Hard carbon composite material and preparation method thereof

Abstract

The invention provides a hard carbon composite material, a preparation method thereof, a negative electrode containing the hard carbon composite material, and a lithium ion battery containing the negative electrode. The preparation method comprises the following steps: 1) crushing an asphalt material to obtain a crushed material; 2) in a dry environment, the crushed material obtained in the step 1) and mesoporous silica are ground to obtain a composite material precursor, and the use amount of the mesoporous silica is 1-8 wt% relative to the total weight of the asphalt material; and 3) calcining the composite material precursor at the temperature of 900-1100 DEG C in an inert atmosphere, and then cooling along with a furnace. When the hard carbon composite material is used as a negative electrode of a secondary battery, the ion transmission rate can be increased, and the charging and discharging speed can be increased.

Description

Technical Field

[0001] The present invention belongs to the field of secondary batteries, and more specifically, relates to a hard carbon composite material with high ion transport efficiency and a preparation method thereof. Background Art

[0002] Lithium-ion batteries are widely used in power batteries, energy storage batteries, 3C consumer batteries, drones and other fields due to their high energy density, no memory effect, large specific capacity and long cycle life. With the increasing market requirements for the fast charging performance and power density of lithium-ion batteries, the anode materials of lithium-ion batteries are required to have high specific capacity and energy power density. Currently, graphite, as a commercial anode material for lithium-ion batteries, has poor rate performance and is difficult to meet the higher power density and fast charging requirements of lithium-ion batteries. Therefore, it is urgent to find a suitable carbon-based material to replace graphite and improve the electrochemical performance of the battery. Among them, hard carbon anode materials have attracted much attention due to their excellent rate performance and the ability to provide more lithium storage sites for lithium ions.

[0003] In order to improve the ion transport efficiency of hard carbon anodes, element doping is often used to improve the ion transport rate of pitch-based hard carbon anode materials, such as elements like phosphorus and tin. However, the doping process is usually complex, the material preparation cycle is long, the controllability of the doping amount is poor, and the raw material cost is high, which is not conducive to commercial application.

[0004] Currently, common hard carbon materials are mainly prepared using pitch materials as the carbon source. This preparation process is simple and low-cost, and can reduce environmental pollution. However, due to the structural complexity, difficult pore size control, surface defects and functional groups of pitch-based anode materials, lithium ions face various obstacles during internal transport, thereby reducing the migration rate of lithium ions, making it difficult for the material to meet the requirements of long life, high-power discharge and fast charging. Therefore, there is an urgent need for a hard carbon composite material and a manufacturing method that can improve ion transport efficiency and thus have high-power discharge and fast charging performance. Summary of the Invention

[0005] Technical Problem In summary, it is particularly necessary to study a composite material with high thermal conductivity, high strength, low thermal expansion and easy processing. Aiming at the technical problems existing in the prior art, the present invention aims to provide a hard carbon composite material with high ion transport efficiency and a preparation method thereof. When the hard carbon composite material is used as the anode of a secondary battery, it can improve the ion transport rate and the charging and discharging speed.

[0006] Technical Solution The object of the present invention is to provide a simple method for preparing a hard carbon negative electrode material with high ion transport efficiency. To achieve the above object of the invention, the present invention provides a mesoporous silica composite hard carbon material, and the mesoporous silica is a high ion transport material; by compounding and sintering the mesoporous silica with an asphalt material, the mesoporous silica is combined with the hard carbon on the surface of the hard carbon, and by utilizing the mesoporous characteristics of the mesoporous silica, uniform and multi-channel lithium ion transport channels are formed inside the material, a three-dimensional high ion transport efficiency network is formed, the lithium ion transport resistance is reduced, the efficient transport of lithium ions is realized, and thus the fast charging performance requirements of lithium ion batteries are met.

[0007] According to a first aspect of the present invention, there is provided a method for preparing a hard carbon composite material, which comprises the following steps: 1) Crushing the asphalt material to obtain a crushed product, 2) Under a dry environment, grinding the crushed product obtained in step 1) with mesoporous silica to obtain a composite material precursor, wherein, based on the total weight of the asphalt material, the amount of mesoporous silica used is 1 wt% to 8 wt%; 3) Under an inert atmosphere, calcining the composite material precursor at a temperature of 900 to 1100 °C, and then cooling it with the furnace.

[0008] Preferably, the particle size D50 of the mesoporous silica is 20 to 80 nm.

[0009] Preferably, the specific surface area of the mesoporous silica is 150 to 300 m 2 / g.

[0010] The asphalt material is a commercially available asphalt material. For example, it can be one or a mixture of two or more selected from coal tar pitch, petroleum asphalt, natural asphalt, and tar asphalt.

