Graphite negative electrode material and preparation method, application, and lithium-ion battery

Abstract

The present invention discloses a graphite negative electrode material, its preparation method, application, and lithium-ion battery. The preparation method of the graphite negative electrode material of the present invention comprises the following steps: S1: heat-treating a mixture of a soft carbon material, asphalt, and divinylbenzene to obtain material A; the heat treatment temperature is 400-600°C, and the mass ratio of the soft carbon material to divinylbenzene is 100:(3-15); S2: graphitizing material A to obtain material B. The lithium-ion battery of the present invention has high fast charging performance and high-rate cycle performance, as well as high discharge capacity, initial efficiency, and compaction density.

Description

Technical Field

[0001] The present invention specifically relates to a graphite negative electrode material, a preparation method thereof, an application thereof, and a lithium ion battery. Background Art

[0002] Lithium-ion batteries are a new type of chemical power source, widely used in daily life due to their excellent performance. Anode materials are one of the four key materials in lithium-ion batteries, and their rate performance directly determines the fast-charging performance of lithium-ion batteries. Demand for fast charging is increasing in electric vehicles and consumer electronics. However, commercial graphite anode materials, due to their small interlayer spacing, cannot meet the high-rate current requirements and are prone to lithium plating, which seriously affects the fast-charging performance of lithium-ion batteries.

[0003] Currently, approaches to improving fast-charging performance typically focus on material structure design, coating optimization, improved lithium-ion access, lowered internal resistance, and reduced polarization to achieve superior kinetic performance. While a variety of graphite anode materials are currently available, they still fall short of the fast-charging requirements of battery-powered vehicles and consumer electronics.

[0004] Chinese patent document CN112421001A discloses a high-rate upper-layer coated graphite negative electrode material, a lithium-ion battery and a preparation method thereof. The material adopts liquid-phase hard carbon to coat a soft carbon graphite composite material, thereby avoiding particle adhesion caused by the high-temperature carbonization process, allowing the hard carbon to fill the pores generated by the volatilization of soft carbon small molecules during the carbonization process, achieving uniform coating, reducing the increase in specific surface area, and reducing the irreversible capacity loss of graphite. However, the fast charging performance of the lithium-ion battery made of the graphite negative electrode material prepared by this patent still cannot meet the growing demand. Summary of the Invention

[0005] The present invention addresses the technical problem of overcoming the drawback of prior art graphite negative electrode materials, which lack the fast-charging performance required for lithium-ion batteries. The present invention provides a graphite negative electrode material, a preparation method, applications, and a lithium-ion battery. The lithium-ion battery of the present invention exhibits high fast-charging performance and high-rate cycling performance, as well as high discharge capacity, initial efficiency, and compaction density.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] The present invention provides a method for preparing a graphite negative electrode material, which comprises the following steps:

[0008] S1: heat-treating a mixture of a soft carbon material, asphalt, and divinylbenzene to obtain material A; the heat-treating temperature is 400-600° C., and the mass ratio of the soft carbon material to the divinylbenzene is 100:(3-15);

[0009] S2: The material A is graphitized to obtain material B.

[0010] In S1, the soft carbon material can be conventional in the art, generally an amorphous carbon material that can be graphitized above 2500°C, preferably one or more of needle coke, petroleum coke, carbon fiber and non-graphitized mesophase carbon microbeads, more preferably needle coke.

[0011] The needle coke may be conventional green needle coke or cooked needle coke in the art.

[0012] In S1, the particle size of the soft carbon material can be conventional in the art, preferably the particle size D50 is 3 to 50 μm, more preferably 5 to 15 μm, for example 6 μm.

[0013] In S1, the particle size D50 of the asphalt is preferably 1 to 50 μm, more preferably 1 to 10 μm, for example 3 μm.

[0014] In S1, the asphalt may be conventional petroleum asphalt or coal asphalt in the art.

[0015] The inventor creatively uses asphalt to mix with the soft carbon material and the pore-forming agent divinylbenzene, which has a stabilizing effect on the pore structure formed by divinylbenzene in the soft carbon material, thereby improving the fast charging performance and cycle performance of the resulting graphite negative electrode material. The effect of the present invention cannot be achieved without adding asphalt or adding other commonly used binder materials.

[0016] In S1, the softening point of the asphalt can be conventional in the art, preferably 100-300°C.

