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

Abstract

The invention provides a surface-modified spherical natural graphite negative electrode material, a preparation method thereof and a lithium battery. The preparation method comprises the steps that a titanium source and spherical graphite are mixed and then subjected to ball milling treatment, and a mixture is obtained; the mixture is compacted in a mold, and a compacted mixture is obtained; and sequentially carrying out preheating treatment and hot pressing treatment on the compacted mixture to obtain the 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] The present invention relates to the technical field of lithium-ion battery materials, and in particular, to a surface-modified spherical natural graphite anode material, a preparation method thereof, and a lithium battery. Background Art

[0002] As the most widely commercialized anode material at present, graphite has a theoretical specific capacity of up to 372 mAh / g. However, with the increasing market demand and the development of technology, the performance of traditional graphite can no longer meet the requirements of high-end applications. During the cycling process, the graphite layers of spherical graphite are prone to exfoliation, damaging its cycle life. Surface coating modification is a common material modification method. Preparing a uniform coating layer on the surface of graphite can improve the structure of the material during electrochemical cycling, thereby enhancing some material properties.

[0003] The technical solution disclosed in CN116454272A combines the surface coating process with the element doping process. By mixing a phosphorus-containing compound with organic compounds such as asphalt and resin, and then uniformly coating them on the surface of graphite, a phosphorus-doped graphite anode material is obtained after carbonization and sintering. This method adds phosphorus elements to the carbon coating layer and then coats the graphite. This structure is relatively complex, there are many factors to be controlled in the process, and the strength and cycle life of the prepared material need to be improved. Summary of the Invention

[0004] In order to solve the above problems in the prior art, the purpose of the present invention is to provide a surface-modified spherical natural graphite anode material, a preparation method thereof, and a lithium battery. The lithium battery using this anode material has good cycle performance.

[0005] In order to achieve the above purpose, according to the first aspect of the present invention, a preparation method of a surface-modified spherical natural graphite anode material is provided, which includes:

[0006] Mixing a titanium source and spherical graphite and then performing ball milling treatment to obtain a mixed material;

[0007] Compacting the mixed material in a mold to obtain a compacted mixed material;

[0008] Successively performing preheating treatment and hot pressing treatment on the compacted mixed material to obtain the graphite anode material;

[0009] Wherein, the temperature of the hot pressing treatment is 2100 - 2500 °C, the pressure is 20 - 25 MPa, and the pressure is increased to the pressure within 1.5 - 2 h.

[0010] The present invention conducts surface modification on spherical graphite with a titanium source, forming a titanium dioxide coating layer on the surface of the spherical graphite, which can effectively improve the reversible capacity of the graphite material and enhance the cycling performance. Moreover, through a specific hot pressing treatment process, the density of the material can be effectively increased, pores and defects can be reduced, and uniform coating of titanium dioxide on the graphite surface can be achieved.

[0011] Controlling the pressure of the hot pressing treatment within the above range is beneficial to forming a modified material with a dense coating layer. If the pressure of the hot pressing treatment exceeds the above preferred range, it may cause the rupture of graphite particles, ultimately leading to a decline in the cycling performance of the material.

[0012] In particular, the temperature, pressure, and pressure increasing time in the hot pressing process selected in the present invention can effectively ensure the stability of the graphite structure during the cycling process, thereby enhancing the cycling performance of the lithium battery using this graphite negative electrode 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 particle size of the spherical graphite is 10 - 20 microns.

[0016] In some preferred embodiments, 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.

[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 temperature of the preheating treatment is 60 - 120 °C, and the time is 8 - 20 h.

[0019] According to another aspect of the present invention, there is provided a surface-modified spherical natural graphite negative electrode material prepared by the above preparation method.

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

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

[0022] Compared with the prior art, the beneficial effects of the present invention include: enhancing the mechanical strength of the graphite negative electrode material and effectively enhancing the cycling life of the lithium battery using this modified graphite negative electrode material. Brief Description of the Drawings

[0023] Figure 1 Shows the charge and discharge data comparison diagrams of the button cells of each example and the comparative example.

[0024] Figure 2 Shows the XRD diagrams of the graphite anode materials in Example 3 and Comparative Example 1.

[0025] Figure 3 Shows the EDS spectrum diagram of the graphite anode material of Example 3.

[0026] Figure 4 Shows the SEM micrograph of the graphite anode material of Example 3.

[0027] Figure 5 Shows the SEM micrograph of the graphite anode material of Example 3.

[0028] Figure 6 Shows the SEM micrograph of the graphite anode material of Comparative Example 1.

[0029] Figure 7 Shows the SEM micrograph of the graphite anode material of Comparative Example 2.

[0030] Figure 8 Shows the SEM micrograph of the graphite anode material of Comparative Example 3.

