WO2023210869A1 - Method for preparing silicon anode material, for lithium-ion secondary battery, to which boron oxide is applied - Google Patents

Abstract

The present invention relates to a method for preparing a silicon anode material, for a lithium-ion secondary battery, to which boron oxide is applied and, more specifically, to a method for preparing a silicon anode material, for a lithium-ion secondary battery, to which boron oxide is applied, which can not only lower the unit price of an anode material by using planar silicon formed from silicon kerf, but also prepare a silicon material having a suppressed initial irreversible capacity by including boron oxide.

Description

Manufacturing method of silicon anode material for lithium-ion secondary battery using boron oxide

The present invention relates to a method of manufacturing a silicon anode material for a lithium-ion secondary battery to which boron oxide is applied. More specifically, by using plate-shaped silicon formed from a waste silicon kerf, not only can the unit cost of the anode material be lowered, but also boron oxide can be used. This relates to a method of manufacturing a silicon anode material for a lithium-ion secondary battery using boron oxide, which can produce a silicon anode material with improved initial capacity and lifespan performance.

Generally, graphite has been used as the negative electrode active material for lithium-ion secondary batteries. Graphite has a theoretical capacity of 372 mAh/g of lithium ion charging capacity, and in reality, it is a material with a capacity of 360 mAh/g and has a layered structure, with a mechanism in which lithium is inserted between layers and charged.

Meanwhile, silicon is a lithium ion storage material for anode materials that has a larger capacity than graphite. Silicon is a material with a theoretical capacity of 4200mAh/g. However, when charged to 4200 mAh/g, four lithium ions are combined with one silicon, causing the volume to expand more than three times. Silicon, which has expanded in volume, cannot return to its original state when lithium escapes, cracks occur, and is separated into fine nanoparticles, many of which are electrically disconnected from the electrolyte or electrolyte solution, making it impossible to recharge lithium. For this reason, silicon anode active material has a short charge/discharge life and has not been used as an anode active material to replace graphite.

Many technological improvements have been attempted to prevent cracks caused by charging and discharging of silicon anode active materials or to make them smaller to prevent cracks from occurring, but they have not been successful.

Silicon used as a negative electrode active material is mainly made of metallic silicon with a purity of 99.9% or higher. Since it was discovered that cracks caused by lithium charging and discharging are reduced when nano-sized silicon is used, much effort has been made to create nano-silicon.

Specifically, a method of using plasma to decompose micro particles and recombine them into nano size, a method of making silicon into a small rod and explosively vaporizing it in a solution by passing a large current to make it into nano size, melting it with silane gas or liquid and thermally decomposing it, and then making it into nano size. How to recombine by size, etc.

In the present invention, waste silicon kerf (silicon kerf) generated in the process of cutting a lump of metal silicon into thin pieces to obtain a silicon wafer in the solar cell industry or semiconductor industry is used. Here, the waste silicon cuff is high-purity silicon with a purity of 99.9999999% to 99.999999999% used in the solar cell industry or semiconductor industry, and by using a wire-shaped saw, it comes off as a nano-thick plate-shaped material. Such high-purity plate-shaped silicon is a good candidate for anode active material for lithium secondary batteries.

As a prior art, Republic of Korea Patent Publication No. 10-1847235, “Graphite material for negative electrode of lithium ion secondary battery and manufacturing method thereof, lithium ion secondary battery” is described.

Therefore, the present invention was proposed to improve this conventional problem. By using plate-shaped silicon formed from a waste silicon kerf, the unit cost of the anode material can be lowered, and by applying boron oxide, the initial capacity and lifespan can be improved. The purpose is to provide a method for manufacturing silicon anode materials for lithium-ion secondary batteries using boron oxide, which can produce silicon anode materials with improved performance.

In order to solve the above problem, the method for manufacturing a silicon anode material for a lithium-ion secondary battery to which boron oxide is applied according to an embodiment of the present invention is to crush the plate-shaped silicon formed from a waste silicon kerf to an apparent particle size of 0.1 to 0.4 g/cm3. First disintegration step to create density; An oxidation step of oxidizing the surface of the plate-shaped silicon particles to form silicon oxide with an oxide film; It may include a boron oxide coating step of coating boron oxide on the surface of the silicon oxide to form a boron oxide coating film, and a carbon coating step of coating the surface of the boron oxide coating film with conductive carbon to form a plate-shaped silicon composite with a carbon coating film. there is.

In addition, before the first disintegration step, a pretreatment step of wet milling and drying the plate-shaped silicon to form plate-shaped silicon particles may be further included.

In addition, after the boron oxide coating step, a secondary disintegration step of disintegrating the silicon oxide on which the boron oxide coating film is formed may be further included.

In addition, after the carbon coating step, a mixing step of mixing the plate-shaped silicon composite and graphite to form a mixture may be further included.

In addition, the plate-shaped silicon is characterized in that it is formed with an average thickness of 10 to 100 nm and an average length of 10 μm or less.

Additionally, the oxidation step is characterized in that the silicon oxide film is formed with an average thickness of 2 to 10 nm.

Additionally, the oxidation step is characterized in that an oxidizing agent is added to the plate-shaped silicon particles and heated to 700 to 1,100°C.

Additionally, the boron oxide coating step is characterized by adding an aqueous boric acid solution to the silicon oxide and heating it to 550 to 700°C.

