KR20190142051A - Silicon-Graphene Composite powder and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a silicon-graphene composite powder. More specifically, the present invention relates to: a silicon-graphene composite powder exhibiting an effect that volume expansion is suppressed and conductivity is improved to improve a capacity maintenance rate, and at the same time, side reaction with electrolyte is decreased; and a manufacturing method thereof.

Description

Silicon-graphene composite powder and manufacturing method thereof

The present invention relates to a silicon-graphene composite powder, and more particularly, a silicon-graphene composite powder exhibiting an effect of suppressing volume expansion, improving conductivity, improving capacity retention, and reducing side reactions with an electrolyte. It relates to a manufacturing method thereof.

Many applications require high energy density and stable output of batteries. At the same time, low cost and simple processes are required in terms of productivity. In response to these demands, there is a demand for developing a battery cathode using low-cost silicon with high output.

The theoretical capacity of the silicon cathode is about 4,200 mAh / g, and graphite is about 372 mAh / g, which is about 11 times lower than that of silicon. However, because the conventional silicon was difficult to use in the secondary battery, the volume of the silicon was expanded to about 400% during the lithiation and delithiation process generated during the charging and discharging of the secondary battery. It was hard to be used as a negative electrode for a stable secondary battery because it could not be broken and show a stable output.

Accordingly, there is an urgent need to develop a composite powder having the effect of suppressing volume expansion, improving conductivity, improving capacity retention, and reducing side reactions with the electrolyte.

KR 10-0666476 B1 (2007.01.03)

The present invention has been made in order to solve the above-mentioned problems, a silicon-graphene composite powder and a method for producing the same, which exhibits the effect of suppressing volume expansion, improving conductivity, improving capacity retention, and reducing side reactions with the electrolyte. The purpose is to provide.

The present invention to solve the above problems, the step of electrospraying the spray solution containing silicon and graphene; It provides a method for producing a silicon-graphene composite powder comprising a; and filtering the electrosprayed spray solution, and drying to prepare a silicon-graphene composite.

According to an embodiment of the present invention, the spray solution may include silicon and graphene in a weight ratio of 1: 0.03 to 0.5.

In addition, the silicon may have an average particle diameter of 0.5 ~ 4㎛.

In addition, the spray solution may include the silicon and graphene in a concentration of 0.5 to 15% by weight in total.

In addition, after the step of preparing the silicon-graphene composite, the step of pulverizing the silicon-graphene composite; may further include a.

In addition, the electrospray can be carried out at a voltage of 3 ~ 17kV and 0.03 ~ 1 ㎖ / min.

In addition, the total weight of the spray solution, acrylonitrile-butadiene rubber (NBR), styrene-butadiene rubber (styrene-butadiene rubber (SBR), carboxymethyl cellulose (Carboxymethyl cellulose, CMC), carboxymethyl cellulose In the group consisting of sodium salt (Na-CMC), poly acrylic acid (PAA), polyvinyl alcohol (PVA), hydroxypropyl cellulose (HPC) and diacetyl cellulose 0.001 to 0.2% by weight of the aqueous binder including one or more selected.

In addition, the spray solution may be electrosprayed in a non-solvent.

In addition, the cost agent may include one or more selected from the group consisting of acetone, isopropyl alcohol, benzene, toluene, and NMP (N-Methyl-2-pyrrolidone).

In addition, the drying may be performed at 50 ℃ to 120 ℃ for 1.5 to 4.5 hours.

Meanwhile, the present invention has a core-shell shape including a core and a shell, wherein the core includes silicon, and the shell provides a silicon-graphene composite powder including graphene.

According to an embodiment of the present invention, the tap density may be 0.1 to 0.5 g / ml.

In addition, the average particle diameter may be 1 ~ 6㎛.

On the other hand, the present invention provides a secondary battery having the silicon-graphene composite powder;

The silicon-graphene composite powder of the present invention and a method for producing the same may exhibit an effect of suppressing volume expansion, improving conductivity, improving capacity retention, and reducing side reactions with the electrolyte.

