Graphite-based composite negative electrode material, and preparation method and use thereof

Abstract

The present application belongs to the technical field of negative electrode material for lithium ion battery, and particularly relates to a graphite-based composite material and a preparation method and use thereof. The present application firstly constructs a soft carbon structure on the surface of artificial graphite and natural graphite, forms stable primary composite particles through isostatic pressing and heat treatment, thereby effectively utilizing the advantages of artificial graphite and natural graphite, i.e. improving the capacity and cycle performance of the composite negative electrode material while reducing the cost. Then, pitch 2 is used to bond the primary composite particles into secondary composite particles, thereby effectively reducing the trend of the negative electrode material. Through a pre-oxidation treatment process in the granulation process, pitch 2 is oxidized and cross-linked into a hard carbon precursor, and in the graphitization treatment, the purification of natural graphite, the graphitization of the artificial graphite precursor and the carbonization of the hard carbon precursor are simultaneously completed. Finally, a uniform hard carbon coating layer is constructed on the surface of the composite graphitized particles, so that the composite negative electrode material has both the super-high fast charging performance of hard carbon.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of negative electrode materials for lithium ion batteries, and particularly relates to a graphite-based composite material and a preparation method and application thereof. BACKGROUND

[0002] Lithium ion batteries have a series of advantages such as high specific capacity, high working voltage, good safety, no memory effect, etc., and are widely used in notebook computers, mobile phones, instruments and meters and many other portable electronic instruments and equipment. With the popularization of new energy vehicles, its application range has been expanded to electric vehicles and other fields. In recent years, with the increasing requirements of electronic products and vehicle-mounted and energy storage equipment for miniaturization, light weight, multi-function and long-time driving, the requirements for high energy density, high rate performance and long cycle life of lithium ion batteries are increasing.

[0003] As one of the core components of the battery, the negative electrode material plays a key role in the comprehensive performance of the battery. Among the existing negative electrode materials, graphite-based materials have become the negative electrode material for commercial lithium ion batteries due to their low charge-discharge platform, high theoretical lithium intercalation capacity, good electrical conductivity and other advantages.

[0004] Artificial graphite has good compatibility with electrolyte, good cycle and rate performance, but its capacity is low and the price is high, which increases the manufacturing cost of power batteries. Natural graphite has high energy density and high compaction density, but its disadvantages are large expansion and poor cycle performance, which limit its application in power batteries. Hard carbon has high capacity and good rate performance, but its cycle performance and first discharge efficiency are low. In view of the many advantages of the above-mentioned negative electrode materials, there have been reports of simple physical mixing of artificial graphite, natural graphite and hard carbon, but the mixture obtained in the charge-discharge process will cause the separation of graphite, and the comprehensive performance of the graphite negative electrode material has not been significantly improved. SUMMARY

[0005] In order to solve the defects that the composite graphite negative electrode material in the prior art cannot simultaneously meet high capacity, high rate and low expansion, the application provides a graphite-based composite negative electrode material and a preparation method and application thereof. The composite graphite negative electrode material has high discharge capacity, long cycle life and low expansion, and can also consider the fast charging performance of more than 3C.

[0006] The purpose of the application is achieved by the following technical scheme:

[0007] A preparation method of a graphite-based composite negative electrode material, the method comprising the following steps:

[0008] (1) mixing and kneading natural graphite, artificial graphite precursor and pitch 1, and molding to obtain a graphite block;

[0009] (2) heat treating, crushing, and shaping the graphite block of step (1) to obtain primary composite particles;

[0010] (3) mixing and granulating the primary composite particles of step (2) with pitch 2 to obtain secondary composite particles;

[0011] (4) dispersing the secondary composite particles of step (3) and then graphitizing to obtain composite graphitized particles;

[0012] (5) mixing pitch 2, an organic solvent, and the composite graphitized particles of step (4), removing the organic solvent, and then heat treating to obtain the graphite-based composite negative electrode material.

[0013] According to an embodiment of the present application, in step (1), the natural graphite has a spherical shape, and the mass content of fixed carbon is ≥ 85%; the median particle size D50 of the natural graphite is 5-8 μm, for example, 5 μm, 6 μm, 7 μm, or 8 μm. 50

[0014] According to an embodiment of the present application, in step (1), the artificial graphite precursor is selected from at least one of petroleum coke, needle coke, pitch coke, and anthracite; the artificial graphite precursor has a spherical shape, and the median particle size D50 of the artificial graphite precursor is 5-8 μm, for example, 5 μm, 6 μm, 7 μm, or 8 μm. 50

[0015] According to an embodiment of the present application, in step (1), the pitch 1 has a softening point of 60-90 °C and a quinoline insoluble content of ≤ 1%.