In addition, the carbon coating step is characterized in that the average thickness of the carbon coating film is formed to be 3 to 20 nm.

In addition, the carbon coating step is characterized in that one of hydrocarbon gas, liquefied natural gas, and liquefied petroleum gas is selected and added to the silicon oxide that has completed the boron oxide coating step, and thermally decomposed at 750 to 1000 ° C.

The method for manufacturing a silicon anode material for a lithium-ion secondary battery to which boron oxide is applied according to an embodiment of the present invention can lower the unit cost of the anode material by using plate-shaped silicon formed from a waste silicon kerf.

In addition, it is possible to manufacture a silicon anode material with an excellent filling ratio by complexing it with plate-shaped graphite.

Additionally, by increasing the performance of the silicon anode material, more lithium can be charged compared to the same volume.

In addition, by applying boron oxide, a silicon anode material with improved initial capacity and lifespan performance can be manufactured.

In addition, the effects according to the embodiments of the present invention mentioned above are not limited to the contents described, and may further include all effects predictable from the specification and drawings.

Figure 1 is a flow chart of a method for manufacturing a silicon anode material for a lithium ion secondary battery to which boron oxide is applied according to an embodiment of the present invention.

Figure 2 is a flow chart of Figure 1 further including a pretreatment step, a secondary disintegration step, and a mixing step.

Figure 3 is an SEM photo of plate-shaped silicon used in the method of manufacturing a silicon anode material for a lithium-ion secondary battery to which boron oxide is applied according to an embodiment of the present invention.

Figure 4 is an example diagram showing the appearance of the plate-shaped silicon of Figure 3.

Figure 5 is an exemplary diagram showing the appearance of plate-shaped silicon particles formed in the pretreatment step of Figure 2.

Figure 6 is an exemplary diagram showing the appearance of silicon oxide formed in the oxidation step of Figure 2.

FIGS. 7A and 7B are TEM images of the silicon oxide of FIG. 6.

Figure 8 is an example diagram showing boron oxide partially coated on silicon oxide in the boron oxide coating step of Figure 2.

Figure 9 is an exemplary diagram showing the appearance of a plate-shaped silicon composite formed in the carbon coating step of Figure 2.

Figure 10 is a TEM photo of the plate-shaped silicon composite of Figure 9.

Figure 11 is an exemplary view showing the mixture formed in the mixing step of Figure 2.

Figure 12 is an exemplary view showing another type of mixture formed in the mixing step of Figure 2.

Figure 13 is a graph of the half cell charge/discharge test results of Comparative Example 1.

Figure 14 is a graph of the half cell charge/discharge test results of Comparative Example 2.

Figure 15 is a graph of the half cell charge/discharge test results of Comparative Example 3.

Figure 16 is a graph of the half cell charge/discharge test results of Example 1.

Figure 17 is a graph of the half cell charge/discharge test results of Example 2.

The method for manufacturing a silicon anode material for a lithium-ion secondary battery to which boron oxide is applied according to an embodiment of the present invention is a first step of disintegrating plate-shaped silicon formed from a waste silicon kerf to have an apparent density of 0.1 to 0.4 g/cm3. disintegration stage; An oxidation step of oxidizing the surface of the plate-shaped silicon particles to form silicon oxide with an oxide film; It may include a boron oxide coating step of coating boron oxide on the surface of the silicon oxide to form a boron oxide coating film, and a carbon coating step of coating the surface of the boron oxide coating film with conductive carbon to form a plate-shaped silicon composite with a carbon coating film. there is.

Hereinafter, the description of the present invention with reference to the drawings is not limited to specific embodiments, and various changes may be made and various embodiments may be possible. In addition, the content described below should be understood to include all conversions, equivalents, and substitutes included in the spirit and technical scope of the present invention.

In the following description, the terms first, second, etc. are terms used to describe various components, and their meaning is not limited, and is used only for the purpose of distinguishing one component from other components.

Like reference numerals used throughout this specification refer to like elements.

As used herein, singular expressions include plural expressions, unless the context clearly dictates otherwise. In addition, terms such as “comprise,” “provide,” or “have” used below are intended to designate the presence of features, numbers, steps, operations, components, parts, or a combination thereof described in the specification. It should be construed and understood as not excluding in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts or combinations thereof.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying FIGS. 1 to 17.

Figure 1 is a flowchart of a method for manufacturing a silicon anode material for a lithium ion secondary battery to which boron oxide is applied according to an embodiment of the present invention, and Figure 2 is a flowchart further including a pretreatment step, a secondary disintegration step, and a mixing step in Figure 1, Figure 3 is an SEM photograph of plate-shaped silicon used in the method of manufacturing a silicon anode material for lithium ion secondary batteries to which boron oxide is applied according to an embodiment of the present invention, Figure 4 is an exemplary view showing the shape of plate-shaped silicon in Figure 3, and Figure 5 is an exemplary diagram showing the appearance of plate-shaped silicon particles formed in the pretreatment step of FIG. 2, FIG. 6 is an exemplary diagram showing the appearance of silicon oxide formed in the oxidation step of FIG. 2, and FIGS. 7A and 7B are the silicon oxide of FIG. 6. is a TEM photo, and Figure 8 is an example diagram showing boron oxide partially coated on silicon oxide in the boron oxide coating step of Figure 2, and Figure 9 is a view of the plate-shaped silicon composite formed in the carbon coating step of Figure 2. Figure 10 is a TEM photo of the plate-shaped silicon composite of Figure 9, Figure 11 is an example showing the mixture formed in the mixing step of Figure 2, and Figure 12 is another shape formed in the mixing step of Figure 2. This is an example diagram showing the appearance of a mixture.

