A high-capacity coated composite graphite material for lithium-ion batteries and its preparation method

Abstract

The present invention discloses a high-capacity coated composite graphite material for lithium-ion batteries and a preparation method thereof. High-quality anthracite is selected and pulverized to obtain fine anthracite powder as coating material A; natural graphite is selected as matrix material B; asphalt, resin, and tar are used as coating agent C. First, A and C are mixed and heated to fuse until uniformly dispersed; then B is added in batches while controlling the fusion temperature curve and dispersion frequency to obtain a composite graphite precursor. After shaping, pre-carbonization, graphitization, sieving, and demagnetization of the composite graphite precursor, the coated composite graphite material is obtained. The present invention selects high-quality fine anthracite powder, with low material cost. Combining the material characteristics of artificial graphite and natural graphite, it effectively controls the construction of a composite graphite coating structure with natural graphite as the matrix and anthracite particles and a carbon coating layer covering the surface, effectively improving the lithium storage capacity of the material and the compatibility between the material and the electrolyte, and developing a high-capacity and cycle-stable coated composite graphite material.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion anode materials, and particularly to a high-capacity coated composite graphite material for lithium-ion batteries and a preparation method thereof. Background Art

[0002] As one of the important energy storage devices, lithium-ion batteries have many advantages such as high energy density, long cycle life, environmental friendliness, and high safety. They can provide energy for portable electronic devices and new energy vehicles, etc., and have achieved great success in the field of energy applications. With the continuous improvement of people's requirements for the performance of lithium-ion battery products, the performance requirements for anode materials have become increasingly stringent, constantly promoting the innovation and breakthrough of material research and development.

[0003] Graphite materials are the most widely used anode materials for lithium-ion batteries at present due to their low cost advantage, rich raw material sources, and layered structure suitable for lithium-ion deintercalation / insertion. Graphite materials are mainly divided into artificial graphite and natural graphite. Artificial graphite has a stable structure, excellent rate performance, and good electrolyte compatibility, but its specific capacity is relatively low and it is difficult to meet the increasingly high energy density requirements nowadays; while natural graphite has a large lamellar structure, a high specific capacity, and good processing performance, but due to its many structural defects, its cycle performance is poor, and single use cannot meet the current required long cycle life. Therefore, more design and development schemes still need to be tried for high-capacity and cycle-stable graphite anode materials. Summary of the Invention

[0004] To solve the problems that the existing artificial graphite has a relatively low specific capacity and the natural graphite has many structural defects, resulting in poor cycle performance, the present invention provides a high-capacity coated composite graphite material for lithium-ion batteries and a preparation method thereof. Combining the material characteristics of artificial graphite and natural graphite, using amorphous carbon and anthracite, and combining a stepwise feeding and fusion process, effectively control the construction of a composite graphite coating structure with natural graphite as the matrix, covered with anthracite particles and a carbon coating layer on the surface, effectively improving the lithium storage capacity of the material and improving the compatibility between the material and the electrolyte, and developing a high-capacity and cycle-stable coated composite graphite material.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A preparation method of a high-capacity coated composite graphite material for lithium-ion batteries, characterized by comprising the following steps:

[0007] S1. Select high-quality anthracite, and obtain fine anthracite powder after pulverization as coating material A; select natural graphite as matrix material B; select one or a combination of several of asphalt, resin, and tar as coating agent C; mix A, B, and C in a mass ratio of (20-40):(40-80):(8-30).

[0008] S2. First, fully mix coating material A and coating agent C evenly, and then heat to 50-500°C to fuse into a liquid phase and disperse evenly.

[0009] S3. Add matrix material B to the liquid-phase dispersion material in step S2 in batches, control the fusion temperature curve and dispersion frequency to obtain a composite graphite precursor with a surface coating layer.

[0010] S4. Perform shaping, pre-carbonization, graphitization, sieving, and demagnetization processes on the composite graphite precursor obtained in step S3 to obtain a coated-layer composite graphite material.

[0011] Preferably, the asphalt includes any one or at least two combinations of natural asphalt, petroleum asphalt, shale asphalt, and carbon fiber asphalt;

[0012] The resin includes any one or at least two combinations of phenolic resin, epoxy resin, furan resin, furfuryl alcohol resin, and furfural resin;

[0013] The tar includes any one or at least two combinations of coal tar, ethylene tar, bio-oil, and pyrolysis tar of grease.

