Long cycle graphite negative electrode material and preparation method and application thereof

Abstract

The application discloses a long-circulation graphite negative material and a preparation method and application thereof, and belongs to the field of lithium ion battery artificial graphite negative materials, and is characterized by that: the FCC oil slurry is used as raw material, and the artificial graphite negative material is obtained through filtration, delayed coking, crushing and grading and graphitization; the delayed coking treatment adopts a uniform gradient temperature rising, and the temperature curve is 445±5 DEG C -> 50±5 h -> 475±5 DEG C; the long-circulation graphite negative material prepared by using the preparation method of the long-circulation graphite negative material in the protection range of the application can guarantee that the capacity retention rate of the button cell is greater than 87.6% when the Ds50=DH / DQ=67±5% under the premise that the Dv50 particle size size DH is 10.0±0.5 um after graphitization; and the button cell prepared by using the long-circulation graphite negative material has a cycle number of more than 15000 times under the condition that the temperature is 25 DEG C, the charge-discharge rate is 1C / 1C, and the 80% capacity retention rate is used as the evaluation limit.

Description

TECHNICAL FIELD

[0001] The present application relates to a long cycle graphite negative material and its preparation method and application, and belongs to the field of lithium ion battery artificial graphite negative material, in particular to a preparation process of artificial graphite with high particle size shrinkage. BACKGROUND

[0002] As the most mainstream raw material for preparing artificial graphite negative material, the physical and electrochemical properties of needle coke are closely related to the comprehensive performance of artificial graphite negative material. With the rapid development of the new energy industry, the market has increasingly high performance requirements for artificial graphite, and there is an increasing demand for customization and individualization. Currently, there are clear performance requirements in the market, such as long cycle, high capacity, high compaction, high rate, easy processing, etc. With the promotion of CTP battery replacement and V2G operation mode, the demand for long cycle is particularly urgent in the current market, and it is widely used in energy storage system batteries and power system batteries. From a macro perspective, the key factors affecting the cycle performance include raw materials, i.e. needle coke properties, and end product design.

[0003] Currently, for the improvement of the cycle performance of artificial graphite, the published patents and documents are all from a single angle for improvement, such as from the design of needle coke end product or from the product application end of the battery, for product research and design. The cycle performance trend value is difficult to break through 15000 cycles, and the cycle number of more than 18000 cycles is extremely rare. There are almost no cases or products of customized / individualized research and development of artificial graphite negative material based on needle coke for artificial graphite, matching the process design of the end product, developing long cycle individualized products, and used for lithium ion battery artificial graphite negative material. Therefore, it is an inevitable trend to improve the performance of artificial graphite raw material needle coke while matching the end product design.

[0004] This paper invents an artificial graphite negative material, i.e. first preparing needle coke with high volatile matter and high Hardgrove grindability index through multi-level gradient temperature delayed coking process; then taking this as raw material, achieving high particle size shrinkage through crushing and rapid graphitization, and finally obtaining a long cycle artificial graphite negative material. SUMMARY

[0005] The specific technical solution of the present application to solve the above technical problems is: a preparation method of long cycle graphite negative material, characterized by: taking FCC oil slurry as raw material, and obtaining artificial graphite negative material through filtration, delayed coking, crushing and grading, and graphitization, including the following steps:

[0006] First step: filter the FCC oil slurry through a filter to remove solid impurities,

[0007] Second step: the filtered oil slurry is subjected to delayed coking treatment, and the water is cooled to room temperature and then directly decoked to obtain needle coke,

[0008] Third step: the needle coke is subjected to crushing treatment, and the particle size of the crushed needle coke is DQ=Dv50=15.0±0.5 μm,

[0009] Fourth step: the crushed needle coke is subjected to graphitization treatment, the graphitization temperature is 2900-3000 ℃, and the graphitization time is 48-54 h, thereby obtaining the long-cycle graphite negative electrode material, and the particle size of the graphitized needle coke is DH=Dv50=10.0±0.5 μm.

[0010] Further, the delayed coking treatment adopts uniform gradient heating, and the temperature curve is 445±5 ℃→50±5 h→475±5 ℃.

