TWI711209B - Silicon carbon anode material and its application - Google Patents

Abstract

The main purpose of the present invention is to provide a silicon-carbon negative electrode material, which integrates an expanded graphite, a nanosilica powder, and an amorphous carbon coating layer, and a negative electrode with high capacitance and charge and discharge efficiency is made from the silicon-carbon negative electrode material The pole piece can increase the energy density and cycle times of the lithium battery, thereby enhancing the application value of the lithium battery. It can be made into various specifications of lithium ion secondary batteries according to product requirements and used in high energy density electronic products, electric vehicles and other energy storage Device.

Description

Silicon carbon anode material and its application

The present invention relates to a silicon-carbon negative electrode material, in particular to a silicon-carbon negative electrode material prepared by using pitch and expanded graphite.

It is known that graphite is the most commonly used electrode material in lithium ion negative electrodes, but due to factors such as low energy density, it is difficult to apply to high-output power systems (such as electric vehicles, drones and other vehicles), and develop high-capacity The negative electrode material will be the future trend; the theoretical capacity of silicon (~3500mAh/g) is nearly 10 times higher than that of carbon (~372mAh/g). In battery applications, adding a small amount of silicon to the negative electrode material will help increase the negative electrode capacity. It has the advantages of reducing the weight of the negative electrode and increasing the energy density of the battery. The conventional literature also mentions that the use of different types of silicon carbon materials to coat the silicon powder will prolong the service life of the negative electrode material.

However, silicon has the problem of volume expansion and structural fragmentation after charging and discharging, which makes the charging and discharging life shorter. To solve this problem, the size of silicon particles is reduced to slow down the expansion effect, or the silicon surface is coated with a layer of no Stabilizing carbon, inhibiting the volume expansion of charge and discharge and increasing the conductivity of the negative electrode material, will be a simple and effective way.

It is mentioned in the literature that coating amorphous carbon can suppress the volume of silicon powder Expansion, for example, M. Yoshio et al. coated a thin layer of carbon (10wt%) on the surface of micron-sized silicon particles by high-temperature vapor deposition. The capacity can reach 800mAh/g and the number of charge and discharge cycles can reach about 20 cycles. Due to the thinner coating thickness, the relatively small strength and the weaker expansion stress it can withstand, the negative electrode will decrease its capacitance after multiple charges and discharges.

Therefore, there is a great need in the industry to develop a silicon-carbon anode material with higher capacitance and charge-discharge efficiency. Using this silicon-carbon anode material to make a negative electrode can increase the energy density and cycle times of lithium batteries, thereby enhancing the application of lithium batteries. Value, can be made into various specifications of lithium ion secondary batteries according to product requirements, and used in high energy density electronic products, electric vehicles and other energy storage devices.

In view of the shortcomings of the above-mentioned conventional technology, the main purpose of the present invention is to provide a silicon-carbon anode material by uniformly mixing nano-silicon and high-conductivity expanded graphite, and coating the surface of silicon and graphite with pitch using a solvent-liquid mixing method. After carbonization and sintering, a layer of amorphous carbon is formed, and a silicon-carbon anode material composed of nanosilicon, expanded graphite, and hard carbon is prepared; the silicon-carbon anode material has high capacitance and better cycle times, and the silicon-carbon anode material Making the negative pole piece can improve the energy density and cycle times of the lithium battery.

In order to achieve the above objective, the present invention proposes a silicon-carbon negative electrode material, including: an expanded graphite, the expanded graphite is a sheet structure; a nano silicon powder, the nano silicon powder is dispersed on the expanded graphite, and the Nanosilica It has the characteristics of high capacitance; an amorphous carbon coating layer is formed by coating the expanded graphite and nanosilica powder with a pitch to form a coating layer. The coating layer is sintered to form an amorphous carbon coating Floor.

In the silicon-carbon anode material of the present invention, the weight ratio of the nanosilica powder to the expanded graphite is 1:99 to 50:50, and more preferably, the weight mixing ratio of the nanosilica powder is 10-35%.

