A fast-charging graphite, a preparation method thereof, a negative electrode sheet and a battery

Abstract

The present invention discloses a fast-charging graphite and its preparation method, negative electrode sheet and battery. The preparation method of the fast-charging graphite comprises: crushing and shaping carbon materials to obtain aggregates, uniformly mixing the aggregates with a carbon-containing binder and a dispersion medium, and sequentially subjecting the aggregates to granulation, graphitization treatment, and spheroidization shaping to obtain graphitized particles; then mixing the graphitized particles with a carbon source, and subjecting the mixture to a heat treatment under an inert atmosphere to carbonize the carbon and coat the graphitized particles to obtain carbon-coated particles; then dispersing the carbon-coated particles in an electrolyte solution, and drying the resulting fast-charging graphite. The fast-charging graphite obtained by the above method has high thermal stability, can improve the safety performance and cycle stability of the battery, and can be applied to the negative electrode active material layer material on the negative electrode sheet of the battery, which can take into account both the room temperature and high temperature performance of the battery.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to fast-charging graphite and a preparation method thereof, a negative electrode sheet and a battery. Background Art

[0002] Lithium-ion batteries, with their long lifespan, high energy density, and superior safety, are increasingly becoming the preferred power source for electronic devices. Today's fast-paced lives are driving increasing demands for higher charge rates in lithium-ion batteries. As a key component of lithium-ion batteries, graphite anodes significantly contribute to these improvements.

[0003] Existing research is exploring ways to improve graphite materials by improving coating and particle size to increase charge rates. Common methods include coating with resins or conductive agents, increasing the coating amount, and reducing aggregate particle size. However, these methods often result in increased specific surface area and side reactions, which in turn degrades high-temperature performance and prevents both room-temperature and high-temperature cycle life from being achieved. Summary of the Invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention provides a fast-charging graphite and a preparation method thereof, a negative electrode sheet, and a battery.

[0005] The first aspect of the present invention provides a method for preparing fast-filling graphite, comprising the following steps:

[0006] S1. Crushing and shaping carbon materials to obtain aggregates;

[0007] S2. uniformly mixing the aggregate with a carbonaceous binder and a dispersion medium, and sequentially subjecting the mixture to granulation, graphitization, and spheroidization to obtain graphitized particles;

[0008] S3, mixing the graphitized particles with a carbon source, and performing a heat treatment under an inert atmosphere to carbonize the carbon source and coat the graphitized particles, thereby obtaining carbon-coated particles;

[0009] S4. Dispersing the carbon-coated particles in an electrolyte solution and drying the solution to obtain fast-filling graphite.

[0010] According to the preparation method of fast-charging graphite of the embodiment of the present invention, there are at least the following beneficial effects: in the preparation method, after the carbon material is crushed and shaped to obtain an aggregate, the aggregate is evenly mixed with a carbon-containing binder and a dispersion medium to form a mixture, and after granulation and graphitization treatment, the mixture is further spheroidized and shaped to obtain graphitized particles. By spheroidizing and shaping after graphitization treatment, the sharp edges of the particles can be removed, making the particles more rounded, the active sites of the tip side reactions can be reduced, and the high-temperature performance can be improved; the graphitized particles are then mixed with a carbon source and heated under an inert atmosphere until the carbon source carbonizes and coats the graphitized particles to modify the surface of the graphitized particles, which can provide more lithium insertion paths and improve the rate performance; the carbon-coated particles are then dispersed in an electrolyte solution, dried, and the electrolyte is further coated on the surface of the carbon-coated particles, which can improve the thermal stability of the material surface and improve the safety and cycle performance of the battery. The obtained fast-charging graphite can be used as the negative active material layer material on the negative electrode sheet of the battery, and can take into account both the room temperature and high temperature performance of the battery.

[0011] In some embodiments of the present invention, in step S1, the carbon material is selected from at least one of needle coke, petroleum coke, pitch coke, and natural graphite.

