KR20200111877A - Cathode for lithium-sulfur battery comprising siloxene compound - Google Patents

Abstract

The present invention provides a positive electrode for a lithium-sulfur secondary battery including a siloxane compound containing at least one siloxane and a positive electrode active material, and a method for manufacturing the same. The present invention has a high capacity and high energy density.

Description

A cathode for lithium-sulfur secondary battery comprising siloxene compound {Cathode for lithium-sulfur battery comprising siloxene compound}

The present invention relates to a positive electrode for a lithium-sulfur secondary battery including a siloxane compound containing at least one siloxane and a positive electrode active material. Specifically, the present invention relates to a positive electrode for a lithium-sulfur secondary battery to which a siloxane compound and a positive electrode active material, which are effective for immobilizing polysulfide, which is an intermediate product of a lithium-sulfur secondary battery, are added.

Recently, as the demand for portable electronic devices, electric vehicles, and energy storage systems has exploded, research on secondary batteries is actively in progress. Since Sony released a lithium-ion secondary battery (LIB) using a graphite-based anode material in 1991, lithium-ion secondary batteries are still known as the best secondary batteries, but recently, the battery required by smartphones and electric vehicles. Since the capacity far exceeds the performance of lithium-ion secondary batteries, it is considered urgent to develop lithium-sulfur secondary batteries with higher energy density.

Lithium-sulfur secondary batteries are currently being actively researched as one of the most promising next-generation batteries because they use sulfur as a positive electrode active material, which is inexpensive and abundant on Earth, and has a high theoretical capacity (1,672 mAh/g). The biggest obstacle to the commercialization of lithium-sulfur secondary batteries is that polysulfides, which are intermediate products, are eluted into the electrolyte, which causes performance degradation such as reduction of active materials in the positive electrode and reduction of total discharge capacity. Accordingly, there is an urgent need to develop a technology for maximizing the sulfur utilization rate while suppressing the elution of polysulfide. In addition, most recent studies on lithium-sulfur secondary batteries use positive electrodes with a low sulfur content (<2 mg sulfur/cm ² ). In this case, the theoretical capacity is only 3.2 mAh/cm ² , so commercial lithium- There is a problem that the capacity of the ion secondary battery is less than 4 mAh/cm ² . Since the elution of the polysulfide mentioned above is more severe when it has a high loading value, it is very important to test under a high loading condition (>6 mg sulfur/cm ² ) when developing a positive electrode capable of inhibiting elution.

One object of the present invention is to provide a positive electrode for a lithium-sulfur secondary battery comprising a siloxane compound.

Another object of the present invention is to provide a method of manufacturing a positive electrode for a lithium-sulfur secondary battery comprising a siloxane compound.

In order to solve the above-mentioned problems of polysulfide elution and low sulfur loading of lithium-sulfur secondary batteries, it was found that the siloxane compound added to the positive electrode was effective in immobilizing polysulfide, and the present invention was completed.

One aspect of the present invention is to provide a positive electrode for a lithium-sulfur secondary battery comprising a siloxane compound including at least one siloxane and a positive electrode active material.

In an embodiment of the present invention, the siloxane may be in the form of a nanosheet.

In an embodiment of the present invention, the siloxane compound may have a structure in which one or more siloxanes are stacked.

In an embodiment of the present invention, the stacking interval between the one or more siloxanes may be 0.2 nm or more.

In an embodiment of the present invention, the siloxane compound may include a functional group containing oxygen.

In an embodiment of the present invention, the functional group containing oxygen of the siloxane compound may be combined with polysulfide.

In one embodiment of the present invention, the siloxane compound may be included in an amount of 0.1% to 25% by weight based on the total weight of the positive electrode for a lithium-sulfur secondary battery.

In an embodiment of the present invention, the positive electrode active material may include any one selected from the group consisting of inorganic sulfur (S ₈ , elemental sulfur), sulfur-based compounds, and combinations thereof.

In an embodiment of the present invention, the positive electrode for a lithium-sulfur secondary battery may include a current collector.

In one embodiment of the present invention, the positive electrode for a lithium-sulfur secondary battery may further include a binder and/or a conductive material.

One aspect of the present invention provides a lithium-sulfur secondary battery including the positive electrode for the lithium-sulfur secondary battery.

One aspect of the present invention comprises the steps of preparing a siloxane compound; Mixing and processing the siloxane compound and a positive electrode active material to prepare a positive electrode for a lithium-sulfur secondary battery; It provides a method of manufacturing a positive electrode for a lithium-sulfur secondary battery comprising a.

