Silicon-carbon negative electrode material with long cycle performance and preparation method thereof

Abstract

The invention discloses a silicon-carbon negative electrode material with long cycle performance and a preparation method thereof, and belongs to the technical field of new energy materials and energy electrochemistry. The preparation method comprises the following steps: uniformly mixing the nano silicon, the carbon nano tube, the dispersing agent and the solvent, and granulating and drying in a spray drying manner; and depositing a carbon coating layer on the surfaces of the particles obtained in the step 1) by using a vapor deposition method to obtain the CNT / Si / C composite negative electrode material. The long tubular carbon nanotubes wrap the silicon particles to form a core composite material, the carbon nanotubes can limit the expansion of the nano silicon, and based on the conductivity of the carbon tubes, the carbon tubes and the silicon particles are in close contact, a conductive network cannot be damaged due to the expansion / shrinkage of the nano silicon, and the external coated carbon layer can prevent the internal silicon particles from being in direct contact with an electrolyte, so that the service life of the electrolyte is prolonged. When the negative electrode material is applied to the lithium battery, the cycle performance of the battery can be remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy materials and energy electrochemistry, and specifically relates to a silicon-carbon negative electrode material with long cycle performance and a preparation method thereof. Background Art

[0002] With the rapid development of economy, the global energy situation is becoming increasingly severe. The demand for traditional disposable energy such as coal and oil continues to expand, making it increasingly difficult to break the dilemma of the imbalance between production and ecological environment. In order to alleviate the global ecological pressure, the development and application of clean, low-carbon, environmentally friendly and renewable energy is an inevitable choice at present.

[0003] In the current context, the development and application of lithium-ion batteries are extremely valuable. Lithium-ion batteries have the advantages of high operating voltage, high specific energy, long cycle life, and light weight. They have become the main choice of rechargeable power sources in many fields. They have become an ideal energy source for various portable electronic devices, such as laptops, smart phones, etc., especially in the field of electric vehicles. The endurance of new energy vehicles depends on the energy density of the battery. In recent years, consumers' requirements for car range have continued to increase, and the energy density of lithium-ion batteries mainly depends on the lithium storage capacity and voltage of the positive and negative electrode materials. It can be seen that the negative electrode material is a key factor affecting the performance of lithium-ion batteries. Therefore, it is extremely necessary to develop negative electrode materials with high capacity and long cycle performance.

[0004] Although graphite has been widely used as a negative electrode material for lithium-ion batteries, its actual specific capacity is close to the theoretical limit (372mAh / g). When the number of cycles is large, the layered structure is easy to peel off and fall off, which makes it difficult to meet the high energy density requirements of future power batteries. And with the continuous surge in global demand for power batteries, the supply of graphite negative electrode materials is tight, so it is urgent to find high-performance alternatives. Faced with this situation, silicon-based negative electrode materials with a very high theoretical capacity (4200 mAh / g) have begun to enter people's field of vision. Silicon is considered to be an ideal choice for the next generation of negative electrode materials because it also has a low lithium insertion and extraction voltage platform.

[0005] ‌However, the capacity of silicon materials decays rapidly during use, which limits their practical application. The main reason is that the volume of silicon materials expands (about 300%) and shrinks greatly during the process of lithium insertion and extraction, which causes the silicon particles to rupture and the conductive agent to lose conductive contact, resulting in electrochemical failure and affecting the safety and service life of the battery. This is the main reason for the rapid capacity decay of the material. Therefore, it is of great significance to improve the cycle stability of silicon materials by inhibiting the volume expansion of silicon materials and improving the structural stability of the materials. This is also a topic that is currently being studied at home and abroad.

[0006] Designing silicon-carbon composite materials is one of the main ways to solve the drastic volume effect of silicon. Carbon materials have high electrical conductivity, relatively stable structure, small volume expansion during the cycle, and good flexibility and lubricity. They can inhibit the volume expansion of silicon materials during the cycle to a certain extent. Therefore, they need to be compounded with carbon materials that have excellent conductivity and can accommodate the volume change of silicon to greatly improve the energy density and cycle stability. In the prior art, the coating of nano-silicon with carbon materials is often achieved by modifying the surface of carbon materials and nano-silicon. This method has the problems of complex process, high cost and low production capacity, which limits the industrial production and application of such materials and hinders the industrialization process of silicon-carbon negative electrode materials. And simply coating the carbon material on the outside of nano-silicon is difficult to stabilize the expansion of nano-silicon, which may cause the carbon layer to rupture during the expansion of nano-silicon, and thus fail to inhibit the erosion and damage of the electrolyte to the negative electrode material, thereby affecting the cycle life of the material. Summary of the invention

[0007] In view of the above-mentioned problems, the present invention aims to provide a silicon-carbon negative electrode material with long cycle performance and a preparation method thereof. First, long tubular carbon tubes are used to uniformly coat nanosilicon. Based on the excellent conductivity of carbon nanotubes, they can be firmly in contact with silicon particles. After the nanosilicon is filled on the surface of the carbon nanotubes, it is constrained in space and will not cause damage to the conductive network due to the expansion / contraction of the nanosilicon. Then, a carbon layer is deposited on the outside of the carbon nanotube / nanosilicon composite material to prevent the internal silicon particles from directly contacting the electrolyte and consuming the electrolyte. This material is used in lithium batteries as a negative electrode material to improve the cycle performance of the battery.