[0016] According to an embodiment of the present application, in step (1), the kneading is performed under rolling stirring, and the process of the kneading can make the natural graphite, the artificial graphite precursor, and the pitch 1 (particularly the pitch 1 in a molten state or a softened state) fully contact, and coat the pitch 1 on the surfaces of the natural graphite and the artificial graphite precursor, which is beneficial to bonding the natural graphite and the artificial graphite precursor in the pressing process; the temperature of the kneading is higher than the softening point temperature of the pitch 1 by 10 °C or more, for example, higher than the softening point temperature of the pitch 1 by 20 °C or more; and the time of the kneading is 10-60 min.

[0017] According to an embodiment of the present application, in step (1), the mass ratio of the natural graphite, the artificial graphite precursor, and the pitch 1 is 1:(1-2):(0.06-0.15), for example, 1:(1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2):(0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15).​​

[0018] According to an embodiment of the present application, in step (1), the compacting is cold isostatic pressing or warm isostatic pressing, and the temperature during the compacting is 20-300°C, for example, when cold isostatic pressing is used, the temperature during the compacting is 20-40°C (or room temperature), and when warm isostatic pressing is used, the temperature during the compacting is 40-300°C. The pressure during the compacting is 10-100 MPa, preferably 30-80 MPa, for example, 30 MPa, 50 MPa, 60 MPa or 80 MPa, and the dwell time during the compacting is 1-10 min.

[0019] According to an embodiment of the present application, in step (1), the compacting can fill the pitch 1 into the gaps on the inner surface of the curled carbon layer of the natural graphite, and simultaneously bind the natural graphite and the artificial graphite precursor into a block, so as to realize the densification treatment of the natural graphite and the composite of the two kinds of graphite materials.

[0020] According to an embodiment of the present application, in step (2), the heat treatment is carried out in a protective atmosphere.

[0021] According to an embodiment of the present application, in step (2), the temperature of the heat treatment is 800-1200°C, for example, 800°C, 850°C, 900°C, 950°C, 1000°C, 1050°C, 1100°C, 1150°C or 1200°C, and the time of the heat treatment is 4-10 hours, for example, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours or 10 hours.

[0022] According to an embodiment of the present application, in step (2), the equipment for the pulverization is not particularly limited, and can be selected from the equipment known in the art, for example, selected from an air jet pulverizer, a high-pressure pulverizer or a rod-type mechanical pulverizer.

[0023] According to an embodiment of the present application, in step (2), the primary composite particles have a median particle size D 50 of 5-8 μm, for example, 5 μm, 6 μm, 7 μm or 8 μm.

[0024] According to an embodiment of the present application, in step (2), the equipment for the shaping is not particularly limited, and can be selected from the equipment known in the art, for example, selected from a mechanical shaper or an air jet shaper.

[0025] According to an embodiment of the present application, in step (2), the primary composite particles comprise amorphous carbon, natural graphite and artificial graphite precursor, and the amorphous carbon in the primary composite particles is formed after the heat treatment of the pitch 1.

[0026] According to an embodiment of the present application, in step (3), the mass ratio of the primary composite particles to the pitch 2 is 100:(10-30), for example, 100:10, 100:12, 100:15, 100:18, 100:20, 100:22, 100:24, 100:25, 100:26, 100:28 or 100:30.

[0027] According to an embodiment of the present application, in step (3), the pitch 2 has a softening point of 240℃ or higher.

[0028] According to an embodiment of the present application, in step (3), the granulation comprises the following steps: first, heating to 10-30℃ higher than the softening point of the pitch 2 under a protective atmosphere and stirring; then, introducing an oxygen-containing atmosphere and continuing to stir; and finally, heating to 600-650℃ under a protective atmosphere.

[0029] Illustratively, in step (3), the granulation comprises the following steps: first, heating to 10-30℃ higher than the softening point of the pitch 2 under a protective atmosphere and stirring for 1-5h, which can coat the pitch 2 on the surface of the primary composite particles and simultaneously reduce the median particle size D 50 of the primary composite particles to 5-8μm; then, introducing an air or oxygen atmosphere and continuing to stir for 6-24h, which can oxidize and crosslink the pitch 2 to form a hard carbon precursor; and finally, heating to 600-650℃ at a heating rate of 2-5℃ / min under a protective atmosphere, holding for 1-5h and then cooling to room temperature. 50

[0030] Wherein, the stirring rate is 15-40rpm.

[0031] According to an embodiment of the present application, in step (3), the secondary composite particles are formed by bonding the primary composite particles with the pitch 2.

[0032] According to an embodiment of the present application, in step (3), the secondary composite particles have a median particle size D 50 of 14μm, 15μm, 16μm, 17μm, 18μm, 19μm or 20μm.

[0033] According to an embodiment of the present application, in step (4), the dispersing is performed by using a turbo disperser or an air flow disperser.

