A modified artificial graphite anode material, its preparation method, and application

Abstract

The present invention discloses a modified artificial graphite anode material, its preparation method and application. It includes the following steps: S1 Heat-treat a mixture of raw material coke, organic resin and pitch; the mass ratio of the three is 60-90:5-20:5-20; S2 Heat-treat a mixed solution containing the material obtained in S1 and pitch; the mass ratio of the material obtained in S1 and pitch is 100:5-15; S3 Heat-treat the material obtained in S2. The present invention utilizes the thermal decomposition of pitch and organic resin to form three-dimensional void channels on the surface of raw material coke. Taking this as the core, after uniform coating with pitch, a dense layer is formed on the surface of the core after graphitization. Due to the relatively large number and size of the void structures in the internal channels, it can be effectively and quickly transmitted to the innermost layer, reducing the formation of lithium deposition interface on the surface and improving the performance of ultra-fast charging. The anode material of the present invention can effectively reduce the side reactions during the first charge and discharge process of the battery and improve the first Coulomb efficiency.

Description

Technical Field

[0001] The present invention relates to a modified artificial graphite anode material, a preparation method thereof, and an application thereof. Background Art

[0002] With the development of lithium-ion battery technology, the requirements for related anode materials are also getting higher and higher. Among them, for artificial graphite, which has the largest usage in the current market, the improvement of its performance is extremely urgent. Among the key characteristic indicators involved, the Coulombic efficiency of the first cycle directly affects the energy density of the battery, and the fast charging ability is one of the most important prerequisite conditions to meet the market project requirements.

[0003] At present, the methods for improving the first efficiency and fast charging ability of artificial graphite anode materials in the market are limited. Generally, isotropic selection of raw material coke, carbonization coating modification with different types of coating agents, and doping modification during the process are carried out. However, because the coating temperature is too low (below 2800 °C), the carbon layer formed on the surface of the anode material does not completely form a layered structure or a stable structure, resulting in too many side reactions in the battery at high temperature / room temperature, leading to the problem of low first efficiency. Although the optimization of raw materials can improve the fast charging ability, the improvement effect on high-rate fast charging is very small. Moreover, from the characteristics of the material itself, when the fast charging ability is relatively good, the kinetics of the material will be weakened, and there is almost no method that can simultaneously improve the first Coulombic efficiency of artificial graphite anode materials and greatly improve the fast charging ability.

[0004] Chinese Patent Document CN109103438A discloses a core-shell structure anode material for lithium-ion batteries and a preparation method thereof, which includes the following steps: mixing silicon powder, titanium dioxide, lithium carbonate, and a dispersant evenly and then grinding them into a composite slurry; placing the composite slurry in a reactor for high-temperature roasting and mechanical shaping to obtain composite particles; placing the composite particles and graphite in a fusion machine to obtain a precursor of the anode material; placing the precursor of the anode material and an organic pyrolytic carbon source in a reactor for high-temperature sintering to obtain a core-shell structure anode material. The finally obtained material has nano-silicon, lithium titanate, and graphite as the core and an organic pyrolytic carbon layer as the shell. The nano-silicon, lithium titanate, and graphite are freely distributed in the organic pyrolytic carbon layer to solve the problems of low theoretical specific capacity and high platform voltage of lithium titanate materials. The core route of this invention is also a traditional surface modification technology, only the core is nano-silicon, lithium titanate, graphite, etc., and it is also impossible to simultaneously improve the first Coulombic efficiency and the fast charging ability.

[0005] Chinese Patent Document CN106558685A discloses a preparation method of a multi-porous core-shell structured anode material: by introducing cobalt compounds and tin compounds on the surfaces of graphite, hard carbon, and soft carbon, separating the solids, and finally obtaining the final material through key processes such as carbonization and sintering. The purpose is to solve the problem of volume expansion of existing tin anode materials, but no improvement is made in the initial Coulomb efficiency, and no improvement in fast charging is mentioned. In addition, from the perspective of structural design, the material structure in this invention has graphite, hard carbon, soft carbon, etc. as the core, and a shell structure formed by doping other carbon-containing substances and metal elements. The core route is the traditional graphite particle surface modification process. By modifying the "shell", the material performance is improved, but the simultaneous improvement of the initial Coulomb efficiency and fast charging ability cannot be achieved.

