KR20250027694A - A positive active material comprising sulfur-carbon complex and a lithium-sulfur secondary battery having a high power property - Google Patents

Abstract

The present invention relates to a cathode active material for a lithium-sulfur battery, wherein the cathode active material comprises a sulfur-carbon composite, and the sulfur-carbon composite comprises a porous carbon material and a sulfur-based material. At this time, the porous carbon material satisfies at least one of the following: a sum of particle diameters D ₁₀ and D ₉₀ is 60 ㎛ or less, or a distribution ratio of particle diameters D ₉₀ to D ₁₀ is 7 or less, thereby providing a lithium-sulfur battery implementing high power density and high capacity.

Description

{A positive active material comprising sulfur-carbon complex and a lithium-sulfur secondary battery having a high power property}

The present invention relates to a cathode active material for a lithium-sulfur battery, and a lithium-sulfur battery having high power density and high capacity characteristics using the same.

A lithium-sulfur battery is a battery system that uses a sulfur-based material having a sulfur-sulfur bond as a positive electrode active material and lithium metal as an anode active material. Sulfur, the main material of the positive electrode active material, has the advantages of being abundant worldwide, non-toxic, and having a low weight per atom.

As the application areas of secondary batteries are expanding to electric vehicles (EVs) and energy storage systems (ESS), lithium-sulfur battery technology, which can theoretically achieve a high energy storage density per weight (~2,600 Wh/kg) compared to lithium-ion secondary batteries with a relatively low energy storage density per weight (~250 Wh/kg), is attracting attention.

In a lithium-sulfur battery, when discharging, the negative active material lithium is oxidized by releasing electrons and ionizing into lithium cations, and the positive active material sulfur series material is reduced by accepting electrons. Here, through the reduction reaction of the sulfur series material, the SS bond accepts two electrons and is converted into the form of a sulfur anion. The lithium cation generated by the oxidation reaction of lithium is transferred to the positive electrode through the electrolyte, and combines with the sulfur anion generated by the reduction reaction of the sulfur series compound to form a salt. Specifically, sulfur before discharge has a cyclic S ₈ structure, which is converted into lithium polysulfide (Li ₂ Sx, 1 ≤ x ≤ 8) through the reduction reaction, and is completely reduced to generate lithium sulfide (Li ₂ S).

As sulfur (S ₈ ) used in the positive electrode active material is an insulator, porous carbon materials are being studied as a sulfur carrier to improve the reactivity of sulfur. In order to improve the kinetic activity of the electrochemical reaction during charging and discharging of lithium sulfur secondary batteries, there is a continuous demand for technology development for sulfur-carbon composites in which the positive electrode active material is supported on porous carbon materials as a positive electrode material.

In particular, theoretically, if sulfur is loaded onto a porous carbon material having a large specific surface area, the sulfur content should increase, and accordingly, the energy density and life characteristics of the battery should be improved. However, experimentally, even if sulfur is loaded onto a porous carbon material having a large specific surface area, the degree of capacity development of the battery is uneven, the tap density decreases during electrode formation, the compression ratio decreases during rolling, and the swelling phenomenon of the electrode occurs, making it difficult to manufacture and commercialize the electrode.

Accordingly, research and development of sulfur-carbon complexes with various properties for use in lithium-sulfur secondary batteries is continuing.

The present invention is to solve the above-described problem,

According to one aspect, the present invention aims to provide an active material capable of uniformly exhibiting the electrochemical reactivity of sulfur by providing a small particle size of a porous carbon material carrying sulfur, an electrode using the same, and a battery.

According to another aspect, the present invention aims to provide an active material capable of uniformly exhibiting the electrochemical reactivity of sulfur by uniformly providing a particle size of a porous carbon material on which sulfur is supported, an electrode using the same, and a battery.

Specifically, the purpose may be to provide a lithium-sulfur battery having improved energy density, battery capacity, and electrochemical reaction uniformity by reducing the particle size of a porous carbon material carrying sulfur or controlling the particle size distribution at a predetermined ratio.

To solve the above problems,

According to one aspect, the present invention provides cathode active materials for lithium-sulfur batteries of the following embodiments.

The positive electrode active material according to the first embodiment is

Comprising a sulfur-carbon composite including a porous carbon material and a sulfur-based material,

The above porous carbon material satisfies at least one of the particle size conditions (1) and (2) below.

(1) The sum of particle diameter D ₁₀ and particle diameter D ₉₀ is 60 ㎛ or less, and

(2) The ratio of the particle size distribution _D90 to particle size _D10 according to Equation 1 below (Broadness Factor, BF) is 7 or less,

[Formula 1]

Broadness Factor(BF) = [(particle diameter D ₉₀ )/(particle diameter D ₁₀ )]

According to the second embodiment, in the first embodiment,

The above sulfur-based material may include inorganic sulfur (S ₈ ); Li ₂ S _n (n≥1); an organosulfur compound including at least one of 2,5-dimercapto-1,3,4-thiadiazole and 1,3,5-trithiocyanuic acid; a carbon-sulfur polymer ((C ₂ S _x ) _n , x=2.5 to 50, n≥2); or a mixture of two or more of them.

According to a third embodiment, in the first or second embodiment,

The above porous carbon material may have a BET surface area of 150 m ² /g or more.

According to the fourth embodiment, in any one of the first to third embodiments,

The above porous carbon material may include carbon nanotubes, carbon black, graphite, activated carbon, graphene, or a mixture of two or more thereof.

According to the fifth embodiment, in any one of the first to fourth embodiments,

The above porous carbon material may include carbon nanotubes.

According to the sixth embodiment, in any one of the first to fifth embodiments,

The content of elemental sulfur (S) may be 60 wt% or more relative to 100 wt% of the above sulfur-carbon complex.

According to the seventh embodiment, in any one of the first to sixth embodiments,

The above porous carbon material is,

The porous carbon material as a raw material is crushed using a centrifugal crusher,

It is manufactured by filtering the crushed porous carbon material through a sieve with a desired particle size.

The mesh size of the above body may be 2.8 to 4 times the particle size D ₅₀ of the manufactured porous carbon material.

According to the eighth embodiment, in any one of the first to seventh embodiments,

The particle size D ₅₀ of the above porous carbon material may be 100 ㎛ or less.

According to the ninth embodiment, in any one of the first to eighth embodiments,

The above porous carbon material may have a BF value of 4 to 7 according to the above formula 1.

According to another aspect of the present invention, the following embodiments of the positive electrode are provided.

The anode according to the 10th embodiment is

Comprising a cathode active material layer formed on at least one surface of the entire collector and the entire collector,

The above positive electrode active material layer includes a positive electrode active material for a lithium-sulfur battery according to any one of the first to ninth embodiments.

The anode according to the 11th embodiment is

Comprising a cathode active material layer formed on at least one surface of the entire collector and the entire collector,

The above positive electrode active material layer comprises a plurality of sulfur-carbon complexes,

The error value according to the following Equation 2 for the area of 10 arbitrary sulfur-carbon complexes per area of 50 ㎛ X 50 ㎛ based on the plane parallel to the current collector of the positive electrode active material layer is 100% or less.

[Formula 2]

Error (%) = [Standard deviation/Mean] X 100

According to the 12th embodiment, in the 10th embodiment or the 11th embodiment,

The average tortuosity value of the above positive electrode active material layer may be 1.7 or less.

According to the 13th embodiment, in any one of the 10th to 12th embodiments,

The above positive electrode active material layer may further include at least one of a binder and a conductive material.

According to the 14th embodiment, in any one of the 10th to 13th embodiments,

The content of elemental sulfur (S) may be 60 wt% or more relative to 100 wt% of the above-mentioned positive electrode active material layer.

According to the 15th embodiment, in any one of the 10th to 14th embodiments,

The sulfur loading can be from 1.67 mg _s /cm ² to 2.92 mg _s /cm ² .

According to the 16th embodiment, in any one of the 10th to 15th embodiments,

The above sulfur-carbon composite comprises a porous carbon material and a sulfur-based material,

The above porous carbon material may satisfy at least one of the particle size conditions (1) and (2) below.

(1) The sum of particle diameter D ₁₀ and particle diameter D ₉₀ is 60 ㎛ or less, and

(2) The ratio of the particle size distribution _D90 to particle size _D10 according to Equation 1 below (Broadness Factor, BF) is 7 or less,

[Formula 1]

Broadness Factor(BF) = [(particle diameter D ₉₀ )/(particle diameter D ₁₀ )]

According to another aspect of the present invention, lithium-sulfur batteries of the following embodiments are provided.

A lithium-sulfur battery according to the 17th embodiment,

An anode, a cathode, and a separator interposed between the anode and the cathode, and an electrolyte,

The above anode comprises an anode according to any one of the 11th to 16th embodiments.

According to the 18th embodiment, in the 17th embodiment,

The ratio of the total weight of the electrolyte to the total weight of elemental sulfur (S) in the anode (El/S) may be 3.5 g/g or less.

According to the 19th embodiment, in the 17th embodiment or the 18th embodiment,

The power density can be greater than 2.1 kW/kg for 10 seconds.

According to the 20th embodiment, in any one of the 17th to 19th embodiments,

It may have a discharge capacity of 1,000 mAh/g _s or more per weight of sulfur (S) in the above positive electrode.

When the particle size of the carbon material is large, there may be a problem of low cell capacity expression because the gap between adjacent carbon materials is larger than necessary.

In addition, when the particle size distribution of the carbon material is wide, the reaction of the sulfur-based material, such as sulfur (S ₈ ), supported on the carbon material of non-uniform size also occurs non-uniformly, which may cause a problem of low cell capacity expression.

The present invention produces a porous carbon material having a small and uniform particle size distribution to increase the uniformity of the reaction, and when a carbon material having a small particle size and a uniform size is used as a carrier for a sulfur-based material, there is an effect of exhibiting superior cell capacity and power density compared to a cell using a carbon material having a large particle size or an uneven size as a carrier.

For example, according to one aspect of the present invention, a lithium-sulfur battery having a 10-second power density of 2.1 kW/kg or more throughout the entire discharge process can be provided.

In addition, according to one aspect of the present invention, a lithium-sulfur battery having a discharge capacity of 1,000 mAh/gs or more at 1.0C discharge can be provided.