[0034] ​According to an embodiment of the present application, in step (4), the graphitization temperature is 2800-3000℃, for example 2850-2950℃, and an example is 2800℃, 2900℃ or 3000℃. Further, the graphitization time is 2-10 hours, for example 3-8 hours, and an example is 3 hours or 6 hours.

[0035] According to an embodiment of the present application, in step (4), the graphitization is performed by using a conventional graphitization processing furnace, and the graphitization is performed under normal pressure.

[0036] According to an embodiment of the present application, in step (4), the graphitization can convert the amorphous carbon formed by heat treatment of pitch 1 into graphite, and convert the hard carbon precursor formed by oxidative crosslinking of pitch 2 into hard carbon.

[0037] According to an embodiment of the present application, step (5) specifically comprises the following steps: mixing pitch 2 and an organic solvent, then adding the composite graphitized particles of step (4), continuing to stir for 4-10 hours, removing the solvent by vacuum drying, and finally performing heat treatment to prepare the graphite-based composite negative electrode material.

[0038] According to an embodiment of the present application, in step (5), the organic solvent is selected from a hydrocarbon solvent, for example at least one of washing oil, naphthalene oil or phenol oil.

[0039] According to an embodiment of the present application, in step (5), the mass ratio of pitch 2: organic solvent: composite graphitized particles is (1-6):(80-200):100, and preferably (2-5):(100-150):100.

[0040] According to an embodiment of the present application, in step (5), the drying temperature is 80-120℃.

[0041] According to an embodiment of the present application, in step (5), the heat treatment comprises the following steps: first, heating to 250-300℃ at a temperature rising rate of 0.5-2℃ / min under an air atmosphere, and holding for 2-10 hours; then, switching the air atmosphere in the high-temperature furnace to a protective atmosphere, and heating to 800-1600℃ at a temperature rising rate of 2-5℃ / min, and holding for 1-5 hours, and then cooling to room temperature.

[0042] According to an embodiment of the present application, in step (5), pitch 2 coated on the surface of the composite graphitized particles forms a hard carbon coating layer after heat treatment.

[0043] According to an embodiment of the present application, the protective atmosphere is nitrogen or argon.

[0044] The present application also provides a graphite-based composite negative electrode material prepared by the above method.

[0045] The application also provides a graphite-based composite negative electrode material, which has a core-shell structure and comprises a shell layer and a core.

[0046] According to an embodiment of the application, the core is formed by artificial graphite and natural graphite being bonded by hard carbon.

[0047] According to an embodiment of the application, the graphite-based composite negative electrode material has a median particle size D50 of 14 μm to 20 μm, for example 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm or 20 μm. 50

[0048] According to an embodiment of the application, the graphite-based composite negative electrode material has a mass percentage of artificial graphite of 40% to 72%, for example 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 52%, 53%, 54%, 55%, 56%, 58%, 60%, 62%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71% or 72%; a mass percentage of natural graphite of 20% to 40%, for example 20%, 21%, 22%, 23%, 24%, 25%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39% or 40%; and a mass percentage of hard carbon of 8% to 20%, for example 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19% or 20%.

[0049] The application also provides a use of the graphite-based composite negative electrode material as described above for a lithium ion battery.

[0050] The application also provides a negative electrode comprising the graphite-based composite negative electrode material as described above.

[0051] The application also provides a lithium ion battery comprising the graphite-based composite negative electrode material as described above, or alternatively, a lithium ion battery comprising the negative electrode as described above.

[0052] The application has the following advantages:

[0053] ​The present application firstly constructs a soft carbon structure on the surface of artificial graphite and natural graphite, forms stable primary composite particles through isostatic pressing and heat treatment, thereby effectively utilizing the advantages of artificial graphite and natural graphite, i.e. improving the capacity and cycle performance of the composite negative electrode material while reducing the cost. Then pitch 2 with good adhesive property is used to bond the primary composite particles into secondary composite particles, effectively reducing the tendency of the negative electrode material. Through a pre-oxidation treatment process in the granulation process, pitch 2 is oxidized and cross-linked into a hard carbon precursor, and in the graphitization treatment, the purification of natural graphite, graphitization of the artificial graphite precursor and carbonization of the hard carbon precursor are simultaneously completed. Finally, a uniform hard carbon coating layer is constructed on the surface of the composite graphitized particles, so that the composite negative electrode material has both the super-high fast-charging performance of hard carbon. Therefore, on the basis of ensuring high capacity and long cycle of graphite, the lithium ion transmission channel can be fully improved and the transmission distance can be effectively shortened, so that the graphite-based composite negative electrode material has the characteristics of high capacity, long cycle, fast-charging performance and low cost. DETAILED DESCRIPTION

[0054] The preparation method of the present application will be further described in detail below in combination with specific examples. It should be understood that the following examples are only illustratively described and explained, and should not be interpreted as limiting the scope of protection of the present application. Any technology realized based on the above description of the present application is covered within the scope intended to be protected by the present application.

