Coated graphite negative electrode material and preparation method thereof

Abstract

The invention discloses a preparation method of a coated graphite negative electrode material. The preparation method comprises the steps of mixing, granulating and coating, graphitizing and the like. Pelleting and coating are carried out before the graphitization process, unstable components in asphalt are decomposed and release small molecules in the asphalt in the hot atmosphere of oxygen, oxidative dehydrogenation is carried out at the same time, oxygen molecules in the oxygen and asphalt molecules are crosslinked to form stable macromolecules in a mode of forming C = O bonds and C-O-C bonds, the asphalt molecules are difficult to graphitize, and the graphitization performance of the asphalt is improved. An ordered structure is not easy to form in the graphitization process, the hard carbon characteristic is achieved, a coating layer formed after coating is of a two-layer structure, the coating layer is composed of a hard carbon outer layer and a hard carbon-graphite transition phase, the binding force between a graphite inner core and the hard carbon coating layer can be improved due to the existence of the hard carbon-graphite transition phase, the hard carbon-graphite composite material is more suitable for high-rate charging and discharging, and meanwhile, the hard carbon-graphite composite material has a good application prospect. And coating and carbonization are not needed after graphitization, so that the preparation time is shortened, the preparation efficiency is improved, the preparation energy consumption is greatly reduced, and the preparation cost is effectively reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of anode materials, and in particular to a coated graphite anode material and a preparation method thereof. Background Art

[0002] The market has an extreme fast charging demand for graphite anode materials of lithium-ion batteries. The most common method to improve the fast charging performance of graphite is to coat a layer of amorphous carbon on the surface of graphite. The interlayer spacing of amorphous carbon is larger than that of graphite, the disorder degree between layers is higher, and there are many lithium insertion paths, which can drain the lithium ions on the graphite basal plane to the end face for insertion, improving the fast charging performance of graphite. The preparation steps of traditional amorphous carbon-coated graphite are to first granulate to obtain secondary particles, graphitize the granulated material, and then coat it with asphalt or resin, and obtain the anode material after carbonization.

[0003] Although the existing soft carbon or hard carbon-coated graphite can improve the fast charging performance to a certain extent, however, since it is necessary to coat asphalt or resin on the graphitized graphite embryo and then carbonize, the increase in the process will inevitably lead to an increase in the preparation time, reducing the preparation efficiency of the finished product. Moreover, the energy consumption of the carbonization process is very high, resulting in a substantial increase in the preparation cost of the finished product, which does not meet the market requirements for reducing the cost of producing anode materials and is not conducive to the promotion and application of the finished product. Therefore, it is necessary to propose a new solution to improve the above problems. Summary of the Invention

[0004] In view of this, in view of the deficiencies of the existing technology, the main purpose of the present invention is to provide a coated graphite anode material and a preparation method thereof, which can effectively solve the problems that the existing coated graphite anode material needs to be coated and carbonized after graphitization, resulting in an increase in the preparation time, reducing the preparation efficiency of the finished product, and moreover, the energy consumption of the carbonization process is very high, resulting in a substantial increase in the preparation cost of the finished product, which does not meet the market requirements for reducing the cost of producing anode materials and is not conducive to the promotion and application of the finished product.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions:

[0006] A preparation method of a coated graphite anode material, which includes the following steps:

[0007] (1) Mix coke powder and asphalt powder evenly in a certain proportion. The mass ratio of coke powder to asphalt powder is (10 - 300):(1 - 10) to obtain a mixed raw material;

[0008] (2) Place the mixed raw material obtained in step (1) in a reactor, introduce oxygen into the reactor, so that the mixed raw material is heated and stirred in the oxygen atmosphere in the reactor. The heating temperature is 150 - 400 °C, and the reaction time is 3 - 12 h to obtain a granulated coating precursor;

[0009] (3) Graphitize the granulated and coated precursor obtained in step (2) to obtain a graphitized embryo body;

[0010] (4) Crush the graphitized embryo body obtained in step (3) to obtain a coated graphite anode material.