Figure 1 is a graph showing the results of measuring the particle size distribution of Comparative Example 1 and Examples 1 to 3.
Figure 2 is a SEM image of the porous carbon material used in the manufacture of the sulfur-carbon composite of Example 4. The image on the left is at 1,000x magnification, and the image on the right is at 10,000x magnification.
Figure 3 is a SEM image of the porous carbon material used in the manufacture of the sulfur-carbon composite of Comparative Example 2. The image on the left is at a magnification of 1,000 times, and the image on the right is at a magnification of 10,000 times.
Figure 4a is a 400× magnification SEM image of the upper surface of the positive electrode active material layer of the positive electrode manufactured using the sulfur-carbon composite of Example 1, measuring 200 μm X 200 μm.
Figure 4b is a 1,000× magnification SEM image of the upper surface of the positive electrode active material layer of the positive electrode manufactured using the sulfur-carbon composite of Example 1, measuring 70 μm X 70 μm.
Figure 4c is an image showing the process of measuring the curvature in the horizontal and vertical directions on a 400x magnification SEM image of the upper surface of the positive electrode active material layer of the positive electrode manufactured using the sulfur-carbon composite of Example 1, measuring 200 ㎛ X 200 ㎛.
Figure 5a is a 400× magnification SEM image of the upper surface of the positive electrode active material layer of the positive electrode manufactured using the sulfur-carbon composite of Comparative Example 1, measuring 200 μm X 200 μm.
Figure 5b is a 1,000x magnification SEM image of the upper surface of the positive electrode active material layer of the positive electrode manufactured using the sulfur-carbon composite of Comparative Example 1, measuring 70 μm X 70 μm.
FIG. 5c is a 400× SEM image of the upper surface of a 200 μm X 200 μm positive electrode active material layer of a positive electrode obtained from a lithium-sulfur battery disassembled after charge and discharge according to Evaluation Example 2 in the present specification. Specifically, the positive electrode is a positive electrode manufactured using the sulfur-carbon composite of Comparative Example 1.
FIG. 5d is a 1,000× magnification SEM image of the upper surface of a 70 μm X 70 μm positive electrode active material layer of a positive electrode obtained from a lithium-sulfur battery disassembled after charge and discharge according to Evaluation Example 2 in the present specification. Specifically, the positive electrode is a positive electrode manufactured using the sulfur-carbon composite of Comparative Example 1.
Figure 5e is an image showing the process of measuring the curvature in the horizontal and vertical directions on a 400x magnification SEM image of the upper surface of the positive electrode active material layer of the positive electrode manufactured using the sulfur-carbon composite of Comparative Example 1, measuring 200 ㎛ X 200 ㎛.
Figure 6a is an SEM image of a vertical cross-section of an anode manufactured using the sulfur-carbon composite of Comparative Example 2. The image on the left is at a magnification of 1,000 times, and the image on the right is at a magnification of 5,000 times.
Figure 6b is an image showing the process of measuring the average curvature of the positive electrode active material layer using the image on the left side of Figure 6a.
Figure 7a is a SEM image of a vertical cross-section of an anode manufactured using the sulfur-carbon composite of Example 4. The image on the left is at a magnification of 1,000 times, and the image on the right is at a magnification of 5,000 times.
Figure 7b is an image showing the process of measuring the average curvature of the positive electrode active material layer using the image on the left side of Figure 7a.
Figure 8 is a graph showing the results of evaluating changes in discharge capacity according to repeated charge and discharge cycles of Comparative Example 1 and Examples 1 to 3.
Figure 9 is a graph showing the results of comparing and evaluating the relative capacities of Comparative Example 1 and Examples 1 to 3.
Figure 10 is a graph showing the results of a comparative evaluation of the relative nominal voltages of Comparative Example 1 and Examples 1 to 3.
Figure 11 is a graph showing the results of evaluating the 0.5C discharge capacity for batteries using the sulfur-carbon composites of Example 1 and Comparative Example 1.
Figure 12 is a graph showing the results of evaluating the 0.5C discharge capacity for batteries using the sulfur-carbon composites of Example 4 and Comparative Example 2.

Hereinafter, the present invention will be described in more detail.

The terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as having meanings and concepts that conform to the technical idea of the present invention, based on the principle that the inventor can appropriately define the concept of the term in order to explain his or her own invention in the best manner.

Throughout this specification, whenever a part is said to "include" or "have" a component, this does not exclude other components, but rather implies that other components may be included, unless otherwise specifically stated.

In addition, the terms “about,” “substantially,” etc., used throughout the specification of this application are used in the sense that they are numerical or close to numerical values when manufacturing and material tolerances inherent in the meanings stated are presented, and are used to prevent unscrupulous infringers from unfairly exploiting the disclosure contents in which exact or absolute values are mentioned to aid the understanding of this application.

Throughout this specification, references to “A and/or B” mean “A or B or both.”

In the present invention, the “specific surface area” is measured by the BET method, and specifically, can be calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77K) using BELSORP-mini II of BEL Japan.

The term "polysulfide" as used in this specification is a concept that includes both "polysulfide ion (Sx ^2- , 1≤ x ≤8)" and "lithium polysulfide (Li ₂ S _x or LiS _x ^- , 1≤ x ≤8)".

The term "composite" as used in this specification refers to a material in which two or more materials are combined to form physically and chemically different phases and exhibit more effective functions.

In the present invention, “particle diameter D ₁₀ ” means a particle size based on 10% of the volume cumulative particle size distribution of the target particle, “particle diameter D ₅₀ ” means a particle size based on 50% of the volume cumulative particle size distribution of the target particle, and “particle diameter D ₉₀ ” means a particle size based on 90% of the volume cumulative particle size distribution of the target particle.

The above particle diameters D ₁₀ , D ₅₀ , and D ₉₀ can be measured, respectively, using a laser diffraction method. For example, after dispersing the target particle powder in a dispersion medium, introducing it into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), irradiating it with ultrasonic waves of about 28 kHz with an output of 60 W, obtaining a volume cumulative particle size distribution graph, and then measuring it by finding the particle sizes corresponding to 10%, 50%, and 90% of the volume cumulative distribution, respectively. That is, for example, the average particle diameter D ₅₀ represents the median value or median diameter in the particle distribution graph, and represents the particle size at the 50% point in the cumulative distribution. The particle diameter represents the diameter of a particle, and the particle diameter represents the longest length within a particle.

The unit "mAh/g _s " used in this specification is intended to indicate capacity per weight of sulfur (S) unless otherwise specifically stated, and may be used interchangeably with other expressions such as mAh/g(s), mAh/gs, etc.

The unit "mg _s /cm ² " used in this specification is intended to express the weight of sulfur (S) per unit area unless otherwise specifically stated, and may be used interchangeably with other expressions such as mg(s)/cm ² , mAh/gs, etc.

The term "porosity" used in this specification means the ratio of the volume occupied by pores to the total volume of a structure, and uses vol% as its unit, and can be used interchangeably with terms such as void ratio and porosity. The porosity can be measured according to the method of ISO 15901:2019 known in the art.

The present invention relates to a cathode active material for an electrochemical device, a cathode comprising the same, and a secondary battery comprising the cathode. The secondary battery may be a lithium ion secondary battery. In particular, the cathode active material according to the present invention comprises a sulfur-carbon complex, and the lithium ion secondary battery is a lithium-sulfur secondary battery.

According to one aspect of the present invention, the positive electrode active material comprises a sulfur-carbon composite including a porous carbon material and a sulfur-based material.

In one embodiment of the present invention, the porous carbon material includes pores that are not fixed in the interior of the particle (closed pores) and/or on the surface of the particle (open pores). At this time, the average diameter of the pores is, for example, in the range of 1 to 200 nm, and the porosity can be 10 to 90 vol% of the total volume of the porous carbon material. The average diameter of the pores can be measured according to a known method, such as, for example, a BET measurement method using gas adsorption or a mercury intrusion method.

In one embodiment of the present invention, the sulfur-carbon complex may be provided in a form in which the sulfur-based material is supported on all or at least a portion of the interior and exterior surfaces of the pores of the porous carbon material. In addition, the sulfur-carbon complex may be provided in a form in which the sulfur-based material covers all or at least a portion of the interior and exterior surfaces of the pores of the porous carbon material.

According to one aspect of the present invention, the present invention is characterized in that it uses a porous carbon material satisfying at least one particle size condition among the following (1) and (2).

Condition (1) The sum of particle diameter D ₁₀ and particle diameter D ₉₀ is 60 ㎛ or less, and

Condition (2) The ratio of the distribution of particle diameter D ₉₀ to particle diameter D ₁₀ according to Equation 1 below (Broadness Factor, BF) is 7 or less.

[Formula 1]

Broadness Factor(BF) = [(particle diameter D ₉₀ )/(particle diameter D ₁₀ )]

In one embodiment of the present invention, the porous carbon material may have a structural characteristic in which the sum of particle diameters D ₁₀ and D ₉₀ is 60 ㎛ or less.

In another embodiment of the present invention, the porous carbon material may have a structural characteristic that a ratio of the distribution of particle diameter D ₉₀ to particle diameter D ₁₀ (Broadness Factor, BF) is 7 or less. The BF refers to a ratio of the particle size distribution of particle diameter D ₉₀ to particle diameter D ₁₀ of the porous carbon material, and can be calculated according to the above Equation 1 [(particle diameter D ₉₀ )/(particle diameter D ₁₀ )].

In another embodiment of the present invention, the porous carbon material may have a structural characteristic in that the sum of particle diameters D ₁₀ and D ₉₀ is 60 ㎛ or less, and BF is 7 or less.

In one embodiment of the present invention, when the particle size of the porous carbon material is large or the particle size distribution is wide, that is, when the size of the porous carbon material is uneven, a phenomenon occurs in which the reaction of the sulfur-based material supported on the porous carbon material also occurs unevenly. This causes a problem in that the capacity expression of the electrode and the battery is reduced. Accordingly, the present invention can be characterized in that the power density and capacity expression of the electrode and the battery are improved by making the particle size of the porous carbon material small (particle size condition (1)), using a porous carbon material having a small particle size distribution (particle size condition (2)), or using a porous carbon material having a small particle size and a small particle size distribution (particle size conditions (1) and (2)).

In the present specification, the BF value may be a value measured based on the time before the porous carbon material supports the sulfur-based material to provide the sulfur-carbon composite. That is, it may be measured based on the raw material before manufacturing the sulfur-carbon composite. In addition, the BF value may be measured even in the final product state, such as the cathode active material, the cathode, or the lithium-sulfur battery. For example, a lithium-sulfur battery having a state of SOC (state of charge) of 70 to 100, preferably a lithium-sulfur battery having a state of SOC 100, is decomposed under inactive conditions to obtain a cathode, and a binder and a sulfur-based material are extracted and removed from the obtained cathode using a known extraction method, and then the remaining porous carbon material is measured for D ₉₀ and D ₁₀ according to the above-described particle size Dn (n = 10, 50, or 90) measuring method, and then the value of D ₉₀ /D ₁₀ is calculated and measured.

In one embodiment of the present invention, in order to use a small-sized porous carbon material, the sum of the particle diameters D ₁₀ and D ₉₀ of the porous carbon material may be, for example, 10 µm to 60 µm, 20 µm to 55 µm, 30 µm to 55 µm, 35 µm to 55 µm, 40 µm to 55 µm, 45 µm to 55 µm, or 50 µm to 55 µm. For example, the sum of the particle diameters D ₁₀ and D ₉₀ of the porous carbon material may be 50 µm to 52 µm, or 51 µm. When the sum of the particle diameters D ₁₀ and D ₉₀ is within the above-described range, the size of the porous carbon material is small, the content of the sulfur-based material supported per porous carbon material is uniform, and the gap between the plurality of porous carbon materials in the positive electrode manufactured using the sulfur-carbon composite formed using the same is narrow, and the reactivity of the lithium-sulfur battery using the same can advantageously exhibit a uniform effect.

In one embodiment of the present invention, referring to the method for measuring the particle diameter Dn, in the present invention, the particle diameter D ₁₀ of the porous carbon material has a smaller value than the particle diameter D _90. At this time, a smaller ratio of the particle size distribution of the particle diameter D ₉₀ to the particle diameter D ₁₀ indicates that the particle size is more uniform. The present invention can have the effect of uniformly exhibiting the electrochemical reactivity of the active material by providing the porous carbon material such that the BF is 7 or less, but the mechanism of the present invention is not limited thereto. The BF value of the porous carbon material can be, for example, greater than 1 and less than or equal to 7, greater than 1 and less than or equal to 6, 2 to 6, 3 to 6, 4 to 7, 4 to 6, and more specifically, 5.3 to 5.6.

In one embodiment of the present invention, the particle size D ₅₀ of the porous carbon material may be, for example, 100 ㎛ or less, 70 ㎛ or less, or 50 ㎛ or less. Specifically, the particle size D ₅₀ of the porous carbon material may be, for example, 1 to 100 ㎛, 5 to 90 ㎛, 10 to 80 ㎛, 15 to 70 ㎛, 20 to 60 ㎛, 10 to 50 ㎛, 15 to 40 ㎛, or 20 to 40 ㎛. When the particle size D ₅₀ of the porous carbon material is within the above-described range, the tap density of the positive electrode using the porous carbon material may be improved, thereby exhibiting a beneficial effect in terms of increasing the energy density of the battery, but the present invention is not limited thereto. For example, when the particle size of the porous carbon material is large, the size of the pores between each carbon material in the particle form may become large, which may decrease the expression of the battery capacity. Accordingly, the present invention can have another structural feature of controlling the particle size of the porous carbon material to an appropriate range to have a small and uniform particle size distribution. When the porous carbon material having such a small particle size and a uniform distribution is used as a carrier for a sulfur-based material, the electrochemical performance is expressed uniformly compared to a carbon material having a large particle size and an uneven particle size distribution, and a further improved battery capacity can be expressed. The method of measuring the particle size D ₅₀ is as described above.