[0055] The experimental methods used in the following examples are conventional methods unless otherwise specified; the reagents, materials, etc. used in the following examples can be obtained from commercial channels unless otherwise specified.

[0056] Example 1

[0057] (1) Put 15 kg of petroleum pitch (softening point 80℃, quinoline insoluble content 0.4%), 100 kg of natural graphite (D 50 50μm) with a fixed carbon mass content of 90% and 100 kg of petroleum coke (D 50 50μm) into a kneading pot, knead at 100℃ for 30 minutes, then use a cold isostatic pressing forming equipment to process at 80MPa for 3min, to obtain a graphite block. Put the graphite block directly into a high-temperature furnace, under N2 protection, heat from room temperature to 800℃ at a rate of 5℃ / min, treat for 4 hours and then cool down; then crush the graphite block with an air flow crusher to D 50 50μm, and shape in a shaper to obtain composite particles 1 with D 50 50μm.

[0058] (2) 100 kg of the composite particles 1 and 25 kg of petroleum pitch (softening point 240℃) were mixed uniformly and placed in a reaction kettle, the stirring rate was 40 rpm, first heated from room temperature to 260℃ at a rate of 1℃ / min under N2 protection, stirred for 2 h, then air was introduced, and stirring was continued for 12 h, finally N2 was introduced again, and heated to 650℃ at a rate of 2℃ / min, and kept for 3 h, then cooled to room temperature, to obtain D 50 The composite particles 2 were 15 μm.

[0059] (3) The composite particles 2 were placed in a graphite crucible, and then the crucible was placed in a graphitization furnace, and treated at 2800℃ for 4 hours to cool, to obtain the composite graphitized particles.

[0060] (4) 4 kg of petroleum pitch (softening point 240℃) was added to 150 kg of wash oil, and the petroleum pitch was fully dissolved by high-speed stirring to obtain a petroleum pitch solution, 100 kg of the composite graphitized particles was added, and stirring was continued for 5 hours, and the solvent was removed by drying at 100℃ under vacuum to obtain a powder; the powder was placed in a high-temperature furnace, first heated to 300℃ at a rate of 0.5℃ / min under air atmosphere, kept for 10 h, then N2 was introduced, and heated to 1600℃ at a rate of 2.5℃ / min, kept for 5 h, and then cooled to room temperature, to obtain the graphite-based composite negative electrode material.

[0061] The mass percentage content of natural graphite in the graphite-based composite negative electrode material was 42%, the mass percentage content of artificial graphite was 42%, and the mass percentage content of hard carbon was 16%.

[0062] Example 2

[0063] (1) Petroleum pitch (softening point 70℃, quinoline insoluble content 0.2%) 12 kg, natural graphite (D 50 6 μm) with a mass content of fixed carbon of 92% 100 kg, and petroleum coke (D 50 6 μm) 130 kg were placed in a kneading pot, kneaded at 90℃ for 40 minutes, and then treated by cold isostatic pressing equipment at 60 MPa for 4 min to obtain a graphite block. The graphite block was directly placed in a high-temperature furnace, heated to 900℃ at a rate of 3℃ / min under Ar protection for 3 hours, and then cooled; then the graphite block was pulverized by an air flow pulverizer to D 50 6 μm, and shaped in a shaper to obtain composite particles 1 with D 50 6 μm.

[0064] (2) 100 kg of the composite particles 1 and 20 kg of petroleum pitch (softening point 250℃) were mixed uniformly and placed in a reaction kettle, the stirring rate was 20 rpm, first heated from room temperature to 280℃ at a rate of 1.5℃ / min under N2protection, stirred for 4 h, then air was introduced, continued to stir for 10 h, finally N2was introduced again, heated to 620℃ at a rate of 3℃ / min, kept for 4 h, and then cooled to room temperature to obtain D 50 The composite particles 2 were 16 μm.

[0065] (3) The composite particles 2 were placed in a graphite crucible, and then the crucible was placed in a graphitization furnace, treated at 3000℃ for 5 hours and cooled to obtain the composite graphitized particles.

[0066] (4) 3 kg of pitch (softening point 250℃) was added to 120 kg of wash oil, and the pitch was fully dissolved by high-speed stirring to obtain a pitch solution, 100 kg of the composite graphitized particles was added, and the stirring was continued for 7 hours, and then the solvent was removed by drying at 100℃ under vacuum to obtain a powder; the powder was placed in a high-temperature furnace, first heated to 280℃ at a rate of 0.5℃ / min under air atmosphere, kept for 8 h, then N2was introduced, heated to 1400℃ at a rate of 3℃ / min, kept for 5 h, and then cooled to room temperature to obtain the graphite-based composite negative electrode material.

