TWI805421B - Particles of silicon-carbon composite material and method of manufacturing the same - Google Patents

Abstract

The present invention relates to particles of silicon-carbon composite material and a method of manufacturing the same. The particles of the silicon-carbon composite material include a carbon matrix, in which silicon particles and pores distributed. In a cross section of the particles of the silicon-carbon composite material, these pores have a specific size and a specific distribution density, thereby enhancing a capacitance of the resulted negative electrode.

Description

Silicon carbon composite particle and its manufacturing method

The present invention relates to a silicon-carbon composite material particle and a manufacturing method thereof, and in particular to a silicon-carbon composite material particle with holes of a specific size and a specific distribution density and a manufacturing method thereof.

The battery includes a primary cell and a secondary cell, and the secondary cell includes a lithium ion battery. With the improvement of the performance of portable electronic appliances and electric vehicles, the requirements for the capacity of lithium-ion batteries are becoming more and more stringent.

The negative electrode material of the common lithium-ion battery is graphite, and the measured value of its capacitance is close to the theoretical value (about 372mAh/g), so it is necessary to introduce a negative electrode material with a higher capacitance (such as silicon material) to improve the entire lithium-ion battery. The capacity of the battery. As far as silicon material is concerned, the theoretical capacitance value of Li ₁₅ Si ₄ alloy formed from pure silicon is 3580mAh/g.

Although silicon materials can increase the capacity of lithium-ion batteries, the volume change caused by silicon materials in the process of charging and discharging is as high as 280%. The strain caused by the volume change easily causes the particles of the silicon material to be pulverized, thereby reducing the capacitance of the prepared negative electrode.

In view of this, there is an urgent need to develop a new silicon-carbon composite material and its manufacturing method to improve the above-mentioned shortcomings.

In view of the above-mentioned problems, one aspect of the present invention is to provide a silicon-carbon composite material particle, which has a plurality of silicon particles and a plurality of holes dispersed in the carbon matrix, and in the cross-section of the silicon-carbon composite material particle , these pores have a specific size and distribution density, so as to improve the capacitance of the negative electrode produced.

Another aspect of the present invention is to provide a method for manufacturing silicon-carbon composite particles. This manufacturing method is used to manufacture the aforementioned silicon-carbon composite material particles.

According to an aspect of the present invention, a silicon-carbon composite particle is provided. These silicon-carbon composite material particles include carbon matrix, which has a plurality of silicon particles and a plurality of holes. The average particle size of these silicon particles is 45nm to 55nm. The size of these holes is less than 1 μm, and in the cross-section of these silicon-carbon composite particles, the distribution density of these holes is not less than 20/μm ² . The silicon particles and the holes are uniformly dispersed in the carbon matrix.

According to an embodiment of the present invention, the average particle size of the silicon-carbon composite particles is 6 μm to 8 μm.

According to another embodiment of the present invention, the specific surface area of the silicon-carbon composite particles is greater than 35 m ² /g.

According to another embodiment of the present invention, the specific surface area of the silicon-carbon composite particles is greater than 35 m ² /g and not greater than 50 m ² /g.

According to another aspect of the present invention, a method for manufacturing silicon-carbon composite particles is proposed. In this manufacturing method, a plurality of silicon particles are coated with coal tar series pitch to obtain a plurality of pitch coated particles, wherein the softening temperature of coal tar series pitch is 75°C to 95°C, based on coal tar series pitch The weight is 100% by weight, the fixed carbon ratio of coal tar series pitch is 35% to 45% by weight, and the average particle size of these silicon particles is 45nm to 55nm. Then, a carbonization step is performed on these pitch-coated particles to obtain a plurality of silicon-carbon composite particles. Then, the crushing step is performed on the silicon-carbon composite particles to obtain the silicon-carbon composite material particles.

According to an embodiment of the present invention, before performing the coating step, the manufacturing method optionally includes nanonized silicon raw materials to obtain the silicon particles.

According to another embodiment of the present invention, the weight ratio of the coal tar series pitch to the silicon particles is 1:1 to 1:3.

According to yet another embodiment of the present invention, the coating temperature in the coating step is 150°C to 170°C.

According to yet another embodiment of the present invention, prior to the carbonization step, the manufacturing method optionally includes removing the solvent contained in the pitch-coated particles.