In an embodiment of the present invention, the step of preparing the siloxane compound may be performed at a temperature of 0 °C or higher.

The present invention provides a positive electrode for a lithium-sulfur secondary battery containing a siloxane compound, thereby fixing polysulfide, which is an intermediate product during charging and discharging of a lithium-sulfur secondary battery, to the positive electrode to suppress elution, and contains sulfur content as a positive electrode active material. By increasing the, it is possible to provide a lithium-sulfur secondary battery having a high capacity and high energy density.

The effects of the present invention are not limited to the above effects, and should be understood to include all effects that can be inferred from the configuration of the invention described in the detailed description or claims of the present invention.

1 is a schematic diagram of a reaction of a siloxane compound prepared according to an embodiment of the present invention (a), SEM (b and c), TEM (d) photographs, nitrogen adsorption/desorption (e and f), and XRD experiments (g ) Shows the result.
2 shows the results of FT-IR (a), Raman spectra (b) and XPS experiments (c, d and e) of a siloxane compound prepared according to an embodiment of the present invention.
3 shows the test results of the sulfur active material adsorption capacity of the siloxane compound prepared according to an embodiment of the present invention.
4 shows the results of a cycling test of a lithium-sulfur secondary battery manufactured according to an example and a comparative example of the present invention.
5 shows a separator and a lithium metal portion of a lithium-sulfur secondary battery manufactured according to an embodiment and a comparative example of the present invention.
6 shows CV (a to d) and GCPL (e) experimental results of lithium-sulfur secondary batteries manufactured according to an embodiment and a comparative example of the present invention.
7 shows the XPS test results of the lithium-sulfur secondary battery prepared according to an embodiment and a comparative example of the present invention.

Hereinafter, the present invention will be described with reference to the accompanying drawings. However, the present invention may be implemented in various different forms, and therefore is not limited to the embodiments described herein. In the drawings, parts not related to the description are omitted in order to clearly describe the present invention.

Throughout the specification, when a part is said to be "connected (connected, contacted, bonded)" with another part, it is not only "directly connected", but also "indirectly connected" with another member in the middle. "Including the case. In addition, when a part "includes" a certain component, it means that other components may be further provided, rather than excluding other components unless specifically stated to the contrary.

In the present specification, when a part such as a layer, film, region, plate, etc. is said to be "on" another part, this includes not only the case where the other part is "directly above", but also the case where there is another part in the middle.

The terms used in the present specification are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

One aspect of the present invention provides a positive electrode for a lithium-sulfur secondary battery comprising a siloxane compound containing at least one siloxane and a positive electrode active material.

In the present specification, “siloxene” refers to a material that has a basic skeleton in which a plurality of hexagonal rings composed of silicon (Si) elements are bonded and exists in a planar form, for example, in the form of a nanosheet.

In the present invention, the "siloxane compound" may be a form in which one or more siloxanes are randomly distributed, a wide plate is formed, or may be arranged in one direction, for example, stacked in one direction. It can be in the form that there is.

The lamination interval between the stacked one or more siloxanes provides a space for adsorbing and/or fixing polysulfide, an intermediate product generated during charging and discharging of a lithium-sulfur secondary battery.

The stacking interval between the stacked one or more siloxanes may be 0.2 nm or more, for example, 0.4 nm or more.

The siloxane compound may include a functional group containing oxygen.

The functional group containing oxygen of the siloxane compound may be bonded to the polysulfide.

The oxygen-containing functional group may be, for example, one or more selected from the group consisting of a hydroxyl group, a carbonyl group, an aldehyde group, a carboxylic acid ester group, a hydroperoxy group, and a combination thereof, for example, a hydroxyl group.

The oxygen-containing functional group may be included in an amount of 20% to 50% by weight, for example, 33% by weight based on the total weight of the siloxane compound.

In this specification "polysulfide" the polysulfide ions (S _x ^2-, wherein, x is 8, 6, 4 or 2), and a lithium polysulfide (Li ₂ S _x, or LiS _x ^-, wherein, x is 8, 6, 4, or 2).

Since most of the lithium-sulfur secondary battery research conducted so far uses a low sulfur content (≤2 mg/cm ² ), the area capacity is about 3.35 mAh/cm ² even if 100% efficiency is assumed, resulting in the existing lithium ion secondary battery. It is lower than the maximum area capacity of the battery (about 4 mAh/cm ² ).