The present invention not only lowers the unit cost of the anode material by using plate-shaped silicon formed from a waste silicon kerf, but also uses boron oxide to produce a silicon anode material with improved initial capacity and lifespan performance. It relates to a method of manufacturing silicon anode materials for secondary batteries.

Referring to Figure 1, the method for manufacturing a silicon anode material for a lithium ion secondary battery using boron oxide according to an embodiment of the present invention includes a first disintegration step (S10), an oxidation step (S20), a boron oxide coating step (S30), and a carbon It may include a coating step (S40).

In the first disintegration step (S10), the plate-shaped silicon 10 formed of a waste silicon kerf is disintegrated to have an apparent density of 0.1 to 0.4 g/cm3.

This is for easy reaction with gas in the post-process, and the plate-shaped silicon 10 can be disintegrated to form spaces between particles. As the average distance between particles of the plate-shaped silicon 10 increases in this way, the oxide film 31 can be formed uniformly in the oxidation step (S20), which is a post-process.

Here, the plate-shaped silicon 10 may be a powder formed in a plate shape, as shown in FIGS. 3 and 4. Plate-shaped silicon can be formed from waste silicon cuffs (cutting fines) generated during the process of thinly slicing a silicon ingot for solar cells or semiconductors.

There are generally 3 to 4 types of silicon ingot cutting methods, and in all methods, a waste silicon cuff can be obtained through classification, washing, precipitation, and drying steps. In order to obtain a waste silicone cuff with high thickness uniformity, it is preferable to use a waste silicone cuff made through a diamond wire saw, but is not limited to this.

Specifically, a diamond wire saw is a method of cutting silicon ingots using water or diethylene glycol as a lubricant with diamond particles randomly embedded on the surface of a carbon steel wire called a piano wire of about 50㎛. Silicon ingots include single crystal ingots and polycrystalline ingots, and have the advantage that all cutting fines are suitable for the plate-shaped silicon (10) of the present invention.

The plate-shaped silicon 10 formed of a waste silicon kerf may be formed to have an average thickness of 10 to 100 nm and an average length of 10 μm or less.

Here, if the average thickness of the plate-shaped silicon 10 is less than 10 nm, too much is lost when forming the oxide film 31, and the initial capacity may be less than 60% of the pre-processing value, which may greatly reduce economic efficiency. If the average thickness exceeds 100 mm, This is because in the case where the ratio of the oxide film 31 is less than 20%, the number of particles increases, and the effect of improving lifespan performance may be greatly reduced.

In addition, when the average length of the plate-shaped silicon 10 is more than 10㎛, when mixed with graphite particles, a lot of empty space is formed between the graphite 51 and the plate-shaped silicon composite 40 particles, so that the porosity in the same space increases and the filling rate increases. Otherwise, the discharge capacity may drop significantly in the same volume.

On the other hand, the plate-shaped silicon 10 may be bent and curled as strong force is applied during the cutting process and the silicon separates from the single crystal into a plate shape, and many fine single crystals may be weakly attached. Accordingly, the plate-shaped silicon 10 can be made into a state more suitable for an anode material through crushing pretreatment.

To this end, referring to FIG. 2, the method for manufacturing a silicon anode material for a lithium ion secondary battery of the present invention may include a pretreatment step (S5) before the first disintegration step (S10).

The pretreatment step (S5) can produce plate-shaped silicon particles (2) as shown in FIG. 5 by wet milling and drying the plate-shaped silicon (10) before the first disintegration step (S10).

At this time, the method of wet milling the plate-shaped silicon 10 may be a bead mill (ball mill), ultrasonic dispersion, or high-pressure homogenizer dispersion method.

First, the bead mill mixes 5 to 30% of plate-shaped silicon (10) in water or an organic solvent, then rotates it with zirconia or alumina beads in a zirconia or alumina container and crushes it by friction and impact force between balls. The bead mill preferably uses beads with a diameter of 0.5 to 3 mm, and crushes them by rotating them at 1,000 to 5,000 rpm based on a container diameter of 100 mm.

When using a bead mill, if the bead diameter is less than 0.5mm, the impact force may be weak and crushing may not be possible, and if it is more than 3mm, the number of beads may be too small, reducing the probability of collision with the plate-shaped silicon (10), making crushing time unnecessary. It can be long.

In addition, if the rotation speed is less than 1000 rpm, the energy required for crushing may be low and the energy required for crushing may not be sufficient, and if it exceeds 5000 rpm, bead wear may occur due to excessive high energy and may be mixed with the plate-shaped silicon 10 as an impurity.

Ultrasonic dispersion is a method of attaching an amplifying horn and a vibrating horn to an ultrasonic vibrator and applying ultrasonic vibration to the solution to disperse or destroy the particles in the solution. It is desirable for ultrasonic dispersion to process the plate-shaped silicon 10 under the conditions of a frequency of 20 to 35 KHz, an amplitude of 20 to 200 μm, and a vibrator power consumption of 200 W or more. In addition, ultrasonic dispersion is possible by mixing plate-shaped silicon 10 in water or an organic solvent in a range of 30% or less and then receiving ultrasonic vibrations from a plurality of oscillators while passing through a passage in which a plurality of oscillators are arranged in a row.

