Surface-modified spherical natural graphite negative electrode material, preparation method thereof and lithium battery

Abstract

The application provides a surface-modified spherical natural graphite negative electrode material and a preparation method and a lithium battery thereof. The preparation method comprises the following steps: mixing a titanium source and spherical graphite, and then performing ball milling treatment to obtain a mixture; performing compaction treatment on the mixture in a mold to obtain a compacted mixture; and sequentially performing preheating treatment and hot-pressing treatment on the compacted mixture to obtain a graphite negative electrode material; wherein the temperature of the hot-pressing treatment is 2100-2500 DEG C, the pressure is 20-25 MPa, and the pressure is increased to the pressure within 1.5-2 h. The lithium battery using the negative electrode material has good cycle performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery materials technology, and more specifically, to a surface-modified spherical natural graphite anode material, its preparation method, and a lithium battery. Background Technology

[0002] Graphite, currently the most widely used commercial anode material, boasts a theoretical specific capacity of up to 372 mAh / g. However, with increasing market demand and technological advancements, the performance of traditional graphite can no longer meet the requirements of high-end applications. Spherical graphite is prone to flake-off during cycling, impairing its cycle life. Surface coating modification is a common material modification method. Preparing a uniform coating layer on the graphite surface can improve the material's structure during electrochemical cycling, thereby enhancing some of its properties.

[0003] The technical solution disclosed in CN116454272A combines surface coating with element doping. It involves mixing a phosphorus-containing compound with organic compounds such as pitch and resin, then uniformly coating the mixture onto the graphite surface, followed by carbonization and sintering to obtain a phosphorus-doped graphite anode material. This method involves adding phosphorus to a carbon coating layer before coating the graphite. This structure is relatively complex, requiring control of many factors during the process, and the strength and cycle life of the prepared material need improvement. Summary of the Invention

[0004] To address the problems in the prior art, the present invention aims to provide a surface-modified spherical natural graphite anode material, its preparation method, and a lithium battery thereof. Lithium batteries using this anode material exhibit excellent cycle performance.

[0005] To achieve the above objectives, according to a first aspect of the present invention, a method for preparing a surface-modified spherical natural graphite anode material is provided, comprising:

[0006] The titanium source and spherical graphite were mixed and then ball-milled to obtain a mixture.

[0007] The mixture is compacted in a mold to obtain a compacted mixture;

[0008] The compacted mixture is subjected to preheating and hot pressing treatment in sequence to obtain the graphite anode material;

[0009] The hot pressing process is carried out at a temperature of 2100-2500℃ and a pressure of 20-25MPa, and the pressure is increased to the specified pressure within 1.5-2 hours.

[0010] This invention modifies the surface of spherical graphite using a titanium source, forming a titanium dioxide coating layer on the surface of the graphite. This effectively improves the reversible capacity and cycle performance of the graphite material. Furthermore, a specific hot-pressing process effectively increases the material's density, reduces porosity and defects, and achieves uniform titanium dioxide coating on the graphite surface.

[0011] Controlling the pressure of hot pressing within the above-mentioned range is beneficial for forming modified materials with a dense coating layer. However, if the pressure of hot pressing exceeds the above-mentioned preferred range, it may cause the graphite particles to break, ultimately leading to a decrease in the material's cycle performance.

[0012] In particular, the temperature, pressure, and pressurization time selected in the hot pressing process of this invention can effectively ensure the stability of the graphite structure during cycling, thereby improving the cycle performance of lithium batteries using this graphite anode material.

[0013] In some preferred embodiments, the titanium source is titanium powder and / or titanium dioxide.

[0014] In some preferred embodiments, the spherical graphite is natural graphite.

[0015] In some preferred embodiments, the spherical graphite has a particle size of 10-20 micrometers.

[0016] In some preferred embodiments, the ball milling process is carried out in a ball mill, and the ball mill operates at a speed of 100-200 r / min for a time of 10-40 min.

