A graphite negative electrode material and preparation method thereof

Abstract

The invention discloses a graphite negative electrode material and a preparation method, comprising the following steps: a certain amount of modified precursor is loaded into a supercritical fluid reactor, a supercritical fluid is injected after sealing, the temperature is adjusted to 50-250°C and the pressure is 10-30MPa, so that the precursor is completely dissolved in the supercritical fluid; a certain amount of spherical graphite is sprayed into the supercritical reactor, and the magnetic stirring reaction is carried out for 1-8h; after cooling, the gas is released, the reaction product is taken out, and the coated spherical graphite is obtained; the coated spherical graphite is subjected to high temperature carbonization treatment under an inert atmosphere to obtain a graphite negative electrode material. The present invention uses supercritical fluid as a medium, greatly improves the spherical graphite coating efficiency, reduces the amount of modified precursor, and realizes the controllable adjustment of the coating thickness, compactness and uniformity; and greatly improves the performance of the negative electrode material compared to conventional processes.

Description

Technical Field

[0001] The present invention relates to the technical field of negative electrode materials for lithium ion batteries, and in particular to a graphite negative electrode material and a preparation method thereof. Background Art

[0002] Lithium-ion batteries have high energy density, long cycle life, and high output voltage, and are the focus of current new energy battery development. As one of the four major components of lithium batteries, negative electrode materials play a very important role in the performance of lithium batteries and are the core link in the midstream of the lithium battery industry. At present, the negative electrode materials for large-scale commercial applications are mainly graphite materials, among which spherical graphite is the main one.

[0003] However, during the charge and discharge process of spherical graphite, the interlayer spacing changes due to the embedding and de-embedding of lithium ions, which can easily cause the graphite layer to peel off and pulverize. Organic solvents can also co-embed into the graphite layer or decompose, affecting the battery cycle performance. Therefore, modifying spherical graphite is an important means to improve its performance, and carbon coating is currently the most widely used and mature method.

[0004] At present, the carbon coating process mainly involves melting asphalt and mixing it with spherical graphite, and then carbonizing it at high temperature. The main problem with this process is that the combination of asphalt and graphite is not sufficient, the powder may agglomerate, and the quality controllability is not high; in addition, the amount of asphalt is large (generally >5%), and the production cost is high. Therefore, how to provide a new spherical graphite modification process technology is an urgent problem to be solved in the processing of negative electrode materials.

[0005] The present invention prepares a graphite negative electrode material and a preparation method, utilizes the effect of supercritical fluid to improve performance and reduce the amount of modified precursor used, which obviously has positive practical significance. Summary of the invention

[0006] The invention aims to provide a graphite negative electrode material and a preparation method thereof, which uses a supercritical fluid as a medium, greatly improves the spherical graphite coating efficiency, reduces the amount of modified precursor, and realizes controllable adjustment of the coating layer thickness, density and uniformity.

[0007] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is: a method for preparing a graphite negative electrode material, comprising the following steps:

[0008] (1) A certain amount of modified precursor is loaded into a supercritical fluid reactor, which is sealed and then injected with supercritical fluid, and the temperature is adjusted to 50-250° C. and the pressure is adjusted to 10-30 MPa, so that the precursor is completely dissolved in the supercritical fluid;

[0009] (2) spraying a certain amount of spherical graphite into a supercritical reactor and reacting with magnetic stirring for 1-8 hours;

[0010] (3) After cooling, releasing the gas, taking out the reaction product, and obtaining coated spherical graphite;

[0011] (4) The coated spherical graphite is subjected to high-temperature carbonization treatment under an inert atmosphere to obtain a graphite negative electrode material.

[0012] Preferably, in step (1), the modified precursor comprises one or more combinations of asphalt, phenolic resin, epoxy resin, and coal tar.

[0013] Preferably, in step (1), the amount of the modified precursor added is less than 1% by weight of the total raw materials.

[0014] Preferably, the mass ratio of the modified precursor to the spherical graphite is 0.1%-1%.

[0015] Preferably, in step (1), the supercritical fluid includes any one of CO2, CF3Cl, and C2H4.

[0016] Preferably, in step (2), the spherical graphite comprises natural spherical graphite or artificial spherical graphite, and the fixed carbon content is greater than 99.9%.

[0017] Preferably, the modified precursor comprises 0.1 to 1 part and spherical graphite 100 to 120 parts by weight.

[0018] Preferably, in step (1), the temperature adjusted in the supercritical fluid reactor includes but is not limited to 50°C, 80°C, 100°C, 120°C, 150°C, 160°C, 180°C, 200°C, 220°C, 240°C, and 250°C.