Therefore, in order to develop a lithium-sulfur secondary battery having a high energy density, the sulfur content is 6 mg/cm ² or more, while maximizing the mass ratio and sulfur utilization rate of the sulfur active material in the positive electrode, and minimizing the mass of the electrolyte in the battery. Should be.

In the lithium-sulfur secondary battery, cyclic S ₈ is converted to linear lithium polysulfide (Li ₂ S _x , where x is 3 to 8) at the time of discharge, and at this time, the reduction behavior step by step at a specific voltage see. Therefore, when an intermediate of lithium polysulfide is formed during charging and discharging, and the intermediate is dissolved in the organic electrolyte and eluted, or when an insoluble end product (Li ₂ S) is deposited on the inside and the surface of the cathode pores, the cathode active material decreases and capacity decreases. There are subsequent problems.

The oxygen-containing functional group exists in a direction perpendicular to the basic skeleton of the siloxane compound, and helps adsorption of lithium polysulfide, an intermediate product of a lithium-sulfur secondary battery, thereby preventing lithium polysulfide from eluting into an organic electrolyte. Can be controlled.

The degree of substitution of the oxygen-containing functional group can be controlled by adjusting the synthesis temperature of the siloxane compound. For example, by using a siloxane compound synthesized at room temperature in a positive electrode for a lithium-sulfur secondary battery, it is possible to effectively control the elution of polysulfide into an organic electrolyte.

The siloxane compound of the present invention can easily cause penetration of linear lithium polysulfide, and functional groups containing oxygen facilitate the trapping of polysulfide through adsorption, thus preventing the loss of sulfur active material in the positive electrode and using efficiency. Can be maximized.

In an embodiment of the present invention, the area of the siloxane compound may be 0.02 μm ² to 100 μm ² _, for example, 0.04 μm ² to 60 μm ² , and the thickness of the siloxane compound may be 0.2 μm to 12 μm, For example, it may be 0.5 μm to 8 μm.

In one embodiment of the present invention, the siloxane compound is 0.1% to 25% by weight, for example, 0.2% to 21% by weight, for example, 0.6% by weight based on the total weight of the positive electrode for a lithium-sulfur secondary battery. % To 14.6% by weight.

When the siloxane compound is included in an amount of less than 0.1% by weight, the adsorption capacity of polysulfide may be insufficient, and when it is included in an amount of more than 25% by weight, the performance may be further reduced due to low electrical conductivity of the positive electrode.

In an embodiment of the present invention, the positive electrode active material is inorganic sulfur (S ₈ , elemental sulfur), a sulfur-based compound, for example, cyclic-S ₈ , Li ₂ S ₆ dissolved in a catholyte, and organic sulfur Any one selected from the group consisting of an organosulfur compound and a carbon-sulfur polymer ((C ₂ S _x ) _n , x is 2.5 to 50, n≥2) and combinations thereof, for example Li ₂ S ₆ Can be

In the lithium-sulfur secondary battery, the oxidation number of S decreases as SS bonds are cut off during the reduction reaction (during discharge), and the oxidation number of sulfur (S) increases during the oxidation reaction (when charging), and the SS bonds are re-formed. It stores and generates electrical energy using a reduction reaction.

In an embodiment of the present invention, the sulfur may be included in an amount of 4 mg/cm ² or more, for example, 6 mg/cm ² to 10 mg/cm ² . When the sulfur is contained in an amount of less than 4 mg/cm ² , it may exhibit a low energy density that is difficult to commercialize.

In an embodiment of the present invention, the positive electrode for a lithium-sulfur secondary battery may include a current collector.

The current collector serves as a passage for transferring electrons from the outside so that an electrochemical reaction occurs in the active material or receiving electrons from the active material and passing them to the outside, and is particularly limited as long as it has conductivity without causing a chemical change in the battery. It doesn't work. For example, selected from the group consisting of carbon (C), nickel (Ni), stainless steel (SUS), aluminum (Al), molybdenum (Mo), chromium (Cr), titanium (Ti), and combinations thereof Any one that is, for example, may include carbon (C).

In one embodiment of the present invention, the positive electrode for a lithium-sulfur secondary battery may further include a binder and/or a conductive material.