[0017] In S1, the divinylbenzene can be conventional in the art, and generally can be one or more of o-divinylbenzene, m-divinylbenzene and p-divinylbenzene.

[0018] The inventors discovered in their research that divinylbenzene activator can form more micropores in soft carbon materials during heat treatment, providing access channels for the embedding and de-embedding of lithium ions, thereby effectively alleviating the polarization phenomenon in the initial stage of fast charging and improving fast charging performance. Other common inorganic or organic pore-forming agents cannot achieve the effects of the present invention.

[0019] In S1, the mass ratio of the soft carbon material to the asphalt is preferably 100:(5-30), more preferably 100:(10-20), for example 100:15 or 100:18.

[0020] In S1, the mass ratio of the soft carbon material to the divinylbenzene is preferably 100:(5-12), for example, 100:8 or 100:10.

[0021] In certain preferred embodiments of the present invention, the mass ratio of the soft carbon material, the asphalt and the divinylbenzene is 100:(5-30):(3-15).

[0022] In some more preferred embodiments of the present invention, the mass ratio of the soft carbon material, the asphalt and the divinylbenzene is 100:(10-20):(5-12).

[0023] In S1, the preparation method of the mixture can be conventional in the art, and generally the soft carbon material, the asphalt and the divinylbenzene are stirred and mixed.

[0024] In S1, the heat treatment is preferably performed under stirring.

[0025] The stirring speed may be conventional in the art, preferably 25-40 r / min.

[0026] In S1, the temperature of the heat treatment is preferably 450-580°C, more preferably 500°C.

[0027] In the present invention, the temperature of the heat treatment not only causes the divinylbenzene to volatilize to form microporous channels, but also causes the asphalt to convert and coke, removing the volatile components therein. The carbon material formed after the conversion can combine small particles of soft carbon material together to form a stable channel structure.

[0028] In S1, the heat treatment time is preferably 0.8 to 8 hours, more preferably 3 to 7 hours, for example 6 hours.

[0029] In S2, the graphitization treatment can be performed using conventional methods in the art, generally by performing a high-temperature heat treatment under a protective atmosphere.

[0030] The protective atmosphere may be conventional in the art, and generally includes one or more of nitrogen and inert gas.

[0031] In S2, the temperature of the graphitization treatment may be conventional in the art, preferably above 2500°C, more preferably 2800-3200°C, and even more preferably 3000°C.

[0032] In S2, the graphitization treatment time can be conventional in the art, preferably 12 to 96 hours, more preferably 48 hours.

[0033] In the present invention, the graphitization treatment preferably further includes a hard carbon coating step.

[0034] The inventors found in their research that coating with hard carbon materials can better stabilize the pore structure formed by divinylbenzene, thereby making the resulting graphite negative electrode material have better fast charging performance and cycle performance.

[0035] The hard carbon coating can be performed by conventional methods in the art. Generally, the material B and the hard carbon material are heated under a protective atmosphere.

[0036] In the hard carbon coating, the hard carbon material may be conventional carbon that is difficult to graphitize in the art, generally one or more of resin carbon, organic polymer pyrolytic carbon and carbon black, preferably resin carbon, more preferably phenolic resin.

[0037] In the hard carbon coating, the amount of the hard carbon material can be conventional in the art. Preferably, the mass ratio of the material B to the hard carbon material is 100:(5-30), more preferably 100:(5-15), for example 100:8 or 100:10.

[0038] In the hard carbon coating, the protective atmosphere is preferably as described above.

[0039] In the hard carbon coating, the heating temperature can be conventional in the art, generally enough to melt the hard carbon material, preferably not less than 900°C, more preferably 1000-1200°C, such as 1100°C.

[0040] In the hard carbon coating, the heating time may be conventional in the art, preferably 2 to 48 hours, more preferably 24 hours.

[0041] In the present invention, those skilled in the art can generally understand that the preparation method further includes a post-processing step.

[0042] Wherein, when the preparation method includes hard carbon coating, the post-treatment is performed after the hard carbon coating.

[0043] The post-treatment can be carried out by conventional methods in the art, generally including cooling, mixing, screening and magnetic separation.

[0044] The cooling, mixing, screening and magnetic separation can all be performed using conventional methods in the art.

[0045] The present invention also provides a graphite negative electrode material obtained by the preparation method described above.