[0017] In some preferred embodiments, the mass ratio of the spherical graphite to the titanium source is 100:(1-4).

[0018] In some preferred embodiments, the preheating treatment is performed at a temperature of 60-120°C for 8-20 hours.

[0019] According to another aspect of the present invention, a surface-modified spherical natural graphite anode material prepared according to the above-described preparation method is provided.

[0020] According to another aspect of the present invention, a graphite anode comprising the above-described surface-modified spherical natural graphite anode material is provided.

[0021] According to another aspect of the present invention, a lithium battery comprising the above-described graphite negative electrode is provided.

[0022] Compared with the prior art, the beneficial effects of the present invention include: improving the mechanical strength of graphite anode materials and effectively improving the cycle life of lithium batteries using modified graphite anode materials. Attached Figure Description

[0023] Figure 1 A comparison chart of charge and discharge data for coin cells in each embodiment and the comparative example is shown.

[0024] Figure 2 The XRD patterns of the graphite anode materials in Example 3 and Comparative Example 1 are shown.

[0025] Figure 3 The EDS spectrum of the graphite anode material of Example 3 is shown.

[0026] Figure 4 The SEM image of the graphite anode material of Example 3 is shown.

[0027] Figure 5 The SEM image of the graphite anode material of Example 3 is shown.

[0028] Figure 6 The SEM image of the graphite anode material of Comparative Example 1 is shown.

[0029] Figure 7 The SEM image of the graphite anode material of Comparative Example 2 is shown.

[0030] Figure 8 The SEM image of the graphite anode material of Comparative Example 3 is shown.

[0031] Figure 9 The SEM image of the graphite anode material of Comparative Example 4 is shown.

[0032] Figure 10 The RAMAN test results of the graphite anode materials of Example 3 and Comparative Example 2 are shown. Detailed Implementation

[0033] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0034] Example 1:

[0035] This embodiment provides a method for preparing a graphite anode material, which includes:

[0036] 0.1g of titanium dioxide and 10g of spherical graphite were mixed in a ball mill at a speed of 150r / min for 30min; the particle size of the spherical graphite was D. 50 =18 micrometers;

[0037] The above mixture was placed in a mold and compacted under a pressure of 5 MPa to obtain a compacted mixture.

[0038] The compacted mixture was preheated in an oven at 100°C for 16 hours.

[0039] The preheated mixture was placed in a hot press and pressed under high temperature and high pressure conditions. The hot pressing temperature was 2200℃ and the pressure was 20MPa. The pressure was increased to the specified pressure within 2 hours. After the pressing time was reached, the mold was cooled at room temperature to obtain the prepared graphite anode material, which was named Example 1.

[0040] Example 2:

[0041] This embodiment provides a method for preparing a graphite anode material, which includes:

[0042] 0.2g of titanium dioxide and 10g of spherical graphite were mixed in a ball mill at a speed of 150r / min for 30min; the particle size of the spherical graphite was D. 50 =18 micrometers;

[0043] The above mixture was placed in a mold and compacted under a pressure of 5 MPa to obtain a compacted mixture.

[0044] The compacted mixture was preheated in an oven at 100°C for 16 hours.

[0045] The preheated mixture was placed in a hot press and pressed under high temperature and high pressure conditions. The hot pressing temperature was 2200℃ and the pressure was 20MPa. The pressure was increased to the specified pressure within 2 hours. After the pressing time was reached, the mold was cooled at room temperature to obtain the prepared graphite anode material, which was named Example 2.

[0046] Example 3:

[0047] This embodiment provides a method for preparing a graphite anode material, which includes:

[0048] 0.3g of titanium dioxide and 10g of spherical graphite were mixed in a ball mill at a speed of 150r / min for 30min; the particle size of the spherical graphite was D. 50 =18 micrometers;

[0049] The above mixture was placed in a mold and compacted under a pressure of 5 MPa to obtain a compacted mixture.