In one embodiment of the present invention, the porous carbon material serves as a support that provides a framework in which sulfur can be uniformly and stably fixed, and complements the low electrical conductivity of sulfur to enable the electrochemical reaction to proceed smoothly. The porous carbon material can be used without particular limitation on its type as long as it satisfies the particle size conditions described above.

In one embodiment of the present invention, the porous carbon material includes pores that are not fixed in the interior of the particle (closed pores) and/or on the surface of the particle (open pores). At this time, the average diameter of the pores is, for example, in the range of 1 to 200 nm, and the porosity can be 10 to 90 vol% of the total volume of the porous carbon material. The average diameter of the pores can be measured according to a known method, such as, for example, a BET measurement method using gas adsorption or a mercury intrusion method.

In one embodiment of the present invention, the BET surface area of the porous carbon material is not particularly limited, but may be, for example, 150 m ² /g or more. By utilizing the large surface area of the porous carbon material, the loading rate of the sulfur-based material can be increased, and thus, the electrochemical performance of the cathode and lithium-sulfur battery using the porous carbon material can be advantageously improved. However, the present invention is not limited thereto. The sulfur-carbon composite according to the present invention can exhibit the characteristics of a high sulfur loading amount, low irreversible capacity, and high energy density because the carbon material that serves as a sulfur carrier has a large BET surface area and an appropriate particle size range. That is, there is an advantage of being able to have a structure in which the utilization rate of sulfur can be improved during an electrochemical reaction, but the present invention is not limited thereto.

In one embodiment of the present invention, the BET specific surface area of the porous carbon material may be, for example, 150 to 2,500 m ² /g, 150 to 2,000 m ² /g, 150 to 1,500 m ² /g, 150 to 1,000 m ² /g, 130 to 300 m ² /g, or 170 to 200 m ² /g, but is not limited thereto. The BET specific surface area is measured by the BET method and may represent a value measured according to a known method for measuring the BET specific surface area. For example, the BET specific surface area may be a value calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77 K) using BELSORP-max of BEL Japan.

In one embodiment of the present invention, the shape of the porous carbon material may be used without limitation in the form of a sphere, rod, needle, plate, tube or bulk.

The above porous carbon material is not particularly limited in type as long as it has a porous structure or a high specific surface area. For example, it may include carbon nanotubes, carbon black, graphite, activated carbon, graphene, or a mixture of two or more thereof, and preferably, it may include carbon nanotubes.

The above carbon nanotubes may include at least one selected from the group consisting of single-walled carbon nanotubes and multi-walled carbon nanotubes, but are not limited thereto. The carbon black may include at least one selected from the group consisting of Denka black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black, but are not limited thereto. In addition, the porous carbon material may include carbon nanofibers, and the carbon nanofibers may include at least one selected from the group consisting of graphite nanofibers, carbon nanofibers, and activated carbon fibers, but are not limited thereto. The graphite may include at least one selected from the group consisting of natural graphite, artificial graphite, and expanded graphite, but are not limited thereto.

In one embodiment of the present invention, the porous carbon material may include a porous and conductive carbon-based material commonly used in the art. For example, the porous carbon material may include at least one selected from the group consisting of graphite; graphene; carbon black such as Denka black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; carbon nanotubes (CNTs) such as single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs); carbon fibers such as graphite nanofibers (GNFs), carbon nanofibers (CNFs), and activated carbon fibers (ACFs); graphite such as natural graphite, artificial graphite, and expanded graphite; carbon nanoribbons; carbon nanobelts, carbon nanorods, and activated carbon.

In one embodiment of the present invention, the porous carbon material may include carbon nanotubes. The carbon nanotubes are formed by carbons connected in a hexagonal shape to form a tube. According to one embodiment of the present invention, the carbon nanotubes may be single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), or a combination thereof, depending on the number of carbon atom layers (also referred to as 'carbon walls') constituting the carbon nanotubes. Here, the length of individual carbon nanotubes is not particularly limited.

In one embodiment of the present invention, the porous carbon material may include carbon nanotubes in order to improve the sulfur loading rate, and specifically may include multi-walled carbon nanotubes, but the present invention is not limited thereto.

In another embodiment of the present invention, the carbon nanotubes may exist in a form in which two or more carbon nanotubes are closely attached and entangled with each other due to cohesion therebetween. Specifically, in one embodiment of the present invention, the carbon nanotubes may be provided in the form of a carbon nanotube dispersion in which the carbon nanotubes are dispersed in a dispersion medium or the like to exist as single strands, but may also be provided in the form of a secondary structure in which carbon nanotubes of a primary structure are cohesively provided.

In this aspect, when the porous carbon material includes carbon nanotubes, the carbon nanotubes may include a bundle-shaped secondary structure, an entangled-shaped secondary structure, or both.

The above bundle-shaped secondary structure of carbon nanotubes is a form in which a single strand of carbon nanotubes is used as a primary structure, and the plurality of primary structures are aligned in the longitudinal direction of the carbon nanotubes and are clumped together by cohesive forces between carbons, etc., and can also be called a bundled CNT.

In one embodiment of the present invention, the carbon nanotube may include, for example, an entangled multi-walled carbon nanotube.

In one embodiment of the present invention, the porous carbon material may include carbon nanotubes having a BET specific surface area of, for example, 100 to 2,500 m ² /g, 100 to 400 m ² /g, for example, 150 to 350 m ² /g, specifically 200 m ² /g, but is not limited thereto.

In one embodiment of the present invention, the graphene may be a carbon layer composed solely of carbon, or may be graphene oxide, reduced graphene oxide, or a mixture thereof depending on its form, but the present invention is not limited thereto.

Meanwhile, in another embodiment of the present invention, the carbon material can be produced by carbonizing a precursor of various carbon materials.

In one embodiment of the present invention, the porous carbon material may be pretreated and used through a pretreatment process of being pulverized by a centrifugal crusher to have the above-described particle size and then classified using a sieve according to the particle size, but the method for manufacturing the porous carbon material of the present invention is not limited thereto.

In one embodiment of the present invention, the porous carbon material may be manufactured with a particle size controlled to satisfy the particle size condition (1) and/or particle size condition (2) according to the pretreatment method described below.

In one embodiment of the present invention, the porous carbon material may be manufactured by crushing a porous carbon material as a raw material using a centrifugal crusher and filtering the crushed porous carbon material through a sieve having a desired particle size. At this time, in order to satisfy the particle size condition (1) and/or the particle size condition (2), the mesh size of the sieve may be 2.8 to 4 times the particle size D ₅₀ of the manufactured porous carbon material.

In the past, in order to control the particle size of porous carbon materials, porous carbon materials were pulverized using a ball mill or blade, etc. However, in the above-mentioned conventional pulverization method, the porous carbon materials randomly came into contact with the balls or blades, so that large-sized porous carbon materials and small-sized porous carbon materials coexisted, and thus there was a problem of a wide particle size distribution.

The present invention may be manufactured by performing a step of crushing the porous carbon material using a centrifugal crusher (step 1) and then a step of filtering the crushed porous carbon material through a sieve (step 2).

In one embodiment of the present invention, the step (1) may be to perform pulverization by rotating at a linear velocity of 30 to 125 m/s using a centrifugal pulverizer. Specifically, the pulverization may be performed by rotating at an angular velocity of 30 to 95 m/s. When the speed of the centrifugal pulverization in the step (1) is the above-described speed, it may be advantageous in terms of uniformly controlling the particle size of the porous carbon material while pulverizing it to a small size and not increasing the tap density.

In one embodiment of the present invention, the centrifugal grinder may have a plurality of rotating teeth, and the rotating teeth may grind the porous carbon material while rotating. Specifically, the centrifugal grinder may include, for example, 2 to 20, 4 to 18, 6 to 16, 8 to 14, 10 to 14, or 10 to 12 rotating teeth.

In addition, in one embodiment of the present invention, the plurality of rotating teeth may each have a shape of a triangular prism, and the plurality of rotating teeth may be arranged to face the rotation axis of the centrifugal crusher. Specifically, in a top view along the rotation axis of the centrifugal crusher, the vertical cross sections of the triangular prisms may be arranged to meet each other at the center of the centrifugal crusher.

In one embodiment of the present invention, the plurality of rotating teeth may be made of, for example, but not limited to, stainless steel, titanium, or stainless steel with a protective coating.

In one embodiment of the present invention, a centrifugal grinder having a rotating tooth may be used in the step (1), and for example, a ZM 200 device from Retsch may be used.

In one embodiment of the present invention, the centrifugal pulverization may be performed at 6,000 to 18,000 rpm, and the particle size of the porous carbon material may be controlled within the above range. Specifically, the centrifugal pulverization may be performed at a speed of 6,000 to 23,000 rpm, specifically 6,000 to 18,000 rpm, using a ZM 200 device from Retsh.

In one embodiment of the present invention, since the magnitude of the force applied may vary even at the same rpm depending on the size of the centrifugal crusher, the rpm may be adjusted to crush at a linear speed of 30 to 125 m/s according to the following equation, taking into account the size of the centrifugal crusher.

Linear velocity = (RPM X circumference) / 60 seconds

In the above equation, 'circumference' represents the distance that one rotary tooth moves while making one rotation. Specifically, when the radius of rotation of one rotary tooth is r, the circumference represents the value 2πr.

The above step (2) is a step of sieving the porous carbon material centrifugally crushed in the above step (1).

In one embodiment of the present invention, the sieve is provided in a centrifugal grinder, and may be provided on an outer periphery of the centrifugal grinder. Specifically, the sieve may be provided to surround a plurality of rotating blades within the centrifugal grinder.

In one embodiment of the present invention, the sieve may have a cylindrical shape and may be arranged to surround the plurality of rotating teeth. For example, on the upper surface of the centrifugal crusher, the shortest distance between the plurality of rotating teeth and the sieve may be 0.1 to 5 mm or 0.5 to 2 mm, for example, 1 mm. The sieve may include a mesh having trapezoidal and/or circular holes.

In one embodiment of the present invention, as the rotating teeth rotate, the porous carbon material is pulverized, and the porous carbon material whose particle size is controlled to a target size passes through a sieve located outside the rim on which a series of rotating teeth are arranged while receiving centrifugal force, thereby solving the problem of the particle size becoming smaller and/or the surface being damaged. According to one aspect of the present invention, by simultaneously performing the steps (1) and (2), the particle size is controlled to a target size, and a porous carbon material having a narrow particle size distribution can be obtained.

Thus, in one embodiment of the present invention, it may be preferable that step (2) be performed while centrifugal force is applied to the pulverized porous carbon material.

The above step (2) is a process in which the porous carbon material centrifugally crushed in step (1) is moved to a sieve and filtered, and the above steps (1) and (2) may be continuous processes performed simultaneously.

The sieve used in the above step (2) can control the particle size of the porous carbon material by adjusting the mesh size. The mesh size of the sieve can be 2.8 to 4 times (2.8 ≤mesh size/target D _{50 ≤4} ) the particle size D ₅₀ of the target porous carbon material, and by limiting the mesh size range of the sieve as described above, the particle size D ₅₀ of the target porous carbon material can be obtained, and a porous carbon material having a narrow particle size distribution can be obtained.

In one embodiment of the present invention, the target particle size D ₅₀ of the porous carbon material may _be , for example, the particle size D ₅₀ of the porous carbon material manufactured according to one aspect of the present invention, and may be, for example, 10 ㎛ to 100 ㎛, 5 to 90 ㎛, 10 to 80 ㎛, 15 to 70 ㎛, 20 to 60 ㎛, 10 to 50 ㎛, 15 to 40 ㎛, or 20 to 40 ㎛.

