KR20230043661A - Manufacturing Method of Carbon Nano Tube Electrode For Lithium-sulfur Battery And Sulfur Deposited Carbon Nano Tube Cathode, And Lithium-sulfur Battery Comprising The Same - Google Patents

Abstract

A method for manufacturing a carbon nanotube electrode structure for supporting sulfur is disclosed. The present invention provides a method for manufacturing a carbon nanotube electrode for a lithium sulfur battery, including the steps of: (a) growing carbon nanotubes on a substrate to form a carbon nanotube array in which a plurality of carbon nanotubes are arranged; and (b) opening an end of the carbon nanotubes of the array and forming defects on the surface of the carbon nanotubes of the array.

Description

Manufacturing Method of Carbon Nano Tube Electrode For Lithium-sulfur Battery And Sulfur Deposited Carbon Nano Tube Cathode, And Lithium-sulfur Battery Comprising The Same}

The present invention relates to a method for manufacturing a carbon nanotube (CNT) electrode, and more particularly, to a method for manufacturing a carbon nanotube electrode structure for supporting sulfur.

As the wearable market gradually expands, the development of flexible devices having various sizes and shapes is also accelerating. Accordingly, there is an urgent need to develop flexible batteries having high-density energy that can be applied to various mobile devices, EVs (Electric Vehicles), and ESSs (Energy Storage Systems).

Until now, flexible batteries have been developed in thin film, paper/fiber, cable, etc. to secure flexibility of batteries, but have problems such as low energy density, poor durability, and limited capacity.

Therefore, in order to manufacture a high-density, high-flux battery while maintaining flexibility for application to flexible devices, attempts have been made to minimize the thickness and weight of the current collector, but as the thickness of the current collector becomes thinner, the electrolyte and surrounding battery constituent materials There was a problem of accelerating the deterioration of the battery by affecting it.

In addition, studies using carbon-based materials such as CNT (Carbon Nano Tube), CNF (Carbon Nano Fiber), and graphene as current collectors have been reported to secure flexibility in flexible batteries, but carbon-based materials are used as current collectors. When used as a whole, the mechanical strength of the electrode is weak, so it is difficult to commercialize or use it in a large area.

On the other hand, research on the use of sulfur as a cathode active material for lithium secondary batteries with large theoretical capacity is being actively conducted. Due to the low sulfur-based cathode active material, it is difficult to secure high performance due to poor electron transfer during charging and discharging. In addition, when sulfur is used as a cathode active material, not only does sulfur flow into the electrolyte during the oxidation-reduction reaction, which deteriorates battery life, but also lithium polysulfide, a reducing material of sulfur, is eluted and passes through the separator to the anode, which is used as an anode. On the surface of lithium metal, lithium sulfur compounds are oxidized to final solid-state single molecules (Li ₂ S ₂ , Li ₂ S), which are irreversible reactants, or Li ₂ O through reaction with oxygen or reaction with decomposition products of electrolyte materials. There was a problem in that the amount of sulfur and lithium that can be generated and participate in the reaction is depleted, so that they can no longer participate in the electrochemical reaction.

Moreover, as the capacity of batteries has recently increased, interest in electrode materials and electrode structures that can reproduce the fast charging speed required for lightening batteries and charging is increasing. Accordingly, as the utilization of lithium-sulfur batteries among various types of next-generation batteries has emerged, development of electrode structures capable of improving the performance of lithium-sulfur batteries has been continuously conducted.

US 2013-0065128 A KR 10-1698052 B KR 10-2019-0098401 A

In order to solve the problems of the prior art, an object of the present invention is to provide a carbon nanotube (CNT) electrode for a lithium-sulfur battery capable of stably supporting sulfur.

In addition, an object of the present invention is to provide a carbon nanotube electrode for a lithium-sulfur battery capable of suppressing the elution of lithium polysulfide, which is a sulfur reducing material.