[0031] Figure 9 Shows the SEM micrograph of the graphite anode material of Comparative Example 4.

[0032] Figure 10 Shows the RAMAN test results of the graphite anode materials in Example 3 and Comparative Example 2. Detailed Description of the Invention

[0033] For a clearer understanding of the technical features, objectives, and beneficial effects of the present invention, the technical solutions of the present invention are described in detail below, but it should not be construed as a limitation on the scope of implementation of the present invention.

[0034] Example 1:

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

[0036] Mix 0.1 g of titanium dioxide with 10 g of spherical graphite in a ball mill. The rotation speed of the ball mill is 150 r / min, and the time is 30 min; wherein, the particle size of the spherical graphite is D 50 = 18 microns;

[0037] Place the above mixture in a mold and compact it under a pressure of 5 MPa to obtain a compacted mixture.

[0038] Preheat the compacted mixture in an oven. The preheating temperature of the oven is 100 °C and the time is 16 h;

[0039] Place the preheated mixture in a hot press and press the raw materials under high temperature and high pressure. The hot pressing temperature is 2200 °C, the pressure is 20 MPa, and the pressure is increased to the specified pressure within 2 h. After reaching the pressing time, cool the mold with the room temperature to obtain the prepared graphite anode material, named Example 1.

[0040] Example 2:

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

[0042] Mix 0.2 g of titanium dioxide and 10 g of spherical graphite in a ball mill. The rotation speed of the ball mill is 150 r / min and the time is 30 min; among them, the particle size of the spherical graphite is D 50 = 18 microns;

[0043] Place the above mixture in a mold and compact it under a pressure of 5 MPa to obtain a compacted mixture;

[0044] Preheat the compacted mixture in an oven. The preheating temperature of the oven is 100 °C and the time is 16 h;

[0045] Place the preheated mixture in a hot press and press the raw materials under high temperature and high pressure. The hot pressing temperature is 2200 °C, the pressure is 20 MPa, and the pressure is increased to the specified pressure within 2 h. After reaching the pressing time, cool the mold with the room temperature to obtain the prepared graphite anode material, named Example 2.

[0046] Example 3:

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

[0048] Mix 0.3 g of titanium dioxide and 10 g of spherical graphite in a ball mill. The rotation speed of the ball mill is 150 r / min and the time is 30 min; among them, the particle size of the spherical graphite is D 50 = 18 microns;

[0049] Place the above mixture in a mold and compact it under a pressure of 5 MPa to obtain a compacted mixture;

[0050] Preheat the compacted mixture in an oven. The preheating temperature of the oven is 100 °C and the time is 16 h;

[0051] Place the preheated mixture in a hot press and press the raw materials under high temperature and high pressure. The hot pressing temperature is 2200 °C, the pressure is 20 MPa, and the pressure is increased to the specified pressure within 2 h. After reaching the pressing time, cool the mold with the room temperature to obtain the prepared graphite negative electrode material, named Example 3.

[0052] Example 4:

[0053] This example provides a method for preparing a graphite negative electrode material, which includes:

[0054] Mix 0.4 g of titanium dioxide and 10 g of spherical graphite in a ball mill. The rotation speed of the ball mill is 150 r / min and the time is 30 min; among them, the particle size of the spherical graphite is D 50 = 18 microns;

[0055] Place the above mixture in a mold and compact it under a pressure of 5 MPa to obtain a compacted mixture;

[0056] Preheat the compacted mixture in an oven. The preheating temperature of the oven is 100 °C and the time is 16 h;

[0057] Place the preheated mixture in a hot press and press the raw materials under high temperature and high pressure. The hot pressing temperature is 2200 °C, the pressure is 20 MPa, and the pressure is increased to the specified pressure within 2 h. After reaching the pressing time, cool the mold with the room temperature to obtain the prepared graphite negative electrode material, named Example 4.

[0058] Comparative Example 1:

[0059] Mix 10 g of spherical graphite in a ball mill. The rotation speed of the ball mill is 150 r / min and the time is 30 min; among them, the particle size of the spherical graphite is D 50 = 18 microns;

[0060] Place the above mixture in a mold and compact it under a pressure of 5 MPa to obtain a compacted mixture;

[0061] Preheat the compacted mixture in an oven. The preheating temperature of the oven is 100 °C and the time is 16 h;

[0062] Place the preheated mixture in a hot press and press the raw materials under high temperature and high pressure. The hot pressing temperature is 2200 °C, the pressure is 20 MPa, and the pressure is increased to the specified pressure within 2 h. After reaching the pressing time, cool the mold with the room temperature to obtain the prepared graphite negative electrode material, named Comparative Example 1.