1 is a process flowchart for preparing a silicon-graphene composite powder according to an embodiment of the present invention,
2 is a process flowchart of manufacturing a silicon-graphene composite powder according to another embodiment of the present invention, and
3 is an SEM image of a silicon-graphene composite powder according to an embodiment of the present invention, FIG. 3a is an SEM image of a silicon-graphene composite powder expanded at 3,000 magnification according to an embodiment of the present invention. 3b is an SEM image of the silicon-graphene composite powder at 10,000 magnification according to an embodiment of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. The drawings and description are to be regarded as illustrative in nature and not restrictive. Like reference numerals designate like elements throughout the specification.

As described above, although silicon was conventionally used in a secondary battery, a structure in which the volume of silicon is expanded to about 400% in the lithiation and delithiation processes generated during the charging and discharging of the secondary battery has been previously included. It was difficult to use as a cathode for a rechargeable secondary battery because it could not show stable output because

Thus, the present invention sought to solve the above problems through the silicon-graphene composite powder to be described later and a method for producing the same. Accordingly, the effect of suppressing volume expansion, improving conductivity, improving capacity retention rate, and reducing side reactions with the electrolyte solution can be simultaneously achieved.

Silicon-graphene composite powder according to an embodiment of the present invention comprises the steps of electrospraying the spray solution containing silicon and graphene as shown in Figure 1 (S1); And filtration and drying of the electrosprayed spray solution to prepare a silicon-graphene composite (S2).

First, the step (S1) of electrospraying the spray solution containing silicon and graphene will be described.

The spray solution may include silicon and graphene in a weight ratio of 1: 0.03 to 0.5, preferably silicon and graphene in a weight ratio of 1: 0.05 to 0.35. If the weight ratio of silicon (Si) and graphene is less than 1: 0.03, the volume expansion of silicon may not be suppressed, and the capacity retention may be lowered due to a slight increase in conductivity, and the weight ratio of silicon and graphene is 1: 0.5. If exceeded, there may be a problem in that the side reaction with the electrolyte increases and the initial efficiency decreases.

The silicon may be used without limitation as long as it is a silicon having a particle size commonly used in the art, preferably silicon having an average particle diameter of 0.5 to 4 μm, and more preferably having an average particle diameter of 1 to 3.5 μm. Silicon can be used, More preferably, silicon with an average particle diameter of 2-3 micrometers can be used. If the average particle diameter of the silicon is less than 0.5㎛ relatively side reaction with the electrolyte increases as the surface area of the silicon-graphene composite powder increases, there may be a problem that the initial efficiency is reduced, the average particle diameter of the silicon When it exceeds 4 µm, the volume expansion of the silicon cannot be suppressed, and the conductivity improvement is insignificant and the capacity retention rate can be lowered.

In addition, the graphene may be used without limitation as long as the graphene having a size that can be commonly used in the art, preferably using a graphene having a particle size of less than 1 ㎛, more preferably 600 nm or less More preferably, graphene having a particle size of 500 nm or less may be used. If the particle size of the graphene is 1 μm or more, as the flexibility of the graphene is lowered, the effect of wrapping the core may be reduced.

The spray solution may contain the total concentration of 0.5 to 15% by weight of the silicon and graphene, preferably the total concentration of 1 to 10% by weight of the silicon and graphene. If the silicon and graphene provided in the spray solution is out of the concentration range there may be a problem that can not produce a silicon-graphene composite powder expressing the desired level of effect.

In addition, the spray solution, the total weight of the spray solution, acrylonitrile-butadiene rubber (acrylonitrile-butadiene rubber, NBR), styrene-butadiene rubber (styrene-butadiene rubber, SBR), carboxymethyl cellulose (CMC) ), Carboxymethylcellulose sodium salt (Na-CMC), poly acrylic acid (PAA), polyvinyl alcohol (PVA), hydroxypropyl cellulose (HPC) and diacetyl cellulose It may be provided with an aqueous binder containing at least one selected from the group consisting of 0.001 to 0.2% by weight, preferably 0.001 to 0.1% by weight. If the content of the aqueous binder in the total weight of the spray solution is out of the range may cause a problem that the dispersibility of silicon and graphene in the spray solution is lowered.