In the present invention, the sulfur-based material can be used without particular limitation as long as it is a material capable of providing sulfur (S ₈ ) as an active material of a lithium-sulfur battery. For example, the sulfur-based material includes at least one of sulfur (S ₈ ) and a sulfur compound.

In one embodiment of the present invention, the sulfur-based material may be an inorganic sulfur (S ₈ ); Li ₂ S _n (n≥1); an organosulfur compound including at least one of 2,5-dimercapto-1,3,4-thiadiazole and 1,3,5-trithiocyanuic acid; a carbon-sulfur polymer ((C ₂ S _x ) _n , x=2.5 to 50, n≥2); or two or more thereof.

In one embodiment of the present invention, the sulfur-based material in the sulfur-carbon composite may be included by physical adsorption with the porous carbon material, or chemical bonding such as covalent bonding or van der Waals bonding between sulfur element (S) and carbon in the porous carbon material. In particular, the sulfur-based material may be chemically bonded to the surface of the porous carbon material to form a composite.

In one embodiment of the present invention, the sulfur-carbon complex preferably has a content of elemental sulfur (S) of 60 wt% or more, 70 wt% or more, or 75 wt% or more and 99 wt% or less, relative to 100 wt% of the sulfur-carbon complex. For example, the sulfur-carbon complex may preferably have a content of elemental sulfur (S) of 60 wt% to 99 wt%, 70 wt% to 99 wt%, 60 wt% to 90 wt%, 75 wt% to 90 wt%, 70 wt% to 85 wt%, 70 wt% to 80 wt%, 75 wt% to 80 wt%, or 70 wt% to 75 wt%, relative to 100 wt% of the sulfur-carbon complex.

In the sulfur-carbon composite according to the present invention, the sulfur-based material is located on at least one of the inner and outer surfaces of the pores of the porous carbon material, and at this time, it may be present in an area of less than 100%, preferably 1 to 95%, and more preferably 60 to 90% of the entire inner and outer surfaces of the porous carbon material. When the sulfur is present on the surface of the porous carbon material within the above range, it can exhibit the maximum effect in terms of electron transfer area and wettability of the electrolyte. Specifically, since sulfur is thinly and evenly impregnated on the surface of the porous carbon material in the above range area, the electron transfer contact area during the charge and discharge process can be increased. If the sulfur is located in an area of 100% of the entire surface of the porous carbon material, the porous carbon material is completely covered with sulfur, so that the wettability of the electrolyte is reduced and the contact with the conductive material included in the electrode is reduced, so that electron transfer is not received and the reaction cannot be participated in.

The above sulfur-carbon complex may be a composite formed by simply mixing the sulfur-based material and the carbon material, or may have a coating form or a support form of a core-shell structure. The coating form of the core-shell structure is one in which either the sulfur-based material or the carbon material coats another material, for example, the surface of the carbon material may be wrapped with sulfur, or vice versa. In addition, the support form may be a form in which the sulfur-based material is filled inside the carbon material, particularly in the internal pores. Any form of the sulfur-carbon complex may be used as long as it satisfies the content ratio of the sulfur and carbon material presented above, and is not limited thereto in the present invention.

Next, a method for producing the sulfur-carbon complex is provided. The method for producing the sulfur-carbon complex according to the present invention is not particularly limited and is commonly known in the art, and can be produced by a composite method comprising the steps of (S1) mixing a porous carbon material and a sulfur-based material, and then (S2) composite-forming.

The mixing in the above step (S1) is performed to increase the mixing degree between the sulfur-based material and the porous carbon material, and can be performed using a stirring device commonly used in the art. At this time, the mixing time and speed can also be selectively adjusted according to the content and conditions of the raw materials.

The method for compounding in the above step (S2) is not particularly limited in the present invention, and a method commonly used in the art can be used. For example, a method commonly used in the art, such as dry compounding or wet compounding such as spray coating, can be used. For example, a method can be used in which a mixture of sulfur and carbon material obtained after mixing is ball milled to pulverize the mixture, and then placed in an oven at 120 to 160° C. for 20 minutes to 1 hour so that the molten sulfur can evenly coat the inner and outer surfaces of the first carbon material.

The sulfur-carbon composite manufactured through the above-described manufacturing method has a structure in which the specific surface area is high, the sulfur loading amount is high, and the sulfur utilization rate is improved, so that not only the electrochemical reactivity of sulfur is improved, but also the accessibility and contactability of the electrolyte are improved, thereby improving the capacity and life characteristics of the lithium-sulfur battery.

Another aspect of the present invention provides an anode formed using the sulfur-carbon complex.

A positive electrode for a lithium-sulfur battery according to one aspect of the present invention comprises a current collector and a positive electrode active material layer formed on at least one surface of the current collector, wherein the positive electrode active material layer comprises the positive electrode active material for a lithium-sulfur battery described above as an active material.

The above-described positive electrode for a lithium-sulfur battery comprises a current collector and a positive electrode active material layer formed on at least one surface of the current collector, the positive electrode active material layer comprises a sulfur-carbon composite, and the sulfur-carbon composite comprises a porous carbon material and a sulfur-based material supported on all or at least a portion of the inner and outer surfaces of the pores of the porous carbon material.

At this time, the positive electrode active material layer may have a structural feature including the positive electrode active material described above.

That is, the positive active material includes a sulfur-carbon complex, and the sulfur-carbon complex includes a porous carbon material satisfying at least one of the particle size conditions (1) and (2) described above. Specifically, the porous carbon material may include one satisfying at least one of the particle size conditions (1) that the sum of the particle size D ₁₀ and the particle size D ₉₀ is 60 ㎛ or less and the particle size condition (2) that the ratio of the particle size D ₁₀ to the particle size D ₉₀ distribution according to the following Equation 1 (Broadness Factor, BF) is 7 or less.

[Formula 1]

Broadness Factor(BF) = [(particle diameter D ₉₀ )/(particle diameter D ₁₀ )]

In one embodiment of the present invention, the particle size D ₅₀ of the porous carbon material may include, for example, 100 ㎛ or less.

A positive electrode according to one embodiment of the present invention includes a current collector and a positive electrode active material layer formed on at least one surface of the current collector.

According to one embodiment of the present invention, the positive electrode active material layer may include a plurality of sulfur-carbon complexes, and the positive electrode may satisfy the following equation 2.

[Formula 2]

X _L /X _S ≤ 15

In the above equation 2,

The above X _L is the average value of the length of the longest axis in the top five sulfur-carbon complexes based on the area in the top view of the positive electrode active material layer,

The above X _S is the average value of the length of the longest axis in the lower five sulfur-carbon complexes based on the area in the top view of the positive electrode active material layer.

The positive electrode satisfying the above formula 2 may exhibit characteristics in which the particle size of the sulfur-carbon complex included in the positive electrode active material layer is small and/or uniform. In addition, the pores between the plurality of sulfur-carbon complexes in the positive electrode active material layer are narrow, and the reactivity of the lithium-sulfur battery using the same may exhibit an advantageous effect in exhibiting a uniform effect.

Specifically, according to one embodiment of the present invention, the value of X _L /X _S can be, for example, 15 or less, 10 or less, or 5 or less. In addition, the value of X _L /X _S can be 1 or more, 1.5 or more, 2 or more, 2.5 or more, 3 or more, or 3.5 or more within a range satisfying the upper limit described above. For example, the value of X _L /X _S can have a value of 1 to 15, 1.5 to 10, 2.0 to 5, 2.5 to 5.0, 3.0 to 5.0, 3.0 to 4.0, or 3.0 to 4.5. When the value of X _L /X _S is in the above-described range, the gap between the sulfur-carbon complexes in the positive electrode active material layer is narrow, and an advantageous effect can be exhibited in terms of showing the uniformity of the electrochemical reaction in the positive electrode.

In this specification, when the direction of lamination of the current collector and the positive electrode active material layer in the positive electrode is referred to as the 'upper and lower direction', the surface of the positive electrode active material layer facing the current collector is referred to as the 'lower surface of the positive electrode active material layer', and the back surface of the surface facing the current collector is referred to as the 'upper surface of the positive electrode active material layer'.

In one embodiment of the present invention, when manufacturing an electrode assembly including a positive electrode, a negative electrode, and a separator using the positive electrode, the upper surface of the positive electrode active material layer may mean a surface that comes into contact with the separator.

In this specification, the 'top view of the positive electrode active material layer' is an image for confirming the area and major axis length of the sulfur-carbon complex distributed on the surface and inside of the positive electrode active material layer, and may be, for example, an SEM image obtained for the top surface of the positive electrode active material layer.

According to one embodiment of the present invention, the gaps between sulfur-carbon complexes, grain boundaries and grain surfaces of the sulfur-carbon complexes can be distinguished by the difference in brightness on the top surface of the positive electrode active material layer.

At this time, in order to measure the longest axis within the upper five sulfur-carbon complexes and the lower five sulfur-carbon complexes based on the area of the sulfur-carbon complexes, it may be preferable to use an image having a magnification of, for example, 400 times or more for the top view of the positive electrode active material layer. For example, the top view of the positive electrode active material layer may be an image having a magnification of 400 times, 1,000 times, 2,000 times, or 5,000 times.

In one embodiment of the present invention, the upper five sulfur-carbon complexes and the lower five sulfur-carbon complexes based on the area of the sulfur-carbon complexes may be selected on images having the same magnification, but may also be selected on images having different magnifications for ease of measurement of the length of the longest axis in each sulfur-carbon complex.

For example, based on the area of the sulfur-carbon complexes, the top five sulfur-carbon complexes may be selected on an SEM image at 400x magnification, and the bottom five sulfur-carbon complexes may be selected on an SEM image at 1,000x magnification.

In one embodiment of the present invention, the upper five and lower five sulfur-carbon complexes may be selected from the entire area of the positive electrode active material layer, but for ease of measurement, a part of the positive electrode active material layer may be selected and selected from the same selected area.

In one embodiment of the present invention, the upper five sulfur-carbon complexes and the lower five sulfur-carbon complexes may be selected, for example, within the same area of the positive electrode active material layer, or within different areas.

For example, the upper five sulfur-carbon complexes and the lower five sulfur-carbon complexes may be selected within a region of 50 ㎛ X 50 ㎛ to 1,000 ㎛ to 1,000 ㎛ on the upper surface of the positive electrode active material layer.

In one embodiment of the present invention, the upper five sulfur-carbon complexes may be selected within an area of 150 ㎛ X 150 ㎛ to 1,000 ㎛ X 1,000 ㎛ on the upper surface of the positive electrode active material layer.

In one embodiment of the present invention, the five lower sulfur-carbon complexes may be selected within an area of 50 ㎛ X 50 ㎛ to 100 ㎛ X 100 ㎛ on the upper surface of the positive electrode active material layer.

For example, the upper five and lower five sulfur-carbon complexes may be selected within an area of 200 μm X 200 μm on the upper surface of the positive electrode active material layer.

At this time, as described above, when the upper five and lower five sulfur-carbon complexes are selected on images of different magnifications, the upper five sulfur-carbon complexes may be selected within an area of 200 ㎛ X 200 ㎛ on the upper surface of the positive electrode active material layer, and the lower five sulfur-carbon complexes may be selected within an area of 70 ㎛ X 70 ㎛ located within the area of 200 ㎛ X 200 ㎛.

In one embodiment of the present invention, the area of the sulfur-carbon complex may be determined by the pixel area occupied by the sulfur-carbon complex on the top view of the positive active material layer. That is, the top five sulfur-carbon complexes based on the area of the sulfur-carbon complex may mean the top five in order of the largest pixel area occupied by the elevation surface on the top view of the positive active material layer. In addition, the bottom five sulfur-carbon complexes based on the area of the sulfur-carbon complex may mean the bottom five in order of the smallest pixel area occupied by the elevation surface on the top view of the positive active material layer.

In one embodiment of the present invention, the longest axis within the sulfur-carbon complex means the longest straight line within one sulfur-carbon complex on the top surface of the positive electrode active material layer.