In addition, an object of the present invention is to provide a carbon nanotube positive electrode for a lithium-sulfur battery that solves the problem of the electrochemical reaction of a lithium-sulfur battery by modifying the surface of a CNT-based sulfur carrier.

In addition, an object of the present invention is to provide a method for manufacturing the above-described carbon nanotube anode.

In order to achieve the above technical problem, the present invention provides a method for manufacturing a carbon nanotube electrode for a lithium sulfur battery, (a) growing carbon nanotubes on a substrate to form a carbon nanotube array in which a plurality of carbon nanotubes are arranged. doing; and (b) opening ends of the carbon nanotubes of the array and forming defects on the surface of the carbon nanotubes of the array.

In the present invention, step (b) may include exposing the surface of the carbon nanotube to oxygen plasma.

In addition, the step (a) may include a PE-CVD step using a source gas containing a carbon precursor, a hydrogen precursor, and an oxygen precursor.

In the present invention, the step (b) may include opening the ends of the carbon nanotubes with plasma using an oxygen precursor as a source gas.

In addition, the step (b) may include forming COOH functional groups on the surface of the carbon nanotubes using plasma using an oxygen precursor as a source gas.

The present invention may further include (c) vapor-depositing sulfur on the carbon nanotube array. At this time, the vapor deposition step is preferably performed in a vacuum atmosphere. In addition, in step (c), sulfur may be physically adsorbed by forming an induced dipole between adjacent carbon nanotubes. In addition, in the step (c), sulfur may be chemically adsorbed to the carbon nanotubes.

In order to achieve the above other technical problem, the present invention is a conductive substrate; a carbon nanotube array in which a plurality of carbon nanotubes that directly contact the substrate and grow upward on the substrate are arranged; and sulfur filling the carbon nanotube array, wherein the sulfur is physically adsorbed by forming an induced dipole by a surface functional group of the carbon nanotube in a gap between the carbon nanotubes. A nanotube electrode is provided.

In the present invention, the surface functional group of the carbon nanotube electrode preferably includes COOH.

According to the present invention, it is possible to provide a three-dimensional electrode structure that has high energy density and high capacity while maintaining the flexibility of the battery and can be usefully used as a flexible battery.

In addition, according to the present invention, compared to conventional CNT-based electrodes using sulfur as an active material, by controlling the surface of the CNT, it is possible to improve the bonding force with sulfur, thereby maximizing the performance of the lithium-sulfur battery.

1 is a diagram schematically showing a carbon nanotube electrode structure according to an embodiment of the present invention.
2 is a diagram schematically illustrating a process of manufacturing a carbon nanotube electrode structure according to an embodiment of the present invention.
3 is a graph showing the results of Raman spectroscopy analysis on a carbon nanotube electrode structure manufactured according to an embodiment of the present invention.
4 is a graph showing the results of SEM, TEM, and TGA analysis of a carbon nanotube electrode structure observed according to surface treatment and sulfur insertion content according to an embodiment of the present invention.
5 is a graph showing the results of evaluating the electrochemical characteristics of a three-dimensional electrode structure according to an embodiment of the present invention.
6 is a graph showing the results of EIS analysis to determine the electrode resistance of an electrode made of a three-dimensional electrode structure according to an embodiment of the present invention.
7 is a photograph and a graph showing the results of measuring the sulfur content in the electrolyte solution after charging and discharging a battery sample made of a carbon nanotube electrode structure according to an embodiment of the present invention for 150 cycles.
8 is a graph showing the results of XPS analysis of the surface of a lithium anode after charging and discharging a coin cell made of a carbon nanotube electrode structure according to an embodiment of the present invention for 150 cycles.
9 is a view for explaining a sulfur supporting mechanism of a carbon nanotube electrode structure according to an embodiment of the present invention.

Hereinafter, the present invention will be described in detail by describing preferred embodiments of the present invention with reference to the drawings.