[0011] Further, the aromatic content of the FCC oil slurry is 60±5%, the carbon residue content is 10±2%, and the total content of 2-ring and below aromatic hydrocarbons and 2-ring and below naphthenes is 25±5%.

[0012] Further, the volatile content of the needle coke after decoking is 10%±3%, and the Hardgrove grindability index is 110±10.

[0013] A long-cycle graphite negative electrode material is characterized in that the long-cycle graphite negative electrode material is prepared by using the preparation method of the long-cycle graphite negative electrode material, the particle size shrinkage Ds50 of the long-cycle graphite negative electrode material is the ratio of Dv50 after graphitization to Dv50 before graphitization, Ds50=DH / DQ=67±5%, and the Dv50 refers to the particle size corresponding to 50% in the volume distribution, and the particle size is DH=Dv50=10.0±0.5 μm.

[0014] The long-cycle graphite negative electrode material is used for preparing a button cell.

[0015] Further, the capacity retention rate of the button cell is greater than 87.6% at 5000 cycles.

[0016] Further, the cycle number trend value of the button cell is above 15000+.

[0017] Further, the cycle number trend value of the button cell is above 18000+.

[0018] The beneficial effects of the application are:

[0019] The application provides a long-circulation graphite negative electrode material and a preparation method thereof, and the long-circulation graphite negative electrode material prepared by the preparation method of the long-circulation graphite negative electrode material within the protection scope of the application can ensure that the capacity retention rate of a button cell is greater than 87.6% at 5000 cycles under the premise that the Dv50 particle size size DH of the graphitized long-circulation graphite negative electrode material is 10.0±0.5 μm and the Ds50=DH / DQ=67±5%,

[0020] The button cell prepared by using the long-circulation graphite negative electrode material has a cycle number of more than 15000 cycles under the condition that the charge-discharge rate is 1C / 1C at 25 DEG C, and the 80% capacity retention rate is used as the evaluation limit. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is an SEM image of the product after graphitization of the long-circulation graphite negative electrode material of the application; Figure 1

[0022] Figure 2 is a schematic diagram of the relationship between the feeding time and the cycle performance of the application; Figure 2

[0023] Figure 3 is a Dv50 particle size spectrum of the needle coke after crushing of the long-circulation graphite negative electrode material of the application; Figure 3

[0024] Figure 4 is a Dv50 particle size spectrum of the long-circulation graphite negative electrode material after graphitization of the long-circulation graphite negative electrode material of the application; Figure 4

[0025] Figure 5 is a cycle performance test and cycle trend prediction diagram of the application. Figure 5 DETAILED DESCRIPTION

[0026] In the description of the application, specific details are merely for the purpose of enabling a full understanding of the embodiments of the application, but as a person skilled in the art should know that the implementation of the application is not limited to these details. In addition, well-known structures and functions are not described or shown in detail to avoid obscuring the key points of the embodiments of the application. For those skilled in the art, the specific meanings of the above terms in the application can be understood in specific circumstances.

[0027] Specific embodiments of the application: EMBODIMENT

[0028] FCC oil slurry is used as the raw material, the aromatic content of the FCC oil slurry is 60±5%, the carbon residue content is 10±2%, and the total content of 2-ring and below aromatic hydrocarbons and 2-ring and below naphthenes is 25±5%;

[0029] The artificial graphite negative electrode material is obtained through the following steps of filtering, delayed coking, crushing and grading, and graphitization.

[0030] ​​​​​First step: filter the FCC slurry through a filter to remove solid impurities,

[0031] Second step: perform delayed coking treatment on the filtered slurry, the delayed coking treatment adopts uniform gradient heating, the temperature curve is 445±5℃→50±5h→475±5℃; after water cooling to room temperature, directly remove the coke to obtain needle coke,

[0032] Third step: perform crushing treatment on the needle coke, the particle size of the crushed needle coke is DQ=Dv50=15.0±0.5μm;

[0033] Fourth step: perform graphitization treatment on the crushed needle coke, the graphitization temperature is 2900-3000℃, and the graphitization time is 48h-54h, thereby obtaining the long cycle graphite negative electrode material.