According to another embodiment of the present invention, the carbonization temperature in the carbonization step is 800°C to 1000°C.

The silicon-carbon composite particle and its manufacturing method are applied in the present invention, wherein a plurality of silicon particles and a plurality of holes are uniformly dispersed in the carbon matrix. Furthermore, in the cross-section of the silicon-carbon composite particle, the pores have specific size and distribution density, so as to increase the capacitance of the negative electrode produced.

The making and using of embodiments of the invention are discussed in detail below. It should be appreciated, however, that the embodiments provide many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are illustrative only and do not limit the scope of the invention.

The silicon-carbon composite particle of the present invention includes a carbon matrix, wherein a plurality of silicon particles and a plurality of holes are uniformly dispersed in the carbon matrix. These silicon particles have a specific average particle size to reduce the strain difference between the silicon particles and the lithium-silicon alloy, thereby inhibiting the pulverization of the silicon particles during the charging and discharging process, and the silicon particles can also shorten the diffusion path of lithium ions to improve the silicon carbon density. The capacitance of the composite material particles, thereby increasing the capacitance of the prepared negative electrode.

The above-mentioned holes have a specific distribution density to buffer the volume change (such as expansion and contraction) caused by the reaction between the silicon-carbon composite material particles and lithium ions during the charge and discharge process of the negative electrode, thereby improving the stability of the structure of the silicon-carbon composite material particles properties, and increase the life of the lithium-ion battery produced, and the holes can be used as a fast channel to transport lithium ions to silicon particles, so as to improve the capacitance of silicon-carbon composite particles. Furthermore, the pores can increase the reactivity of the silicon-carbon composite particles, so that the lithium-ion battery has fast charging performance and improves the first-time charge-discharge Coulombic efficiency.

Silicon-carbon composite material particles use coal tar series pitch with specific softening temperature and specific fixed carbon ratio to coat silicon particles, and then carbonize to obtain silicon-carbon composite material particles, in which the carbon matrix is formed by carbonization of pitch. This softening temperature can control the texture and fluidity of asphalt, so as to facilitate its uniform mixing with silicon particles, so as to completely and uniformly cover silicon particles. Therefore, the silicon particles and the pores do not contact each other substantially, so as to improve the electronic conductivity of the silicon-carbon composite material particles, and reduce the reaction of the silicon particles in direct contact with the electrolyte (that is, reduce the solid-liquid interface layer), thereby improving the negative electrode. capacitance. Furthermore, the fixed carbon ratio can make the carbon matrix of the obtained silicon-carbon composite material particles have the aforementioned specific size and distribution density of holes, thereby increasing the capacitance of the silicon-carbon composite material particles.

Please refer to FIG. 1 , in the method 100 for producing silicon-carbon composite material particles, a plurality of silicon particles are coated with coal tar series pitch to obtain a plurality of pitch-coated particles, as shown in operation 110 . The softening temperature of coal tar series pitch is 75°C to 95°C, and preferably 80°C to 90°C. If the softening temperature is lower than 75°C, the asphalt contains too many components that are easy to gasify. After the subsequent carbonization step, the carbon matrix formed after carbonization of the asphalt is too thin or has uneven thickness, so the coating effect on silicon particles is not good. good, and reduce the charge and discharge stability of the electrode. On the contrary, if the softening temperature is higher than 95° C., the fluidity of the asphalt is poor, and it is not easy to coat the silicon particles uniformly, thus reducing the charging and discharging stability of the electrode. Based on the weight of the coal tar series pitch being 100% by weight, the fixed carbon ratio of the pitch is 35% by weight to 45% by weight, and preferably 38% by weight to 42% by weight. If the fixed carbon ratio is less than 35% by weight, the carbon matrix formed by carbonization cannot completely cover the silicon particles, or the size of the pores is too large (eg, greater than 1 μm). On the contrary, if the proportion of fixed carbon is greater than 45% by weight, the distribution density of pores is too low (such as less than 20/μm ² ), which reduces the capacitance of the silicon-carbon composite particles.