1 is a diagram schematically showing a carbon nanotube electrode structure according to an embodiment of the present invention.

Referring to FIG. 1 , the carbon nanotube electrode structure 100 is an array structure in which a conductive substrate 110 and a plurality of carbon nanotubes 120 on the conductive substrate are arranged. Sulfur 130 is deposited on the outer and/or inner surfaces of the individual carbon nanotubes 120 .

As shown in FIG. 1 , the carbon nanotubes 120 have good electrical conductivity because they are in direct electrical contact with a conductive substrate 110 such as a current collector. To this end, it is preferable that the carbon nanotube 120 array is directly grown on the conductive substrate. A method of directly growing carbon nanotubes on a conductive substrate will be described later.

Meanwhile, the carbon nanotube electrode structure 100 is composed of an array of carbon nanotubes 120 arranged at predetermined intervals. At this time, the carbon nanotubes may have a diameter of about 1 to 10 nm. In addition, the spacing between the carbon nanotubes may be preferably 0.1 to 100 nm.

2 is a diagram schematically illustrating a process of manufacturing a carbon nanotube electrode structure according to an embodiment of the present invention.

Referring to (a) of FIG. 2 , a conductive metal substrate 110 is provided. In the present invention, one metal selected from the group consisting of Al, Ni, Si, and W or an alloy thereof may be used as the conductive metal substrate 110 . Also, stainless steel may be used as the conductive metal substrate.

In the present invention, the conductive metal substrate 110 may be a porous substrate, and a conventional etching method may be used for manufacturing the porous substrate. For example, a porous pore structure may be formed on or inside the substrate by chemically etching the substrate with a solution containing an acid catalyst, an oxidizing agent, and purified water. At this time, nitric acid (HNO ₃ ) or sulfuric acid (H ₂ SO ₄ ) may be used as the acid catalyst.

Next, as shown in (b) of FIG. 2, a catalyst layer 122 for growing carbon nanotubes is formed on the substrate. The catalyst layer 122 may include at least one metal selected from the group consisting of nickel (Ni), cobalt (Co), titanium (Ti), and iron (Fe), or an alloy of the metal. In addition, the catalyst layer 122 may further include a buffer layer (not shown) such as an Al layer between substrates. The catalyst layer 122 may be formed by a solution dropping method, electron beam evaporation, or sputtering.

Next, as shown in (c) of FIG. 2, carbon nanotubes 120 are grown on the substrate on which the catalyst layer is formed (c). At this time, the carbon nanotube structure is composed of a plurality of CNT arrays grown over the entire substrate on which the catalyst layer is formed. In the present invention, the carbon nanotubes grow in a columnar shape (pillar shape) in a direction perpendicular or almost perpendicular to the surface of the substrate. However, in the present invention, 'vertical' does not exclude growth at an inclination angle other than 90°.

In the present invention, a vapor deposition method such as PE-CVD may be used to form the CNT structure. At this time, a carbon precursor such as C ₂ H ₂ , hydrogen gas (H ₂ ), and oxygen gas (O ₂ ) may be used as a source gas, and a CNT plasma is formed at a temperature of 500 to 800° C. and an output of 500 to 800 W. can grow.

In this process, carbon nanotube growth may be achieved through the following process. Hydrocarbon gas molecules containing carbon are adsorbed to the surface of the catalyst metal particle for decomposition, and the decomposed carbon atoms are dissolved and diffused into the catalyst to form a graphite-like layer. It is leached and grown on the surface of the growth substrate.

In the present invention, the CNTs constituting the array may be single walled nanotubes (SWNTs), multi-walled nanotubes (MWNTs), or rope nanotubes, but surface defects MWCNTs are preferred from the viewpoint of being advantageous in formation.

At this time, in the growth of CNTs, it is important to select a substrate with an appropriate thickness because the rate of heat transfer to the catalyst surface varies depending on the thickness of the substrate and the reaction control form between the catalyst and the CNT source gas varies. Illustratively, a low growth temperature range of 600° C. or less on a substrate having a thickness of 40 μm to 70 μm enables control of the growth rate.

