KR102320909B1 - Carbon nanowalls and their manufacturing method and Anode for lithium secondary battery containing thereof - Google Patents

Abstract

The present invention relates to a carbon nano-wall, a manufacturing method thereof, and a negative electrode material for a lithium secondary battery including the same, wherein the carbon nano-wall has an excellent deposited section height to improve energy density when being applied as an active material for a secondary battery, and can easily cause ion diffusion phenomena by superior vertical orientation so as to improve a charging and discharging speed of the secondary battery. The carbon nano-wall is regularly deposited to have a section height of 160-2.20 ㎛, wherein a height difference caused by flexure of a surface thereof is less than 0.03 ㎛. The present research is supported by a research grant for a basic research and development project selected in 2016 by the Korea Electric Power Corporation (Project number: R17XA05-1).

Description

Carbon nanowalls, manufacturing method thereof, and negative electrode for lithium secondary battery including same {Carbon nanowalls and their manufacturing method and Anode for lithium secondary battery containing thereof}

The present invention relates to a carbon nanowall, a method for manufacturing the same, and an anode for a lithium secondary battery to which the same is applied.

Carbon NanoWall (CNW) is a crystal with high integrity composed of nano-sized graphene crystallites. Carbon nanowalls are nanostructures generated by overlapping graphene sheets grown perpendicular to the substrate surface through a graphene layer formed on the substrate surface. The height of the wall of the carbon nanowall increases up to several hundred nm in proportion to the growth time, but the growth is saturated when the wall thickness is about 40 nm.

Carbon nanowall can be said to be an ideal structure as an anode (negative electrode) material for improving the high-speed charging and discharging characteristics of lithium secondary batteries. As a study on this, a lithium secondary battery using a nanostructure using graphene nanowalls and silicon crystals has been known (G. Lin et al., Journal of Power Sources, 437, 2019, 226909.). In this announcement, experimental results of a lithium secondary battery using a graphene nanowall structure as an anode are disclosed.

However, the graphene nanowall provided in the above known has a problem that the irreversible capacity is very large, the electric capacity per unit weight is somewhat lower than the theoretical value (372 mAh/g), and only the half cell experiment is known. .

The problem of the above-mentioned irreversible capacity is a phenomenon that occurs because the height of the wall does not grow sufficiently, so that the area where lithium ions can be intercalated is small compared to the large surface area. In the above study, the problem was not highlighted because a lithium-graphene nanowall half cell was used. have.

In the case of the above study, an initial charging graph that consumes more than twice the theoretical capacity of the graphene nanowall can be confirmed. This is because the irreversible capacity is equal to or higher than the theoretical capacity of the graphene nanowall, so there is a problem that it is impossible to apply the graphene nanowall used in the study as it is to the complete paper.

The above-described irreversible capacity problem is also a cause of the problem that the electric capacity per unit weight of the active material is lower than the theoretical value. Although the graphene nanowall proposed in the above study has a very large surface area compared to a conventional graphite or graphene sheet electrode, the area in which lithium ions can be intercalated and stored is small, so that the electric capacity per unit weight is reduced.

In addition, in the above study, since the growth of graphene nanowalls is not vertically oriented, there is a problem that a dead space is generated that cannot be used for intercalation and deintercalation of lithium ions, which is also per unit weight. It causes the problem of lowering the electric capacity.

In addition, most carbon nanowalls including the above study have a difference in height, so there is a problem that reliability may be deteriorated when used in a nano-unit structure.

Therefore, it is possible to increase the area where lithium ions can be intercalated, and to reduce the dead space to increase the electric capacity per unit weight when used in a lithium secondary battery, and to improve charging and discharging efficiency. , the development of a carbon nanowall material deposited to a sufficient height by being vertically oriented is required.

This research was supported by a research grant for a basic research and development project selected in 2016 by the Korea Electric Power Corporation. (Project No.: R17XA05-1)

Republic of Korea Patent Publication No. 10-2209666 (2015. 03. 11) Republic of Korea Patent Publication No. 10-2015-0027022 (2021. 01. 25) Republic of Korea Patent Publication No. 10-2020-0033469 (2020.03.30)

G. Lin et al., “Graphene nanowalls conformally coated with amorphous/nanocrstalline Si as high-performance binder-free nanocomposite anode for lithium-ion batteries”, Journal of Power Sources, 437, 2019, 226909.

