Artificial graphite single-particle negative electrode active material, preparation method therefor and use thereof

Abstract

The present application discloses an artificial graphite single-particle negative electrode active material, satisfying: 1.0<(Dv50(aggregate)) / (Dv50(finished product))<2.0, and L=(PD×100×Dv50(aggregate)) / (SA×OA×Dv50(finished product)), L≥4.0, wherein Dv50(aggregate) represents the 50% volume average particle size of a material obtained by means of shaping treatment during the preparation of the artificial graphite single-particle negative electrode active material; Dv50(finished product) represents the 50% volume average particle size of the artificial graphite single-particle negative electrode active material; OA represents the oil absorption value of the artificial graphite single-particle negative electrode active material, expressed in mL / 100 g; PD represents the compaction density of the artificial graphite single-particle negative electrode active material, expressed in g / cm3; and SA represents the specific surface area of the artificial graphite single-particle negative electrode active material, expressed in m2 / g.

Description

Artificial graphite single-particle negative electrode active material and preparation method and application thereof

[0001] Cross-reference to related applications

[0002] The present application is based on and claims priority to Chinese patent application No. 202411131845.4, filed on August 16, 2024, the entire contents of which are hereby incorporated by reference into the present application. TECHNICAL FIELD

[0003] The present application belongs to the technical field of secondary batteries, and specifically relates to an artificial graphite single-particle negative electrode active material and a preparation method thereof, further, the present application also relates to a secondary battery and an electric device, and still further, the present application also relates to an evaluation method for the cycle life of an artificial graphite single-particle negative electrode active material. BACKGROUND

[0004] Lithium ion batteries have the characteristics of small size, lightweight, high energy density, long cycle life, etc., and have been widely used in the fields of electronics, electrical appliances and new energy vehicles. The negative electrode active material is a key component of the lithium ion battery, which determines the specific capacity, rate performance, cycle life, etc. of the battery.

[0005] Graphite is the most common negative electrode active material in lithium ion batteries. It has good electrical conductivity, chemical stability and mechanical strength, and can withstand lithium ion discharge and charging. At the same time, graphite also has a relatively low price and a wide source. Graphite materials include natural graphite and artificial graphite, and artificial graphite is usually made of needle coke, carbon fiber and mesocarbon microbeads, etc. soft carbon materials through high-temperature absolute oxygen graphitization processing. Compared with natural graphite, artificial graphite has more balanced discharge capacity, charge-discharge efficiency and smooth performance, and is the most widely used negative electrode active material at present. However, the current artificial graphite negative electrode active material still has problems such as low cycle life and high preparation cost, therefore, it is necessary to further research and improve the artificial graphite negative electrode active material to obtain a long-life artificial graphite negative electrode active material, so as to improve the cycle performance of the lithium ion battery. SUMMARY

[0006] The present application aims to at least partially solve one of the technical problems in the related art. To this end, the embodiments of the present application provide an artificial graphite single-particle negative electrode active material, which has a low oil absorption value, a low specific surface area and a low expansion rate, and the artificial graphite single-particle negative electrode active material is beneficial to long-term deintercalation of lithium ions, has a stable structure and excellent long cycle life.

[0007] The embodiments of the present application provide an artificial graphite single-particle negative electrode active material, which satisfies:

[0008] 1.0 < (Dv50 (骨料) ) / (Dv50 (成品) ) < 2.0, and

[0009] L = (P D × 100 × Dv50 (骨料) ) / (S A × O A × Dv50 (成品) ), L ≥ 4.0;

[0010] wherein Dv50 (骨料) is a 50% volume average particle size of the artificial graphite single-particle negative active material obtained after the shaping treatment in the preparation process of the artificial graphite single-particle negative active material;

[0011] Dv50 (成品) is a 50% volume average particle size of the artificial graphite single-particle negative active material;

[0012] O A is an oil absorption value of the artificial graphite single-particle negative active material, in mL / 100g;

[0013] P D is a tap density of the artificial graphite single-particle negative active material, in g / cm 3 ;

[0014] S A is a specific surface area of the artificial graphite single-particle negative active material, in m 2 / g;

[0015] L is a cycle performance index of the artificial graphite single-particle negative active material.