[0063] Comparative Example 2:

[0064] Mix 0.3 g of titanium dioxide with 10 g of spherical graphite in a ball mill. The rotational speed of the ball mill is 150 r / min and the time is 30 min. Among them, the particle size of the spherical graphite is D 50 = 18 microns;

[0065] Place the above mixture in a mold and compact it under a pressure of 5 MPa to obtain a compacted mixture;

[0066] Preheat the compacted mixture in an oven. The preheating temperature of the oven is 100 °C and the time is 16 h;

[0067] Place the preheated mixture in a hot press and press the raw materials under high temperature and high pressure. The hot pressing temperature is 2000 °C, the pressure is 20 MPa, and the pressure is increased to the specified pressure within 2 h. After reaching the pressing time, cool the mold with the room temperature to obtain the prepared graphite anode material, named Comparative Example 2.

[0068] Comparative Example 3:

[0069] Mix 0.3 g of titanium dioxide with 10 g of spherical graphite in a ball mill. The rotational speed of the ball mill is 150 r / min and the time is 30 min. Among them, the particle size of the spherical graphite is D 50 = 18 microns;

[0070] Place the above mixture in a mold and compact it under a pressure of 5 MPa to obtain a compacted mixture;

[0071] Preheat the compacted mixture in an oven. The preheating temperature of the oven is 100 °C and the time is 16 h;

[0072] Place the preheated mixture in a hot press and press the raw materials under high temperature and high pressure. The hot pressing temperature is 2200 °C, the pressure is 30 MPa, and the pressure is increased to the specified pressure within 2 h. After reaching the pressing time, cool the mold with the room temperature to obtain the prepared graphite anode material, named Comparative Example 3.

[0073] Comparative Example 4:

[0074] Mix 0.3 g of titanium dioxide with 10 g of spherical graphite in a ball mill. The rotational speed of the ball mill is 150 r / min and the time is 30 min. Among them, the particle size of the spherical graphite is D 50 = 18 microns;

[0075] Place the above mixture in a mold and compact it under a pressure of 5 MPa to obtain a compacted mixture;

[0076] Preheat the compacted mixture in an oven. The preheating temperature of the oven is 100 °C and the time is 16 h;

[0077] Place the preheated mixture in a hot press and press the raw materials under high temperature and high pressure conditions. The hot pressing temperature is 2200 °C, the pressure is 20 MPa, and the pressure is increased to the specified pressure within 1 h. After reaching the pressing time, cool the mold with the room temperature to obtain the prepared graphite anode material, named Comparative Example 4.

[0078] Assemble the anode materials of the examples and comparative examples into 2032-type button cells for electrochemical testing. This electrochemical testing is carried out according to the following steps: Mix the material to be tested evenly according to the mass ratio of anode material: conductive agent (Super P): binder (LA133) = 90:5:5, coat it on the copper foil, the coating thickness is 150 μm, and place it in a vacuum oven at 80 °C for drying for 12 h to obtain the anode electrode sheet. Assemble the CR2032-type button cell in a glove box (the water and oxygen are both less than 0.01 ppm), where the lithium sheet is used as the counter electrode and the electrolyte is 1 mol / L LiF 6 dissolved in DMC:DEC:EC (volume ratio 1:1:1). The assembled button cell is subjected to charge and discharge cycle testing on a Blue Electric system at a current density of 1C. The test results are shown in Table 1.

[0079] Table 1

[0080]

[0081] It can be seen from Table 1 that the first-week reversible capacity and cycle performance of the examples are both better than those of Comparative Example 1 without modification. This is because the coating of titanium dioxide introduces new active lithium storage sites on the graphite surface, improving the reversible capacity of the material. At the same time, the coating layer with good mechanical properties avoids the direct contact between graphite and the electrolyte, inhibits the exfoliation of graphite lamellae during the cycle, and improves the cycle performance.

[0082] Comparing Example 3 with Comparative Example 2, it can be found that the change of the hot pressing temperature will also affect the electrochemical performance of the material. Graphite will undergo high-temperature graphitization at about 2200 °C, and the graphite structure begins to change. Therefore, the electrochemical performance will be significantly improved after the hot pressing temperature reaches 2200 °C.

[0083] Comparing Example 3 with Comparative Example 3, it can be found that too high a hot pressing pressure will cause partial fragmentation of graphite particles (as shown in the SEM electron micrograph of Figure 4 and Figure 8 ), which is because too high a pressure destroys the surface coating layer, so that the electrolyte penetrates into the graphite matrix through the particle cracks caused by overpressure during the cycle, resulting in a decrease in the cycle performance of the material.

[0084] Comparing Example 3 with Comparative Example 4, it can be found that: under the same conditions, when heated and pressurized to the specified temperature and pressure in a shorter time, the electrochemical performance decreases. This is because heating and pressurizing at a relatively higher rate generates stress inside the material, resulting in uneven coating, thus affecting the cycle life of the material.