At this time, if the vibrator power consumption is less than 200W, the energy may be too low and almost no shredding may occur. In addition, if the frequency is less than 20 KHz, it may not be easy to operate because it cannot exceed the audible frequency, and if it is more than 35 KHz, it only reduces the durability of the vibrator and vibration generator and has no effect on shredding or improving the working environment.

In addition, if the plate-shaped silicon 10 is mixed in water or an organic solvent in an amount exceeding 30%, the viscosity may become too high and the transmission range of ultrasonic vibration may not be wide.

A high-pressure homogenizer is a device that disperses or destroys the powder in the solution by applying pressure using a pump to pass the solution through a fine nozzle in the opposite direction. There are also methods of using a high-pressure homogenizer that combine collision, such as a method of colliding with a diamond plate after passing through a fine nozzle, or a method of colliding solutions with each other by passing through a nozzle in both directions. In the present invention, a method of mixing plate-shaped silicon (10) in water or an organic solvent in the range of 30% or less, pressurizing at 500 bar or more, passing through a fine nozzle of 50 to 200㎛, and colliding or mutually colliding with a diamond plate is used. It's good.

At this time, if the plate-shaped silicon 10 is mixed in water or an organic solvent in an amount exceeding 30%, the viscosity may become too high, making it difficult to inject into the fine nozzle. Additionally, if the pressure is less than 500 bar, the collision energy may be weakened and crushing may be almost impossible.

Additionally, if the fine nozzle diameter is less than 50㎛, nozzle clogging may occur frequently, which may make process operation difficult. If it exceeds 200㎛, the collision energy may be so weak that crushing may hardly occur.

In addition, it is preferable that the crushed plate-shaped silicon particles 20 obtained from one of the above bead mills, dispersers, and homogenizers are recovered in a dried powder state. At this time, various drying devices capable of vaporizing moisture and organic solvents can be used, but it is preferable to use a spray dryer or a disk dryer.

Here, the spray dryer spreads the dispersion solution containing the crushed plate-shaped silicon particles 20 into the atmosphere through a spray nozzle or a rotating disk nozzle (atomizer) and injects heated gas to rotate around the nozzle, causing the solution to scatter. There is an advantage in obtaining dry powder with a low apparent density using a drying device, but the thermal efficiency is not good.

The disk dryer has high thermal efficiency, and the dispersion solution containing the crushed plate-shaped silicon particles (20) is dropped little by little onto a heated rotating disk, dried, and the dried residue, the crushed and dried plate-shaped silicon particles (20), is recovered by scraping with a ceramic knife. This is the way to do it. Disk dryers have good thermal efficiency, but have the disadvantage of recovering powder with a high apparent density.

Although the moisture and lubricant in the waste silicon cuff were removed from the plate-shaped silicon particles 20 that were crushed and dried through the pretreatment step (S1) as described above, for easy reaction with gas in the post-process, the first crushing step (S10) ), the crushed and dried plate-shaped silicon particles 20 can be pulverized to form spaces between the particles.

The crushed and dried plate-shaped silicon particles 20 have an apparent density of 1 to 2 g/cm3, which is pulverized at 3,000 rpm under air in the first crushing step (S10), and have an apparent density of 0.2 to 0.4 g/cm3. Plate-shaped silicon particles 20 can be obtained.

Accordingly, the average distance between particles of the plate-shaped silicon particles 20 may be 3 to 10 times greater than that of the crushed and dried plate-shaped silicon 10. Therefore, the first disintegration step (S10) can ensure that the oxide film 31 is formed uniformly in the subsequent oxidation step (S20).

In addition, the primarily pulverized plate-shaped silicon 10 or plate-shaped silicon particles 20 have a high specific surface area of 10 m 2 /g or more, and thus have a large contact area with the electrolyte solution or electrolyte. These characteristics of plate-shaped silicon ensure high charging and discharging speeds, but there is a problem in that silicon shattering occurs quickly due to rapid charging and discharging. To solve this problem, the present invention reduces the charge and discharge speed by forming an oxide film 31 on the plate-shaped silicon 10 or plate-shaped silicon particles 20 in the oxidation step (S20), which will be described below.

Referring to FIG. 6, the oxidation step (S20) oxidizes the surface of the plate-shaped silicon 10 or the plate-shaped silicon particles 20 to create silicon oxide 30 on which the oxide film 31 is formed. In the following, the description will be based on the plate-shaped silicon particles 20.

The oxidation step (S20) may be performed by additionally oxidizing the naturally formed oxide film on the surface of the plate-shaped silicon particle 20 to form a thick oxide film.

At this time, the oxide film 31 is formed in an amorphous state, and when lithium approaches the oxide film 31, the gap between the oxide films 31 is filled with lithium and a battery conductive line penetrating the oxide film 31 may be formed. The oxide film 31 can allow the electrolyte solution or lithium in the electrolyte to slowly diffuse into the plate-shaped silicon particles 20. Accordingly, the silicon anode material manufactured by the manufacturing method of the present invention lowers the bonding speed between lithium and the plate-shaped silicon particles 20 through the oxide film 31, so the charging capacity is somewhat lower than that of existing silicon, but the charge and discharge life is dramatically increased. You can.

