High-dispersity and high-specific-capacity silicon-carbon negative electrode material and preparation method thereof

Abstract

The invention relates to a silicon-carbon negative electrode material with high dispersity and high specific capacity and a preparation method thereof, the negative electrode material is formed by embedding nano silicon particles wrapped with a carbon shell and amorphous carbon, the particle size of the nano silicon particles is 60-700nm, and the amorphous carbon is an organic carbon source. According to the invention, the surface of nano silicon is coated with a layer of carbon shell, so that a buffer effect is provided for volume expansion of silicon, and meanwhile, the mechanical strength of the carbon shell is enhanced through high-temperature carbonization and calcination processes. According to the invention, the coating asphalt is used for coating the nano silicon, so that the dispersity of the nano silicon in the liquid petroleum asphalt or coal pitch is improved, and the agglomeration phenomenon of the nano silicon in the mixing process of the nano silicon and the liquid asphalt is also prevented.

Description

Technical Field

[0001] This application relates to the technical field of secondary batteries, and specifically relates to a silicon-carbon anode material with high dispersion and high specific capacity and a preparation method therefor. Background Art

[0002] With the rapid development of the new energy industry and intelligent devices, lithium-ion batteries are widely used in the power field, but there are pain points such as short driving ranges for electric vehicles, short standby times for electronic products, and high charging frequencies. Silicon has been found to be easily alloyed with lithium to form a silicon-lithium alloy, thus having a theoretical lithium storage capacity of 4200 mAh / g and excellent cycling performance. This discovery has received great attention in the industry, and silicon-based anodes are listed as the most promising next-generation lithium battery anode materials. Since silicon is a semiconductor and cannot be used as an independent battery anode material, it needs to be combined with a good conductor as the anode material. At the same time, silicon will undergo a large volume expansion (about 300%) during charge and discharge, causing the electrode material to powder and fall off. Carbon is the most commonly used good conductor in batteries, so silicon-based anodes actually appear in the form of silicon-carbon anodes, and at the same time provide a buffer medium for the volume expansion of silicon during charge and discharge.

[0003] Patent document CN118763208A discloses a high specific capacity silicon-carbon anode material and a preparation method therefor. In this method, nano-silicon particles are wet-milled to prepare micron-sized silicon secondary particles, and then mixed with an organic carbon source and a solvent, and after high-temperature carbonization, crushing, and screening, a silicon-carbon anode material is obtained. However, in this method, the silicon secondary particles are micron-sized particles composed of a large amount of nano-silicon, which causes agglomeration of nano-silicon to a certain extent, thus affecting the uniform dispersion of silicon materials in the carbon source. Therefore, it is very important to invent a method to improve the dispersion of nano-silicon in the carbon source. Summary of the Invention

[0004] The present invention provides a silicon-carbon anode material with high dispersion and high specific capacity and a preparation method therefor. The purpose is to provide a method for improving the dispersion of nano-silicon in view of the deficiencies of the existing technology, and to provide a high specific capacity silicon-carbon anode material, in which the silicon particles are nano-silicon particles wrapped with a carbon shell and are uniformly dispersed and embedded in amorphous carbon, reducing the agglomeration problem of nano-silicon particles.

[0005] To achieve the above object, the present invention is implemented by adopting the following technical solutions:

[0006] A silicon-carbon anode material with high dispersion and high specific capacity, wherein the anode material is formed by mutual embedding of nano-silicon particles wrapped with a carbon shell and amorphous carbon, and the particle size of the nano-silicon particles is 60-700 nm, and the amorphous carbon is an organic carbon source.

[0007] Preferably, the particle size of the nano-silicon particles is 80-200 nm.

[0008] Preferably, the organic carbon source includes petroleum-based asphalt and coal-based asphalt.

[0009] Preferably, the mass ratio of the nano-silicon particles is 5% to 20%.

[0010] A method for preparing a high-dispersion and high specific capacity silicon-carbon anode material includes the following steps:

[0011] 1) Place the coated asphalt with a particle size D50 = 5 - 10 μm in a vacuum drying oven and dry it at a temperature of 80 - 100 °C for 12 - 16 h.

[0012] 2) Mix and granulate the dried coated asphalt with nano-silicon particles, denoted as nano-silicon secondary particles.

[0013] 3) Mix the nano-silicon secondary particles obtained in step 2) with a liquid organic carbon source.