In one embodiment of the present invention, the longest axis of the sulfur-carbon complex may pass through the center of gravity of one sulfur-carbon complex. However, when the shape of the sulfur-carbon complex on the top surface of the positive electrode active material layer is not a sphere or an oval, the longest axis may not pass through the center of gravity of the sulfur-carbon complex. Therefore, the longest axis in the sulfur-carbon complex is not limited to a line passing through the center of the sulfur-carbon complex.

In one embodiment of the present invention, the length of the longest axis in the sulfur-carbon complex can be determined by the longest distance between pixels where the longest axis is located on the top view of the positive electrode active material layer.

In the above equation 2, X _L is the average value of the length of the longest axis in the top five sulfur-carbon complexes based on the area in the top view of the positive electrode active material layer, and X _S is the average value of the length of the longest axis in the bottom five sulfur-carbon complexes based on the area in the top view of the positive electrode active material layer.

In this specification, the 'average value' means an arithmetic mean. Therefore, the X _L can be measured by measuring the length of the longest axis of each of the top five sulfur-carbon complexes in terms of area on the top surface of the positive active material layer, and then calculating the average. In addition, the X _S can be measured by measuring the length of the longest axis of each of the bottom five sulfur-carbon complexes in terms of area on the top surface of the positive active material layer, and then calculating the average.

In one embodiment of the present invention, particles having a longest axis length of less than 1 ㎛ may appear on the top surface of the positive electrode active material layer. At this time, the particles having a longest axis length of less than 1 ㎛ are not sulfur-carbon complexes supporting sulfur on the outer surface and/or inside the pores, but represent porous carbon materials broken during the manufacture of the positive electrode or other impurities. Therefore, when selecting the bottom five sulfur-carbon complexes in terms of area on the top surface of the positive electrode active material layer for the Xs measurement, particles having a longest axis length of less than 1 ㎛ are not selected, and only particles having a longest axis length of 1 ㎛ or more are selected.

In one embodiment of the present invention, whether the positive electrode satisfies Equation 2 may be measured immediately after manufacturing the positive electrode or after charge/discharge.

For example, immediately after manufacturing the positive electrode, a top view of the positive electrode active material layer is obtained before activation, and X _L and X _S can be measured on the obtained top view according to the above-described method to confirm whether Equation 2 is satisfied.

In addition, by disassembling a lithium-sulfur battery assembled using the above positive electrode to obtain a positive electrode, and measuring X _L and X _S on the top surface of the positive electrode active material layer of the obtained positive electrode according to the above-described method, it is possible to confirm whether Equation 2 is satisfied.

Specifically, when the lithium-sulfur battery is disassembled to confirm whether the above formula 2 is satisfied, the lithium-sulfur battery may be disassembled in a charged state. Specifically, a lithium-sulfur battery in a charged state is disassembled under an inert atmosphere to obtain a cathode, and an electrolyte impregnated in the obtained cathode is extracted using an appropriate solvent, washed, and dried, and then a top view of the cathode active material layer is obtained to confirm whether the above formula 2 is satisfied.

In one embodiment of the present invention, the state of charge of the lithium-sulfur battery may be, for example, a state of SOC 50% to 90%, specifically a state of SOC 60% to 80%, but the present invention is not limited thereto. In addition, the inert atmosphere may be, for example, an Ar atmosphere, but the present invention is not limited thereto.

In one embodiment of the present invention, the lithium-sulfur battery may cause the active material to be detached from the positive electrode active material layer by external pressure due to repeated charge and discharge, or the positive electrode may be deformed due to repeated expansion and contraction of the positive electrode active material. Therefore, when disassembling the assembled lithium-sulfur battery to obtain the positive electrode, it may be desirable to confirm whether the above equation 2 is satisfied from a lithium-sulfur battery that exhibits a capacity retention rate of 80% or more compared to the initial capacity immediately after manufacture.

In one embodiment of the present invention, the positive electrode active material layer may include a plurality of sulfur-carbon complexes, and the positive electrode may satisfy the following equation 2'.

[Formula 2']

X _L /X _A ≤ 2

In the above equation 2',

The above X _L is the average value of the length of the longest axis in the top five sulfur-carbon complexes based on the area in the top view of the positive electrode active material layer,

The above X _A is the average value of the length of the longest axis in all sulfur-carbon complexes confirmed in the top view of the positive electrode active material layer.

The method of measuring the above X _L and X _A is based on the method of measuring the above XL and XS.

At this time, the above X _A is calculated as the average value after measuring the length of the longest axis in all sulfur-carbon complexes confirmed in the top view of the positive electrode active material layer.

In one embodiment of the present invention, the positive electrode active material layer may have an average tortuosity value of 1.7 or less. Specifically, the average tortuosity value may be 1.6 or less, for example, 1.3 to 1.6.

In one embodiment of the present invention, the 'curvature' may indicate the degree of curvature of the transport path of ions, etc., within the positive electrode active material layer. That is, the smaller the curvature, the shorter the transport path of ions, etc., within the positive electrode active material layer, and accordingly, the electrochemical activity of the electrode and the battery using the electrode may be improved, and in particular, the effect of exhibiting a favorable effect of exhibiting high output characteristics may be exhibited.

In one embodiment of the present invention, the average curvature of the positive electrode active material layer can be measured by the following method. For example, first, an image of a vertical cross-section along the stacking direction (up-down direction) of the current collector-positive electrode active material layer is obtained for the positive electrode as a measurement target, and from the obtained image, a point on the surface of the current collector is arbitrarily selected, and the vertical distance (L) is measured by connecting the ends of the electrodes in a direction perpendicular to the point from the point to the positive electrode surface. Next, the minimum distance (C) is measured along the boundary line between the particles (sulfur-carbon complexes) located between the arbitrarily selected point and the end point of the electrode. The curvature (C/L) is calculated using the measured L and C values. After selecting at least three different points on the surface of the current collector and repeating the above processes, the average value of the obtained C/L values is calculated to measure the average curvature.

That is, the curvature can be calculated by measuring the vertical distance (L) between the end points of the positive electrode located in the vertical direction from any point on the surface of the collector and the minimum distance (C) of the curve along the particle (sulfur-carbon complex) interface, and then using the following equation.

Curvature = [Curve minimum distance (C) / vertical distance (L)]

In one embodiment of the present invention, the vertical cross-sectional image of the positive electrode may be, for example, a SEM image. For example, FIGS. 6B and 7B each show SEM images indicating the vertical distance (L) and the minimum curve distance (C) for evaluating the curvature of the positive electrode active material layer using the sulfur-carbon composite of Comparative Example 2 and Example 4 in the present specification. The SEM image may be an image at a magnification of 1,000 times, but the method for measuring the curvature is not limited thereto.

In one embodiment of the present invention, the average curvature in the horizontal and vertical directions in the top view of the positive electrode active material layer may be 1.7 or less.

For example, in the top view of the positive electrode active material layer, the value of [(transverse curvature + vertical curvature)/2] may be 1.7 or less. Specifically, the average curvature in the transverse and vertical directions may be 1 to 1.7.

At this time, each degree of curvature in the horizontal direction and the degree of curvature in the vertical direction can be calculated according to the equation [minimum curve distance (C)/vertical distance (L)] as described above.

In one embodiment of the present invention, the average curvature in the transverse direction and the vertical direction in the top view of the positive electrode active material layer can be measured as follows. On the above-described top view of the positive electrode active material layer, two straight lines extending in the transverse direction and the vertical direction and separating each other are drawn. The straight-line distance (L) of each straight line is measured. After measuring the minimum distance (C) along the boundary line between particles (sulfur-carbon complexes) located between each point, the C/L value is calculated, and the average value of the transverse curvature and the vertical curvature is calculated.

For example, in order to evaluate the top surface curvature of the positive electrode active material layer for the positive electrode using the sulfur-carbon composite of Example 1 and Comparative Example 1 in the present specification, SEM images indicating the vertical distance and the minimum curve distance are shown in FIG. 4c (Example 1) and FIG. 5e (Comparative Example 1), respectively.

In one embodiment of the present invention, the positive electrode active material layer may further include at least one of a binder and a conductive material. Specifically, the positive electrode active material layer may further include a binder resin together with the sulfur-carbon complex. In addition, the positive electrode active material layer may further include a conductive material, as needed, in addition to the positive electrode active material and the binder resin. At this time, in one embodiment of the present invention, it may be preferable that the positive electrode active material layer includes 70 wt% or more, 85 wt% or more, or 90 wt% or more of the positive electrode active material relative to 100 wt% of the positive electrode active material layer.

The above-described positive electrode active material comprises the above-described sulfur-carbon complex. In one embodiment of the present invention, it may be preferable that the sulfur element (S) in the sulfur-carbon complex is included in an amount of 60 wt% or more, 65 wt% or more, 70 wt% or more, or 75 wt% or more relative to 100 wt% of the positive electrode active material layer.

When the content of elemental sulfur (S) in the positive electrode is less than 60 wt%, it may be difficult to improve the energy density of the battery due to a lack of electrode active material, but the present invention is not limited thereto. In addition, in one embodiment of the present invention, the positive electrode active material layer may contain 50 wt% or more, 70 wt% or more, 90 wt% or more, or 95 wt% or more of the sulfur-carbon complex having the above-described characteristics relative to 100 wt% of the positive electrode active material. In one embodiment of the present invention, the positive electrode active material may be composed solely of the sulfur-carbon complex.

In one embodiment of the present invention, the loading amount of the positive electrode may be, for example, 1.67 mg _s /cm ² or more, specifically 1.67 to 2.92 mg _s /cm ² , more specifically 1.67 to 2.08 mg _s /cm ² . The loading amount can be calculated from the content of the active material in the positive electrode and the content of sulfur (S) in the active material.

In one embodiment of the present invention, when the loading amount of the positive electrode is converted into capacity, for example, the loading amount may be 2.0 mAh/cm ² or more, specifically 2.0 mAh/cm ² to 3.5 mAh/cm ² , and more specifically 2.0 mAh/cm ² to 2.5 mAh/cm ² , but the present invention is not limited thereto.

In addition, the positive electrode active material layer may further include a typical positive electrode active material that can be used in a lithium secondary battery, in addition to the above-described sulfur-carbon composite. Such typical positive electrode active materials include, for example, lithium transition metal oxide; lithium metal iron phosphate; lithium nickel-manganese-cobalt oxide; lithium nickel-manganese-cobalt oxide, an oxide in which some of the lithium nickel-manganese-cobalt oxide is substituted with another transition metal; or two or more thereof, but are not limited thereto. Specifically, the positive electrode active material may include, for example, a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; lithium manganese oxide having the chemical formula Li _1+x Mn _2-x O ₄ (wherein, x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ , and the like; lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiV ₃ O ₄ , V ₂ O ₅ , and Cu ₂ V ₂ O ₇ ; Ni-site type lithium nickel oxide represented by the chemical formula LiNi _1-x M _x O ₂ (wherein, M = Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x = 0.01 to 0.3); lithium manganese composite oxides represented by the chemical formula LiMn _2-x M _x O ₂ (wherein, M = Co, Ni, Fe, Cr, Zn, or Ta, and x = 0.01 to 0.1) or Li ₂ Mn ₃ MO ₈ (wherein, M = Fe, Co, Ni, Cu, or Zn); lithium metal phosphate LiMPO ₄ (wherein, M is M = Fe, CO, Ni, or Mn); Lithium nickel-manganese-cobalt oxide Li _1+x (Ni _a Co _b Mn _c ) _1-x O ₂ (x = 0 to 0.03, a = 0.3 to 0.95, b = 0.01 to 0.35, c = 0.01 to 0.5, a+b+c=1); Lithium nickel-manganese-cobalt oxide partially substituted with aluminum oxide Li _a [Ni _b Co _c Mn _d Al _e ] _1-f M1 _f O ₂ (M1 is at least one selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, and 0.8≤a≤1.2, 0.5≤b≤0.99, 0<c<0.5, 0<d<0.5, 0.01≤e≤0.1, 0≤f≤0.1); Lithium nickel-manganese-cobalt oxide, in which some of the atoms are substituted with other transition metals, Li _1+x (Ni _a Co _b Mn _c M _d ) _1-x O ₂ (x = 0 to 0.03, a = 0.3 to 0.95, b = 0.01 to 0.35, c = 0.01 to 0.5, d = 0.001 to 0.03, a+b+c+d=1, M is any one selected from the group consisting of Fe, V, Cr, Ti, W, Ta, Mg, and Mo), disulfide compounds; Fe ₂ (MoO ₄ ) ₃ , but are not limited thereto.

