Artificial graphite and preparation method thereof, negative electrode sheet, secondary battery, battery module, battery pack and power-consuming device

Abstract

The present application discloses an artificial graphite and its preparation method, negative electrode plate, secondary battery, battery module, battery pack and power device. The particle size Dv50 of the artificial graphite is ≤16μm, and the air oxidation peak temperature T peak ≥830℃, wherein the peak temperature of the artificial graphite under air oxidation is T peak This refers to the peak temperature of the maximum peak in the differential thermogravimetric analysis curve obtained by thermogravimetric testing of the artificial graphite under the conditions of a weighing mass of 10±0.05 mg, air purge gas at a flow rate of 60 mL / min, a heating rate of 5°C / min, and a test temperature range of 40°C to 950°C. This application enables secondary batteries to have higher first-cycle coulombic efficiency and longer cycle life while maintaining good fast charging performance.

Description

Technical Field

[0001] The present application belongs to the technical field of secondary batteries, and specifically relates to artificial graphite and a preparation method thereof, a negative electrode sheet, a secondary battery, a battery module, a battery pack, and an electrical device. Background Art

[0002] Secondary batteries rely on the reciprocating intercalation and deintercalation of active ions between the positive and negative electrodes to charge and discharge. They offer outstanding characteristics such as high energy density, long cycle life, zero pollution, and no memory effect. Therefore, as a clean energy source, secondary batteries have gradually spread from electronic products to large-scale devices such as electric vehicles, adapting to sustainable environmental and energy development strategies. However, compared to traditional fuel vehicles that can be quickly and easily refueled, electric vehicles generally charge at a lower rate, often requiring longer charging times. This has caused anxiety among consumers about range and limited their rapid adoption. Summary of the Invention

[0003] The purpose of this application is to provide an artificial graphite and its preparation method, a negative electrode plate, a secondary battery, a battery module, a battery pack and an electrical device, which aims to reduce the irreversible consumption of active ions so that the secondary battery has a higher first-cycle coulombic efficiency and a longer cycle life while having good fast charging performance.

[0004] The first aspect of the present application provides an artificial graphite, wherein the particle size Dv50 of the artificial graphite is ≤ 16 μm, and the peak temperature of the artificial graphite in air oxidation is T peak ≥830℃, where the peak temperature of artificial graphite in air oxidation is T peak It refers to the peak temperature of the maximum peak of the differential thermogravimetric analysis curve obtained by thermogravimetric testing of the artificial graphite under the conditions of a weighing mass of 10±0.05 mg, air purge gas with an air flow rate of 60 mL / min, a heating rate of 5°C / min, and a test temperature range of 40°C to 950°C.

[0005] When the particle size of artificial graphite Dv50≤16μm and the peak temperature of air oxidation T peak At ≥830℃, the number and activity of electrochemical active sites on the surface of artificial graphite are moderate, and the irreversible consumption of active ions by artificial graphite is low. The secondary battery can have a higher first-cycle coulombic efficiency and a longer cycle life while having good fast charging performance.

[0006] In any embodiment of the present application, the particle size Dv50 of the artificial graphite is 13 μm to 16 μm. Alternatively, the particle size Dv50 of the artificial graphite is 13 μm to 15.5 μm.

[0007] When the particle size Dv50 of artificial graphite is within an appropriate range, artificial graphite can have higher active ion and electron transport properties and better fast charging performance. At the same time, artificial graphite can also have a higher powder compaction density.

[0008] In any embodiment of the present application, the peak temperature of the artificial graphite oxidized by air T peak 830°C to 840°C. Optionally, the peak temperature of artificial graphite oxidized by air T peak It is 831℃~838℃.

[0009] Peak temperature T of artificial graphite oxidized by air peak Within an appropriate range, the secondary battery can better combine good fast charging performance, higher first-cycle coulombic efficiency and longer cycle life.

[0010] In any embodiment of the present application, the surface of the artificial graphite does not have an amorphous carbon coating layer.

[0011] In any embodiment of the present application, the particle size Dv10 of the artificial graphite is ≥5 μm. Optionally, the particle size Dv10 of the artificial graphite is 5 μm to 9 μm.

[0012] When the particle size Dv10 of the artificial graphite is within an appropriate range, the artificial graphite can have a more appropriate specific surface area so as to reduce the irreversible consumption of active ions.

[0013] In any embodiment of the present application, the specific surface area of ​​artificial graphite is 0.8m 2 / g~1.1m 2 / g. Optionally, the specific surface area of ​​artificial graphite is 0.95m 2 / g~1.05m 2 / g.

[0014] Artificial graphite has an appropriate specific surface area, which can reduce the side reactions of the electrolyte on the surface of artificial graphite, reduce the gas production inside the secondary battery, reduce the volume expansion during the cycle of the secondary battery, and also make the negative electrode sheet and the secondary battery have higher dynamic performance.

[0015] In any embodiment of the present application, the tap density of the artificial graphite is ≥1g / cm 3 Optionally, the tap density of artificial graphite is 1.10 g / cm 3 ~1.30g / cm 3 .

[0016] By adopting the artificial graphite with the tap density of the above embodiment, the negative electrode plate can have a more appropriate porosity, ensuring that the negative electrode plate has better electrolyte infiltration performance, so that the secondary battery has a longer cycle life and a higher energy density.

[0017] In any embodiment of the present application, the powder compaction density of artificial graphite under a force of 20000N is ≥1.6g / cm 3 Optionally, the powder compaction density of artificial graphite under a force of 20,000 N is 1.6 g / cm 3 ~1.85g / cm 3 .

[0018] In any embodiment of the present application, the powder compaction density of artificial graphite under a force of 50000N is ≥1.7g / cm 3 Optionally, the powder compaction density of artificial graphite under a force of 50,000 N is 1.7 g / cm 3 ~2.0g / cm 3 .

[0019] By adopting the powder compaction density of the above embodiment, the artificial graphite can have a higher gram capacity. The negative electrode sheet using the artificial graphite also has a higher compaction density, and the secondary battery also has a higher energy density.

[0020] In any embodiment of the present application, the gram capacity of the artificial graphite is ≥353 mAh / g. Optionally, the gram capacity of the artificial graphite is 353 mAh / g to 360 mAh / g.

[0021] In any embodiment of the present application, the first-cycle coulombic efficiency of the artificial graphite is ≥95%. Optionally, the first-cycle coulombic efficiency of the artificial graphite is ≥95.3%.

[0022] The second aspect of the present application provides a method for preparing artificial graphite, the method comprising the following steps: S10, providing raw coke powder containing volatile components, S20, performing a thermal deposition treatment on the raw coke powder to deposit at least part of the volatile components in the raw coke powder on the surface of the raw coke powder, S30, performing a graphitization treatment on the raw coke powder after the thermal deposition treatment, S40, cooling and discharging the material to obtain a particle size Dv50≤16μm and an air oxidation peak temperature T peak Artificial graphite ≥830℃. Among them, the peak temperature of artificial graphite in air oxidation is T peak It refers to the peak temperature of the maximum peak of the differential thermogravimetric analysis curve obtained by thermogravimetric testing of the artificial graphite under the conditions of a weighing mass of 10±0.05 mg, air purge gas with an air flow rate of 60 mL / min, a heating rate of 5°C / min, and a test temperature range of 40°C to 950°C.

[0023] In any embodiment of the present application, in step S10, the mass content of volatile components contained in the provided green coke powder is ≥ 8.5%. Optionally, the mass content of volatile components contained in the provided green coke powder is 9% to 10.5%.

[0024] When the raw coke powder has a high content of volatile components, the volatile components can be deposited on the surface of the prepared artificial graphite and form a complete protective layer. The protective layer can fully modify the defect sites on the surface of the artificial graphite, reduce the specific surface area of ​​the artificial graphite, reduce the irreversible consumption of active ions, and improve the first-cycle coulombic efficiency and cycle life of the secondary battery.

[0025] In any embodiment of the present application, in step S10 , the particle size Dv10 of the provided green coke powder is ≥3.0 μm.

[0026] When the particle size Dv10 of the green coke powder is within an appropriate range, the content of fine powder in the green coke powder can be reduced, and the irreversible consumption of active ions by the prepared artificial graphite can be reduced.

[0027] In any embodiment of the present application, in step S10, the particle size Dv50 of the provided green coke powder is ≤16 μm.

[0028] The particle size Dv50 of the green coke powder is within an appropriate range, which can ensure that the prepared artificial graphite has good fast charging performance.

[0029] In any embodiment of the present application, in step S10, the method for providing green coke powder containing volatile components includes the steps of: coking the green coke raw material to obtain green coke, and grinding the obtained green coke to obtain green coke powder.

[0030] Optionally, the temperature of the coking treatment of the raw coke material is ≤ 550° C. Further, the temperature of the coking treatment of the raw coke material is 450° C. to 550° C. Selecting an appropriate coking treatment temperature is conducive to obtaining raw coke with a high volatile component content.

[0031] Optionally, the preheating preparation time for the coking treatment of the green coke raw material is ≥5 hours. Selecting an appropriate preheating preparation time can reduce the bulk structural defects of the obtained green coke.

[0032] Optionally, mechanical grinding equipment is used during the grinding process.

[0033] Mechanical grinding equipment breaks up lump coke into coke powder through collision. During collision, it can grind irregular coke powder particles, transforming them from irregular morphology to spherical morphology, thereby reducing defect sites on the surface of artificial graphite and irreversible consumption of active ions.

