KR102468265B1 - Cathode active material for lithium secondary battery and pnaufacturing method thereof - Google Patents

Abstract

The present invention relates to a cathode active material for a lithium secondary battery and a manufacturing method thereof. The cathode active material includes a matrix including a metal and macromolecules coordinated with the metal, a plate-shaped carbon material, and elemental sulfur, and the matrix and the carbon material are π-π stacking It is characterized in that the elemental sulfur is covalently bonded to the matrix.

Description

Cathode active material for lithium secondary battery and manufacturing method thereof

The present invention relates to a cathode active material for a lithium secondary battery and a manufacturing method thereof.

As the limitations of lithium ion batteries are revealed in terms of energy density, cost, lifespan, and safety, interest in next-generation batteries is increasing.

Among various candidates, a lithium-sulfur battery has a theoretical energy density of about 2,600 Wh/kg, so it is attracting much attention in the technology field requiring high power and high energy density.

A lithium-sulfur battery refers to a battery using sulfur as a positive electrode active material and lithium metal as a negative electrode. The charging and discharging process of the lithium-sulfur battery is as follows.

During discharge, electrons move from the lithium anode (Li metal) to the anode. The electrons move along the conductive material in the anode and combine with sulfur adjacent to the surface of the conductive material. Sulfur, a cathode active material, is reduced to an ionic state and combined with lithium ions to form lithium polysulfide (Li ₂ S _n , 4<n<8). Lithium polysulfide continuously reacts with lithium ions and turns into Li ₂ S ₂ /Li ₂ S (short-chain polysulfide), which is a discharge product on the surface of the lithium anode.

During charging, a reverse oxidation reaction occurs to form sulfur ions, which return to sulfur by losing electrons on the surface of the conductive material.

There are many technical challenges to overcome for the commercialization of lithium-sulfur batteries. First, since sulfur and its discharge products, Li ₂ S and Li ₂ S ₂ , are electrical insulators, internal resistance is increased, and thus the conversion rate is lowered. In addition, a shuttling effect occurs in which lithium polysulfide is dissolved in the liquid electrolyte and diffused and outflowed. In addition, since the degree of volume expansion and contraction of sulfur during charging and discharging of the battery is large, it is necessary to supplement in terms of safety.

Conventionally, in order to solve the above problems, attempts have been made such as adding carbon nanostructures to the positive electrode of a lithium-sulfur battery or using an electrolyte that does not dissolve lithium polysulfide, but satisfactory results have not been achieved.

Korean Patent Publication No. 10-2020-0109476

An object of the present invention is to provide a positive electrode active material capable of improving electrochemical characteristics such as lifespan, overvoltage, internal resistance, and charge/discharge rate of a lithium-sulfur battery.

The object of the present invention is not limited to the object mentioned above. The objects of the present invention will become more apparent from the following description, and will be realized by means and combinations thereof set forth in the claims.

A cathode active material for a lithium secondary battery according to an embodiment of the present invention includes a matrix including a metal and macromolecules coordinated with the metal; plate-shaped carbon material; and elemental sulfur, wherein the matrix and the carbon material are bonded by forming π-π stacking, and the elemental sulfur may be covalently bonded to the matrix.

The metal may include at least one selected from the group consisting of Fe, Mg, Ni, Co, Cu, Pd, Zn, V, Ti, In, Mn, Si, Sn, and combinations thereof.

The macromolecule may include at least one selected from the group consisting of phthalocyanine, naphthalocyanine, porphyrin, and combinations thereof.

The macromolecule may include a halogen functional group.

The matrix may include a compound represented by Formula 1 below.

[Formula 1]

Here, Me includes at least one selected from the group consisting of Fe, Mg, Ni, Co, Cu, Pd, Zn, V, Ti, In, Mn, Si, Sn, and combinations thereof, and X is a halogen element or It is a linking site with the elemental sulfur.

The carbon material may include at least one selected from the group consisting of graphene, graphene oxide, reduced graphene oxide, and combinations thereof.

The elemental sulfur may be covalently bonded to the matrix through nucleophilic aromatic substitution.

The elemental sulfur includes an unshared electron pair, and the unshared electron pair may be bonded to a carbon element of a carbon material.

