performed using equipment known in the art, for example a graphitization furnace, further for example an Acheson graphitization furnace.

[0176] (3) Pulverization

[0177] A crusher is used to crush the graphitized compact into powder, the powder is passed through a 325-mesh sieve, and the powder product passing through the sieve is collected. A demagnetizer is used to remove magnetism from the sieved powder product, such that the total content of elements Fe+Co+Ni+Cr+Zn in the powder product is <0.1ppm. Artificial graphite (powder) is obtained.

[0178] Comparative Examples 1 to 9

[0179] The main difference between Comparative Examples 1 to 2 and Example 1 lies in the different apparent density and / or bulk density of the green compact, as detailed in Table 2

[0180] The main difference between Comparative Examples 3 to 9 and Example 1 lies in the different precursor formulation, as detailed in Table 2.

[0181] III. Analysis and Testing Items

[0182] Tests are performed on the artificial graphite prepared in the examples and comparative examples and the intermediate products obtained in each step. The main test methods include:

[0183] The test method for green compact integrity (V2 / V1) is as follows: randomly select 20 green compacts, test the total volume V1 of the 20 green compacts by the water displacement method; after graphitization treatment, randomly select 20 graphite compacts, test the total volume V2 of the 20 graphite compacts by the water displacement method. The value of V2 / V1 is used to represent the degree of compact integrity. If V2 / V1 ≥ 70%, the structure remains good; if 30% < V2 / V1 < 70%, the degree of compact integrity is average; if V2 / V1 ≤ 30%, the degree of compact integrity is severely deteriorated.

[0184] In order to further evaluate the performance of artificial graphite as a negative electrode active material for secondary batteries, secondary batteries were assembled using the artificial graphite prepared above, and battery performance tests were carried out. The assembly method of the secondary battery includes:

[0185] (1) Preparation of positive electrode sheet

[0186] LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523), conductive agent (acetylene black), and binder (PVDF) are mixed in a mass ratio of 96:2:2. NMP solvent is added and the mixture is stirred to obtain a positive electrode slurry. The positive electrode slurry is uniformly coated on a positive electrode current collector (aluminum foil), and after drying, cold pressing, and slitting, a positive electrode sheet is obtained.

[0187] (2) Preparation of negative electrode sheet

[0188] The artificial graphite powder, conductive agent acetylene black, thickener CMC, and binder SBR of each embodiment and comparative example are mixed in a mass ratio of 96.4:1:1.2:1.4. Deionized water is added as a solvent and mixed evenly to obtain a negative electrode slurry. The negative electrode slurry is uniformly coated on a negative electrode current collector (copper foil), and after drying, cold pressing, and slitting, a positive electrode sheet is obtained.

[0189] (3) Electrolyte

[0190] The electrolyte is a 1 mol / L lithium salt LiPF6 as the solute and a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 1:1:1 as the solvent.

[0191] (4) Separating membrane

[0192] The separator is a polyethylene film.

[0193] (5) Preparation of secondary batteries

[0194] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator between the positive and negative electrode sheets, and then wound to obtain a bare cell. The bare cell is placed in an outer packaging shell, electrolyte is injected, and after vacuum sealing, standing, and formation processes, a secondary battery is obtained.

[0195] The performance parameters of secondary batteries include the following test items:

[0196] (1) Cyclic performance test, which includes: at 25°C, the secondary battery is fully charged and fully discharged at a rate of 1C until the capacity of the secondary battery decays to 80% of the initial capacity, and the number of cycles is recorded.

[0197] (2) Expansion performance test, which includes: measuring the thickness of the negative electrode sheet before winding it into a cell, denoted as h1. After winding the negative electrode sheet into a cell and preparing it into a secondary battery, the secondary battery is fully charged at 1C, then the battery is disassembled, the negative electrode sheet is separated, and the thickness of the negative electrode sheet is measured, denoted as h2. Then the full-charge expansion rate of the negative electrode sheet of the secondary battery is (h2-h1) / h1.

[0198] (3) Storage life test, which includes: First, a 25°C charge-discharge capacity test is performed on the secondary battery: After standing at 25°C for 2 hours, the secondary battery is fully discharged at 0.33C, then fully charged at 0.33C, and then fully discharged at 0.33C again. The capacity of the second full discharge is taken as the capacity C0 of the secondary battery. Then, the secondary battery is stored at 60°C, and the capacity is tested at 25°C every fixed number of days. The capacity C after N days of storage is recorded. N Define capacity retention ratio R = C N / C0, when R is first less than or equal to 0.8, record the number of days N that can be stored at this time, which is the storage life of the secondary battery.