[0034] According to the above method, the FCC slurry is obtained by purchasing, the model characteristics of the FCC slurry are as follows: the aromatic content (one of the four components, and the other three components are saturates, resins and asphaltenes) in the FCC slurry is 60±5%, the residual carbon content is 10±2%, the total content of 2-ring and below aromatic hydrocarbons and 2-ring and below naphthenes is 25±5%, and the total amount of filtered metals (calcium, vanadium, manganese, iron, nickel, copper, lead, titanium and chromium) is less than 10ppm. The same batch of FCC slurry is used as the raw material, different delayed coking treatments are performed in parallel, and relevant indexes are detected,

[0035] In order to more intuitively show the process advantages of the present application, the preparation method of the long cycle graphite negative electrode material of the present application and the equivalent replacement method of the same process are compared,

[0036] Comparative examples 1-8:

[0037] The preparation method is the same as that of the examples, except that in the preparation process of the present comparative example, different delayed coking treatments are performed in parallel,

[0038] The same batch of FCC slurry is used as the raw material, and after filtration, delayed coking, crushing and classification, and graphitization, the graphite negative electrode material is prepared, the processes and effect parameters of examples 1-6 and comparative examples 1-6 are shown in table 1.

[0039] The evaluation of the cycle performance is represented by the cycle number at the time of 80% capacity retention rate by full cell normal temperature cycle test. The full cell is designed as a soft package battery of 1 Ah, wherein the preparation of the negative electrode sheet is that polyvinylidene fluoride (PVDF) is dissolved in N-methyl pyrrolidone (NMP) solvent, a conductive agent (SP) is added, stirred uniformly, then the modified artificial graphite negative material (wherein the modified artificial graphite negative material: PVDF: NMP: SP = 95.0: 1.5: 1.5: 2.0) is added, stirred uniformly again, then the slurry is completed, and then coating (the single-sided area density is 7 g / cm3), preheating and drying, rolling, drying, secondary rolling, die cutting, cutting and assembling are performed to obtain the button cell; wherein the electrolyte is 1M LiPF6, EC: DEC: DMC = 1: 1: 1 (volume ratio), the counter electrode is lithium cobaltate, the charge and discharge cut-off voltage is 3.0V-4.3V, the charge and discharge rate is 1C / 1C, and the test temperature is 25℃,

[0040] It is to be noted that, because the cycle performance test cycle of the long cycle characteristic is too long (generally ≥10 years), the industry-recognized evaluation method is to predict the final cycle performance through the trend of the cycle capacity retention rate curve after a period of test (≥2000 weeks), and the cycle performance test and cycle trend prediction graph are as shown in Figure 5

[0041] Ds50 is the particle size shrinkage of the long cycle graphite negative material, which is the ratio of Dv50 after graphitization to Dv50 before graphitization, and the index affects the capacity retention rate and cycle number at 5000 weeks;

[0042] Wherein, Dv50 after graphitization is DH=10.0±0.5μm; Dv50 before graphitization is DQ=15.0±0.5μm; and Dv50 refers to the particle size corresponding to 50% in the volume distribution,

[0043] The particle size is measured by a Malvern 3000 laser particle size analyzer by laser diffraction method; and the specific test data are shown in Table 1:

[0044]

[0045] According to the data analysis in Table 1, it can be known that:

[0046] (1) The long cycle graphite negative material prepared by the preparation method of the long cycle graphite negative material within the protection scope of the application in examples 1-6 can guarantee that the Dv50 particle size size DH after graphitization is 10.0±0.5μm, the capacity retention rate of the button cell at 5000 weeks is greater than 87.6% when Ds50=DH / DQ=67±5%, and the cycle number trend value of the battery is all above 15000+, and the highest can reach 18000+; ​

[0047] (2) Example 1 compared with Comparative Examples 5-6: the same uniform gradient heating rate as the present application, i.e. 0.5℃ / h, but the temperature interval is different, i.e. both the initial temperature and the terminal temperature are out of the range defined in the present application, but have the same uniform gradient heating rate as the present application;