[0034] In any embodiment of the present application, in step S10, green coke powder containing volatile components, or a mixture of green coke powder containing volatile components and pitch powder is provided.

[0035] Pitch powder can assist the deposition of volatile components contained in the raw coke powder and form a complete protective layer on the surface of artificial graphite, thereby preventing the agglomeration of artificial graphite particles.

[0036] In any embodiment of the present application, in step S20 , the thermal deposition temperature is 250° C. to 700° C. Optionally, the thermal deposition temperature is 500° C. to 700° C.

[0037] The purpose of thermal deposition treatment is to convert the volatile components in the raw coke powder into a protective layer on the surface of artificial graphite, modify the defect sites on the surface of artificial graphite, reduce the specific surface area of ​​artificial graphite, reduce the irreversible consumption of active ions, and improve the first-cycle coulombic efficiency and cycle life of secondary batteries.

[0038] In any embodiment of the present application, in step S30, the graphitization treatment temperature is 2800°C to 3000°C.

[0039] Graphitization treatment can effectively eliminate the bulk structural defects of artificial graphite, reduce the irreversible consumption of active ions by artificial graphite, and improve the first-cycle coulombic efficiency and cycle life of secondary batteries.

[0040] In any embodiment of the present application, in step S40, the discharge temperature is ≤350°C.

[0041] Selecting an appropriate discharge temperature can reduce the number of active groups on the surface of artificial graphite, reduce the irreversible consumption of active ions, and make the artificial graphite have a higher first-cycle coulombic efficiency, and thus the secondary battery has a higher first-cycle coulombic efficiency and a longer cycle life.

[0042] The third aspect of the present application provides a negative electrode plate, which includes one of the artificial graphite described in the first aspect of the present application and the artificial graphite prepared according to the method described in the second aspect of the present application.

[0043] The fourth aspect of the present application provides a secondary battery, which includes at least one of the artificial graphite described in the first aspect of the present application, the artificial graphite prepared according to the method described in the second aspect of the present application, and the negative electrode sheet described in the third aspect of the present application.

[0044] A fifth aspect of the present application provides a battery module, which includes the secondary battery according to the fourth aspect of the present application.

[0045] A sixth aspect of the present application provides a battery pack, which includes the secondary battery of the fourth aspect of the present application and one of the battery modules of the fifth aspect of the present application.

[0046] A seventh aspect of the present application provides a device comprising at least one of the secondary battery of the fourth aspect of the present application, the battery module of the fifth aspect of the present application, and the battery pack of the sixth aspect of the present application.

[0047] The battery module, battery pack and electric device of the present application include the secondary battery provided by the present application, and thus have at least the same advantages as the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without paying any creative work.

[0049] Figure 1 This is a schematic diagram of one embodiment of the secondary battery of the present application.

[0050] Figure 2 It is an exploded schematic diagram of one embodiment of the secondary battery of the present application.

[0051] Figure 3 It is a schematic diagram of an embodiment of a battery module of the present application.

[0052] Figure 4 It is a schematic diagram of an embodiment of the battery pack of the present application.

[0053] Figure 5 yes Figure 4 Exploded diagram of .

[0054] Figure 6 This is a schematic diagram of an embodiment of an electric device using a secondary battery as a power source. DETAILED DESCRIPTION

[0055] Below, with appropriate reference to the accompanying drawings, the embodiments of the artificial graphite and its preparation method, the negative electrode sheet, the secondary battery, the battery module, the battery pack and the electrical device of the present application are described in detail. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0056] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0057] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0058] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0059] Unless otherwise specified, all steps of the present 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 may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0060] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0061] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0062] Artificial graphite

[0063] The key to improving the fast charging capability of secondary batteries lies in improving the performance of the negative electrode sheet and the negative electrode active material. In order to prepare graphite with high gram capacity and fast charging capability, the existing technology usually adopts a process of reducing the particle size or coating carbon on the graphite surface. In general, the smaller the particle size of the graphite, the better the fast charging performance of the graphite. However, in order to obtain graphite with a smaller particle size (for example, Dv50≤16μm), the existing technology often needs to increase the intensity during grinding, which will produce more defect sites on the graphite surface and increase the irreversible consumption of active ions. The carbon coated on the graphite surface is generally amorphous carbon such as soft carbon or hard carbon. This amorphous carbon has low thermal stability, is easy to decompose, and has a large number of active groups on the surface of amorphous carbon. Therefore, the existing process obtains more electrochemical active sites on the graphite surface and stronger activity, which increases the irreversible consumption of active ions during the use of the secondary battery, and cannot make the secondary battery have a higher first-cycle coulomb efficiency and a longer cycle life.

[0064] Typically, smaller graphite particles have a larger specific surface area, more electrochemically active sites on the graphite surface, and greater irreversible consumption of active ions, resulting in a lower first-cycle coulombic efficiency and a shorter cycle life for secondary batteries. The inventors unexpectedly discovered that by rationally controlling the number of electrochemically active sites, or active groups, on the surface of graphite particles with smaller particle sizes, secondary batteries can achieve higher first-cycle coulombic efficiency and longer cycle life, while maintaining good fast-charging performance.

[0065] The first aspect of the embodiment of the present application provides an artificial graphite having no amorphous carbon coating layer on its surface and having fast charging capability, which can enable a secondary battery to have a higher first-cycle coulombic efficiency and a longer cycle life. The particle size of the artificial graphite Dv50 is ≤ 16 μm, and the peak temperature of the artificial graphite under air oxidation is T peak ≥830℃. The peak temperature of the artificial graphite oxidized by air is T peak It refers to the peak temperature of the maximum peak of the differential thermogravimetric analysis curve obtained by thermogravimetric testing of the artificial graphite under the conditions of a weighing mass of 10±0.05 mg, air purge gas with an air flow rate of 60 mL / min, a heating rate of 5°C / min, and a test temperature range of 40°C to 950°C.

[0066] The inventor unexpectedly discovered through extensive research that the peak temperature of artificial graphite during air oxidation is T peak It is closely related to the number of electrochemically active sites or active groups on the surface of artificial graphite. The peak temperature of artificial graphite in air oxidation, T peak The numerical value can intuitively and accurately reflect the number of electrochemically active sites or active groups on the surface of artificial graphite. The peak temperature of artificial graphite in air oxidation, T peak The higher the value, the fewer electrochemically active sites or active groups on the surface of the artificial graphite. The inventors have found that the existing artificial graphite with smaller particle size, such as artificial graphite with particle size Dv50≤16μm, usually has a larger specific surface area and a larger number of electrochemically active sites or active groups on the surface. The peak temperature of the artificial graphite under air oxidation, T peak During the use of secondary batteries, the existing artificial graphite has a high irreversible consumption of active ions, making it difficult to further improve the first-cycle coulombic efficiency and cycle life of secondary batteries.

[0067] The inventors further discovered that when the particle size of artificial graphite Dv50≤16μm and the peak temperature of air oxidation T peak At ≥830℃, the number and activity of electrochemical active sites on the surface of artificial graphite are moderate, and the irreversible consumption of active ions by artificial graphite is low. The secondary battery can have a higher first-cycle coulombic efficiency and a longer cycle life while having good fast charging performance.

[0068] The particle size of artificial graphite Dv50≤16μm, which has good fast charging ability; at the same time, the peak temperature of artificial graphite air oxidation T peak ≥830℃, indicating that the number of electrochemically active sites and active groups on the surface of artificial graphite is small, and the irreversible consumption of active ions by artificial graphite is low, which can enable secondary batteries to have both higher first-cycle coulombic efficiency and longer cycle life.

[0069] The surface of artificial graphite does not have an amorphous carbon coating layer, so the thermal stability of artificial graphite is higher.

[0070] The inventors also unexpectedly discovered that when the peak temperature of the artificial graphite is T peak When the temperature is less than 830℃, the cycle life of the secondary battery is strongly related to the irreversible consumption of active ions by artificial graphite. peak When the temperature is ≥830℃, the cycle life of the secondary battery is weakly correlated with the irreversible consumption of active ions by artificial graphite. At this time, further improvement of the secondary battery performance mainly depends on improvements to the positive electrode, isolation membrane, electrolyte, etc.

[0071] The advantages of the applicant's artificial graphite can be better reflected in battery systems where the first-cycle coulombic efficiency of the negative electrode active material is lower than that of the positive electrode active material, and in battery systems where the cycle life is dominated by irreversible consumption of active ions by the negative electrode active material.

[0072] In some embodiments, the air oxidation peak temperature T of the artificial graphite is peak It may be ≥830°C, ≥831°C, ≥832°C, ≥833°C, ≥834°C, ≥835°C, ≥836°C, ≥837°C, ≥838°C, ≥839°C, or ≥840°C.

[0073] In some embodiments, the air oxidation peak temperature T of the artificial graphite is peak It can be 830℃~840℃, 831℃~840℃, 832℃~840℃, 833℃~840℃, 834℃~840℃, 835℃~840℃, 836℃~840℃, 830℃~839℃, 831℃~839℃, 832℃~839℃, 833℃~839℃, 834℃~839℃, 835℃~839℃, 836℃~839℃, 830℃ ~838℃, 831℃~838℃, 832℃~838℃, 833℃~838℃, 834℃~838℃, 835℃~838℃, 830℃~837℃, 831℃~837℃, 832℃~837℃, 833℃~837℃, 834℃~837℃, 830℃~836℃, 831℃~836℃, 832℃~836℃, or 833℃~836℃.