[0199] The precursor formulations, green body parameters, and graphite blank parameters of the examples and comparative examples are shown in Table 2.

[0200] The parameters of the artificial graphite (powder) in the examples and comparative examples are shown in Table 3.

[0201] The performance of the secondary batteries assembled using artificial graphite as the cathode material in the examples and comparative examples is shown in Table 4.

[0202]

[0203]

[0204] Analyzing the experimental data in Table 1-2, the following experimental conclusions can be drawn:

[0205] (1) About PD 5t / PD 0.5t value

[0206] PD of artificial graphite in Examples 1-7 5t / PD 0.5t ≤1.35, specifically between 1.28 and 1.31. PD 5t / PD 0.5t Reflecting the sensitivity of graphite density to pressure changes, PD 5t PD is the compaction density of the artificial graphite measured under 5 tons of pressure. 0.5t The compaction density of the artificial graphite was measured under a pressure of 0.5 tons. Graphite materials, used as the negative electrode in secondary batteries, also undergo significant changes during repeated lithium insertion / extraction processes, thus affecting the PD (Power Generation Device).5t / PD 0.5t It can reflect the expansion changes of graphite during repeated lithium insertion / extraction processes. When PD 5t / PD 0.5t When the coefficient of performance (COP) is ≤1.35, the lithium-ion anode material exhibits less expansion force during cycling, which is beneficial for improving cycle performance. Battery test results show that when the graphite materials of Examples 1-7 are used as anode active materials for secondary batteries, the secondary batteries exhibit one or more of the following advantages: higher specific capacity, higher first-cycle efficiency, better cycle performance, lower full-charge expansion rate, and longer storage life.

[0207] (2) Regarding the apparent density of the green body

[0208] A key difference between Comparative Examples 1-2 and Examples 1-7 lies in the apparent density of the green bodies. Apparent density affects the stability and internal stress of the green bodies; the apparent density of the green bodies in Examples 1-7 was 1.3 g / cm³. 3 The above; for example, 1.3 g / cm³ 3 -1.5g / cm 3 1.35g / cm 3 -1.45g / cm 3 During graphitization, graphite particles are strengthened by stress, meaning their resistance to deformation is enhanced, thus resulting in the PD (polydimer) of artificial graphite. 5t / PD 0.5t The value is ≤1.35. Furthermore, experimental results show that the green bodies of Examples 1-7 exhibit structural stability and do not collapse during the graphitization stage, with the obtained graphite green bodies maintaining an integrity of over 98%. Simultaneously, the adhesion strength between graphite particles after graphitization is low, and deagglomeration can be achieved through slight crushing, resulting in little or no damage to the graphite surface. Battery testing results show that when the graphite materials of Examples 1-7 are used as negative electrode active materials in secondary batteries, the secondary batteries exhibit one or more of the following advantages: higher specific capacity, higher first-cycle efficiency, better cycle performance, lower full-charge expansion rate, and longer storage life.

[0209] The apparent density of the green body in Comparative Example 1 was less than 1.3 g / cm³. 3 The graphite particles are not subjected to sufficient stress, resulting in insufficient strengthening effect and insufficient (or poor) resistance to deformation, thus producing artificial graphite PD. 5t / PD 0.5t The value is greater than 1.35. This indicates insufficient strength during the graphitization stage, making the green body's structure prone to collapse and pulverization, resulting in low integrity of the graphite green body. Furthermore, the pulverization of the green body can cause powder accumulation, making it difficult for volatile gases to escape, thus posing an explosion risk.

[0210] The apparent density of the green body in Comparative Example 2 was higher than 1.45 g / cm³. 3After graphitization, the graphite particles are tightly bound together, making them difficult to deagglomerate into powder, or requiring forceful crushing to form powder. Forceful crushing introduces numerous irreversible processing defects into the graphite surface, resulting in an excessively high specific surface area (reaching 3.05 g / m²). 2 Thus, the PD of artificial graphite was obtained. 5t / PD 0.5t A value greater than 1.35 reduces the cycle performance and storage performance of the secondary battery.

[0211] (3) Regarding the formulation of precursors

[0212] The key difference between Comparative Examples 3-10 and Examples 1-7 lies in the different precursor formulations. In the precursor formulations, the coke component facilitates the volatilization of volatiles at temperatures above 1000°C, thus acting as a binder; the binder component mainly serves to bind the coke particles together at temperatures below 1000°C.

[0213] The precursor formulations in Examples 1-7 yielded green bodies with high integrity after graphitization and easy depolymerization, resulting in PD (Potential Density) of the obtained artificial graphite powder. 5t / PD 0.5t ≤1.35, between 1.23 and 1.3.