[0019] Preferably, in step (1), the pressure in the supercritical fluid reactor includes but is not limited to 10 MPa, 12 MPa, 14 MPa, 15 MPa, 18 MPa, 20 MPa, 22 MPa, 25 MPa, 28 MPa, and 30 MPa.

[0020] Preferably, in step (1), the time of magnetic stirring includes but is not limited to 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, 6 h, 6.5 h, 7 h, 7.5 h, and 8 h.

[0021] The present application also claims protection for a spherical graphite with high tap density, which is prepared by the preparation method as described above.

[0022] Preferably, the first discharge specific capacity of the graphite negative electrode material is ≥372 mA·h / g, and the first coulombic efficiency is ≥97.7%.

[0023] In the above, the preparation principle of the graphite negative electrode material is as follows: supercritical fluid has ultra-high solubility, fluidity and diffusivity. Using it as a solvent and reaction medium, the modified precursor can be evenly wrapped on the surface of spherical graphite and penetrate into the micro-gaps of spherical graphite, reducing the internal void defects of spherical graphite; at the same time, the supercritical fluid can be inserted between the graphite sheets, thereby effectively expanding the interlayer spacing of the graphite, which helps to reduce the diffusion resistance of lithium ions and improve its rate performance.

[0024] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0025] 1. By adopting the technical solution of the present invention and utilizing the effect of supercritical fluid, multiple controls such as coating, filling and intercalation of spherical graphite are completed, which greatly improves the performance of the negative electrode material compared with conventional processes.

[0026] 2. This method can control the thickness of the coating layer, and has high uniformity and density. The amount of modified precursor can be reduced to less than 1% compared with more than 5% in the conventional process, which greatly reduces the waste of precursors and reduces production costs.

[0027] 3. The method is simple and easy to implement, and is convenient for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, some of the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0029] Figure 1 This is a scanning electron microscope photograph of the graphite negative electrode material prepared in Example 1.

[0030] Figure 2 This is a scanning electron microscope photograph of the graphite negative electrode material prepared in Example 2.

[0031] Figure 3 This is a scanning electron microscope photograph of the graphite negative electrode material prepared in Example 3.

[0032] Figure 4 This is a scanning electron microscope photograph of the graphite negative electrode material prepared in Comparative Example 1. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] Example 1

[0035] This embodiment provides a graphite negative electrode material and a preparation method thereof, comprising the following steps:

[0036] (1) 0.5 parts of asphalt was loaded into a supercritical fluid reactor, which was sealed and injected with supercritical CO2. The temperature was adjusted to 180°C and the pressure to 17 MPa to completely dissolve the asphalt in the supercritical fluid.

[0037] (2) Spray 100 parts of spherical graphite into a supercritical reactor and stir the reactor with magnetic stirring for 5 hours;

[0038] (3) After cooling, releasing the gas, taking out the reaction product, and obtaining coated spherical graphite;

[0039] (4) The coated spherical graphite is subjected to high-temperature carbonization treatment under an inert atmosphere to obtain a graphite negative electrode material.

[0040] Example 2

[0041] This embodiment provides a graphite negative electrode material and a preparation method thereof, comprising the following steps:

[0042] (1) 0.8 parts of phenolic resin was placed in a supercritical fluid reactor, which was sealed and injected with supercritical CO2. The temperature was adjusted to 100°C and the pressure was adjusted to 12 MPa, so that the precursor was completely dissolved in the supercritical fluid;

[0043] (2) Spray 100 parts of spherical graphite into a supercritical reactor and stir the reactor with magnetic stirring for 4 hours;

[0044] (3) After cooling, releasing the gas, taking out the reaction product, and obtaining coated spherical graphite;

[0045] (4) The coated spherical graphite is subjected to high-temperature carbonization treatment under an inert atmosphere to obtain a graphite negative electrode material.

[0046] Example 3

[0047] This embodiment provides a graphite negative electrode material and a preparation method thereof, comprising the following steps:

[0048] (1) 0.6 parts of coal tar was loaded into a supercritical fluid reactor, which was sealed and injected with supercritical CO2. The temperature was adjusted to 150°C and the pressure was adjusted to 15 MPa to completely dissolve the precursor in the supercritical fluid.

[0049] (2) Spray 100 parts of spherical graphite into a supercritical reactor and stir the reactor with magnetic stirring for 4 hours;

[0050] (3) After cooling, releasing the gas, taking out the reaction product, and obtaining coated spherical graphite;

[0051] (4) The coated spherical graphite is subjected to high-temperature carbonization treatment under an inert atmosphere to obtain a graphite negative electrode material.