[0006] Chinese Patent Document CN105280890A discloses a preparation method of a core-shell structured silicon-carbon composite anode material: adding ultrafine silicon powder to the prepared precursor slurry of hard carbon or soft carbon, stirring evenly, removing volatile components at 50 - 200°C, pyrolyzing at 500 - 1000°C, and performing heat treatment in a tube furnace with inert gas and carbon source gas, heat treatment at 500 - 1000°C, sieving, and grading to obtain the product. The core route is the traditional particle surface modification process. By modifying the "shell", the material performance is improved, and similarly, the simultaneous improvement of the initial Coulomb efficiency and fast charging ability cannot be achieved. Summary of the Invention

[0007] The technical problem solved by the present invention is to overcome the defect that the hard carbon anode material in the prior art cannot simultaneously achieve the simultaneous improvement of the initial Coulomb efficiency and fast charging ability, and provides a modified artificial graphite anode material, its preparation method, and application.

[0008] The present invention solves the above technical problems through the following technical solutions.

[0009] The present invention provides a preparation method of a modified artificial graphite anode material, which includes the following steps:

[0010] S1 Perform a first heat treatment on the mixture of raw material coke, organic resin, and pitch; wherein, the mass ratio of the raw material coke, the organic resin, and the pitch is 60 - 90:5 - 20:5 - 20;

[0011] S2 Perform a second heat treatment on the mixed liquid containing the material obtained in S1 and pitch; wherein, the mass ratio of the material obtained in S1 and the pitch is 100:5 - 15;

[0012] S3 Perform a third heat treatment on the material obtained in S2 to prepare a modified artificial graphite anode material.

[0013] In S1, the raw material coke can be needle coke or petroleum coke.

[0014] In S1, the particle size D50 of the raw coke may be 2 - 10 μm, preferably 4 - 6 μm, such as 5 μm or 6 μm.

[0015] In S1, the particle size of the raw coke with a specific particle size is generally obtained through a crushing step. The crushing process may be a conventional process in the art, such as mechanical grinding.

[0016] In S1, the particle size of the raw coke with a specific particle size is generally obtained through a crushing step. The crushing process may be a conventional process in the art, such as mechanical grinding.

[0017] In S1, the organic resin may be a resin that can decompose at a temperature of 100°C - 500°C (the temperature of the first heat treatment) which is conventional in the art, preferably one or more of liquid epoxy resin, phenolic resin, furfural resin, acrylic resin, etc. It is generally commercially available through conventional channels.

[0018] In S1, the pitch may be of the oil-based or coal-based type. Different specifications of pitch are generally obtained through conventional commercial channels. In S1, the softening point of the pitch may be 220 - 280°C, such as 250°C. The coking value of the pitch may be 70 - 80%, such as 75%.

[0019] In S1, the mass ratio of the raw coke, the organic resin, and the pitch may be 60:20:20, 70:15:15, 80:10:10, or 90:5:5, preferably 76 - 86:8 - 12:8 - 12.

[0020] In S1, the temperature of the first heat treatment may be 100°C - 500°C, preferably 150°C - 300°C, such as 180°C, 200°C, or 250°C.

[0021] In S1, the time of the first heat treatment may be 120 min - 360 min, preferably 180 min - 300 min, such as 240 min.

[0022] In S1, the atmosphere of the first heat treatment may be an atmosphere formed by a conventional inert gas in the art or a nitrogen atmosphere. The inert gas may be conventional in the art, such as argon.

[0023] In S1, it is preferably to perform crushing after the first heat treatment. The crushing process may be a conventional process in the art, such as mechanical grinding.

[0024] Among them, the particle size D50 of the crushed material may be 6 - 20 μm, such as 6 μm or 12 μm, preferably 10 - 15 μm.

[0025] In S2, the mass ratio of the material obtained in S1 to the asphalt is preferably 100:6 - 14, more preferably 100:8 - 12, such as 100:10.

[0026] In S2, the asphalt can be oil-based or coal-based. Generally, asphalts of different specifications are obtained through conventional commercial channels. In S2, the softening point of the asphalt can be 220 - 280 °C, such as 250 °C. The coking value of the asphalt can be 70 - 80%, such as 75%.