In order to solve the above problems, the present invention has a vertical orientation through a plasma-enhanced chemical vapor deposition process made in a vacuum state, and a carbon nanowall deposited with a uniform cross-sectional height, a manufacturing method thereof, and a lithium secondary battery negative electrode to which the same is applied intended to provide

One aspect of the present invention for achieving the above object relates to a carbon nanowall uniformly deposited with a height of a cross section of 1.60 to 2.20 μm by a plasma enhanced chemical vapor deposition method.

In the above aspect, the carbon nanowall may have a height difference of 0.03 μm or less in cross-sectional height caused by the curvature of the surface.

In the one aspect, the carbon nanowall may be deposited to have a vertical orientation at an angle of 80 to 90 ° on the substrate.

In the one aspect, the carbon nanowall may be deposited on a silicon, ITO (Indium Tin Oxide) or TiN (Titanium Nitride) thin film substrate.

In addition, another aspect of the present invention relates to a method of manufacturing a carbon nanowall.

In the other aspect, the manufacturing method of the carbon nanowall,

(First step) removing impurities by washing the substrate with a solvent;

(Second step) ultrasonically cleaning the substrate;

(third step) drying the substrate in a nitrogen gas atmosphere;

(Step 4) supplying hydrogen gas and methane gas in a specific ratio on the substrate dried in a vacuum state, and depositing carbon nanowalls using a plasma enhanced chemical vapor deposition method;

may include.

In the other aspect, the hydrogen gas and methane gas is a method of manufacturing carbon nanowalls supplied at a flow ratio of 1:0.5 to 1:2.5.

In addition, another aspect of the present invention relates to a negative electrode material for a lithium secondary battery comprising the carbon nanowall.

Since the carbon nanowall according to the present invention has an excellent height of a deposited cross-section, it is possible to improve energy density when applied as an active material for a secondary battery. In addition, since the vertical alignment property is superior, the ion diffusion phenomenon may easily occur, thereby improving the charging/discharging speed of the secondary battery.

1 is a scanning electron microscope (SEM) photograph of a carbon nanowall according to an embodiment of the present invention.
2 is a schematic diagram of a carbon nanowall provided by the present invention.
Figure 3 (a) is a deposition mechanism of the carbon nanowall used in the present invention.
Figure 3 (b) is a schematic diagram of plasma enhanced chemical vapor deposition (Plasma Enhanced Chemical Vapor Deposition, PECVD) used in the present invention.
4 (a) is an SEM photograph of Comparative Example 12.
Figure 4 (b) is an SEM photograph taken after applying ultrasonic waves by immersing Comparative Example 12 in acetone according to the evaluation method of an embodiment of the present invention.
Figure 4 (c) is a SEM photograph of Example 4.
Figure 4 (d) is an SEM photograph taken after applying ultrasonic waves by immersing Example 4 in acetone according to the evaluation method of an embodiment of the present invention.
4(e) is an SEM photograph of Example 5;
4(f) is an SEM photograph taken after applying ultrasonic waves by immersing Example 5 in acetone according to the evaluation method of an embodiment of the present invention.

Hereinafter, a carbon nanowall according to the present invention, a manufacturing method thereof, and a negative electrode for a lithium secondary battery to which the same is applied will be described in detail. The drawings introduced below are provided as examples so that the spirit of the present invention can be sufficiently conveyed to those skilled in the art. Accordingly, the present invention is not limited to the drawings presented below and may be embodied in other forms, and the drawings presented below may be exaggerated to clarify the spirit of the present invention. At this time, if there is no other definition in the technical terms and scientific terms used, it has the meaning commonly understood by those of ordinary skill in the technical field to which this invention belongs, and the gist of the present invention in the following description and accompanying drawings Descriptions of known functions and configurations that may be unnecessarily obscure will be omitted.

One aspect of the present invention for achieving the above object relates to a carbon nanowall uniformly deposited with a height of a cross section of 1.60 to 2.20 μm by a plasma enhanced chemical vapor deposition method. The carbon nanowall provided by the present invention has a high cross-sectional height and is deposited with good vertical orientation, and thus has the advantage of greatly improving energy density when applied as an active material for secondary batteries compared to the prior art.

In the above aspect, the carbon nanowall may have a height difference of 0.03 μm or less in cross-sectional height caused by the curvature of the surface. The carbon nanowall provided in the present invention can improve reliability by alleviating the height difference due to the curvature of the surface, thereby reducing the performance gap according to the height distribution.

In the one aspect, the carbon nanowall may be deposited to have a vertical orientation at an angle of 75 to 90 ° on the substrate. As the carbon nanowalls presented in the present invention have a certain orientation, the diffusion rate of ions required for the intercalation reaction and the deintercalation reaction of ions is increased, which can ultimately contribute to the improvement of the charge/discharge rate.