[0016] The artificial graphite single-particle negative active material according to the embodiments of the present application has the following advantages and technical effects: by controlling Dv50 (骨料) and Dv50 (成品) of the artificial graphite single-particle negative active material in the preparation process to satisfy 1.0 < (Dv50 (骨料) ) / (Dv50 (成品) ) < 2.0, and by designing Dv50 (骨料)、 Dv50 (成品) , O A , P D , S A of the artificial graphite single-particle negative active material into a relationship (P D × 100 × Dv50 (骨料) ) / (S A × O A × Dv50 (成品) ), L ≥ 4.0, the cycle performance of the artificial graphite single-particle negative active material is improved.), the relationship can represent the cycle performance of the negative active material, and the cycle performance is set as the cycle performance index L of the artificial graphite single-particle negative active material. When L≥4.0 is controlled, the artificial graphite single-particle negative active material is beneficial to long-term deintercalation of lithium ions, the negative active material has the characteristics of low expansion rate and stable structure, and excellent long cycle life is exhibited.

[0017] In some embodiments, Dv50 (成品) is 4-19 μm, Dv50 (骨料) is 5-20 μm.

[0018] In some embodiments, O A is 20-100 mL / 100 g, and optionally, O A is 30-60 mL / 100 g.

[0019] In some embodiments, P D is 1.00-2.00 g / cm 3 , and optionally, P D is 1.40-1.70 g / cm 3 .

[0020] In some embodiments, S A is 0.60-3.00 m 2 / g, and optionally, S A is 0.60-1.00 m 2 / g.

[0021] The application also provides a preparation method of the artificial graphite single-particle negative active material, comprising the following steps:

[0022] a. crushing, drying and grinding raw materials, and then performing shaping treatment to obtain shaped materials;

[0023] b. performing calcination treatment on the shaped materials of step a to obtain calcined materials;

[0024] c. performing graphitization treatment on the calcined materials of step b to obtain the artificial graphite single-particle negative active material.

[0025] The preparation method of the artificial graphite single-particle negative active material of the application does not need to set a granulation low-temperature heat treatment process and does not need to set a coating process, has a short process flow, is simple, uses less equipment, significantly reduces production cost, and has no requirements on raw materials, can adapt to all raw materials for preparing artificial graphite, is beneficial to industrial application, and effectively improves the cycle performance of the negative active material.

[0026] In some embodiments, in the step a, the Dv50 of the shaped material is 5-20 pm. (骨料) 5-20 pm.

[0027] In some embodiments, in the step a, the raw material comprises at least one of needle coke and pitch coke.

[0028] In some embodiments, in the step a, the particle diameter of the crushed material is ≤10 mm.

[0029] In some embodiments, in the step a, the grinding is performed by mechanical grinding, and the frequency of the mechanical grinder is controlled to be 10-40 Hz, and the classification frequency is controlled to be 10-40 Hz.

[0030] In some embodiments, in the step a, the moisture content of the dried material is ≤3 wt%.

[0031] In some embodiments, in the step a, in the step b, the calcination temperature is 1000-1200°C, and the calcination time is 1-12 h.

[0032] Optionally, the calcination process comprises: first, increasing the temperature to 400-600°C at a temperature increasing rate of 2-5°C / min, performing first calcination for 0.5-2 h, then increasing the temperature to 1000-1200°C at a temperature increasing rate of 2-5°C / min, performing second calcination for 1-12 h, then decreasing the temperature to 400-600°C at a temperature decreasing rate of 1-3°C / min, maintaining the temperature for 4-12 h, and finally decreasing the temperature to 20-30°C, to obtain the calcined material.

[0033] In some embodiments, in the step c, the graphitization temperature is 2400-3500°C, and the graphitization time is 3-6 h.

[0034] In some embodiments, in the step c, the graphitization process is performed by using an Acheson furnace, a box furnace, a horizontal continuous graphitization furnace, a vertical continuous graphitization furnace, a medium-frequency furnace, a medium-frequency continuous furnace, or an electric arc smelting furnace.

[0035] In some embodiments, in the step c, after the graphitization process, a screening process and a magnetic removal process are performed, wherein the screening process is performed by using a screen mesh with a mesh number of 100-500 meshes.

[0036] The embodiments of the present application also provide a secondary battery comprising the artificial graphite single-particle negative electrode active material of the embodiments of the present application. The secondary battery of the embodiments of the present application has all the advantages of the artificial graphite single-particle negative electrode active material of the embodiments of the present application, and details are not repeated here.

[0037] This application also provides an electrical device that includes the secondary battery described in this application. The electrical device of this application possesses all the advantages of the secondary battery described in this application, which will not be elaborated further here.