[0046] The present invention also provides an application of the graphite negative electrode material described above in a lithium ion battery.

[0047] The present invention also provides a lithium ion battery comprising the graphite negative electrode material described above.

[0048] On the basis of conforming to the common sense in this field, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0049] The reagents and raw materials used in the present invention are commercially available.

[0050] The positive progress effect of the present invention is:

[0051] (1) A large number of stable micropores are formed in the graphite negative electrode material prepared by the present invention, which provide access channels for the insertion and deinsertion of lithium ions, thereby improving the fast charging performance and cycle performance; the 3C constant current ratio can be ≥80%, even as high as 85%, and the capacity retention rate after 100 cycles of 3C can be ≥83%, even as high as 95%.

[0052] (2) The lithium-ion battery made of the graphite negative electrode material of the present invention has a high discharge capacity and initial efficiency. The discharge capacity of 0.3mA constant current charge and discharge can be ≥348.7mAh / g, and even as high as 355.9mAh / g; the initial efficiency can be higher than 88%, and even as high as 93.5%.

[0053] (3) The graphite negative electrode material of the present invention has a moderate particle size and specific surface area and a high tap density. DETAILED DESCRIPTION

[0054] The present invention is further illustrated by way of examples below, but the present invention is not limited to the scope of the examples. Experimental methods in the following examples where specific conditions are not specified were performed according to conventional methods and conditions, or selected according to the product specifications.

[0055] The needle coke used in the following examples and comparative examples was produced by Jinzhou Petrochemical and had a volatile matter content of 2%; the asphalt was produced by Liaoning Xinde New Materials Technology Co., Ltd. and had a softening point of 205°C; the phenolic resin was produced by Wuxi Xinyehao Chemical Co., Ltd. and had a softening point of 100°C. Other raw materials were commercially available.

[0056] Example 1

[0057] (1) The needle coke is crushed to obtain a powder with a particle size D50 of 6 μm; the asphalt is crushed to obtain a powder with a particle size D50 of 3 μm.

[0058] (2) The needle coke powder, asphalt powder (softening point 205°C) and divinylbenzene obtained in step (1) are uniformly mixed in a mass ratio of 100:15:5, and then added into a reactor for heat treatment. The heat treatment process is to heat to 500°C under stirring and then keep the temperature constant for 300 minutes, with a stirring speed of 25-40 r / min, to obtain material A.

[0059] (3) Under inert atmosphere conditions, material A was graphitized at a temperature of 3000°C and a time of 48 hours to obtain material B.

[0060] (4) Material B and phenolic resin were mixed evenly in a mass ratio of 100:8, and then heated to 1100°C under an inert atmosphere and kept at this temperature for 24 hours for hard carbon coating modification.

[0061] (5) Cooling the product obtained in step (4) to room temperature, mixing, screening and magnetic separation are carried out in sequence to obtain a graphite negative electrode material.

[0062] Example 2

[0063] In step (2), the mass ratio of needle coke powder, pitch powder and divinylbenzene is 100:15:8, and the other conditions are the same as those in Example 1, to obtain a graphite negative electrode material.

[0064] Example 3

[0065] In step (2), the mass ratio of needle coke powder, pitch powder and divinylbenzene is 100:15:10, and the other conditions are the same as those in Example 1, to obtain a graphite negative electrode material.

[0066] Example 4

[0067] In step (2), the mass ratio of needle coke powder, asphalt powder and divinylbenzene is 100:18:10; in step (4), the mass ratio of material B and phenolic resin is 100:10, and the rest are the same as in Example 1, to obtain a graphite negative electrode material.

[0068] Example 5

[0069] In step (4), the mass ratio of material B to phenolic resin is 100:10, and the other conditions are the same as those in Example 3, to obtain a graphite negative electrode material.

[0070] Example 6

[0071] In step (4), the mass ratio of material B to phenolic resin is 100:30, and the other conditions are the same as those in Example 3, to obtain a graphite negative electrode material.

[0072] Example 7

[0073] The time of the constant temperature heat treatment in step (2) is 60 min, and the other steps are the same as those in Example 3, to obtain a graphite negative electrode material.

[0074] Example 8

[0075] In step (2), the mass ratio of needle coke powder, pitch powder and divinylbenzene is 100:5:10, and the other conditions are the same as those in Example 3, to obtain a graphite negative electrode material.