A method of manufacturing a cathode active material for a lithium secondary battery according to the present invention includes preparing a solution containing a precursor of elemental sulfur; preparing a mixed solution by injecting a matrix including a metal and macromolecules coordinated with the metal and a plate-like carbon material into the solution; stirring the mixed solution; precipitating elemental sulfur from the mixed solution and filtering to obtain a precipitate; and heat-treating the precipitate.

The elemental sulfur precursor may include at least one selected from the group consisting of Li ₂ S ₈ , Li ₂ S ₆ , and combinations thereof.

The manufacturing method may be to form π-π stacking of the matrix and the carbon material by stirring the mixed solution.

The manufacturing method may be to precipitate elemental sulfur by injecting an acid solution into the mixed solution.

The heat treatment may be performed at 300° C. to 400° C. for 20 hours to 30 hours.

Electrochemical characteristics such as lifespan, overvoltage, internal resistance, and charge/discharge rate of a lithium-sulfur battery can be greatly improved by using the cathode active material according to the present invention.

The effects of the present invention are not limited to the effects mentioned above. It should be understood that the effects of the present invention include all effects that can be inferred from the following description.

1 is a cross-sectional view showing a lithium secondary battery according to the present invention.
2 shows a cathode active material according to the present invention.
Figure 3 is a result of analyzing the result obtained through the stirring step in Preparation Example by UV-visible spectroscopy.
Figure 4 is a scanning electron microscope (Scanning electron microscopy, SEM) and energy-dispersive X-ray spectroscopy (energy-dispersive X-ray spectroscopy) analysis results for the powder before causing the aromatic nucleophilic substitution reaction in the preparation example.
5 is a scanning electron microscope and energy dispersive X-ray spectroscopy analysis result for the cathode active material according to the present invention obtained in Preparation Example.
6 shows F 1s X-ray photoelectron spectroscopy (XPS) analysis results of F-Co(II)Pc and SG-Co(II)Pc.
7 shows S 2p X-ray photoelectron spectroscopy (XPS) results of SG—Co(II)Pc.
8 shows Co 2p X-ray photoelectron spectroscopy (XPS) analysis results of F-Co(II)Pc and SG-Co(II)Pc.
9 is a CV analysis result for lithium-sulfur batteries of Examples and Comparative Examples.
10 is a result of electrostatic potential measurement for lithium-sulfur batteries of Examples and Comparative Examples.
11 is a result of evaluating cycle characteristics of lithium-sulfur batteries according to Examples and Comparative Examples.
12 is a result of measuring speed characteristics of lithium-sulfur batteries of Examples and Comparative Examples.
13 is a result of evaluating internal resistance of lithium-sulfur batteries according to Examples and Comparative Examples.
14 is a result of evaluating cycle characteristics of lithium-sulfur batteries according to Examples and Comparative Examples in which the loading amount of sulfur in the positive electrode was increased.
15 illustrates galvanostatic charge-discharge profiles of lithium-sulfur batteries according to Examples and Comparative Examples in which the loading amount of sulfur in the positive electrode was increased.

The above objects, other objects, features and advantages of the present invention will be easily understood through the following preferred embodiments in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms. Rather, the embodiments introduced herein are provided so that the disclosed content will be thorough and complete and the spirit of the present invention will be sufficiently conveyed to those skilled in the art.

Like reference numerals have been used for like elements throughout the description of each figure. In the accompanying drawings, the dimensions of the structures are shown enlarged than actual for clarity of the present invention. Terms such as first and second may be used to describe various components, but the components should not be limited by the terms. These terms are only used for the purpose of distinguishing one component from another. For example, a first element may be termed a second element, and similarly, a second element may be termed a first element, without departing from the scope of the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

In this specification, terms such as "include" or "have" are intended to designate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, but one or more other features It should be understood that it does not preclude the possibility of the presence or addition of numbers, steps, operations, components, parts, or combinations thereof. In addition, 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 it is "directly on" the other part, but also the case where another part is present in the middle. Conversely, when a part such as a layer, film, region, plate, etc. is said to be "under" another part, this includes not only the case where it is "directly below" the other part, but also the case where another part is in the middle.

Unless otherwise specified, all numbers, values and/or expressions expressing quantities of components, reaction conditions, polymer compositions and formulations used herein refer to the number of factors that such numbers arise, among other things, to obtain such values. Since these are approximations that reflect the various uncertainties of the measurement, they should be understood to be qualified by the term "about" in all cases. Also, when numerical ranges are disclosed herein, such ranges are contiguous and include all values from the minimum value of such range to the maximum value inclusive, unless otherwise indicated. Furthermore, where such ranges refer to integers, all integers from the minimum value to the maximum value inclusive are included unless otherwise indicated.

