KR20240103938A - A cathode active material comprising sulfur-carbon complex and a lithium-sulfur secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a positive electrode active material comprising a sulfur-carbon composite, wherein the sulfur-carbon composite includes a porous carbon material and a sulfur-based material, wherein the sulfur-based material includes at least one type of sulfur and a sulfur compound, and the sulfur-based material includes -The carbon composite is one in which the sulfur-based material is supported on all or at least part of the inside and surface of the pores of the porous carbon material, and the porous carbon material has a particle size distribution ratio of particle size D ₉₀ to particle size D ₁₀ (Broadness Factor, BF) is characterized by being 7 or less.

Description

A cathode active material comprising sulfur-carbon complex and a lithium-sulfur secondary battery comprising the same}

The present invention relates to a positive electrode active material containing a sulfur-based material and a lithium-sulfur secondary battery containing the positive electrode active material with high energy density and improved output characteristics.

A lithium-sulfur battery is a battery system that uses a sulfur-based material with an S-S bond (sulfur-sulfur bond) as a positive electrode active material and lithium metal as a negative electrode active material. Sulfur, the main material of the positive electrode active material, has the advantage of being abundant in resources worldwide, non-toxic, and having a low weight per atom.

As the application area of secondary batteries expands to electric vehicles (EV), energy storage devices (ESS), etc., compared to lithium-ion secondary batteries, which have a relatively low energy storage density to weight (~250 Wh/kg), theoretically higher Lithium-sulfur battery technology that can achieve energy storage density-to-weight (~2,600 Wh/kg) is in the spotlight.

When a lithium-sulfur battery is discharged, lithium, the negative electrode active material, is oxidized as it gives up electrons and is ionized into lithium cations, and the sulfur-based material, which is the positive electrode active material, accepts electrons and is reduced. Here, through the reduction reaction of the sulfur-based material, the SS bond accepts two electrons and is converted to a sulfur anion form. Lithium cations generated by the oxidation reaction of lithium are transferred to the anode through the electrolyte, and combine with sulfur anions generated by the reduction reaction of sulfur-based compounds to form salts. Specifically, sulfur before discharge has a cyclic S ₈ structure, which is converted to lithium polysulfide (Li ₂ Sx) through a reduction reaction, and is completely reduced to generate lithium sulfide (Li ₂ S).

Since sulfur used in positive electrode active materials is a nonconductor, porous carbon materials are being studied as sulfur carriers to improve the reactivity of sulfur. In order to improve the kinetic activity of electrochemical reactions during charging and discharging of lithium-sulfur secondary batteries, there is a continuous need for technology development for sulfur-carbon composites in which a positive electrode active material is supported on a porous carbon material as a positive electrode material.

In particular, theoretically, if sulfur is supported on a porous carbon material with a large specific surface area, the sulfur content should increase and the energy density and lifespan characteristics of the battery should be improved accordingly. However, even if sulfur is supported experimentally using a porous carbon material with a large specific surface area, the degree of capacity development of the battery is uneven, the tap density during electrode formation becomes small, the compressibility during rolling decreases, and the electrode It is difficult to manufacture and commercialize electrodes due to the swelling phenomenon.

Accordingly, research and development on sulfur-carbon composites with various physical properties for use in lithium-sulfur secondary batteries continues.

The present invention solves the above-described problems,

The object of the present invention is to provide an active material capable of uniformly exhibiting the electrochemical reactivity of sulfur by having a uniform particle size of a porous carbon material in which sulfur is supported, an electrode using the same, and a battery.

Specifically, the goal may be to provide a lithium-sulfur battery with improved energy density, battery capacity, and electrochemical reaction uniformity by adjusting the particle size of the porous carbon material in which sulfur is supported at a predetermined ratio.

In order to solve the above-mentioned problems,

The present invention according to one aspect provides positive electrode active materials of the following embodiments.

The positive electrode active material for lithium-sulfur batteries according to the first embodiment is:

It is a positive electrode active material containing a sulfur-carbon complex,

The sulfur-carbon composite includes a porous carbon material and a sulfur-based material supported on all or at least part of the inner and outer surfaces of the pores of the porous carbon material,

The sulfur-based material includes one or more of sulfur (S ₈ ) and sulfur compounds,

The porous carbon material has a particle size distribution ratio (Broadness Factor, BF) of particle size D ₉₀ to particle size D ₁₀ of 7 or less.

According to the second embodiment, in the first embodiment,

The sulfur-based material includes inorganic sulfur (S ₈ ), Li ₂ S _n (n≥1), 2,5-dimercapto-1,3,4-thiadiazole (2,5-dimercapto-1,3,4- disulfide compounds including one or more of thiadiazole) and 1,3,5-trithiocyanuic acid; organosulfur compounds; and carbon-sulfur polymer ((C ₂ S _x ) _n , x=2.5 to 50, n≥2);

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

The porous carbon material may have a BET surface area of 1,500 cm ² /g or more.

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

The porous carbon material may include one or more selected from activated carbon, carbon black, carbon nanotubes, and graphene.

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

The porous carbon material may include carbon nanotubes.

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

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

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

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

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

The positive electrode for a lithium-sulfur battery according to the eighth embodiment is,

It includes 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 includes a sulfur-carbon composite, and the sulfur-carbon composite includes a porous carbon material and pores of the porous carbon material and A positive electrode for a lithium-sulfur battery comprising a sulfur-based material supported on all or at least part of the external surface,

In the cross section of the positive electrode active material layer, the standard error of the area of any 10 sulfur-carbon composites per area of 50 ㎛

According to the ninth embodiment, in the eighth embodiment,

The porous carbon material may have a particle size distribution ratio (Broadness Factor, BF) of particle size D ₉₀ to particle size D ₁₀ of 7 or less.

According to the tenth embodiment, in the eighth or ninth embodiment,

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

According to the eleventh embodiment, in any one of the eighth to tenth embodiments,

The sulfur-based material includes one or more of sulfur (S ₈ ) and sulfur compounds,

The content of the sulfur-based material may be 60 wt% or more compared to 100 wt% of the positive electrode active material layer.