[0038] This application also provides a method for evaluating the cycle life of a single-particle artificial graphite anode active material, comprising the following steps:

[0039] (1) The 50% volume average particle size Dv50 of the material obtained after shaping treatment was measured during the preparation of artificial graphite single-particle negative electrode active material. (骨料) ;

[0040] (2) The 50% volume average particle size Dv50 of the prepared artificial graphite single-particle negative electrode active material was measured. (成品) Oil absorption value O A Compacted density P D Specific surface area S A ;

[0041] (3) Set the cycle performance index of artificial graphite single-particle negative electrode active material L=(P D ×100×Dv50 (骨料) ) / (S A ×O A ×Dv50 (成品) );

[0042] (4) Based on the Dv50 measured in step (1) (骨料) And the Dv50 measured in step (2) (成品) O A P D S A Calculate the L value. When L≥4.0, the cycle life of the prepared artificial graphite single-particle negative electrode active material is qualified.

[0043] The method for evaluating the cycle life of artificial graphite single-particle negative electrode active materials in this application embodiment measures the Dv50 of the artificial graphite single-particle negative electrode active material. (骨料) Dv50 (成品) O A P D S A These five parameters are designed into a relational expression (P) D ×100×Dv50 (骨料) ) / (S A ×O A ×Dv50 (成品)), and the relationship is used as a cycle performance index L of the artificial graphite single-particle negative active material. By judging the size of the L value, the cycle life of the artificial graphite single-particle negative active material can be effectively evaluated. The evaluation method of the embodiments of the present application is simple and effective, and is conducive to screening artificial graphite single-particle negative active materials with excellent performance. DETAILED DESCRIPTION

[0044] The embodiments of the present application are described in detail below, which are exemplary and are intended to explain the present application, and cannot be understood as a limitation of the present application.

[0045] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs; the terms used herein are only for the purpose of describing specific embodiments of the present application, and are not intended to limit the present application; the terms "include" and "have" and any variations thereof in the specification and claims of the present application are intended to cover non-exclusive inclusion.

[0046] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "a plurality of" is two or more, unless otherwise explicitly and specifically limited.

[0047] Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the present application. The phrase appears at various places in the specification is not necessarily all referring to the same embodiment, nor is it necessarily referring to a preferred or alternative embodiment to the exclusion of other embodiments. It is explicitly and implicitly understood that the embodiments described herein can be combined with other embodiments.

[0048] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0049] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0050] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0051] In this application, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0052] This application provides a single-particle artificial graphite anode active material, wherein the anode active material satisfies the following:

[0053] 1.0 < (Dv50 (骨料) ) / (Dv50 (成品) ) < 2.0, and

[0054] L = (P D × 100 × Dv50 (骨料) ) / (S A × O A × Dv50 (成品) ), L ≥ 4.0;

[0055] wherein Dv50 (骨料) is a 50% volume average particle size of the artificial graphite single particle negative active material after a shaping treatment in a preparation process of the artificial graphite single particle negative active material;

[0056] Dv50 (成品) is a 50% volume average particle size of the artificial graphite single particle negative active material;

[0057] O A is an oil absorption value of the artificial graphite single particle negative active material, in mL / 100g;

[0058] P D is a tap density of the artificial graphite single particle negative active material, in g / cm 3 ;

[0059] S A is a specific surface area of the artificial graphite single particle negative active material, in m 2 / g;

[0060] L is a cycle performance index of the artificial graphite single particle.

[0061] In the embodiments of the present application, Dv50 refers to a particle size corresponding to a cumulative volume distribution percentage of 50%, i.e., a volume content of particles less than or equal to the particle size accounts for 50% of the total particle volume;

[0062] The oil absorption value O A refers to a volume of dibutyl phthalate absorbed by 100g of artificial graphite;

[0063] The tap density P D refers to a density reached after pores are filled due to close contact between graphite particles under the action of pressure.

[0064] The specific surface area S A refers to a total area possessed by unit mass of graphite powder.

[0065] The artificial graphite single particle negative active material of the embodiments of the present application controls Dv50(骨料) and Dv50 (成品) satisfies 1.0 < (Dv50 (骨料) ) / (Dv50 (成品) )<2.0, while the Dv50 (骨料)、 of the artificial graphite single-particle negative active material is controlled to be 5-20 μm, the artificial graphite single-particle negative active material is beneficial to long-term deintercalation of lithium ions, and the negative active material has the characteristics of low expansion rate and stable structure, thereby showing excellent long cycle life. (成品) , O A , P D , S A The five parameters are designed into a relationship formula (P D ×100×Dv50 (骨料) ) / (S A ×O A ×Dv50 (成品) ), which can represent the cycle performance of the negative active material, and is set as a cycle performance index L of the artificial graphite single-particle negative active material. When L is controlled to be greater than or equal to 4.0, the artificial graphite single-particle negative active material is beneficial to long-term deintercalation of lithium ions, and the negative active material has the characteristics of low expansion rate and stable structure, thereby showing excellent long cycle life.