[0014] Preferably, in step S1, the D50 particle size of the fine anthracite powder is 1-4 μm; the D50 particle size of the matrix material B is 10-16 μm; the D50 particle size of the coating agent C is 1-8 μm.

[0015] Preferably, in step S1, the coking value of the coating agent C is 10-80%.

[0016] Preferably, in step S3, the batch addition ratio of the matrix material B is set to 5-30%.

[0017] Preferably, in step S3, the fusion temperature is controlled at 50-500°C, the holding time is 0.5-4 h, and the dispersion frequency is controlled at 1-50 Hz.

[0018] Preferably, in step S4, the pre-carbonization treatment temperature is 500°C - 1300°C, the heating rate is 5-10°C / min; the carbonization treatment time is 2-4 h.

[0019] Preferably, in step S4, the graphitization temperature is set at 2800-3200°C.

[0020] Preferably, in the step S4, the particle size D50 of the coated composite graphite material is 10-20 μm.

[0021] The present invention also provides a high-capacity coated composite graphite material for a lithium-ion battery, characterized in that: the high-capacity coated composite graphite material is obtained by the above preparation method.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention uses high-quality anthracite fine powder as the coating material, effectively reducing the material cost. Combining the material characteristics of artificial graphite and natural graphite, using amorphous carbon and anthracite, and combining the step-by-step feeding and fusion process, effectively controls the construction of a composite graphite coating structure with natural graphite as the matrix material and anthracite particles and a carbon coating layer covering the surface, effectively improving the lithium storage capacity of the material. The reaction interface between the anthracite particle-coated material and the electrolyte is completely superior to the reaction interface between the matrix material and the electrolyte, improving the compatibility between the material and the electrolyte, and solving the problems of low specific capacity of artificial graphite and poor cycle stability of natural graphite, thereby developing a high-capacity and cycle-stable coated composite graphite material. Description of the Drawings

[0023] Figure 1 : SEM diagram of the coated composite graphite material in Example 2 of the present invention;

[0024] Figure 2 : SEM diagram of the coated composite graphite material in Example 3 of the present invention. Detailed Embodiments

[0025] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention. Embodiment

[0026] S1. Weigh 25 kg of high-quality anthracite, and after pulverization treatment, obtain anthracite fine powder with D50 of 2 μm as coating material A; weigh 50 kg of natural graphite with D50 of 11 μm as matrix material B; weigh 15 kg of natural asphalt with D50 of 2 μm and a coking value of 50% as coating agent C;

[0027] S2. First, put all the coating material A and the coating agent C into the reaction kettle and mix them evenly, and then heat and stir to 300 °C until they are fused into a liquid phase and dispersed evenly;

[0028] S3. Add the matrix material B to the liquid-phase dispersion material in step S2 in batches, 10% each time, and control the fusion temperature curve and dispersion frequency to obtain a composite graphite precursor with a surface coating layer;

[0029] Preferably, in step S3, the fusion temperature is 300 °C, the heat preservation time is 2 h, and the dispersion frequency is controlled at 30 Hz.

[0030] S4. Shape the composite graphite precursor obtained in step S3, then put it into a carbonization furnace for pre-carbonization treatment, and the pre-carbonization treatment temperature is 800 °C; the carbonization treatment time is 3 h, then put it into a graphitization furnace and conduct graphitization treatment at 3000 °C. Screen and demagnetize the material after graphitization treatment to obtain a coated composite graphite material with a D50 of 14.72 μm. Example

[0031] S1. Weigh 35 kg of high-quality anthracite, and after pulverization, obtain anthracite fine powder with a D50 of 2.5 μm as the coating material A; weigh 70 kg of natural graphite with a D50 of 12.3 μm as the matrix material B; weigh 20 kg of epoxy resin with a D50 of 5 μm and a coking value of 30% as the coating agent C;

[0032] S2. First, put all the coating material A and the coating agent C into the reaction kettle and mix them evenly, then heat and stir while heating to 150 °C until they are fused into a uniformly dispersed liquid phase;

[0033] S3. Add the matrix material B to the liquid-phase dispersion material in step S2 in batches, 20% each time, and control the fusion temperature curve and dispersion frequency to obtain a composite graphite precursor with a surface coating layer;

[0034] Preferably, in step S3, the fusion temperature is controlled at 150 °C, the heat preservation time is 1.5 h, and the dispersion frequency is controlled at 40 Hz.