In some embodiments, at a heating rate of 10°C/min, the first, second, and third weight losses of asphalt occur at 260°C to 265°C, 370°C to 375°C, and 480°C, respectively to 485°C, and the weight loss rates are 22% to 28%, 16% to 22% and 13% to 19%, preferably 25%, 19% and 16%. When the weight loss temperature and weight loss rate of asphalt meet the above conditions, in the subsequent carbonization step, the low molecular weight organic matter in the asphalt (such as organic matter that is easy to gasify) can be gasified to form a size of less than 1 μm and a distribution density of not less than 20 /μm ² pores, so the capacitance of the electrode is further improved.

The average particle size of the aforementioned silicon particles is 45nm to 55nm, and preferably 50nm. If the average particle size is greater than 55nm, the strain difference between silicon and lithium-silicon alloy will increase, which will easily cause the silicon-carbon composite material particles to break after repeated charge and discharge, thus reducing the charge and discharge stability of the electrode. If the average particle size is less than 45nm, the silicon particles are easy to aggregate, and it is difficult to exert the effect of nanometerization, so it is not helpful to improve the capacitance and electrode charge and discharge stability.

In some embodiments, the weight ratio of pitch to silicon particles is 1:1 to 1:3, preferably 1:1.5 to 1:2.5, and more preferably 1:2. When the weight ratio is within the aforementioned range, the pitch can completely cover the silicon particles to increase the capacitance of the electrode.

In some embodiments, the coating temperature in the coating step is 150°C to 170°C. When the coating temperature is in the above range, the pitch can completely cover the silicon particles to increase the capacitance of the electrode. The coating time is not particularly limited, but is for the purpose of completely coating the silicon particles.

Before performing the coating step, the manufacturing method 100 may optionally include nanonized silicon raw materials to obtain silicon particles. There are no special restrictions on nanonization, but the purpose is to make silicon raw materials into silicon particles with an average particle size of 45nm to 55nm, and the conditions can be known to those with ordinary knowledge.

After operation 110 , a carbonization step is performed on the pitch-coated particles to obtain a silicon-carbon composite, as shown in operation 120 . The carbonization step can be performed under the environment of inert gas (such as nitrogen, argon, helium and combinations thereof).

The carbonization temperature in the carbonization step is 800°C to 1000°C. When the carbonization temperature is within the aforementioned range, the carbonization effect is relatively complete, thereby improving the conductivity of the electrode. The carbonization time of the carbonization step is aimed at achieving the aforementioned complete carbonization effect.

In some embodiments, before the carbonization step, the manufacturing method 100 may optionally include removing the solvent contained in the pitch-coated particles, so as to obtain the aforementioned silicon particles with a specific average particle size. The method for removing the solvent may be heating.

After operation 120 , a crushing step is performed on the silicon-carbon composite particles to obtain silicon-carbon composite material particles, as shown in operation 130 . The crushing step is not particularly limited, but the purpose is to achieve the above-mentioned specific average particle size.

The manufacturing method 100 can exclude the use of graphite and/or surfactants, so the carbon matrix of the obtained silicon-carbon composite particles does not have graphite. This is because additional graphite and surfactant will affect the coating of silicon particles and the formation of holes. In addition, the manufacturing method 100 may also exclude the use of organic acids and/or inorganic acids. This is because the coal tar series pitch of the present invention has specific softening temperature and fixed carbon ratio, so the low molecular weight organic matter contained in it can be gasified or oxidized into gas (such as carbon dioxide or carbon dioxide) in the drying step and/or carbonization step. /and low-carbon oxide gas) to leave holes, so it is not necessary to use acid to etch and/or oxidize the carbon matrix to create holes.

Please refer to FIG. 2 , the silicon-carbon composite particle 200 produced by the aforementioned manufacturing method includes a carbon matrix 230 having a plurality of silicon particles 210 and a plurality of holes 220 . The two are uniformly distributed in the carbon matrix 230 formed by the aforementioned pitch carbonization.

The silicon particle 210 is the silicon particle used in the aforementioned manufacturing method, which has high temperature stability, so after the aforementioned coating step, carbonization step, drying step, and crushing step, the average particle diameter d of the silicon particle 210 does not change. 45nm to 55nm.

The size of the hole 220 is less than 1 μm, and preferably 50 nm to 500 nm. If the size is not less than 1 μm, the pores 220 cannot buffer the volume change caused by the reaction between the silicon-carbon composite particle 200 and lithium ions during the charging and discharging process.