Then, as shown in (d) of FIG. 2, the catalyst layer at the end of the CNT is removed to open the end of the CNT. Various methods such as acid treatment, combustion, or laser trimming may be used for this process.

For example, in the present invention, a method of opening CNTs by plasma-treating them may be used. When oxygen gas (O ₂ ) is used as a source for plasma formation in the plasma device, the generated O ₂ plasma spans the tip of the CNT end, and the carbon at the end of the CNT reacts with oxygen to be removed as CO ₂ . Along with the removal of the terminal carbon, the catalyst layer may also be removed. According to one embodiment of the present invention, the opening at the end of the CNT may be implemented as a subsequent process of CNT growth in a PE-CVD growth apparatus by using only O ₂ gas among source gases for CNT growth.

In addition, the present invention forms defects on the surface of the CNT simultaneously with or separately from the opening at the end of the CNT after the growth of the CNT. According to one embodiment of the present invention, this process may be performed by plasma treating the surface of the CNT, and at this time, the aforementioned O ₂ plasma may be used.

Oxygen gas (O ₂ ) is used as a source for plasma formation in the plasma apparatus, and when the generated O ₂ plasma touches the CNT, the CNT surface is also exposed to the plasma along with the removal of the catalyst layer at the end of the CNT surface. Carbon on the surface of the CNT reacts with the plasma by the O ₂ plasma, and surface defects are formed.

Subsequently, sulfur is inserted into the CNT array structure in which the surface defects are formed. In the present invention, sulfur preferentially binds to defects on the CNT surface, and the binding mechanism is as follows.

Defects formed on the surface of CNTs, such as carbon in COOH functional groups, exhibit permanent + polarity. On the other hand, the sulfur atom constituting the sulfur molecule (S8) forms a covalent bond, and - polarity is induced as it comes into contact with the carbon molecule of permanent + polarity. Strong physisorption occurs between the nanotube and the sulfur.

As will be described later, such physical adsorption is very strong in a vacuum atmosphere, and sulfur molecules can be strongly fixed to the inner and outer surfaces. In particular, the bonding by physisorption with sulfur occurs very strongly at the defective part of the outer surface of the CNT, so that sulfur can be fixed.

In the present invention, the method of fixing sulfur inside and/or outside of the carbon nanotubes may be performed under vacuum or pressurized conditions.

Specifically, sulfur insertion under reduced pressure conditions places an electrode structure including carbon nanotubes and sulfur in a system in a vacuum state in a state of being separated from each other, vaporizes sulfur, induces it into carbon nanotubes, and then fixes it on the surface of the carbon nanotubes. can be made In the present invention, the sulfur fixation is preferably performed at a temperature of 100 to 200 °C. A high temperature of 200° C. or higher is undesirable because it causes separation of sulfur.

Hereinafter, the present invention will be described in more detail through specific examples. The following examples describe a preferred embodiment of the present invention, and the scope of the present invention is not limited and interpreted by the matters described in the following examples.

Preparation Example 1: Preparation of CNT electrode structure

Catalyst solution (0.1M Fe(NO ₃ ) ₃ ㆍ9H ₂ O + Al(NO ₃ ) ₃ ㆍ 9H ₂ O in Ethanol + 4wt% water) is dropped onto a stainless steel substrate (substrate thickness 15, 40 or 70μm) and dried to form a catalyst layer.

CNTs were grown on a substrate on which a catalyst layer was formed using a PE (plasma enhanced)-CVD device. At this time, as the source gas, C ₂ H ₂ , H ₂ and O 2 gas were used as the carbon precursor. The temperature of the chamber in which the substrate was mounted was maintained at 500 to 800° C. to stabilize it, and CNTs were grown by forming a plasma of 500 to 800 W.