In addition, the electrospray may be used without limitation, so long as it is a condition that can be commonly used in the art, preferably at a speed of voltage 3 ~ 17kV and 0.03 ~ 1 ml / min, more preferably voltage 5 ~ 15kV and 0.05 It may be carried out at a rate of ˜0.5 mL / min. If the voltage of the electrospray is less than 3kV, there may be a problem that the average particle diameter of the silicon-graphene composite powder becomes excessively large as the size of the droplets formed by the electric field increases, and if the voltage exceeds 19kV, it is uneven due to overvoltage. There may be a problem that one particle is to be produced. In addition, if the spraying speed is less than 0.03 ml / min, the amount of the solution to be injected is not enough to be uniform droplet spraying, and if the speed exceeds 1 ml / min, as the size of the sprayed droplets increases, the silicon -There may be a problem that the average particle diameter of graphene composite powder becomes excessively large.

The spray solution may be electrosprayed to a grounded collector or a liquid collector, preferably to an electrospray on the liquid collector, and more preferably to a liquid collector having a non-paying agent. Electrospray is more advantageous for producing a silicon-graphene composite powder having a core-shell shape.

In this case, the cost agent may be used without limitation as long as it is a commonly used in the art, preferably a group consisting of acetone, isopropyl alcohol, benzene, toluene, and NMP (N-Methyl-2-pyrrolidone) It may include one or more selected from, more preferably may comprise one or more selected from the group consisting of acetone and isopropyl alcohol.

By spraying the spray solution on the non-consumer, it is possible to prepare a silicon-graphene composite powder having a core-shell shape, to prevent volume expansion, to improve conductivity, to improve capacity retention, and at the same time to react with the electrolyte. All of these deteriorating effects can be expressed simultaneously.

Next, filtering the electrosprayed spray solution and drying to prepare a silicon-graphene composite (S2);

The filtration may be used without limitation as long as it is a filtration method conventionally used in the art, and preferably may be filtered through any one method selected from the group consisting of reduced pressure filtration, pressure filtration, and centrifugal filtration, and more preferably. Decompression filtration or pressure filtration may be used, and more preferably, may be carried out by vacuum filtration.

In addition, the drying may be used without limitation as long as it is a drying condition that can be commonly used in the art, preferably can be carried out at 50 ℃ to 120 ℃ for 1.5 to 4.5 hours, more preferably 60 ℃ to 100 ℃ In 2-4 hours. If the drying temperature is less than 60 ℃, or if the drying time is less than 2 hours, there may be a problem to cause secondary battery side reactions due to the remaining of the non-solvent used in the manufacture of the particles, the drying temperature exceeds 120 ℃, or drying time If it exceeds 4 hours, there is a possibility that the oxidation reaction of silicon may occur, and there may be a problem of decomposition of the aqueous binder used in preparing the spray solution.

On the other hand, according to an embodiment of the present invention, the silicon-graphene composite powder manufacturing method of the present invention, as shown in Figure 2, after the step of preparing the silicon-graphene composite (S2), the silicon-graph Disintegrating the pin complex (S3); may further include.

The disintegration may be used without limitation as long as it is a disintegration method commonly used in the art, and may be prepared as the silicon-graphene composite powder by disintegrating the silicon-graphene composite.

On the other hand, the silicon-graphene composite powder prepared according to the silicon-graphene composite powder manufacturing method according to the present invention, as shown in Figure 3a and 3b core (core) including a core (shell) and (shell)- It has a shell shape, the core includes silicon, and the shell includes graphene.

As the core includes silicon and the shell has a core-shell shape including graphene, volume expansion is suppressed, conductivity is improved, capacity retention is improved, and side reactions with electrolytes are simultaneously reduced. Can be expressed.