[0027] In S2, the solvent in the mixed solution can be a solvent that can conventionally dissolve asphalt in the art, such as wash oil.

[0028] In S2, the amount of the solvent in the mixed solution is generally such that the asphalt is dissolved to a saturated state at normal temperature and pressure.

[0029] In S2, the temperature of the second heat treatment can be 400 - 1000 °C, such as 500 °C or 600 °C.

[0030] In S2, the time of the second heat treatment can be 300 min - 720 min, such as 480 min or 600 min.

[0031] In S2, the atmosphere of the second heat treatment can be an atmosphere formed by a conventional inert gas in the art or a nitrogen atmosphere. The inert gas can be conventional in the art, such as argon.

[0032] In S2, the dissolved asphalt can form a uniform coating film on the surface of the material obtained in S1, and after the second heat treatment, it can be cured on its surface to form a prototype of a core-shell structure with a porous core and a dense shell.

[0033] In S3, the temperature of the third heat treatment can be above 2800 °C, preferably 3000 °C - 3400 °C, such as 2800 °C, 3100 °C or 3200 °C.

[0034] In S3, the time of the third heat treatment can be above 24 h, preferably 48 h - 72 h, such as 36 h, 60 h.

[0035] In S3, the process of the third heat treatment is a high-temperature graphitization process, the purposes of which are, firstly, to form a layered structure of the asphalt coated on the surface, and secondly, to solidify and stabilize the core-shell structure.

[0036] The present invention also provides a modified artificial graphite anode material prepared by the above preparation method.

[0037] The present invention also provides a modified artificial graphite anode material, which has a core-shell structure, and the shell coats the outer surface of the core;

[0038] The core includes a solid core and a void layer coated on the surface of the solid core; the solid core is the raw coke after graphitization, and the void layer is obtained by graphitization of a mixture of organic resin and pitch; the shell is the pitch after graphitization.

[0039] The mass ratio of the solid core, the organic resin in the void layer, and the pitch in the void layer is 60-90:5-20:5-20.

[0040] The total mass ratio of the solid core, the organic resin in the void layer, and the pitch in the void layer to the shell is 100:5-15.

[0041] Preferably, the mass ratio of the solid core, the organic resin in the void layer, and the pitch in the void layer can be 60:20:20, 70:15:15, 80:10:10, or 90:5:5, preferably 76-86:8-12:8-12.

[0042] Preferably, the total mass ratio of the solid core, the organic resin in the void layer, and the pitch in the void layer to the shell is preferably 100:6-14, more preferably 100:8-12, such as 100:10.

[0043] Preferably, the voids in the void layer are formed by thermal degradation of the organic resin, and the framework in the void layer is the pitch after graphitization.

[0044] The present invention also provides an application of the modified artificial graphite negative electrode material as described above in a lithium-ion battery.

[0045] On the basis of conforming to the common knowledge in the art, the above preferred conditions can be combined arbitrarily to obtain various preferred examples of the present invention.

[0046] The reagents and raw materials used in the present invention are all commercially available.

[0047] The positive progressive effect of the present invention is as follows:

[0048] In the preparation method of the modified artificial graphite negative electrode material of the present invention, by using the thermal decomposition of pitch and organic resin, a three-dimensional void channel is formed on the surface of the raw coke. Taking this as the core, after uniform coating with pitch and graphitization, a dense layer is formed on the surface of the core. Due to the relatively large number and large size of the void structures in the internal channels, it can be effectively and quickly transmitted to the innermost layer, reducing the formation of a lithium deposition interface on the surface and improving the performance of ultra-fast charging. The modified artificial graphite negative electrode material of the present invention can effectively reduce the side reactions during the first charge and discharge of the battery and improve the first Coulomb efficiency.

[0049] Through the assembly of coin cell tests, the initial Coulomb efficiency of the coin cell prepared with the modified artificial graphite anode material of the present invention can reach more than 96%. During the fast charging capacity test, the charge-discharge capacity retention rate at 10C / 0.1C can reach more than 48%. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 It is a schematic structural diagram of the modified artificial graphite anode material prepared in Example 1. Among them, 1 is the void in the void layer, 2 is the shell, and 3 is the solid core. DETAILED DESCRIPTION OF THE INVENTION

[0051] The present invention will be further described below by way of examples, but the present invention is not limited to the scope of the described examples. For the experimental methods without specific conditions in the following examples, they are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0052] All raw materials in the following examples are conventional commercially available products.