1 is a cross-sectional view showing a lithium secondary battery according to the present invention. The lithium secondary battery may include a lithium-sulfur battery. Referring to FIG. 1 , the lithium secondary battery may include a positive electrode 10, a negative electrode 20, and a separator 30 positioned between the positive electrode 10 and the negative electrode 20. In addition, the positive electrode 10, the negative electrode 20 and the separator 30 may be impregnated with an electrolyte.

The cathode 10 may include a cathode active material, a conductive material, a binder, and the like according to the present invention. The cathode active material will be described later.

The conductive material is a component responsible for the movement of electrons in the anode 10 . As the conductive material, any material having excellent conductivity and a large surface area may be used. For example, the conductive material may include graphite, carbon black, carbon fiber, carbon nanotube, and the like.

The binder is for binding each component of the positive electrode 10, and any binder may be used as long as it is widely used in the technical field to which the present invention belongs. For example, the binder may include polyvinylidene fluoride, polytetrafluoroethylene, butadiene rubber, carboxymethylcellulose, or a polyolefin-based binder.

The anode 20 may include lithium metal, graphite, a silicon-based material, a tin-based material, or a mixture thereof.

The separator 30 is configured to prevent physical contact between the positive electrode 10 and the negative electrode 20 . The separation membrane 30 may be porous, and may be a single membrane or a multilayer membrane of two or more layers. The separator 30 may include a polyethylene-based, polypropylene-based, polyvinylidene fluoride-based, or polyolefin-based polymer.

The electrolyte is for the movement of lithium ions between the positive electrode 10 and the negative electrode 20, and may include a non-aqueous solvent and a metal salt.

Any non-aqueous solvent may be used as long as it is widely used in the technical field to which the present invention belongs. For example, it may include a carbonate-based solvent, an ester-based solvent, an ether-based solvent, a ketone-based solvent, an alcohol-based solvent, or an aprotic solvent. The non-aqueous solvents may be used alone or in combination with one or more of them, and the mixing ratio when one or more of the non-aqueous solvents are used may be appropriately adjusted according to the desired battery performance.

Any metal salt may be used as long as it is widely used in the technical field to which the present invention belongs. For example, it may be a salt having a structural formula of A ⁺ B ^- . Here, A ⁺ may be an ion containing an alkali metal cation such as Li ⁺ , Na ⁺ , K ⁺ , or a combination thereof. In addition. B ^- is PF ₆ ^- , BF ₄ ^- , Cl ^- , Br ^- , I ^- , ClO ₄ ^- , CH ₃ CO ₂ ^- , CF ₃ SO ₃ ^- , N(CF ₃ SO ₂ ) ₂ ^- , C(CF ₂ It may be an ion including an anion such as SO ₂ ) ₃ ^- or a combination thereof. For example, the metal salt may be a lithium-based salt, for example, LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiN(SO ₂ C ₂ F ₅ ) ₂ , Li(CF ₃ SO ₂ ) ₂ N, LiN (SO ₃ C ₂ F ₅ ) ₂ , LiC ₄ F ₉ SO ₃ , LiClO ₄ , LiAlO ₂ , LiAlCl ₄ , LiN(C _x F _{2x + 1} SO ₂ )(C _y F _{2y + 1} SO ₂ ) (where x and y are natural numbers), LiCl, LiI, and LiB(C ₂ O ₄ ) ₂ .

2 shows a cathode active material according to the present invention. Referring to this, the cathode active material may include a matrix 100 including a metal and macromolecules coordinated with the metal, a plate-shaped carbon material 200, and elemental sulfur 300.

The matrix 100 may have a metal located at the center and macromolecules located around the metal so that the metal and the macromolecules are coordinated.

The metal promotes a conversion reaction between sulfur and discharge products generated during charging and discharging of a lithium-sulfur battery. The metal may include at least one selected from the group consisting of Fe, Mg, Ni, Co, Cu, Pd, Zn, V, Ti, In, Mn, Si, Sn, and combinations thereof.