The silicon-graphene composite powder of the present invention may have a tap density of 0.1 to 0.5 g / ml, and preferably, a tap density of 0.15 to 0.45 g / ml. If the tap density is less than 0.1 g / ml, there may be a problem in that a side reaction with the electrolyte increases. If the tap density exceeds 0.5 g / ml, the volume expansion of the silicon cannot be suppressed and the conductivity improvement is insignificant. There may be a problem of this deterioration.

In addition, the silicon-graphene composite powder may have an average particle diameter of 1 to 6 μm, preferably an average particle diameter of 1.5 to 5 μm. If the average particle diameter of the silicon-graphene composite powder is less than 1 μm, there may be a problem in that a side reaction with the electrolyte increases as the surface area of the silicon-graphene composite powder is relatively increased, and the average particle diameter exceeds 6 μm. If there is a problem that the volume expansion of the silicon can not be suppressed, the conductivity improvement is insignificant and the capacity retention rate may be lowered. On the other hand, it is obvious that the average particle diameter of the silicon-graphene composite powder is formed to have a larger average particle diameter than that of the silicon described above.

The silicon-graphene composite powder of the present invention and a method for producing the same may exhibit an effect of suppressing volume expansion, improving conductivity, improving capacity retention, and reducing side reactions with the electrolyte.

Although the present invention will be described in more detail with reference to the following examples, the following examples are not intended to limit the scope of the present invention, which will be construed as to aid the understanding of the present invention.

<Example 1>

First, the spray solvent contains silicon having a tap density of 1.59 g / ml and an average particle diameter of 2.5 μm, graphene having a tap density of 0.016 g / ml and a particle size of 300 nm and a thickness of 1 nm in a total concentration of 5 wt%. A spray solution was prepared. At this time, the weight ratio of the silicon and graphene was 1: 0.2. Then, the electrospray was carried out at a rate of 10 kV and 0.3 ml / min through an electrospray apparatus containing acetone as a non-solvent in the liquid collector, followed by reduced pressure filtration (Filter 1 µm or less), followed by 3 hours at 80 ° C. Drying was carried out to prepare a silicon-graphene composite powder. Thereafter, the prepared silicon-graphene composite powder was pulverized using an inducer to prepare a silicon-graphene composite powder. The tap density of the prepared silicon-graphene composite powder was 0.18 g / ml and the average particle diameter was 4.5 µm.

<Examples 2 to 11 and Comparative Examples 1 to 2>

Prepared in the same manner as in Example 1, but the weight ratio of silicon and graphene, the average particle diameter of silicon, the liquid type of the liquid collector, the electrospray conditions, the composition and composition of the composite powder as shown in Table 1 and Table 2 By changing to prepare a silicon-graphene composite powder as shown in Table 1 and Table 2.

Experimental Example

For each silicon-graphene composite powder prepared according to Examples and Comparative Examples, a slurry was prepared by mixing the prepared composite particles, a commercial binder, a conductive agent, and a graphite cathode material, and applied to an anode current collector with an applicator. And dried and pressed to prepare an electrode. In this case, the binder, the conductive agent, and the graphite cathode material used were 3 wt% based on the total weight of the electrode. After preparing a coin half cell (coin half cell) with the prepared electrode was evaluated in the following physical properties are shown in Table 1 and Table 2.

1. Battery capacity measurement

In order to measure the capacity of the coin-type battery including the silicon-graphene composite powder prepared according to Examples and Comparative Examples, the charging capacity was measured by charging a constant current of 0.1 C-rate to 1.0V.

2. Battery capacity retention rate evaluation

After measuring the capacity, it was charged to 1.0V under constant constant current test conditions of 0.5C, and then discharged to 5mV under 0.5C constant current test conditions, and this was repeated in 50 cycles.