[0011] As a preferred solution, in step (1), the D50 of the coke powder is 5 - 15 μm, and the D50 of the asphalt powder is 1 - 5 μm.

[0012] As a preferred solution, in step (1), the asphalt powder is at least one of petroleum asphalt and coal asphalt.

[0013] As a preferred solution, in step (2), the reactor is any one of a fluidized bed, a rotary kiln, and a reaction kettle, and its reaction volume is 500 - 3000 L.

[0014] As a preferred solution, in step (2), the oxygen flow rate ≥ 50 L / min.

[0015] As a preferred solution, in step (2), the stirring frequency in the reactor is 5 - 30 Hz.

[0016] As a preferred solution, in step (3), perform gradient temperature - rising graphitization treatment on the granulated and coated precursor obtained in step (2), and the highest graphitization temperature ≥ 2500 °C.

[0017] As a preferred solution, in step (3), raise the temperature to 900 - 1100 °C at a heating rate of 100 °C / h, hold for 10 - 18 h, then raise the temperature to ≥ 2500 °C at a heating rate of 50 °C / h, hold for 20 - 30 h, and the total graphitization time is 70 - 90 h.

[0018] As a preferred solution, in step (4), the D50 of the coated graphite anode material is 10 - 25 μm.

[0019] A coated graphite anode material is prepared by the preparation method of the foregoing coated graphite anode material.

[0020] Compared with the prior art, the present invention has obvious advantages and beneficial effects. Specifically, as can be seen from the above technical solutions:

[0021] By granulating and coating before the graphitization process, and in the thermal atmosphere of oxygen, the unstable components in the pitch are decomposed, releasing small molecules, while oxidative dehydrogenation occurs. The oxygen molecules in the oxygen and the pitch molecules crosslink to form stable macromolecules by forming C=O bonds and C-O-C bonds, making it difficult to graphitize, not easily forming an ordered structure during the graphitization process, and having the characteristics of hard carbon. The coating layer formed after coating is a two-layer structure, and the coating layer is composed of an outer hard carbon layer and a hard carbon-graphite transition phase. The existence of the hard carbon-graphite transition phase can improve the bonding force between the graphite core and the hard carbon coating layer, making it more suitable for high-rate charge and discharge. At the same time, there is no need to perform coating and carbonization after graphitization, shortening the preparation time, improving the preparation efficiency, greatly reducing the preparation energy consumption, effectively reducing the preparation cost, meeting the market requirements for reducing the cost of producing anode materials, and being conducive to popularization and application.

[0022] To more clearly elaborate on the structural features and effects of the present invention, the present invention will be described in detail below in conjunction with the drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a TEM schematic diagram of the preferred Embodiment 2 of the present invention;

[0024] Figure 2 It is a structural schematic diagram of the coated anode material prepared by the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] The present invention discloses a preparation method of a coated graphite anode material, which includes the following steps:

[0026] (1) Mix coke powder and pitch powder evenly in a certain proportion. The mass ratio of coke powder to pitch powder is (10 - 300):(1 - 10) to obtain a mixed raw material; the D50 of the coke powder is 5 - 15 μm, and the D50 of the pitch powder is 1 - 5 μm; the pitch powder is at least one of petroleum pitch and coal pitch.

[0027] (2) Place the mixed raw material obtained in step (1) in a reactor, introduce oxygen into the reactor, heat and stir the mixed raw material in an oxygen atmosphere in the reactor. The heating temperature is 150 - 400 °C, and the reaction time is 3 - 12 h to obtain a granulated and coated precursor; the reactor is any one of a fluidized bed, a rotary kiln, and a reaction kettle, its reaction volume is 500 - 3000 L, the oxygen flow rate ≥ 50 L / min, and the stirring frequency in the reactor is 5 - 30 Hz.