The macromolecule may have a structure in which a plurality of aromatic rings containing a nitrogen element are combined. Since the nitrogen element can combine with the lithium polysulfide, the shuttling phenomenon of the lithium polysulfide can be alleviated. The macromolecule may include at least one selected from the group consisting of phthalocyanine, naphthalocyanine, porphyrin, and combinations thereof.

The macromolecule may include a halogen functional group. When the matrix 100 into which a halogen functional group is introduced is heat-treated under specific conditions in the presence of elemental sulfur, a nucleophilic aromatic substitution reaction occurs and the halogen functional group and elemental sulfur are substituted. As a result, since sulfur element is combined with the matrix 100, the loading amount of sulfur in the positive electrode of a lithium-sulfur battery can be increased compared to the prior art.

The matrix 100 may include a compound represented by Chemical Formula 1 below.

[Formula 1]

Here, Me includes at least one selected from the group consisting of Fe, Mg, Ni, Co, Cu, Pd, Zn, V, Ti, In, Mn, Si, Sn, and combinations thereof, and X is a halogen element or It is a linking site with the elemental sulfur.

The carbon material 200 serves as a kind of substrate, and may include a material having a large specific surface area and high electrical conductivity.

The carbon material 200 may include at least one selected from the group consisting of graphene, graphene oxide, reduced graphene oxide, and combinations thereof.

The carbon material 200 may be combined with the matrix 100 by forming π-π stacking. Accordingly, electrons moved to the cathode active material may more easily reach elemental sulfur through the carbon material 200 and the matrix 100 .

In addition, since the carbon material 200 has a plate-like structure and the matrix 100 is bonded thereto, it is possible to prevent the matrices 100 from aggregating with each other. As a result, it is possible to prevent aggregation of the metal, which is a catalytic reaction region located in the center of the matrix 100, to improve the conversion rate of the sulfur redox reaction.

The elemental sulfur 300 may be covalently bonded to the matrix 100 . As described above, the elemental sulfur 300 and the halogen functional group contained in the macromolecule of the matrix 100 are substituted through nucleophilic aromatic substitution, so that the elemental sulfur 300 forms the matrix 100. can be covalently bonded to

The elemental sulfur 300 includes an unshared electron pair, and the unshared electron pair may be bonded to a carbon element of the carbon material.

In the present invention, the matrix 100, the carbon material 200, and the elemental sulfur 300 have a specific bonding relationship with each other as described above. Accordingly, the sulfur loading amount of the positive electrode for a lithium-sulfur battery can be increased, the shuttling phenomenon of lithium polysulfide can be suppressed, the aggregation of the catalytic reaction region can be prevented, and the electronic conductivity in the positive electrode active material can be greatly improved.

A method for manufacturing a cathode active material for a lithium secondary battery according to the present invention comprises the steps of preparing a solution containing a precursor of elemental sulfur, injecting a matrix containing a metal and a macromolecule coordinated with the metal and a plate-shaped carbon material into the solution, It may include preparing a mixed solution, stirring the mixed solution, precipitating and filtering elemental sulfur in the mixed solution to obtain a precipitate, and heat-treating the precipitate.

The solution may be prepared by directly introducing the precursor of elemental sulfur into a solvent or synthesizing by adding and reacting a starting material of the precursor.

The elemental sulfur precursor may include at least one selected from the group consisting of Li ₂ S ₈ , Li ₂ S ₆ , and combinations thereof.

The input ratio of the matrix and the carbon material is not particularly limited, and may be added in a weight ratio of, for example, 1:9 to 9:1.

The mixed solution may be stirred to form π-π stacking of the matrix and the carbon material. The stirring conditions are not particularly limited, and the stirring may be performed at a temperature and time that do not damage the matrix and the carbon material.

In a state in which the matrix and the carbon material are bonded through π-π stacking, the elemental sulfur precursor may be precipitated in the form of elemental sulfur by injecting an acid solution into the mixed solution.

The precipitate of the mixed solution includes elemental sulfur, a matrix bonded through π-π stacking, and a carbon material.

After the precipitate is obtained by filtration, it is heat-treated under specific conditions to cause a nucleophilic aromatic substitution of the halogen functional group of the matrix with the element sulfur to covalently bond the element sulfur to the matrix.

The heat treatment may be performed under conditions of 300° C. to 400° C. and 20 hours to 30 hours.