The binder is added for bonding of an active material and a conductive material, and for bonding of an active material and a current collector, and may be a thermoplastic resin or a thermosetting resin. The binder is, for example, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), tetrafluoroethylene-perfluoro alkyl vinyl ether copolymer. , Vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, vinylidene fluoride-pentafluoropropylene copolymer , Propylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethylvinylether-tetrafluoro Ethylene copolymer, ethylene-acrylic acid copolymer, polyvinyl alcohol (PVA), polyacrylic acid (PAA), polymethacrylic acid (PMA), polymethyl methacrylate (PMMA) polyacrylamide (PAM), polymethacrylamide , Polyacrylonitrile (PAN), Polymethacrylonitrile, Polyimide (PI), Alginic acid, Alginate, Chitosan, Carboxymethylcellulose (CMC), Starch, Hydroxypropylcellulose , Recycled cellulose, polyvinylpyrrolidone, and any one selected from the group consisting of a combination thereof, for example, polyvinylidene fluoride (PVDF), but is not limited thereto, and as a binder in the art Anything that can be used is possible.

The conductive material is not particularly limited as long as it has conductivity without causing chemical changes to the battery, and examples thereof include graphite such as natural graphite or artificial graphite; Carbon blacks such as carbon black, acetylene black, Ketjen black, Denka black, channel black, furnace black, lamp black, and summer black; Graphene; Conductive fibers such as carbon fibers and metal fibers such as carbon nanotubes (CNT) and carbon nanofibers (CNF); Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Any one selected from the group consisting of polyphenylene derivatives and combinations thereof, for example, may be Super P.

One aspect of the present invention provides a lithium-sulfur secondary battery including a positive electrode for a lithium-sulfur secondary battery.

The lithium-sulfur secondary battery includes a positive electrode, a negative electrode, and an electrolyte and a separator present therebetween.

The positive electrode may be a positive electrode for a lithium-sulfur secondary battery according to an embodiment of the present invention.

The configuration of the negative electrode, the separator, and the electrolyte of the lithium-sulfur secondary battery is not particularly limited in the present invention, and follows what is known in the art.

The negative electrode includes a negative active material formed on the negative current collector.

The negative electrode current collector is from the group consisting of carbon (C), nickel (Ni), stainless steel (SUS), aluminum (Al), molybdenum (Mo), chromium (Cr), titanium (Ti), and combinations thereof. It may include any one selected, for example, may include carbon (C).

As the negative active material, lithium ions (Li ⁺ ) may be reversibly intercalated or de-intercalated, and lithium metal or lithium alloy capable of reversibly forming a lithium-containing compound by reacting with lithium ions may be used. have.

The lithium alloy is, for example, lithium (Li) and sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), beryllium (Be), magnesium (Mg), calcium ( It may be an alloy of a metal selected from the group consisting of Ca), strontium (Sr), barium (Ba), radium (Ra), aluminum (Al), and tin (Sn).

The negative electrode may further include a binder for bonding of the negative active material and the conductive material and bonding to the current collector. The binder is added for bonding of an active material and a conductive material, and for bonding of an active material and a current collector, and may be a thermoplastic resin or a thermosetting resin. The binder is, for example, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), tetrafluoroethylene-perfluoro alkyl vinyl ether copolymer. , Vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, vinylidene fluoride-pentafluoropropylene copolymer , Propylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethylvinylether-tetrafluoro Ethylene copolymer, ethylene-acrylic acid copolymer, polyvinyl alcohol (PVA), polyacrylic acid (PAA), polymethacrylic acid (PMA), polymethyl methacrylate (PMMA) polyacrylamide (PAM), polymethacrylamide , Polyacrylonitrile (PAN), Polymethacrylonitrile, Polyimide (PI), Alginic acid, Alginate, Chitosan, Carboxymethylcellulose (CMC), Starch, Hydroxypropylcellulose , Regenerated cellulose, polyvinylpyrrolidone, and any one selected from the group consisting of a combination thereof may be used, but it is not necessarily limited thereto, and any one that can be used as a binder in the art may be used.

The separator is a physical separator having a function of physically separating an electrode, and may be used without particular limitation as long as it is used as a conventional separator. In addition, the separator separates or insulates the positive electrode and the negative electrode from each other and enables transport of lithium ions between the positive electrode and the negative electrode. This separator may be made of a porous, non-conductive or insulating material. The separator may be an independent member such as a film, or may be a coating layer added to the anode and/or cathode. For example, a porous polymer film, for example, a porous polymer film made of polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer May be used alone or by stacking them, but is not limited thereto.

The positive electrode, negative electrode, and separator included in the lithium-sulfur secondary battery may be prepared according to conventional components and manufacturing methods, respectively, and the appearance of the lithium-sulfur secondary battery is not particularly limited, but cylindrical, box-shaped, pouch It may be a (pouch) type or a coin type, for example, a coin type.