From this, it was confirmed that CNT growth is possible at a low temperature of 600 ° C or less on a substrate having a thickness of 40 to 70 μm, and the growth rate is also controllable. In addition, it was confirmed that the catalyst can be coated even in the form of a solution, and it was confirmed that CNTs can be grown by coating the catalyst regardless of the model of the substrate.

Preparation Example 2: Preparation of surface-treated CNT structure

After growing the CNT structure in the plasma device in which the electrode structure of Preparation Example 1 was manufactured, the supply of the precursor material as a source gas was stopped and only oxygen was injected so that the plasma was spread across the tip end of the CNT to react with the oxygen to form carbon at the tip of the CNT. The catalyst layer was removed while removing with CO ₂ . In this process, the CNTs on the substrate were exposed to plasma, and a number of defects were formed on the surface of the CNTs exposed to the plasma.

Specifically, in the surface treatment process, the pressure in the vacuum chamber was maintained at a level of 1 x 10 ^-1 torr, the flow rate of O2 gas was about 60 sccm, and 50 W of RF (radio frequency) power was applied to treat for 1 minute. Of course, the pressure, gas flow rate, and plasma power can be variously adjusted according to utilization conditions.

<Example 1>

Sulfur was inserted into the electrode structure prepared in Preparation Example 2 in a vacuum state through the following process. After putting the fabricated electrode structure in a closed system, a vacuum pump was connected to the outlet of the system to lower the pressure inside the system. A container containing sulfur was heated outside the closed system to vaporize the sulfur, and a line connected to the container was opened at the inlet of the closed system so that the vaporized sulfur was inserted by a pressure difference.

<Examples 2 to 4>

Sulfur was inserted into the electrode structure prepared in Preparation Example 2 through the following process.

After placing the container containing sulfur and the electrode structure of Preparation Example 2 in a state separated from each other in the chamber, the chamber was maintained in a vacuum (<10 ^-3 torr) state. When the inside of the chamber is in a vacuum state, after closing the vacuum line, the temperature of the chamber is heated to 120 ~ 180 ℃ to vaporize sulfur, and sulfur is inserted into the electrode structure. At this time, the sulfur content was adjusted by varying the treatment time in the chamber. A sample with a sulfur content of 0% (Example 2), a sample with a sulfur content of 48% (Example 3), and a sample with a sulfur content of 78% (Example 4) were prepared with respect to the total weight of the electrode structure. At this time, the sulfur content was calculated by subtracting the weight of the electrode before the sulfur insertion process from the weight of the electrode after sulfur insertion. It was calculated as a ratio of The weight of the CNT was calculated by subtracting the weight of the current collector from the weight of the current collector after CNT growth.

<Comparative Example>

The sample without surface treatment and sulfur insertion, that is, the CNT structure sample of Preparation Example 1 was taken as Comparative Example 1, and the sample with 78% sulfur inserted was used as in Example 4 except that it was not subjected to surface treatment. 2.

3a and b are graphs showing the results of analyzing the carbon nanotube electrode structures of Examples and Comparative Examples through Raman spectroscopy, and Table 1 is a table summarizing the analysis results.

First, samples #1 and #2 in a of FIG. 3 are the sample before sulfur is inserted (Comparative Example 1) without surface treatment after carbon nanotube growth and the state without surface treatment after carbon nanotube growth, respectively. is a sample after sulfur is inserted (Comparative Example 2), and sample #3 and #4 are respectively a sample before sulfur is inserted after surface treatment after carbon nanotube growth (Example 2) and a sample after insertion (Example 2). 4) is.