[0053] Example 1

[0054] Figure 1 It is a schematic structural diagram of the modified artificial graphite anode material. Among them, 1 is the void in the void layer, 2 is the shell, and 3 is the solid core.

[0055] The modified artificial graphite anode material of the present invention has a core-shell structure, and the shell is coated on the outer surface of the core;

[0056] The core includes a solid core 3 and a void layer coated on the surface of the solid core 3; the solid core 3 is the raw material coke after graphitization, and the void layer is obtained by graphitizing the mixture of organic resin and pitch; the void 1 in the void layer is formed by the thermal degradation of the organic resin, and the skeleton in the void layer is the pitch after graphitization; the shell is a dense coating layer - the pitch after graphitization.

[0057] The preparation method of the modified artificial graphite anode material includes the following steps:

[0058] (1) Use mechanical grinding to crush the needle coke to a particle size of D50 = 5 μm, and mix and stir evenly according to the weight ratio of graphite: epoxy resin: pitch of 80:10:10 to obtain semi-finished product 1;

[0059] (2) Use a conventional heat treatment device (heating kettle) in the art to heat-treat semi-finished product 1 in a nitrogen atmosphere at 200 °C for 240 minutes, and then use mechanical grinding to crush it to D50 = 12 μm to obtain semi-finished product 2;

[0060] (3) Mix the semi-finished product 2 evenly with the asphalt-containing solution, where the weight ratio of the semi-finished product 2 to the asphalt is 100:10. The solvent in the asphalt-containing solution is wash oil, and the asphalt is dissolved to saturation (at normal temperature and pressure). Then, use a conventional heat treatment equipment (heating kettle) in the art to perform heat treatment at 600 °C for 480 min to obtain the semi-finished product 3;

[0061] (4) Use a conventional graphitization equipment (Acheson furnace) in the art to perform heat treatment on the semi-finished product 3 at 3100 °C for 60 h to obtain the modified artificial graphite anode material.

[0062] Example 2

[0063] Compared with Example 1, Example 2 is the same as Example 1 in other operations and steps except for the following operations and conditions: In step (4), the heat treatment temperature of the semi-finished product 3 is 2800 °C and the time is 36 h.

[0064] Example 3

[0065] Compared with Example 1, Example 3 is the same as Example 1 in other operations and steps except for the following operations and conditions: In step (1), the weight ratio of graphite: epoxy resin: asphalt is 70:15:15.

[0066] Example 4

[0067] Compared with Example 1, Example 4 is the same as Example 1 in other operations and steps except for the following operations and conditions: In step (1), the weight ratio of graphite: epoxy resin: asphalt is 90:5:5.

[0068] Example 5

[0069] Compared with Example 1, Example 5 is the same as Example 1 in other operations and steps except for the following operations and conditions: In step (2), the heat treatment temperature is 150 °C and the time is 180 min, and it is ground to D50 = 20 μm using a mechanical mill.

[0070] Example 6

[0071] Compared with Example 1, Example 6 is the same as Example 1 in other operations and steps except for the following operations and conditions: In step (1), the semi-finished product 1 is obtained by mixing and stirring evenly at a weight ratio of graphite: epoxy resin: asphalt of 60:20:20.

[0072] Example 7

[0073] Compared with Example 1, Example 7 is the same as Example 1 in other operations and steps except for the following operations and conditions: In step (1), the type of resin selected is phenolic resin.

[0074] Example 8

[0075] Example 8 is the same as Example 1 in other operations and steps except for the following operations and conditions: in step (1), the particle size D50 of the raw coke is 6 μm.

[0076] Example 9

[0077] Example 9 is the same as Example 1 in other operations and steps except for the following operations and conditions: in step (2), the particle size D50 after pulverization is 6 μm.

[0078] Example 10

[0079] Example 10 is the same as Example 1 in other operations and steps except for the following operations and conditions: in step (3), the mass ratio of semi-finished product 2 to pitch is 100:14.