[0074] Peak temperature T of artificial graphite oxidized by air peak Within an appropriate range, the secondary battery can better combine good fast charging performance, higher first-cycle coulombic efficiency and longer cycle life.

[0075] In some embodiments, the particle size Dv50 of the artificial graphite may be ≤16 μm, ≤15.7 μm, ≤15.5 μm, ≤15.2 μm, ≤15 μm, ≤14.7 μm, ≤14.5 μm, ≤14.2 μm, ≤14 μm, ≤13.7 μm, or ≤13.5 μm.

[0076] In some embodiments, the particle size Dv50 of the artificial graphite may be 13 μm to 16 μm. Alternatively, the particle size Dv50 of the artificial graphite may be 13 μm to 15.5 μm. Further, the particle size Dv50 of the artificial graphite may be 13.5 μm to 15.5 μm.

[0077] When the particle size Dv50 of artificial graphite is within an appropriate range, artificial graphite can have higher active ion and electron transport properties and better fast charging performance. At the same time, artificial graphite can also have a higher powder compaction density.

[0078] In some embodiments, the particle size Dv10 of the artificial graphite may be ≥5 μm. Alternatively, the particle size Dv10 of the artificial graphite may be 5 μm to 9 μm. Further, the particle size Dv10 of the artificial graphite may be 7 μm to 9 μm.

[0079] When the particle size Dv10 of the artificial graphite is within an appropriate range, the artificial graphite can have a more appropriate specific surface area so as to reduce the irreversible consumption of active ions.

[0080] The Dv10 and Dv50 values ​​of artificial graphite are well known in the art and can be measured using instruments and methods known in the art. For example, they can be measured using a laser particle size analyzer (e.g., Mastersizer 3000) in accordance with GB / T 19077.1-2016. Dv10 represents the particle size at which the cumulative volume distribution percentage of the material reaches 10%, and Dv50 represents the particle size at which the cumulative volume distribution percentage of the material reaches 50%.

[0081] In some embodiments, the specific surface area of ​​the artificial graphite may be 0.8 m 2 / g~1.1m 2 / g. Optionally, the specific surface area of ​​the artificial graphite may be 0.95m 2 / g~1.05m 2 / g.

[0082] Artificial graphite has an appropriate specific surface area, which can reduce side reactions of the electrolyte on its surface, lower gas production within the secondary battery, and reduce volume expansion during the secondary battery cycle. This appropriate specific surface area also imparts suitable electrochemical reactivity, enabling the negative electrode and secondary battery to achieve high kinetic performance. Furthermore, this appropriate specific surface area strengthens the bond between the artificial graphite and the binder, improving the cohesion and adhesion of the negative electrode and reducing volume expansion during cycling.

[0083] The specific surface area of ​​artificial graphite is well known in the art and can be measured using instruments and methods known in the art. For example, it can be measured using the nitrogen adsorption specific surface area analysis test method in accordance with GB / T 19587-2017 and calculated using the BET (Brunauer Emmett Teller) method. The nitrogen adsorption specific surface area analysis test can be performed using a Micromeritics Tri-Star 3020 specific surface area pore size analyzer.

[0084] In some embodiments, the tap density of the artificial graphite may be ≥1 g / cm 3 Optionally, the tap density of the artificial graphite may be 1.10 g / cm 3 ~1.30g / cm 3 .

[0085] By using artificial graphite with the tap density described above, the negative electrode plate can have a more appropriate porosity, ensuring better electrolyte wettability, thereby extending the cycle life of the secondary battery. Furthermore, the tap density of artificial graphite facilitates achieving a higher specific capacity, thereby improving the energy density of the secondary battery.

[0086] The tap density of artificial graphite is well known in the art and can be measured using instruments and methods known in the art. For example, the tap density of artificial graphite can be measured using a powder tap density tester (e.g., Dandong Better BT-301) in accordance with GB / T 5162-2006.

[0087] In some embodiments, the powder compaction density of the artificial graphite under a force of 20,000 N can be ≥1.6 g / cm 3 Optionally, the powder compaction density of the artificial graphite under a force of 20,000 N may be 1.6 g / cm 3 ~1.85g / cm 3 .

[0088] In some embodiments, the powder compaction density of the artificial graphite under a force of 50,000 N can be ≥1.7 g / cm 3 Optionally, the powder compaction density of the artificial graphite under a force of 50,000 N can be 1.7 g / cm 3 ~2.0g / cm 3 .

[0089] By adopting the powder compaction density of the above embodiment, the artificial graphite can have a higher gram capacity. The negative electrode sheet using the artificial graphite also has a higher compaction density, and the secondary battery also has a higher energy density.

[0090] The compacted density of artificial graphite powder is well known in the art and can be measured using instruments and methods known in the art. For example, referring to GB / T 25 24533-2009, an electronic pressure testing machine (such as the UTM7305) can be used to test the compacted density. A certain amount of powder is placed on a compaction mold and various pressures are set. The thickness of the powder at different pressures can be read on the machine, and the compacted density at different pressures can be calculated.

[0091] In some embodiments, the gram capacity of the artificial graphite may be ≥353 mAh / g. Alternatively, the gram capacity of the artificial graphite may be 353 mAh / g to 360 mAh / g.

[0092] In some embodiments, the first-cycle coulombic efficiency of the artificial graphite may be ≥95%. Alternatively, the first-cycle coulombic efficiency of the artificial graphite may be ≥95.3%.

[0093] Preparation method of artificial graphite

[0094] A second aspect of the embodiment of the present application provides a method for preparing artificial graphite, the method comprising the following steps: S10, providing raw coke powder containing volatile components, S20, performing a thermal deposition treatment on the raw coke powder to deposit at least part of the volatile components in the raw coke powder on the surface of the raw coke powder, S30, performing a graphitization treatment on the raw coke powder after the thermal deposition treatment, S40, cooling and discharging the material to obtain a particle size Dv50≤16μm and an air oxidation peak temperature T peak Artificial graphite with a temperature of ≥830°C. The peak temperature of the artificial graphite in air oxidation is T peak It refers to the peak temperature of the maximum peak of the differential thermogravimetric analysis curve obtained by thermogravimetric testing of the artificial graphite under the conditions of a weighing mass of 10±0.05 mg, air purge gas with an air flow rate of 60 mL / min, a heating rate of 5°C / min, and a test temperature range of 40°C to 950°C.

[0095] The preparation method of the artificial graphite of the present application can obtain artificial graphite with low irreversible consumption of surface active ions, no amorphous carbon coating layer on the surface and fast charging capability.

[0096] In some embodiments, in step S10, the mass content of volatile components in the provided raw coke powder may be ≥8.5%. Alternatively, the mass content of volatile components in the provided raw coke powder may be 9% to 10.5%. When the raw coke powder has a high content of volatile components, the volatile components can deposit on the surface of the prepared artificial graphite and form a complete protective layer. The protective layer can fully modify the defect sites on the surface of the artificial graphite, reduce the specific surface area of ​​the artificial graphite, reduce the irreversible consumption of active ions, and improve the first-cycle coulombic efficiency and cycle life of the secondary battery.

[0097] In some embodiments, in step S10, the particle size Dv10 of the provided green coke powder may be ≥3.0 μm. A particle size Dv10 of the green coke powder within an appropriate range can reduce the content of fine powder in the green coke powder and reduce irreversible consumption of active ions by the prepared artificial graphite.

[0098] In some embodiments, in step S10, the particle size Dv50 of the provided green coke powder may be ≤16 μm. When the particle size Dv50 of the green coke powder is within an appropriate range, the prepared artificial graphite can have good fast charging performance.

[0099] In some embodiments, in step S10 , green coke powder having Dv10 ≥ 3.0 μm and Dv50 ≤ 16 μm is provided.

[0100] In some embodiments, in step S10, the method for providing green coke powder containing volatile components includes the steps of: coking the green coke raw material to obtain green coke, and grinding the obtained green coke to obtain green coke powder.

[0101] "Raw coke raw materials" refer to components that can be processed to obtain "raw coke", that is, raw materials for preparing raw coke. Optionally, the raw coke raw materials can be selected from one or more of petroleum-based raw materials and coal-based raw materials. As an example, the petroleum-based raw materials are selected from one or more of heavy oil, residual oil, and vacuum residue oil, and the coal-based raw materials are mainly selected from coal tar. Among them, heavy oil, residual oil, and vacuum residue oil are usually produced in petroleum refining processes, and coal tar is usually produced in coal dry distillation processes. "Raw coke" refers to the block product obtained by coking raw coke raw materials. "Raw coke" and "raw coke powder" are completely consistent in composition, and the content of volatile components is also the same. Only the particle size is different. "Raw coke" is ground into "raw coke powder".

[0102] Optionally, the coking process of the raw coke material is carried out in a delayed coking unit. The delayed coking unit comprises a heating furnace and a coke drum. The delayed coking process involves rapidly heating the raw coke material to the desired coking temperature in the heating furnace before it enters the coke drum, where it undergoes preheating and cooling processes to produce green coke.