In the silicon-carbon anode material of the present invention, the weight of the pitch is 0.01 to 0.5 times the weight of the expanded graphite and the nanosilica powder, and more preferably, the weight of the pitch is the expanded graphite and the nanosilica 0.2 to 0.4 times the weight of the powder.

In the silicon-carbon anode material of the present invention, the particle size of the nanosilica powder is 10-1000 nm, and more preferably, the particle size of the nanosilica powder is 50-700 nm.

In the silicon-carbon anode material of the present invention, the particle size of the expanded graphite is about 1-50 μm.

Another solution proposed by the present invention is a negative electrode sheet comprising: a silicon-carbon negative electrode material, the silicon-carbon negative electrode material comprising: an expanded graphite, the expanded graphite having a sheet structure, a nanosilica powder, the nano Rice silica powder is dispersed on expanded graphite, and the nano silica powder has high capacitance characteristics. An amorphous carbon coating layer is formed by coating the expanded graphite and nano silica powder with a pitch. , The coating layer is sintered to form the amorphous carbon coating layer; a mesocarbon microsphere, the mesocarbon microsphere is dry mixed with the silicon carbon material; an adhesive is used for the silicon The carbon anode material and the mesophase carbon microspheres are mixed and solidified Fixed; A promoter is used to improve the conductivity of the negative pole piece; wherein, the proportion of the silicon-carbon negative electrode material to the negative pole piece ranges from 1 to 40%.

The above summary and the following detailed description and drawings are for the purpose of further explaining the ways, means and effects of the present invention to achieve the intended purpose, and other objectives and advantages of the present invention will be described in the subsequent descriptions and drawings. Explained in the formula.

10‧‧‧Silicon carbon anode material

11‧‧‧Amorphous carbon coating

12‧‧‧Expanded graphite

13‧‧‧Nanosilicon powder

The first figure is a schematic diagram of the silicon-carbon anode material of the present invention; the second figure is a schematic diagram of the capacitance change (Si/CTP/EG+MCMB) in Example 1 within 100 cycles; the third figure is a schematic diagram of Example 1 with added expansion The schematic diagram of the capacitance retention rate before and after graphite; the fourth diagram is the schematic diagram of the capacitance change (Si/AR/EG+MCMB) in Example 2 within 100 cycles; the fifth diagram is the schematic diagram of the capacitance change of silicon carbon material; The sixth figure is a schematic diagram of the change of the capacitance retention rate of the silicon carbon material.

The following is a specific example to illustrate the implementation of the present invention. Those familiar with the art can easily understand the contents disclosed in this specification. Understand the advantages and effects of the present invention.

Please refer to the first figure, which is a schematic diagram of the silicon-carbon anode material of the present invention. As shown in the figure, the present invention proposes a silicon-carbon anode material. The silicon-carbon anode material (10) includes: an expanded graphite (12) , The expanded graphite (12) can have a sheet-like structure; a nanosilica powder (13), the nanosilica powder (13) can be dispersed on the expanded graphite (12), and the nanosilica powder (13) It has the characteristics of high capacitance; an amorphous carbon coating layer (11) is formed by coating the expanded graphite (12) and the nanosilica powder (13) with a pitch to form a coating layer, and the coating layer is sintered After processing, the amorphous carbon coating layer (11) is formed, wherein the weight ratio of the nanosilica powder and expanded graphite is 1:99 to 50:50, more preferably, the weight of the nanosilica powder and expanded graphite The ratio is 20:80 to 45:55. The reason is that too much nanosilicon will be more difficult to suppress the swelling effect (a larger decrease in capacitance), on the contrary, too little nanosilicon will have lower energy density; the pitch The weight is 0.01 to 0.5 times the weight of the expanded graphite and the nanosilica powder. More preferably, the weight of the pitch is 0.2 to 0.4 times the weight of the expanded graphite and the nanosilica powder. The reason is Too much bitumen coating reduces the overall conductivity of the negative electrode material. On the contrary, too little bitumen can not inhibit the volume expansion of silica powder; the particle size of the nanosilica powder is 10-1000nm, more preferably, the nanometer The particle size of rice silicon powder is 50-700nm. The reason is that the nano silicon powder of too large size expands greatly during charging and discharging. On the contrary, the nano silicon powder of too small size has a high cost and the first round of coulomb. Shortcomings such as low efficiency; the particle size of the expanded graphite is 1-50μm, which has high conductivity after graphitization, and this particle size can make the nanosilica powder be dispersed on the expanded graphite, and get a good result The electrical effect.