In the oxidation step (S20), an oxidizing agent may be added to the plate-shaped silicon particles 20 using a rotary kiln and heated to 700 to 1,100°C.

At this time, if the heating temperature is less than 700°C, the formation rate of the oxide film 31 becomes too slow and the reaction time becomes excessively long, so the oxide film 31 may not be formed entirely or may be difficult to form to the desired thickness. If the heating temperature exceeds 1,100°C, In this case, the plate-shaped silicon particles 20 may be damaged due to excessive temperature or the process cost may be unnecessarily increased, which may result in inefficiency.

Here, one or more of oxygen, water, and hydrogen peroxide can be used as the oxidizing agent, and the heating temperature can be adjusted depending on the type of oxidizing agent.

Specifically, when hydrogen peroxide is used as an oxidizing agent, it can be heated to 700 to 1,100°C, and when oxygen is used as an oxidizing agent, it can be heated to 900 to 1,100°C.

Here, the rotary kiln uses a continuous heating furnace, so it has good thermal efficiency and can shorten working time. The rotary kiln is composed of an input part for feeding the material to be treated into the kiln main body, a heat treatment section equipped with a kiln body for heating, and a discharge portion for discharging the heat-treated material. In the rotary kiln, the objects to be treated are continuously mixed and moved, so a uniform and thick oxide film 31 is formed, and the difference in the ratio of the oxide film 31 between particles can be reduced.

The average thickness of the oxide film 31 formed in the oxidation step (S20) may be 2 to 10 nm. If the average thickness of the oxide film 31 is less than 2 nm, a non-uniform oxide film 31 in the form of a point may be formed on the surface of the plate-shaped silicon particle 20, and the unoxidized portion on the surface of the plate-shaped silicon particle 20 may be in the form of a point. Since a large number of oxides are generated between the oxide films 31, the effect provided by the uniform oxide film 31 cannot be achieved. In other words, the lifespan performance improvement effect may not be desired.

Additionally, if the oxide film 31 exceeds 10 nm, the irreversible capacity, which is the main reason for the decrease in initial discharge capacity, increases significantly to more than 30%, which may increase lithium consumption.

As observed in FIGS. 7A and 7B, an oxide film 31 may be formed on the surface of the plate-shaped silicon particle 20 through the oxidation step (S20).

Referring to FIG. 8, the boron oxide coating step (S30) may form a boron oxide coating film 32 by coating boron oxide on the surface of the silicon oxide 30.

The boron oxide coating step (S30) is to improve the disadvantage of increasing initial irreversibility because the oxide film 31 combines with lithium during initial charging and cannot release lithium during discharging, and forms a boron oxide coating film 32 by coating boron oxide. can do.

Here, boron oxide has the characteristic of being crystalline at a relatively low temperature, so crystalline quality can be added to the amorphous oxide film 31, and through this, the bond between the oxide film 31 and lithium can be reduced without consuming lithium. . Boron oxide also has the advantage of being an inexpensive material that does not react with lithium.

That is, the boron oxide coating step (S30) forms a boron oxide coating film 32 on the surface of the silicon oxide 30, thereby reducing the amount of bonding with lithium of the oxide film 31 to prevent initial irreversibility from increasing and initial capacity. and life performance can be improved.

In the boron oxide coating step (S30), the boron oxide coating film 32 can be formed partially rather than coating the entire surface of the silicon oxide 30. This is because boric acid is coated and thermally decomposed to form the boron oxide coating film 32. A non-uniform coating film may be formed.

In the boron oxide coating step (S30), the silicon oxide (30) that has completed the oxidation step (S20) is dispersed by adding it to an aqueous solution of boric acid, then dried through a dryer such as a spray dryer or disk dryer, and then reduced to 0.1 to 0.4 g using a grinder. It can be pulverized to an apparent density of /cm3. Next, the boric acid can be converted to boron oxide by heating to 550 to 700° C. using a rotary kiln to form the boron oxide coating film 32.

At this time, if the heating temperature is less than 550°C, the boron oxide does not melt all and the adhesion to the oxide film 31 may decrease, and if the heating temperature exceeds 700°C, the amount that melts and flies away through vaporization increases, which may reduce the coating effect.

Meanwhile, in the boron oxide coating step (S30), the process of converting boric acid to boron oxide involves an exothermic process and agglomeration occurs between particles, so the particles are pulverized through a grinder to form a distance between them. At this time, the apparent density of the particles is preferably 0.1 to 0.4 g/cm3 as described above, but is not limited thereto.

Referring to FIG. 9, the carbon coating step (S40) may be performed by coating the surface of the silicon oxide 30 with conductive carbon to form a plate-shaped silicon composite 40 with a carbon coating film 41 formed thereon. The carbon coating step (S40) forms a carbon coating film 41 on the surface of the silicon oxide 30, thereby imparting electrical conductivity and smooth electron flow to the oxide film 31 and the boron oxide coating film 32, which are insulating layers. .

Here, the carbon coating film 41 serves to maintain the amount and formation relationship of SEI (solid electrolyte interface), which is the interface between graphite and electrolyte (or electrolyte) in existing lithium ion secondary batteries, and plays a role in maintaining the formation relationship due to material changes. This can eliminate the inconvenience of having to change the electrolyte (or electrolyte).