[0035] S4. Shape the composite graphite precursor obtained in step S3, then put it into a carbonization furnace for pre-carbonization treatment, and the pre-carbonization treatment temperature is 1000 °C; the carbonization treatment time is 2.5 h, then put it into a graphitization furnace and conduct graphitization treatment at 2900 °C. Screen and demagnetize the material after graphitization treatment to obtain a coated composite graphite material with a D50 of 15.26 μm.

[0036] As Figure 1 shown is the SEM image of the coated composite graphite material in Example 2. Example

[0037] S1. Weigh 35 kg of high-quality anthracite. After crushing, anthracite fine powder with a D50 of 3.5 μm is obtained as coating material A; weigh 80 kg of natural graphite with a D50 of 15 μm as matrix material B; weigh 25 kg of a composition of carbon fiber pitch and coal tar with a D50 of 8 μm and a coking value of 40% as coating agent C.

[0038] S2. First, put all of coating material A and coating agent C into a reaction kettle and mix them evenly. Then, while heating and stirring, heat to 250 °C until it fuses into a liquid phase and is evenly dispersed.

[0039] S3. Add matrix material B to the liquid-phase dispersion material in step S2 in batches, 30% each time. Control the fusion temperature curve and dispersion frequency to obtain a composite graphite precursor with a surface coating layer.

[0040] Preferably, in step S3, control the fusion temperature to 240 °C, the heat preservation time to 2 h, and the dispersion frequency to 40 Hz.

[0041] S4. Shape the composite graphite precursor obtained in step S3, and then put it into a carbonization furnace for pre-carbonization treatment. The pre-carbonization treatment temperature is 1250 °C; the carbonization treatment time is 4 h. Then put it into a graphitization furnace and conduct graphitization treatment at 2800 °C. Screen and demagnetize the material after graphitization treatment to obtain a coated composite graphite material with a D50 of 15.05 μm.

[0042] As Figure 2 shown is the SEM image of the coated composite graphite material in Example 3.

[0043] Comparative Example 1:

[0044] Using high-quality anthracite as raw material, through processes such as crushing, shaping, pre-carbonization, graphitization, screening, and demagnetization, an artificial graphite material with a D50 of 14.51 μm is obtained.

[0045] Comparative Example 2:

[0046] Using natural graphite as raw material, through processes such as crushing, impurity removal, purification, spheroidization, purification, screening, and demagnetization, a natural spherical graphite material with a D50 of 14.66 μm is obtained.

[0047] Performance testing:

[0048] 1. Make button cells with the anode materials prepared in Examples 1 - 3 and Comparative Examples 1 and 2 for performance testing:

[0049] At room temperature, the obtained anode material, dispersant CMC, conductive agent SP, and binder SBR were mixed uniformly in pure water at a mass percentage of 96:1.5:1:1.5 to prepare a slurry; the slurry was evenly coated on a copper foil, and the coating areal density was about 5 mg / cm 2 , and then the copper foil was placed in a vacuum drying oven and dried at 80 °C for 12 h. The dried copper foil was cut into circular pieces with an area of 2 cm 2 to make a working electrode; then it was assembled into a button cell with a lithium metal sheet as the counter electrode, 1 mol / L LiPF6 / EC+DEC (volume ratio 1:1) electrolyte, and a PE separator in a vacuum glove box. After the assembled button cell was left standing at room temperature for 24 h, electrochemical tests were started, and the test results are shown in Table 1.