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

The lithium-sulfur battery according to the twelfth embodiment,

An electrode assembly including an anode, a cathode, and a separator interposed between the anode and the cathode; and electrolyte;

The positive electrode includes a positive electrode active material according to any one of the first to seventh embodiments.

According to the thirteenth embodiment, in the twelfth embodiment,

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

When the particle size distribution of the carbon material is wide, the reaction of the sulfur-based material supported on the carbon material of non-uniform size also occurs non-uniformly, resulting in low cell capacity development.

The present invention manufactured a porous carbon material with a uniform particle size distribution to increase the uniformity of the reaction, and when a carbon material with a uniform particle size distribution was used as a support for a sulfur-based material, it was compared to a carbon material with a non-uniform particle size distribution. It has the effect of developing superior cell capacity.

Figure 1 is an SEM image of the porous carbon material used to manufacture the sulfur-carbon composite of Example 1.
Figure 2 is an SEM image of the porous carbon material used to manufacture the sulfur-carbon composite of Comparative Example 1.
Figure 3 is an SEM image of a vertical cross section of the anode manufactured using the sulfur-carbon composite of Example 1. The left is an image at 1,000 magnification, and the right is an image at 5,000 magnification.
Figure 4 is an SEM image of a vertical cross-section of a positive electrode manufactured using the sulfur-carbon composite of Comparative Example 1. The left is an image at 1,000 magnification, and the right is an image at 5,000 magnification.
Figure 5 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 6 is a graph showing the results of evaluating the 0.5C discharge capacity for batteries using the sulfur-carbon composites of Example 2 and Comparative Example 2.

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

Terms or words used in this specification and claims should not be construed as limited to their common or dictionary meanings, and the inventor may appropriately define the concept of terms in order to explain his or her invention in the best way. It should be interpreted with meaning and concept consistent with the technical idea of the present invention based on the principle that it is.

Throughout the specification of the present application, when a part is said to “include” or “have” a certain component, this does not exclude other components but may further include other components unless specifically stated to the contrary. it means.

In addition, the terms "about", "substantially", etc. used throughout the specification of the present application are used as meanings at or close to the numerical value when manufacturing and material tolerances inherent in the mentioned meaning are presented, and to aid understanding of the present application. It is used to prevent unscrupulous infringers from unfairly exploiting disclosures in which precise or absolute figures are mentioned.

Throughout this specification, the description of “A and/or B” means “A or B or both.”

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

The term "polysulfide" used in this specification includes "polysulfide ion (Sx ^2- , x 8, 6, 4, 2)" and "lithium polysulfide (Li ₂ S _x or LiS _x ^- , x = 8, It is a concept that includes “6, 4, 2)”.

The term "composite" as used herein refers to a material that combines two or more materials to form physically and chemically different phases while exhibiting more effective functions.

The term "porosity" used in this specification refers to the ratio of the volume occupied by pores to the total volume in a structure, and % is used as its unit, and can be used interchangeably with terms such as porosity and porosity. You can.

In the present invention, “particle size D ₁₀ ” refers to the particle size based on 10% of the volumetric cumulative particle size distribution of the particle to be measured, and “particle size D ₅₀ ” refers to the particle size based on 50% of the cumulative volumetric particle size distribution of the particle to be measured. means, and “particle diameter D ₉₀ ” means the particle size based on 90% of the volumetric cumulative particle size distribution of the particles to be measured.

The particle sizes D ₁₀ , D ₅₀ and D ₉₀ may each be measured using a laser diffraction method. For example, after dispersing the particle powder to be measured in a dispersion medium, introducing it into a commercially available laser diffraction particle size measuring device (e.g. Microtrac MT 3000), irradiating ultrasonic waves at about 28 kHz with an output of 60 W, and then measuring the volume cumulative particle size distribution graph. After obtaining, it can be measured by determining the particle sizes corresponding to 10%, 50%, and 90% of the volume cumulative distribution, respectively.

The present invention relates to a positive electrode active material for an electrochemical device, a positive electrode containing the same, and a secondary battery containing the positive electrode. The secondary battery may be a lithium ion secondary battery. In particular, the positive electrode active material according to the present invention includes a sulfur-carbon composite, 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 includes a sulfur-carbon composite, and the sulfur-carbon composite includes a porous carbon material; and a sulfur-based material supported on all or at least part of the inner and outer surfaces of pores of the porous carbon material. The present invention is characterized in that the porous carbon material has a particle size distribution in a specific range.

Specifically, the positive electrode active material according to the present invention includes a sulfur-carbon composite, and the sulfur-carbon composite includes a porous carbon material and a sulfur-based material, and all or at least part of the inner and outer surfaces of the pores of the porous carbon material. supports the sulfur-based material and/or is coated with the sulfur-based material.

In the present invention, the porous carbon material is characterized in that the ratio of the particle size distribution (Broadness Factor, BF) of the particle size D ₉₀ to the particle size D ₁₀ is 7 or less. The BF means the ratio of the particle size distribution of the particle size D ₉₀ to the particle size D ₁₀ of the porous carbon material.

As described above, when the particle size distribution of the porous carbon material is wide, that is, when the size of the porous carbon material is non-uniform, the reaction of the sulfur-based material supported on the porous carbon material also occurs non-uniformly. This causes a problem in that cell capacity development decreases. Accordingly, the present invention uses a porous carbon material with a small particle size distribution. That is, the present invention is characterized by improved cell capacity development by including a porous carbon material with a uniform particle size distribution.

In the present invention, the particle size D ₁₀ of the porous carbon material has a value smaller than the particle size D ₉₀ . At this time, the smaller the ratio of the particle size distribution of the particle size D ₉₀ to the particle size D ₁₀ , the more uniform the particle size is. The present invention can have the effect of uniformly exhibiting the electrochemical reactivity of the active material by providing the porous carbon material with a BF of 7 or less, but the mechanism of the present invention is not limited to this.