[0048] According to the experimental results, the Ds50=DH / DQ of Comparative Examples 5-6 is 99% and 50%, the capacity retention rate of the button cell at 5000 cycles is 11.0% and 27.4%, and the battery cycle number trend value is 2000+ and 5000+;

[0049] Therefore, under the same uniform gradient heating rate as the present application, i.e. the temperature curve is 445±5℃→50±5h→475±5℃, it is proved that the temperature interval affects the Ds50 and the capacity retention rate of the button cell at 5000 cycles and the battery cycle number trend value;

[0050] (3) Example compared with Comparative Examples 1-4: the difference lies in the different temperature intervals and heating rates, at this time, although Comparative Examples 1-4 have the same initial temperature or terminal temperature end value as the present application, the heating rate is different,

[0051] According to the experimental results, the Ds50=DH / DQ of Comparative Examples 1-4 is 80%, 55%, 55% and 90%, the capacity retention rate of the button cell at 5000 cycles is 43.8%, 49.3%, 60.2% and 21.9%, and the battery cycle number trend value is 8000+, 9000+, 11000+ and 4000+, which is much lower than 18000+ of the present application; the Ds50 has a certain correlation with the capacity retention rate of the button cell at 5000 cycles and the battery cycle number trend value,

[0052] It can be seen that the different temperature intervals and heating rates also affect the Ds50, and the Ds50 has an impact on the capacity retention rate of the button cell at 5000 cycles and the battery cycle number trend value;

[0053] In addition, Comparative Examples 5-6 compared with Comparative Examples 1-4, although Comparative Examples 5-6 have the same uniform gradient heating rate as the present application, but the effect is lower than that of Comparative Examples 1-4; therefore, the different temperature intervals, i.e. both the initial temperature and the terminal temperature are out of the range defined in the present application, have a greater impact on the Ds50, the capacity retention rate of the button cell at 5000 cycles and the battery cycle number trend value, but excluding the simple linear relationship;

[0054] And the uniform gradient heating rate of the temperature curve 445±5℃→50±5h→475±5℃ has no significant effect on the Ds50, the capacity retention rate of the button cell at 5000 cycles and the battery cycle number trend value.

[0055] (4) Comparative Example 3 vs. Comparative Example 7: the difference lies in the different constant gradient heating rates,

[0056] According to Table 4, the Ds50=DH / DQ of Comparative Example 1, Comparative Example 7 and Comparative Example 8 is 80%, 80%, 55%, the capacity retention rate of the button cell at 5000 cycles is 43.8%, 32.8%, 54.8%, and the battery cycle number trend value is 8000+, 6000+ and 10000+.

[0057] It can be seen that under the same temperature interval, i.e. the temperature curve is 445±5℃→475±5℃, it is proved that the different constant gradient heating rates also affect the Ds50, the capacity retention rate of the button cell at 5000 cycles and the battery cycle number trend value;

[0058] (5) Example 1 vs. Comparative Example 7:

[0059] The difference lies in the different Dv50 particle size DH after graphitization, and the Dv50 particle size after graphitization depends on the Dv50 before graphitization DQ under the same delayed coking treatment conditions.

[0060] According to Table 4, Example 1 and Comparative Example 7 have the same delayed coking treatment conditions and the same Ds50, i.e. the Ds50=DH / DQ of Example 1 and Example 7 is 67%, and the capacity retention rate of the button cell at 5000 cycles is 98.6%, 66.7%, and the battery cycle number trend value is 18000+, 12000+.

[0061] This shows that when Ds50=DH / DQ=67±5%, the capacity retention rate of the button cell at 5000 cycles is greater than 87.6%, and the battery cycle number trend value is all above 15000+, and the highest can reach 18000+, provided that the Dv50 particle size DH after graphitization is 10.0±0.5μm, otherwise even if Ds50=DH / DQ=67±5%, the capacity retention rate of the button cell at 5000 cycles cannot be greater than 87.6%, and the battery cycle number trend value cannot be all above 15000+.