[0066] In some embodiments, 1.0 < (Dv50 (骨料) ) / (Dv50 (成品) )<1.5, for example, (Dv50 (骨料) ) / (Dv50 (成品) ) can be 1.02, 1.05, 1.08, 1.1, 1.15, 1.20, 1.25, 1.30, 1.35, 1.40, 1.45, etc., and optionally 1.0 < (Dv50 (骨料) ) / (Dv50 (成品) )<1.20.

[0067] In some embodiments, Dv50 (成品) is 4-19 μm, for example, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, etc., and Dv50 (骨料) is 5-20 μm, for example, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, etc. Optionally, Dv50 (成品) is 6-14 μm, and Dv50 (骨料) is 7-15 μm.

[0068] In the embodiments of the present application, Dv50 (成品) and Dv50 (成品)controlling the ratio of (Dv50 (骨料) ) and (Dv50 (成品) ) within a certain range is beneficial to improve the cycle performance of the negative material.

[0069] In some embodiments, O A is 20-100 mL / 100 g, optionally, O A is 30-60 mL / 100 g, for example, 30 mL / 100 g, 35 mL / 100 g, 40 mL / 100 g, 45 mL / 100 g, 50 mL / 100 g, 55 mL / 100 g, 60 mL / 100 g, or the like.

[0070] In some embodiments, P D is 1.00-2.00 g / cm 3 , optionally, P D is 1.40-1.70 g / cm 3 , for example, 1.40 g / cm 3 , 1.45 g / cm 3 , 1.50 g / cm 3 , 1.55 g / cm 3 , 1.60 g / cm 3 , 1.65 g / cm 3 , 1.70 g / cm 3 , or the like.

[0071] In some embodiments, S A is 0.60-3.00 m 2 / g, optionally, S A is 0.60-1.10 m 2 / g, for example, 0.6 m 2 / g, 0.65 m 2 / g, 0.70 m 2 / g, 0.75 m 2 / g, 0.80 m 2 / g, 0.85 m 2 / g, 0.90 m 2 / g, 0.95 m 2 / g, 1.00 m 2 / g, 1.05 m 2 / g, 1.10 m 2 / g.

[0072] In the embodiments of the present application, by controlling the ratio of (Dv50 (骨料) ) and (Dv50 (成品) ) within a certain range, the cycle performance of the negative material is improved.The ratio of the specific surface area of the artificial graphite single particle negative active material to the oil absorption value of the artificial graphite single particle negative active material is greater than 1, the oil absorption value of the artificial graphite single particle negative active material is controlled to be in a lower range, the compaction density is controlled to be in a higher range, and the specific surface area is controlled to be in a lower range, which is beneficial to improving the cycle performance index L of the artificial graphite single particle, thereby being beneficial to improving the cycle life of the negative active material.

[0073] The application further provides a preparation method of the artificial graphite single particle negative active material, including the following steps:

[0074] a. crushing, drying and grinding the raw material, and then performing shaping treatment to obtain a shaped material;

[0075] b. performing calcination treatment on the shaped material of step a to obtain a calcined material;

[0076] c. performing graphitization treatment on the calcined material of step b to obtain the artificial graphite single particle negative active material.

[0077] The preparation method of the artificial graphite single particle negative active material provided by the application does not need to set a low-temperature heat treatment process and does not need to set a coating process, has a short process flow, is simple, uses less equipment, significantly reduces the production cost, and does not have requirements on the raw material, can be adapted to all raw materials, is beneficial to industrial application, and can effectively improve the cycle performance of the negative active material by using the method provided by the application to prepare the negative active material meeting the cycle performance index L requirement of the artificial graphite single particle negative active material.

[0078] In some embodiments, in step a, the Dv50 of the shaped material is 5-20 μm, for example, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, or the like. (骨料) For example, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, or the like. (骨料) For example, 8 μm to 12 μm.

[0079] In some embodiments, in step a, the raw material includes at least one of needle coke and pitch coke. The method provided by the application does not have any limitation on the raw material for preparing artificial particles, and the raw material commonly used in the prior art can be applied to the method provided by the application.