[0028] (3) Gradiently heat the granulated and coated precursor obtained in step (2) for graphitization treatment, raise the temperature to 900 - 1100 °C at a heating rate of 100 °C / h, keep the temperature for 10 - 18 h, then raise the temperature to ≥2500 °C at a heating rate of 50 °C / h, keep the temperature for 20 - 30 h, and the total graphitization time is 70 - 90 h to obtain a graphitized embryo.

[0029] (4) Crush the graphitized embryo obtained in step (3) to obtain a coated graphite anode material, and the D50 of the coated graphite anode material is 10 - 25 μm.

[0030] The following is a detailed description in combination with specific embodiments.

[0031] Example 1

[0032] (1) Mix coke powder and asphalt powder evenly in a certain proportion. The mass ratio of coke powder to asphalt powder is 10:3 to obtain a mixed raw material; the D50 of the coke powder is 5 - 15 μm, and the D50 of the asphalt powder is 1 - 5 μm; the asphalt powder is petroleum asphalt.

[0033] (2) Place the mixed raw material obtained in step (1) in a reactor, introduce oxygen into the reactor, heat and stir the mixed raw material in an oxygen atmosphere. The heating temperature is 150 °C, and the reaction time is 8 h to obtain a granulated and coated precursor; the reactor is a fluidized bed with a reaction volume of 500 L, an oxygen flow rate of 60 L / min, and a stirring frequency of 20 Hz in the reactor.

[0034] (3) Gradiently heat the granulated and coated precursor obtained in step (2) for graphitization treatment, raise the temperature to 1000 °C at a heating rate of 100 °C / h, keep the temperature for 15 h, then raise the temperature to 2600 °C at a heating rate of 50 °C / h, keep the temperature for 20 h to obtain a graphitized embryo.

[0035] (4) Crush the graphitized embryo obtained in step (3) to obtain a coated graphite anode material, and the D50 of the coated graphite anode material is 10 - 25 μm.

[0036] Example 2

[0037] (1) Mix coke powder and asphalt powder evenly in a certain proportion. The mass ratio of coke powder to asphalt powder is 80:7 to obtain a mixed raw material; the D50 of the coke powder is 5 - 15 μm, and the D50 of the asphalt powder is 1 - 5 μm; the asphalt powder is coal tar pitch.

[0038] (2) Place the mixed raw materials obtained in step (1) into a reactor, introduce oxygen into the reactor, and heat and stir the mixed raw materials in an oxygen atmosphere in the reactor. The heating temperature is 400 °C, and the reaction time is 6 h to obtain a granulated coated precursor; the reactor is a rotary kiln with a reaction volume of 3000 L, an oxygen flow rate of 50 L / min, and a stirring frequency in the reactor of 5 Hz.

[0039] (3) Perform graphitization treatment with a gradient temperature increase on the granulated coated precursor obtained in step (2). Raise the temperature to 900 °C at a heating rate of 100 °C / h, hold for 16 h, and then raise the temperature to 2800 °C at a heating rate of 50 °C / h and hold for 28 h to obtain a graphitized embryo.

[0040] (4) Crush the graphitized embryo obtained in step (3) to obtain a coated graphite anode material, and the D50 of the coated graphite anode material is 10 - 25 μm.

[0041] Example 3

[0042] (1) Mix coke powder and pitch powder evenly in a certain proportion. The mass ratio of coke powder to pitch powder is 10:1 to obtain mixed raw materials; the D50 of the coke powder is 5 - 15 μm, and the D50 of the pitch powder is 1 - 5 μm; the pitch powder is a mixture of petroleum pitch and coal pitch.

[0043] (2) Place the mixed raw materials obtained in step (1) into a reactor, introduce oxygen into the reactor, and heat and stir the mixed raw materials in an oxygen atmosphere in the reactor. The heating temperature is 350 °C, and the reaction time is 3 h to obtain a granulated coated precursor; the reactor is a reaction kettle with a reaction volume of 3000 L, an oxygen flow rate of 65 L / min, and a stirring frequency in the reactor of 20 Hz.