[0103] Alternatively, the coking temperature of the raw coke material may be ≤550°C. Furthermore, the coking temperature of the raw coke material may be between 450°C and 550°C. Selecting an appropriate coking temperature facilitates obtaining green coke with a high volatile content. Furthermore, excessively high coking temperatures increase the brittleness of the green coke, making it more likely to produce fines when ground into green coke powder.

[0104] Optionally, the preheating preparation time for the coking treatment of the green coke raw materials can be ≥5h. Selecting an appropriate preheating preparation time can reduce the bulk structural defects of the green coke obtained. A preheating preparation time that is too short will cause the green coke obtained to have more bulk structural defects, and when the green coke is ground into powder, the prepared green coke powder will be more easily broken and expose more defects. At the same time, a preheating preparation time that is too short will increase the number of sites for irreversible deintercalation of active ions inside the green coke powder particles, increase the irreversible consumption of active ions by artificial graphite, and reduce the first-cycle coulombic efficiency and cycle life of the secondary battery.

[0105] Optionally, the cooling time of the coking treatment of the raw coke material may be ≥5h.

[0106] Optionally, a mechanical grinding device is used for the grinding process. Furthermore, a mechanical grinding device with an impact hammer grinding disc is used for the grinding process. Generally, roller grinding equipment or mechanical grinding equipment can be used for particle grinding. Among them, the roller grinding equipment crushes the block coke to obtain coke powder by extrusion. However, the coke powder obtained by extrusion has many surface defect sites, and the interior of the coke powder particles after extrusion is prone to cracking, and the coke powder also has many body structure defects. In addition, the coke powder obtained by extrusion has a high content of fine powder, and due to the large number of defect sites on the surface of the fine powder, the irreversible consumption of active ions is also increased. The mechanical grinding equipment crushes the block coke to obtain coke powder by collision, and can grind the irregular morphology of the coke powder particles during collision, so that the coke powder particles are transformed from irregular morphology to spherical morphology, reducing the surface defect sites of artificial graphite and reducing the irreversible consumption of active ions.

[0107] In some embodiments, in step S10, a raw coke powder containing volatile components, or a mixture of raw coke powder containing volatile components and asphalt powder, can be provided. The asphalt powder can assist in the deposition of the volatile components contained in the raw coke powder and form a complete protective layer on the surface of the artificial graphite, thereby preventing the artificial graphite particles from agglomerating softly. Because the artificial graphite particles agglomerate softly, the agglomerated artificial graphite particles will disintegrate under the action of pressure during the cold pressing of the negative electrode sheet. This process increases the number of electrochemically active sites on the surface of the artificial graphite, increases the consumption of active ions, and thus reduces the first-cycle coulombic efficiency and cycle life of the secondary battery.

[0108] Optionally, the particle size Dv50 of the pitch powder is smaller than the particle size Dv50 of the coke powder. In this case, on average, multiple pitch powders may be present on each coke powder, and the contact area between the pitch powder and the coke powder is small. After the pitch powder is softened by heat, its bonding effect on the coke powder is weak, which does not affect the volatilization of volatile components in the coke powder or their deposition on the surface of the coke powder particles. When the pitch powder particle size is larger, multiple coke powders share one pitch powder. After the pitch powder is softened by heat, its contact area with the coke powder is larger, resulting in a stronger bonding effect, which will hinder the volatilization of volatile components in the coke powder and their deposition on the surface of the coke powder.

[0109] Optionally, based on the mass of the green coke powder, the mass percentage of the pitch powder may be ≤5%. Further, the mass percentage of the pitch powder may be ≤2%.

[0110] Optionally, the softening point of the asphalt powder may be ≤250°C. Furthermore, the softening point of the asphalt powder may be ≤200°C. The softening point of asphalt is the temperature at which it softens and sags upon heating, and to some extent indicates the temperature stability of the asphalt. Selecting asphalt powder with an appropriate softening point can prevent coke-producing powder from sticking or agglomerating.

[0111] The softening point test of asphalt powder can refer to GB / T 4507-2014.

[0112] In some embodiments, in step S20 , the thermal deposition temperature may be 250° C. to 700° C. Alternatively, the thermal deposition temperature may be 500° C. to 700° C.

[0113] The purpose of thermal deposition treatment is to convert the volatile components in the raw coke powder into a protective layer on the surface of artificial graphite, modify the defect sites on the surface of artificial graphite, reduce the specific surface area of ​​artificial graphite, reduce the irreversible consumption of active ions, and improve the first-cycle coulombic efficiency and cycle life of secondary batteries.

[0114] In some embodiments, the thermal deposition process can be performed in stages. For example, the temperature may be first raised to a relatively low temperature (e.g., 250°C to 450°C, optionally 350°C to 450°C) for a period of thermal deposition to allow volatile components in the green coke powder to settle; the temperature may then be further raised to a higher temperature (e.g., 500°C to 700°C) to ensure that any volatile components in the green coke powder that may not have been thermally deposited are completely volatilized, thereby preventing the prepared artificial graphite from agglomerating or sticking.

[0115] In some embodiments, in step S20, the thermal deposition time may be ≥ 1 hour. Alternatively, the thermal deposition time may be 1 hour to 3 hours.

[0116] In some embodiments, in step S20, the thermal deposition process can be performed in a vertical stirred tank, a horizontal stirred tank, or a horizontal drum furnace. The thermal deposition process can be performed while heating and stirring, which is conducive to the sufficient deposition of volatile components in the green coke powder.

[0117] In some embodiments, in step S30, the graphitization temperature may be 2800° C. to 3000° C. Graphitization can effectively eliminate bulk structural defects of artificial graphite, reduce irreversible consumption of active ions by artificial graphite, and improve the first-cycle coulombic efficiency and cycle life of the secondary battery.

[0118] In some embodiments, in step S30, the graphitization treatment time may be 6 hours to 8 hours.

[0119] In some embodiments, in step S30, the graphitization process may be performed in an Acheson graphitization device.

[0120] In some embodiments, in step S40, the discharge temperature may be ≤350°C. When the discharge temperature is high, a large number of active groups (such as dangling bonds) are generated on the surface of the artificial graphite under air oxidation, reducing the first-cycle coulombic efficiency of the artificial graphite and the secondary battery. Therefore, selecting an appropriate discharge temperature can reduce the number of active groups on the surface of the artificial graphite, reduce the irreversible consumption of active ions, and enable the artificial graphite to have a higher first-cycle coulombic efficiency, thereby achieving a higher first-cycle coulombic efficiency and a longer cycle life for the secondary battery.

[0121] In some embodiments, the ratio of the particle size Dv50 of the green coke powder provided in step S10 to the particle size Dv50 of the artificial graphite obtained in step S40 may be ≥0.85. Alternatively, the ratio of the particle size Dv50 of the green coke powder provided in step S10 to the particle size Dv50 of the artificial graphite obtained in step S40 may be 0.85 to 0.95. In this case, it can be ensured that the prepared artificial graphite does not exhibit significant adhesion or agglomeration.

[0122] In some embodiments, the ratio of the specific surface area of ​​the green coke powder provided in step S10 to the specific surface area of ​​the artificial graphite obtained in step S40 may be ≥1.5. Alternatively, the ratio of the specific surface area of ​​the green coke powder provided in step S10 to the specific surface area of ​​the artificial graphite obtained in step S40 may be ≥1.76. In this case, the volatile components in the green coke powder are ensured to be fully deposited and modify the defect sites on the surface of the artificial graphite.

[0123] In some embodiments, the method for preparing artificial graphite may include the following steps: providing a coke powder having a mass content of volatile components ≥ 8.5%, optionally a mass content of volatile components of 9% to 10.5%; thermally depositing the coke powder at 250°C to 700°C, optionally 500°C to 700°C, so that at least part of the volatile components in the coke powder are deposited on the surface of the coke powder; graphitizing the coke powder after thermal deposition treatment at 2800°C to 3000°C; cooling the coke powder to a temperature ≤ 350°C and discharging the material to obtain a particle size Dv50 ≤ 16 μm and an air oxidation peak temperature T peak Artificial graphite ≥830℃.

[0124] In some embodiments, the method for preparing artificial graphite may include the following steps: providing a coke powder having a mass content of volatile components ≥8.5%, Dv10 ≥3.0 μm, and Dv50 ≤16 μm; thermally depositing the coke powder at 250°C to 700°C, optionally 500°C to 700°C, so that at least part of the volatile components in the coke powder are deposited on the surface of the coke powder; graphitizing the coke powder after thermal deposition at 2800°C to 3000°C; cooling the coke powder to a temperature ≤350°C and discharging the material to obtain a particle size Dv50 ≤16 μm and an air oxidation peak temperature T peak Artificial graphite ≥830℃.

[0125] secondary batteries

[0126] Secondary batteries, also known as rechargeable batteries or storage batteries, are batteries that can be recharged to activate the active materials after discharge and continue to be used.

[0127] Typically, a secondary battery consists of a positive electrode, a negative electrode, a separator, and an electrolyte. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing the active ions to pass through. The electrolyte conducts the active ions between the positive and negative electrodes.

[0128] [Negative electrode]

[0129] In the secondary battery of the present application, the negative electrode plate includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector. For example, the negative electrode current collector has two surfaces that oppose each other in the thickness direction of the negative electrode current collector, and the negative electrode film layer is disposed on either or both of the two opposing surfaces of the negative electrode current collector.