Meanwhile, as the positive electrode collector, various positive electrode collectors used in the relevant technical field can be used. For example, as the positive electrode collector, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. can be used. The positive electrode collector can typically have a thickness of 3 ㎛ to 500 ㎛, and fine unevenness can be formed on the surface of the positive electrode collector to increase the adhesive strength of the positive electrode active material. The positive electrode collector can be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

The above binder resin serves to improve the adhesion between positive electrode active material particles and the adhesiveness between the positive electrode active material and the positive electrode current collector, and specific examples thereof include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof may be used. The above binder resin may be included in an amount of 1 to 30 wt%, preferably 1 to 20 wt%, and more preferably 1 to 10 wt%, based on the total weight of the positive electrode active material layer.

The conductive material is used to provide conductivity to the electrode, and can be used without special restrictions as long as it does not cause a chemical change in the battery to be formed and has electronic conductivity. Specific examples thereof include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, carbon fiber, and carbon nanotube; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like, and one of these may be used alone or a mixture of two or more may be used. When the conductive material is used, the conductive material may be typically included in an amount of 1 to 30 wt%, preferably 1 to 20 wt%, and more preferably 1 to 10 wt%, based on the total weight of the positive electrode active material layer.

The above anode can be manufactured by a conventional method known in the art.

For example, specifically looking at the method for manufacturing the positive electrode of the present invention, first, the binder resin is dissolved in a solvent for manufacturing a slurry, and then the conductive material is dispersed. As the solvent for manufacturing the slurry, it is preferable to use one that can uniformly disperse the positive electrode active material, the binder resin, and the conductive material used as needed, and is easily evaporated. Representative examples thereof include acetonitrile, methanol, ethanol, tetrahydrofuran, water, and isopropyl alcohol.

Next, the positive electrode active material, or optionally together with an additive, is uniformly dispersed again in the solvent in which the conductive agent is dispersed to prepare a positive electrode slurry. The amount of the solvent, positive electrode active material, or optionally an additive included in the slurry is not particularly important in the present application, and it is sufficient that the slurry has an appropriate viscosity to facilitate coating.

The slurry thus manufactured is applied to a current collector and vacuum dried to form a positive electrode. The slurry can be coated on the current collector to an appropriate thickness depending on the viscosity of the slurry and the thickness of the positive electrode to be formed.

The above application can be performed by a method commonly known in the art, for example, by distributing the positive electrode active material slurry on one upper surface of the positive electrode current collector and then uniformly dispersing it using a doctor blade or the like. In addition, it can be performed by a method such as die casting, comma coating, or screen printing.

The above drying is not particularly limited, but may be performed in a vacuum oven at 50 to 200°C for less than 1 day.

According to another aspect of the present invention, a lithium-sulfur battery comprising the above-described positive electrode is provided.

Specifically, the lithium-sulfur battery includes a cathode, an anode, a separator interposed between the cathode and the anode, and an electrolyte.

According to one aspect of the present invention, the positive electrode may include the positive electrode active material described above as a positive electrode active material.

According to one aspect of the present invention, the positive electrode may include a positive electrode active material layer including a plurality of sulfur-carbon complexes, and a ratio of an average value of the lengths of the longest axes in the top five sulfur-carbon complexes based on area in a top view of the positive electrode active material layer and an average value of the lengths of the longest axes in the bottom five sulfur-carbon complexes based on area may satisfy the above-described Equation 2.

In one embodiment of the present invention, the unit structure of the anode/separator/cathode may be referred to as an electrode assembly, and the electrode assembly may be, for example, laminated with the separator interposed between the cathode and the anode to form a stacked or stacked/folded structure, or may be wound to form a jellyroll structure. In addition, when the jellyroll structure is formed, a separator may be additionally arranged on the outside to prevent the cathode and the anode from coming into contact with each other.

The negative electrode includes a negative current collector; and a negative active material layer formed on at least one side of the negative current collector; and the negative active material layer includes a negative active material, a conductive material, and a binder.

Next, the above cathode will be described in more detail.

The above negative electrode may be formed as a structure in which a negative electrode active material layer is formed on one side or both sides of a long sheet-shaped negative electrode collector, and the negative electrode active material layer may include a negative electrode active material and a binder resin. In addition, the negative electrode active material layer may further include a conductive material as needed.

Specifically, the negative electrode can be manufactured by a method of applying a negative electrode slurry prepared by dispersing a negative electrode active material, a conductive material, and a binder in a solvent such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water on one or both sides of a long sheet-shaped negative electrode collector, removing the solvent of the negative electrode slurry through a drying process, and then rolling. Meanwhile, an anode including a non-coated region can be manufactured by not applying the negative electrode slurry to some areas of the negative electrode collector, for example, one end of the negative electrode collector, during the application of the negative electrode slurry.

The above negative active material may include a material capable of reversibly intercalating or deintercalating lithium (Li ⁺ ), a material capable of reversibly forming a lithium-containing compound by reacting with lithium ions, lithium metal, or a lithium alloy. The material capable of reversibly intercalating or deintercalating lithium ions may be, for example, crystalline carbon, amorphous carbon, or a mixture thereof, and specific examples thereof include, but are not limited to, artificial graphite, natural graphite, graphitized carbon fiber, amorphous carbon, soft carbon, and hard carbon.

The material capable of reversibly forming a lithium-containing compound by reacting with the lithium ion may be, for example, tin oxide, titanium nitrate, or a silicon-based compound.

The above lithium alloy may be an alloy of a metal selected from the group consisting of, for example, lithium (Li) and sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), radium (Ra), aluminum (Al), and tin (Sn). Preferably, the negative electrode active material may be lithium metal, and specifically, may be in the form of a lithium metal thin film or lithium metal powder.

The above silicon-based compound may be Si, a Si-Me alloy (wherein Me is at least one selected from the group consisting of Al, Sn, Mg, Cu, Fe, Pb, Zn, Mn, Cr, Ti, and Ni), SiO _y (wherein 0<y<2), a Si-C composite, or a combination thereof, and preferably SiO _y (wherein 0<y<2). Since the silicon-based compound has a high theoretical capacity, when the silicon-based compound is included as a negative electrode active material, the capacity characteristics can be improved.

As the above negative electrode collector, negative electrode collectors generally used in the relevant technical field can be used, and for example, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. The negative electrode collector can typically have a thickness of 3 to 500 ㎛, and, like the positive electrode collector, fine unevenness can be formed on the surface of the collector to strengthen the bonding strength of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a non-woven fabric.

The above binder resin serves to improve the adhesion between negative active material particles and the adhesive strength between the negative active material and the negative current collector. Specific examples thereof include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof may be used. The above binder may be included in an amount of 1 to 30 wt%, preferably 1 to 20 wt%, and more preferably 1 to 10 wt%, based on the total weight of the negative electrode active material layer.

The conductive material included according to the above needs is used to provide conductivity to the negative electrode, and in the battery to be formed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without special restrictions. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, carbon fiber, and carbon nanotube; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like, and one of these may be used alone or a mixture of two or more may be used. When the conductive material is used, the conductive material may be typically included in an amount of 1 to 30 wt%, preferably 1 to 20 wt%, and more preferably 1 to 10 wt%, based on the total weight of the negative electrode active material layer.

The above separator is arranged in the electrode assembly in such a way that it is interposed between the negative electrode and the positive electrode. The separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. If it is generally used as a separator in a lithium secondary battery, it can be used without any particular limitation. Specifically, the separator may be a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene/butene copolymer, an ethylene/hexene copolymer, and an ethylene/methacrylate copolymer, or a laminated structure of two or more layers thereof. In addition, a general porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fibers, polyethylene terephthalate fibers, etc. may be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength.

Another aspect of the present invention relates to an electrochemical device including the electrode assembly. The electrochemical device comprises an electrode assembly and an electrolyte housed together in a battery case. As the battery case, any suitable type, such as a pouch type, a metal can type, a cylindrical type, a stack type, a coin type, or the like, commonly used in the art may be selected without any particular limitation.

The electrolyte used in the present invention may include various electrolytes that can be used in lithium secondary batteries, for example, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., and the type thereof is not particularly limited.

Specifically, the electrolyte may include an organic solvent and a lithium salt.

As the organic solvent, any solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move may be used without particular limitation. Specifically, the organic solvent may include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; Examples of solvents that can be used include carbonate solvents, such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents, such as ethyl alcohol and isopropyl alcohol; nitriles, such as R-CN (wherein R represents a C2 to C20 linear, branched, or cyclic hydrocarbon group, and may include a double-bonded aromatic ring or an ether bond); amides, such as dimethylformamide; dioxolanes, such as 1,3-dioxolane; and sulfolanes.

Meanwhile, in one embodiment of the present invention, it is preferable to include a heterocyclic compound containing an oxygen atom or a sulfur atom in terms of forming a polymer protective film capable of suppressing the formation of lithium dendrites, reducing electrolyte decomposition and side reactions on the surface of a lithium-based metal. The heterocyclic compound may be a heterocyclic compound having 3 to 15 members, preferably 3 to 7 members, and more preferably 5 to 6 members.

The above heterocyclic compound may be a heterocyclic compound unsubstituted or substituted with at least one selected from the group consisting of an alkyl group having 1 to 4 carbon atoms, a cyclic alkyl group having 3 to 8 carbon atoms, an aryl group having 6 to 10 carbon atoms, a halogen group, a nitro group (-NO ₂ ), an amine group (-NH ₂ ), and a sulfonyl group (-SO ₂ ); or a multicyclic compound of at least one selected from the group consisting of a cyclic alkyl group having 3 to 8 carbon atoms and an aryl group having 6 to 10 carbon atoms and a heterocyclic compound.

When the heterocyclic compound is a heterocyclic compound substituted with an alkyl group having 1 to 4 carbon atoms, the radical is stabilized, which can suppress side reactions between the additive and the electrolyte, and is therefore preferable. In addition, when the heterocyclic compound is substituted with a halogen group or a nitro group, it is preferable because a functional protective film can be formed on the surface of the lithium-based metal. The functional protective film is a stable, compact protective film, which enables uniform deposition of the lithium-based metal, and can suppress side reactions between the polysulfide and the lithium-based metal.

The above heterocyclic compounds are specifically, for example, furan, 2-methylfuran, 3-methylfuran, 2-ethylfuran, 2-propylfuran, 2-butylfuran, 2,3-dimethylfuran, 2,4-dimethylfuran, 2,5-dimethylfuran, pyran, 2-methylpyran, 3-methylpyran, 4-methylpyran, benzofuran, 2-(2-Nitrovinyl)furan, thiophene, thiophene, It may include at least one selected from the group consisting of 2-methylthiophene, 2-ethylthiophene, 2-propylthiophene, 2-butylthiophene, 2,3-dimethylthiophene, 2,4-dimethylthiophene, and 2,5-dimethylthiophene, and preferably at least one selected from the group consisting of 2-methylfuran and 2-methylthiophene.