In addition, in the cross-section of the silicon-carbon composite particle 200 , the distribution density of the holes 220 is not less than 20/μm ² , and preferably greater than 30/μm ² and not greater than 50/μm ² . If the distribution density is less than 20/μm ² , the pores 220 cannot buffer the aforementioned volume change during the charging and discharging process. When the distribution density is greater than 30/μm ² and not greater than 50/μm ² , the pores 220 can not only buffer the volume change mentioned above, but also facilitate the faster transmission of lithium ions to the silicon particles 210, so as to further improve the silicon-carbon recombination. Capacitance of material particles 200 .

The specific surface area of the silicon-carbon composite particle 200 refers to the sum of the external surface area of the silicon-carbon composite particle 200 and the surface area of the internal hole 220 per unit weight. In some embodiments, the specific surface area of the silicon-carbon composite particle 200 is greater than 35 m ² /g. When the specific surface area is within the aforementioned range, the reactivity of the silicon-carbon composite particle 200 can be increased to increase its capacitance. Preferably, the specific surface area may be greater than 35m ² /g and not greater than 50m ² /g, and more preferably may be 35m ² /g to 45m ² /g.

In some embodiments, the average particle diameter D of the silicon-carbon composite particles 200 may be 6 μm to 8 μm. When the average particle size D is within the aforementioned range, the silicon-carbon composite material particles 200 can be uniformly dispersed in the slurry and facilitate the coating of the slurry on the substrate during the subsequent preparation of the negative electrode, thereby increasing the capacitance of the electrode.

In some embodiments, based on 100% by weight of the silicon-carbon composite particle 200 , the silicon content of the silicon-carbon composite particle 200 may be 71 to 88% by weight. When the silicon content is within the aforementioned range, the capacitance of the silicon-carbon composite particle 200 is increased, thereby increasing the capacitance of the electrode. In some specific examples, based on 100% by weight of the silicon-carbon composite particle 200 , the carbon content of the silicon-carbon composite particle 200 may be 12% by weight to 29% by weight.

The following examples are used to illustrate the application of the present invention, but they are not intended to limit the present invention. Anyone skilled in this art can make various changes and modifications without departing from the spirit and scope of the present invention.

Preparation of Silicon Carbon Composite Particles

Example 1

The silicon-carbon composite material in Example 1 was prepared by grinding micron-sized silicon wafer cutting waste with yttrium-stabilized zirconia beads with a particle size of 0.05 mm to obtain a grinding liquid containing silicon particles. Add coal tar pitch (model is RBP-85, softening temperature is 85°C, fixed carbon is 40% by weight, manufacturer is China Steel Carbon Co., Ltd.) into the grinding liquid, heated to 160°C, stirred for 30 minutes to coat, Then, the temperature was raised to 310° C. to remove the solvent to obtain pitch-coated particles. Carbonization is carried out under nitrogen to obtain silicon-carbon composite particles. Then, the silicon-carbon composite particles were pulverized by a vibrating grinder, and sieved with a 400-mesh sieve to obtain silicon-carbon composite particles, the silicon content of which was 71 to 88% by weight. Then, an evaluation test described later was performed.

Embodiment 2 and Comparative Example 1

The silicon-carbon composite material particles of Example 2 and Comparative Example 1 were produced in a method similar to that of Example 1. The difference is that Example 2 uses half the amount of pitch, and Comparative Example 1 uses different pitch (model is HSP-260, softening temperature is 260°C, fixed carbon is 60% by weight, and the manufacturer is Sinosteel Carbon Corporation). The specific conditions and evaluation results of Examples 1 to 2 and Comparative Example 1 are shown in Table 1 below.

Electrodes for lithium-ion batteries

Application example 1

Based on the total weight of silicon-carbon composite material particles and mesophase pitch graphite as 100% by weight, application example 1 is to mix 14% by weight of silicon-carbon composite material particles of Example 1 into mesophase pitch graphite evenly to obtain negative electrode active substance. Then the active material of the negative electrode, carboxymethyl cellulose, styrene-butadiene rubber and conductive carbon black (manufactured by TIMCAL, and the model is super P) with a weight ratio of 92:1.5:3:3.5 were formulated into Water-based slurry. Then, the aqueous slurry was coated on the copper foil with a doctor blade in an amount of 6 mg/cm ² . After vacuum baking at 110°C for 8 hours, the negative electrode (also known as silicon carbide/graphite negative electrode) of Application Example 1 was prepared, and the negative electrode was used to assemble a lithium-ion battery for subsequent evaluation.