[0080] In some embodiments, in step a, the particle diameter of the crushed material is ≤10 mm.

[0081] In some embodiments, in step a, the grinding is performed by mechanical grinding, and the frequency of the grinder is controlled to be 10-40 Hz, and the frequency of the classifier is controlled to be 10-40 Hz. In the embodiments, the frequency of the grinder and the frequency of the classifier are controlled to obtain the artificial graphite single-particle negative active material with the desired particle size and low oil absorption value, and improve the cycle performance of the negative active material.

[0082] In some embodiments, in step a, the moisture content of the dried material is less than or equal to 3 wt%, the drying temperature is 90-120°C, and the drying time is 3-6 h.

[0083] In some embodiments, in step a, in step b, the calcination temperature is 1000-1200°C, and the calcination time is 1-12 h.

[0084] Optionally, the calcination process comprises: first, increasing the temperature to 400-600°C at a rate of 2-5°C / min, performing first calcination for 0.5-2 h; then, increasing the temperature to 1000-1200°C at a rate of 2-5°C / min, performing second calcination for 1-12 h; then, decreasing the temperature to 400-600°C at a rate of 1-3°C / min, and keeping the temperature for 4-12 h; and finally, decreasing the temperature to 20-30°C, to obtain the calcined material.

[0085] In the method of the embodiments, the stage calcination process can reduce the volatile content of the powder and improve the loading capacity and safety in the graphitization process.

[0086] In some embodiments, in step c, the graphitization temperature is 2400-3500°C, and the graphitization time is 3-6 h.

[0087] In some embodiments, in step c, the graphitization process is performed by using an Acheson furnace, a box furnace, a horizontal continuous graphitization furnace, a vertical continuous graphitization furnace, a medium-frequency furnace, a medium-frequency continuous furnace, or an electric arc smelting furnace.

[0088] In some embodiments, in step c, after the graphitization process, the material is subjected to screening and demagnetization, and the mesh number of the screen used in the screening process is 100-500 mesh.

[0089] In the method of the embodiments, there is no special requirement for the graphitization process, and the existing graphitization methods and equipment can be used in the method.

[0090] In the method of the embodiments, the skilled person in the art can adjust the specific process conditions as needed to obtain the desired Dv50 (成品) , oil absorption value O A , compaction density P D , and specific surface area SA , so that the prepared negative electrode active material meets the requirement of L≥4.0 of the cycle performance index of the artificial graphite single-particle negative electrode active material set in the embodiments of the present application. For example, by regulating the mill frequency and the classification frequency of the mechanical mill during the grinding in step a, the Dv50 (骨料) and the oil absorption value O A of the desired artificial graphite single-particle negative electrode active material are obtained. (成品) By regulating the temperature and the time of the graphitization treatment in step c, the Dv50 D , the compaction density P A and the specific surface area S (骨料) of the desired negative electrode active material are obtained.

[0091] The embodiments of the present application also provide an evaluation method of the cycle life of an artificial graphite single-particle negative electrode active material, comprising the following steps:

[0092] (1) measuring the 50% volume average particle size Dv50 (成品) of the material obtained after the shaping treatment in the preparation process of the artificial graphite single-particle negative electrode active material;

[0093] (2) measuring the 50% volume average particle size Dv50 A , the oil absorption value O D , the compaction density P A and the specific surface area S D of the artificial graphite single-particle negative electrode active material prepared;

[0094] (3) setting the cycle performance index L of the artificial graphite single-particle negative electrode active material as L=(P (骨料) ×100×Dv50 A ) / (S A ×O (成品) ×Dv50 (骨料) );

[0095] (4) calculating the L value according to the Dv50 (成品) , the Dv50 A , the O D , the P A and the S (骨料) measured in steps (1) and (2), and when L≥4.0, the cycle life of the artificial graphite single-particle negative electrode active material prepared is evaluated as qualified.

[0096] The evaluation method of the cycle life of the artificial graphite single-particle negative electrode active material according to the embodiments of the present application measures the Dv50 (成品) , the Dv50 A , the O D , the P A and the SThese five parameters are designed into a relational expression (P) D ×100×Dv50 (骨料) ) / (S A ×O A ×Dv50 (成品) Using this relationship as the cycle performance index L of the artificial graphite single-particle negative electrode active material, the cycle life of the artificial graphite single-particle negative electrode active material can be effectively evaluated by judging the value of L. The evaluation method of the present application embodiment is simple and effective, which is conducive to screening and obtaining artificial graphite single-particle negative electrode active materials with excellent performance.