3b is a sample in which sulfur is inserted into an electrode surface-treated with carbon nanotubes with sulfur content of 0% (Example 2), sulfur content of ~48% (Example 3), and sulfur content of ~78% (Example 4). This is a graph of the result of observing the change of the Raman spectrum of

As can be seen from the results of a and Table 1 in Figure 3, when the surface treatment is performed, a bond between sulfur and carbon nanotubes is formed, resulting in a bond between carbon-sulfur and 1250 cm ^-1 corresponding to CS mode on the Raman spectrum, It was confirmed that peaks appeared at 1450 cm ^-1 and 2780 cm ^-1 . In addition, in b of FIG. 3, it was confirmed that when sulfur was added to the surface-treated sample after carbon nanotube growth according to the content, a peak corresponding to the SS mode appeared when sulfur was inserted at ~50% or more. It was confirmed that sulfur was accumulated on it when all the bonding of the primary occurred and the exposed surface disappeared. When sulfur is accumulated in a form without contact with the surface of the carbon nanotubes, the electron transfer path is lost, which acts as a factor that deteriorates the performance of the battery, so that proper bonding between sulfur and carbon nanotubes is secured, and Content will act as an important factor.

4 is a photograph and a graph showing the analysis results of the carbon nanotube electrode structure related to Example 4 of the present invention.

4a and b are SEM images of a sample before plasma treatment (Comparative Example 1) and a sample after plasma treatment (Example 2), respectively, on the surface of the grown carbon nanotubes, and c and d are respectively sulfur without surface treatment. It is a SEM picture of a sample (Comparative Example 2) inserted with sulfur and a sample (Example 4) with sulfur inserted (sulfur content 78%) after surface treatment.

In the present invention, the growth of carbon nanotubes is achieved through the following process. Hydrocarbon gas molecules containing carbon are decomposed by plasma, and the decomposed carbon atoms are dissolved and diffused into the catalyst, and graphite-like layers are leached to form the surface of the growth substrate. grow up Carbon nanotubes formed by the above-described process have hexagonal honeycomb-shaped graphite planes in which one carbon atom is bonded to three other carbon atoms, rolled into a nano-sized diameter. Referring to a and b of FIG. 4 , columnar carbon nanotubes grown in a direction substantially perpendicular to the substrate are densely arranged to form a carbon nanotube bundle.

On the other hand, as can be seen from c and d of FIG. 4, the sulfur insertion (or deposition) pattern is significantly different depending on whether or not plasma treatment is performed. First, as shown in c of FIG. 4, since the sample without surface treatment after growing the carbon nanotubes has insufficient defects for bonding with sulfur on the surface of the carbon nanotubes, the supplied sulfur is preferentially applied to the top of the carbon nanotubes. It accumulates in the part and prevents excess sulfur from entering the space between the carbon nanotubes. Accordingly, most of the introduced sulfur is accumulated on the upper part of the carbon nanotube bundle. On the other hand, as shown in d of FIG. 4 , it can be confirmed that sulfur is well filled in the space between the carbon nanotubes in the surface-treated sample. It is understood that the sulfur layer formed on the top of the carbon nanotubes in FIG. 4d is because the sulfur content used in this experiment is very high.

Meanwhile, e to h of FIG. 4 are photographs showing the results of TEM and EDS analysis by taking some carbon nanotubes from samples subjected to plasma surface treatment. Referring to the photo, it was confirmed that sulfur was even inside the carbon nanotubes. That is, as shown in f of FIG. 4, the sulfur (S) component clearly observed in the center of the carbon (C) element constituting the carbon nanotubes shows that the inside of the carbon nanotubes is filled with sulfur. On the other hand, for comparison with FIG. 4 , FIG. 5 shows TEM and EDS analysis pictures observed by collecting carbon nanotubes from the sample after inserting sulfur into the sample without surface treatment after growing the carbon nanotubes. FIG. 5 shows that sulfur did not penetrate into the inside of the carbon nanotubes because the ends of the carbon nanotubes were blocked by iron, which is a catalyst.

Meanwhile, h in FIG. 4 is a graph showing the results of TGA analysis of the samples taken from the surfaces of the electrodes of Examples 2 and 4 and the sulfur material itself. Referring to h of FIG. 4 , as a result of the TGA, it can be confirmed that the sulfur supporting ability is increased through the surface treatment of the carbon nanotubes.