Meanwhile, in one embodiment of the present invention, the non-aqueous solvent of the electrolyte may include an ether solvent in order to improve the charge/discharge performance of the battery. These ether solvents include cyclic ethers (e.g., 1,3-dioxolane, tetrahydrofuran, tetrohydropyran, etc.), linear ether compounds (e.g., 1,2 dimethoxyethane, etc.), low-viscosity fluorinated ethers, such as (1H,1H,2'H,3H-decafluorodipropyl ether, difluoromethyl 2,2,2-trifluoroethyl ether, 1,2,2,2-tetrafluoroethyl trifluoromethyl ether, 1,1,2,3,3,3-hexafluoropropyl difluoromethyl Ether (1,1,2,3,3,3-Hexafluoropropyl difluoromethyl ether, 1H,1H,2'H,3H-decafluorodipropyl ether, pentafluoroethyl 2,2,2-trifluoroethyl ether, 1H,1H,2'H-perfluorodipropyl ether) and a mixture of one or more of these may be included as a non-aqueous solvent.

The lithium salt above can be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt may be LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAl0 ₄ , LiAlCl ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN(C ₂ F ₅ SO ₃ ) ₂ , LiN(C ₂ F ₅ SO ₂ ) ₂ , LiN(CF ₃ SO ₂ ) ₂ , LiCl, LiI, or LiB(C ₂ O ₄ ) ₂ . It is preferable to use the concentration of the lithium salt in the range of 0.1 to 5.0 M, preferably 0.1 to 3.0 M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, so that it can exhibit excellent electrolyte performance and lithium ions can move effectively.

In addition to the electrolyte components, the electrolyte may further contain additives for the purposes of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. For example, the additives may include, but are not limited to, LiNO ₃ , haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexamethylphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxy ethanol, or aluminum trichloride. The additives may be contained in an amount of 0.1 to 10 wt%, preferably 0.1 to 5 wt%, based on the total weight of the electrolyte.

Meanwhile, in one embodiment of the present invention, the lithium-sulfur battery of the present invention may preferably have a ratio (El/S) of the total weight of the electrolyte to the total weight of the sulfur element (S) in the positive electrode of, for example, 3.5 g/g or less, for example, 3.3 g/g or less or 3.2 g/g or less. In addition, the lithium-sulfur battery may have a ratio (El/S) of the total weight of the electrolyte to the total weight of the sulfur element (S) in the positive electrode of 3.0 to 3.5 g/g/, for example, 3.1 g/g to 3.2 g/g.

When the sulfur-carbon complex according to the present invention is used, a lithium-sulfur battery having an El/S ratio within the above-described range can be implemented, and thus the effect of improving energy density can be exhibited. However, a lithium-sulfur battery using the sulfur-carbon complex having an El/S ratio higher than the above-described range can also be implemented, and the present invention is not limited thereto.

The shape of the above lithium-sulfur battery is not particularly limited and can be made into various shapes such as cylindrical, stacked, and coin-shaped.

In addition, the present invention provides a battery module including the lithium-sulfur battery as a unit battery. The battery module can be used as a power source for medium and large-sized devices that require high-temperature stability, long cycle characteristics, and high capacity characteristics.

According to one embodiment of the present invention, the lithium-sulfur battery can exhibit an effect of maintaining a high power density during discharge by using the above-described positive electrode active material or by using the above-described positive electrode. Specifically, it can exhibit an effect of maintaining a power density of 2.1 kW/kg or more for 10 seconds during discharge.

In one embodiment of the present invention, the power density for 10 seconds can be measured by calculating according to Equation 4 after flowing current for 10 seconds through the lithium-sulfur battery as the measurement target, but the measurement method is not limited thereto. At this time, the measurement can be performed under discharge conditions of 1.5 V and 5 C.

[Formula 4]

Power density (kW/kg) = [(V min) X (Max C-rate) X (Discharge capacity)]/(Battery weight)

According to one embodiment of the present invention, the lithium-sulfur battery can have a capacity of 1,000 mAh/g _s or more as a discharge capacity per weight of sulfur (S) by using the above-described positive electrode active material or by using the above-described positive electrode, but the present invention is not limited thereto.

Examples of the above medium-to-large-sized devices include, but are not limited to, power tools that are powered by an electric motor; electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); electric two-wheeled vehicles including electric bicycles (E-bikes) and electric scooters (Escooters); electric golf carts; and power storage systems.

In one embodiment of the present invention, the lithium-sulfur battery may be a pouch-type, coin-type, or cylindrical battery, and may be, for example, a pouch-type battery, but the present invention is not limited thereto.

Hereinafter, preferred examples are presented to help understand the present invention, but the following examples are only illustrative of the present invention, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope and technical idea of the present invention, and it is natural that such changes and modifications fall within the scope of the appended patent claims.

[Preparation of sulfur-carbon complex]

Manufacturing Example 1. Preparation of porous carbon material

Carbon nanotubes (CNTs) (Entangled multi-wall carbon nanotubes, BET surface area 200 m ² /g) were placed into a centrifugal mill equipped with a sieve (Retsch ZM200), and the carbon nanotubes were pulverized while centrifugal force was applied so that the pulverized carbon nanotubes were filtered through the sieve to control the particle size. In order to obtain the target D ₅₀ particle size of the carbon nanotubes, the mesh size and rotation speed of the sieve were adjusted to obtain carbon nanotubes with controlled particle _size . The particle size conditions of the obtained porous carbon material are shown in Table 1 below.

Manufacturing Example 2. Preparation of porous carbon material

Entangled multi-wall carbon nanotubes (CNTs, BET surface area 200 m ² /g) were pulverized by jet milling to obtain pulverized carbon nanotubes.

Preparation of sulfur-carbon complexes

The carbon nanotubes obtained in Manufacturing Example 1 or Manufacturing Example 2 were used as a porous carbon material, and the porous carbon material and sulfur (S ₈ ) were mixed in the weight ratios shown in Table 1 below, ball milled, and then placed in an oven at 155° C. for 30 minutes to produce a sulfur-carbon composite.

Sulfur-carbon complex porous carbon material Sulfur (S) content Manufacturing method D ₁₀ +D ₉₀ BF (D ₉₀ /D ₁₀ ) Entry D ₅₀ Example 1 Manufacturing example 1,
Mesh size 80 ㎛
RPM 18,000
Linear velocity 94.2 m/s 51 ㎛ 5.49 24 ㎛ 75 wt% Example 2 Manufacturing example 1,
Mesh size 120 ㎛
RPM 10,000
Linear velocity 31.4 m/s 86 ㎛ 5.55 35 ㎛ 75 wt% Example 3 Manufacturing example 1,
Mesh size 80 ㎛
RPM 14,000
Linear velocity 73.3 m/s 70 ㎛ 5.38 29 ㎛ 75 wt% Comparative Example 1 Manufacturing example 2 128 ㎛ 11.05 38 ㎛ 75 wt%

porous carbon material Sulfur-carbon complex Manufacturing method D ₁₀ +D ₉₀ BF (D ₉₀ /D ₁₀ ) Entry D ₅₀ Sulfur (S) content Example 4 Manufacturing example 1,
Mesh size 80 ㎛
RPM 18,000
Linear velocity 94.2 m/s 90 ㎛ 5.42 38 ㎛ 70 wt% Comparative Example 2 Manufacturing example 2 128 ㎛ 10.68 38 ㎛ 70 wt%

[Measurement of shape and particle size of porous carbon material]

The particle sizes corresponding to D ₁₀ , D ₅₀ , and D ₉₀ of the porous carbon material obtained above were measured by dry method using a particle size analyzer (model name: Bluewave, manufacturer: Microtrac). In cases where the carbon material was secondary particle-ized by agglomeration, the primary particle size was observed and measured using a scanning electron microscope (model name: SEM, manufacturer: JEOL).

The BF value is the ratio of the particle diameter D ₉₀ to the particle diameter D ₁₀ , and is calculated as the value of D ₉₀ /D _10. Figure 1 shows the results of measuring the particle size distribution of the porous carbon materials used in Examples 1 to 3 and Comparative Example 1.

Figures 2 and 3 show SEM images of the porous carbon material used in Example 4 (Figure 2) and Comparative Example 2 (Figure 3), respectively.

[Making of anodes]

Using the sulfur-carbon complexes obtained in each of Examples 1 to 4 and Comparative Example 1 and Comparative Example 2, a positive electrode for a lithium-sulfur battery was manufactured as follows.

A slurry composition of a cathode was prepared by adding 90 wt% of a sulfur-carbon composite as a cathode active material, 5 wt% of Denkablack as a conductive material, and 5 wt% of styrene butadiene rubber/carboxymethyl cellulose (weight ratio of SBR:CMC = 7:3) as a binder to a solvent and mixing them.

The prepared positive electrode slurry composition was applied to a thickness of 350 μm on a 20 μm thick aluminum collector, dried at 50° C. for 12 hours, and pressed using a roll press to prepare a positive electrode.

The content of elemental sulfur (S) in the anode to which the sulfur-carbon complexes of Examples 1 to 3 and Comparative Example 1 were applied was 67.5 wt%, and the content of elemental sulfur (S) in the anode to which the sulfur-carbon complexes of Example 4 and Comparative Example 2 were applied was 63.0 wt%.

[Evaluation of whether the equation 2 of the two poles is satisfied]

Evaluation Example 1

SEM images of the upper surface of the positive electrode active material layer of the positive electrode manufactured using the sulfur-carbon composite of Example 1 and Comparative Example 1 were obtained, respectively. At this time, the SEM images were obtained with a size of 200 ㎛ X 200 ㎛ at 400 magnification and a size of 70 ㎛ X 70 ㎛ at 1,000 magnification, respectively, based on the center of each positive electrode obtained.

Next, the top five sulfur-carbon complexes were selected based on the area of the sulfur-carbon complexes in the obtained 200 ㎛ X 200 ㎛ image, and the bottom five sulfur-carbon complexes were selected based on the area of the sulfur-carbon complexes in the obtained 70 ㎛ X 70 ㎛ image.

The length of the longest axis within each selected sulfur-carbon complex was measured, and their average value was calculated to obtain the value according to Equation 2 below, which is shown in Table 3 below.

[Formula 2]

X _L /X _S ≤ 15

In the above equation 2,

The above X _L is the average value of the length of the longest axis in the top five sulfur-carbon complexes based on the area in the top view of the positive electrode active material layer, and the above X _S is the average value of the length of the longest axis in the bottom five sulfur-carbon complexes based on the area in the top view of the positive electrode active material layer.

FIGS. 4A and 4B show SEM images obtained for the positive electrode of Example 1, respectively, wherein FIG. 4A shows the longest axes of the top five sulfur-carbon complexes selected above, and FIG. 4B shows the longest axes of the bottom five sulfur-carbon complexes selected above. FIGS. 5A and 5B show SEM images obtained for the positive electrode of Comparative Example 1, respectively, wherein FIG. 5A shows the longest axes of the top five sulfur-carbon complexes selected above, and FIG. 5B shows the longest axes of the bottom five sulfur-carbon complexes selected above.

At this time, particles with a longest axis length of less than 1 ㎛ in each SEM image were confirmed to be not sulfur-bearing porous carbon materials, i.e., not sulfur-carbon composites, and were therefore excluded from the selection target.

X _L /X _S Whether condition 2 is satisfied (True/Fail) Example 1 3.5 True Comparative Example 1 20.8 Fail

Evaluation Example 2

After manufacturing a lithium-sulfur battery using the above positive electrode, the following experiment was conducted to evaluate whether the satisfaction of Equation 2 would change with repeated charge and discharge.

First, a lithium-sulfur battery was manufactured as follows.

Using the sulfur-carbon complex of Comparative Example 1, a cathode was manufactured, a separator was interposed between the cathode and the anode, and an electrode assembly was manufactured. The electrode assembly was placed in a pouch-type case and filled with an electrolyte to manufacture a lithium-sulfur battery. A 35 ㎛ thick lithium metal film was used as the cathode. A 16 ㎛ thick porous polyethylene was applied as the separator. The electrolyte was prepared by adding LiNO ₃ at a concentration of 3 wt% and LiPF ₆ at a concentration of 1 M to an organic solvent containing a mixture of 2-methyl furan and dimethoxyethane (volume ratio of 33/77). A pouch cell including the cathode and anode manufactured as described above was manufactured. In each manufactured battery, El/S was controlled to a condition of 3.1 g/g.