[0008] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is as follows: The preparation method of the silicon-carbon negative electrode material with long cycle performance is as follows: The nano-silicon, carbon nanotubes, dispersant and solvent are uniformly mixed, and granulated and dried by spray drying; A carbon coating layer is deposited on the surface of the particles obtained in step 1) by using a vapor deposition method to obtain a CNT / Si / C composite material.

[0009] Furthermore, in step 1), the carbon nanotubes have a diameter of 0.4-30 nm and a length of 1-50 μm.

[0010] Furthermore, in step 1), the particle size of nano-silicon is 10-100 nm.

[0011] Furthermore, in step 1), the dispersant is one or a combination of sodium dodecyl sulfonate, sodium dodecylbenzene sulfonate, dodecyltrimethylammonium bromide, didodecyldimethylammonium bromide, didodecyldimethylammonium bromide, hexadecyltrimethylammonium bromide, sodium lignin sulfonate, alkali lignin, sodium dodecyl sulfate, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, and polyvinyl pyrrolidone; and the solvent is water, ethanol, or methane.

[0012] Furthermore, in step 1), the mass ratio of nano-silicon, carbon nanotubes, dispersant and solvent is 80~150:3~10:1~5:800~2000; the mixing process is completed by a stirrer or a ball mill, the stirring or ball milling speed is 300~2500 rpm, and the mixing time is 0.5~6 h.

[0013] Furthermore, in step 1), spray drying is performed using a spray dryer, the inlet temperature is controlled at 150-200°C, the outlet temperature is controlled at 70-100°C, and the granulation particle size is 8-20 µm.

[0014] Furthermore, in step 2), the carbon source gas used for vapor deposition is one of methane and acetylene gas or a mixture of the two, the vapor deposition temperature is 600-1100° C., and the deposition time is 0.5-8 h.

[0015] The CNT / Si / C silicon-carbon negative electrode material prepared according to the above method includes a core composite material and a carbon layer coated on the surface of the core composite material. The core composite material is a carbon nanotube / nano-silicon composite material, and silicon nanoparticles are attached to the surface of the carbon nanotube.

[0016] Furthermore, the mass ratio of carbon nanotubes, nano-silicon and amorphous carbon in the silicon-carbon negative electrode material is 20~50: 30~70: 2~20.

[0017] The prepared CNT / Si / C silicon-carbon negative electrode material is coated on the surface of the current collector to form a negative electrode, and assembled with the positive electrode to prepare a lithium-ion battery with long cycle performance.

[0018] The beneficial effects of the present invention are: 1. The silicon-carbon negative electrode material prepared in this application is a composite material with a core-shell structure, wherein the core is composed of nano-silicon particles coated with carbon nanotubes, and the shell is a deposited carbon layer. The preparation process is simple, the preparation cost is low, and it is easy to promote industrialization; 2. The present application utilizes carbon nanotubes to coat silicon particles to form the core of the silicon-carbon negative electrode material. The flexibility of the carbon nanotubes provides mechanical support, adapts to the drastic volume effect of silicon-based materials, and can limit the shrinkage and expansion of silicon during lithium extraction and insertion. In addition, since the carbon nanotubes have excellent electrical conductivity, the silicon and the carbon nanotubes can be more closely connected, which can also effectively solve the problem of poor electrical conductivity of silicon. 3. The purpose of depositing a carbon layer on the outside of the core composite material is to prevent the internal silicon particles from directly contacting the electrolyte and consuming the electrolyte, so that the silicon-carbon negative electrode material can be used to prepare the battery negative electrode to effectively improve the battery's cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a cyclic charge and discharge capacity curve diagram of Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0020] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention is further described below in conjunction with the accompanying drawings and embodiments. Example