[0012] In some embodiments of the present invention, in step S1, the aggregate has a particle size Dv50 of (5-7) ± 3 μm. Step S1 may specifically include crushing, fine-grinding, ball-milling, and screening the carbonaceous material to obtain an aggregate of the target particle size. Using a small-sized aggregate for granulation can reduce the OI value (i.e., degree of orientation) and lower room-temperature cyclic expansion, thereby improving battery performance.

[0013] In step S2, the carbon-containing binder can act as a binder, and after subsequent graphitization treatment, a carbon skeleton will be formed between the particles, firmly bonding the particles together. In some embodiments of the present invention, in step S2, the carbon-containing binder is selected from asphalt.

[0014] In some embodiments of the present invention, in step S2, the dispersion medium is selected from at least one of gasoline, kerosene, and benzene. For example, a combination of gasoline, kerosene, and benzene can be used as the dispersion medium, and the mass ratio of aggregate, carbon-containing binder, gasoline, kerosene, and benzene can be controlled to be (100-200):(5-15):(5-10):(1-5):(1-2). Specifically, the aggregate, carbon-containing binder, and dispersion medium can be mixed, and the mixture can be heated to 150-200°C and stirred evenly to obtain a mixture.

[0015] In some embodiments of the present invention, in step S2, the graphitization temperature is 2500-3000° C. The graphitization treatment time can be controlled to be 12-60 hours.

[0016] In some embodiments of the present invention, in step S3, the carbon source is selected from a resin material; preferably, the carbon source is selected from at least one of rosin, α-terpene resin, β-terpene resin, phenolic resin, epoxy resin, and furan resin.

[0017] In some embodiments of the present invention, in step S3, the heating temperature can be controlled at 250-300° C., and the heating time can be controlled at 0.5-5 h.

[0018] In some embodiments of the present invention, in step S4, the components of the electrolyte solution include a polyurethane solution and an electrolyte; preferably, the electrolyte is selected from at least one of a lithium salt and a sodium salt. The electrolyte solution can be prepared by first mixing the polyurethane with a solvent to form a polyurethane solution, and then mixing it with the electrolyte to obtain the electrolyte solution. The mass concentration of the polyurethane solution can be controlled at 10% to 30%, the mass ratio of the polyurethane solution to the electrolyte can be controlled at 1: (0.3 to 1), and the solvent of the polyurethane solution can be N,N-dimethylformamide. After the polyurethane solution and the electrolyte are mixed, they can be fully stirred at 30 to 70°C. The polyurethane has good hardness, tensile properties and heat resistance, and can effectively inhibit the growth of metal salt dendrites, thereby improving the conductivity of the electrolyte membrane and the thermal stability of the fast-charging graphite.

[0019] The second aspect of the present invention provides a fast-filling graphite, which is prepared by any one of the preparation methods of the fast-filling graphite provided in the first aspect of the present invention.

[0020] In a third aspect of the present invention, a negative electrode sheet is provided, comprising a negative electrode current collector and a negative electrode active material layer covering the surface of the negative electrode current collector, wherein the material of the negative electrode active material layer comprises any one of the fast-charging graphites provided in the second aspect of the present invention.

[0021] A fourth aspect of the present invention provides a battery comprising any one of the negative electrode sheets provided in the first aspect of the present invention. DETAILED DESCRIPTION

[0022] The following will clearly and completely describe the concept and technical effects of the present invention in conjunction with the embodiments to fully understand the purpose, features and effects of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0023] Example 1

[0024] This embodiment prepares a fast-filling graphite, and its preparation method includes the following steps:

[0025] S1. The needle coke is coarsely crushed and finely ground, and then ball-milled and shaped using a ball mill, and sieved to obtain aggregate with a Dv50 particle size of 6±3μ;

[0026] S2. Take 100 g of the aggregate obtained in step S1 and add it to an asphalt liquid containing 50 g of asphalt, 100 g of gasoline, 5 g of kerosene, and 2 g of industrial benzene. Then, raise the temperature of the liquid to 150° C. and stir continuously to obtain a mixed liquid.