[0044] (3) Perform graphitization treatment with a gradient temperature increase on the granulated coated precursor obtained in step (2). Raise the temperature to 1100 °C at a heating rate of 100 °C / h, hold for 10 h, and then raise the temperature to 3200 °C at a heating rate of 50 °C / h and hold for 30 h to obtain a graphitized embryo.

[0045] (4) Crush the graphitized embryo obtained in step (3) to obtain a coated graphite anode material, and the D50 of the coated graphite anode material is 10 - 25 μm.

[0046] Example 4

[0047] (1) Mix coke powder and pitch powder evenly in a certain proportion. The mass ratio of coke powder to pitch powder is 263:10 to obtain mixed raw materials; the D50 of the coke powder is 5 - 15 μm, and the D50 of the pitch powder is 1 - 5 μm; the pitch powder is petroleum pitch.

[0048] (2) Place the mixed raw materials obtained in step (1) in a reactor, introduce oxygen into the reactor, and heat and stir the mixed raw materials in an oxygen atmosphere in the reactor. The heating temperature is 200 °C, and the reaction time is 12 h to obtain a granulated coated precursor; the reactor is a fluidized bed with a reaction volume of 2000 L, an oxygen flow rate of 80 L / min, and a stirring frequency in the reactor of 5 Hz.

[0049] (3) Perform graphitization treatment with gradient temperature increase on the granulated coated precursor obtained in step (2). Raise the temperature to 1100 °C at a heating rate of 100 °C / h, hold for 16 h, and then raise the temperature to 3000 °C at a heating rate of 50 °C / h and hold for 30 h to obtain a graphitized embryo.

[0050] (4) Crush the graphitized embryo obtained in step (3) to obtain a coated graphite anode material, and the D50 of the coated graphite anode material is 10 - 25 μm.

[0051] Example 5

[0052] (1) Mix coke powder and asphalt powder evenly in a certain proportion. The mass ratio of coke powder to asphalt powder is 90:8 to obtain mixed raw materials; the D50 of the coke powder is 5 - 15 μm, and the D50 of the asphalt powder is 1 - 5 μm; the asphalt powder is at least one of petroleum asphalt and coal asphalt.

[0053] (2) Place the mixed raw materials obtained in step (1) in a reactor, introduce oxygen into the reactor, and heat and stir the mixed raw materials in an oxygen atmosphere in the reactor. The heating temperature is 380 °C, and the reaction time is 9 h to obtain a granulated coated precursor; the reactor is a reaction kettle with a reaction volume of 2000 L, an oxygen flow rate of 55 L / min, and a stirring frequency in the reactor of 10 Hz.

[0054] (3) Perform graphitization treatment with gradient temperature increase on the granulated coated precursor obtained in step (2). Raise the temperature to 1000 °C at a heating rate of 100 °C / h, hold for 17 h, and then raise the temperature to 3500 °C at a heating rate of 50 °C / h and hold for 25 h to obtain a graphitized embryo.

[0055] (4) Crush the graphitized embryo obtained in step (3) to obtain a coated graphite anode material, and the D50 of the coated graphite anode material is 10 - 25 μm.

[0056] Example 6

[0057] (1) Mix coke powder and asphalt powder evenly in a certain proportion. The mass ratio of coke powder to asphalt powder is 110:8 to obtain a mixed raw material. The D50 of the coke powder is 5 - 15 μm, and the D50 of the asphalt powder is 1 - 5 μm. The asphalt powder is a mixture of petroleum asphalt and coal tar pitch.

[0058] (2) Place the mixed raw material obtained in step (1) into a reactor, introduce oxygen into the reactor, and heat and stir the mixed raw material in an oxygen atmosphere in the reactor. The heating temperature is 260 °C, and the reaction time is 7 h to obtain a granulated coating precursor. The reactor is a fluidized bed with a reaction volume of 2500 L, an oxygen flow rate of 50 L / min, and a stirring frequency in the reactor of 20 Hz.