In the one aspect, the carbon nanowall may be deposited on a silicon, ITO (Indium Tin Oxide) or TiN thin film substrate. At this time, it is preferable to use silicon to increase the height of the deposited cross-section, and when depositing on an ITO or TiN thin film substrate, the height of the deposited cross-section compared to silicon hardly changes, and the carbon nanowall is more strongly adhered to the substrate. It is more preferable to be able to

In the one aspect, the plasma enhanced chemical vapor deposition method for carbon nanowall deposition in a state where the temperature is 650 to 750 ℃, the power of the microwave is 1.1 to 1.5 kW, and the internal pressure is ^{controlled to 1.0 × 10 -3 torr or less} It may be carried out under the condition that the internal pressure is increased to 0.5×10 ^-3 to 5.0×10 ^{-2 torr by the supplied hydrogen gas and methane gas.} In this range, the conditions in which the carbon nanowalls are vertically oriented are formed.

In one aspect, the plasma enhanced chemical vapor deposition method may be performed while supplying hydrogen gas and methane gas at a flow ratio of 1:0.5 to 1:2.5. At this time, it is preferable to supply in a flow ratio of 1:0.5 to 1:2.0, and more preferably supply in a flow ratio of 1:0.5 to 1:1.5. In this range, the height growth of the carbon nanowall can be maximized.

In addition, another aspect of the present invention relates to a method of manufacturing a carbon nanowall.

In the other aspect, the manufacturing method of the carbon nanowall,

(First step) removing impurities by washing the substrate with a solvent;

(Second step) ultrasonically cleaning the substrate;

(third step) drying the substrate in a nitrogen gas atmosphere;

(Step 4) supplying hydrogen gas and methane gas in a specific ratio on the substrate dried in a vacuum state, and depositing carbon nanowalls using a plasma enhanced chemical vapor deposition method;

may include.

In the first step, the solvent may be trichloroethylene, acetone, methanol, and deionized distilled water, but is not particularly limited as long as it is a known solvent.

In the second step, the ultrasonic cleaning may be performed using the same solvent as the solvent used in the first step, and ultrasonic cleaning by immersing the substrate in the solvent.

In the second step, the ultrasonic cleaning may be performed for 1 to 30 minutes per solvent used.

In the third step, the substrate may be dried in a chamber in a nitrogen gas atmosphere to remove a surface solvent remaining during the ultrasonic cleaning.

In the fourth step, the plasma-enhanced chemical vapor deposition may be carried out under the condition that the temperature is 650 to 750 °C. When the temperature is exceeded, the deposition rate of the carbon nanowalls may be increased, but the yield of deposition is not good, and when the temperature is less than the temperature, the deposition rate of the carbon nanowalls is slow and the height of the carbon nanowalls is not sufficiently grown.

In the fourth step, the power of the microwave may be 1.1 to 1.5 kW. At this time, preferably 1.2 to 1.4 kW, more preferably 1.25 to 1.35 kW.

In the fourth step, the plasma-enhanced chemical vapor deposition may be performed in a vacuum state. More specifically, in the chamber in which plasma enhanced chemical vapor deposition is performed, the internal pressure may be controlled to ^{1.0×10 −3 torr or less by a vacuum pump.} Thereafter, the internal pressure may be increased ^{to 0.5×10 −3} to 5.0×10 ⁻² torr by hydrogen gas and methane gas supplied for carbon nanowall deposition. In this case, the flow rate of hydrogen gas is preferably 35 to 45 sccm, and the flow rate of methane gas is preferably 17.5 to 22.5 sccm.

In the fourth step, the hydrogen gas and the methane gas may be supplied at a flow ratio of 1:0.5 to 1:2.5. At this time, it is preferable to supply in a flow ratio of 1:0.5 to 1:2.0, and more preferably supply in a flow ratio of 1:0.5 to 1:1.5. In this range, the height growth of the carbon nanowall can be maximized.

In the fourth step, the plasma-enhanced chemical vapor deposition may be performed for 300 to 1500 seconds. At this time, as the plasma-enhanced chemical vapor deposition time is increased, the height of the carbon nanowall increases, but the height of the carbon nanowall does not increase significantly compared to the material consumed when the time is exceeded, so the efficiency is reduced, and the durability of the carbon nanowall is serious There may be problems with degradation. In addition, when the time is less than the above, the height of the carbon nanowall does not grow sufficiently, so it is difficult to use.

In addition, another aspect of the present invention relates to a negative electrode material for a lithium secondary battery comprising the carbon nanowall.