One aspect of the present invention comprises the steps of preparing a siloxane compound; Mixing and processing the siloxane compound and a positive electrode active material to prepare a positive electrode for a lithium-sulfur secondary battery; It provides a method of manufacturing a positive electrode for a lithium-sulfur secondary battery comprising a.

First, the present invention includes the step of preparing a siloxane compound.

Step for preparing the siloxane-metallocene compound, for example, using a CaSi ₂ hydrochloric acid (HCl) of the Ca ions in CaSi ₂ D-can be carried out in a manner that intercalation (de-intercalation), The related reaction scheme is described in Equation 1 below:

[Equation 1]

3CaSi ₂ + 6HCl + 3H ₂ O → Si ₆ H ₃ (OH) ₃ + 3CaCl ₂ + 3H ₂ ↑

In the present specification, “intercalation/de-intercalation” refers to a phenomenon in which molecules, atoms, and/or ions are inserted/emitted between layers in a material having a layered structure. The products of intercalation are called intercalation compounds.

Depending on the temperature at which the step of preparing the siloxane compound is performed, whether or not a functional group including oxygen in the siloxane is included may be controlled.

In an embodiment of the present invention, the process of synthesizing the siloxane compound may be performed at 0° C. or higher, for example, 20° C. to 30° C., for example 25° C.

When the temperature of the process of synthesizing the siloxane compound is less than 0° C., a polysilane, which is a structure in which only hydrogen is present in a direction perpendicular to the hexagonal plural structure of silicon, is formed without oxygen-containing functional groups. I can.

For example, when synthesized at room temperature (25° C.), the synthesized siloxane compound is appropriately substituted with a functional group containing oxygen. In this case, polysulfide is eluted from the positive electrode for a lithium-sulfur secondary battery into an organic electrolyte. Can be effectively controlled.

For example, when synthesized at room temperature, oxygen may be included in an amount of 33% by weight based on the total weight of the synthesized siloxane compound.

Next, the present invention includes the step of preparing a positive electrode for a lithium-sulfur secondary battery by mixing and processing the siloxane compound prepared in the above step and a positive electrode active material.

The step of manufacturing a positive electrode for a lithium-sulfur secondary battery may be performed, for example, through a process of casting on a current collector.

The current collector serves as a passage for transferring electrons from the outside so that an electrochemical reaction occurs in the active material or receiving electrons from the active material and passing them to the outside, and is particularly limited as long as it has conductivity without causing a chemical change in the battery. It doesn't work. For example, selected from the group consisting of carbon (C), nickel (Ni), stainless steel (SUS), aluminum (Al), molybdenum (Mo), chromium (Cr), titanium (Ti), and combinations thereof Any one that is, for example, may include carbon (C).

The casting process may be performed by spinning and coating a liquid and/or semi-liquid material such as the positive electrode slurry onto a solid and/or semi-solid material such as the current collector. The casting process is performed by a general method in the art, and the method of performing it is not limited.

Hereinafter, a preferred embodiment is presented to aid the understanding of the present invention. However, it is obvious that the following examples are only illustrative of the present invention and the scope of the present invention is not limited to the following examples.

Example

Preparation Example 1. Preparation of siloxane compound

CaSi ₂ 5 g was added to a mixed solution in which 3.79 g of hydrochloric acid (HCl, 35%) and 0.94 g of water were mixed, stirred at 30° C. for 6 hours under a nitrogen atmosphere, and washed with acetone. Thereafter, it was dried at 110° C. for one day to obtain a siloxane compound (Fig. 1(a)).

Example 1. Preparation of lithium-sulfur secondary battery

1.1. Preparation of lithium-sulfur secondary battery positive electrode

70 mg of the siloxane compound obtained in Preparation Example 1, 20 mg of Super P as a conductive material, and 10 mg of polyvinylidene fluoride (PVDF) as a binder were added to 1 ml of N-methylpyrrolidone as a solvent for 3 hours. After dispersing the contents by sonication, the mixture was stirred on a stirring plate overnight to prepare a siloxane compound slurry.

Li ₂ S (99.9% Alfa-Aesar, Haverhill, Miami, USA) 50 mg and 48 mg of sulfur were 1,3-dioxolane (DOL) and 1,2-dimethoxyethane (DME) in which 1 M of LiTFSI was dissolved. ) (1:1 volume ratio) was added to 20 ml to prepare 1 M of Li ₂ S ₆ .