Other forms of the present invention will be described in more detail through the following examples. The following examples are merely examples to aid understanding of the present invention, and the scope of the present invention is not limited thereto.

manufacturing example

A solution containing Li ₂ S ₆ , a precursor of elemental sulfur, was prepared by dissolving 95.7 mg of lithium sulfide (Li ₂ S) and 334.0 mg of sulfur in about 30 ml of ethyl alcohol.

Cobalt (II) 1,2,3,4,8,9,10,11,15,16,17,18,22,23,24,25-hexadecafluoro-29H,31H-phthalocyanine (hereinafter referred to as F-Co(II)Pc) and 50 mg of reduced graphene oxide (hereinafter rGO), respectively, were added to obtain a mixed solution.

The mixed solution was stirred at about 70° C. for about 24 hours to form π-π stacking between the matrix and the carbon material. To verify this, the stirred product was analyzed by UV-visible spectroscopy. The result is shown in FIG. 3 . In view of the fact that the peaks at 300 nm and 628 nm found in F-Co(II)Pc disappeared in the stirred product (rGO+F-Co(II)Pc in FIG. 3), the F-Co(II)Pc was added to rGO. It can be seen that all of them are combined.

A hydrochloric acid solution was added to the stirred product to precipitate the Li ₂ S ₆ as elemental sulfur. The precipitate was vacuum filtered and washed with deionized water.

The precipitate was heated at about 160° C. for about 12 hours to melt elemental sulfur. In a state where the molten elemental sulfur was uniformly mixed with the matrix and the carbon material, heat treatment was performed at about 400° C. for about 20 hours to induce an aromatic nucleophilic substitution reaction in which elemental sulfur was replaced with a halogen functional group in the matrix. Finally, the cathode active material (hereinafter referred to as SG-Co(II)Pc) according to the present invention was obtained in the form of a black powder.

Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy analysis were performed on the powder before and after the heat treatment. 4 is a result of the powder before heat treatment, that is, the powder before the aromatic nucleophilic substitution reaction occurs, and FIG. 5 is a result of the powder after heat treatment, that is, the positive electrode active material according to the present invention. Referring to this, it can be seen that the matrix is not damaged even after heat treatment, as there is no significant difference in the results for cobalt. In addition, in light of the decrease in the amount of fluorine and the increase in the amount of elemental sulfur, it can be seen that the aromatic nucleophilic substitution reaction between the halogen functional group and elemental sulfur was successfully performed.

6 to 8 are experimental results for more clearly verifying the above results.

6 shows F 1s X-ray photoelectron spectroscopy (XPS) analysis results of F-Co(II)Pc and SG-Co(II)Pc. Referring to this, it can be seen that the peak found in F-Co(II)Pc is eliminated in SG-Co(II)Pc due to the aromatic nucleophilic substitution reaction of the halogen functional group and elemental sulfur.

7 shows S 2p X-ray photoelectron spectroscopy (XPS) results of SG—Co(II)Pc. Referring to this, it can be seen that peaks corresponding to S-S and C-S bonds are found at 164.5 eV and 164.0 eV in the cathode active material according to the present invention.

8 shows Co 2p X-ray photoelectron spectroscopy (XPS) analysis results of F-Co(II)Pc and SG-Co(II)Pc. Referring to this, it can be seen that cobalt ions are maintained without being damaged even after heat treatment, in light of the fact that the same peaks are found around 780 eV and around 796 eV in both results. Meanwhile, in the result of F-Co(II)Pc, peaks are found at 780.8 eV and 796.4 eV, and in the result of SG-Co(II)Pc, peaks are found at 780.4 eV and 796.0 eV. That is, a slight peak shift occurs, which is due to the soft-soft interaction between elemental sulfur and cobalt ions.

Comparative Manufacturing Example

A mixture of elemental sulfur and reduced graphene oxide in a weight ratio of 7:3 was heat-treated at about 160° C. for about 12 hours to obtain a composite powder (S-rGO composite).

Example

After mixing the cathode active material (SG-Co(II)Pc), carbon black, and PVDF of the above Preparation Example in a mass ratio of 7:2:1, they were added to a solvent to obtain a slurry. The slurry was coated on an aluminum foil and dried to prepare a positive electrode.

A lithium metal disk was used as an anode and a polypropylene membrane was used as a separator. As an electrolyte, a mixture containing 1.0 M LiN(CF ₃ SO ₂ ) ₂ (LiFSI) and 0.2 M LiNO ₃ in a non-aqueous organic solvent having a volume ratio of 1:1 of dioxolane (DOL) and dimethyl ether (DME). solution was used.