[0097] The technical solutions in the embodiments of this application are described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0098] Example 1

[0099] a. The needle coke was ground into powder using a mechanical mill with a milling frequency of 30Hz and a classification frequency of 35Hz. The powder particle size Dv50 was 7.0μm. After grinding, the powder was shaped using an 800 shaping machine to achieve a shaped particle size Dv50. (骨料) The thickness is 7.5 μm, and the shaped material is obtained.

[0100] b. The shaped material is calcined at high temperature in a tunnel kiln. The high-temperature calcination process includes: heating to 500℃ at a heating rate of 5℃ / min and holding for 1.5h for the first calcination treatment; then heating to 1200℃ at a heating rate of 5℃ / min and holding for 10h for the second calcination treatment; then cooling to 600℃ at a cooling rate of 2℃ / min and holding for 10h; and finally discharging at room temperature of 20℃ to obtain the material after high-temperature calcination.

[0101] c. The material after high-temperature calcination is graphitized in a medium-frequency continuous furnace at a graphitization temperature of 2800℃ and a holding time of 3h to obtain the graphitized material.

[0102] d. After the graphitized material is mixed evenly, it is sieved and demagnetized to obtain artificial graphite single-particle negative electrode active material.

[0103] Example 2

[0104] The method is the same as in Example 1, except that the grinding frequency of the mechanical mill in step a is 28 Hz, the grinding particle size Dv50 is 8.5 μm, and the shaping particle size Dv50 is... (骨料) It is 9.0 μm.

[0105] Example 3

[0106] The same as the method of Example 1, except that in step a, the raw material used was Baowu pitch coke, the mill frequency of the mechanical mill was 23 Hz, the ground powder particle size Dv50 was 12.0 pm, and the shaped particle size Dv50 (骨料) was 13.0 pm.

[0107] Example 4

[0108] The same as the method of Example 1, except that in step a, the raw material used was Baowu pitch coke, the mill frequency of the mechanical mill was 23 Hz, the ground powder particle size Dv50 was 12.0 pm, and the shaped particle size Dv50 (骨料) was 13.0 pm.

[0109] Example 5

[0110] The same as the method of Example 1, except that in step a, the raw material used was Baowu pitch coke, the mill frequency of the mechanical mill was 23 Hz, the ground powder particle size Dv50 was 12.0 pm, and the shaped particle size Dv50 (骨料) was 13.0 pm.

[0111] Comparative Example 1

[0112] The same as the method of Example 1, except that in step c, the graphitization process was different, the graphitization temperature was 2800 degrees Celsius, and the holding time was 6 h.

[0113] Comparative Example 2

[0114] The same as the method of Example 1, except that in step a, the classification frequency control of the mechanical mill was 39 Hz.

[0115] Comparative Example 3

[0116] The same as the method of Example 1, except that in step c, the graphitization process was different, the graphitization temperature was 2700 degrees Celsius, and the holding time was 3 h.

[0117] Comparative Example 4

[0118] The same as the method of Example 1, except that in step a, the mill frequency control of the mechanical mill was 35 Hz, and the classification frequency control was 38 Hz.

[0119] Comparative Example 5

[0120] The same as the method of Example 2, except that in step a, the classification frequency control of the mechanical mill was 38 Hz, and in step c, the graphitization process was different, the graphitization temperature was 2800 degrees Celsius, and the holding time was 5 h.

[0121] The artificial graphite single-particle negative active materials prepared from Examples 1-5 and Comparative Examples 1-5 were subjected to performance tests.

[0122] 1. The artificial graphite single-particle negative active materials prepared from Examples 1-5 and Comparative Examples 1-5 were subjected to particle size, specific surface area, oil absorption value and compacted density tests, and the test results are shown in Table 1.

[0123] The volume particle size Dv50 of the artificial graphite single-particle negative active material was measured by laser method using a Malvern Mastersizer 3000;

[0124] The specific surface area of the artificial graphite single-particle negative active material was measured using a Micromeritics TriStar 3000 specific surface area instrument;

[0125] The oil absorption value of the artificial graphite single-particle negative active material was measured using a Japan ASAHI, S-500 type oil absorption value tester, specifically the volume of 100 g of artificial graphite absorbing dibutyl phthalate;

[0126] The compacted density of the artificial graphite single-particle negative active material was calculated by testing the thickness of the electrode sheet after cold pressing after uniformly slurry-coating the graphite on a copper foil.