[0076] Example 9

[0077] Step (4) is not performed, and the material B obtained in step (3) is directly subjected to step (5). Other steps are the same as those in Example 3 to obtain a graphite negative electrode material.

[0078] Comparative Example 1

[0079] In step (2), no divinylbenzene was added, the mass ratio of needle coke powder to asphalt powder was 100:18, and the other steps were the same as those in Example 1.

[0080] Comparative Example 2

[0081] The divinylbenzene in step (2) was replaced by potassium chloride, and the rest was the same as in Example 3 to obtain a graphite negative electrode material.

[0082] Comparative Example 3

[0083] In step (2), the mass ratio of needle coke powder to divinylbenzene is 100:20; the rest is the same as in Example 1, and a graphite negative electrode material is obtained.

[0084] Comparative Example 4

[0085] The temperature of the heat treatment in step (2) is 650° C., and the other conditions are the same as those in Example 3, to obtain a graphite negative electrode material.

[0086] Comparative Example 5

[0087] In step (2), no asphalt is added, and the rest is the same as in Example 3 to obtain a graphite negative electrode material.

[0088] Effect embodiment

[0089] 1. Constant current ratio test

[0090] The graphite negative electrode material obtained in the above embodiment and comparative example and the conductive agent SP, binder SBR / CMC and copper foil were respectively assembled into a soft-pack lithium-ion battery negative electrode sheet; the positive electrode material was a lithium-containing transition oxide LiCoO2, the electrolyte included an electrolyte LiPF6 and an organic solvent (EC:EMC:DMC=1:1:1 (volume ratio), wherein the concentration of the electrolyte was 1 mol / L, the separator was a PP-PE-PP three-layer composite film, the positive and negative electrode collectors were aluminum foil and copper foil, respectively, and the battery outer packaging was an aluminum-plastic film to obtain a soft-pack lithium-ion battery. Fast charging and cycle performance were carried out on a Wuhan Blue Electric Battery Tester, using a 3C (constant current constant voltage) / 1C (constant current) charge and discharge mode, and the constant current ratio was recorded; a 3C (constant current constant voltage) / 1C (constant current) charge and discharge mode was used, and the capacity retention rate was tested after 100 cycles. The results are shown in Table 1.

[0091] 2. Capacity and initial efficiency test

[0092] Coin-type batteries were used for testing. The specific testing method was as follows: N-methylpyrrolidone (NMP) and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 95:5 and stirred thoroughly to prepare a slurry. This slurry was then mixed evenly with the graphite anode materials obtained in the Examples and Comparative Examples in a weight ratio of 97:3 to prepare a slurry. The slurry was evenly coated on a 6-12 μm thick copper foil and vacuum-dried for 8 hours before use. A simulated battery was then assembled in an argon-filled glove box. The electrolyte was 1 mol / L LiPF6, the organic solvent was an EC:EMC:DMC ratio of 1:1:1 (volume ratio), and the counter electrode was a lithium sheet. Electrochemical performance was measured on a Wuhan Blue Electric Battery Tester using the following test steps: constant current discharge: 0.3 mA, 0.001 V; rest: 5 min; constant current charge: 0.3 mA, 2.0 V. The results are shown in Table 1.

[0093] 2. Particle size test

[0094] The test method refers to the particle size distribution laser diffraction method in GB / T 19077-2016. The instrument used is MalvernMaster Size 2000. The sample particle size D50 is measured using the laser diffraction principle. The results are shown in Table 1.

[0095] 3. Tap density test

[0096] The test method refers to GB / T5162-2006 Determination of the tap density of metal powders. The instrument used is a US Quantachrome AUTOTAP tap density meter. 10-20g of sample is added to a 26ml graduated cylinder, vibrated 3000 times, and the tap density is recorded. The results are shown in Table 1.

[0097] 4. Specific surface area test

[0098] The test method refers to GB / T 19587-2017 gas adsorption BET method for determining the specific surface area of ​​solid substances. The instrument uses a Quantachrome NOVA Touch specific surface area tester. The specific surface area is measured by multi-point BET. The results are shown in Table 1.