[0130] In the secondary battery of the present application, the negative electrode film layer generally comprises a negative electrode active material, an optional binder, an optional conductive agent, and other optional additives. The negative electrode film layer is generally formed by coating a negative electrode slurry on a negative electrode current collector, drying, and cold pressing. The negative electrode slurry is generally formed by dispersing the negative electrode active material, an optional conductive agent, an optional binder, and other optional additives in a solvent and stirring them evenly. The solvent may be N-methylpyrrolidone (NMP) or deionized water, but is not limited thereto.

[0131] In the secondary battery of the present application, the negative electrode active material may include one of the artificial graphite according to the first embodiment of the present application and the artificial graphite prepared according to the method of the second embodiment of the present application.

[0132] In the secondary battery of the present application, the negative electrode active material may also include other negative electrode active materials for secondary batteries that are well known in the art. As an example, other negative electrode active materials may include one or more of natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. Silicon-based materials may include one or more of elemental silicon, silicon oxide, silicon-carbon composites, silicon-nitrogen composites, and silicon alloy materials. Tin-based materials may include one or more of elemental tin, tin oxide, and tin alloy materials. The present application is not limited to these materials, and other traditionally known materials that can be used as negative electrode active materials for secondary batteries may also be used. These other negative electrode active materials may be used alone or in combination of two or more.

[0133] As an example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. As an example, the binder may include one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). Other optional additives may include thickeners (e.g., sodium carboxymethyl cellulose CMC-Na), PTC thermistor materials, etc.

[0134] In the secondary battery of the present application, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may be selected from one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may be selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0135] [Positive electrode]

[0136] In the secondary battery of the present application, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector and comprising a positive electrode active material. For example, the positive electrode current collector has two opposing surfaces in the thickness direction of the positive electrode current collector, and the positive electrode film layer is disposed on either or both of the two opposing surfaces of the positive electrode current collector.

[0137] In the secondary battery of the present application, the positive electrode active material may be a positive electrode active material for a secondary battery known in the art. For example, the positive electrode active material may include one or more of a lithium transition metal oxide, a lithium phosphate containing an olivine structure, and their respective modified compounds. Examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds. Examples of lithium phosphate containing an olivine structure may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite material of lithium manganese iron phosphate and carbon, and their respective modified compounds. The present application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for secondary batteries may also be used.

[0138] In some embodiments, in order to further improve the energy density of the secondary battery, the positive electrode active material may include one or more of the lithium transition metal oxides and modified compounds thereof shown in Formula 1.

[0139] Li a Ni b Co c M d O e A f Formula 1,

[0140] In formula 1, 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, M is selected from one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A is selected from one or more of N, F, S and Cl.

[0141] In the present application, the modified compounds of the above materials may be doping modification or surface coating modification of the positive electrode active material.

[0142] In the secondary battery of the present application, the positive electrode film layer generally comprises a positive electrode active material and an optional binder and an optional conductive agent. The positive electrode film layer is generally formed by coating a positive electrode slurry on a positive electrode current collector, drying, and cold pressing. The positive electrode slurry is generally formed by dispersing a positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring them evenly. The solvent may be N-methylpyrrolidone (NMP), but is not limited thereto. As an example, the binder for the positive electrode film layer may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0143] In the secondary battery of the present application, the positive electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may be selected from one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may be selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0144] [Electrolytes]

[0145] The secondary battery of the present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be selected from at least one of a solid electrolyte and a liquid electrolyte (ie, an electrolyte solution).

[0146] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0147] The present application does not specifically limit the type of electrolyte salt, and it can be selected according to needs. In some embodiments, as an example, the electrolyte salt can be selected from one or more of LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiClO4 (lithium perchlorate), LiAsF6 (lithium hexafluoroarsenate), LiFSI (lithium bisfluorosulfonyl imide), LiTFSI (lithium bistrifluoromethanesulfonyl imide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalatoborate), LiBOB (lithium dioxalatoborate), LiPO2F2 (lithium difluorophosphate), LiDFOP (lithium difluorooxalatophosphate), and LiTFOP (lithium tetrafluorooxalatophosphate).

[0148] The present application does not specifically limit the type of solvent and can be selected according to demand. In some embodiments, as an example, the solvent can be selected from ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS) and diethyl sulfone (ESE). One or more.

[0149] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, or additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature performance.

[0150] [Isolation film]

[0151] Secondary batteries using electrolytes and some secondary batteries using solid electrolytes also include an isolation membrane. The isolation membrane is arranged between the positive electrode plate and the negative electrode plate to play an isolation role. The present application has no special restrictions on the type of isolation membrane, and any well-known porous structure isolation membrane with good chemical stability and mechanical stability can be selected. In some embodiments, the material of the isolation membrane can be selected from one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film. When the isolation membrane is a multi-layer composite film, the materials of each layer are the same or different.

[0152] In some embodiments, the positive electrode sheet, the separator, and the negative electrode sheet may be formed into an electrode assembly by a winding process or a lamination process.

[0153] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0154] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

[0155] The present application has no particular restrictions on the shape of the secondary battery, which can be cylindrical, square or any other shape. Figure 1 The secondary battery 5 is a square structure as an example.

[0156] In some embodiments, reference Figure 2 The outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 is used to cover the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, which can be adjusted according to needs.

[0157] In some embodiments, secondary batteries may be assembled into a battery module. The battery module may contain multiple secondary batteries, and the specific number may be adjusted according to the application and capacity of the battery module.

[0158] Figure 3 4 is an example of a battery module. Figure 3 In the battery module 4, the plurality of secondary batteries 5 may be arranged in sequence along the length of the battery module 4. Of course, they may also be arranged in any other manner. The plurality of secondary batteries 5 may further be fixed by fasteners.

[0159] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0160] In some embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0161] Figure 4 and Figure 5 The battery pack 1 is used as an example. Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 is used to cover the lower box body 3 and form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner in the battery box.

[0162] The method for preparing the secondary battery of the present application is well known. In some embodiments, a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte can be assembled to form a secondary battery. As an example, the positive electrode sheet, separator, and negative electrode sheet can be formed into an electrode assembly through a winding process or a lamination process. The electrode assembly is placed in an outer packaging, dried, and then injected with electrolyte. The secondary battery is then vacuum packaged, allowed to stand, formed, and shaped.

[0163] Electrical devices

[0164] The embodiments of the present application also provide an electric device, which includes at least one of the secondary battery, battery module, or battery pack of the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device can be, but is not limited to, a mobile device (such as a mobile phone, a laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship, a satellite, an energy storage system, etc.

[0165] The electrical device may select a secondary battery, a battery module or a battery pack according to its usage requirements.

[0166] Figure 6 This is an example of an electric device. This electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of this electric device, a battery pack or battery module can be used.

[0167] As another example, the electric device may be a mobile phone, a tablet computer, a laptop computer, etc. Such an electric device is usually required to be lightweight and thin, and may use a secondary battery as a power source.

[0168] Example

[0169] The following examples describe the present disclosure in more detail and are intended to be illustrative only, as various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise indicated, all parts, percentages, and ratios reported in the following examples are by weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and used directly without further processing, and all instruments used in the examples are commercially available.

[0170] Example 1

[0171] (1) Preparation of artificial graphite

[0172] The petroleum raw material was subjected to delayed coking at 500°C, wherein the preheating was performed for 6 hours and the cooling was performed for 6 hours, to obtain petroleum non-needle coke with a volatile component content of 10.2%. A mechanical grinding device with an impact hammer mill was used to crush the lump coke into coke powder, and the particle size Dv10 of the coke powder was controlled to be 3.0 μm, the particle size Dv50 was 13.0 μm, and the specific surface area was 1.93 m 2 / g; placing green coke powder in a horizontal stirring kettle and heating it to 650°C and maintaining it for 1 hour to deposit the volatile components in the green coke powder; placing the deposited green coke powder in a graphite crucible, and then placing the graphite crucible in an Acheson graphitization furnace, filling the periphery of the graphite crucible with a resistor material, applying power so that current flows through the resistor material to generate heat energy, and making the temperature in the graphite crucible reach 2800°C and maintaining it for 8 hours to graphitize the green coke powder; naturally cooling until the surface temperature of the graphite crucible is below 300°C and discharging the material to obtain artificial graphite.

[0173] (2) Preparation of negative electrode sheet

[0174] The artificial graphite prepared as above is used as the negative electrode active material, and is mixed with the conductive agent acetylene black, the binder styrene butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC-Na) in a mass ratio of 96:1:1:1. Then, deionized water is added as a solvent and fully stirred according to a method known in the art to form a negative electrode slurry; the negative electrode slurry is evenly coated on the negative electrode current collector copper foil, and after drying, a negative electrode film layer is obtained, which is then subjected to a cold pressing process to obtain a negative electrode sheet.

[0175] (3) Preparation of positive electrode sheet

[0176] The positive electrode active material lithium iron phosphate, the binder polyvinylidene fluoride, and the conductive agent acetylene black are mixed in a mass ratio of 97:2:1, and then the solvent N-methylpyrrolidone (NMP) is added to adjust the viscosity. The mixture is fully stirred into a positive electrode slurry according to a method known in the art; the positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil, and after drying, a positive electrode film layer is obtained, which is then subjected to a cold pressing process to obtain a positive electrode sheet.