[0050] The compacted mixture was preheated in an oven at 100°C for 16 hours.

[0051] The preheated mixture was placed in a hot press and pressed under high temperature and high pressure conditions. The hot pressing temperature was 2200℃ and the pressure was 20MPa. The pressure was increased to the specified pressure within 2 hours. After the pressing time was reached, the mold was cooled at room temperature to obtain the prepared graphite anode material, which was named Example 3.

[0052] Example 4:

[0053] This embodiment provides a method for preparing a graphite anode material, which includes:

[0054] 0.4 g of titanium dioxide and 10 g of spherical graphite were mixed in a ball mill at a speed of 150 r / min for 30 min; the particle size of the spherical graphite was D. 50 =18 micrometers;

[0055] The above mixture was placed in a mold and compacted under a pressure of 5 MPa to obtain a compacted mixture.

[0056] The compacted mixture was preheated in an oven at 100°C for 16 hours.

[0057] The preheated mixture was placed in a hot press and pressed under high temperature and high pressure conditions. The hot pressing temperature was 2200℃ and the pressure was 20MPa. The pressure was increased to the specified pressure within 2 hours. After the pressing time was reached, the mold was cooled at room temperature to obtain the prepared graphite anode material, which was named Example 4.

[0058] Comparative Example 1:

[0059] 10g of spherical graphite was mixed in a ball mill at a speed of 150r / min for 30min; the particle size of the spherical graphite was D. 50 =18 micrometers;

[0060] The above mixture was placed in a mold and compacted under a pressure of 5 MPa to obtain a compacted mixture.

[0061] The compacted mixture was preheated in an oven at 100°C for 16 hours.

[0062] The preheated mixture was placed in a hot press and pressed under high temperature and high pressure conditions. The hot pressing temperature was 2200℃ and the pressure was 20MPa. The pressure was increased to the specified pressure within 2 hours. After the pressing time was reached, the mold was cooled at room temperature to obtain the prepared graphite anode material, which was named Comparative Example 1.

[0063] Comparative Example 2:

[0064] 0.3g of titanium dioxide and 10g of spherical graphite were mixed in a ball mill at a speed of 150r / min for 30min; the particle size of the spherical graphite was D. 50 =18 micrometers;

[0065] The above mixture was placed in a mold and compacted under a pressure of 5 MPa to obtain a compacted mixture.

[0066] The compacted mixture was preheated in an oven at 100°C for 16 hours.

[0067] The preheated mixture was placed in a hot press and pressed under high temperature and high pressure conditions. The hot pressing temperature was 2000℃ and the pressure was 20MPa. The pressure was increased to the specified pressure within 2 hours. After the pressing time was reached, the mold was cooled at room temperature to obtain the prepared graphite anode material, which was named Comparative Example 2.

[0068] Comparative Example 3:

[0069] 0.3g of titanium dioxide and 10g of spherical graphite were mixed in a ball mill at a speed of 150r / min for 30min; the particle size of the spherical graphite was D. 50 =18 micrometers;

[0070] The above mixture was placed in a mold and compacted under a pressure of 5 MPa to obtain a compacted mixture.

[0071] The compacted mixture was preheated in an oven at 100°C for 16 hours.

[0072] The preheated mixture was placed in a hot press and pressed under high temperature and high pressure conditions. The hot pressing temperature was 2200℃ and the pressure was 30MPa. The pressure was increased to the specified pressure within 2 hours. After the pressing time was reached, the mold was cooled to room temperature to obtain the prepared graphite anode material, which was named Comparative Example 3.

[0073] Comparative Example 4:

[0074] 0.3g of titanium dioxide and 10g of spherical graphite were mixed in a ball mill at a speed of 150r / min for 30min; the particle size of the spherical graphite was D. 50 =18 micrometers;

[0075] The above mixture was placed in a mold and compacted under a pressure of 5 MPa to obtain a compacted mixture.