In the carbon coating step (S40), one of hydrocarbon gas, liquefied natural gas, and liquefied petroleum gas can be selected and added to the silicon oxide 30 using a rotary kiln or kiln, and thermally decomposed at 750 to 1000 ° C.

Here, hydrocarbon gas is a gas composed of carbon and hydrogen bonds, C ₂ H ₂ (acetylline), C ₂ H ₆ (ethane), C ₂ H ₄ (ethylene), CH ₄ (methane), C ₃ H ₈ ( Propane), C ₄ H ₁₀ (butane), C ₃ H ₆ (propylene), C ₄ H ₈ (butylene), etc. may be used. Hydrocarbon gas can be produced by vaporizing and thermally decomposing a hydrocarbon solution consisting of C, H, and O, such as ethanol, methanol, and toluene.

In the carbon coating step (S40), silicon oxide (30) is thermally decomposed at 750 to 800°C using ethylene gas as a hydrocarbon gas, or silicon oxide (30) is thermally decomposed at 950 to 1,000°C using liquefied natural gas to produce carbon. It is preferable to form a coating film 41, but it is not limited thereto.

When using ethylene gas, if the temperature is less than 750℃, the decomposition rate is less than 50%, resulting in unnecessary gas consumption, and if the temperature is higher than 800℃, the decomposition speed increases and a large amount of unnecessary by-product called carbon black can be produced.

When using liquefied natural gas, if the temperature is less than 950℃, the decomposition rate is less than 50%, which results in unnecessary gas consumption. If it exceeds 1000℃, the decomposition rate is accelerated and a large amount of unnecessary by-products called carbon black can be produced. there is.

In the carbon coating step (S40), the carbon coating film 41 may be formed to have an average thickness of 3 to 20 nm.

At this time, if the average thickness of the carbon coating film 41 is less than 3 nm, the carbon coating film 41 is formed unevenly in the form of dots on the surface of the silicon oxide 30, resulting in many uncoated areas, which may not have a significant lifespan improvement effect. If it exceeds 20 nm, excessive coating increases the number of pores inside the carbon coating film 41, so lithium fills the pores and does not escape again, resulting in a significant increase in irreversible capacity.

As confirmed in FIG. 10, a carbon coating film 41 may be formed on the surface of silicon oxide (30, in which an oxide film is formed on the surface of plate-shaped silicon particles) through the carbon coating step (S40).

Referring to Figure 2, the method for manufacturing a silicon anode material for a lithium ion secondary battery of the present invention may further include a secondary disintegration step (S35) after the boron oxide coating step (S30).

The second disintegration step (S35) can disintegrate the silicon oxide 30 that has been aggregated after the boron oxide coating step (S30) to reduce density. In the second crushing step (S35), the silicon oxide 30 can be pulverized with air in a pin mill with a radius of 110 to 130 mm and 3300 to 3500 rpm.

This second disintegration step (S35) separates the aggregated silicon oxide 30, and, like the first disintegration step (S10), the particles can have an apparent density of 0.1 to 0.4 g/cm3. Accordingly, the second disintegration step (S35) facilitates the formation of the boron oxide coating film 32 in the post-process boron oxide coating step (S30), and ensures that the carbon coating film 41 is formed uniformly in the carbon coating step (S40). can do.

In addition, the method for manufacturing a silicon anode material for a lithium ion secondary battery to which boron oxide of the present invention is applied may further include a mixing step (S50) after the carbon coating step (S40).

The mixing step (S50) may be performed by mixing the plate-shaped silicon composite 40 and graphite 51 after the carbon coating step (S40) to form mixtures 50a and 50b, for lithium ion secondary batteries to which spherical boron oxide is applied. A silicon anode material 50a or a silicon anode material 50b for a lithium ion secondary battery to which simple boron oxide is applied can be formed.

Here, the graphite 51 is a plate-shaped material, and even if it is spherical, an empty space is formed.

In the mixing step (S50), the empty space of the graphite 51 is filled with the plate-shaped silicon composite 40, thereby preventing the entire electrode from expanding due to expansion when lithium is combined and maintaining an electrical connection with the electrode due to shrinkage. The mixture (50a, 50b) formed in the mixing step (S50) is a form in which the plate-shaped silicon composite (40) is bonded to the empty space of the graphite (51), and can prevent separation from the electrode when expanded by lithium. At this time, the empty space of the graphite 51 serves as a buffer space.

The mixing step (S50) is a method of adding the plate-shaped silicon composite 40 in the process of spheroidizing the graphite 51, or a method of mixing the graphite 51 and the plate-shaped silicon composite 40 that have completed the spheroidization or spheroidization process. there is.

Specifically, when adding the plate-shaped silicon composite 40 in the process of spheroidizing the graphite 51 in the mixing step (S50), as shown in FIG. 11, the plate-shaped silicon composite 40 is formed between the plates of the graphite 51. ) is inserted, a spheroidized mixture 50a in the form of spheroidized or spheroidized graphite 51 may be formed. On the other hand, when mixing the graphite 51 and the plate-shaped silicon composite 40 that have completed the spheroidization or spheronization process in the mixing step (S50), as shown in FIG. 12, the plate-shaped silicon composite 40 is formed between the graphite 51. ) A simple mixture 50b in the form of an arrangement may be formed.