[0127] 2. The artificial graphite single-particle negative active materials prepared from Examples 1-5 and Comparative Examples 1-5 were subjected to performance tests, and the test results are shown in Table 2.

[0128] The test method for the specific capacity and the first efficiency was as follows: the artificial graphite single-particle negative active material was made into an electrode sheet, a lithium sheet was used as a counter electrode, an electrolyte (the electrolyte was a solution of 1 mol / L LiPF6 in EC (ethylene carbonate) and DMC (diethyl carbonate) with a volume ratio of 1:1), and a CR2032 button cell was assembled in a vacuum glove box. Using a Shenzhen Xinwei button cell test system, 0.1C was discharged to 0.005V, and after 120 min of standing, 20μA was discharged to 0.005V to obtain the first lithium intercalation capacity of the material. After 120 min of standing, the material was charged to 2.0V at 0.1C to complete the first cycle, and the first lithium extraction capacity of the material was obtained, which was the material capacity. The ratio of the first lithium extraction capacity to the lithium intercalation capacity was the first efficiency.

[0129] The test method for the cycle performance was as follows: the artificial graphite single-particle negative active material was made into a 5 Ah soft package battery, the positive electrode used lithium iron phosphate, and 1C / 1C was charged and discharged to complete the first cycle to obtain the first lithium extraction capacity. Then, 1C / 1C was cycled to charge and discharge, and each discharge capacity was recorded. The ratio of this discharge capacity to the first lithium extraction capacity was the capacity retention rate, and the higher the capacity retention rate, the better the long-life performance.

[0130] Table 1

[0131] Table 2

[0132] As can be seen from Tables 1 and 2, the artificial graphite single-particle negative electrode active materials of Examples 1-5 of this application achieve a finished particle size Dv50. (成品) Aggregate particle size Dv50 (骨料) Oil absorption value O A Compacted density P D Specific surface area S A Satisfy (P) D ×100×Dv50 (骨料) ) / (S A ×O A ×Dv50 (成品) The requirement of not less than 4.0 means that the cycle performance index L≥4.0 of the artificial graphite single-particle negative electrode active material set in the embodiments of this application effectively improves the cycle performance of the negative electrode active material. The capacity retention rate after 1C / 1C 1000 cycles can still be maintained at more than 97.8%, which has excellent rate performance and long cycle life.

[0133] Compared with Example 1, the artificial graphite single-particle negative electrode active material of Comparative Example 1 has a significantly larger specific surface area, which makes the cycle performance index L of the negative electrode active material set in this application example only 2.5, and the capacity retention rate after 1C / 1C 1000 cycles can only be maintained at 84.6%, and the cycle performance is significantly reduced.

[0134] Compared with Example 1, the artificial graphite single-particle negative electrode active material of Comparative Example 2 has an excessively high oil absorption value, resulting in the cycle performance index L of the negative electrode active material set in this application being only 2.7, and the capacity retention rate after 1C / 1C 1000 cycles dropping to 85.6%.

[0135] Compared with Example 1, the compaction density of the artificial graphite single-particle negative electrode active material in Comparative Example 3 is too small, which causes the cycle performance index L of the negative electrode active material set in this application to drop to 3.7, and the capacity retention rate after 1C / 1C 1000 cycles can only be maintained at 88.3%.

[0136] Compared with Example 1, the artificial graphite single-particle negative electrode active material of Comparative Example 4 has a finished particle size Dv50. (成品) Aggregate particle size Dv50 (骨料) Decrease, oil absorption value O A and specific surface area S A Increase, compaction density P DThe decrease caused the cycle performance index L of the negative electrode active material set in the embodiments of this application to drop to 2.0, and the capacity retention rate after 1C / 1C 1000 cycles to drop to 83.5%.

[0137] Compared with Example 2, the artificial graphite single-particle negative electrode active material of Comparative Example 5 has a finished particle size Dv50. (成品) Reduce, making Dv50 (骨料) / Dv50 (成品) Increased, but oil absorption value O A and specific surface area S A Increase, compaction density P D The decrease caused the cycle performance index L of the negative electrode active material set in the embodiments of this application to drop to 2.3, and the capacity retention rate after 1C / 1C 1000 cycles to drop to 84.1%.

[0138] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. Artificial graphite single-particle negative active material, the negative active material satisfies: 1.0 < (Dv50 (骨料) ) / (Dv50 (成品) ) < 2.0, and L = (P D × 100 × Dv50 (骨料) ) / (S A × O A × Dv50 (成品) ), L ≥ 4.