Referring to the TGA graph, it shows that sulfur starts to vaporize from the carbon nanotube surface from around 180 ° C, and the weight decreases. In addition, it can be seen from the graph that when TGA is measured after sulfur insertion under the same conditions and the weight ratio is compared, the weight difference between the treated and untreated carbon nanotube surfaces is 73.2% and 5.8%, respectively. Through this, it can be inferred that sulfur adsorption and insertion are more smoothly performed in the case of the surface-treated sample compared to the untreated sample.

5 is a graph showing the results of evaluating the electrochemical characteristics of cells manufactured with three-dimensional electrode structures according to Example 3 and Comparative Example 2 of the present invention. 5 shows a comparison of capacity and coulombic efficiency of carbon nanotube electrodes with and without sulfur support, and capacity change rates according to charging and discharging rates.

The battery cell was manufactured in the following way. After manufacturing an electrode structure according to each Example or Comparative Example, punching out an electrode of a size that can be mounted on a 2032 coin cell, inserting it into the lower case of the coin cell, placing a separator thereon, and then wrapping the edge of the separator with a ring-shaped insulating spacer. After fixing, the electrolyte was filled, Li metal was attached to the upper case of the coin cell, and the upper case and the lower case were pressed and sealed.

Referring to a to c of FIG. 5, in the case of the surface treatment (surface treatment (O)), the cycle characteristics maintain the capacity retention rate of 88.5% or more even up to 100 cycles based on the data except for the first cycle of the formation cycle. On the other hand, in the case of the sample without surface treatment (surface treatment (X)), it can be seen that the deterioration of the battery is rapidly progressing to the 50% level, and the improvement of the result value due to the surface treatment is clearly shown. In addition, as shown in d and e of FIG. 5, even in the C-rate characteristic evaluation based on the charging rate, the rate of maintaining capacity even when the charging and discharging rate is increased is much better in the case of the surface-treated sample. It can be seen that the performance of the battery is improved because the bonding strength between the functional group and sulfur at the defect site of the carbon nanotube is improved.

Figure 6 is EIS to find out the electrode resistance of the three-dimensional electrode structure according to Example 3 and Comparative Example 2 of the present invention and the electrode made by mixing sulfur and carbon nanotubes in the conventional slurry method rather than the electrode structure of the direct growth method It shows the result of running the analysis.

Referring to FIG. 6, in the case of the electrode (Direct write/surface treatment (O)) made of the three-dimensional electrode structure of Example 3, the electrode made of the electrode structure of Comparative Example 2 (Direct write/surface treatment (X)) ) and the existing slurry method showed the lowest electrical resistance compared to the electrode (S / CNT slurry), demonstrating the effectiveness of the present invention.

7 is a C-S analysis of the sulfur content contained in the electrolyte solution in the battery through cell disassembly after 150 cycles of charging and discharging after the battery is configured with a cell made of a three-dimensional electrode structure according to Example 3 and Comparative Example 2 of the present invention It is a diagram showing the results measured through

In FIG. 7, a and b are photographs of cell disassembly, c and d are photographs of the electrolyte solution, and e is a graph showing the sulfur content. Referring to FIG. 7 , as can be seen from the results, it was confirmed that the elution of sulfur was much lower in the electrode with defects than in the electrode without defects.

8 is a three-dimensional electrode structure according to Example 3 and Comparative Example 2 of the present invention, a coin cell is constructed using an existing slurry-type electrode structure rather than a direct-growth electrode structure, and then 150 cycles of charging and discharging are performed. After disassembling the cell, it is a graph showing the result of elemental analysis of the surface of the lithium metal anode side through XPS analysis.