In one embodiment of the present invention, the BF of the porous carbon material is 7 or less, and may specifically be 6.5 or less, 6 or less, or 5.5 or less. For example, the BF of the porous carbon material may be 1 to 7, 1 to 6.5, 1 to 6, 1.5 to 6, 2 to 6, 3 to 5.5, or 4 to 5.5. When the BF is in the above-mentioned range, the uniformity of the size of the porous carbon material increases, and the content of the sulfur-based material supported per one porous carbon material is uniform, so that a lithium-sulfur battery using a sulfur-carbon composite formed using the same increases. Reactivity can be advantageous in producing a uniform effect.

In one embodiment of the present invention, the particle diameter D ₅₀ of the porous carbon material may have a value of, for example, 100 ㎛ or less, 70 ㎛ or less, or 50 ㎛ or less. Specifically, the particle diameter D ₅₀ of the porous carbon material is 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 ㎛. It may be ㎛. When the particle size D ₅₀ of the porous carbon material is within the above-mentioned range, the tap density of the positive electrode using the porous carbon material can be improved, which can have an advantageous 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 particulate carbon material increases, which may reduce the development of battery capacity. Accordingly, another structural feature of the present invention is that it is designed to have a small and uniform particle size distribution by controlling the particle size of the porous carbon material to an appropriate range. In this way, when a porous carbon material with a uniform distribution of small particle sizes is used as a carrier for a sulfur-based material, electrochemical performance is more uniform compared to a carbon material with a large particle size and non-uniform particle size distribution, and further improved battery capacity can be achieved. . The method for measuring the particle size D ₅₀ is as described above.

In the present invention, the carbon material serves as a support that provides a framework on which sulfur can be uniformly and stably immobilized, and compensates for the low electrical conductivity of sulfur to allow electrochemical reactions to proceed smoothly. The carbon material may include a large number of irregular pores on the surface and inside.

In one embodiment of the present invention, the BET specific surface area of the porous carbon material is not particularly limited, but may be, for example, 1,500 cm ² /g or more. By using the porous carbon material with a large specific surface area, it can have an advantageous effect in terms of increasing the support rate of the sulfur-based material and thereby improving the electrochemical performance of the positive electrode and lithium-sulfur battery using the same, but the present invention does not provide this. It is not limited. The sulfur-carbon composite according to the present invention has a high BET specific surface area and an appropriate particle size range because the carbon material serving as a sulfur carrier has a high sulfur loading amount, low irreversible capacity, and high energy density. In other words, there is an advantage in having a structure that can improve the utilization rate of sulfur during electrochemical reaction, but the present invention is not limited to this.

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

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 under liquid nitrogen temperature (77K) using BELSORP-max of BEL Japan.

In one embodiment of the present invention, the porous carbon material may include a carbon-based material that has porosity and conductivity and is commonly used in the art. For example, 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 (GNF), carbon nanofibers (CNF), and activated carbon fibers (ACF); Graphites such as natural graphite, artificial graphite, and expanded graphite; Carbon nanoribbon; It may include one or more types selected from the group consisting of carbon nanobelts, carbon nanorods, and activated carbon.

In one embodiment of the present invention, the porous carbon material may include carbon nanotubes. The carbon nanotube is made up of hexagonally connected carbons forming a tube shape. According to one embodiment of the present invention, the carbon nanotubes are either single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), or It can be a combination of these. 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 terms of improving the sulfur carrying rate, and may specifically include multi-walled carbon nanotubes, but the present invention is limited thereto. It doesn't work.

In another embodiment of the present invention, the carbon nanotubes may exist in a form in which two or more carbon nanotubes are closely adhered to and entangled with each other due to the cohesive force between them. 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 as single strands in a dispersion medium, etc.; however, the carbon nanotubes of the primary structure are aggregated with each other to form 2 It may also be provided in the form of a primary structure.

In this respect, when the porous carbon material includes carbon nanotubes, the carbon nanotubes may include a bundle-type secondary structure, an entangled secondary structure, or all of these.

The secondary structure in the form of a bundle of carbon nanotubes uses a single-stranded carbon nanotube as the primary structure, and the plurality of primary structures are oriented in the longitudinal direction of the carbon nanotubes due to cohesive force between carbons, etc. and are clustered together. As it has a certain form, it can also be called a bundled CNT (bundled CNT).

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

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

In one embodiment of the present invention, the graphene may be a carbon layer composed only 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. no.

Meanwhile, in another embodiment of the present invention, the carbon material can be manufactured by carbonizing precursors of various carbon materials.

In the present invention, the sulfur-based material can be used without particular limitation as long as it is a material that can provide sulfur (S ₈ ) as an active material for a lithium-sulfur battery. For example, the sulfur-based material includes one or more of sulfur (S ₈ ) and sulfur compounds.

In one embodiment of the present invention, the sulfur-based material is inorganic sulfur (S ₈ ), Li ₂ S _n (n≥1), 2,5-dimercapto-1,3,4-thiadiazole (2,5 -dimercapto-1,3,4-thiadiazole) and 1,3,5-trithiocyanuic acid (1,3,5-trithiocyanuic acid); organosulfur compounds; and a carbon-sulfur polymer ((C ₂ S _x ) _n , x=2.5 to 50, n≥2).

In one embodiment of the present invention, in the sulfur-carbon composite, the sulfur-based material is physically adsorbed with the porous carbon material, or a covalent bond, van der Waals bond, etc. between the sulfur element (S) and the carbon in the porous carbon material. May be included by chemical bonding.

In one embodiment of the present invention, the sulfur-carbon composite preferably has a content of the sulfur-based material of 60 wt% or more or 70 wt% or more relative to 100 wt% of the sulfur-carbon composite. For example, the sulfur-carbon composite has a content of the sulfur-based material of 60 wt% to 99 wt%, 70 wt% to 99 wt%, 75 wt% to 90 wt%, and 70 wt% compared to 100 wt% of the sulfur-carbon composite. to 85 wt%, 70 wt% to 80 wt%, or 70 wt% to 75 wt%.