[0027] S3, transferring the mixed liquid obtained in step S2 into a sprayer, connecting the nozzle of the sprayer to a drying tower, raising the temperature of the drying tower to 200°C, and allowing the liquid sprayed from the sprayer to form powdery small particles in the drying tower. The small particles fall down and are discharged into a mechanical fusion machine to complete granulation and obtain granules;

[0028] S4, placing the particles obtained by granulation in step S3 in a graphitization furnace and graphitizing them at 2500° C. for 60 hours; then transferring them to a ball mill for spheroidization to remove sharp edges and corners of the particles, make the particles round, reduce the number of active sites at the tip, and obtain graphitized particles;

[0029] S5, mixing the graphitized particles obtained in step S4 with phenolic resin, and heating to 250° C. in an inert atmosphere for 5 hours to carbonize the phenolic resin and coat the graphitized particles, thereby obtaining carbon-coated particles;

[0030] S6. Polyurethane and N,N-dimethylformamide are mixed to form a polyurethane solution with a mass concentration of 10%, and then the polyurethane solution is mixed with lithium bis(trifluoromethylsulfonyl)imide in a mass ratio of 1:0.3, and the mixture is thoroughly stirred at 50°C to obtain an electrolyte solution; the carbon-coated particles prepared in step S5 are added to the electrolyte solution, and after being evenly dispersed by magnetic stirring, the mixture is dried and sieved to obtain fast-charging graphite with a particle size Dv50 of 8±3 μm.

[0031] Example 2

[0032] This embodiment prepares a fast-filling graphite. The difference between this embodiment and Example 1 is that petroleum coke is used in step S1 of this embodiment instead of needle coke used in step S1 of Example 1. Other operations are the same as those of Example 1.

[0033] Example 3

[0034] This embodiment prepares a fast-filling graphite. The difference between this embodiment and Example 1 is that pitch coke is used in step S1 of this embodiment instead of needle coke used in step S1 of Example 1. Other operations are the same as those of Example 1.

[0035] Example 4

[0036] This embodiment prepares a fast-charging graphite. The difference between this embodiment and Example 1 is that in the electrolyte solution preparation process in step S6, the mass ratio of the polyurethane solution to lithium bis(trifluoromethylsulfonyl)imide is adjusted from 1:0.3 in Example 1 to 1:0.5. Other operations are the same as in Example 1.

[0037] Example 5

[0038] This embodiment prepares a fast-charging graphite. The difference between this embodiment and Example 1 is that in the electrolyte solution preparation process in step S6, the mass ratio of the polyurethane solution to lithium bis(trifluoromethylsulfonyl)imide is adjusted from 1:0.3 in Example 1 to 1:0.8. Other operations are the same as in Example 1.

[0039] Example 6

[0040] This embodiment prepares a fast-filling graphite. The difference between this embodiment and Example 1 is that the mass concentration of the polyurethane solution prepared in step S6 of this embodiment is adjusted from 10% in Example 1 to 20%, and other operations are the same as Example 1.

[0041] Example 7

[0042] This embodiment prepares a fast-filling graphite. The difference between this embodiment and Example 1 is that the mass concentration of the polyurethane solution prepared in step S6 of this embodiment is adjusted from 10% in Example 1 to 30%, and other operations are the same as Example 1.

[0043] Comparative Example 1

[0044] In this comparative example, a fast-filling graphite was prepared. The difference between this comparative example and Example 1 is that the electrolyte coating operation in step S6 of Example 1 was cancelled in this comparative example. After the carbon-coated particles were obtained according to the operations of steps S1 to S5 in Example 1, they were directly sieved to obtain fast-filling graphite with a particle size Dv50 of 8±3 μm.