[0014] 4) Carbonize and calcine the mixture of the nano-silicon secondary particles and the organic carbon source obtained in step 3) in sequence to obtain a nano-silicon / amorphous carbon mixture. During the carbonization process, place the mixture in a glass test tube with a diameter of 20 mm and a height of 200 mm, where the carbonization temperature is 480 - 520 °C and the calcination temperature is 1100 - 1300 °C.

[0015] 5) Crush and screen the calcined nano-silicon / amorphous carbon mixture obtained in step 4) to obtain a silicon-carbon anode material with a particle size D50 of 5 - 50 μm.

[0016] Preferably, the softening point of the coated asphalt is ≥240 °C.

[0017] Preferably, the mass ratio of the coated asphalt to the nano-silicon particles is (3 - 1):1.

[0018] Preferably, the mixing and granulation is high-speed stirring granulation or dry spray granulation.

[0019] Preferably, the mixing method in step 3) is one of mechanical stirring, ultrasonic or oscillation, and the mixing time is 2 - 4 h.

[0020] Preferably, the liquid organic carbon source is petroleum asphalt or coal asphalt with a softening point ≤60 °C.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] 1) The present invention wraps a carbon shell on the surface of nano-silicon, providing a buffering effect for the volume expansion of silicon. At the same time, through the high-temperature carbonization and calcination processes, the mechanical strength of the carbon shell is enhanced.

[0023] 2) The present invention uses coated asphalt to wrap nano-silicon, which improves the dispersibility of nano-silicon in liquid petroleum asphalt or coal tar pitch and also hinders the agglomeration of nano-silicon during the mixing process with liquid asphalt. Description of the Drawings

[0024] Figure 1 It is a scanning electron microscope (SEM) photograph of the silicon-carbon negative electrode of Example 1.

[0025] Figure 2 It is a transmission electron microscope (TEM) photograph of the silicon-carbon negative electrode of Example 1. Detailed Description of the Invention

[0026] The following further illustrates the specific implementation manners of the present invention in conjunction with the examples. The following examples are used to specifically illustrate the content of the present invention. These examples are only general descriptions of the content of the present invention and do not limit the content of the present invention.

[0027] Example 1:

[0028] This example provides a silicon-carbon negative electrode material with high dispersibility and high specific capacity. The negative electrode material consists of nano-silicon particles wrapped with a carbon shell and amorphous carbon. Among them, the nano-silicon particles wrapped with a carbon shell are evenly dispersed and embedded in the amorphous carbon. Figure 1 And Figure 2 They are respectively the scanning electron microscope image and the transmission electron microscope image of the silicon-carbon negative electrode material.

[0029] This example also provides a preparation method for a silicon-carbon negative electrode material with high dispersibility and high specific capacity, including the following steps:

[0030] 1) Select petroleum asphalt with a high softening point of 250°C as the coated asphalt, and the particle size of the coated asphalt is D50 = 5 μm.

[0031] 2) Place the coated asphalt in a vacuum drying oven and dry it at 80°C for 16 h.

[0032] 3) Mix the coated asphalt and nano-silicon particles with a particle size of 80 nm in a mass ratio of 1:1 for granulation, specifically using dry spray granulation, denoted as nano-silicon secondary particles.

[0033] 4) Ultrasonically mix the nano-silicon secondary particles obtained in step 3) with coal tar pitch with a softening point of 40°C for 2 h to form a nano-silicon / organic carbon source mixture, where the mass fraction of nano-silicon is 5%, the coated asphalt accounts for 5%, and the organic carbon source accounts for 90%.

[0034] 5) The nano-silicon / organic carbon source mixture obtained in step 4) is carbonized and calcined in sequence to obtain a nano-silicon / amorphous carbon mixture. During the carbonization process, the mixture is placed in a glass test tube with a diameter of 20 mm and a height of 200 mm, where the carbonization temperature is 490 °C and the calcination temperature is 1100 °C.

[0035] 6) The calcined nano-silicon / amorphous carbon mixture obtained in step 5) is crushed and sieved to obtain a silicon-carbon anode material with a particle size D50 of 20 μm.