In the sulfur-carbon composite according to the present invention, the sulfur-based material is located on at least one of the pore inner and outer surfaces of the carbon material, and at this time, less than 100% of the entire inner and outer surface of the carbon material, preferably It may be present in the range of 1 to 95%, more preferably 60 to 90%. When the sulfur is within the above range on the surface of the carbon material, the maximum effect can be achieved in terms of electron transfer area and wettability of the electrolyte solution. Specifically, since sulfur is thinly and evenly impregnated on the surface of the carbon material in the above range, the electron transfer contact area can be increased during the charging and discharging process. If the sulfur is located on 100% of the entire surface of the carbon material, the carbon material is completely covered with sulfur, which reduces the wettability of the electrolyte and reduces contact with the conductive material contained in the electrode, so it cannot receive electron transfer and participate in the reaction. There will be no more.

The sulfur-carbon composite may be complexed by simply mixing the sulfur-based material and the carbon material, or may have a coating or support form of a core-shell structure. The coating form of the core-shell structure is one in which either a sulfur-based material or a carbon material is coated with another material. For example, the surface of the carbon material may be covered with sulfur, or vice versa. Additionally, the supported form may be a form in which the interior of the carbon material, especially the internal pores, is filled with a sulfur-based material. The form of the sulfur-carbon composite can be used as long as it satisfies the content ratio of sulfur and carbon materials presented above, and is not limited in the present invention.

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

The mixing in step (S1) is to increase the degree of mixing 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, mixing time and speed can also be selectively adjusted depending on the content and conditions of the raw materials.

The complexation method of step (S2) is not particularly limited in the present invention, and methods commonly used in the art may be used. For example, methods commonly used in the industry, such as dry compounding or wet compounding such as spray coating, can be used. For example, the mixture of sulfur and carbon material obtained after mixing is ground by ball milling and placed in an oven at 120 to 160° C. for 20 minutes to 1 hour so that the molten sulfur can be evenly coated on the inner and outer surfaces of the first carbon material. A method may be used to enable this.

The sulfur-carbon complex manufactured through the above-mentioned manufacturing method has a structure that has a high specific surface area, a high amount of sulfur supported, and improved sulfur utilization, so not only does the electrochemical reactivity of sulfur improve, but it also improves accessibility and contact with the electrolyte solution. The capacity and lifespan characteristics of lithium-sulfur batteries can be improved.

Another aspect of the present invention provides a positive electrode formed using the sulfur-carbon composite.

A positive electrode according to another aspect 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, wherein the positive electrode active material layer includes a sulfur-carbon composite, and the sulfur-carbon composite includes a porous carbon material and pores inside and outside of the porous carbon material. It includes a sulfur-based material supported on all or at least part of the surface.

At this time, a structural feature is that the standard error of the area of any 10 sulfur-carbon composites per area of 50 ㎛ x 50 ㎛ in the cross section of the positive active material layer is 100% or less.

In this specification, when indicating the 'area' of the sulfur-carbon composite per 'area' in the cross section of the positive active material layer, the 'area' means the surface area, for example, measuring the area on the plane of the cross section. It can be measured according to a known method, and the measurement method is not particularly limited. For example, in one embodiment of the present invention, the cross-sectional area may be measured according to a method of measuring the cross-sectional area on an SEM image of the cross-section of the positive active material layer.

In this specification, when the stacking direction of the current collector and the positive electrode active material layer in the positive electrode is referred to as the 'up and down direction', the cross section of the positive electrode active material layer is a cross section in the vertical direction of the positive electrode or a cross section perpendicular to the vertical direction of the positive electrode. It can refer to any cross section in any direction, and is not particularly limited to the direction of the cross section.

Figure 3 shows a cross-section in the vertical direction of the anode according to one embodiment of the present invention. Referring to FIG. 3, a vertical cross-section of the positive electrode shows a positive electrode active material layer including a lower current collector and a plurality of sulfur-carbon composites on one surface of the current collector.

In the positive electrode according to one aspect of the present invention, it can be confirmed through a cross section of the positive electrode that the positive electrode active material layer includes a plurality of sulfur-carbon complexes with a uniform area.

As described above, the positive electrode includes a positive electrode active material according to one aspect of the present invention. That is, the anode is a sulfur-carbon composite and is used to include a porous carbon material with a particle size distribution ratio (Broadness Factor, BF) of particle size D ₉₀ to particle size D ₁₀ of 7 or less. Accordingly, when a positive electrode active material layer is formed using a sulfur-carbon composite in which a sulfur-based material is supported on a porous carbon material of uniform size, there is a deviation in the cross-sectional area of the sulfur-carbon composite even in the vertical cross section of the positive electrode active material layer. It may have a decreasing effect.

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

Accordingly, the standard error of the area of any 10 sulfur-carbon composites per area of 50 ㎛ x 50 ㎛ in the cross section of the positive active material layer may be 100% or less.

In one embodiment of the present invention, the standard error of the area of any 10 sulfur-carbon composites per area of 50 ㎛ % to 100%, 30% to 100%, 50% to 90%, 50% to 80%, 50% to 70%, or 60% to 70%.

In this specification, the area of any 10 sulfur-carbon composites per area of 50 ㎛ For example, on the SEM image of the cross section of the positive electrode active material layer, the area of one sulfur-carbon composite is measured centered on the interface between a plurality of sulfur-carbon composites, and the average and standard deviation for any 10 areas are calculated. By measuring, the standard error of the area of any 10 sulfur-carbon composites per area of 50 ㎛

In this specification, the 'standard error' represents a value calculated according to the following equation.

[ceremony]

Standard error (%) = (standard deviation/mean)

In one embodiment of the present invention, the positive electrode active material layer may include a binder resin together with the sulfur-carbon composite. Additionally, the positive electrode active material layer may further include a conductive material as needed in addition to the positive electrode active material and binder resin. At this time, in one embodiment of the present invention, it may be preferable that the positive electrode active material layer contains 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 positive electrode active material includes the sulfur-carbon complex described above. In one embodiment of the present invention, the sulfur element (S) in the sulfur-carbon composite may preferably be included in an amount of 60 wt% or more, 65 wt% or more, or 70 wt% or more based on 100 wt% of the positive electrode active material layer. If the content of elemental sulfur (S) in the positive electrode does not reach 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 to this. 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 a sulfur-carbon composite having the above-described characteristics relative to 100 wt% of the positive electrode active material. there is. In one embodiment of the present invention, the positive electrode active material may be composed of only the sulfur-carbon composite.