Referring to FIG. 8, in the case of the battery using the three-dimensional electrode structure of Example 3, the electrolyte by-products formed on the surface of the negative electrode appeared to be the lowest. The decrease in the decomposition reaction of the electrolyte on the surface of the anode seems to be due to the decrease in the elution of lithium polysulfide.

In addition, the three-dimensional electrode structure of the present invention traps sulfur inside the CNT to generate polysulfide during charging and discharging, for example, Li ₂ S ₈ , Li ₂ S ₆ , Li ₂ S ₄ , By fixing Li ₂ S ₃ to reduce external exposure, it was confirmed that the cycle retention rate could be increased by reducing the shuttle effect, which is a chronic problem of Li—S.

The above sulfur insertion mechanism step will be described in detail with reference to FIG. 9 below.

As shown in FIG. 9, when sulfur is inserted into carbon nanotubes, physisorption between carbon nanotubes and sulfur is preferentially caused by induced dipole interaction between carbon nanotubes and sulfur in vacuum. rises strongly in the atmosphere. This adsorption can strongly fix sulfur on the inner/outer surfaces of the carbon nanotubes compared to solution-type adsorption. In particular, physisorption bonding with sulfur occurs much stronger at the defect part outside the carbon nanotube, so that binding through sulfidication is performed, enabling sulfur to be fixed. In addition, as described above, when sulfur is fixed inside/outside the carbon nanotubes grown on the surface of the porous metal foam and the metal thin film, the electron transfer rate is increased. When the electron transfer rate improves in this way, chemisorption occurs with the carbon nanotubes in the molten state of lithium polysulfide on the electrochemical reaction mechanism that occurs during charging and discharging after battery manufacturing, forming a stronger bond to shuttle You can suppress the shuttle effect.

100: three-dimensional electrode structure
110: substrate
120: carbon nanotube
130: sulfur

Claims (11)

In the method for manufacturing a carbon nanotube electrode for a lithium sulfur battery,
(a) growing carbon nanotubes on a substrate to form a carbon nanotube array in which a plurality of carbon nanotubes are arranged; and
(b) opening the ends of the carbon nanotubes of the array and forming defects on the surface of the carbon nanotubes of the array. According to claim 1,
Wherein step (b) comprises exposing the surface of the carbon nanotubes to oxygen plasma. According to claim 2,
In the step (a),
A method for producing a carbon nanotube electrode for a lithium sulfur battery, comprising a PE-CVD step by a source gas containing a carbon precursor, a hydrogen precursor and an oxygen precursor. According to claim 3,
The method of manufacturing a carbon nanotube electrode for a lithium sulfur battery, characterized in that the step (b) comprises opening an end of the carbon nanotube with a plasma using an oxygen precursor as a source gas. According to claim 4,
The step (b) is a method for producing a carbon nanotube electrode for a lithium sulfur battery, characterized in that it comprises the step of forming a COOH functional group on the surface of the carbon nanotube with a plasma using an oxygen precursor as a source gas. According to any one of claims 1 to 5,
(c) vapor deposition of sulfur on the carbon nanotube array. According to claim 6,
The vapor deposition method of manufacturing a carbon nanotube electrode, characterized in that carried out in a vacuum atmosphere. According to claim 7,
In step (c), sulfur is physically adsorbed by forming an induced dipole between adjacent carbon nanotubes. According to claim 7,
Method for producing a carbon nanotube electrode for a lithium sulfur battery, characterized in that in step (c), sulfur is chemically adsorbed to the carbon nanotube. conductive substrate;
a carbon nanotube array in which a plurality of carbon nanotubes that directly contact the substrate and grow upward on the substrate are arranged; and
Including sulfur filling the carbon nanotube array,
The carbon nanotube electrode for a lithium sulfur battery, characterized in that the sulfur is physically adsorbed by forming an induced dipole by the surface functional group of the carbon nanotube in the gap between the carbon nanotubes. According to claim 10,
The surface functional group is a carbon nanotube electrode for a lithium sulfur battery, characterized in that it comprises COOH.

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