[0067] The mass percentage content of natural graphite in the graphite-based composite negative electrode material was 37%, the mass percentage content of artificial graphite was 49%, and the mass percentage content of hard carbon was 14%.

[0068] Example 3

[0069] (1) 10 kg of coal pitch (softening point 65℃, quinoline insoluble content 0.8%), 100 kg of natural graphite (D 50 6 μm) with a mass content of fixed carbon of 88%, and 150 kg of needle coke (D 50 7 μm) were placed in a kneading pot, kneaded at 80℃ for 30 minutes, and then treated by cold isostatic pressing equipment at 50 MPa for 2 min to obtain a graphite block. The graphite block was directly placed in a high-temperature furnace, treated at 900℃ for 5 hours under Ar protection, and then cooled; and then the graphite block was pulverized by an air flow pulverizer to D 50 7 μm, and then shaped in a shaper to obtain the composite particles 1 with D 50 7 μm.

[0070] (2) 100 kg of the composite particles 1 were mixed with 15 kg of coal pitch (softening point 260℃) uniformly, and then placed in a reaction kettle, with a stirring rate of 25 rpm. First, the temperature was raised to 300℃ at a rate of 1℃ / min under N2protection, and stirred for 6 h. Then, air was introduced, and stirring was continued for 8 h. Finally, N2was introduced again, and the temperature was raised to 600℃ at a rate of 3.5℃ / min, and held for 5 h. After cooling to room temperature, D 50 was obtained.

[0071] (3) The composite particles 2 were placed in a graphite crucible, and then the crucible was placed in a graphitization furnace, and treated at 2800℃ for 6 h to cool, to obtain the composite graphitized particles.

[0072] (4) 2.5 kg of coal pitch (softening point 260℃) was added to 120 kg of naphthalene oil, and stirred at high speed to dissolve the coal pitch completely, to obtain a coal pitch solution. Then, 100 kg of the composite graphitized particles were added, and stirring was continued for 3 h. The solvent was removed by drying at 100℃ under vacuum, to obtain a powder. The powder was placed in a high-temperature furnace, and first, the temperature was raised to 280℃ at a rate of 1.5℃ / min under air atmosphere, and held for 6 h. Then, N2was introduced, and the temperature was raised to 1300℃ at a rate of 2.5℃ / min, and held for 2 h. After cooling to room temperature, the graphite-based composite negative electrode material was obtained.

[0073] The mass percentage of the natural graphite in the graphite-based composite negative electrode material was 35%, the mass percentage of the artificial graphite was 53%, and the mass percentage of the hard carbon was 12%.

[0074] Example 4

[0075] (1) Petroleum pitch (softening point 85℃, quinoline insoluble content 0.3%) 8 kg, natural graphite (D 50 8 μm) 100 kg, and needle coke (D 50 7 μm) 180 kg were placed in a kneading pot, and kneaded at 100℃ for 60 min. Then, the graphite block was treated by cold isostatic pressing at 30 MPa for 2 min, to obtain a graphite block. The graphite block was directly placed in a high-temperature furnace, and treated at 900℃ under Ar protection for 5 h, and then cooled. The graphite block was then pulverized by a jet mill to D 50 8 μm, and shaped in a shaper, to obtain the composite particles 1 with D 50 8 μm.

[0076] (2) 100 kg of the composite particles 1 and 20 kg of coal pitch (softening point 280℃) were mixed uniformly and placed in a reaction kettle, the stirring rate was 40 rpm, first heated from room temperature to 300℃ at a rate of 1℃ / min under N2 protection, stirred for 4 h, then air was introduced, continued to stir for 6 h, finally N2 was introduced again, heated to 650℃ at a rate of 3.0℃ / min, kept for 5 h, then cooled to room temperature, to obtain D 50 The composite particles 2 were 18 μm.

[0077] (3) The composite particles 2 were placed in a graphite crucible, then the crucible was placed in a graphitization furnace, treated at 3000℃ for 8 hours and cooled to obtain the composite graphitized particles.

[0078] (4) 2 kg of coal pitch (softening point 280℃) was added to 100 kg of naphthalene oil, and the coal pitch was fully dissolved by high-speed stirring to obtain a coal pitch solution, then 100 kg of the composite graphitized particles was added and stirred for 2 hours, and the solvent was removed by drying at 100℃ under vacuum to obtain a powder; the powder was placed in a high-temperature furnace, first heated to 300℃ at a rate of 2℃ / min under air atmosphere, kept for 5 h, then N2 was introduced, heated to 1100℃ at a rate of 4℃ / min, kept for 2 h, then cooled to room temperature to obtain the graphite-based composite negative electrode material.