A lithium-sulfur battery was prepared by stacking the positive electrode, the separator, and the negative electrode, and impregnating the electrolyte.

comparative example

A lithium-sulfur battery was prepared in the same manner as in the above example, except that the powder (S-rGO composite) of Comparative Preparation Example was used as the cathode active material.

Experimental Example 1 - CV (Cyclic voltammetry) analysis and potentiostatic test

CV analysis was performed on the lithium-sulfur batteries of Examples and Comparative Examples. The results are shown in FIG. 9 . Referring to this, it can be seen that the example (SG-Co(II)Pc) has an anode peak and a cathode peak at -0.25 V and 0.25 V, respectively, while the comparative example (S-rGO composite) does not. . This means that cobalt, which is a metal included in the cathode active material according to the present invention, also serves as an electrochemical catalyst for the S ₈ ↔ Li ₂ S ₈ reaction.

Electrostatic potential measurements were performed on the lithium-sulfur batteries of Examples and Comparative Examples. The results are shown in FIG. 10 . Referring to this, it can be seen that the nucleation of Li ₂ S was significantly activated in the example (SG-Co(II)Pc) compared to the comparative example (S-rGO composite).

In light of the above two results, it can be clearly seen that cobalt, which is a metal included in the positive electrode active material according to the present invention, plays a role as an electrochemical catalyst in the charging and discharging process of the lithium-sulfur battery.

Experimental Example 2 - Cycle Characteristics

Cycle characteristics of the lithium-sulfur batteries of Examples and Comparative Examples were evaluated. The results are shown in FIG. 11 . Referring to this, Example (SG-Co(II)Pc) and Comparative Example (S-rGO composite) show initial discharge capacities of 821.8 mAh/g and 814.8 mAh/g, respectively, which are similar. However, when charging and discharging were repeated 700 times, the Example (SG-Co(II)Pc) showed a capacity retention rate of about 70%, whereas the Comparative Example (S-rGO composite) was only about 37.5%.

Experimental Example 3 - Speed Characteristics

The rate characteristics of the lithium-sulfur batteries according to Examples and Comparative Examples were measured at various discharge rates (C-rate) of 0.1 C to 5 C. The results are shown in FIG. 12 . Referring to this, Example (SG-Co(II)Pc) showed a higher capacity than Comparative Example (S-rGO composite) in all sections.

Experimental Example 4 - Analysis of Galvanostatic Intermittent Titration Technique (GITT)

In order to evaluate the internal resistance of the lithium-sulfur batteries according to Examples and Comparative Examples, GITT analysis was performed on them. The results are shown in FIG. 13 . Referring to this, it can be seen that the embodiment (SG-Co(II)Pc) shows a lower internal resistance than the comparative example (S-rGO composite) in the entire charge/discharge period. This is because, as described above, in the cathode active material according to the present invention, the metal serves as an electrochemical catalyst and compatibility between the matrix, the carbon material, and elemental sulfur is maximized.

Experimental Example 5 - Analysis of electrochemical properties in a cell with high sulfur loading

In the lithium-sulfur batteries according to Examples and Comparative Examples, the loading amount of sulfur (elemental sulfur) in the positive electrode was increased ^to 12 mg _sulfur cm ^-2 _and their cycle characteristics were measured. The results are shown in FIG. 14 . Referring to this, Example (SG-Co(II)Pc) has an initial capacity of 6.13 mAh cm ^-2 _, which is significantly higher than 1.57 mAh cm ^-2 of the comparative example (S-rGO composite) _, and is charged and discharged 50 times. After implementation, an excellent capacity retention rate of about 91.2% was shown.

FIG. 15 illustrates galvanostatic charge-discharge profiles of lithium-sulfur batteries according to Examples and Comparative Examples. Referring to this, it can be seen that a high overvoltage occurred in the comparative example (S-rGO composite).

Through the above two results, it was confirmed that the positive electrode containing the positive electrode active material in high capacity according to the present invention had very excellent electrochemical properties.

As above, the experimental examples and examples of the present invention have been described in detail, the scope of the present invention is not limited to the above-described experimental examples and examples, and the basic concept of the present invention defined in the following claims Various modifications and improvements made by those skilled in the art are also included in the scope of the present invention.