[0214] In Comparative Example 3, if the bulk density of the green body is too high (1.00 g / cm³), it will cause problems. 3 If the resistivity is too low, according to Joule's law, the heat generated in the graphitization furnace will decrease, resulting in a lower graphitization temperature. A lower temperature leads to a weaker strengthening effect on the coke particles, thus causing PD (photovoltaic particle) degradation. 5t / PD 0.5t Larger (PD) 5t / PD 0.5t 1.39).

[0215] In Comparative Example 7, the mass fraction of raw coke was less than 35%, resulting in lower volatile matter content at temperatures above 1000℃, insufficient bonding strength, easy collapse of the blocks, and poor integrity of the green body. If the content of raw coke particles is too low, the bonding effect of graphite during the high-temperature graphitization stage is weak, and the strengthening effect is insufficient, leading to poor PD (Potentially Differential Processing). 5t / PD 0.5t Relatively large.

[0216] In Comparative Example 8, the mass fraction of raw coke was higher than 55%, there was too much volatile matter at high temperatures above 1000℃, the adhesion between particles was too strong, and it was not easy to deagglomerate after graphitization.

[0217] In Comparative Example 9, the binder mass fraction was less than 3%, resulting in low bonding strength during heating at temperatures below 1000℃, unstable structure prone to collapse, and poor green body integrity. If the binder content is too low, the adhesion between coke particles is insufficient, compressive stress is difficult to maintain, and the strengthening effect is inadequate, leading to poor particle size distribution (PD).5t / PD 0.5t Too large.

[0218] In Comparative Example 10, the mass fraction of the adhesive was higher than 10%, resulting in more residual carbon in the adhesive and reducing the performance of the graphite material.

[0219] In Comparative Example 11, the volatile matter content of the coke was below 8%, resulting in poor preservation of the structural integrity of the green body. If the volatile matter content of the coke particles is too low, the adhesion of graphite during the high-temperature graphitization stage is weak, leading to a lower strengthening effect and consequently, reduced PD (Potentially Differential Processing). 5t / PD 0.5t Relatively large.

[0220] Figure 1 Images (a) and (b) are scanning electron microscope photographs of artificial graphite, representing a pair of proportions, from an embodiment of this application. Figure 1 As shown in (a), for the sample of this embodiment of the invention, due to the good adhesion effect of the raw material particles during graphitization, the particle size is relatively large, the particles exhibit an irregular geometric shape, and the surface defects are low. Figure 1 As shown in (b), for the comparative sample, the particle size is small and the particle shape is irregular because the bonding effect of the raw material particles is poor during the graphitization process.

[0221] The experimental phenomena described above, and the rules summarized from them, are all discoveries made for the first time in this application, and were not anticipated by those skilled in the art prior to this application. The technical effects achieved by the artificial graphite prepared in Examples 1-7 are also discoveries made for the first time in this application, and were not anticipated by those skilled in the art prior to this application.

Claims

1. An artificial graphite, wherein the artificial graphite satisfies: PD 5t / PD 0.5t ≤1.35, where, PD 5t PD is the compaction density of the artificial graphite measured under 5 tons of pressure. 0.5t The compaction density of the artificial graphite was measured under a pressure of 0.5 tons.

2. The artificial graphite according to claim 1, wherein, The artificial graphite satisfies: 1.23 ≤ PD 5t / PD 0.5t ≤1.

3.

3. The artificial graphite according to claim 1, wherein, The artificial graphite satisfies: PD 5t ≥1.8 g / cm 3 .

4. The artificial graphite according to claim 3, wherein, The artificial graphite satisfies the following condition: 1.8 g / cm³ 3 ≤PD 5t ≤1.95g / cm 3 .

5. The artificial graphite according to claim 1, wherein, The artificial graphite satisfies: PD 5t ≥1.4 g / cm 3 .

6. The artificial graphite according to claim 5, wherein, 1.4 g / cm 3 ≤PD 5t ≤1.5 g / cm 3 。 7. The artificial graphite according to any one of claims 1-6, wherein, The median particle size D of the artificial graphite V 50 satisfies: D V 50≥10μm.

8. The artificial graphite according to claim 7, wherein, 14μm ≤D V 50≤17μm.

9. The artificial graphite according to any one of claims 1-6, wherein, The specific surface area (SSA) of the artificial graphite satisfies: SSA ≤ 1.5 g / m² 2 .

10. The artificial graphite according to claim 9, wherein, The specific surface area (SSA) of the artificial graphite satisfies: 1.0 g / m² 2 ≤SSA≤1.4g / m 2 .