6 mg of the siloxane compound was cast onto a carbon current collector having a diameter of 14 mm, and then dried in a vacuum oven at 120° C. for 24 hours.

1.2. Manufacture of lithium-sulfur secondary battery

A carbon current collector cast with the siloxane compound prepared above was added to the coin cell, and Li ₂ S ₆ (1 M) 83 After injecting μl, the separation membrane, 1,3-dioxolane (DOL) and 1,2-dimethoxyethane (DME) (1:1 volume ratio) in which 1 M LiTFSI was dissolved, and 1% by weight of LiNO ₃ were added. Added electrolyte 117 µl, lithium foil, space, and spring were sequentially stacked to prepare a lithium-sulfur secondary battery.

Examples 2 to 3. Preparation of lithium-sulfur secondary battery

In Example 1, a lithium-sulfur secondary battery was prepared in the same manner as in Example 1, except that 83 μl of Li ₂ S ₆ (1 M) was injected instead of 17 μl and 50 μl, respectively. Obtained.

Comparative Examples 1 to 3. Preparation of lithium-sulfur secondary battery

In Example 1.1, a siloxane compound was not added, and Li ₂ S ₆ (1 M) was injected with 83 μl, 17 μl, and 50 μl, respectively, and lithium- A sulfur secondary battery was obtained.

Experimental Example 1. Morphology Analysis of Siloxen Compound

1.1 Analysis of SEM and TEM results

In order to observe the surface and shape of the siloxane compound obtained in Preparation Example 1, it was observed with a scanning electron microscope (SEM) and a transmission electron microscope (TEM).

As a result of observation, it was found that the siloxane compound was in a form in which a two-dimensional sheet was stacked (Fig. 1(b) and (c)), and the size of the sheet was about 500 nm from the sample observed by peeling ( (D) of Figure 1).

1.2 Analysis of nitrogen adsorption/desorption experiment results

A nitrogen adsorption/desorption experiment was performed to observe the surface area and the presence of pores of the siloxane compound obtained in Preparation Example 1.

As a result of the experiment, it was confirmed that the surface area calculated from the results of the nitrogen adsorption/desorption experiment was very small, about 7 m ² /g (Fig. 1(e)), and micropores having a size of about 2 nm, It was confirmed that there were no mesopores having a size of nm to 50 nm and macro pores of 50 nm or more (FIG. 1(f)). Therefore, it was found that there was no physical adsorption of polysulfide by micropores.

1.3 XRD result analysis

The XRD pattern was analyzed in order to confirm whether de-intercalation of Ca ²⁺ was well performed in the siloxane compound obtained in Preparation Example 1.

As a result of the experiment, it was confirmed that the peak corresponding to the existing CaSi ₂ did not exist after the HCl treatment, and it was confirmed that the di-intercalation of Ca ²⁺ was well performed (Fig. 1(g)).

1.4 FT-IR result analysis

In order to confirm the functional groups present in the siloxane compound obtained in Preparation Example 1, the results of FT-IR were analyzed.

As a result of the analysis, peaks corresponding to wave numbers 2150 cm ^-1 , 1060 cm ^-1 , and 460 cm ^-1 could be confirmed, and through this, it was found that surface functional groups such as oxygen functional groups or hydroxyl groups exist in the siloxane compound ( Figure 2 (a)).

1.5 Raman spectrum result analysis

In order to determine whether a plurality of hexagonal structures (in-plane structures) exist in the siloxane compound obtained in Preparation Example 1, a Raman-spectrum was analyzed.

As a result of the analysis, a gentle peak due to the vibration energy of the Si-Si bond was shown between 400 cm ^-1 and 550 cm ^-1 (Fig. 2 (b)). In particular, the peak of 470 cm ^-1 means Si (Si ₆ ring structure) composed of a hexagonal structure. Therefore, it was confirmed that the synthesis at room temperature for the purpose of partial oxidation did not affect the in-plane structure as intended, and the oxidation reaction proceeded only outside the in-plane structure.

1.6. Analysis of XPS results

XPS results were analyzed to confirm the mass content of the surface of the siloxane compound obtained in Preparation Example 1.