[0036] Example 2:

[0037] This example provides a preparation method of a silicon-carbon anode material with high dispersion and high specific capacity, including the following steps:

[0038] 1) Select petroleum asphalt with a high softening point of 260 °C as the coating asphalt, and the particle size of the coating asphalt is D50 = 7 μm;

[0039] 2) Place the coating asphalt in a vacuum drying oven and dry it at 90 °C for 14 h;

[0040] 3) Mix and granulate the coating asphalt and nano-silicon particles with a particle size of 70 nm at a mass ratio of 2:1. Specifically, high-speed stirring granulation is used, denoted as nano-silicon secondary particles;

[0041] 4) The nano-silicon secondary particles obtained in step 3) and petroleum asphalt with a softening point of 40 °C are mixed by mechanical stirring for 3 h to form a nano-silicon / organic carbon source mixture, where the mass fraction of nano-silicon is 5%, the coating asphalt accounts for 10%, and the organic carbon source accounts for 85%;

[0042] 5) The nano-silicon / organic carbon source mixture obtained in step 4) is carbonized and calcined in sequence to obtain a nano-silicon / amorphous carbon mixture. During the carbonization process, the mixture is placed in a glass test tube with a diameter of 20 mm and a height of 200 mm, where the carbonization temperature is 500 °C and the calcination temperature is 1200 °C;

[0043] 6) The calcined nano-silicon / amorphous carbon mixture obtained in step 5) is crushed and sieved to obtain a silicon-carbon anode material with a particle size D50 of 40 μm.

[0044] Example 3:

[0045] This example provides a preparation method of a silicon-carbon anode material with high dispersion and high specific capacity, including the following steps:

[0046] 1) Select petroleum asphalt with a high softening point of 270 °C as the coating asphalt, and the particle size of the coating asphalt is D50 = 8 μm.

[0047] 2) Place the coated asphalt in a vacuum drying oven and dry it at 100 °C for 12 h.

[0048] 3) Mix and granulate the coated asphalt and nano-silicon particles with a particle size of 100 nm in a mass ratio of 3:1. Specifically, use dry spray granulation, denoted as nano-silicon secondary particles.

[0049] 4) Use oscillation to mix the nano-silicon secondary particles obtained in step 3) with coal tar pitch with a softening point of 60 °C for 2 h to form a nano-silicon / organic carbon source mixture, where the mass fraction of nano-silicon is 10%, the coated asphalt accounts for 30%, and the organic carbon source accounts for 60%.

[0050] 5) Carbonize and calcine the nano-silicon / organic carbon source mixture obtained in step 4) in sequence to obtain a nano-silicon / amorphous carbon mixture. During the carbonization process, place the mixture in a glass test tube with a diameter of 20 mm and a height of 200 mm. The carbonization temperature is 510 °C and the calcination temperature is 1300 °C.

[0051] 6) Crush and screen the calcined nano-silicon / amorphous carbon mixture obtained in step 5) to obtain a silicon-carbon negative electrode material with a particle size D50 of 30 μm.

[0052] Example 4:

[0053] This example provides a preparation method for a silicon-carbon negative electrode material with high dispersion and high specific capacity, including the following steps:

[0054] 1) Select petroleum asphalt with a high softening point of 260 °C as the coated asphalt, and the particle size of the coated asphalt is D50 = 10 μm.

[0055] 2) Place the coated asphalt in a vacuum drying oven and dry it at 80 °C for 14 h.

[0056] 3) Mix and granulate the coated asphalt and nano-silicon particles with a particle size of 80 nm in a mass ratio of 1:1. Specifically, use dry spray granulation, denoted as nano-silicon secondary particles.

[0057] 4) Use oscillation to mix the nano-silicon secondary particles obtained in step 3) with coal tar pitch with a softening point of 30 °C for 3 h to form a nano-silicon / organic carbon source mixture, where the mass fraction of nano-silicon is 5%, the coated asphalt accounts for 5%, and the organic carbon source accounts for 90%.

[0058] 5) Carbonize and calcine the nano-silicon / organic carbon source mixture obtained in step 4) in sequence to obtain a nano-silicon / amorphous carbon mixture. During the carbonization process, place the mixture in a glass test tube with a diameter of 20 mm and a height of 200 mm. The carbonization temperature is 490 °C and the calcination temperature is 1300 °C.

[0059] 6) Crush and screen the calcined nano-silicon / amorphous carbon mixture obtained in step 5) to obtain a silicon-carbon anode material with a D50 particle size of 35 μm.

[0060] Example 5:

[0061] This example provides a method for preparing a silicon-carbon anode material with high dispersion and high specific capacity, including the following steps:

[0062] 1) Select petroleum pitch with a high softening point of 265 °C as the coating pitch, and the coating pitch particle size is D50 = 6 μm.