In addition, the positive electrode active material layer may further include a common positive electrode active material that can be used in lithium secondary batteries in addition to the sulfur-carbon composite described above. Such common positive electrode active materials include, for example, lithium transition metal oxide; lithium metal iron phosphate; lithium nickel-manganese-cobalt oxide; An oxide in which lithium nickel-manganese-cobalt oxide is partially replaced with another transition metal; Or, it may include two or more of these, but is not limited thereto. Specifically, the positive electrode active material may be, for example, a layered compound such as lithium cobalt oxide (LiCoO ₂ ) or lithium nickel oxide (LiNiO ₂ ) or a compound substituted with one or more transition metals; Lithium manganese oxide with the formula Li _1+x Mn _2-x O ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ , etc.; 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 formula LiNi _1-x M _x O ₂ (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga and x = 0.01 to 0.3); _{Chemical formula} LiMn _{2 - x M} Lithium manganese complex oxide expressed as Ni, Cu or Zn); lithium metal phosphate LiMPO ₄ (where 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 ~ 0.03, a = 0.3 ~ 0.95, b = 0.01 ~ 0.35, c = 0.01 ~ 0.5, a +b+c=1); Lithium nickel-manganese-cobalt oxide partially substituted with aluminum Li _a [Ni _b Co _c Mn _d Al _e ] _1-f M1 _f O ₂ (M1 is Zr, B, W, Mg, Ce, Hf, Ta , La, Ti, Sr, Ba, F, P and S, 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 partially substituted with another transition metal oxide Li _1+x (Ni _a Co _b Mn _c M _d ) _1-x O ₂ (x = 0 ~ 0.03, a = 0.3 ~ 0.95, b = 0.01 ~ 0.35, c = 0.01 ~ 0.5, d = 0.001 ~ 0.03, a+b+c+d=1, M is any selected from the group consisting of Fe, V, Cr, Ti, W, Ta, Mg and Mo. one), a disulfide compound; Fe ₂ (MoO ₄ ) ₃ etc. may be mentioned, but it is not limited to these alone.

Meanwhile, as the positive electrode current collector, various positive electrode current collectors used in the relevant technical field may be used. For example, the positive electrode current collector may be stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. The positive electrode current collector may typically have a thickness of 3㎛ to 500㎛, and fine irregularities may be formed on the surface of the positive electrode current collector to increase the adhesion of the positive electrode active material. The positive electrode current collector may be used in various forms, such as films, sheets, foils, nets, porous materials, foams, and non-woven fabrics.

The binder resin serves to improve adhesion between positive electrode active material particles and adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF) and vinylidene fluoride-hexafluoropropylene. Copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone , polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene butadiene rubber (SBR), fluorine rubber, or various copolymers thereof. , one type of these may be used alone or a mixture of two or more types may be used. The 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 particular limitation as long as it does not cause chemical change and has electronic conductivity in the battery being constructed. Specific examples include graphite such as natural graphite and 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 powders or metal fibers 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, etc., of which one type alone or a mixture of two or more types may be used. When the conductive material is used, the conductive material may typically 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 anode can be manufactured by conventional methods known in the art.

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

Next, a positive electrode slurry is prepared by uniformly dispersing the positive electrode active material, or optionally together with an additive, into the solvent in which the conductive material is dispersed. The amount of solvent, positive electrode active material, or optionally additives 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 prepared in this way is applied to a current collector and dried in vacuum to form a positive electrode. The slurry can be coated on the current collector at an appropriate thickness depending on the viscosity of the slurry and the thickness of the positive electrode to be formed.

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

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

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

Specifically, the lithium-sulfur battery includes an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; and an electrolyte; wherein the positive electrode includes the positive electrode active material described above as the positive electrode active material.

For example, the electrode assembly may be laminated with a separator interposed between the cathode and the anode to form a stacked or stacked/folded structure, or may be wound to form a jelly roll structure. In addition, when forming the jelly roll structure, a separator may be additionally disposed on the outside to prevent the cathode and anode from contacting each other.

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

Next, the cathode will be described in more detail.

The negative electrode may have a structure in which a negative electrode active material layer is formed on one or both sides of a long sheet-shaped negative electrode current collector, and the negative electrode active material layer may include a negative electrode active material and a binder resin. Additionally, the negative electrode active material layer may further include a conductive material if necessary.

Specifically, the negative electrode is made by adding a negative electrode active material, a conductive material, and a binder to one or both sides of a long sheet-shaped negative electrode current collector such as dimethyl sulfoxide (DMSO), isopropyl alcohol, or N-methylpyrroli. It can be manufactured by applying a negative electrode slurry prepared by dispersing it in a solvent such as NMP, acetone, water, etc., removing the solvent of the negative electrode slurry through a drying process, and then rolling it. Meanwhile, a negative electrode including an uncoated portion can be manufactured by not applying the negative electrode slurry to some areas of the negative electrode current collector, for example, one end of the negative electrode current collector, when applying the negative electrode slurry.

The negative electrode active material is a material that can reversibly intercalate or deintercalate lithium (Li ⁺ ), a material that can reversibly form a lithium-containing compound by reacting with lithium ions, lithium metal, or a lithium alloy. It can be included. The material capable of reversibly inserting or de-inserting lithium ions may be, for example, crystalline carbon, amorphous carbon, or a mixture thereof, and specifically, artificial graphite, natural graphite, graphitized carbon fiber, amorphous carbon, and soft carbon. ), hard carbon, etc., but are not limited thereto.

The material that can react with the lithium ion to reversibly form a lithium-containing compound may be, for example, tin oxide, titanium nitrate, or a silicon-based compound.