Application Example 2 and Comparative Application Example 1

Both application example 2 and comparative application example 1 were carried out in a method similar to application example 1. The difference is that Application Example 2 and Comparative Application Example 1 use the silicon-carbon composite material particles of Example 2 and Comparative Example 1, respectively. The evaluation results of Application Examples 1 to 2 and Comparative Application Example 1 are shown in Table 2 below.

Evaluation method

1. Test of softening temperature and fixed carbon ratio

The test of the softening temperature and the ratio of fixed carbon uses a thermogravimetric analyzer to measure the softening temperature of asphalt and its weight loss rate at 850°C at a heating rate of 10°C/min, and expresses the fixed carbon of the asphalt Ratio, wherein the thermogravimetric analysis diagram is shown in Figure 3 and Figure 4.

2. Test of average particle size

The average particle size is measured by electron micrographs of silicon particles and silicon-carbon composite particles taken by an electron microscope.

3. Test of hole size and distribution density

The test of the size and distribution density of the pores is to observe the cross-sectional image of a single particle of silicon-carbon composite material particles with an electron microscope, and measure the size of the internal pores of a single silicon-carbon composite material particle, so as to pass through the cross-sectional image of the hole The average value of the longest and shortest straight lines at the center of mass represents the size of the hole, and the average value of multiple measured values is used to represent the internal hole size of a single silicon-carbon composite material. In addition, in the cross-sectional image of the holes, the number of holes within an area of 1 μm ² is calculated to represent the density of the inner holes of a single silicon-carbon composite material.

4. Test of specific surface area

The specific surface area test is to measure the specific surface area of the silicon-carbon composite particles with a specific surface area analyzer and according to the BET theory.

5. Capacitance test

Capacitance test is a CR2032 button half-cell composed of silicon carbide/graphite negative electrode and carbonate electrolyte. Then charge the half-cell with a charge-discharge machine (manufactured by Arbin Instruments, model BT 2043). First charge to 0.001V with a constant current of 0.1C, then charge at a constant voltage until the current is less than 0.01C, then discharge at a constant current of 0.1C to 1.5V, and then charge at a constant voltage until the current is less than 0.01C, this is one cycle. Repeat 3 cycles in this way as a formation procedure to obtain the capacitance of the silicon carbide/graphite negative electrode. In addition, the aforementioned 4 cycles were performed using the graphite negative electrode to measure the capacitance of the graphite negative electrode. Then, the capacitance of the silicon carbon/graphite negative electrode is deducted from the capacitance of the graphite negative electrode to calculate the capacitance of the silicon-carbon composite particle.

6. The test of cycle charge and discharge capacity maintenance rate and first charge and discharge coulombic efficiency

The test of the cycle charge and discharge capacity maintenance rate is carried out in the same way as the capacity test, and the cut-off conditions are also the same. The difference is that the cycle life test is to adjust the charge and discharge current to 0.5C, and repeat 100 cycles , to measure the cycle charge-discharge capacity maintenance rate, where the ratio of the discharge capacity measured for the first time to the charge capacity is called the first charge-discharge coulombic efficiency, and the cycle charge-discharge capacity retention rate measured by repeating 100 cycles is used for evaluation cycle life.

Table 1

Table 2

Please refer to Table 1 and Figures 3 to 8, compared with Comparative Example 1 using too high softening temperature and fixed carbon ratio pitch, Examples 1 to 2 use appropriate softening temperature and fixed carbon ratio pitch, so obtained The silicon-carbon composite material particles have a porous structure, and the carbon matrix coats the silicon particles, and in the cross-section of the silicon-carbon composite material particles, the holes in Example 1 (as shown in Figure 5) and the holes in Example 2 (as shown in Figure 5) 6 to 7) have appropriate size and distribution density, thereby improving the capacitance of the negative electrode. However, the silicon-carbon composite particles of Comparative Example 1 do not have a porous structure (as shown in FIG. 8 ), thus reducing the capacitance of the negative electrode.