At this time, the graphite 51 undergoes a spheroidization or spheroidization process, because spherical graphite has a low anisotropy and is advantageous for maintaining uniformity of voltage and current distribution. On the other hand, due to the anisotropy of the material itself, flake-shaped graphite deteriorates the processability due to reduced fluidity during the subsequent mixing and slurry process with solvents or binders, and it is difficult to form a coating layer of a certain thickness, which can cause problems such as peeling. there is. In general, the spheroidization process removes the rough parts of the flake-shaped carbon material through mechanical rotation and smoothes the surface of the particle to make it spherical.

Meanwhile, the plate-shaped silicon composite 40 and the graphite 51 can be mixed at a weight ratio of 31 to 10:90 to 99, and more preferably at a weight ratio of 5:95.

At this time, if the content of the plate-shaped silicon composite 40 is lower than 1% by weight, the effect of increasing the charging capacity of the silicon anode material due to the mixing of the graphite 51 falls within the charging capacity deviation, making it difficult to determine the effect, and if it exceeds 10% by weight, the silicon particles As the number becomes greater than the number of graphite 51 particles, the uniform dispersion effect between the silicon particles and the graphite 51 may be reduced.

As described above, the method for manufacturing a silicon anode material for a lithium-ion secondary battery to which boron oxide is applied according to an embodiment of the present invention uses plate-shaped silicon formed from a waste silicon kerf, which can lower the unit cost of the anode material.

In addition, it is possible to manufacture a silicon anode material with an excellent filling ratio by complexing it with plate-shaped graphite.

Additionally, by increasing the performance of the silicon anode material, more lithium can be charged compared to the same volume.

In addition, by applying boron oxide, a silicon anode material with improved initial capacity and lifespan performance can be manufactured.

Hereinafter, the present invention will be described in more detail through examples, but these are merely for illustrating preferred embodiments of the present invention, and the examples do not limit the scope of the present invention.

[Example]

[Example 1]

The polycrystalline silicon ingot was cooled, lubricated, and cut with a mixture of water and diethylene glycol using a 50㎛ diameter diamond wioso, and 5,000 ml of a 5% mixed solution of plate-shaped silicon was recovered. The dispersion solution was injected from a spray dryer into an atomizer disk rotating at 15,000 rpm at a rate of 20 ml per minute and dried at 140 degrees to obtain plate-shaped silicon particles. Low-density plate-shaped silicon particles were made by grinding with air in a pin mill with a radius of 120 mm and 3400 rpm. The plate-shaped silicon particles were oxidized by bubbling and injecting hydrogen peroxide with nitrogen while remaining in a rotary kiln at 800°C for 10 minutes. The plate-shaped silicon particles changed from black gray to dark brown and became silicon oxide. The silicon oxide was dispersed in an aqueous solution of boric acid for 30 minutes using a mixer at 3,000 rpm, and then injected into an atomizer disk rotating at 15,000 rpm in a spray dryer at a rate of 20 ml per minute and dried at 140°C. Next, boric acid was decomposed while remaining in a rotary kiln at 700°C for 10 minutes, and boron oxide was partially coated on the silicon oxide to form a boron oxide coating film. The silicon oxide on which the boron oxide coating film was formed was stored in a rotary kiln at 800°C for 10 minutes while exhaling ethylene gas at 0.1 M/min. It was added at a high rate to form a carbon coating film on the surface, creating a plate-shaped silicon composite.

The prepared plate-shaped silicon composite was mixed with a binder and a conductive material, applied to copper foil, and punched into a coin shape. To make a battery cell, a positive electrode was used by punching lithium foil into a coin shape, a separator and electrolyte were added, and the battery was assembled into a half-cell lithium ion battery.

[Example 2]

The plate-shaped silicon composite prepared in Example 1 and the spherical graphite were added to a dry ball mill at a weight ratio of 5:95 and mixed for 10 seconds to obtain a mixture. A half-cell lithium ion battery was manufactured in the same manner as Example 1 using the above mixture.

[Comparative Example 1]

It was mixed with graphite, binder, and conductive material, applied to copper foil, and punched into a coin shape. To make a battery cell, a positive electrode was used by punching lithium foil into a coin shape, a separator and electrolyte were added, and the battery was assembled into a half-cell lithium ion battery.

[Comparative Example 2]

The polycrystalline silicon ingot was cooled, lubricated, and cut with a mixture of water and diethylene glycol using a 50㎛ diameter diamond wioso, and 5,000 ml of a 5% mixed solution of plate-shaped silicon was recovered. The dispersion solution was injected from a spray dryer into an atomizer disk rotating at 15,000 rpm at a rate of 20 ml per minute and dried at 140 degrees to obtain plate-shaped silicon particles. Low-density plate-shaped silicon particles were made by grinding with air in a pin mill with a radius of 120 mm and 3400 rpm. While plate-shaped silicon particles were kept in a rotary kiln at 800°C for 10 minutes, ethylene gas was blown at 0.1 M/min. Carbon-coated silicon particles were manufactured by adding the product at a high rate to form a carbon coating film on the surface.

The prepared carbon-coated silicon particles, graphite, binder, and conductive material were mixed, applied to copper foil, and punched into a coin shape. To make a battery cell, a positive electrode was used by punching lithium foil into a coin shape, a separator and electrolyte were added, and the battery was assembled into a half-cell lithium ion battery.

[Comparative Example 3]

The carbon-coated silicon particles prepared in Comparative Example 2 and spheroidized graphite were added to a dry ball mill at a weight ratio of 5:95 and mixed for 10 seconds to obtain a mixture.