[0177] (4) Preparation of electrolyte

[0178] In an argon atmosphere glove box with a water content of <10 ppm, equal volumes of ethylene carbonate (EC) and propylene carbonate (PC) were mixed uniformly to obtain an organic solvent, and then 1 mol / L LiPF6 was uniformly dissolved in the above organic solvent to obtain an electrolyte.

[0179] (5) Preparation of isolation membrane

[0180] A polyethylene (PE) film was used as the separator.

[0181] (6) Preparation of secondary batteries

[0182] The positive electrode sheet, separator, and negative electrode sheet are stacked and wound in sequence to obtain an electrode assembly; the electrode assembly is added to the outer packaging aluminum-plastic film, dried and then injected with electrolyte, and after packaging, standing, formation, aging, secondary packaging, capacity and other processes, a secondary battery is obtained.

[0183] Example 2

[0184] The preparation method of the secondary battery is similar to that of Example 1, except for the preparation process of the artificial graphite (step 1), which specifically includes the following steps.

[0185] The petroleum raw material was subjected to delayed coking at 500°C, wherein the preheating was performed for 6 hours and the cooling was performed for 6 hours, to obtain petroleum non-needle coke with a volatile component content of 10.2%. A mechanical grinding device with an impact hammer mill was used to crush the lump coke into coke powder, and the particle size Dv10 of the coke powder was controlled to be 3.2 μm, the particle size Dv50 was 13.2 μm, and the specific surface area was 1.83 m 2 / g; placing green coke powder in a horizontal stirring kettle and heating it to 650°C and maintaining it for 1 hour to deposit the volatile components in the green coke powder; placing the deposited green coke powder in a graphite crucible, and then placing the graphite crucible in an Acheson graphitization furnace, filling the periphery of the graphite crucible with a resistor material, applying power so that current flows through the resistor material to generate heat energy, and making the temperature in the graphite crucible reach 2800°C and maintaining it for 8 hours to graphitize the green coke powder; naturally cooling until the surface temperature of the graphite crucible is below 300°C and discharging the material to obtain artificial graphite.

[0186] Example 3

[0187] The preparation method of the secondary battery is similar to that of Example 1, except for the preparation process of the artificial graphite (step 1), which specifically includes the following steps.

[0188] The petroleum raw material was subjected to delayed coking at 500°C, wherein the preheating was performed for 6 hours and the cooling was performed for 6 hours, to obtain petroleum non-needle coke with a volatile component content of 10.2%. A mechanical grinding device with an impact hammer mill was used to crush the lump coke into coke powder, and the particle size Dv10 of the coke powder was controlled to be 3.2 μm, the particle size Dv50 was 13.2 μm, and the specific surface area was 1.83 m 2 / g; adding 2% coal-based pitch powder (softening point of 250°C, particle size Dv50 of 3μm) to the above-mentioned green coke powder; placing the green coke powder in a horizontal stirring kettle and heating it to 650°C and maintaining it for 1 hour to deposit the volatile components in the green coke powder; placing the deposited green coke powder in a graphite crucible, and then placing the graphite crucible in an Acheson graphitization furnace, filling the graphite crucible with resistor material, applying power so that current flows through the resistor material to generate heat energy, and making the temperature in the graphite crucible reach 2800°C and maintaining it for 8 hours to graphitize the green coke powder; naturally cooling until the surface temperature of the graphite crucible is lower than 300°C and discharging the material to obtain artificial graphite.

[0189] Example 4

[0190] The preparation method of the secondary battery is similar to that of Example 1, except for the preparation process of the artificial graphite (step 1), which specifically includes the following steps.

[0191] The petroleum raw material was subjected to delayed coking at 500°C, with a preheating period of 7 hours and a cooling period of 6 hours, to obtain a petroleum needle coke with a volatile component content of 9.4%. A mechanical grinding device with an impact hammer mill was used to crush the lump coke into coke powder, and the particle size Dv10 of the coke powder was controlled to be 3.1μm, the particle size Dv50 was 14.3μm, and the specific surface area was 1.97m. 2 / g; placing green coke powder in a horizontal stirring kettle and heating it to 650°C and maintaining it for 1 hour to deposit the volatile components in the green coke powder; placing the deposited green coke powder in a graphite crucible, and then placing the graphite crucible in an Acheson graphitization furnace, filling the periphery of the graphite crucible with a resistor material, applying power so that current flows through the resistor material to generate heat energy, and making the temperature in the graphite crucible reach 2800°C and maintaining it for 8 hours to graphitize the green coke powder; naturally cooling until the surface temperature of the graphite crucible is below 300°C and discharging the material to obtain artificial graphite.

[0192] Comparative Example 1

[0193] The preparation method of the secondary battery is similar to that of Example 1, except for the preparation process of the artificial graphite (step 1), which specifically includes the following steps.

[0194] The petroleum raw material was subjected to delayed coking at 600°C, wherein the preheating was performed for 4.5 hours and the cooling was performed for 3 hours, to obtain petroleum non-needle coke with a volatile component content of 7.8%. The lump coke was crushed into coke powder using a mechanical grinding device with an impact hammer mill. The particle size Dv10 of the coke powder was controlled to be 2.6 μm, the particle size Dv50 was 14.3 μm, and the specific surface area was 1.32 m 2 / g; placing green coke powder in a horizontal stirring kettle and heating it to 650°C and maintaining it for 1 hour to deposit the volatile components in the green coke powder; placing the deposited green coke powder in a graphite crucible, and then placing the graphite crucible in an Acheson graphitization furnace, filling the periphery of the graphite crucible with a resistor material, applying power so that current flows through the resistor material to generate heat energy, and making the temperature in the graphite crucible reach 2800°C and maintaining it for 8 hours to graphitize the green coke powder; naturally cooling until the surface temperature of the graphite crucible is below 300°C and discharging the material to obtain artificial graphite.

[0195] Comparative Example 2

[0196] The preparation method of the secondary battery is similar to that of Example 1, except for the preparation process of the artificial graphite (step 1), which specifically includes the following steps.

[0197] The petroleum raw material was subjected to delayed coking at 500°C, wherein the preheating was performed for 6 hours and the cooling was performed for 6 hours, to obtain petroleum non-needle coke with a volatile component content of 10.2%. The lump coke was crushed into coke powder using a mechanical grinding device with an impact hammer mill. The particle size Dv10 of the coke powder was controlled to be 2.4 μm, the particle size Dv50 was 9.8 μm, and the specific surface area was 2.73 m 2 / g; placing green coke powder in a horizontal stirring kettle and heating it to 650°C and maintaining it for 1 hour to deposit the volatile components in the green coke powder; placing the deposited green coke powder in a graphite crucible, and then placing the graphite crucible in an Acheson graphitization furnace, filling the periphery of the graphite crucible with a resistor material, applying power so that current flows through the resistor material to generate heat energy, and making the temperature in the graphite crucible reach 2800°C and maintaining it for 8 hours to graphitize the green coke powder; naturally cooling until the surface temperature of the graphite crucible is below 300°C and discharging the material to obtain artificial graphite.

[0198] Comparative Example 3

[0199] The preparation method of the secondary battery is similar to that of Example 1, except for the preparation process of the artificial graphite (step 1), which specifically includes the following steps.

[0200] The petroleum raw material was subjected to delayed coking at 500°C, wherein the preheating was performed for 6 hours and the cooling was performed for 6 hours, to obtain petroleum non-needle coke with a volatile component content of 10.2%. A mechanical grinding device with an impact hammer mill was used to crush the lump coke into coke powder, and the particle size Dv10 of the coke powder was controlled to be 3.2 μm, the particle size Dv50 was 13.2 μm, and the specific surface area was 1.83 m 2 / g; the raw coke powder is placed in a horizontal stirred kettle and heated to 650°C for 1 hour to deposit the volatile components in the raw coke powder; the deposited raw coke powder is placed in a graphite crucible, which is then placed in an Acheson graphitization furnace. A resistor material is filled around the graphite crucible, and current is passed through the resistor material to generate heat energy. The temperature in the graphite crucible reaches 2800°C and is maintained for 8 hours to graphitize the raw coke powder; the crucible is cooled naturally until the surface temperature of the graphite crucible is below 300°C, and the material is discharged to obtain artificial graphite. The artificial graphite is mixed with asphalt in a mass ratio of 100:3, and the mixed material is transferred to a carbonization furnace and carbonized at 1150°C under nitrogen protection to obtain amorphous carbon-coated artificial graphite.

[0201] Comparative Example 4

[0202] The preparation method of the secondary battery is similar to that of Example 1, except for the preparation process of the artificial graphite (step 1), which specifically includes the following steps.

[0203] The petroleum raw material was subjected to delayed coking at 500°C, wherein the preheating was performed for 6 hours and the cooling was performed for 6 hours, to obtain petroleum non-needle coke with a volatile component content of 10.2%. A mechanical grinding device with an impact hammer mill was used to crush the lump coke into coke powder, and the particle size Dv10 of the coke powder was controlled to be 3.2 μm, the particle size Dv50 was 13.2 μm, and the specific surface area was 1.83 m 2 / g; placing green coke powder in a horizontal stirring kettle and heating it to 650°C and maintaining it for 1 hour to deposit the volatile components in the green coke powder; placing the deposited green coke powder in a graphite crucible, and then placing the graphite crucible in an Acheson graphitization furnace, filling the periphery of the graphite crucible with a resistor material, applying power so that current flows through the resistor material to generate heat energy, and making the temperature in the graphite crucible reach 2800°C and maintaining it for 8 hours to graphitize the green coke powder; naturally cooling to a surface temperature of the graphite crucible of 400°C and discharging the material to obtain artificial graphite.