The negative electrode material for the lithium secondary battery may be one using the carbon nanowall provided in the present invention as the negative electrode active material and the substrate as the current collector.

Hereinafter, a carbon nanowall according to the present invention, a manufacturing method thereof, and a negative electrode for a lithium secondary battery including the same will be described in more detail through examples. However, the following examples are only a reference for describing the present invention in detail, and the present invention is not limited thereto, and may be implemented in various forms.

Further, unless otherwise defined, all technical and scientific terms have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used herein is for the purpose of effectively describing particular embodiments only and is not intended to limit the invention. In addition, the unit of additives not specifically described in the specification may be weight %.

[Production Example 1]

A p-type silicon wafer substrate having a size of 2×2 (cm×cm) was prepared. Next, the substrate was first washed using trichlorethylene, acetone, methanol, and distilled water in sequence. Next, using the same solvent as used in the first washing, each solvent was subjected to ultrasonic washing for 10 minutes in turn. Next, the cleaned substrate was dried in a nitrogen gas atmosphere.

[Example 1]

The dried substrate of Preparation Example 1 was mounted in a chamber of a plasma enhanced chemical vapor deposition apparatus. At this time, the temperature of the chamber is 700 ° C, the microwave power is 1300 W, and the internal atmospheric pressure during operation ^{was measured to be 4.0 × 10 -2} torr, hydrogen gas was supplied at 40 sccm and methane gas was supplied at 20 sccm, and carbon nanowalls were applied for 900 seconds. deposited.

[Examples 2 to 3]

Except for changing the deposition time as shown in Table 1, the same procedure as in Example 1 was performed.

[Comparative Examples 1 to 11]

The same procedure as in Example 1 was performed except that the chamber temperature, microwave power, vacuum pressure, deposition time, and gas flow rate were changed as shown in Table 1 below.

[Characteristic evaluation method]

A. Deposition height measurement

For Examples 1 to 3 and Comparative Examples 1 to 7, the height of the side surface of the carbon nanowall on which the deposition was completed was measured using SEM, and is shown in Table 1 below.

Temperature
/℃ power
/kW pressure
/torr hour
/s flow/sccm Deposition height
/μm H ₂ CH ₄ Example 1 700 1.3 4.0×10 ^-2 900 40 20 2.1 Example 2 600 1.8 Example 3 1200 2.2 Comparative Example 1 2.7×10 ^-2 900 30 15 1.4 Comparative Example 2 5.5×10 ^-2 25 55 1.2 Comparative Example 3 1.0 4.0×10 ^-2 40 20 1.4 Comparative Example 4 800 1.3 4.0×10 ^-2 40 20 1.4 Comparative Example 5 2.7×10 ^-2 30 15 1.1 Comparative Example 6 5.5×10 ^-2 25 55 0.7 Comparative Example 7 1.0 4.0×10 ^-2 40 20 0.9 Comparative Example 8 600 1.3 4.0×10 ^-2 40 20 1.4 Comparative Example 9 2.7×10 ^-2 30 15 1.2 Comparative Example 10 5.5×10 ^-2 25 55 0.6 Comparative Example 11 1.0 4.0×10 ^-2 40 20 1.0

As shown in Table 1 above, the deposition heights of Examples 1 to 3 were the best. In Comparative Example 1 in which the flow rate ratio of hydrogen gas and methane gas was changed to 2:1 and the flow rate was reduced, the deposition height was significantly reduced compared to the Example group. In addition, in the case of Comparative Example 2 in which the flow ratio of hydrogen gas and methane gas was changed to 1:2.2, the deposition height was decreased compared to Comparative Example 1, which was not good. Therefore, it can be seen that the flow rate ratio of hydrogen gas and methane gas and flow rate conditions have a great influence on the deposition height.

In the case of Comparative Example 3, in which the microwave output was lowered to 1.0 kW under the conditions of Example 1, the deposition height was 1.4 μm, which was only 66% of that of Comparative Example 1. Accordingly, it can be seen that the microwave output condition has a large effect on the deposition height.

Comparative Examples 4 to 7 were carried out to correspond to Examples 1 and 1 to 3, except that the reaction temperature was raised to 800 °C. In this case, Comparative Example 4 was conducted under conditions corresponding to Example 1, Comparative Example 5, Comparative Example 1, Comparative Example 6, Comparative Example 2, and Comparative Example 7, and Comparative Example 3. As shown in Table 1, Comparative Examples 4 to 7 can be confirmed that the deposition height is further reduced.