As a result of the experiment, the mass of calcium was 1.21 atom% and the mass of chlorine was 2.82 atom%, which was almost non-existent, indicating that de-intercalation of Ca was well performed, and oxygen was 45.6 atom%. It was found that a siloxane compound containing a large amount of oxygen functional groups and hydroxyl groups was well formed. In the high-resolution spectrum of Si 2p and O 1s, it was confirmed that bonds of Si-Si (99 eV), Si-O (102 eV), Si-OH (531 eV), and Si-O (533 eV) exist ( 2(c), (d) and (e)).

The content of the elements as a result of the experiment is shown in Table 1 below:

element Content (% by mass) Content (atom%) carbon 3.45 6.28 Oxygen 33.37 45.6 silicon 56.46 44.09 calcium 2.21 1.21 Goat 4.51 2.82 total 100 100

Experimental Example 2: Adsorption capacity of a siloxane compound to a sulfur active material

In order to confirm the sulfur active material adsorption ability of the siloxane compound obtained in Preparation Example 1, 0 mg, 50 mg, 100 mg, and 300 mg of the siloxane compound were added to 20 ml of 1 M Li ₂ S ₆ , respectively, for 4 hours. It was left at room temperature for a while.

As a result of the experiment, it was found that the samples to which the siloxane compound was added became transparent in color, indicating that lithium polysulfide (Li ₂ S ₆ ) was adsorbed. In addition, it was found that the more the siloxane compound content was, the more transparent it became (FIG. 3).

Experimental Example 3. Charging/discharging experiment of lithium-sulfur secondary battery

3.1 Cycling test of lithium-sulfur secondary battery

In order to confirm the capacity per unit area of the lithium-sulfur secondary batteries prepared in Examples 1 to 3 and Comparative Examples 1 to 3, a charge/discharge cycle stability test was performed.

As a result of the experiment, it was confirmed that as the sulfur content increased, the performance of the siloxane compound was remarkable. In addition, the utilization efficiency of sulfur was increased by about 10% or more in Examples 1 to 3 than in Comparative Examples 1 to 3. Specifically, when the amount of sulfur supported was 6 mg/cm ² (Example 3 and Comparative Example 3), it was 41% to 52%, and when the amount of sulfur supported was 10 mg/cm ² (Example 1 and Comparative Example 1), it was 31%. It was confirmed that the increase was increased to 44% (FIG. 4), and through this, it was found that the increase in utilization efficiency increased as the amount of sulfur supported increased.

In addition, the battery was opened after 100 cycles, and the separator and the lithium metal part were confirmed as photographic images.

In the case of the lithium-sulfur secondary battery of Comparative Example 2, it was confirmed that the yellow color indicating the presence of polysulfide remained in the separator as well as the lithium metal after charging and discharging (Fig. 5(a)). Under the same conditions, in the case of the lithium-sulfur secondary battery of Example 1, a yellow residue could not be observed on the lithium metal and the separator (Fig. 5(b)). This result shows the ability of the siloxane compound to adsorb polysulfide, and it was found that the active material can be effectively immobilized in the positive electrode.

3.2 Analysis of CV and GCPL results of lithium-sulfur secondary battery

Cyclic voltammetry (CV) and charge/discharge curve (GCPL) experiments were performed to confirm the discharge capacity of the lithium-sulfur secondary batteries prepared in Example 1 and Comparative Example 1.

First, a CV experiment was performed by varying the scan speed from 0.01 mV/s to 0.04 mV/s, and the kinetic mechanism was analyzed using the power-law relationship. In the above analysis method, a linear relationship (log-log) is derived from each current at peak 1 generated in the oxidation process, peak 2 and peak 3 generated in the reduction process, and each slope is obtained and analyzed, the closer the slope is to 0.5. It is a process closer to diffusion-control, and closer to 1 is a process closer to surface reaction.

As a result of the experiment, the biggest difference between Example 1 and Comparative Example 1 was that the slope value was inverted at peak 2, and it was found that Example 1 induced a larger current at peak 2. The step of reducing Li ₂ S ₄ to Li ₂ S is subject to a lot of space limitations, and Comparative Example 1 is gradually pushed out due to insufficient space for the sulfur active material to react in the second reduction step, whereas Example 1 Silver helps the electrode to convert Li ₂ S ₄ to Li ₂ S while adsorbing more sulfur active material, and is created by the space created when the siloxane compound rises on the three-dimensional current collector while casting the additive to the electrode. It was found that it was a discharge capacity (Fig. 6 (a), (b) and (c)).