The lithium alloy includes, for example, lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), beryllium (Be), magnesium (Mg), calcium ( It may be an alloy of a metal selected from the group consisting of Ca), strontium (Sr), barium (Ba), radium (Ra), aluminum (Al), and tin (Sn). 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 silicon-based compound is Si, Si-Me alloy (where Me is one or more selected from the group consisting of Al, Sn, Mg, Cu, Fe, Pb, Zn, Mn, Cr, Ti, and Ni), SiO _y (here, 0<y<2), may be a Si-C composite, or a combination thereof, and preferably may be SiO _y (here, 0<y<2). Since silicon-based compounds have high theoretical capacity, when silicon-based compounds are included as a negative electrode active material, capacity characteristics can be improved.

As the negative electrode current collector, negative electrode current collectors commonly used in the art may be used, for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, carbon on the surface of copper or stainless steel, Surface treatment with nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. The negative electrode current collector may typically have a thickness of 3 to 500㎛, and like the positive electrode current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it can be used in various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven materials.

The binder resin serves to improve adhesion between negative electrode active material particles and adhesion between the negative electrode active material and the negative electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, and carboxymethyl cellulose (CMC). ), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, Examples include styrene-butadiene rubber (SBR), fluorine rubber, or various copolymers thereof, and one type of these may be used alone or a mixture of two or more types may be used. The 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 as necessary is used to provide conductivity to the negative electrode, and can be used without particular limitation as long as it does not cause chemical change and has electronic conductivity in the battery being constructed. Specific examples include graphite such as natural graphite and 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 powders or metal fibers 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, etc., of which one type alone or a mixture of two or more types may be used. When the conductive material is used, the conductive material may typically 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 separator is disposed within the electrode assembly in such a way that it is interposed between the cathode and the anode. The separator separates the cathode from the anode and provides a passage for lithium ions, and can be used without particular restrictions as long as it is normally used as a separator in lithium secondary batteries. Specifically, the separator is a porous polymer film, for example, a porous film made of polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer. A polymer film or a laminated structure of two or more layers thereof may be used. In addition, conventional porous non-woven fabrics, for example, non-woven fabrics made of high melting point glass fibers, polyethylene terephthalate fibers, etc., may be used. Additionally, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength.

Another aspect of the present invention relates to an electrochemical device including the electrode assembly. The electrochemical device is one in which an electrode assembly and an electrolyte are stored together in a battery case. The battery case may be an appropriate battery case, such as a pouch type or a metal can type, as long as it is commonly used in the field of technology, without any particular restrictions.

Electrolytes used in the present invention include various electrolytes that can be used in lithium secondary batteries, such as organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes. and the type is not particularly limited.

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

The organic solvent may be used without particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent includes ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; Ether-based solvents such as dibutyl ether or tetrahydrofuran; Ketone-based solvents such as cyclohexanone; Aromatic hydrocarbon solvents such as benzene and fluorobenzene; Dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate Carbonate-based solvents such as PC); Alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (R is a C2 to C20 straight-chain, branched or ring-structured hydrocarbon group and may include a double bond aromatic ring or ether bond); Amides such as dimethylformamide; Dioxolanes such as 1,3-dioxolane; Alternatively, sulfolane, etc. may be used.

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

The heterocyclic compound includes 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. A heterocyclic compound substituted or unsubstituted with one or more types selected from the group consisting of (-SO ₂ ); or a multi-ring compound of at least one member 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, it is preferable because the radical is stabilized and side reactions between the additive and the electrolyte solution can be suppressed. Additionally, in the case of a heterocyclic compound substituted with a halogen group or nitro group, it is preferable because it can form a functional protective film on the surface of the lithium-based metal. The functional protective film is a stable, compact protective film that enables uniform deposition of lithium-based metal and suppresses side reactions between polysulfide and lithium-based metal.

The heterocyclic compound specifically includes, for example, furan, 2-methylfuran, 3-methylfuran, 2-ethylfuran, and 2-propylfuran. (2-propylfuran), 2-butylfuran, 2,3-dimethylfuran, 2,4-dimethylfuran, 2,5-dimethylfuran (2,5-dimethylfuran), pyran, 2-methylpyran, 3-methylpyran, 4-methylpyran, benzofuran, 2 -(2-Nitrovinyl)furan, thiophene, thiophene, 2-methylthiophene, 2-ethylthiophene, 2 -2-propylthiophene, 2-butylthiophene, 2,3-dimethylthiophene, 2,4-dimethylthiophene and 2,5-dimethylthiophene, and preferably 1 selected from the group consisting of 2-methylfuran and 2-methylthiophene. It may include more than one species.

Meanwhile, in one embodiment of the present invention, the non-aqueous solvent of the electrolyte solution may include an ether-based solvent in terms of improving charge/discharge performance of the battery. These ether-based solvents include cyclic ethers (e.g., 1,3-dioxolane, tetrahydrofuran, tetrohydropyran, etc.) and linear ether compounds (e.g., For example, 1,2 dimethoxyethane, etc.), low viscosity fluorinated ether, for example (1H,1H,2'H,3H-Decafluorodipropyl ether) , Difluoromethyl 2,2,2-trifluoroethyl ether, 1,2,2,2-tetrafluoroethyl trifluoromethyl 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 (1H,1H,2'H,3H-Decafluorodipropyl ether), Pentafluoroethyl 2,2,2-trifluoroethyl ether (Pentafluoroethyl 2,2,2) -trifluoroethyl ether), 1H,1H,2'H-Perfluorodipropyl 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 can be used without particular limitations as long as it is a compound that can provide lithium ions used in lithium secondary batteries. Specifically, the lithium salt is 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 , etc. may be used. The concentration of the lithium salt is preferably used within the range of 0.1 to 5.0M, preferably 0.1 to 3.0M. When the concentration of lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, so excellent electrolyte performance can be achieved and lithium ions can move effectively.