[0079] The mass percentage of the natural graphite in the graphite-based composite negative electrode material was 31%, the mass percentage of the artificial graphite was 55%, and the mass percentage of the hard carbon was 14%.

[0080] Comparative Example 1

[0081] (1) 15 kg of petroleum pitch (softening point 80℃, quinoline insoluble content 0.4%), 100 kg of natural graphite (D 50 5 μm) with a mass content of fixed carbon of 90%, and 100 kg of petroleum coke (D 50 5 μm) were placed in a kneading pot, kneaded at 100℃ for 30 minutes, then treated by cold isostatic pressing equipment at 80 MPa for 3 min to obtain a graphite block. The graphite block was directly placed in a high-temperature furnace, heated from room temperature to 800℃ at a rate of 5℃ / min under N2 protection for 4 hours and then cooled; then the graphite block was crushed by an air flow crusher to D 50 5 μm, and shaped in a shaper to obtain the composite particles 1 with D 50 5 μm.

[0082] (2) Put 100 kg of the composite particles 1 and 25 kg of petroleum pitch (softening point 200℃) into a reaction kettle, and stir at a rate of 40 rpm. First, heat from room temperature to 260℃ at a rate of 1℃ / min under N2protection, stir for 2 h, then continue to stir for 12 h while passing in air, and finally continue to pass in N2, heat to 650℃ at a rate of 2℃ / min, and keep the temperature for 3 h before cooling to room temperature to obtain D 50 The composite particles 2 are 15 μm.

[0083] (3) Put the composite particles 2 into a graphite crucible, then put the crucible into a graphitization furnace, and treat at 2800℃ for 4 h to cool to obtain the composite graphitized particles.

[0084] (4) Add 4 kg of petroleum pitch (softening point 200℃) to 150 kg of wash oil, and stir at high speed to fully dissolve the petroleum pitch to obtain a petroleum pitch solution. Add 100 kg of the composite graphitized particles, continue to stir for 5 h, and dry at 100℃ under vacuum to remove the solvent to obtain a powder. First, heat from room temperature to 300℃ at a rate of 0.5℃ / min under an air atmosphere, keep the temperature for 10 h, then pass in N2, heat to 1600℃ at a rate of 2.5℃ / min, keep the temperature for 5 h, and then cool to room temperature to obtain the graphite-based composite negative electrode material.

[0085] The graphite-based composite negative electrode material contains 43% by mass of natural graphite, 55% by mass of artificial graphite, and 2% by mass of amorphous carbon.

[0086] Comparative Example 2

[0087] (1) Put 15 kg of petroleum pitch (softening point 80℃, quinoline insoluble content 0.4%), 100 kg of natural graphite (D 50 5 μm) with a mass content of fixed carbon of 90%, and 100 kg of petroleum coke (D 50 5 μm) into a kneading pot, knead at 100℃ for 30 min, then treat at 80 MPa for 3 min using a cold isostatic pressing forming device to obtain a graphite block. Put the graphite block directly into a high-temperature furnace, heat from room temperature to 800℃ at a rate of 5℃ / min under N2protection for 4 h, and then cool; then crush the graphite block using an air jet pulverizer to D 50 5 μm, and shape in a shaper to obtain composite particles 1 with D 50 5 μm.

[0088] (2) 100 kg of the composite particles 1 and 25 kg of petroleum pitch (softening point 240℃) were mixed uniformly and placed in a reaction kettle, and then heated from room temperature to 260℃ at a rate of 1℃ / min under N2protection, stirred for 12 h, and then heated to 650℃ at a rate of 2℃ / min, and then cooled to room temperature after holding for 3 h, to obtain D 50 The composite particles 2 were 15 μm.

[0089] (3) The composite particles 2 were placed in a graphite crucible, and then the crucible was placed in a graphitization furnace, and then treated at 2800℃ for 4 h to obtain the composite graphitized particles.

[0090] (4) 4 kg of petroleum pitch (softening point 240℃) was added to 150 kg of wash oil, and the petroleum pitch was fully dissolved by high-speed stirring to obtain a petroleum pitch solution, and then 100 kg of the composite graphitized particles was added, and the stirring was continued for 5 h, and then the solvent was removed by drying at 100℃ under vacuum to obtain a powder, and then the powder was placed in a high-temperature furnace, and then heated to 300℃ at a rate of 0.5℃ / min under N2protection, and then held for 10 h, and then N2was introduced, and then heated to 1600℃ at a rate of 2.5℃ / min, and then held for 5 h, and then cooled to room temperature to obtain the graphite-based composite negative electrode material.

[0091] The graphite-based composite negative electrode material contained 43% by mass of natural graphite, 55% by mass of artificial graphite, and 2% by mass of amorphous carbon.