As a result of a CV experiment with a scan speed of 0.01 mV/s, open circuit voltage (OCV) was found, respectively, 2.1 V vs. Li/Li ⁺ and 2.3 V vs. As Li/Li ^{+, it} was found that the lithium-sulfur secondary battery of Example 1 was higher than that of the lithium-sulfur secondary battery of Comparative Example 1, and this resulted in relatively less self-discharge. , About 2.1 V vs. When looking at each peak current density in the vicinity of Li/Li ⁺ , it could be seen that it has more discharge capacity (Fig. 6(d)).

GCPL experiment result 2.1 V vs. It was confirmed that the expression of the discharging capacity in the vicinity of Li/Li ^{+ was significantly different} at about 7.0 mAh/cm ² (FIG. 6(e)).

This was thought to be because polysulfide (Li ₂ S _n , n is 4 to 8) was well immobilized on the siloxane compound, resulting in a better reaction in the anode, resulting in increased sulfur utilization.

Experimental Example 4. Analysis of XPS results of lithium-sulfur secondary battery

After charging and discharging, ex-situ XPS analysis was performed to find out the chemical structure of the sulfur active material in the positive electrode. The sulfur active material forms polysulfide, an intermediate product between S ₈ and Li ₂ S, and undergoes a stepwise oxidation/reduction reaction. Polysulfide has a binding energy between S ₈ (164 eV) and Li ₂ S (160 eV). In the case of Example 1, the formation of polysulfide can be confirmed from the presence of a peak having a binding energy of about 162 eV, but in the case of Comparative Example 1, the formation of polysulfide was confirmed because there was no peak in the vicinity of 164 eV to 160 eV. Could not (Fig. 7). Therefore, in the presence of the siloxane compound, it can be seen that the reduction reaction actually proceeds in the discharge process, which means that the chemical adsorption capacity for polysulfide is actually present.

The above description of the present invention is for illustrative purposes only, and those of ordinary skill in the art to which the present invention pertains will be able to understand that it can be easily modified into other specific forms without changing the technical spirit or essential features of the present invention. will be. Therefore, it should be understood that the embodiments described above are illustrative in all respects and not limiting. For example, each component described as a single type may be implemented in a distributed manner, and similarly, components described as being distributed may also be implemented in a combined form.

The scope of the present invention is indicated by the claims to be described later, and all changes or modified forms derived from the meaning and scope of the claims and their equivalent concepts should be interpreted as being included in the scope of the present invention.

Claims (13)

A lithium-sulfur secondary battery positive electrode comprising a siloxane compound containing one or more siloxanes and a positive electrode active material. The method of claim 1,
The siloxane is a lithium-sulfur secondary battery positive electrode, characterized in that in the form of a nanosheet. The method of claim 1,
The siloxane compound is a lithium-sulfur secondary battery positive electrode, characterized in that the structure in which one or more siloxanes are stacked. The method of claim 3,
A positive electrode for a lithium-sulfur secondary battery, characterized in that the lamination interval between the one or more siloxanes is 0.2 nm or more. The method of claim 1,
The siloxane compound is a lithium-sulfur secondary battery positive electrode, characterized in that it contains a functional group containing oxygen. The method of claim 5,
A positive electrode for a lithium-sulfur secondary battery, characterized in that the functional group containing oxygen of the siloxane compound is bonded to polysulfide. The method of claim 1,
The siloxane compound is a lithium-sulfur secondary battery positive electrode, characterized in that contained in 0.1% to 25% by weight based on the total weight of the positive electrode for a lithium-sulfur secondary battery. The method of claim 1,
The positive electrode active material is a lithium-sulfur secondary battery positive electrode comprising any one selected from the group consisting of inorganic sulfur (S ₈ , elemental sulfur), sulfur-based compounds, and combinations thereof. The method of claim 1,
The lithium-sulfur secondary battery positive electrode is a lithium-sulfur secondary battery positive electrode, characterized in that it comprises a current collector. The method of claim 1,
The lithium-sulfur secondary battery positive electrode is a lithium-sulfur secondary battery positive electrode, characterized in that it further comprises a binder and/or a conductive material. A lithium-sulfur secondary battery comprising the positive electrode for a lithium-sulfur secondary battery according to any one of claims 1 to 10. Preparing a siloxane compound;
Mixing and processing the siloxane compound and a positive electrode active material to prepare a positive electrode for a lithium-sulfur secondary battery;
Method for producing a positive electrode for a lithium-sulfur secondary battery comprising a. The method of claim 12,
The manufacturing method of the positive electrode for a lithium-sulfur secondary battery, characterized in that the step of preparing the siloxane compound is performed at a temperature of 0 °C or higher.

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