11. The artificial graphite according to any one of claims 1-6, wherein, The tap density of the artificial graphite is 0.9 g / cm³. 3 above.

12. The artificial graphite according to claim 11, wherein, The tap density of the artificial graphite is 1.0 g / cm³. 3 -1.4g / cm 3 .

13. The artificial graphite according to any one of claims 1-6, wherein, The degree of graphitization of the artificial graphite is above 90%.

14. The artificial graphite according to claim 13, wherein, The degree of graphitization of the artificial graphite is above 94%.

15. The artificial graphite according to any one of claims 1-6, wherein, The specific capacity of the artificial graphite is above 340 mAh / g.

16. The artificial graphite according to claim 15, wherein, The specific capacity of the artificial graphite is 345 mAh / g - 355 mAh / g.

17. A method for preparing artificial graphite, comprising the following steps: (1) Prepare a mixture of raw coke particles, calcined coke particles, binder and solvent; (2) The mixture is shaped to obtain an intermediate; (3) Remove at least part of the solvent from the intermediate to obtain a green body; (4) The green blank is graphitized to obtain a graphite blank; (5) The graphite blank is made into powder to obtain artificial graphite; in, The artificial graphite satisfies: PD 5t / PD 0.5t ≤1.35, where PD 5t PD is the compaction density of the artificial graphite measured under 5 tons of pressure. 0.5t The compaction density of the artificial graphite was measured under a pressure of 0.5 tons. The total mass of raw coke particles, calcined coke particles, and binder is 100%, wherein the content of raw coke particles is 35% or more, and the volatile matter content of the raw coke particles is ≥6 wt% or more; the apparent density of the green body is 1.3 g / cm³. 3 -1.5g / cm 3 The bulk density of the green body is 0.85 g / cm³. 3 the following.

18. The method according to claim 17, wherein, The total mass of raw coke particles, calcined coke particles, and binder is 100%, and the content of raw coke particles is 35-55 wt%.

19. The method according to claim 17, wherein, The total mass of raw coke particles, calcined coke particles, and binder is 100%, and the content of the binder is 2 wt% or more.

20. The method according to claim 19, wherein, The total mass of raw coke particles, calcined coke particles, and binder is 100%, and the content of the binder is 3wt%-10wt%.

21. The method according to claim 17, wherein, The volatile matter content of the raw coke particles is 8wt%-12wt%.

22. The method of claim 17, wherein, The bulk density of the green body is 0.45-0.85 g / cm³. 3 .

23. The method according to any one of claims 17-22, wherein, The green body has one or more of the following characteristics (1)-(4): (1) The green body has a dimension ≥1cm in at least one direction; (2) The dimensions of the green blank are ≥1cm in at least two mutually perpendicular directions; (3) The dimensions of the green body are ≥1cm in all three mutually perpendicular directions; (4) The shape of the green blank is selected from one or more of columnar, spherical, ellipsoidal and blocky shapes.

24. The method according to claim 23, wherein, The green body has one or more of the following characteristics (1)-(3): (1) The dimensions of the green body in at least one direction are 1cm-10cm; (2) The green body has a size of 1cm-10cm in at least two mutually perpendicular directions; (3) The dimensions of the green blank are 1cm-10cm in three mutually perpendicular directions.

25. The method according to any one of claims 17-22, wherein, The method satisfies one or more of the following characteristics: (1) The median particle size Dv50 of the raw coke particles is smaller than the median particle size Dv50 of the calcined coke particles; (2) The median particle size Dv50 of the coke particles is less than 15 μm; (3) The median particle size Dv50 of the calcined coke particles is less than 20 μm.

26. The method of claim 25, wherein, The median particle size Dv50 of the coke particles is 8 μm - 14 μm; and / or The median particle size Dv50 of the calcined coke particles is 15μm-17μm.

27. The method according to any one of claims 17-22, wherein, The adhesive can evaporate or decompose at temperatures above 1000°C.

28. The method according to any one of claims 17-22, wherein, The adhesive is a polymer adhesive; and / or The polymer binder includes water-soluble polymer binders, non-water-soluble polymer binders, or combinations thereof; and / or The water-soluble polymer binder is selected from: polyvinyl alcohol, starch, cellulose, or combinations thereof; and / or the non-water-soluble polymer binder is selected from: rubber binders, thermosetting resin binders, or combinations thereof.

29. A secondary battery comprising artificial graphite as described in any one of claims 1-16 or comprising artificial graphite prepared using the method described in any one of claims 17-28.

30. An electrical device comprising the secondary battery of claim 29.

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