[0204] Comparative Example 5

[0205] The preparation method of the secondary battery is similar to that of Example 1, except for the preparation process of the artificial graphite (step 1), which specifically includes the following steps.

[0206] The petroleum raw material was subjected to delayed coking at 600°C, with a preheating period of 4.5 hours and a cooling period of 3 hours, to obtain petroleum non-needle coke with a volatile component content of 7.8%. A mechanical grinding device with an impact hammer mill was used to crush the lump coke into coke powder, and the particle size Dv10 of the coke powder was controlled to be 7.9 μm, the particle size Dv50 was 19.3 μm, and the specific surface area was 0.98 m 2 / g; placing the above-mentioned green coke powder in a graphite crucible, then placing the graphite crucible in an Acheson graphitization furnace, filling the graphite crucible with a resistor material, applying power so that current flows through the resistor material to generate heat energy, and making the temperature in the graphite crucible reach 2800°C and maintain it for 8 hours to graphitize the green coke powder; naturally cooling until the surface temperature of the graphite crucible is lower than 300°C, discharging the material, and obtaining artificial graphite.

[0207] Example 5

[0208] The preparation method of the secondary battery is similar to that of Example 2, except that during the preparation of the positive electrode sheet, the positive electrode active material is LiNi 0.6 Co 0.2 Mn 0.2 O2.

[0209] Comparative Example 6

[0210] The preparation method of the secondary battery is similar to that of Comparative Example 1, except that during the preparation of the positive electrode sheet, the positive electrode active material is LiNi 0.6 Co 0.2 Mn 0.2 O2.

[0211] Example 6 and Comparative Example 7 were prepared according to the following method.

[0212] (1) Preparation of negative electrode sheet

[0213] The artificial graphite prepared in Example 2 and Comparative Example 2 was respectively mixed with SiO (Dv50 of 6 μm) in a mass ratio of 95:5 as the negative electrode active material, and then mixed with a conductive agent acetylene black, a binder styrene-butadiene rubber (SBR), and a thickener sodium carboxymethyl cellulose (CMC-Na) in a mass ratio of 96:1:1:1. After that, deionized water was added as a solvent, and the mixture was fully stirred according to a method known in the art to form a negative electrode slurry. The negative electrode slurry was evenly coated on the negative electrode current collector copper foil, dried to obtain a negative electrode film layer, and then subjected to a cold pressing process to obtain a negative electrode sheet.

[0214] (2) Preparation of positive electrode sheet

[0215] Positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O2, binder polyvinylidene fluoride, and conductive agent acetylene black are mixed in a mass ratio of 97:2:1, and then solvent N-methylpyrrolidone (NMP) is added to adjust the viscosity. The mixture is fully stirred into a positive electrode slurry according to a method known in the art; the positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil, and the positive electrode film layer is obtained after drying, and then the positive electrode sheet is obtained through a cold pressing process.

[0216] (3) Preparation of electrolyte

[0217] In an argon atmosphere glove box with a water content of <10 ppm, ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 30:40:3 to obtain an organic solvent, 1% by mass of vinylene carbonate (VC) was added, and then 1 mol / L of LiPF6 was uniformly dissolved in the above organic solvent to obtain an electrolyte.

[0218] (4) Preparation of isolation membrane

[0219] A polyethylene (PE) film was used as the separator.

[0220] (5) Preparation of secondary batteries

[0221] The positive electrode sheet, separator, and negative electrode sheet are stacked and wound in sequence to obtain an electrode assembly; the electrode assembly is added to the outer packaging aluminum-plastic film, dried and then injected with electrolyte, and after packaging, standing, formation, aging, secondary packaging, capacity and other processes, a secondary battery is obtained.

[0222] Performance Testing

[0223] The Dv10, Dv50, specific surface area, tap density and powder compaction density of artificial graphite were tested according to the method described above in the manual.

[0224] (1) Peak temperature T of artificial graphite during air oxidation peak test

[0225] The maximum peak of the differential thermogravimetric analysis curve obtained by thermogravimetric testing of artificial graphite under the conditions of weighing mass of 10±0.05 mg, purge gas of air at a flow rate of 60 mL / min, heating rate of 5°C / min, and test temperature range of 40°C to 950°C is the air oxidation peak of artificial graphite, and the peak temperature of the maximum peak is T peak .

[0226] Specifically, the test was conducted using a German NETZSCH STA 449 F3 synchronous thermal analyzer. First, 10±0.05mg of artificial graphite sample was weighed into a flat-bottomed Al2O3 crucible without the lid. Instrument parameters were set: air was used as the purge gas at a flow rate of 60mL / min, and nitrogen was used as the shielding gas at a flow rate of 20mL / min. The heating rate was set to 5°C / min, and the test temperature range was 40°C to 950°C. When the temperature is below 500°C, since there are no characteristic peaks at this stage, a rapid heating rate of, for example, 10°C / min can be used.

[0227] (2) Fast charging performance test

[0228] At 25°C, the secondary battery was charged and discharged for the first time at a current of 0.33C (where 1C represents the current value corresponding to completely discharging the theoretical capacity of the secondary battery within 1 hour). The specific steps included: charging the secondary battery at a constant current of 0.33C to the upper cutoff voltage, then charging at a constant voltage until the current was ≤ 0.05C; the secondary battery was allowed to rest for 5 minutes, and then discharged at a constant current of 0.33C to the lower cutoff voltage, and the actual discharge capacity C0 of the secondary battery was recorded.

[0229] The secondary battery was charged at different charge rates (0.5C0, 0.8C0, 1.2C0, 1.5C0, 2.0C0, 2.5C0, 3.0C0, 4.0C0, and 5.0C0) at a constant current until the upper cutoff voltage or the negative electrode potential dropped to 0V (whichever occurred first). After each charge, it was discharged at 0.33C0 to the lower cutoff voltage. The corresponding negative electrode potential was recorded when the secondary battery was charged to 10% SOC, 20% SOC, 30% SOC, 40% SOC, 50% SOC, 60% SOC, 70% SOC, and 80% SOC (SOC represents the state of charge of the secondary battery) at different charge rates.

[0230] The charge rate-negative electrode potential curves at different states of charge are drawn, and the charge rate corresponding to the negative electrode potential of 0V at different states of charge is obtained by linear fitting. The charge rate is the charge window at the state of charge. The charge windows at different states of charge are denoted as C 10％SOC 、C 20％SOC 、C 30％SOC 、C 40％SOC 、C 50％SOC 、C 60％SOC 、C 70％SOC 、C 80％SOC .

[0231] According to the formula (60 / C 20％SOC +60 / C 30％SOC +60 / C 40％SOC +60 / C 50％SOC +60 / C 60％SOC +60 / C 70％SOC +60 / C 80％SOC )×10%, and the charging time T for the secondary battery to charge from 10% SOC to 80% SOC is calculated. The shorter the charging time, the better the rapid charging performance of the secondary battery.

[0232] (3) Cyclic performance test

[0233] At 25°C, charge the secondary battery at a constant current of 1C to the upper cut-off voltage, then charge at a constant voltage to a current ≤ 0.05C, and record the charging capacity at this time, which is the first-cycle charging capacity; discharge the secondary battery at a constant current of 1C to the lower cut-off voltage, and then let it stand for 5 minutes. This is a cyclic charge and discharge process. Record the discharge capacity at this time, which is the first-cycle discharge capacity.

[0234] The secondary battery is subjected to a cyclic charge and discharge test according to the above method, and the discharge capacity after each cycle is recorded until the discharge capacity of the secondary battery decays to 80% of the first cycle discharge capacity. The number of cycles at this time is used to represent the cycle performance of the secondary battery.

[0235] The first cycle coulombic efficiency of a secondary battery = first cycle discharge capacity / first cycle charge capacity × 100%.

[0236] The charge and discharge voltage range of the secondary batteries of Examples 1 to 4 and Comparative Examples 1 to 5 is 2.5 V to 3.65 V. The charge and discharge voltage range of the secondary batteries of Example 5 and Comparative Example 6 is 2.8 V to 4.35 V. The charge and discharge voltage range of the secondary batteries of Example 6 and Comparative Example 7 is 2.5 V to 4.25 V.

[0237] Table 1 shows the test results of the artificial graphite of Examples 1 to 4 and Comparative Examples 1 to 5. Table 2 shows the performance test results of the secondary batteries of Examples 1 to 4 and Comparative Examples 1 to 5. Table 3 shows the performance test results of the secondary batteries of Example 5 and Comparative Example 6. Table 4 shows the performance test results of the secondary batteries of Example 6 and Comparative Example 7.