The present invention proposes to uniformly mix nano-silicon powder and expanded graphite, use solvent-liquid mixing method to coat pitch on the surface of silicon and graphite, and form a layer of amorphous carbon after carbonization and sintering to prepare nano-silicon, expanded graphite and hard A silicon-carbon composite material composed of carbon. Among them, the use of graphite with higher conductivity can make up for the shortcomings of the lower conductivity of hard carbon. The outer hard carbon structure can not only inhibit the volume expansion of silicon powder, but also help transfer lithium ions and protect the interior The material is not affected by the electrolyte. As a negative electrode material, it can maintain the capacity of multiple charge and discharge as a whole. It has a higher energy density than graphite materials. This silicon-carbon composite material is used as an additive to mix a small amount of powder into commercially available graphite. The negative electrode material can increase the energy density of the negative electrode and make the charge and discharge life reach a certain standard.

The silicon-carbon negative electrode material of the present invention uses expanded graphite as the main body, and has uniformly dispersed nano-silicon particles on the surface. The pitch is dissolved in an organic solvent and coated on the outer layer of silicon and graphite. After sintering, a conductive hard carbon can be obtained. Structure, its main function is to inhibit the capacity decline caused by the volume expansion of silicon powder, and to protect the internal materials from direct contact with the electrolyte. The hard carbon internal structure can help lithium ions quickly diffuse to the silicon carbon anode material (improve the rapid charge and discharge performance) , The proportion of mixed nano-silicon is about 20%, and the capacitance of silicon-carbon composite is about 900~1000mAh/g; 25% silicon-carbon composite and meso-carbon microbeads (Meso-Carbon Micro Beads, MCMB) are mixed The estimated capacity of the negative electrode is about 450~500mAh/g.

The source of carbon material coating can be pitch, polymer, resin, For oils and other types, depending on the difference in structure and carbon yield, the structural strength is also different: for example, if a polymer is dissolved in an organic solution, and nanosilica is added, if it can be effectively dispersed in the solution, a precursor of the polymer and silicon can be formed. After carbonization, a silicon-carbon material with a core-shell structure is formed. In the conventional technology, a liquid phase mixing method is used to coat the polymer poly(acrylonitrile) (PAN) in the form of physical dispersion. After the silicon surface is formed by anti-solvent, drying, pre-oxidation, carbonization and pulverization, the amorphous carbon formed by polyacrylonitrile is coated on the nanosilicon to prepare a uniformly dispersed silicon-carbon composite material. After 100 times of charging and discharging, the electric capacity can reach about 680mAh/g, which proves that this amorphous carbon should not only limit the expansion effect of silicon particles, but also provide some conductive paths and make the negative electrode maintain a relatively stable electric capacity. Changing the coating phase in the core-shell structure to pitch can increase the carbon yield and coating efficiency, so the structural strength is stronger than that of macromolecules, and better, coal tar pitch has better carbon yield than petroleum pitch. The structural strength is stronger than petroleum asphalt.

Adding graphite powder to silicon powder to form a silicon/graphite anode material can reduce the capacity loss after charging and discharging. The main reason is that graphite can be used as a carrier for the dispersion of silicon powder in the silicon carbon anode to prevent serious aggregation of silicon powder and cause defects. It also has the effect of improving the overall conductivity of the negative electrode and stabilizing the surface solid electrolyte interface film. Compared with the negative electrode of pure silicon powder, it shows that graphite can slow down the volume expansion of silicon powder, so that the overall mechanical strength of the silicon carbon negative electrode is enhanced, and the charge and discharge cycle is improved. Life, however, as the number of charging and discharging of the silicon graphite negative electrode increases, the defects caused by the expansion of the silicon powder gradually lose contact between the graphite powder, and the negative electrode conductivity and capacitance In addition, the interface affinity between silicon powder and graphite powder is not good, and the expansion effect of silicon powder in the silicon/graphite anode material is limited. Therefore, the present invention covers the silicon/graphite material with a layer of organic carbon source. Amorphous carbon, with a strong structure, can limit the volume expansion of silicon, and can evenly disperse silicon powder on the surface of graphite. The surface affinity between the two is strong to achieve high capacitance and long cycle life.