[0059] (3) Perform graphitization treatment with a gradient temperature rise on the granulated coating precursor obtained in step (2). Raise the temperature to 1000 °C at a heating rate of 100 °C / h, hold for 15 h, then raise the temperature to 3000 °C at a heating rate of 50 °C / h, and hold for 28 h to obtain a graphitized embryo.

[0060] (4) Crush the graphitized embryo obtained in step (3) to obtain a coated graphite anode material. The D50 of the coated graphite anode material is 10 - 25 μm.

[0061] Comparative Example 1

[0062] (1) Mix coke powder and asphalt powder evenly in a certain proportion. The mass ratio of coke powder to asphalt powder is 10:3 to obtain a mixed raw material. The D50 of the coke powder is 5 - 15 μm, and the D50 of the asphalt powder is 1 - 5 μm. The asphalt powder is petroleum asphalt.

[0063] (2) Place the mixed raw material obtained in step (1) into a reactor, add a binder and stir to perform binder granulation. The stirring time is 8 h to obtain a granulation precursor. The reactor is a fluidized bed with a reaction volume of 500 L, and the stirring frequency in the reactor is 20 Hz.

[0064] (3) Perform graphitization treatment with a gradient temperature rise on the granulation coating precursor obtained in step (2). Raise the temperature to 1000 °C at a heating rate of 100 °C / h, hold for 15 h, then raise the temperature to 2600 °C at a heating rate of 50 °C / h, and hold for 20 h to obtain a graphitized embryo.

[0065] (4) Crush the graphitized embryo obtained in step (3), add asphalt to coat the crushed graphitized embryo. The mass ratio of the crushed graphitized embryo to asphalt is 100:6, and then carbonize. The carbonization temperature is 1000 °C, and the carbonization time is 14 h to obtain a graphite anode material.

[0066] Comparative Example 2

[0067] (1) Mix coke powder and asphalt powder evenly in a certain proportion. The mass ratio of coke powder to asphalt powder is 10:3 to obtain a mixed raw material. The D50 of the coke powder is 5 - 15 μm, and the D50 of the asphalt powder is 1 - 5 μm. The asphalt powder is petroleum asphalt.

[0068] (2) Place the mixed raw material obtained in step (1) into a reactor, add a binder and stir to carry out binder granulation. The stirring time is 8 h to obtain a granulation precursor. The reactor is a fluidized bed with a reaction volume of 500 L, and the stirring frequency in the reactor is 20 Hz.

[0069] (3) Perform graphitization treatment with gradient heating on the granulation-coated precursor obtained in step (2). Heat it to 1000 °C at a heating rate of 100 °C / h, hold for 15 h, then heat it to 2600 °C at a heating rate of 50 °C / h and hold for 20 h to obtain a graphitized embryo.

[0070] (4) Crush the graphitized embryo obtained in step (3), add phenolic resin to coat the crushed graphitized embryo. The mass ratio of the crushed graphitized embryo to phenolic resin is 100:6, and then carbonize it. The carbonization temperature is 1000 °C and the carbonization time is 14 h to obtain a graphite negative electrode material.

[0071] Comparative Example 3

[0072] (1) Mix coke powder and asphalt powder evenly in a certain proportion. The mass ratio of coke powder to asphalt powder is 10:3 to obtain a mixed raw material. The D50 of the coke powder is 5 - 15 μm, and the D50 of the asphalt powder is 1 - 5 μm. The asphalt powder is petroleum asphalt.

[0073] (2) Place the mixed raw material obtained in step (1) into a reactor, add a binder and stir to carry out binder granulation. The stirring time is 8 h to obtain a granulation precursor. The reactor is a fluidized bed with a reaction volume of 500 L, the oxygen flow rate is 60 L / min, and the stirring frequency in the reactor is 20 Hz.

[0074] (3) Perform graphitization treatment with gradient heating on the granulation-coated precursor obtained in step (2). Heat it to 1000 °C at a heating rate of 100 °C / h, hold for 15 h, then heat it to 2600 °C at a heating rate of 50 °C / h and hold for 20 h to obtain a graphitized embryo.