In summary, the silicon-carbon composite particle and its manufacturing method of the present invention utilize a plurality of silicon particles and a plurality of holes uniformly dispersed in the carbon matrix, and in the cross-section of the silicon-carbon composite particle, these holes It has a specific size and a specific distribution density to improve the capacitance of the prepared negative electrode.

Although the present invention has been disclosed above in terms of implementation, it is not intended to limit the present invention. Anyone with ordinary knowledge in the technical field of the present invention can make various modifications and changes without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be defined by the scope of the appended patent application.

100: method 110, 120, 130: operation 200: silicon carbon composite particles 210: silicon particles 220: hole d, D: particle size 230: carbon matrix

In order to have a more complete understanding of the embodiments of the present invention and their advantages, please refer to the following descriptions together with the corresponding drawings. It must be emphasized that the various features are not drawn to scale and are for illustration purposes only. The contents of relevant diagrams are explained as follows: FIG. 1 is a flowchart illustrating a method for manufacturing silicon-carbon composite material particles according to an embodiment of the present invention. FIG. 2 is a schematic diagram illustrating silicon-carbon composite material particles according to an embodiment of the present invention. FIG. 3 is a thermogravimetric analysis diagram of coal tar series pitch according to Embodiment 1 and Embodiment 2 of the present invention. Fig. 4 is a graph showing the thermogravimetric analysis of the coal tar series pitch according to Comparative Example 1 of the present invention. FIG. 5 is an electron micrograph showing the cross-section of the silicon-carbon composite particle according to Example 1 of the present invention. 6 and 7 are electron micrographs showing the cross-section of the silicon-carbon composite particle according to Example 2 of the present invention. FIG. 8 is an electron micrograph showing the cross-section of the silicon-carbon composite particle according to Comparative Example 1 of the present invention.

200: silicon carbon composite particles

210: silicon particles

220: hole

d, D: particle size

230: carbon matrix

Claims (9)

A silicon-carbon composite particle, comprising: a carbon matrix, having: a plurality of silicon particles, wherein the average particle diameter of one of the silicon particles is 45nm to 55nm; and a plurality of holes, wherein the size of one of the holes is less than 1 μm , and in a cross-section of the silicon-carbon composite material particles, a distribution density of the pores is greater than 30/μm ² and not greater than 50/μm ² ; wherein the silicon particles and the pores are uniformly dispersed in the carbon matrix. The silicon-carbon composite particle according to claim 1, wherein an average particle diameter of the silicon-carbon composite particle is 6 μm to 8 μm. The silicon-carbon composite particle according to claim 1, wherein a specific surface area of the silicon-carbon composite particle is greater than 35m ² /g. The silicon-carbon composite particle according to claim 3, wherein a specific surface area of the silicon-carbon composite particle is greater than 35m ² /g and not greater than 50m ² /g. A method for manufacturing silicon-carbon composite particles, comprising: using a coal tar series pitch to coat a plurality of silicon particles to obtain a plurality of pitch coated particles, wherein the softening temperature of one of the coal tar series pitches is 75 ℃ to 95℃, based on one of the coal tar series pitch The amount is 100% by weight, the fixed carbon ratio of the coal tar series pitch is 35% to 45% by weight, the weight ratio of the coal tar series pitch to the silicon particles is 1:1 to 1:3, and the One of the silicon particles has an average particle size of 45nm to 55nm; a carbonization step is performed on the pitch-coated particles to obtain a plurality of silicon-carbon composite particles, wherein a carbonization temperature of the carbonization step is 800°C to 1000°C; and A crushing step is performed on the silicon-carbon composite particles to obtain the silicon-carbon composite material particles. The manufacturing method as described in Claim 5, wherein before the coating step, the manufacturing method further includes nanonizing silicon raw materials to obtain the silicon particles. The manufacturing method according to claim 5, wherein in a cross section of the silicon-carbon composite particles, a distribution density of the pores is greater than 30/μm ² and not greater than 50/μm ² . The manufacturing method according to claim 5, wherein a coating temperature in the coating step is 150°C to 170°C. The manufacturing method according to claim 5, wherein before the carbonization step, the manufacturing method further includes removing a solvent contained in the pitch-coated particles.

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