The silicon-carbon negative electrode material of the present invention is used to make a negative pole piece. The negative pole piece may include: a silicon-carbon negative electrode material. The silicon-carbon negative electrode material includes: an expanded graphite, the expanded graphite having a sheet structure, and a nanometer Silicon powder, the nano silicon powder is dispersed on expanded graphite, and the nano silicon powder has high capacitance characteristics, an amorphous carbon coating layer, the expanded graphite and nano silicon powder are coated with a pitch A coating layer is formed. After the coating layer is sintered, an amorphous carbon coating layer is formed: a meso-carbon microbead (Meso-Carbon Micro Beads, MCMB), and the meso-carbon microsphere can be combined with the silicon carbon The negative electrode material is dry mixed; an adhesive can be used to fix the silicon-carbon negative electrode material and the mesocarbon microspheres after mixing; a promoter can be used to improve the conductivity of the negative electrode piece; wherein, the silicon-carbon negative electrode material The proportion of the negative pole piece is in the range of 1~40%. With this, the capacitance per unit weight of the first turn of the negative pole piece measured is 400-550mAh/g. When the charge and discharge times reach 100 cycles, the capacity retention rate It can reach more than 80%.

Please refer to the second to third figures, which are the measurement results of Example 1 of the silicon-carbon anode material of the present invention. Example 1 uses nanosilica, coal tar pitch, and expanded graphite powder in a liquid phase ratio of 1:1:3. After evenly mixing (using N-methyl-2-pyrrolidone (NMP) as the dispersed phase), calcined at 300℃ and pre-oxygenated After the silicon carbon material is crushed, ground and sieved, the silicon carbon anode material can be obtained. 25% silicon carbon material and 75% interphase carbon micro After the ball is dry-mixed, the negative pole piece is prepared with PAA/CMC/SBR (Poly-(acrylic acid)/Carboxylmethyl Cellulose/Butadiene Rubber) binder and assistant (conductive carbon black). The test results of the half-cell are as As shown in the second figure, the first lap capacity is about 443mAh/g (the general commercial specification in 2018 is 430~450mAh/g), the coulombic efficiency is more than 90%, and the charge and discharge rate is 0.5C down to 100 cycles and can maintain about 80% of the power The silicon-carbon material can suppress the volume expansion of silicon to a certain extent, and can reduce the capacity decline after multiple charging and discharging, and the average decline is only about 0.20% per cycle; in addition, because the expanded graphite acts as a conductive connection between silicon and hard carbon The circuit improves the overall conductivity of the negative electrode and should also be helpful to the cycle life. As shown in the third figure, comparing Example 1 to the control example 1 without adding expanded graphite, the 50th lap capacitance retention rate increased from 83% to 89%.

Please refer to the fourth figure, which is a schematic diagram of the capacitance change (nanosilica/AR pitch/expanded graphite + mesocarbon microspheres, Si/AR/EG+MCMB) of Example 2 of the silicon-carbon anode material of the present invention within 100 cycles The method of Example 2 is the same as that of Example 1. The pitch coating phase is changed to Japanese AR pitch (Aromatic Resin, sourced from Mitsubishi Gas Chemical) with a higher content of the interphase. The silicon-carbon material is made to compare the capacity decline effect. The fourth picture shows the charge and discharge capacity of the silicon carbon material coated with AR pitch. The initial capacity is about 434mAh/g, and then 0.5C charge and discharge. After 100 cycles of charge and discharge, the capacity remains about 395mAh/g. The retention rate is about 91%, and the average lap decline is about 0.09%. The decline of AR asphalt capacity is relatively small; possible reasons The amorphous carbon structure formed by AR pitch with high mesophase content is stronger, and the effect of suppressing the volume expansion of silicon is better. Charging and discharging can reduce the generation of silicon defects; and the capacitance and conductivity of the AR pitch coating layer are higher than that of ordinary coal char The high pitch is helpful for the negative electrode capacity and cycle life. Compared with the pure graphite negative electrode (the capacity is about 350mAh/g), the capacity of the AR pitch-coated silicon-carbon negative electrode after 100 cycles of charge and discharge increases 12.8%.