[0011] Preferably, in step 1), the asphalt material is crushed to a particle size D50 of 5 to 10 microns.

[0012] Preferably, in step 2), the amount of mesoporous silica used is 1 wt% to 5 wt%.

[0013] Preferably, the calcination conditions in step 3) are as follows: Heating to 500 °C at a heating rate of 0.2 to 1 °C / min, and then heating to 900 to 1100 °C at a heating rate of 3 to 10 °C / min, and holding for 2 to 5 h.

[0014] According to a second aspect of the present invention, there is provided a negative electrode, which comprises the hard carbon composite material according to the present invention.

[0015] According to a third aspect of the present invention, there is provided a lithium ion battery, which comprises the negative electrode according to the present invention.

[0016] Beneficial effects The advantages of the present invention are as follows: By means of sintering, mesoporous silica is added during the sintering process of the asphalt-based hard carbon material. Through sintering, during the formation of hard carbon, the hard carbon is combined with mesoporous silica on the surface of the hard carbon. Among them, mesoporous silica can not only form a three-dimensional multi-channel lithium-ion transmission channel, solving the problem of large powder resistivity caused by the difficult control of the pore size of hard carbon; but also improve the infiltration of the electrolyte; compared with the traditional method of adding mesoporous silica through a binder during battery preparation, it eliminates the influence of the interface impedance caused by the non-conductive binder and solves the interface problem between silica and hard carbon. All these are beneficial to improving the lithium-ion transmission efficiency; thereby improving the fast charging performance, power discharge, and cycle life of the battery, and having a wide application prospect in the field of batteries. Description of the drawings

[0017] Figure 1 It is a flowchart showing the preparation method of a hard carbon composite material with high ion transmission efficiency according to the present invention.

[0018] Figure 2 It is an XRD pattern of the hard carbon composite material prepared according to Example 1 of the present invention.

[0019] Figure 3 It is an SEM image of the hard carbon composite material prepared according to Example 1 of the present invention.

[0020] Figure 4 and Figure 5 It is an SEM image of the hard carbon composite material prepared according to Comparative Example 1.

[0021] Figure 6 It is a graph of discharge rate-capacity retention of the hard carbon composite materials prepared according to the examples and comparative examples of the present invention. Detailed description of the specific embodiments

[0022] The present invention will be described in detail below in conjunction with specific embodiments, but the scope of the present invention is not limited to the specific embodiments described below.

[0023] Figure 1 It is a flowchart for the preparation of a hard carbon composite material with high ion transmission efficiency in Examples 1 and 2 of the present invention. Among them, the preparation process is divided into three steps. In step S1, the asphalt material is crushed, that is, the hard carbon raw material, namely the asphalt material, is mechanically pulverized so that the hard carbon raw material is pulverized to a particle size consistent with or close to the finished product particle size; in step S2, that is, the grinding step, the mesoporous silica is uniformly mixed with the crushed asphalt material; step S3 is the pyrolysis treatment step, and pyrolysis is carried out under a nitrogen protection environment to obtain a hard carbon composite material.

[0024] Material source Asphalt: Purchased from Liaoning Xinde, with an oxygen content > 20% and a softening temperature < 150 °C.

[0025] Preparation Example 1 Preparation of mesoporous silica Mesoporous silica was prepared using the sol-gel method. Preparation of CTAB solution: 10 g of CTAB was added to 990 g of water, and then 500 g of ethanol was added thereto and mixed evenly; the pH was gradually adjusted to alkaline with ammonia water, and the amount of ammonia water used was 40 mL and mixed evenly.

[0026] Preparation of gel: 10 g of TEOS (tetraethyl orthosilicate) was slowly added dropwise to the above-prepared alkaline (ammonia water) mixed solution of CTAB (cetyltrimethylammonium bromide) to form a sol-gel, and silica without removing CTAB was obtained by centrifugation and washing; Removal of CTAB: CTAB was removed by high-temperature calcination (560 °C, 10 h) to form mesoporous silica; Ground to obtain powdery mesoporous silica, and the measured particle size D50 was 72 nm and the specific surface area was 170 m 2 / g.

[0027] Preparation Example 2 Preparation of mesoporous silica Mesoporous silica was prepared using the sol-gel method. Preparation of CTAB solution: 10 g of CTAB was added to 990 g of water, and then 500 g of ethanol was added thereto and mixed evenly; the pH was gradually adjusted to alkaline with ammonia water, and the amount of ammonia water used was 20 mL and mixed evenly.