[0050] 2. Perform performance tests on the anode materials prepared in Examples 1 to 3 and Comparative Examples 1 and 2 as lithium-ion full cells:

[0051] The obtained anode material, conductive agent SP, dispersant CMC, and binder SBR were dissolved in a solvent and mixed and formulated into an anode slurry at a mass percentage of 94.5:1.5:2:2, controlling the solid content at 40%, coated on a copper foil current collector, vacuum dried, and an anode plate was obtained. The compaction density of the anode plate was 1.50 g / cm 3 , and the single-sided density was 10 mg / cm 2 ; then it was assembled with a ternary cathode plate prepared by a traditional mature process, 1 mol / L LiPF6 / EC+DMC+EMC (volume ratio 1:1:1) electrolyte, separator, and shell using a conventional production process to assemble a 18650 cylindrical single cell. The assembled 18650 cylindrical single cell was tested for the capacity retention rate at 25 °C with 1C charge / 1C discharge for 100 cycles, and the test results are shown in Table 1

[0052] Table 1

[0053]

[0054] As can be seen from Table 1, the first discharge capacity of the high-capacity coated composite graphite material prepared in Examples 1 to 3 of the present invention can reach 363-366 mAh / g, the first charge-discharge efficiency ≥ 95.21%, and the capacity retention rate at 25 °C with 1C charge / 1C discharge for 100 cycles ≥ 96.72%, all higher than those of Comparative Examples 1 and 2.

[0055] The above is only the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and substitutions can be made, and these improvements and substitutions should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a high-capacity coating composite graphite material for a lithium-ion battery, characterized in that: The following steps are involved: S1. Select high-quality anthracite and grind it to obtain anthracite fine powder as coating material A; select natural graphite as base material B; use one or a combination of asphalt, resin, tar as coating agent C; mix A, B, C in a mass ratio of (20-40): (40-80): (8-30); S2, firstly mix the coating material A and the coating agent C thoroughly, and then heat to 50-500°C to fuse until the liquid phase is evenly dispersed; S3, adding the matrix material B to the liquid phase dispersion in step S2 in batches, controlling the fusion temperature curve and the dispersion frequency, and obtaining a composite graphite precursor with a surface coating layer; S4, subjecting the composite graphite precursor obtained in step S3 to shaping, pre-carbonization, graphitization, screening and demagnetization processes to obtain a coating layer composite graphite material; The particle size D50 of the anthracite fine powder in step S1 is 1-4 μm; the particle size D50 of the matrix material B is 10-16 μm; the particle size D50 of the coating agent C is 1-8 μm; In the step S3, the proportion of matrix material B added in batches is set to 5-30%.

2. The method for preparing a high-capacity coating layer composite graphite material for a lithium-ion battery according to claim 1, characterized in that: The asphalt includes any one or a combination of at least two of natural asphalt, petroleum asphalt, shale asphalt and carbon fiber asphalt; The resins include any one or a combination of at least two of phenolic resin, epoxy resin, furan resin, furfuryl alcohol resin and furfural resin; The tars include any one of coal tar, ethylene tar, bio-oil and grease pyrolysis tar, or a combination of at least two of them.

3. The method for preparing a high-capacity coating layer composite graphite material for a lithium-ion battery according to claim 1, characterized in that: The coking value of the coating agent C in step S1 is 10-80%.

4. The method for preparing a high-capacity coating layer composite graphite material for a lithium-ion battery according to claim 1, characterized in that: In step S3, the fusion temperature is controlled to be 50-500° C., the insulation time is 0.5-4 hours, and the dispersion frequency is controlled to be 1-50 Hz.

5. The method for preparing a high-capacity coating layer composite graphite material for a lithium-ion battery according to claim 1, characterized in that: The pre-carbonization treatment temperature is 500°C to 1300°C, the heating rate is 5 to 10°C / min, and the carbonization treatment time is 2 to 4h.

6. The method for preparing a high-capacity coating layer composite graphite material for a lithium-ion battery according to claim 1, characterized in that: In the step S4, the graphitization temperature is set to 2800-3200°C.

7. The method for preparing a high-capacity coating layer composite graphite material for a lithium-ion battery according to claim 1, characterized in that: In the step S4, the particle size D50 of the composite graphite material of the coating layer is 10-20 μm.

8. A high-capacity coating composite graphite material for lithium-ion batteries, characterized in that: The high-capacity coating layer composite graphite material for lithium-ion batteries is prepared by the preparation method according to any one of claims 1 to 7.

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