[0063] 2) Place the coating pitch in a vacuum drying oven and dry it at 100 °C for 14 h.

[0064] 3) Mix and granulate the coating pitch and nano-silicon particles with a particle size of 90 nm at a mass ratio of 2:1, specifically using dry spray granulation, denoted as nano-silicon secondary particles.

[0065] 4) Mix the nano-silicon secondary particles obtained in step 3) and petroleum pitch with a softening point of 40 °C using magnetic stirring for 4 h to form a nano-silicon / organic carbon source mixture, where the mass fraction of nano-silicon is 10%, the coating pitch accounts for 20%, and the organic carbon source accounts for 70%.

[0066] 5) Carbonize and calcine the nano-silicon / organic carbon source mixture obtained in step 4) to obtain a nano-silicon / amorphous carbon mixture. During the carbonization process, place the mixture in a glass test tube with a diameter of 20 mm and a height of 200 mm, where the carbonization temperature is 500 °C and the calcination temperature is 1200 °C.

[0067] 6) Crush and screen the calcined nano-silicon / amorphous carbon mixture obtained in step 5) to obtain a silicon-carbon anode material with a D50 particle size of 30 μm.

[0068] Example 6:

[0069] This example provides a method for preparing a silicon-carbon anode material with high dispersion and high specific capacity, including the following steps:

[0070] 1) Select petroleum pitch with a high softening point of 250 °C as the coating pitch, and the coating pitch particle size is D50 = 10 μm.

[0071] 2) Place the coating pitch in a vacuum drying oven and dry it at 100 °C for 12 h.

[0072] 3) Mix and granulate the coating pitch and nano-silicon particles with a particle size of 100 nm at a mass ratio of 3:1, specifically using dry spray granulation, denoted as nano-silicon secondary particles.

[0073] 4) The nano-silicon secondary particles obtained in step 3) and coal tar pitch with a softening point of 40 °C are mixed by ultrasound for 4 h to form a nano-silicon / organic carbon source mixture, where the mass ratio of nano-silicon is 15%, the coated pitch accounts for 45%, and the organic carbon source accounts for 40%.

[0074] 5) The nano-silicon / organic carbon source mixture obtained in step 4) is carbonized and calcined in sequence to obtain a nano-silicon / amorphous carbon mixture. During the carbonization process, the mixture is placed in a glass test tube with a diameter of 20 mm and a height of 200 mm, where the carbonization temperature is 490 °C and the calcination temperature is 1300 °C.

[0075] 6) The calcined nano-silicon / amorphous carbon mixture obtained in step 5) is crushed and sieved to obtain a silicon-carbon anode material with a particle size D50 of 40 μm.

[0076] Comparative Example 1:

[0077] This comparative example provides a preparation method of a silicon-carbon anode material with high specific capacity, including the following steps:

[0078] 1) Nano-silicon particles with a particle size of 80 nm are directly mixed with coal tar pitch with a softening point of 40 °C to form a nano-silicon / organic carbon source mixture, where the addition amount of nano-silicon is 5%.

[0079] 2) The nano-silicon / organic carbon source mixture obtained in step 1) is carbonized and calcined in sequence to obtain a nano-silicon / amorphous carbon mixture. During the carbonization process, the mixture is placed in a glass test tube with a diameter of 20 mm and a height of 200 mm, where the carbonization temperature is 500 °C and the calcination temperature is 1200 °C.

[0080] 3) The calcined nano-silicon / amorphous carbon mixture obtained in step 2) is crushed and sieved to obtain a silicon-carbon anode material with a particle size D50 of 20 μm.

[0081] It should be noted that in order to investigate the dispersion of nano-silicon in the organic carbon source, during the carbonization process, the nano-silicon / organic carbon source mixture is placed in a glass test tube with a diameter of 20 mm and a height of 200 mm. The height of the carbonized material obtained is about 100 mm. Samples with a height of about 20 mm are taken from the upper and lower parts of the carbonized material as samples for calcination. By comparing the difference in discharge specific capacity between the upper and lower samples in the subsequent test results, the dispersion of nano-silicon in the organic carbon source can be judged. The battery performance of the calcined anode material is evaluated.