[0028] Preparation of gel: 10 g of TEOS (tetraethyl orthosilicate) was slowly added dropwise to the above-prepared alkaline (ammonia water) mixed solution of CTAB (cetyltrimethylammonium bromide) to form a sol-gel, and silica without removing CTAB was obtained by centrifugation and washing; Removal of CTAB: CTAB was removed by high-temperature calcination (560 °C, 10 h) to form mesoporous silica; Ground to obtain powdery mesoporous silica, and the measured particle size D50 was 37 nm and the specific surface area was 262 m 2 / g.

[0029] Example 1 The hard carbon composite material was prepared according to the following steps. Use an air jet mill to crush the asphalt material to obtain a crushed product, and crush it to a particle size D50 of 8 microns; add 10 g of the mesoporous silica obtained in Preparation Example 1 to 500 g of the crushed asphalt material, and use a ball mill (the ball-to-material ratio ranges from 4:1) to grind for 1 h to obtain a composite material precursor; Transfer the composite material precursor to a tubular furnace and calcine it under a nitrogen protection environment, at a rate of 0.5 °C min -1 gradually increase the temperature to 500 °C, and then increase the temperature at a rate of 5 °C min -1 to 1000 °C and hold for 3 h. Cool with the furnace and collect to obtain a hard carbon composite material.

[0030] Figure 2 is the XRD pattern of the hard carbon composite material prepared in Example 1. As Figure 2 shown, the hard carbon composite material exhibits two diffraction peaks, which reflects the characteristics of the disordered structure and low graphitization degree of the composite material.

[0031] Figure 3 is the SEM image of the hard carbon composite material prepared in Example 1. As Figure 3 shown, the hard carbon composite material shows that the mesoporous silica is uniformly distributed on the surface of the massive hard carbon material.

[0032] Example 2 Prepare a hard carbon composite material according to the following steps Use an air jet mill to crush the asphalt material to obtain a crushed product and crush it to a particle size D50 of 8 microns; add 20 g of the mesoporous silica obtained in Preparation Example 2 to 500 g of the crushed asphalt material, and use a ball mill (the ball-to-material ratio ranges from 4:1) to grind for 1 h to obtain a composite material precursor; Transfer the composite material precursor to a tubular furnace, under a nitrogen protection environment, at a rate of 0.5 °C min -1 gradually increase the temperature to 500 °C, and then increase the temperature at a rate of 5 °C min -1 to 1000 °C and hold for 3 h. Cool with the furnace and collect to obtain a hard carbon composite material.

[0033] Comparative Example 1 Prepare a hard carbon material according to the following steps Use an air jet mill to crush the asphalt material to obtain a crushed product and crush it to a particle size D50 of 8 microns; then, use a ball mill (the ball-to-material ratio is 4:1) to grind for 1 h to obtain a hard carbon material precursor; Transfer the hard carbon material precursor to a tubular furnace and carbonize it under a nitrogen protection environment, at a rate of 0.5 °C min -1 gradually increase the temperature to 500 °C, and then increase the temperature at a rate of 5 °C min -1Heat it to 1000 °C at a heating rate, and hold for 3 h. Cool it in the furnace and collect the obtained hard carbon material.

[0034] Figure 4 It is the SEM image of the hard carbon material prepared in Comparative Example 1. As Figure 4 shown, the hard carbon material prepared in Comparative Example 1 is in a block structure.

[0035] Figure 5 It is the SEM image of the hard carbon material prepared in Comparative Example 1. As Figure 5 shown, there are only a small part of hard carbon particles on the surface of this hard carbon material, and there are no other impurities.

[0036] Comparative Example 2 Prepare the hard carbon composite material according to the following steps Use an air jet mill to crush the asphalt material to obtain a crushed product, and crush it to a particle size D50 of 8 μm; then, transfer the crushed product to a tubular furnace, and under a nitrogen protection environment, gradually heat it to 500 °C at a rate of 0.5 °C / min -1 and then heat it to 1000 °C at a heating rate of 5 °C / min -1 and hold for 3 h. Cool it in the furnace and collect. After cooling, add 10 g of mesoporous silica to 500 g of crushed asphalt material, and grind it with a ball mill (the ball-to-material ratio ranges from 4:1) for 1 h to obtain the hard carbon composite material.