[0045] Comparative Example 2

[0046] This comparative example prepares a fast-filling graphite. The difference between this comparative example and Example 1 is that the order of graphitization and hard carbon coating is adjusted in this comparative example. Specifically, the hard carbon coating operation is performed first after granulation is completed, and then the graphitization operation is performed. The preparation method of the fast-filling graphite in this comparative example includes the following steps:

[0047] S1. The needle coke is coarsely crushed and finely ground, and then ball-milled and shaped using a ball mill, and sieved to obtain aggregate with a Dv50 particle size of 6±3μ;

[0048] S2. Take 100 g of the aggregate obtained in step S1 and add it to an asphalt liquid containing 50 g of asphalt, 100 g of gasoline, 5 g of kerosene, and 2 g of industrial benzene. Then, raise the temperature of the liquid to 150° C. and stir continuously to obtain a mixed liquid.

[0049] S3, transferring the mixed liquid obtained in step S2 into a sprayer, connecting the nozzle of the sprayer to a drying tower, raising the temperature of the drying tower to 200°C, and allowing the liquid sprayed from the sprayer to form powdery small particles in the drying tower. The small particles fall down and are discharged into a mechanical fusion machine to complete granulation and obtain granules;

[0050] S4, mixing the granules obtained by granulation in step S3 with phenolic resin, and heating to 250° C. in an inert atmosphere for 5 hours to carbonize the phenolic resin and coat the granules, thereby obtaining carbon-coated granules;

[0051] S5. The carbon-coated particles obtained in step S4 are placed in a graphitization furnace and graphitized at 2500° C. for 60 hours; the particles are then transferred to a ball mill for spheroidization to remove sharp edges and corners of the particles, round the particles, and reduce the number of active sites at the tip, thereby obtaining graphitized particles.

[0052] S6. Polyurethane and N,N-dimethylformamide are mixed to form a polyurethane solution with a mass concentration of 10%, and the polyurethane solution is mixed with lithium bis(trifluoromethylsulfonyl)imide in a mass ratio of 1:0.3, and the mixture is thoroughly stirred at 50° C. to obtain an electrolyte solution; the graphitized particles prepared in step S5 are added to the electrolyte solution, magnetically stirred to disperse the particles, dried, and sieved to obtain fast-charging graphite with a particle size D50 of 8±3 μm.

[0053] Application Examples

[0054] The fast-charging graphite obtained in the above embodiments and comparative examples can be further used to prepare negative electrode sheets, and then assembled into batteries. The preparation of electrode sheets and batteries can be specifically carried out according to the following method: 97wt% fast-charging graphite is mixed with 1.5wt% conductive carbon black and 1.5wt% polyvinylidene fluoride, and an appropriate amount of N-methylpyrrolidone is added to form a negative electrode active material slurry, which is then coated on a copper foil current collector. The coated sample is then placed in an 80°C vacuum oven and dried for 12 hours to form a negative electrode active material layer on the surface of the copper foil current collector to prepare a negative electrode sheet. Then, 1 mol / L LiPF6 is used as the electrode liquid, wherein the solvent is ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) in a volume ratio of 1:1:1; a metal lithium sheet is used as the counter electrode, and a PP / PE composite film is used as a separator to assemble the battery.

[0055] The fast-charging graphites prepared in Examples 1 to 7 and Comparative Examples 1 to 2 were used to prepare negative electrode sheets according to the above method, and then assembled into batteries. The corresponding batteries were recorded as batteries C#1 to C#9. In order to examine the performance of each fast-charging graphite, the performance of each battery was further tested. The specific test method is as follows:

[0056] (1) First discharge capacity and first efficiency: The test conditions for the first discharge capacity are to discharge at 0.05C to 0.005V at room temperature (25°C); the test conditions for the first charge capacity are to discharge at 0.1C to 2V at room temperature (25°C); and the first efficiency is calculated as first efficiency = first discharge capacity / first charge capacity.