[0076] The compacted mixture was preheated in an oven at 100°C for 16 hours.

[0077] The preheated mixture was placed in a hot press and pressed under high temperature and high pressure conditions. The hot pressing temperature was 2200℃ and the pressure was 20MPa. The pressure was increased to the specified pressure within 1 hour. After the pressing time was reached, the mold was cooled at room temperature to obtain the prepared graphite anode material, which was named Comparative Example 4.

[0078] Electrochemical tests were conducted on CR2032 coin cells assembled with the negative electrode materials from the examples and comparative examples. The electrochemical tests were performed according to the following steps: The test materials were mixed uniformly at a mass ratio of negative electrode material: conductive agent (Super P): binder (LA133) = 90:5:5, coated onto copper foil to a thickness of 150 μm, and dried in a vacuum oven at 80°C for 12 h to obtain the negative electrode sheet. CR2032 coin cells were assembled in a glove box (water and oxygen levels less than 0.01 ppm), with lithium foil as the counter electrode and 1 mol / L LiF6 dissolved in DMC:DEC:EC (volume ratio 1:1:1) as the electrolyte. The assembled coin cells were then subjected to charge-discharge cycle tests at a current density of 1C on a Blue Electric system. The test results are shown in Table 1.

[0079] Table 1

[0080]

[0081] As can be seen from Table 1, the first-week reversible capacity and cycle performance of the embodiment are better than those of the unmodified Comparative Example 1. This is because coating with titanium dioxide introduces new active lithium storage sites on the graphite surface, which improves the reversible capacity of the material. At the same time, the coating layer with good mechanical properties avoids direct contact between graphite and electrolyte, inhibits the peeling of graphite sheets during cycling, and improves cycle performance.

[0082] Comparing Example 3 with Comparative Example 2, it can be found that the change in hot pressing temperature also affects the electrochemical performance of the material. At around 2200℃, graphite undergoes high-temperature graphitization, and the graphite structure begins to change. Therefore, the electrochemical performance will be significantly improved after the hot pressing temperature reaches 2200℃.

[0083] Comparing Example 3 with Comparative Example 3, it can be found that excessively high hot-pressing pressure can cause partial breakage of graphite particles (e.g., Figure 4 and Figure 8 (As shown in the SEM image), this is because excessive pressure damages the surface coating, allowing the electrolyte to penetrate into the graphite bulk phase through particle cracks caused by overpressure during cycling, resulting in a decrease in the material's cycling performance.

[0084] Comparing Example 3 with Comparative Example 4, it can be found that under the same conditions, heating and pressurizing to the specified temperature and pressure in a shorter time results in a decrease in electrochemical performance. This is because the relatively higher rate of heating and pressurization causes stress inside the material, leading to uneven coating and thus affecting the cycle life of the material.

[0085] The performance of the graphite anode materials in the examples and comparative examples was tested, and the results were obtained. Figure 1 The diagram shows a comparison of charge and discharge data of the button cells in each embodiment and the comparative example. Figure 2 The XRD patterns of the graphite anode materials in Example 3 and Comparative Example 1 are shown. Figure 3 The EDS spectrum of the graphite anode material of Example 3 is shown. Figure 4 The SEM image of the graphite anode material of Example 3 is shown. Figure 5 The SEM image of the graphite anode material of Example 3 is shown. Figure 6 The SEM image of the graphite anode material of Comparative Example 1 is shown. Figure 7 The SEM image of the graphite anode material of Comparative Example 2 is shown. Figure 8 The SEM image of the graphite anode material of Comparative Example 3 is shown. Figure 9 The SEM image of the graphite anode material of Comparative Example 4 is shown. Figure 10 The RAMAN test results of the graphite anode materials of Example 3 and Comparative Example 2 are shown.