[0052] Example 4

[0053] This embodiment provides a graphite negative electrode material and a preparation method thereof, comprising the following steps:

[0054] (1) 0.5 parts of asphalt was loaded into a supercritical fluid reactor, which was sealed and injected with supercritical C2H4. The temperature was adjusted to 80°C and the pressure to 12 MPa to completely dissolve the asphalt in the supercritical fluid.

[0055] (2) Spray 100 parts of spherical graphite into a supercritical reactor and stir the reactor with magnetic stirring for 6 hours;

[0056] (3) After cooling, releasing the gas, taking out the reaction product, and obtaining coated spherical graphite;

[0057] (4) The coated spherical graphite is subjected to high-temperature carbonization treatment under an inert atmosphere to obtain a graphite negative electrode material.

[0058] Comparative Example 1

[0059] A conventional process was adopted: 5 parts of asphalt were melted and mixed with 100 parts of spherical graphite (same as Example 1), and high-temperature carbonization treatment was performed under an inert atmosphere to obtain a graphite negative electrode material.

[0060] Comparative Example 2

[0061] A conventional process was adopted: 7 parts of phenolic resin were dissolved in ethanol, and then 100 parts of spherical graphite (same as Example 2) were added and mixed, stirred and reacted for 5 hours, and after drying, high-temperature carbonization treatment was performed under an inert atmosphere to obtain a graphite negative electrode material.

[0062] The physical and chemical indicators of the spherical graphite of Examples 1-4 and Comparative Examples 1-2 were tested according to standard GB / T24533-2019, and the test results are shown in the table below.

[0063]

[0064] Through Examples 1-4, Comparative Examples 1-2, Figure 1-4As can be seen from the above table, the graphite negative electrode material prepared by the technical solution of the present invention has high first discharge specific capacity, first coulomb efficiency and compaction density, and is significantly superior to the graphite negative electrode material prepared by the conventional method; in addition, the amount of modified precursor used in Examples 1-4 can be reduced to less than 1% by weight of the total raw materials compared to more than 5% in the conventional process, which greatly reduces the waste of precursors and reduces production costs.

[0065] In the above, the high-temperature carbonization treatment method under an inert atmosphere used in Examples 1-4 and Comparative Examples 1-2 includes placing the cooled coated spherical graphite in a carbonization activation furnace, introducing an inert gas and heating to 400-700° C. under the protection of the inert gas, and carbonizing for 1-4 hours. The high-temperature carbonization treatment method under an inert atmosphere used in this application can also be replaced by other conventional technical means in the art, which will not be described in detail in this application.

[0066] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a graphite negative electrode material, characterized in that: The following steps are involved: (1) Load a certain amount of modified precursor into a supercritical fluid reactor, seal it, and inject supercritical fluid, adjust the temperature to 50-250°C and the pressure to 10-30MPa, so that the precursor is completely dissolved in the supercritical fluid; (2) Spray a certain amount of spherical graphite into the supercritical reactor and stir the reaction with magnetic stirring for 1-8 hours; (3) After cooling, releasing the gas, taking out the reaction product, and obtaining coated spherical graphite; (4) subjecting the coated spherical graphite to high-temperature carbonization treatment under an inert atmosphere to obtain a graphite negative electrode material; In step (1), the amount of the modified precursor added is less than 1% by weight of the total raw materials; In step (1), the modified precursor includes one or more combinations of asphalt, phenolic resin, epoxy resin, and coal tar.

2. The preparation method according to claim 1, characterized in that: The mass ratio of the modified precursor to the spherical graphite is 0.1%-1%.

3. The preparation method according to claim 1, characterized in that: In step (1), the supercritical fluid includes any one of CO2, CF3Cl, and C2H4.

4. The preparation method according to claim 1, characterized in that: In step (2), the spherical graphite includes natural spherical graphite or artificial spherical graphite, and the fixed carbon content is greater than 99.9%.

5. The preparation method according to claim 1, characterized in that: In parts by weight, the modified precursor comprises 0.1 to 1 part and the spherical graphite comprises 100 to 120 parts.

6. A spherical graphite with high tap density, characterized in that: The method is prepared according to any one of claims 1 to 5.

7. The spherical graphite with high tap density according to claim 6, characterized in that: The first discharge specific capacity of the graphite negative electrode material is ≥372 mA·h / g, and the first coulombic efficiency is ≥97.7%.

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