[0080] Example 11

[0081] Example 11 is the same as Example 1 in other operations and steps except for the following operations and conditions: in step (2), the temperature of the first treatment is 250 °C.

[0082] Example 12

[0083] Example 12 is the same as Example 1 in other operations and steps except for the following operations and conditions: in step (2), the time of the first treatment is 300 min.

[0084] Example 13

[0085] Example 13 is the same as Example 1 in other operations and steps except for the following operations and conditions: in step (3), the temperature of the second treatment is 500 °C.

[0086] Example 14

[0087] Example 14 is the same as Example 1 in other operations and steps except for the following operations and conditions: in step (3), the time of the second treatment is 600 min.

[0088] Comparative Example 1

[0089] Comparative Example 1 is the same as Example 1 in other operations and steps except for the following operations and conditions: in step (1), the weight ratio of graphite: epoxy resin: pitch is 94:3:3.

[0090] Comparative Example 2

[0091] Comparative Example 2 is the same as Example 1 in other operations and steps except for the following operations and conditions: in step (1), the weight ratio of graphite: epoxy resin: asphalt is 50:25:25.

[0092] Comparative Example 3

[0093] Comparative Example 3 is the same as Example 1 in other operations and steps except for the following operations and conditions: in step (3), the weight ratio of semi-finished product 2 to asphalt is 100:18.

[0094] Comparative Example 4

[0095] Comparative Example 4 is the same as Example 1 in other operations and steps except for the following operations and conditions: adjust the order of step (3) and step (2), perform step (3) first and then step (2).

[0096] Comparative Example 5

[0097] Example 5 is the same as Example 1 in other operations and steps except for the following operations and conditions: in step (2), the mass ratio of the material obtained from S1 to the asphalt is 100:4.

[0098] Effect Example 1

[0099] Preparation method of CR2032 button battery and method for testing the first discharge efficiency: Dissolve polyvinylidene fluoride (PVDF) in N-methylpyrrolidone (NMP) solvent, add conductive agent (SP), stir evenly and then add modified artificial graphite anode material (wherein, modified artificial graphite anode material: PVDF: NMP: SP = 95.5:1.5:1.5:1.5), stir evenly again to complete the slurry mixing, and then through coating (single-sided surface density is 10 g / cm 3 ), preheating and drying, rolling, drying, secondary rolling, die cutting, cutting and assembling to obtain the button battery; the electrolyte used is 1M LiPF6, EC: DEC: DMC = 1:1:1 (volume ratio), the counter electrode is a metal lithium sheet, the charge and discharge potential is 0.005 - 2.000V, and the charge and discharge rate is 0.1C.

[0100] Method for testing the charging rate of button battery: After the battery is prepared as above, test with different charge / discharge rates, namely 0.1C / 0.1C, 0.5C / 0.1C, 1.0C / 0.1C, 3.0C / 0.1C, 5.0C / 0.1C, 10C / 0.1C, 0.5C / 0.1C, a total of 7 cycles of discharge capacity data. Based on the discharge capacity of 0.1C / 0.1C, the higher the capacity retention rate of the subsequent cycles, the better the fast charging ability.

[0101] The products obtained in Examples 1-14 and Comparative Examples 1-5 were prepared into CR2032 button cells conventional in this field according to the same above-mentioned method, and tested according to the same method. The results are shown in Table 1 below.

[0102] Table 1

[0103]

Claims

1. A preparation method of a modified artificial graphite anode material, characterized in that, it comprises the following steps: S1 Perform a first heat treatment on a mixture of raw coke, organic resin, and pitch; wherein, the mass ratio of the raw coke, the organic resin, and the pitch is 60-80:10-20:10-20; the temperature of the first heat treatment is 100°C-500°C; the organic resin is one or more of liquid epoxy resin, furfural resin, and acrylic resin; S2 Perform a second heat treatment on a mixed liquid containing the material obtained in S1 and pitch; wherein, the mass ratio of the material obtained in S1 and the pitch is 100:5-15; S3 Perform a third heat treatment on the material obtained in S2 to obtain the modified artificial graphite anode material.

2. The preparation method of the modified artificial graphite anode material according to claim 1, characterized in that, in S1, the mass ratio of the raw coke, the organic resin, and the pitch is 60:20:20, 70:15:15, or 80:10:10; and / or, in S2, the mass ratio of the material obtained in S1 and the pitch is 100:6-14.