0. wherein Dv50 (骨料) Dv50 is the 50% volume average particle diameter of the material obtained after the shaping treatment in the process of manufacturing the artificial graphite single-particle negative active material; Dv50 (成品) Dv50 is the 50% volume average particle diameter of the artificial graphite single particle negative active material. O A Oil absorption value for the artificial graphite single-particle negative active material, unit: mL / 100g; P D the compacted density of the artificial graphite single-particle negative active material, in units of g / cm 3 ; S A S 2 / g.

2. The artificial graphite single particle negative active material according to claim 1, wherein, Dv50 (成品) Dv50 is 4-19 μm (骨料) Dv50 is 5-20 μm.

3. The artificial graphite single particle negative active material according to claim 1 or 2, wherein, O A is 20-100 mL / 100 g, optionally, O A is 30-60 mL / 100 g.

4. The artificial graphite single particle negative active material according to any one of claims 1 to 3, wherein, P D is 1.00-2.00 g / cm 3 .

5. Artificial graphite single-particle negative active material according to any one of claims 1 to 4, wherein, S A is 0.60-3.00 m 2 / g, optionally, S A is 0.60-1.10 m 2 / g. 6.A method for preparing the artificial graphite single-particle negative electrode active material according to any one of claims 1 to 5, comprising the following steps: a. crushing, drying and grinding the raw material, and then performing a shaping treatment to obtain a shaped material; b. performing a calcination treatment on the shaped material of step a to obtain a calcined material; c. performing a graphitization treatment on the calcined material of step b to obtain the artificial graphite single-particle negative electrode active material.

7. The production method according to claim 6, wherein In step a, the Dv50 of the shaped material is from 5 to 20 pm (骨 料) from 5 to 20 pm; Optionally, the raw material comprises at least one of needle coke and pitch coke; Optionally, the particle diameter of the crushed material is ≤10 mm; Optionally, the grinding is performed by mechanical grinding, and the frequency of the mechanical grinder is controlled to be 10-40 Hz, and the classification frequency is controlled to be 10-40 Hz; Optionally, the moisture content of the dried material is ≤3 wt%.

8. The production method according to claim 6 or 7, wherein In step b, the calcination temperature is 1000-1200℃, and the calcination time is 1-12 h; Optionally, the calcination treatment comprises: first increasing the temperature to 400-600℃ at a temperature increasing rate of 2-5℃ / min, performing a first calcination treatment for 0.5-2 h, then increasing the temperature to 1000-1200℃ at a temperature increasing rate of 2-5℃ / min, performing a second calcination treatment for 1-12 h, then decreasing the temperature to 400-600℃ at a temperature decreasing rate of 1-3℃ / min, maintaining the temperature for 4-12 h, and finally decreasing the temperature to 20-30℃.

9. The method of making according to any one of claims 6-8, wherein, In step c, the graphitization temperature is 2400-3500℃, and the graphitization time is 3-6 h; Optionally, the equipment used for the graphitization treatment comprises an Acheson furnace, a box furnace, a horizontal continuous graphitization furnace, a vertical continuous graphitization furnace, a medium-frequency furnace, a medium-frequency continuous furnace or an electric arc smelting furnace; Optionally, the graphitization treatment is followed by a screening and demagnetization treatment, wherein the mesh number of the screen used for the screening treatment is 100-500 mesh. 10.A secondary battery comprising the artificial graphite single-particle negative electrode active material according to any one of claims 1 to 5 or the artificial graphite single-particle negative electrode active material prepared by the method according to any one of claims 6 to 9. 11.An electric device comprising the secondary battery according to claim 10. 12.A method for evaluating the cycle life of an artificial graphite single-particle negative electrode active material, comprising the following steps: (1) Determining the 50% volume average particle size Dv50 of the material obtained after the shaping treatment in the process of preparing artificial graphite single-particle negative active material (骨料) ; (2) the 50% volume average particle diameter Dv50 of the artificial graphite single-particle negative active material prepared is measured (成品) , the oil absorption value O A , the compacted density P D , the specific surface area S A ; (3) setting a cycle performance index L of the artificial graphite single-particle negative active material = (P D × 100 × Dv50 (骨料) ) / (S A × O A × Dv50 (成品) ); (4) Dv50 measured according to step (1) (骨料) and Dv50 measured according to step (2) (成品) , O A , P D , S A The cycle life of the artificial graphite single-particle negative active material prepared is evaluated as qualified when L is ≥ 4.0.

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