For each lithium sulfur battery manufactured as described above, it was discharged at 0.5C in CC mode at 25℃ until 1.8 V, charged at a constant current of 0.3C until 2.5 V, and then discharged and charged at 1.0C 200 times. At this time, it was confirmed using a charge/discharge tester that the discharge capacity was maintained at 80% or more based on the initial capacity of 100%.

After the last charge, a lithium-sulfur battery with a SOC of 75% was disassembled in a glove box under an Ar atmosphere, and the cathode was separated. The separated cathode surface was washed and dried using DME, and then whether Equation 2 was satisfied was evaluated in the same manner as in Evaluation Example 1.

Figures 5c and d show the SEM images obtained above, respectively. Figure 5c shows the longest axes of the top five selected sulfur-carbon complexes, and Figure 5d shows the longest axes of the bottom five selected sulfur-carbon complexes. The values calculated according to Equation 2 below are shown in Table 4 below.

(Evaluation after battery disassembly) X _L /X _S Whether condition 2 is satisfied (True/Fail) Comparative Example 1 23.2 Fail

As confirmed in Tables 3 and 4 above, it was confirmed that the positive electrode manufactured using the sulfur-carbon composite of Comparative Example 1 did not satisfy Equation 2 immediately after manufacture and even after repeated charge and discharge when applied to a battery.

Through subsequent experiments, it was confirmed that lithium-sulfur batteries with a cathode that did not satisfy Equation 2 were inferior in terms of battery capacity, power density, and high-speed output performance. It was inferred that this was the result of reduced reactivity due to uneven diffusion of sulfur (S) within the cathode.

[Evaluation of the average curvature of both poles]

SEM images of vertical cross sections of the positive electrodes manufactured using the sulfur-carbon composites of Comparative Example 2 and Example 2 are shown in Fig. 6a (Comparative Example 2) and Fig. 7a (Example 2), respectively. The average curvature of the positive electrode active material layer was evaluated from the SEM images obtained above by the following method.

First, 1) From the obtained SEM image, a point on the surface of the current collector was arbitrarily selected, and the vertical distance (L) was measured by connecting the endpoints of the electrodes in the vertical direction from the point to the positive electrode surface. Next, 2) the minimum distance (C) was measured along the boundary line between the particles (sulfur-carbon complexes) located between the arbitrarily selected point in step 1) and the endpoint of the electrode. 3) The curvature (C/L) was calculated using the L values and C values measured above. 4) After selecting at least three different points on the surface of the current collector and repeating the processes 1) to 3) above, the average value of the obtained C/L values was calculated to evaluate the average curvature.

Curvature = [Curve minimum distance (C) / vertical distance (L)]

Using Figures 6b and 7b, the curvature values measured at three points, A, B, and C, and the average curvature values of the three points are shown in Table 5 below.

Sulfur-carbon complex anode Cross-section image A point curvature (C/L) B point curvature (C/L) C point curvature (C/L) Average curvature Comparative Example 2 Fig. 6b 2.18 2.44 2.15 2.26 Example 2 Fig. 7b 1.55 1.50 1.21 1.42

[Manufacturing of lithium-sulfur batteries]

A positive electrode for a lithium-sulfur battery was manufactured as follows using the positive electrode using the sulfur-carbon complex obtained in each of Examples 1 to 4 and Comparative Example 1 and Comparative Example 2.

An electrode assembly was manufactured by using the positive electrode manufactured as above, providing an anode and interposing a separator between the positive electrode and the negative electrode, storing the electrode assembly in a pouch-shaped case and filling it with an electrolyte to manufacture a lithium-sulfur battery.

A 35 ㎛ thick lithium metal film was used as the cathode. A 16 ㎛ thick porous polyethylene was applied as the separator. The electrolyte was prepared by adding 3 wt% LiNO ₃ and 1 M LiPF ₆ to an organic solvent containing a mixture of 2-methyl furan and dimethoxyethane (volume ratio 33/77).

Pouch cells including the positive and negative electrodes manufactured as described above were manufactured. In each manufactured cell, El/S was controlled to a condition of 3.1 g/g.

[Electrochemical performance evaluation]

1.0C discharge capacity evaluation

For each lithium sulfur battery manufactured as described above, the discharge capacity was measured/compared by discharging at 0.5 C in CC mode at 25°C to 1.8 V, charging at a constant current of 0.3 C to 2.5 V, and then discharging at 1.0 C. The discharge capacity was measured based on the weight of sulfur (S). (mAh/g _s )

A graph of discharge capacity change according to repeated charge and discharge is shown in Fig. 8. When the discharge capacity of Comparative Example 1 is set to 1, the relative capacities of Examples 1 to 3 are shown in Fig. 9, and when the voltage of Comparative Example 1 is set to 1, the relative nominal voltages of Examples 1 to 3 are shown in Fig. 10.

The capacities measured at the first discharge after charging are shown in Table 6 below.

Sulfur (S) content in sulfur-carbon complexes 1.0C discharge capacity (mAh/g _s ) Example 1 75 wt% 1,030 Example 2 75 wt% 989 Example 3 75 wt% 996 Comparative Example 1 75 wt% 976 Example 4 70 wt% 1,035 Comparative Example 2 70 wt% 915

0.5C discharge capacity and energy density evaluation

For each lithium sulfur battery manufactured as described above, the discharge capacity was measured/compared by discharging at a rate of 0.5 C in CC mode at 25°C until 1.8 V, and charging at a constant current of 0.5 C until 2.5 V, and the results are shown in Table 6 above. The discharge capacity was measured based on the weight of sulfur. (mAh/g _s )

In addition, the results of evaluating the 0.5C discharge capacity for the batteries using the sulfur-carbon composites of Example 1, Example 4, Comparative Example 1, and Comparative Example 2 are shown in FIGS. 11 and 12, respectively, and the measured discharge capacities are shown in Table 6 below.

The energy density was measured using the measured 0.5C discharge capacity value according to Equation 3 below, and the relative value of the energy density of Example 1 based on the energy density of Comparative Example 1 and the relative value of the energy density of Example 2 based on the energy density of Comparative Example 2 are shown together in Table 7.

[Formula 3]

Energy density = [(discharge capacity X driving voltage)]/(cell weight)

Sulfur (S) content in sulfur-carbon complexes 0.5C discharge capacity (mAh/g _s ) Energy density (relative) Example 1 75 wt% 1,073 1.06 Comparative Example 1 75 wt% 1,015 1.00 Example 2 70 wt% 1,092 1.07 Comparative Example 2 70 wt% 1,038 1.00

10 second power density evaluation

For each lithium sulfur battery manufactured as described above, after flowing current for 10 seconds (1.5 V, 5 C discharge conditions), the power density was calculated according to Equation 4, and the results are shown in Table 8 below.

[Formula 4]

Power density (kW/kg) = [(V min) X (Max C-rate) X (Discharge capacity)]/(Battery weight)

Target properties 10 sec power density (kW/kg) Example 1 2.1 kW/kg or more 2.44 Example 2 2.21 Example 3 2.30 Example 4 2.32 Comparative Example 1 2.01 Comparative Example 2 1.95

[evaluation]

Referring to Table 2, Figures 2 and 3, it can be confirmed that the porous carbon material (Figure 2) having a BF value (D ₉₀ /D ₁₀ ) of 7 or less not only has a more uniform particle size compared to the porous carbon material having a large BF value (Figure 3), but also has narrower gaps between the porous carbon materials.

In addition, referring to Table 3, Table 4, FIG. 4a, FIG. 4b, FIG. 5a, FIG. 5b, FIG. 6a, and FIG. 7a, when a positive electrode is manufactured using a sulfur-carbon complex in which sulfur (S ₈ ) is loaded on a porous carbon material having a small BF value or a small size, it can be confirmed that the sulfur-carbon complex is evenly distributed in the positive electrode active material layer and the gaps between the sulfur-carbon complexes are narrow, thereby increasing the utilization efficiency of sulfur within the positive electrode.

Accordingly, referring to Tables 6 to 8 and FIGS. 8 to 12, it was confirmed that a lithium-sulfur battery according to an embodiment of the present invention can not only implement a large discharge capacity of 1,000 mAh/g _s or more even at a high rate discharge of 1.0 C, but also implement a higher energy density compared to Comparative Examples 1 and 2 even when the amount of active material in the positive electrode is the same.

In particular, referring to Tables 6 to 8, when the sulfur (S) content is low, the gap between the porous carbon materials is large, and the sulfur-carbon complex is not uniformly distributed on the positive electrode (Comparative Example 2), the power density is low and is not suitable for high power characteristics, whereas when the discharge capacity of the batteries using Examples 1 and 2 is compared, it was confirmed that according to one embodiment of the present invention, the electrochemical activity can be sufficiently improved without increasing the sulfur loading rate, and thus the capacity of the battery can be increased.

Through the above series of experiments, it was confirmed that by applying a porous carbon material with a small size or a uniform particle size distribution as an active material carrier for a lithium-sulfur battery, diffusion of sulfur (S) can be uniformly achieved, and accordingly, the redox reaction of sulfur (S ₈ ) <-> Li ₂ S can be uniformly achieved during charge and discharge of the battery, thereby improving the capacity and charge density of the battery and providing excellent high-speed output performance.

Claims (10)

Comprising a sulfur-carbon composite including a porous carbon material and a sulfur-based material,
The above porous carbon material is a cathode active material that satisfies at least one particle size condition among the following (1) and (2):
(1) The sum of particle diameter D ₁₀ and particle diameter D ₉₀ is 60 ㎛ or less, and
(2) The ratio of the particle size distribution _D90 to particle size _D10 according to Equation 1 below (Broadness Factor, BF) is 7 or less,
[Formula 1]
Broadness Factor(BF) = [(particle diameter D ₉₀ )/(particle diameter D ₁₀ )]. In claim 1,
A cathode active material for a lithium-sulfur battery, wherein the sulfur-based material comprises: inorganic sulfur (S ₈ ); Li ₂ S _n (n≥1); an organosulfur compound including at least one of 2,5-dimercapto-1,3,4-thiadiazole and 1,3,5-trithiocyanuic acid; a carbon-sulfur polymer ((C ₂ S _x ) _n , x=2.5 to 50, n≥2); or a mixture of two or more thereof. In claim 1,
The above porous carbon material is a cathode active material for a lithium-sulfur battery, having a BET surface area of 150 m ² /g or more. In claim 1,
The above porous carbon material is a cathode active material for a lithium-sulfur battery, comprising carbon nanotubes, carbon black, graphite, activated carbon, graphene or a mixture of two or more thereof. In claim 4,
The above porous carbon material is a cathode active material for a lithium-sulfur battery, which contains carbon nanotubes. In claim 1,
A cathode active material for a lithium-sulfur battery, wherein the content of elemental sulfur (S) is 60 wt% or more relative to 100 wt% of the sulfur-carbon complex. In claim 1,
The above porous carbon material is,
The porous carbon material as a raw material is crushed using a centrifugal crusher,
It is manufactured by filtering the crushed porous carbon material through a sieve with a desired particle size.
A cathode active material for a lithium-sulfur battery, wherein the mesh size of the above body is 2.8 to 4 times the particle size D ₅₀ of the manufactured porous carbon material. In claim 1,
A cathode active material for a lithium-sulfur battery, wherein the particle size D ₅₀ of the porous carbon material is 100 ㎛ or less. In claim 1,
The above porous carbon material is a cathode active material for a lithium-sulfur battery, having a BF value of 4 to 7 according to the above formula 1. Comprising a cathode active material layer formed on at least one surface of the entire collector and the entire collector,
A positive electrode for a lithium-sulfur battery, wherein the positive electrode active material layer comprises a positive electrode active material for a lithium-sulfur battery according to any one of claims 1 to 9.