In addition, Comparative Examples 8 to 11 were carried out to correspond to Examples 1 and 1 to 3 in the same manner as Comparative Examples 4 to 7, except that the reaction temperature was lowered to 600 °C. In this case, Comparative Example 8 was carried out under conditions corresponding to Example 1, Comparative Example 9 and Comparative Example 1, Comparative Example 10, Comparative Example 2, and Comparative Example 11, and Comparative Example 3. As can be seen from Table 1, Comparative Examples 8 to 11 showed similar deposition heights to those of Comparative Examples 4 to 7.

Accordingly, it can be seen that the temperature conditions during deposition have a great influence on the deposition height.

[Production Example 2]

ITO was deposited on the substrate of Preparation Example 1 through a sputtering process. At this time, deposition was performed for 10 minutes while supplying argon gas under the condition ^{of 1.0×10 −2 torr with 100W RF power.}

[Production Example 3]

TiN was deposited on the substrate of Preparation Example 1 through a sputtering process. At this time, the deposition was carried out for 45 minutes while supplying argon gas under the condition ^{of 1.5×10 −2 torr with 150W RF power.}

[Example 4]

The substrate on which the deposition of Preparation Example 2 was completed was mounted in a chamber of a plasma enhanced chemical vapor deposition apparatus. At this time, the temperature of the chamber is 700 ° C, the microwave power is 1300 W, and the internal atmospheric pressure during operation ^{was measured to be 2.7 × 10 -2} torr, hydrogen gas was supplied at 40 sccm and methane gas was supplied at 20 sccm, and carbon nanowalls were applied for 600 seconds. deposited.

[Example 5]

The same procedure as in Example 4 was performed except that the substrate on which the deposition of Preparation Example 3 was completed was used.

B. Measurement of adhesion performance between carbon nanowalls and substrates

For Examples 4 to 5 and Comparative Examples 4 to 8, ultrasonic waves were applied for 5 minutes in a state in which the deposited carbon nanowalls were immersed in acetone. Thereafter, the states of the carbon nanowalls remaining on the substrate were expressed as (◎: excellent, ○: good, △: poor, ×: poor), and are shown in Table 2 below.

Carbon nanowall adhesion performance of the substrate Example 1 △ Example 4 ◎ Example 5 ○ Comparative Example 4 × Comparative Example 8 × ◎: Excellent, carbon nanowall adheres well to the substrate
○: Good, some carbon nanowalls are separated from the substrate
△: Not good, only a part of the carbon nanowall remains
×: Defective, the state in which the carbon nanowall does not remain on the substrate

As described in Table 2, Examples 4 to 5 using the ITO thin film or TiN thin film substrate can be seen that the adhesion performance with the carbon nanowall is excellent.

Although the present invention has been described through the specific matters and limited examples as described above, these are only provided to help a more general understanding of the present invention, and the present invention is not limited to the above examples, and the present invention pertains to Various modifications and variations are possible from these descriptions by those of ordinary skill in the art.

Therefore, the spirit of the present invention should not be limited to the described embodiments, and not only the claims to be described later, but also all those with equivalent or equivalent modifications to the claims will be said to belong to the scope of the spirit of the present invention. .

Claims (7)

delete delete delete delete (Step 1) removing impurities by washing the ITO or TiN thin film substrate deposited on silicon with a solvent;
(Second step) ultrasonically cleaning the substrate;
(third step) drying the substrate in a nitrogen gas atmosphere;
(Fourth step) supplying hydrogen gas and methane gas at a specific ratio on the substrate dried in a vacuum state, and depositing carbon nanowalls using plasma-enhanced chemical vapor deposition;
In the (fourth step), the temperature is 650 to 750° C., the microwave power is 1.1 to 1.5 kW, the internal pressure is 0.5×10 ^-3 to 5.0×10 ^-2 torr, and the flow rate of the hydrogen gas is 35 to 45 sccm, the flow rate of the methane gas is 17.5 to 22.5 sccm by proceeding under the conditions of having a vertical orientation at an angle of 75 to 90 ° carbon nanowall characterized in that the deposition of the carbon nanowall having a height of 1.60 to 2.20㎛ cross-section manufacturing method. 6. The method of claim 5,
The hydrogen gas and methane gas is a method of manufacturing carbon nanowalls that are supplied at a flow ratio of 1:0.5 to 1:0.64. A negative electrode material for a lithium secondary battery manufactured by the manufacturing method according to claim 5 or 6 and comprising carbon nanowalls having a cross-sectional height difference within 0.03 μm caused by the curvature of the surface.

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