The mixture was applied to copper foil and punched into a coin shape. To make a battery cell, a positive electrode was used by punching lithium foil into a coin shape, a separator and electrolyte were added, and the battery was assembled into a half-cell lithium ion battery.

[Experimental Example 1] Charging and discharging performance evaluation

To evaluate the charge/discharge performance of the half-cells manufactured in Examples 1 and 2 and Comparative Examples 1 to 3, capacity and lifespan were measured.

At this time, the capacity was measured at 25°C and a charge/discharge current of 0.1C, and the lifespan was measured from 20 to 300 cycles at 25°C and a charge/discharge current of 0.1C.

The results are shown in Figures 13 to 17. Figures 12 to 17 are graphs of half cell charge/discharge test results for Comparative Examples 1 to 3 and Examples 1 and 2, respectively.

As can be seen from Figures 13 to 17, Comparative Example 1 showed a low initial capacity of 358 mAh/g, but it was confirmed that the lifespan performance satisfied 300 cycles (Figure 13)

In Comparative Example 2, the initial capacity was excellent at 3250 mAh/g with carbon coating, but it was confirmed that the lifespan performance was low (FIG. 14).

In Comparative Example 3, the initial capacity was high at 2000 mAh/g, but it was confirmed that the lifespan performance was low (FIG. 15).

In Example 1, the initial capacity was slightly lower compared to Comparative Example 2, but it was confirmed that the lifespan performance was significantly improved, and the initial capacity was confirmed to be significantly increased compared to Comparative Example 1 (FIG. 16).

In Example 2, it was confirmed that both the initial capacity and lifetime performance were improved compared to Comparative Example 2 without an oxide film and a boron oxide coating film (FIG. 17)

Although embodiments of the present invention have been described above with reference to the attached drawings, those skilled in the art can realize that the present invention can be implemented in other specific forms without changing the technical idea or essential features of the present invention. You will be able to understand it. Therefore, the embodiments described above are illustrative in all respects and are not restrictive.

[Explanation of symbols]

10: cotton silicone

20: plate-shaped silicon particles

30: silicon oxide

31: oxide film

32: Boron oxide coating film

40: Plate-shaped silicone composite

41: Carbon coating film

50a: Spheronization mixture

50b: Simple mixture

51: graphite

Claims (10)

1. A first disintegration step of disintegrating the plate-shaped silicon formed from a waste silicon kerf to have an apparent density of 0.1 to 0.4 g/cm3;

   An oxidation step of oxidizing the surface of the plate-shaped silicon particles to form silicon oxide with an oxide film;

   A boron oxide coating step of coating boron oxide on the surface of the silicon oxide to form a boron oxide coating film, and

   A method of manufacturing a silicon anode material for a lithium ion secondary battery to which boron oxide is applied, comprising a carbon coating step of coating the surface of the boron oxide coating film with conductive carbon to form a plate-shaped silicon composite with a carbon coating film.
2. According to paragraph 1,

   Before the first disintegration step, a method of manufacturing a silicon anode material for a lithium-ion secondary battery to which boron oxide is applied, further comprising a pretreatment step of wet milling and drying the plate-shaped silicon to form plate-shaped silicon particles.
3. According to paragraph 1,

   After the oxygen boron coating step, a method of manufacturing a silicon anode material for a lithium ion secondary battery to which boron oxide is applied, further comprising a secondary disintegration step of disintegrating the silicon oxide on which the boron oxide coating film is formed.
4. According to paragraph 1,

   After the carbon coating step, a method of manufacturing a silicon anode material for a lithium ion secondary battery to which boron oxide is applied, further comprising a mixing step of mixing the plate-shaped silicon composite and graphite to form a mixture.
5. According to paragraph 1,

   The plate-shaped silicon is,

   A method of manufacturing a silicon anode material for a lithium ion secondary battery using boron oxide, characterized in that the average thickness is 10 to 100 nm and the average length is 10 μm or less.
6. According to paragraph 1,

   The oxidation step is,

   A method of manufacturing a silicon anode material for a lithium ion secondary battery to which boron oxide is applied, characterized in that the average thickness of the silicon oxide film is formed to be 2 to 10 nm.
7. According to paragraph 1,

   The oxidation step is,

   A method of manufacturing a silicon anode material for a lithium ion secondary battery to which boron oxide is applied, characterized in that an oxidizing agent is added to the plate-shaped silicon particles and heated to 700 to 1,100°C.
8. According to paragraph 1,

   The boron oxide coating step is,

   A method of manufacturing a silicon anode material for a lithium ion secondary battery to which boron oxide is applied, characterized in that adding an aqueous solution of boric acid to the silicon oxide and heating it to 550 to 700°C.
9. According to paragraph 1,

   The carbon coating step is,

   A method of manufacturing a silicon anode material for a lithium ion secondary battery to which boron oxide is applied, characterized in that the carbon coating film is formed with an average thickness of 3 to 20 nm.
10. According to paragraph 1,

    The carbon coating step is,

    A silicon anode for a lithium-ion secondary battery to which boron oxide is applied, characterized in that one of hydrocarbon gas, liquefied natural gas, and liquefied petroleum gas is selected and added to the silicon oxide that has completed the boron oxide coating step, and thermally decomposed at 750 to 1000 ° C. Re-manufacturing method.

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