In addition to the electrolyte components, the electrolyte may further include additives for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity. For example, the additives include haloalkylene carbonate-based compounds such as LiNO ₃ and difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, and hexamethylene. Methyl phosphate triamides, 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. etc. can be used alone or in combination, but are not limited thereto. The additive may be included 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, in the lithium-sulfur battery of the present invention, the ratio of the total weight of the electrolyte to the total weight of the sulfur element (S) in the positive electrode (El/S) is, for example, 3.5 g/g. Below, for example, it may be preferable to be 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, 3.2 g/g.

When using the sulfur-carbon composite according to the present invention, a lithium-sulfur battery with an El/S ratio in the above-mentioned range can also be implemented, thereby showing the effect of improving energy density. However, the El/S ratio of a lithium-sulfur battery using the sulfur-carbon composite can be implemented as a battery higher than the above-mentioned range, and the present invention is not limited thereto.

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

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

Examples of the medium-to-large devices include power tools that are powered by an omni-electric motor; Electric vehicles, including electric vehicles (EV), hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV), etc.; Electric two-wheeled vehicles including electric bicycles (E-bikes) and electric scooters (Escooters); electric golf cart; Examples include, but are not limited to, power storage systems.

Hereinafter, preferred embodiments are presented to aid understanding of the present invention. However, the following examples are merely illustrative of the present invention, and it is clear to those skilled in the art that various changes and modifications are possible within the scope and spirit of the present invention. It is natural that such variations and modifications fall within the scope of the attached patent claims.

[Preparation of sulfur-carbon composite]

For the production of sulfur-carbon composites, carbon nanotubes (CNTs) (Entangled multi-wall carbon nanotubes, BET specific surface area: 200 m ² /g) were prepared as porous carbon materials. The prepared carbon nanotubes were pulverized at room temperature using a centrifugal grinder (Retsch), classified according to particle size, and used to prepare a sulfur-carbon composite as follows.

Example 1

Mix evenly so that the sulfur content is 70wt% based on the total weight of 100wt% of carbon nanotubes (CNT) and sulfur (S ₈ ), grind it by ball milling, and place in an oven at 155 ° C for 30 minutes to prepare a sulfur-carbon composite. did. The CNT had a BF of 5.42 and a D ₅₀ of 38 ㎛.

Example 2

Mix evenly so that the sulfur content is 75 wt% based on the total weight of 100 wt% of carbon nanotubes (CNT) and sulfur (S ₈ ), grind it by ball milling, and place in an oven at 155 ° C for 30 minutes to prepare a sulfur-carbon composite. did. The CNT had a BF of 5.49 and a D ₅₀ of 24 ㎛.

Comparative Example 1

Mix evenly so that the sulfur content is 70 wt% based on the total weight of 100 wt% of carbon nanotubes (CNT) and sulfur (S ₈ ), grind it by ball milling, and place in an oven at 155 ° C for 30 minutes to prepare a sulfur-carbon composite. did. The CNT had a BF of 11.05 and a D ₅₀ of 44 ㎛.

Comparative Example 2

Mix evenly so that the sulfur content is 75 wt% based on the total weight of 100 wt% of carbon nanotubes (CNT) and sulfur (S ₈ ), grind it by ball milling, and place in an oven at 155 ° C for 30 minutes to prepare a sulfur-carbon composite. did. The CNT had a BF of 10.68 and a D ₅₀ of 32 ㎛.

[Manufacture of batteries]

A lithium-sulfur battery was manufactured as follows using the sulfur-carbon composites obtained in Examples 1, 2, Comparative Examples 1, and 2 above.

Manufacturing of anode

90% by weight of sulfur-carbon composite as a positive electrode active material, 5% by weight of Denka Black as a conductive material, and 5% by weight of styrene butadiene rubber/carboxymethyl cellulose (weight ratio of SBR:CMC=7:3) as a binder are added to the solvent and mixed. A positive electrode slurry composition was prepared.

A positive electrode was prepared by applying the prepared positive electrode slurry composition to a thickness of 350 μm on a 20 μm thick aluminum current collector, drying it at 50° C. for 12 hours, and pressing it with a roll press machine.

In Example 1 and Comparative Example 1, the content of elemental sulfur (S) in the anode was 63.0 wt%, and in Example 2 and Comparative Example 2, the content of elemental sulfur (S) in the anode was 67.5 wt%.

Manufacturing of lithium-sulfur batteries

The positive electrode prepared above is used as the positive electrode, and an electrode assembly is manufactured by providing a negative electrode and interposing a separator between the positive electrode and the negative electrode. The electrode assembly is stored in a pouch-type case and filled with an electrolyte solution to form a lithium-sulfur battery. was manufactured.

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

A pouch cell containing the anode and cathode prepared as described above was manufactured. El/S in each manufactured battery was controlled to be 3.1 g/g or less.

[Particle size measurement and particle size distribution measurement]

The particle size corresponding to D ₁₀ , D ₅₀ and D ₉₀ of the porous carbon material was measured using a particle size analyzer (model name: Bluewave, manufacturer: Microtrac) using a dry method. When the carbon material was converted into secondary particles by agglomeration, the primary particle size was observed and measured using a scanning electron microscope (model name: SEM, manufacturer: JEOL).

SEM images of each porous carbon material used to manufacture the sulfur-carbon composite of Example 1 and Comparative Example 1 are shown in Figures 1 (Example 1) and Figure 2 (Comparative Example 1), respectively.

[Evaluation of the cross-section of the electrode]

SEM images of the vertical cross-section of the anode prepared above using the sulfur-carbon composite of Example 1 and Comparative Example 1 are shown in Figures 3 (Example 1) and Figure 4 (Comparative Example 1), respectively.

Measure the area of 10 arbitrary sulfur-carbon composites per 50 ㎛ Measured.