[0238] Table 1

[0239]

[0240] Serial number Charging time T(min) First-cycle Coulomb efficiency Number of cycles Example 1 9.1 93.5％ 7480 Example 2 9.2 93.6％ 7600 Example 3 9.6 93.5％ 7500 Example 4 9.8 93.8％ 7800 Comparative Example 1 11.8 92.2％ 6000 Comparative Example 2 9.5 92.4％ 5900 Comparative Example 3 9.3 91.7％ 5500 Comparative Example 4 9.7 91.8％ 5600 Comparative Example 5 14.7 93.4％ 5950

[0241] Serial number Charging time T(min) First-cycle Coulomb efficiency Number of cycles Example 5 9.3 87.7％ 2200 Comparative Example 6 11.4 87.1％ 2000

[0242] Serial number Charging time T(min) First-cycle Coulomb efficiency Number of cycles Example 6 9.3 89.2％ 1800 Comparative Example 7 9.5 88.2％ 1500

[0243] From the data in Table 2, it can be seen that the secondary batteries of Examples 1 to 4 have higher first-cycle coulombic efficiency and longer cycle life than those of Comparative Examples 1 to 5. This is mainly due to the fact that the peak temperature T of the artificial graphite in air oxidation of Examples 1 to 4 is peak ≥830℃, indicating that the number of electrochemically active sites and active groups on the surface of artificial graphite is small, and the irreversible consumption of active ions by artificial graphite is low. Therefore, the secondary battery can have a higher first-cycle coulombic efficiency and a longer cycle life under the premise of having good fast charging performance.

[0244] The peak temperature T of the artificial graphite in air oxidation of Comparative Examples 1 to 4peak <830℃, indicating that the number of electrochemically active sites and active groups on the surface of the prepared artificial graphite is relatively large. Therefore, the irreversible consumption of active ions by artificial graphite is relatively high, and the secondary battery cannot have a higher first-cycle coulomb efficiency and a longer cycle life under the premise of having good fast charging performance. In Comparative Example 1, the coking treatment temperature of the raw coke raw material is relatively high, resulting in too low a volatile component content in the raw coke powder. The volatile components cannot be fully deposited and form a complete protective layer on the surface of the artificial graphite, and the defect sites on the surface of the artificial graphite cannot be fully modified. Therefore, the irreversible consumption of active ions by artificial graphite is relatively high. The content of fine powder in the raw coke powder of Comparative Example 2 is relatively high, and there are a large number of defect sites on the surface of the fine powder. Therefore, the irreversible consumption of active ions by artificial graphite is also relatively high. Comparative Example 3 is artificial graphite coated with amorphous carbon, and the peak temperature of the air oxidation peak of the artificial graphite is T peak The temperature is only 799°C. This is mainly due to the fact that the carbon coated on the surface of artificial graphite is soft carbon, which has low thermal stability and is easily oxidized and decomposed. In addition, the number of active groups on the surface of soft carbon is large, resulting in a high irreversible consumption of active ions. In Comparative Example 4, when preparing artificial graphite, a higher discharge temperature was selected, resulting in the generation of a large number of active groups on the surface of the artificial graphite under the action of air oxidation, which increased the irreversible consumption of active ions.

[0245] The peak temperature T of the artificial graphite in air oxidation of Comparative Example 5 peak ≥830℃, but the Dv50 of artificial graphite is greater than 16μm, and the secondary battery cannot have good fast charging performance, higher first-cycle coulombic efficiency and longer cycle life at the same time.

[0246] As can be seen from the data in Table 3, compared with Comparative Example 6, the coulombic efficiency of the secondary battery in Example 5 increased by about 0.6% in the first cycle, and the cycle life increased by about 10%. As can be seen from the data in Table 4, compared with Comparative Example 7, the coulombic efficiency of the secondary battery in Example 6 increased by about 1.1% in the first cycle, and the cycle life increased by about 20%.

[0247] It can also be seen from the data in Tables 2 to 4 that the advantages of the applicant's artificial graphite can be better reflected in battery systems where the first-cycle coulombic efficiency of the negative electrode active material is lower than that of the positive electrode active material, and in battery systems where the irreversible consumption of active ions by the negative electrode active material dominates the cycle life.

[0248] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. An artificial graphite, wherein the particle size Dv50 of the artificial graphite is 13 μm to 16 μm, the particle size Dv10 of the artificial graphite is ≥ 5 μm, and the air oxidation peak temperature Tpeak of the artificial graphite is ≥ 830°C, wherein: The air oxidation peak temperature Tpeak of the artificial graphite refers to the peak temperature of the maximum peak of the differential thermogravimetric analysis curve obtained by thermogravimetric testing of the artificial graphite under the conditions of a weighing mass of 10±0.05 mg, air purge gas with an air flow rate of 60 mL / min, a heating rate of 5°C / min, and a test temperature range of 40°C to 950°C.

2. The artificial graphite according to claim 1, wherein The particle size Dv50 of the artificial graphite is 13 μm to 15.5 μm.

3. The artificial graphite according to claim 1 or 2, wherein The air oxidation peak temperature Tpeak of the artificial graphite is 830°C to 840°C.

4. The artificial graphite according to claim 3, wherein The air oxidation peak temperature Tpeak of the artificial graphite is 831° C. to 838° C.

5. The artificial graphite according to claim 1, wherein The surface of the artificial graphite does not have an amorphous carbon coating layer.

6. The artificial graphite according to claim 1, wherein The artificial graphite also satisfies one or more of the following (1) to (7): (1) The particle size Dv10 of the artificial graphite is 5 μm to 9 μm; (2) The specific surface area of ​​the artificial graphite is 0.8m 2 / g~1.1m 2 / g; (3) The tap density of the artificial graphite is ≥1g / cm 3 ; (4) The powder compaction density of the artificial graphite under a force of 20,000 N is ≥ 1.6 g / cm 3 ; (5) The powder compaction density of the artificial graphite under a force of 50,000 N is ≥ 1.7 g / cm 3 ; (6) The gram capacity of the artificial graphite is ≥353 mAh / g; (7) The first-cycle coulomb efficiency of the artificial graphite is ≥95%.

7. The artificial graphite according to claim 6, wherein The artificial graphite also satisfies one or more of the following (1) to (6): (1) The specific surface area of ​​the artificial graphite is 0.95m 2 / g~1.05m 2 / g; (2) The tap density of the artificial graphite is 1.10 g / cm 3 ~1.30g / cm 3 (3) The powder compaction density of the artificial graphite under a force of 20,000 N is 1.6 g / cm 3 ~1.85g / cm 3 ; (4) The powder compaction density of the artificial graphite under a force of 50,000 N is 1.7 g / cm 3 ~2.0g / cm 3 ; (5) The gram capacity of the artificial graphite is 353 mAh / g to 360 mAh / g; (6) The first-cycle coulombic efficiency of the artificial graphite is ≥95.3%.

8. A method for preparing artificial graphite, comprising the steps of: S10, providing green coke powder containing volatile components, S20, performing a thermal deposition treatment on the green coke powder to deposit at least part of the volatile components in the green coke powder on the surface of the green coke powder, S30, graphitizing the green coke powder after thermal deposition treatment, S40, cooling and discharging to obtain artificial graphite with a particle size Dv50 of 13 μm to 16 μm, a particle size Dv10 ≥ 5 μm, and an air oxidation peak temperature Tpeak ≥ 830°C. in, The air oxidation peak temperature Tpeak of the artificial graphite refers to the peak temperature of the maximum peak of the differential thermogravimetric analysis curve obtained by thermogravimetric testing of the artificial graphite under the conditions of a weighing mass of 10±0.05 mg, air purge gas with an air flow rate of 60 mL / min, a heating rate of 5°C / min, and a test temperature range of 40°C to 950°C.

9. The method according to claim 8, wherein In step S10, the mass content of volatile components contained in the provided green coke powder is ≥8.5%.

10. The method according to claim 9, wherein: In step S10, the mass content of volatile components in the provided green coke powder is 9% to 10.5%.

11. The method according to claim 8, wherein In step S10 , the particle size Dv10 of the provided green coke powder is ≥ 3.0 μm.

12. The method according to claim 8, wherein In step S10 , the particle size Dv50 of the provided green coke powder is ≤16 μm.

13. The method according to claim 8, wherein In step S10, the method for providing green coke powder containing volatile components comprises the steps of: The raw coke material is coked to obtain green coke, and the obtained green coke is ground to obtain green coke powder.

14. The method according to claim 13, wherein The grinding process uses mechanical grinding equipment.

15. The method according to claim 13, wherein The temperature of the coking process of the raw coke is ≤ 550°C; and / or, The preheating preparation time for coking treatment of raw coke raw materials is ≥5h.

16. The method according to claim 15, wherein: The temperature of the coking treatment of the raw coke material is 450℃~550℃.

17. The method according to claim 8, wherein In step S10 , green coke powder containing volatile components, or a mixture of green coke powder containing volatile components and pitch powder is provided.

18. The method according to claim 8, wherein In step S20 , the thermal deposition temperature is 250° C. to 700° C.

19. The method according to claim 18, wherein In step S20 , the thermal deposition temperature is 500° C. to 700° C.

20. The method according to claim 8, wherein In step S30 , the graphitization treatment temperature is 2800° C. to 3000° C.

21. The method according to claim 8, wherein In step S40, the discharge temperature is ≤350°C.

22. A negative electrode sheet, comprising the artificial graphite according to any one of claims 1 to 7, or the artificial graphite obtained by the method according to any one of claims 8 to 21.

23. A secondary battery comprising the negative electrode sheet according to claim 22. 24 . A battery module comprising the secondary battery according to claim 23 . 25 . A battery pack comprising: the secondary battery according to claim 23 or the battery module according to claim 24 . 26 . An electric device comprising at least one of the secondary battery according to claim 23 , the battery module according to claim 24 , and the battery pack according to claim 25 .

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