[0021] 10 kg of ethanol solution was put into the dispersion equipment, and the speed of the dispersion equipment was adjusted to 20 rpm. Then 1 kg of nano-silicon (particle size of about 50 nm), 0.05 kg of carbon nanotubes (diameter of about 20 nm, length of about 30 μm) and 0.02 kg of sodium hexadecyl sulfate were put into the dispersion equipment in turn, and the speed was adjusted to 800 rpm. Mixing and dispersion for 2 h, and then granulation and drying were carried out by spray drying. The inlet temperature was controlled at 170 ° C, the outlet temperature was controlled at 70 ° C, and the granulation particle size was 12 μm. The particles obtained by spray drying were put into a gas phase rotary furnace, and a carbon layer was deposited on the outside of the particles by vapor deposition. The carbon source gas was methane, the vapor deposition temperature was set at 800 ° C, and the vapor deposition time was 1 h. The target silicon-carbon negative electrode material CNT / Si / C was obtained by screening and demagnetization of the material. The mass ratio of carbon nanotubes, nano-silicon and amorphous carbon was about 40:50:10. Comparative Example 1 The difference between this comparative example and Example 1 is that carbon nanotubes are not used to coat silicon, but a carbon layer is directly vapor-deposited on the surface of silicon nanoparticles to prepare the Si / C composite material, and the preparation parameters of the corresponding deposition process are exactly the same as those in Example 1.

[0022] The materials prepared in Example 1 and Comparative Example 1 were used as negative electrode materials for the battery, and the lithium batteries were assembled according to the same assembly process. The electrochemical performance of the batteries was tested. The cycle comparison curves are shown in FIG. Figure 1 As shown, from Figure 1 It can be seen that the capacity retention rate of the CNT / Si / C composite material prepared in Example 1 is still maintained at 94.7% after 400 cycles, while the capacity retention rate of the Si / C composite material prepared in Comparative Example 1 is only 81.7%. The CNT / Si / C composite material as a negative electrode material can effectively improve the cycle stability performance of lithium-ion batteries.

Claims

1. A method for preparing a silicon-carbon negative electrode material with long cycle performance, characterized in that: The steps include: The nano-silicon, carbon nanotubes, dispersant and solvent are uniformly mixed, and granulated and dried by spray drying; A carbon coating layer is deposited on the surface of the particles obtained in step 1) by using a vapor deposition method to obtain a CNT / Si / C composite material.

2. The method for preparing a silicon-carbon negative electrode material with long cycle performance according to claim 1, characterized in that: In step 1), the carbon nanotubes have a diameter of 0.4-30 nm and a length of 1-50 μm.

3. The method for preparing a silicon-carbon negative electrode material with long cycle performance according to claim 1, characterized in that: In step 1), the particle size of nano-silicon is 10-100 nm.

4. The method for preparing a silicon-carbon negative electrode material with long cycle performance according to claim 1, characterized in that: In step 1), the dispersant is one or a combination of sodium dodecyl sulfonate, sodium dodecylbenzene sulfonate, dodecyltrimethylammonium bromide, didodecyldimethylammonium bromide, dioctadecyldimethylammonium bromide, hexadecyltrimethylammonium bromide, sodium lignin sulfonate, alkali lignin, sodium dodecyl sulfate, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, and polyvinyl pyrrolidone; and the solvent is water, ethanol, or methane.

5. The method for preparing a silicon-carbon negative electrode material with long cycle performance according to claim 1, characterized in that: In step 1), the mass ratio of nano-silicon, carbon nanotubes, dispersant and solvent is 80~150:3~10:1~5:800~2000; the mixing process is completed by a stirrer or a ball mill, the stirring or ball milling speed is 300~2500 rpm, and the mixing time is 0.5~6 h.

6. The method for preparing a silicon-carbon negative electrode material with long cycle performance according to claim 1, characterized in that: In step 1), spray drying is performed using a spray dryer, the inlet temperature is controlled at 150-200°C, the outlet temperature is controlled at 70-100°C, and the granulation particle size is 8-20 µm.

7. The method for preparing a silicon-carbon negative electrode material with long cycle performance according to claim 1, characterized in that: In step 2), the carbon source gas used for vapor deposition is one of methane and acetylene gas or a mixture of the two, the vapor deposition temperature is 600-1100° C., and the deposition time is 0.5-8 h.

8. A silicon-carbon negative electrode material with long cycle performance, characterized in that: It is prepared based on the preparation method described in any one of claims 1 to 7, and the silicon-carbon negative electrode material comprises a core composite material and amorphous carbon coated on the surface of the core composite material; The core composite material is a carbon nanotube / nano-silicon composite material, and silicon nanoparticles are attached to the surface of the carbon nanotube.

9. The silicon-carbon negative electrode material with long cycle performance according to claim 8, characterized in that: The mass ratio of carbon nanotubes, nano-silicon and amorphous carbon is 20~50: 30~70: 2~20.

10. A lithium ion battery, characterized in that: It comprises a positive electrode and a negative electrode, wherein the negative electrode comprises a current collector and the silicon-carbon negative electrode material as claimed in claim 8 coated on the surface of the current collector.

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