[ceremony]

Standard error (%) = (standard deviation/mean)

[Discharge capacity evaluation]

For each lithium sulfur battery manufactured as above, discharge to 1.8 V at a rate of 0.5C or 1.0C in CC mode at 25°C, and charge to 2.5 V at a constant current of 0.5 C to measure discharge capacity. /The comparison results are shown in Table 1 above. Discharge capacity was measured based on the weight of sulfur. (mAh/g(weight of sulfur)s)

In addition, the results of evaluating the 0.5C discharge capacity for the batteries using the sulfur-carbon composites of Example 1, Example 2, Comparative Example 1, and Comparative Example 2 are shown in Figures 5 and 6, respectively, and the measured discharge The capacities are shown in Table 1 below.

The energy density was measured according to the following equation using the measured 0.5C discharge capacity value, and was performed based on the energy density of Comparative Example 1, the relative value of the energy density of Example 1, and the energy density of Comparative Example 2. The relative values of the energy density of Example 2 are shown in Table 1.

[ceremony]

Energy density = [(discharge capacity

[evaluation]

In the sulfur-carbon complex
Sulfur (S) content (wt%) Particle size of porous carbon material,
D ₅₀ of porous carbon materials
Broadness
Factor(BF) Standard error (%) 0.5C discharge capacity
(mAh/gs) 1.0C discharge capacity
(mAh/gs) energy density
(relative value) Example 1 70 38 5.42 64.1 1092 1035 1.07 Comparative Example 1 70 44 11.05 135.1 1038 915 1.00 Example 2 75 24 5.49 68.7 1073 1005 1.06 Comparative Example 2 75 32 10.68 150.2 1015 938 1.00

Referring to Figures 1 to 4, it was confirmed that in Example 1 using a porous carbon material with a BF of 7 or less, the uniformity of the area of the sulfur-carbon composite in the cross section of the anode was further improved compared to Comparative Example 1.

The results of Table 1 and Figure 5 show that even when a sulfur-carbon composite with the same sulfur content (70 wt%) is used, the discharge capacity is significantly superior when the sulfur-carbon composite of Example 1, where the BF of the porous carbon material is 7 or less, is used. It was confirmed that it did.

The results of Table 1 and Figure 6 show that even when a sulfur-carbon composite with the same sulfur content (75 wt%) is used, the discharge capacity is significantly superior when the sulfur-carbon composite of Example 2, where the BF of the porous carbon material is 7 or less, is used. It was confirmed that it did.

Additionally, referring to Table 1, when comparing the energy densities of Comparative Example 1 and Example 1, it was confirmed that the energy density increased in Example 1 in which the particle size distribution was adjusted compared to Comparative Example 1.

In addition, referring to Table 1, when comparing the energy densities of Comparative Example 2 and Example 2, it was confirmed that the energy density increased in Example 2 in which the particle size distribution was adjusted compared to Comparative Example 2.

From the above results, when sulfur (S) is supported on a porous carbon material with a particle size distribution of BF 7 or less, diffusion of sulfur can be achieved uniformly, and accordingly, when charging/discharging a battery using this, sulfur <-> Li ₂ It was confirmed that the oxidation-reduction reaction of S occurred uniformly. In particular, it was confirmed that a lithium-sulfur battery with greatly improved battery capacity and energy density could be provided by using a porous carbon material with a BF of 7 or less.

Claims (13)

It is a positive electrode active material containing a sulfur-carbon complex,
The sulfur-carbon composite includes a porous carbon material and a sulfur-based material supported on all or at least part of the inner and outer surfaces of the pores of the porous carbon material,
The sulfur-based material includes one or more of sulfur (S ₈ ) and sulfur compounds,
The porous carbon material is a positive electrode active material for a lithium-sulfur battery, characterized in that the ratio (broadness factor, BF) of the particle size distribution of particle size D ₉₀ to particle size D ₁₀ is 7 or less. In claim 1,
The sulfur-based material includes inorganic sulfur (S ₈ ), Li ₂ S _n (n≥1), 2,5-dimercapto-1,3,4-thiadiazole (2,5-dimercapto-1,3,4- disulfide compounds including one or more of thiadiazole) and 1,3,5-trithiocyanuic acid; organosulfur compounds; and a carbon-sulfur polymer ((C ₂ S _x ) _n , x=2.5 to 50, n≥2). In claim 1,
The porous carbon material is a positive electrode active material for a lithium-sulfur battery having a BET surface area of 1,500 cm ² /g or more. In claim 1,
The porous carbon material is a positive electrode active material for a lithium-sulfur battery comprising at least one selected from activated carbon, carbon black, carbon nanotubes, and graphene. In claim 4,
The porous carbon material is a positive electrode active material for a lithium-sulfur battery including carbon nanotubes. In claim 1,
A positive electrode 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,
A cathode active material for a lithium-sulfur battery having a content of sulfur element (S) of 60 wt% or more compared to 100 wt% of the sulfur-carbon composite. Comprising 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 includes a sulfur-carbon complex,
The sulfur-carbon composite is a positive electrode for a lithium-sulfur battery comprising a porous carbon material and a sulfur-based material supported on all or at least part of the inner and outer surfaces of the pores of the porous carbon material,
A positive electrode for a lithium-sulfur battery, characterized in that the standard error of the area of any 10 sulfur-carbon composites per area of 50 ㎛ In claim 8,
The porous carbon material is a positive electrode for a lithium-sulfur battery having a particle size distribution ratio (Broadness Factor, BF) of particle size D ₉₀ to particle size D ₁₀ of 7 or less. In claim 8,
A positive electrode for a lithium-sulfur battery, wherein the particle size D ₅₀ of the porous carbon material is 100 ㎛ or less. In claim 8,
The sulfur-based material includes one or more of sulfur (S ₈ ) and sulfur compounds,
A positive electrode for a lithium-sulfur battery, wherein the content of the sulfur-based material is 60 wt% or more compared to 100 wt% of the positive electrode active material layer. An electrode assembly including an anode, a cathode, and a separator interposed between the anode and the cathode; and electrolyte;
The positive electrode is a lithium-sulfur battery, characterized in that it contains the positive electrode active material according to any one of claims 1 to 7. In claim 12,
A lithium-sulfur battery wherein the ratio (El/S) of the total weight of the electrolyte to the total weight of the sulfur element (S) in the positive electrode is 3.5 g/g or less.