[0075] (4) Crush the graphitized embryo obtained in step (3) to obtain a graphite negative electrode material.

[0076] Perform performance tests on the above-mentioned multiple examples and comparative examples. The test results are shown in Table 1.

[0077]

[0078] Table 1

[0079] It can be clearly seen from the above data that the anode materials prepared by the preparation method of the present invention do not have obvious advantages over the graphite anode materials of Comparative Examples 1-3 in terms of the first reversible capacity and the first Coulombic efficiency. However, after 300 weeks of cycling, the retention rates of Examples 1-6 can reach 93.0%. Moreover, after graphitization of Examples 1-6, there is no need for coating and carbonization, which greatly improves the preparation efficiency and reduces the production cost of the anode material. In addition, the retention rates of Comparative Examples 1-3 are only 90.3%, 89.6%, and 83.7% respectively. Compared with Comparative Examples 1 and 2, the cycling retention rate of Comparative Example 3 is much lower than that of Comparative Examples 1-2. The reason is that no coating is carried out in Comparative Example 3, and the graphite core + coating layer structure cannot be formed. Therefore, the 3C lithium deposition SOC and the cycling retention rate are much lower than those of Comparative Examples 1-2.

[0080] As described above, it is only a preferred embodiment of the present invention, and it does not impose any limitation on the technical scope of the present invention. Therefore, any minor modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A preparation method of a coated graphite anode material, characterized in that: It includes the following steps: (1) Mix coke powder and asphalt powder evenly in a certain proportion. The mass ratio of coke powder to asphalt powder is (10 - 300):(1 - 10) to obtain a mixed raw material; (2) Place the mixed raw material obtained in step (1) in a reactor, introduce oxygen into the reactor, heat and stir the mixed raw material in an oxygen atmosphere in the reactor. The heating temperature is 150 - 400 °C, and the reaction time is 3 - 12 h to obtain a granulated coating precursor; (3) Graphitize the granulated coating precursor obtained in step (2) to obtain a graphitized embryo; (4) Crush the graphitized embryo obtained in step (3) to obtain a coated graphite anode material.

2. The preparation method of the coated graphite anode material according to claim 1, characterized in that: In step (1), the D50 of the coke powder is 5 - 15 μm, and the D50 of the asphalt powder is 1 - 5 μm.

3. The preparation method of the coated graphite anode material according to claim 1, wherein: In step (1), the asphalt powder is at least one of petroleum asphalt and coal tar pitch.

4. The preparation method of the coated graphite anode material according to claim 1, characterized in that: In step (2), the reactor is any one of a fluidized bed, a rotary kiln, and a reaction kettle, and its reaction volume is 500 - 3000 L.

5. The preparation method of the coated graphite anode material according to claim 1, wherein: In step (2), the oxygen flow rate ≥ 50 L / min.

6. The preparation method of the coated graphite anode material according to claim 1, characterized in that: In step (2), the stirring frequency in the reactor is 5 - 30 Hz.

7. The preparation method of the coated graphite anode material according to claim 1, characterized in that: In step (3), the granulated coating precursor obtained in step (2) is subjected to graphitization treatment with a gradient temperature rise, and the highest graphitization temperature ≥ 2500 °C.

8. The preparation method of the coated graphite anode material according to claim 7, characterized in that: In step (3), it is heated to 900 - 1100 °C at a heating rate of 100 °C / h, held for 10 - 18 h, then heated to ≥ 2500 °C at a heating rate of 50 °C / h, and held for 20 - 30 h. The total graphitization time is 70 - 90 h.

9. The preparation method of the coated graphite anode material according to claim 1, wherein: In step (4), the D50 of the coated graphite anode material is 10 - 25 μm.

10. A coated graphite anode material, characterized in that: Prepared by the method for preparing a coated graphite anode material according to any one of claims 1 - 9.

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