[0057] (2) Expansion rate after 500 cycles at room temperature: At room temperature (25°C), the battery was charged to 2 V at a constant current and constant voltage rate of 5 C, with a cut-off current of 0.05 C, and then discharged to 0.005 V at a rate of 0.1 C for 500 cycles; then the expansion rate after 500 cycles at room temperature was calculated as follows: thickness expansion rate after 500 cycles (%) = (thickness after 500 cycles - initial thickness before cycles) / initial thickness before cycles × 100%;

[0058] (3) 5C rate constant current ratio: After the battery is fully discharged, it is charged to 1V at a constant current and constant voltage of 5C at room temperature (25°C). The ratio of the constant current section capacity to the constant current and constant voltage section capacity is calculated.

[0059] (4) Thermal shock resistance: Place a fully charged battery in an incubator and increase the temperature at a rate of 5°C / min to test the temperature at which the battery will catch fire and explode.

[0060] (5) Capacity retention after 500 cycles at 45°C: At 45°C, the battery was charged to 1 V at a constant current and constant voltage rate of 5C, with a cut-off current of 0.05C, and then discharged to 0.005 V at a rate of 0.1C for 500 cycles; then the capacity retention after 500 cycles at 45°C was calculated according to the formula: Capacity retention after 500 cycles (%) = (discharge capacity after 500 cycles / discharge capacity after 1st cycle) × 100%.

[0061] The batteries made with the fast-charging graphite of each embodiment and comparative example were tested according to the above method, and the results are shown in Tables 1 and 2.

[0062] Table 1

[0063] Battery Fast-charging graphite First discharge capacity First efficiency Expansion rate after 500 cycles at room temperature 5C rate charge constant current ratio Battery C#1 Example 1 356 94.5 6.0％ 85.0％ Battery C#2 Example 2 352 93.0 7.3％ 80.3％ Battery C#3 Example 3 349 91.3 8.7％ 78.5％ Battery C#9 Comparative Example 2 356 94.2 7.5％ 83.1％

[0064] Table 2

[0065]

[0066]

[0067] According to Table 1, by comparing batteries C#1 to C#3 prepared using the fast-charging graphite of Examples 1 to 3, it can be seen that compared with using petroleum coke and pitch coke as raw materials, the fast-charging graphene prepared using needle coke as raw material, and the batteries prepared thereby, have higher first discharge capacity and first efficiency, and have better charging capacity. Comparing battery C#1 and battery C#9, battery C#1 uses the fast-charging graphite prepared in Example 1. In the preparation process of the fast-charging graphite in Example 1, the particles are first graphitized and then carbon-coated after granulation. During the graphitization process, the carbon-containing binder between the particles can be converted into a graphite structure with a stable structure and will not disperse during the cycle. Thereafter, carbon coating is performed to modify the surface of the graphitized particles with a carbon coating layer, which can provide more lithium insertion paths, thereby improving the fast-charging rate performance; while battery C#9 uses the fast-charging graphite prepared in Comparative Example 2. In the preparation process of the fast-charging graphite in Comparative Example 2, after granulation, the particles are first carbon-coated and then graphitized. The graphitization process will graphitize the carbon coating layer on the surface of the particles together, turning it into an ordered structure of graphite layers, and then lithium can only be inserted and deintercalated from the end face of the graphite, which greatly reduces the charging capacity.