[0037] Battery test: Perform electrochemical performance tests on the obtained materials according to the following method: Mix the hard carbon composite material, CMC, and SBR prepared in the example or comparative example into a homogeneous slurry at a mass ratio of 95.5:2:2.5, then use a four-sided coater to coat the black slurry on the copper foil, and then dry the film in a vacuum drying oven at 100 °C for 2 h to form a film with a thickness of 120 μm. Use a punching machine to punch the electrode film into circular pieces with a radius of 0.7 mm, use metallic lithium as the counter electrode, 1 mol / L LiPF 6 EC+DEC (1:1 vol%) as the electrolyte, and the separator is a PP / PE separator, and assemble it into a CR2032 type button battery in a glove box. Perform constant current charge and discharge tests on the above button battery, and the voltage range is 2-0.001 V.

[0038] Electrolyte infiltration rate test: The obtained materials were tested for their electrochemical properties as follows: The hard carbon composite materials, CMC, and SBR prepared in the examples or comparative examples were mixed into a homogeneous slurry at a mass ratio of 95.5:2:2.5, and then the black slurry was coated on copper foil using a 120-μm four-sided spreader. Then, the film was dried in a vacuum drying oven at 100 °C for 2 hours. The electrolyte infiltration rate was tested using a contact angle measuring instrument. This test was carried out in an environment of 25 ± 3 °C. The test results are shown in Table 1.

[0039] Table 1: Test results of electrolyte infiltration rate

[0040] Resistivity test: The composite materials obtained in Example 1, Example 2, Comparative Example 1, and Comparative Example 2 above were tested for resistivity and compaction density on a powder resistivity meter. This test was carried out in an environment of 25 ± 3 °C. The test results are shown in Table 1.

[0041] Table 2: Test results of resistivity

[0042] It can be seen from the results of Table 1 and Table 2 that both Example 1 and Example 2 according to the present invention have good compaction density, low resistivity, low liquid absorption time, and better rate discharge ability, which helps to reduce the lithium ion transmission distance, thereby improving the lithium ion transmission efficiency and enabling the battery to have good fast charging performance.

[0043] Figure 6 Performance diagrams of lithium-ion batteries made using the hard carbon materials of Example 1, Example 2, Comparative Example 1, and Comparative Example 2 according to the present invention are as follows. As Figure 6 shown, at a high rate of 20C, the discharge capacity retention rates of Example 1 and Example 2 are 91% and 94% respectively; the discharge capacity retention rates of Comparative Example 1 and Comparative Example 2 are 83% and 86% respectively. Thus, it can be seen that when the hard carbon composite material according to the present invention is used as the negative electrode material, it can reduce the resistance, improve the ion transmission rate, increase the charge and discharge speed, and thus improve the discharge capacity retention rate of the lithium-ion battery.

[0044] Finally, it should be noted that the above examples are only specific descriptions of the technical solutions of the present invention and are not limited thereto. Those skilled in the art should understand that they can still refer to the examples in the present invention, modify the technical parameters therein, or make equivalent replacements for the characterization of the test results. However, for these modifications or replacements, the corresponding technical solutions cannot deviate from the scope protected by the present invention.

Claims

1. A method for preparing a hard carbon composite material, comprising the following steps: 1) crushing the asphalt material to obtain a crushed product; 2) In a dry environment, the crushed product obtained in step 1) is ground with mesoporous silica to obtain a composite material precursor, wherein: Relative to the total weight of the asphalt material, the amount of mesoporous silica is 1wt%~8wt%; 3) In an inert atmosphere, calcining the composite material precursor at a temperature of 900-1100° C., and then cooling it in the furnace.

2. The method for preparing a hard carbon composite material according to claim 1, wherein: The particle size D50 of the mesoporous silica is 20-80 nm.

3. The method for preparing a hard carbon composite material according to claim 1, wherein: The specific surface area of ​​the mesoporous silica is 150-300 m 2 / g.

4. The method for preparing a hard carbon composite material according to claim 1, wherein: The asphalt is one selected from coal tar asphalt, petroleum asphalt, natural asphalt and tar asphalt, or a mixture of two or more thereof.

5. The method for preparing a hard carbon composite material according to claim 1, wherein: In step 1), the asphalt material is crushed to a D50 of 5 to 10 microns.

6. The method for preparing a hard carbon composite material according to claim 1, wherein: In step 2), the amount of mesoporous silica used is 1 wt%~5 wt%.

7. The method for preparing a hard carbon composite material according to any one of claims 1 to 6, wherein: The calcination conditions in step 2) are as follows: Increase the temperature to 500°C at a rate of 0.2~1°C / min, then increase the temperature to 900~1100°C at a rate of 3~10°C / min, and keep warm for 2~5h. 8 . A hard carbon composite material, prepared by the method for preparing a hard carbon composite material according to claim 1 . 9 . A negative electrode comprising the hard carbon composite material according to claim 8 . 10 . A lithium ion battery comprising the negative electrode according to claim 9 .

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