[0092] Comparative Example 3

[0093] (1) 100 kg of natural graphite (D 50 5 μm) having a mass content of fixed carbon of 90% and 100 kg of petroleum coke (D 50 5 μm) were placed in a kneading pot, and then kneaded at 100℃ for 30 min, and then treated at 80 MPa for 3 min using a cold isostatic pressing molding device to obtain a graphite block. The graphite block was directly placed in a high-temperature furnace, and then heated from room temperature to 800℃ at a rate of 5℃ / min under N2protection, and then held for 4 h, and then cooled; and then the graphite block was pulverized by an air jet pulverizer to D 50 5 μm, and then shaped in a shaper to obtain the composite particles 1 having D 50 5 μm.

[0094] (2) 100 kg of the composite particles 1 were mixed with 25 kg of petroleum pitch (softening point 240 °C) and placed in a reaction kettle, with a stirring rate of 40 rpm. First, the temperature was raised to 260 °C at a rate of 1 °C / min under N2protection, and stirred for 2 h. Then, air was introduced, and stirring was continued for 12 h. Finally, N2was continuously introduced, and the temperature was raised to 650 °C at a rate of 2 °C / min. After holding for 3 h, the temperature was cooled to room temperature, to obtain D 50 The composite particles 2 were 8 μm.

[0095] (3) The composite particles 2 were placed in a graphite crucible, which was then placed in a graphitization furnace, and treated at 2800 °C for 4 h to cool, to obtain the composite graphitized particles.

[0096] (4) 4 kg of petroleum pitch (softening point 240 °C) was added to 150 kg of wash oil, and stirred at high speed to fully dissolve the petroleum pitch, to obtain a petroleum pitch solution. Then, 100 kg of the composite graphitized particles were added, and stirring was continued for 5 h. The solvent was removed by drying at 100 °C under vacuum, to obtain a powder. The powder was placed in a high-temperature furnace, and first, the temperature was raised to 300 °C at a rate of 0.5 °C / min under an air atmosphere, and held for 10 h. Then, N2was introduced, and the temperature was raised to 1600 °C at a rate of 2.5 °C / min, and held for 5 h. After cooling to room temperature, a graphite-based composite negative electrode material was obtained.

[0097] The mass percentage of the natural graphite in the graphite-based composite negative electrode material was 42%, the mass percentage of the artificial graphite was 41.2%, and the mass percentage of the hard carbon was 16.8%.

[0098] Electrochemical performance tests of the above Examples 1-4 and Comparative Examples 1-3 were performed as follows:

[0099] Half-cell test method: The graphite-based composite negative electrode materials prepared in Examples 1-4 and Comparative Examples 1-3, conductive carbon black (SP), carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) were mixed at a mass ratio of 95:1:1.5:2.5, and coated on a copper foil. The coated electrode was dried in a vacuum drying oven at 120 °C for 12 h. Simulated battery assembly was performed in an argon-protected Braun glove box, with 1 M-LiPF6+EC:DEC:DMC (volume ratio of 1:1:1) as the electrolyte, and a lithium metal sheet as the counter electrode. Simulated battery tests were performed in a 5 V, 10 mA new Wei battery test cabinet, with a charge-discharge voltage of 0.01-1.5 V, and a charge-discharge rate of 0.1 C. The initial discharge capacity and the initial charge-discharge efficiency were tested, and the test results are shown in Table 1.

[0100] Full battery test method: the graphite-based composite prepared from examples 1-4 and comparative example 3 was used as negative electrode, lithium cobaltate as positive electrode, 1M-LiPF6+EC:DEC:DMC (volume ratio 1:1:1) solution as electrolyte to assemble full battery, to carry out normal temperature charge-discharge at 1C and 2C rate, voltage range 3.0-4.2V, test the cycle performance, the test results are shown in Table 1.

[0101] Charging maximum rate test method: charge the battery to 100% SOC at different rates, disassemble the battery in low temperature and low humidity environment, observe the lithium precipitation of the negative electrode sheet, the test results are shown in Table 1.

[0102] Table 1 physical property parameters and performance test results of negative electrode material in batteries of examples 1-4 and comparative examples 1-3

[0103]