[0085] Performance tests were carried out on the graphite anode materials in the examples and comparative examples, and Figure 1 the charge-discharge data comparison diagrams of the button cells of the respective examples and comparative examples as shown were obtained. Figure 2 The XRD diagrams of the graphite anode materials in Example 3 and Comparative Example 1 are shown. Figure 3 The EDS energy spectrum diagram of the graphite anode material of Example 3 is shown. Figure 4 The SEM electron micrograph of the graphite anode material of Example 3 is shown. Figure 5 The SEM electron micrograph of the graphite anode material of Example 3 is shown. Figure 6 The SEM electron micrograph of the graphite anode material of Comparative Example 1 is shown. Figure 7 The SEM electron micrograph of the graphite anode material of Comparative Example 2 is shown. Figure 8 The SEM electron micrograph of the graphite anode material of Comparative Example 3 is shown. Figure 9 The SEM electron micrograph 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 data of the respective examples and comparative examples cycled at a 1C current density (activated at 0.1C for 5 cycles) as shown, it can be seen that: Example 3 has the most excellent electrochemical performance, with the highest reversible capacity, the highest cycle retention rate after charge-discharge cycling. This is due to more lithium storage sites provided after appropriate titanium dioxide coating, thus increasing the reversible capacity. In Comparative Example 1, no coating was done, so the capacity is the lowest. The capacity of Comparative Example 2 is lower because although titanium dioxide was coated, the hot pressing temperature was low and the graphitization degree was low; this can be referred to Figure 10 the RAMAN test results of Example 3 and Comparative Example 2 as shown, where the Id / Ig ratio can be used to represent the graphitization degree of the material, and the smaller the ratio, the higher the graphitization degree. The test results show that the graphitization degree increases after the temperature rises. The sols of Comparative Examples 3-4 are lower because the uneven coating layer leads to an increase in side reactions of the electrolyte and an increase in the internal resistance of the battery, thus affecting the charge-discharge performance of the battery.

[0087] As Figure 2 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 as shown can prove that the distribution of titanium in Example 3 is uniform.

[0088] From Figures 4 to 9 As can be seen from the results shown, for Comparative Example 1, the surface lamellae of the uncoated graphite are significantly exposed, the graphite flakes are not tight enough, and structural changes such as lamella exfoliation are likely to occur during cycling; while according to the results of Comparative Example 2, with the addition of the coating layer, the graphite surface becomes smooth, but there is a phenomenon of uneven coating; with the increase of the hot pressing temperature, the surface of the graphite particles in Example 3 is smooth and dense, which can ensure the stability of the graphite structure during cycling; for Comparative Example 3, the surface coating layer is damaged due to overpressure, and fragmentation occurs; for Comparative Example 4, the relative coating on the material surface is not uniform enough due to the too fast heating and pressing rate.

[0089] The above results show that by surface-modifying spherical graphite with titanium dioxide, the present invention can effectively improve the reversible capacity of the material by preparing a titanium dioxide coating layer on the graphite surface, and significantly enhance the mechanical strength of the material after coating, effectively improving the cycle life of the battery; at the same time, the hot pressing process is simple, can increase the density of the material, reduce voids and defects, achieve uniform coating of the graphite surface coating layer, and can also enhance the graphitization degree of graphite under high temperature and high pressure.

Claims

1. A method for preparing a surface-modified spherical natural graphite negative electrode material, characterized in that: include: The titanium source and the spherical graphite are mixed and then ball-milled to obtain a mixture; Compacting the mixture in a mold to obtain a compacted mixture; The compacted mixed material is sequentially subjected to preheating treatment and hot pressing treatment to obtain the graphite negative electrode material; The temperature of the hot pressing treatment is 2100-2500° C., the pressure is 20-25 MPa, and the pressure is increased to the pressure within 1.5-2 hours.

2. The preparation method according to claim 1, characterized in that: The titanium source is titanium powder and / or titanium dioxide.

3. The preparation method according to claim 1, characterized in that: The spherical graphite is natural graphite.

4. The preparation method according to claim 1, characterized in that: The particle size of the spherical graphite is 10-20 microns.

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

6. The preparation method according to claim 1, characterized in that: The mass ratio of the spherical graphite to the titanium source is 100:(1-4).

7. The preparation method according to claim 1, characterized in that: The preheating treatment is performed at a temperature of 60-120° C. and for a time of 8-20 hours.

8. A surface-modified spherical natural graphite negative electrode material, characterized in that: Prepared according to the preparation method described in any one of claims 1 to 7.

9. A graphite negative electrode, characterized in that: Contains the graphite negative electrode material according to claim 8.

10. A lithium battery, characterized in that: The graphite negative electrode according to claim 9 is used as the negative electrode.

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