[0082] Test Example:

[0083] The battery performance evaluation of the high specific capacity silicon-carbon anode material includes the following steps:

[0084] 1) Mix the silicon-carbon anode materials prepared in the above embodiments and comparative examples with a binder and a conductive agent in a mass ratio of 8:1:1 to form a slurry, where the binder is sodium carboxymethyl cellulose and the conductive agent is acetylene black.

[0085] 2) Uniformly coat the slurry stirred in step 1) on a copper foil with a coating thickness of about 15 μm. Place the coated copper foil in a vacuum drying oven and dry it at 110 °C for 12 h under a vacuum environment.

[0086] 3) Cut, weigh, and assemble the dried electrode sheets in step 2) into button cells. Use a lithium sheet as the counter electrode, a polypropylene membrane as the separator, and an electrolyte of 1 mol / L LiPF6 dissolved in a mixed solution of EC / DMC / EMC for constant current charge-discharge testing. The voltage range is 0.01 - 1.5 V and the current is 0.1 C.

[0087] In summary:

[0088] Install button cells for the silicon-carbon anode materials in Examples 1 - 6 and Comparative Example 1 above according to the evaluation steps of the test examples. The test results are shown in Table 1;

[0089] Table 1 Test results of button cells in examples and comparative examples

[0090]

[0091] It can be seen from the above battery performance test results that according to the preparation method of this patent, for the prepared silicon-carbon anode material, the difference in the first-cycle discharge specific capacity between the upper and lower samples is very small, indicating that this method can significantly improve the dispersion problem of nano-silicon in the organic carbon source.

[0092] The above are the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A silicon-carbon anode material with high dispersion and high specific capacity, characterized in that The negative electrode material is composed of nano-silicon particles wrapped with a carbon shell and amorphous carbon. The nano-silicon particles wrapped with a carbon shell are uniformly dispersed and embedded in the amorphous carbon. The particle size of the nano-silicon particles is 60-700 nm, and the amorphous carbon is an organic carbon source.

2. The silicon-carbon anode material with high dispersion degree and high specific capacity according to claim 1, characterized in that, The particle size of the nano-silicon particles is 80-200 nm.

3. The silicon-carbon anode material with high dispersion degree and high specific capacity according to claim 1, characterized in that, The organic carbon source includes petroleum-based asphalt and coal-based asphalt.

4. The silicon-carbon anode material with high dispersion degree and high specific capacity according to claim 1, characterized in that The mass ratio of the nano-silicon particles is 5%-20%.

5. A preparation method of a high-dispersion and high specific capacity silicon-carbon anode material as described in any one of claims 1-4, characterized in that, It includes the following steps: 1) Place the coated asphalt with a particle size D50 = 5-10 μm in a vacuum drying oven and dry it at a temperature of 80-100 °C for 12-16 h; 2) Mix and granulate the dried coated asphalt and nano-silicon particles, denoted as nano-silicon secondary particles; 3) Mix the nano-silicon secondary particles obtained in step 2) with a liquid organic carbon source; 4) Carbonize and calcine the mixture of the nano-silicon secondary particles and the organic carbon source obtained in step 3) in sequence to obtain a nano-silicon / amorphous carbon mixture, where the carbonization temperature is 480-520 °C and the calcination temperature is 1100-1300 °C; 5) Crush and screen the calcined nano-silicon / amorphous carbon mixture obtained in step 4) to obtain a silicon-carbon negative electrode material with a particle size D50 of 5-50 μm.

6. The preparation method of a silicon-carbon anode material with high dispersion and high specific capacity according to claim 5, characterized in that, The softening point of the coated asphalt is ≥240 °C.

7. The preparation method of a silicon-carbon anode material with high dispersion and high specific capacity according to claim 5, characterized in that, The mass ratio of the coated asphalt to the nano-silicon particles is (3-1):

1.

8. The preparation method of a high-dispersion and high specific capacity silicon-carbon anode material according to claim 5, characterized in that, The mixing granulation is high-speed stirring granulation or dry spray granulation.

9. The preparation method of a high-dispersion and high specific capacity silicon-carbon anode material according to claim 5, characterized in that, The mixing method in step 3) is one of mechanical stirring, ultrasonic or vibration, and the mixing time is 2-4 h.

10. The preparation method of a high-dispersion and high specific capacity silicon-carbon negative electrode material according to claim 5, characterized in that, The liquid organic carbon source is petroleum asphalt or coal asphalt with a softening point ≤60 °C.

Images