[0068] According to Table 2, by comparing the batteries C#1, C#4, and C#5 prepared using the fast-charging graphite of Examples 1, 4, and 5, respectively, it can be seen that increasing the proportion of electrolyte in the electrolyte solution used for the electrolyte coating in the fast-charging graphite preparation process can improve the charging capacity of the fast-charging graphite, but it will cause the high-temperature performance to be reduced to a certain extent. On the whole, the battery C4# prepared using the fast-charging graphite of Example 4 has a higher comprehensive high-temperature safety performance and charging capacity. By comparing the batteries C#1, C#6, and C#7 prepared using the fast-charging graphite of Examples 1, 6, and 7, respectively, it can be seen that when the concentration of the polyurethane solution used to prepare the electrolyte solution is increased from 10% to 20%, the high-temperature safety performance of the battery is improved, and the high-temperature cycle performance is also improved, but the constant current ratio is reduced; further comparing the batteries C#6 and C#7, it can be seen that when the concentration of the polyurethane solution is increased from 20% to 30%, the safety performance of the battery is no longer improved, and the high-temperature cycle performance is not significantly improved. Therefore, considering all factors, the mass concentration of the polyurethane solution can be controlled at 10-30%. Comparing battery C#1 and battery C#8, compared with battery C#8 which uses the fast-charging graphite of comparative example 1 (not coated with electrolyte), battery C#1 uses the fast-charging graphite of embodiment 1. The thermal shock resistance and high-temperature cycle performance of the battery are significantly improved. Although the charging capacity is reduced to a certain extent, in actual preparation, the charging capacity of the fast-charging graphite can be compensated by increasing the proportion of electrolyte in the electrolyte solution to further improve the charging rate level.

[0069] The above-described embodiments merely illustrate several implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that variations and improvements are possible without departing from the scope of the present invention, and all such variations and improvements fall within the scope of protection of the present invention.

Claims

1. A method for preparing fast-filling graphite, characterized in that: The following steps are involved: S1. Crushing and shaping carbon materials to obtain aggregates; S2. uniformly mixing the aggregate with a carbonaceous binder and a dispersion medium, and sequentially subjecting the mixture to granulation, graphitization, and spheroidization to obtain graphitized particles; S3, mixing the graphitized particles with a carbon source, and performing a heat treatment under an inert atmosphere to carbonize the carbon source and coat the graphitized particles, thereby obtaining carbon-coated particles; S4. Dispersing the carbon-coated particles in an electrolyte solution and drying to obtain fast-charging graphite; the components of the electrolyte solution include a polyurethane solution and an electrolyte, the mass concentration of the polyurethane solution is controlled at 10% to 30%, and the mass ratio of the polyurethane solution to the electrolyte is controlled at 1: (0.3 to 1).

2. The method for preparing fast-filling graphite according to claim 1, characterized in that: In step S1, the carbon material is selected from at least one of needle coke, petroleum coke, pitch coke, and natural graphite.

3. The method for preparing fast-filling graphite according to claim 1, characterized in that: In step S1, the particle size Dv50 of the aggregate is (5-7)±3 μm.

4. The method for preparing fast-filling graphite according to claim 1, characterized in that: In step S2, the carbon-containing binder is selected from asphalt.

5. The method for preparing fast-filling graphite according to claim 1, characterized in that: In step S2, the dispersion medium is selected from at least one of gasoline, kerosene, and benzene.

6. The method for preparing fast-filling graphite according to claim 1, characterized in that: In step S3, the carbon source is selected from a resin material.

7. The method for preparing fast-filling graphite according to claim 6, characterized in that: The carbon source is selected from at least one of rosin, α-terpene resin, β-terpene resin, phenolic resin, epoxy resin, and furan resin.

8. The method for preparing the fast-filling graphite according to any one of claims 1 to 7, characterized in that: In step S4, the electrolyte is selected from at least one of lithium salt and sodium salt.

9. A fast-filling graphite, characterized in that: The fast-filling graphite is prepared by the preparation method of any one of claims 1 to 8.

10. A negative electrode sheet, characterized in that: It comprises a negative electrode current collector and a negative electrode active material layer covered on the surface of the negative electrode current collector, wherein the material of the negative electrode active material layer comprises the fast-charging graphite according to claim 9.

11. A battery, characterized in that: Including the negative electrode sheet according to claim 10.

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