3. Volume change evaluation

If 50 cycles are repeatedly performed to evaluate the capacity retention rate, and no electrical short occurs and the volume change rate with respect to the initial volume is 50% or less-○, an electrical short occurs or the volume change rate exceeds 150% The volume change was evaluated as -x.

The volume change rate was compared with the electrode volume before the first cycle after measuring the electrode thickness by disassembling each coin-type battery in the state of charge of the 50th cycle.

4. Initial Efficiency

When the battery was charged to 1.5 V under constant constant current test conditions of 0.1 C, and then discharged to 5 mV under 0.1 C constant current test conditions, the initial efficiency was measured by the 'discharge capacity / charge capacity' of the first cycle.

Configuration Example
One Example
2 Example
3 Example
4 Example
5 Example
6 Example
7 Spray Solution Silicon to Graphene Weight Ratio 1: 0.2 1: 0.01 1: 0.05 1: 0.35 1: 0.7 1: 0.2 1: 0.2 Silicon Average Particle Size (㎛) 2.5 2.5 2.5 2.5 2.5 0.2 One Electrospray Liquid type Acetone Acetone Acetone Acetone Acetone Acetone Acetone Silicon-graphene composite powder tap density (g / ml) 0.18 0.62 0.36 0.15 0.08 0.03 0.11 Charge capacity (mAh / g) 434.7 455.2 450.8 421.2 395.0 420.5 434.1 Charge capacity retention rate (%) 92.0 82.7 87.2 87.1 71.2 83.2 87.5 Initial Efficiency (%) 85.2 86.5 87.3 83.0 74.7 71.5 84.3 Volume change prevention evaluation ○ × ○ ○ ○ ○ ○

Configuration Example
8 Example
9 Example
10 Example
11 Comparative example
One Comparative example
2 Spray Solution Silicon to Graphene Weight Ratio 1: 0.2 1: 0.2 1: 0.2 1: 0.2 Bare Silicon ^{1 )} 1: 0.2 Silicon Average Particle Size (㎛) 3.5 5 2.5 2.5 2.5 2.5 Electrospray Liquid type Acetone Acetone Isopropyl Alcohol DIW - simple
Mixed ²⁾ Silicon-graphene composite powder tap density (g / ml) 0.17 0.09 0.19 particle
Cannot be manufactured - - Charge capacity (mAh / g) 436.9 450.6 440.1 448.2 411.0 Charge capacity retention rate (%) 87.4 79.6 91.8 79.8 80.9 Initial Efficiency (%) 87.0 88.6 85.3 88.5 83.1 Volume change prevention evaluation ○ × ○ × × 1) Comparative Example 1 is a battery manufactured using bare silicon
2) Comparative Example 2 is a mixture of simple silicon and graphene, not the electric spray

As can be seen from Table 1 and Table 2, the weight ratio of silicon and graphene according to the present invention, the average particle diameter of silicon, the type of liquid of the liquid collector, the electrospray conditions, the composition and the preparation method of the composite powder are all satisfied Examples 1, 3, 4, 7, 8, and 10 have better charge capacity, charge capacity retention rate, and initial efficiency than Examples 2, 5, 6, 9, 11, and Comparative Examples 1 to 2, in which any one of them is missing. At the same time, it can be seen that all of the effects in which volume expansion is suppressed can be achieved at the same time.

Specifically, Examples 1, 3 and 4 satisfying the weight ratio range of silicon and graphene provided in the spray solution according to the present invention is less than the weight ratio range of silicon and graphene provided in the spray solution Compared with 2, the charge capacity retention rate is significantly higher, and it can be seen that volume change can be prevented. In addition, compared to Example 5 exceeding the weight ratio range of silicon and graphene provided in the spray solution, the filling capacity and the filling capacity retention rate are excellent, and side reactions are prevented, and thus the initial efficiency is excellent.

In addition, Example 1, Example 7 and Example 8, which satisfy the average particle size range of the silicon provided in the spray solution according to the present invention, compared to Example 6, which is less than the average particle size range of silicon provided in the spray solution This is excellent, and side reactions are prevented, so it can be confirmed that the initial efficiency is excellent. In addition, compared to Example 9, which exceeds the average particle diameter range of the silicon provided in the spray solution, it can be seen that the charge capacity retention rate is significantly higher and volume change can be prevented.