10: anode 20: cathode 30: separator
100: matrix 20: carbon material 30: elemental sulfur

Claims (20)

a matrix comprising a metal and macromolecules coordinated with the metal;
plate-shaped carbon material; and
Contains elemental sulfur,
The matrix and the carbon material are combined by forming π-π stacking,
The cathode active material for a lithium secondary battery, characterized in that the elemental sulfur is covalently bonded to the matrix. According to claim 1,
The metal is a cathode active material for a lithium secondary battery comprising at least one selected from the group consisting of Fe, Mg, Ni, Co, Cu, Pd, Zn, V, Ti, In, Mn, Si, Sn, and combinations thereof. According to claim 1,
The macromolecule is a cathode active material for a lithium secondary battery comprising at least one selected from the group consisting of phthalocyanine, naphthalocyanine, porphyrin, and combinations thereof. According to claim 1,
The macromolecule is a cathode active material for a lithium secondary battery containing a halogen functional group. According to claim 1,
The matrix is a cathode active material for a lithium secondary battery comprising a compound represented by Formula 1 below.
[Formula 1]

Here, Me includes at least one selected from the group consisting of Fe, Mg, Ni, Co, Cu, Pd, Zn, V, Ti, In, Mn, Si, Sn, and combinations thereof,
X is a halogen element or a linking site with the element sulfur. According to claim 1,
The carbon material is a cathode active material for a lithium secondary battery comprising at least one selected from the group consisting of graphene, graphene oxide, reduced graphene oxide, and combinations thereof. According to claim 1,
The positive electrode active material for a lithium secondary battery, wherein the elemental sulfur is covalently bonded to the matrix through nucleophilic aromatic substitution. According to claim 1,
The elemental sulfur includes an unshared electron pair, and the cathode active material for a lithium secondary battery in which the unshared electron pair and the carbon element of the carbon material are bonded. The cathode active material of any one of claims 1 to 8;
conductive material; and
Positive electrode for lithium secondary battery containing a binder A lithium secondary battery comprising the positive electrode of claim 9. According to claim 10,
A lithium secondary battery including a lithium-sulfur battery. preparing a solution comprising a precursor of elemental sulfur;
preparing a mixed solution by injecting a matrix including a metal and macromolecules coordinated with the metal and a plate-like carbon material into the solution;
stirring the mixed solution;
precipitating elemental sulfur from the mixed solution and filtering to obtain a precipitate; and
Including; heat-treating the precipitate;
The matrix and the carbon material are combined by forming π-π stacking,
The method of manufacturing a cathode active material for a lithium secondary battery, characterized in that the elemental sulfur is covalently bonded to the matrix. According to claim 12,
The precursor of elemental sulfur is a method for producing a cathode active material for a lithium secondary battery comprising at least one selected from the group consisting of Li ₂ S ₈ , Li ₂ S ₆ and combinations thereof. According to claim 12,
The matrix is a method for producing a cathode active material for a lithium secondary battery comprising a compound represented by Formula 1 below.
[Formula 1]

Here, Me includes at least one selected from the group consisting of Fe, Mg, Ni, Co, Cu, Pd, Zn, V, Ti, In, Mn, Si, Sn, and combinations thereof,
X is a halogen element or a linking site with the element sulfur. According to claim 12,
The carbon material is a method for producing a cathode active material for a lithium secondary battery comprising at least one selected from the group consisting of graphene, graphene oxide, reduced graphene oxide, and combinations thereof. According to claim 12,
Method for producing a cathode active material for a lithium secondary battery to form a π-π stacking (π-π stacking) of the matrix and the carbon material by stirring the mixed solution. According to claim 12,
A method for producing a cathode active material for a lithium secondary battery in which an acid solution is added to the mixed solution to precipitate elemental sulfur. According to claim 12,
The heat treatment is a method for producing a cathode active material for a lithium secondary battery, which is performed at 300 ° C. to 400 ° C. for 20 hours to 30 hours. According to claim 12,
The method of manufacturing a cathode active material for a lithium secondary battery, wherein the elemental sulfur is covalently bonded to the matrix through nucleophilic aromatic substitution. According to claim 12,
The elemental sulfur includes an unshared electron pair, and a method for producing a cathode active material for a lithium secondary battery in which the unshared electron pair and the carbon element of the carbon material are combined.

Images