[0104] As can be seen from Table 1, the composite graphite negative electrode material prepared by the application not only has high discharge capacity, long cycle life and low expansion, but also can take into account the fast charging performance above 3C. The softening point of the pitch used in the granulation and surface coating of comparative example 1 is lower than 240℃, which cannot be converted into hard carbon precursor in the oxidation atmosphere, and is converted into artificial graphite in the graphitization process, and is converted into amorphous carbon in the surface coating heat treatment process, and the obtained graphite composite negative electrode material has low capacity and poor cycle performance at high rate. The softening point of the pitch used in the granulation and surface coating of comparative example 2 is 240℃, but the pitch is not oxidized in the oxidation atmosphere, and is converted into artificial graphite in the graphitization process, and is converted into amorphous carbon in the surface coating heat treatment process, and the obtained graphite composite negative electrode material has low capacity and poor cycle performance at high rate. Comparative example 3 is to isostatically press natural graphite and artificial graphite to form a primary particle, and the obtained primary particle is still a mixture of the two kinds of graphite particles, and the natural graphite and artificial graphite cannot be bonded and compounded together in the granulation process, therefore, the prepared graphite negative electrode material is a mixture of natural graphite, artificial graphite and hard carbon, the negative electrode material has high capacity and high initial coulombic efficiency, but has very poor cycle performance at high rate.

[0105] The above describes the embodiments of the application. However, the application is not limited to the above embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the application shall be included in the protection scope of the application.

Claims

1. A method for preparing a graphite-based composite anode material, the method comprising the following steps: (1) Mix natural graphite, artificial graphite precursor and asphalt 1, knead and press to obtain graphite blocks; (2) The graphite block from step (1) is heat-treated, crushed, and shaped to obtain primary composite particles; (3) Mix the primary composite particles from step (2) with asphalt 2 and granulate them to obtain secondary composite particles; (4) After the secondary composite particles in step (3) are broken up, they are graphitized to obtain composite graphitized particles. (5) Mix asphalt 2, organic solvent and composite graphitized particles from step (4), remove the organic solvent, and then perform heat treatment to prepare the graphite-based composite anode material. In step (1), the natural graphite is spherical in shape; the median particle size D of the natural graphite is... 50 The median particle size D of the artificial graphite precursor is 5–8 μm. 50 The thickness is 5-8 μm; the artificial graphite precursor is selected from at least one of petroleum coke, needle coke, pitch coke and anthracite; the softening point of the pitch 1 is 60℃-90℃ and the quinoline insoluble content is ≤1%; In step (1), the mass ratio of natural graphite, artificial graphite precursor, and asphalt 1 is 1:(1~2):(0.06~0.15); In step (1), the mixing temperature is 10℃-20℃ higher than the softening point temperature of asphalt 1, and the mixing time is 10min-40min. In step (1), the molding process is cold isostatic pressing, the temperature of the molding process is 20℃~40℃, the pressure of the molding process is 30MPa~80MPa, and the holding time of the molding process is 1min~10min; In step (3), the mass ratio of the primary composite particles to asphalt 2 is 100:(10-30); In step (3), the softening point of the asphalt 2 is greater than or equal to 240℃; In step (3), the granulation includes the following steps: first, heating to 10°C to 30°C above the softening point of asphalt 2 under a protective atmosphere and stirring; then introducing an oxygen-containing atmosphere and continuing to stir; finally heating to 600°C to 650°C under a protective atmosphere. In step (5), the heat treatment step includes: First, in an air atmosphere, the temperature is increased to 250℃~300℃ at a heating rate of 0.5~2℃ / min and held for 2~10h. Then, the air atmosphere in the high-temperature furnace is switched to a protective atmosphere and the temperature is increased to 800℃~1600℃ at a heating rate of 2~5℃ / min. After holding for 1~5h, the temperature is cooled to room temperature. The graphite-based composite anode material has a core-shell structure, including a shell and a core. The core includes artificial graphite, natural graphite, and hard carbon; the shell includes hard carbon.

2. The preparation method according to claim 1, wherein, In step (1), the mass content of fixed carbon in the natural graphite is ≥85%; In step (2), the temperature of the heat treatment is 800℃~1200℃, and the time of the heat treatment is 4 hours~10 hours.

3. The preparation method according to claim 1, wherein, In step (4), the graphitization temperature is 2800℃~3000℃ and the graphitization time is 2~10 hours.

4. The preparation method according to claim 1, wherein, In step (5), the mass ratio of asphalt 2: organic solvent: composite graphitized particles is (1-6):(80-200):

100.

5. A graphite-based composite anode material prepared by the method according to any one of claims 1-4.

6. The graphite-based composite anode material according to claim 5, wherein, The graphite-based composite anode material has a core-shell structure, including a shell and a core. The core includes artificial graphite, natural graphite, and hard carbon; the shell includes hard carbon.

7. The graphite-based composite anode material according to claim 5 or 6, wherein, The graphite-based composite anode material contains 40%–72% artificial graphite, 20%–40% natural graphite, and 8%–20% hard carbon by mass.

8. A negative electrode, said negative electrode comprising the graphite-based composite negative electrode material according to any one of claims 5-7.

9. A lithium-ion battery, the battery comprising the graphite-based composite negative electrode material according to any one of claims 5-7, or the battery comprising the negative electrode according to claim 8.

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