Please refer to the fifth to sixth figures, which are the experimental results of the silicon-carbon material. As shown in the figure, the silicon-carbon material provided by the present invention uses less than 5% of the binder and can reach a capacitance of 420~450mAh. /g, the capacitance can be maintained 80~90% after 0.5C long cycle charge and discharge. Comparative example 2 uses the mixture of Shin-Etsu SiO _x anode material and mesophase carbon microsphere (SE-SiO _x +MCMB), although the initial charge The capacity is relatively high (approximately 540mAh/g), but the capacity decline is large, and the retention rate to 100 cycles is only 54% (approximately 290mAh/g). This result confirms that the amorphous carbon layer formed by coating asphalt does inhibit silicon Compared with the Shin-Etsu SiO _x negative electrode mixture material that does not use the silicon-carbon negative electrode material of the present invention, the effect of the powder volume expansion is that the negative electrode piece provided by the present invention can maintain a higher capacitance after multiple charge and discharge.

The above-mentioned embodiments are only illustrative to illustrate the features and effects of the present invention, and are not intended to limit the scope of the essential technical content of the present invention. Anyone familiar with this technique can implement the above without departing from the spirit and scope of the invention. Examples are modified and changed. Therefore, the scope of protection of the rights of the present invention should be as listed in the scope of patent application described later.

10‧‧‧Silicon carbon anode material

11‧‧‧Amorphous carbon coating

12‧‧‧Expanded graphite

13‧‧‧Nanosilicon powder

Claims (6)

A silicon-carbon negative electrode material includes: an expanded graphite, the expanded graphite has a sheet-like structure, the particle size of the expanded graphite is 50μm; a nano silicon powder, the nano silicon powder is dispersed on the expanded graphite , And the nanosilica powder has the characteristics of high capacitance, the particle size of the nanosilica powder is 700nm; an amorphous carbon coating layer is an AR pitch dissolved in an organic solvent and then coated with the expanded graphite and Nanosilica powder forms a coating layer, and the coating layer is sintered to form the amorphous carbon coating layer. The silicon-carbon anode material described in item 1 of the scope of patent application, wherein the weight ratio of the nano-silica powder to expanded graphite is 1:99 to 50:50. For the silicon-carbon anode material described in item 1 of the scope of patent application, the weight ratio of the nanosilica powder and expanded graphite is 20:80 to 45:55. The silicon-carbon anode material described in item 1 of the scope of patent application, wherein the weight of the AR pitch is 0.01 to 0.5 times the weight of the expanded graphite and the nanosilica powder. The silicon-carbon anode material described in the first item of the scope of patent application, wherein the weight of the AR pitch is 0.2 to 0.4 times the weight of the expanded graphite and the nanosilica powder. A negative pole piece using the silicon-carbon negative electrode material described in item 1 of the scope of patent application, the negative pole piece comprising: A silicon-carbon anode material, the silicon-carbon anode material includes: an expanded graphite, the expanded graphite having a sheet-like structure, a nanosilica powder, the nanosilica powder is dispersed on the expanded graphite, and the nanosilica powder It has high capacitance characteristics. An amorphous carbon coating layer is formed by dissolving an AR pitch in an organic solvent and coating the expanded graphite and nanosilica powder to form a coating layer, which is formed after sintering. The amorphous carbon coating layer; a mesocarbon microsphere, the mesocarbon microsphere is dry-mixed with the silicon carbon material; an adhesive is used for the silicon carbon anode material and the mesocarbon microsphere Fix after mixing; a promoter is used to improve the conductivity of the negative pole piece; wherein, the ratio of the silicon-carbon negative electrode material to the negative pole piece ranges from 1 to 40%.

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