[0086] according to Figure 1 The cycling data of the various embodiments and comparative examples at a current density of 1C (5 cycles of 0.1C activation) show that: Example 3 exhibits the best electrochemical performance, with the highest reversible capacity and cycle retention after charge-discharge cycles. This is attributed to the increased lithium storage sites provided by the appropriate amount of titanium dioxide coating, thus enhancing the reversible capacity. Comparative Example 1, without coating, has the lowest capacity. The lower capacity of Comparative Example 2 is due to the lower hot-pressing temperature and lower degree of graphitization, although titanium dioxide was coated; this can be referenced... Figure 10 The RAMAN test results for Example 3 and Comparative Example 2 are shown. The Id / Ig ratio represents the degree of graphitization of the material; a smaller ratio indicates a higher degree of graphitization. The test results show that the degree of graphitization increases with increasing temperature. The lower sol yield in Comparative Examples 3-4 is due to the uneven coating layer leading to increased electrolyte side reactions and increased battery internal resistance, thus affecting the battery's charge / discharge performance.

[0087] like Figure 2 As shown, the (002) peak of the graphite anode material in Example 3 shifts to the left, proving the successful coating of titanium dioxide. Figure 3 The results shown demonstrate that the titanium distribution in Example 3 is uniform.

[0088] Depend on Figures 4 to 9 The results show that in Comparative Example 1, the uncoated graphite surface has obvious exposed flakes, and the graphite flakes are not dense enough, making it prone to structural changes such as flake peeling during cycling. According to the results of Comparative Example 2, the graphite surface becomes smoother with the addition of a coating layer, but there is uneven coating. With the increase of hot pressing temperature, the graphite particle surface of Example 3 is smooth and dense, which can ensure the stability of the graphite structure during cycling. In Comparative Example 3, the surface coating layer is damaged due to overpressure, and there is cracking. In Comparative Example 4, the surface coating of the material is relatively uneven due to the excessively fast heating and pressurization rate.

[0089] The above results demonstrate that by modifying spherical graphite with titanium dioxide and preparing a titanium dioxide coating layer on the graphite surface, this invention can effectively improve the reversible capacity of the material and enhance its cycle performance. The coating significantly enhances the mechanical strength of the material and effectively improves the cycle life of the battery. At the same time, the hot pressing process is simple to operate, can increase the density of the material, reduce voids and defects, achieve uniform coating of the graphite surface, and can also enhance the graphitization degree of graphite under high temperature and high pressure.

Claims

1. A method for producing a graphite negative electrode material, characterized by, The application relates to a graphite negative electrode material and a preparation method thereof. A titanium source and spherical graphite are mixed and then subjected to ball milling treatment to obtain a mixture; the mass ratio of the spherical graphite to the titanium source is 100: (1-4); the titanium source is titanium powder and / or titanium dioxide; and the spherical graphite is natural graphite; The mixture is subjected to compaction treatment in a mold to obtain a compacted mixture; The compacted mixture is sequentially subjected to preheating treatment and hot-pressing treatment to obtain the graphite negative electrode material; a dense and uniform titanium dioxide coating layer is formed on the surface of the spherical graphite; The temperature of the hot-pressing treatment is 2100-2500 DEG C, the pressure is 20-25 MPa, and the pressure is increased to the pressure within 1.5-2 h.

2. The production method according to claim 1, characterized by, The particle size of the spherical graphite is 10-20 microns.

3. The preparation method according to claim 1, characterized in that, The ball milling treatment is carried out in a ball mill, and the running speed of the ball mill is 100-200 r / min, and the time is 10-40 min.

4. The method of claim 1, wherein, The temperature of the preheating treatment is 60-120 DEG C, and the time is 8-20 h.

5. A graphite negative electrode material, characterized by, The graphite negative electrode material is prepared by the preparation method according to any one of claims 1-4.

6. A graphite negative electrode, characterized by The graphite negative electrode material according to claim 5 is used as a negative electrode.

7. A lithium battery, characterized by The graphite negative electrode according to claim 6 is used as a negative electrode.

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