3. The preparation method of the modified artificial graphite anode material according to claim 1, characterized in that, in S1, the mass ratio of the raw coke, the organic resin, and the pitch is 76-80:10-12:10-12; and / or, in S2, the mass ratio of the material obtained in S1 and the pitch is 100:8-12.

4. The preparation method of the modified artificial graphite anode material according to claim 1, characterized in that, in S1, the particle size D50 of the raw coke is 2-10 μm; and / or, in S1, pulverization is performed after the first heat treatment; the particle size D50 of the pulverized material is 6-20 μm.

5. The preparation method of the modified artificial graphite anode material according to claim 4, characterized in that, in S1, the particle size D50 of the raw coke is 4-6 μm; and / or, in S1, the particle size D50 of the pulverized material is 10-15 μm.

6. The preparation method of the modified artificial graphite anode material according to claim 4, characterized in that, in S1, the particle size D50 of the raw coke is 5 μm or 6 μm; and / or, in S1, the particle size D50 of the pulverized material is 6 μm or 12 μm.

7. The preparation method of the modified artificial graphite anode material according to claim 1, characterized in that, in S1, the raw coke is needle coke or petroleum coke.

8. The preparation method of the modified artificial graphite anode material according to claim 1, characterized in that, in S1, the time of the first heat treatment is 120 min-360 min; and / or, in S2, the temperature of the second heat treatment is 400-1000°C; and / or, in S2, the time of the second heat treatment is 300 min-720 min; and / or, in S3, the temperature of the third heat treatment is above 2800°C; and / or, in S3, the time of the third heat treatment is above 24 h.

9. The preparation method of the modified artificial graphite anode material according to claim 1, characterized in that, in S1, the temperature of the first heat treatment is 150°C - 300°C; and / or, in S1, the time of the first heat treatment is 180 min - 300 min; and / or, in S2, the temperature of the second heat treatment is 500°C or 600°C; and / or, in S2, the time of the second heat treatment is 480 min or 600 min; and / or, in S3, the temperature of the third heat treatment is 3000°C - 3400°C; and / or, in S3, the time of the third heat treatment is 48 h - 72 h.

10. The preparation method of the modified artificial graphite anode material according to claim 1, characterized in that, in S1, the temperature of the first heat treatment is 180°C, 200°C or 250°C; and / or, in S1, the time of the first heat treatment is 240 min; and / or, in S3, the temperature of the third heat treatment is 2800°C, 3100°C or 3200°C; and / or, in S3, the time of the third heat treatment is 36 h or 60 h.

11. A modified artificial graphite anode material prepared by the preparation method according to any one of claims 1 - 10.

12. A modified artificial graphite anode material, which has a core - shell structure, and the shell is coated on the outer surface of the core; the core includes a solid core and a void layer coated on the surface of the solid core; the solid core is the raw coke after graphitization, and the void layer is obtained by graphitization of a mixture of organic resin and pitch; the shell is the pitch after graphitization; the mass ratio of the solid core, the organic resin in the void layer and the pitch in the void layer is 60 - 80:10 - 20:10 - 20; the total mass ratio of the solid core, the organic resin in the void layer and the pitch in the void layer to the mass of the shell is 100:5 - 10.

13. The modified artificial graphite anode material according to claim 12, characterized in that, the mass ratio of the solid core, the organic resin in the void layer and the pitch in the void layer is 60:20:20, 70:15:15 or 80:10:10; the total mass ratio of the solid core, the organic resin in the void layer and the pitch in the void layer to the mass of the shell is 100:6 - 10; the voids in the void layer are formed by thermal degradation of the organic resin, and the framework in the void layer is the pitch after graphitization.

14. The modified artificial graphite anode material according to claim 12, characterized in that, the mass ratio of the solid core, the organic resin in the void layer and the pitch in the void layer is 76 - 80:10 - 12:10 - 12; the total mass ratio of the solid core, the organic resin in the void layer and the pitch in the void layer to the mass of the shell is 100:8 - 10.

15. Application of the modified artificial graphite anode material according to any one of claims 11 - 14 in a lithium - ion battery.

Images