[0062] In order to more intuitively show the process advantages of the present application, the equivalent replacement method is used for comparison, and the heating rate of delayed coking treatment is studied for product performance,

[0063] The preparation methods of Comparative Example 1-7, Comparative Example 1-8, Comparative Example 1-9 and Comparative Example 1-10 are the same as those of the embodiment, except that the heating rate of the delayed coking treatment is different in Comparative Example 1-7, Comparative Example 1-8, Comparative Example 1-9 and Comparative Example 1-10; and a parallel control is performed, and details are shown in Table 2:

[0064]

[0065] From the data analysis of Table 2, it can be seen that:

[0066] Comparative Example 1-7, Comparative Example 1-8, Comparative Example 1-9 and Comparative Example 1-10 have different heating rates of the delayed coking treatment; with the increase of the feeding time, the heating rate decreases, and under the premise of the same DQ, the change trend of Ds50 is not linear, but a curve of first increasing and then decreasing, so under the premise of the same DQ, the different heating rates of the delayed coking treatment are not positively correlated with Ds50, and further, are not positively correlated with the capacity retention rate of the button cell at 5000 cycles and the cycle number trend value.

[0067] In summary: the application provides a long-cycle graphite negative electrode material and a preparation method thereof, the long-cycle graphite negative electrode material prepared by the preparation method of the long-cycle graphite negative electrode material within the protection scope of the application can ensure that the capacity retention rate of the button cell at 5000 cycles is greater than 87.6% when Ds50=DH / DQ=67±5% under the premise that the DH of the Dv50 particle size after graphitization is 10.0±0.5 μm,

[0068] The button cell prepared by using the long-cycle graphite negative electrode material has a cycle number of more than 15000 cycles under the condition of 25℃ and a charge-discharge rate of 1C / 1C, and the 80% capacity retention rate is used as the evaluation limit.

Claims

1. A method for preparing a long-cycle graphite negative electrode material, characterized in that: The method uses FCC slurry as raw material, filters, delays coking, crushes and classifies, and graphitizes to obtain artificial graphite negative electrode material, including the following steps: Step 1: Filter the FCC slurry through a filter to remove solid impurities. Step 2: The filtered slurry is subjected to delayed coking treatment, cooled to room temperature and then directly decoked to obtain needle coke. The delayed coking treatment adopts a uniform gradient temperature increase, and the temperature curve is 445±5°C → 50±5h → 475±5°C; Step 3: crushing the needle coke to a particle size of DQ = 15.0 ± 0.5 μm; Step 4: The crushed needle coke is graphitized at a temperature of 2900-3000°C for 48-54 hours to obtain a long-cycle graphite anode material. The particle size shrinkage (Ds50) of the long-cycle graphite anode material is the ratio of the Dv50 after graphitization to the Dv50 before graphitization. Dv50 is the particle size corresponding to 50% of the volume distribution, and Ds50 = DH / DQ = 67 ± 5%.

2. The method for preparing a long-cycle graphite negative electrode material according to claim 1, wherein The FCC slurry oil has an aromatic content of 60±5%, a residual carbon content of 10±2%, and a total content of aromatic hydrocarbons with less than 2 rings and cycloalkanes with less than 2 rings of 25±5%.

3. The method for preparing a long-cycle graphite negative electrode material according to claim 1, wherein The volatile matter of the needle coke after decoking is 10%±3%, and the Hardgrove grindability index is 110±10.

4. A long-cycle graphite negative electrode material characterized by It is prepared by the preparation method of the long-circulation graphite negative electrode material according to any one of claims 1 to 3, and the particle size DH after graphitization is 10.0±0.5μm.

5. Use of long-cycle graphite negative electrode material, characterized in that The long-cycle graphite negative electrode material according to claim 4 is used to prepare button batteries.

6. The use of the long-cycle graphite negative electrode material according to claim 5, characterized in that The capacity retention rate of the button battery at 5000 cycles is greater than 87.6%.

7. The use of the long-cycle graphite negative electrode material according to claim 6, characterized in that The trend value of the button battery cycle number is above 15,000.

8. The use of the long-cycle graphite negative electrode material according to claim 7, characterized in that The trend value of the button battery cycle number is above 18,000.

Images