In addition, Example 1 and Example 10 using the non-solvent as the liquid of the liquid collector according to the present invention are superior to the Example 11 using the solvent as the liquid of the liquid collector, and at the same time, All effects of inhibiting volume expansion can be achieved simultaneously, and Example 11 confirms that no particles are produced.

In addition, it can be seen that Example 1 using the silicon-graphene composite powder according to the present invention has a significantly higher charge capacity retention rate and prevents volume change compared to Comparative Example 1 using bare silicon.

In addition, Example 1 using the silicon-graphene composite powder prepared by the manufacturing method including the electrospray process according to the present invention, compared to Comparative Example 2 using a powder prepared by a simple mixing charge capacity and charge capacity retention rate It is noticeably high and can prevent volume change.

Although one embodiment of the present invention has been described above, the spirit of the present invention is not limited to the embodiments set forth herein, and those skilled in the art who understand the spirit of the present invention, within the scope of the same idea, the addition of components Other embodiments may be easily proposed by changing, deleting, adding, and the like, but this will also fall within the spirit of the present invention.

Claims (14)

Electrospraying a spray solution containing silicon and graphene; And
Filtrating the electrosprayed spray solution, and drying to prepare a silicon-graphene composite; silicon-graphene composite powder manufacturing method comprising a. The method of claim 1,
The spray solution is a silicon-graphene composite powder manufacturing method comprising a silicon and graphene in a weight ratio of 1: 0.03 ~ 0.5. The method of claim 1,
The silicon is a silicon-graphene composite powder manufacturing method having an average particle diameter of 0.5 ~ 4㎛. The method of claim 1,
The spray solution is a silicon-graphene composite powder manufacturing method comprising the silicon and graphene in a concentration of 0.5 to 15% by weight in total. According to claim 1, After the step of preparing the silicon-graphene composite,
Disintegrating the silicon-graphene composite; Silicon-graphene composite powder manufacturing method further comprising. The method of claim 1,
The electrospray is a method for producing a silicon-graphene composite powder at a voltage of 3 ~ 17kV and 0.03 ~ 1 ml / min. The method of claim 1, wherein the spray solution,
Acrylonitrile-butadiene rubber (NBR), styrene-butadiene rubber (SBR), Carboxymethyl cellulose (CMC), and carboxymethyl cellulose sodium salt in the total weight of the spray solution (Na-CMC), poly acrylic acid (PAA), polyvinyl alcohol (polyvinyl alcohol, PVA), hydroxypropyl cellulose (Hydroxypropylene cellulose, HPC) and diacetyl cellulose (diacetyl cellulose) selected from the group consisting of Method for producing a silicon-graphene composite powder comprising a 0.001 to 0.2% by weight of an aqueous binder containing more than one species. The method of claim 1,
The spray solution is a silicon-graphene composite powder manufacturing method by electrospraying in a non-solvent (non-solvent). The method of claim 8,
Said cost agent is acetone, isopropyl alcohol, benzene, toluene, and NMP (N-Methyl-2-pyrrolidone) N- (Methyl-2-pyrrolidone) A silicon-graphene composite powder manufacturing method comprising at least one selected from the group consisting of. The method of claim 1,
The drying is a method for producing a silicon-graphene composite powder carried out at 50 ℃ to 120 ℃ for 1.5 to 4.5 hours. It has a core-shell shape including a core and a shell,
The core comprises silicon, the shell comprises a graphene silicon-graphene composite powder. The method of claim 11,
Silicon-graphene composite powder having a tap density of 0.1 to 0.5 g / ml. The method of claim 11,
Silicon-graphene composite powder with an average particle diameter of 1 ~ 6㎛. A secondary battery comprising: a silicon-graphene composite powder according to any one of claims 11 to 13.

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