[0099] Table 1 Performance data of graphite negative electrode materials obtained in Examples and Comparative Examples

[0100]

[0101] As can be seen from Table 1, the graphite negative electrode materials prepared in the embodiments of the present invention have excellent fast charging performance and high-rate cycle performance: the 3C fast charging constant current ratio is ≥80%, and even as high as 85%, and the 3C cycle 100-week capacity retention rate can be ≥83%, and even as high as 95%. In Comparative Example 1, no activator is added, and in Comparative Example 2, the type of activator is changed, and the fast charging performance of the obtained graphite negative electrode materials is significantly reduced; in Comparative Example 3, the amount of activator is increased, and the fast charging performance and cycle performance of the graphite negative electrode material are significantly worse than those of the present invention. Comparative Example 4 uses a higher heat treatment temperature, and the fast charging performance and cycle performance of the graphite negative electrode material obtained are significantly worse than those of the present invention. In Comparative Example 5, no asphalt is added, and the fast charging performance and cycle performance of the obtained graphite negative electrode material are also significantly worse than those of the embodiments of the present invention.

Claims

1. A method for preparing a graphite negative electrode material, characterized in that: It includes the following steps: S1: heat-treating a mixture of a soft carbon material, asphalt, and divinylbenzene to obtain material A; the heat-treating temperature is 450-500° C., and the mass ratio of the soft carbon material to the divinylbenzene is 100:(8-10); S2: The material A is graphitized to obtain material B; In S1, the particle size D50 of the asphalt is 1-50 μm; In S1, the asphalt is petroleum asphalt or coal asphalt; In S1, the mass ratio of the soft carbon material to the asphalt is 100:(5-15); The graphitization treatment further includes a hard carbon coating step; The mass ratio of the material B to the hard carbon material is 100:(5-15).

2. The method for preparing a graphite negative electrode material according to claim 1, wherein The soft carbon material is one or more of needle coke, petroleum coke, carbon fiber and non-graphitized mesophase carbon microspheres; And / or, in S1, the particle size D50 of the soft carbon material is 3-50 μm; and / or, in S1, the particle size D50 of the asphalt is 1-10 μm; And / or, in S1, the softening point of the asphalt is 100~300℃.

3. The method for preparing a graphite negative electrode material according to claim 2, wherein: In S1, the particle size of the soft carbon material is 5-15 μm.

4. The method for preparing a graphite negative electrode material according to claim 1, wherein In S1, the mass ratio of the soft carbon material to the asphalt is 100:15; And / or, in S1, the mass ratio of the soft carbon material to the divinylbenzene is 100:8 or 100:

10.

5. The method for preparing a graphite negative electrode material according to claim 1, wherein: In S1, the heat treatment is carried out under stirring; and / or, in S1, the temperature of the heat treatment is 500° C.; And / or, in S1, the heat treatment time is 0.8~8h.

6. The method for preparing a graphite negative electrode material according to claim 5, wherein: In S1, the heat treatment is performed during stirring, and the stirring speed is 25-40 r / min.

7. The method for preparing a graphite negative electrode material according to claim 5, wherein: In S1, the heat treatment time is 3 to 7 hours.

8. The method for preparing a graphite negative electrode material according to claim 1, wherein: The mass ratio of the material B to the hard carbon material is 100:8 or 100:

10.

9. The method for preparing a graphite negative electrode material according to claim 8, wherein: It meets one or more of the following conditions: (1) The hard carbon coating is performed by heating the material B and the hard carbon material under a protective atmosphere; (2) The hard carbon material is one or more of resin carbon, organic polymer pyrolytic carbon and carbon black; (3) the heating temperature is not less than 900°C; and, (4) The heating time is 2 to 48 hours.

10. The method for preparing a graphite negative electrode material according to claim 9, wherein: It meets one or more of the following conditions: (1) The hard carbon material is a phenolic resin; and (2) The heating temperature is 1000~1200℃.

11. The method for preparing a graphite negative electrode material according to claim 1, wherein: The mass ratio of the soft carbon material, the asphalt and the divinylbenzene is 100:(5-15):(8-10).

12. The method for preparing a graphite negative electrode material according to claim 1, wherein: The preparation method further comprises a post-processing step; the post-processing comprises cooling, mixing, screening and magnetic separation.

13. A graphite negative electrode material obtained by the preparation method according to any one of claims 1 to 12.

14. Use of the graphite negative electrode material according to claim 13 in a lithium ion battery.

15. A lithium ion battery, characterized in that: It comprises the graphite negative electrode material as claimed in claim 13.

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