Positive electrode for lithium-sulfur battery and lithium-sulfur battery having high energy density characteristics

Abstract

The present invention relates to a positive electrode for a lithium-sulfur battery and a lithium-sulfur battery including the positive electrode. The positive electrode uses a porous carbon material manufactured by centrifugal pulverization and having a low tap density, thereby having a high porosity and being able to form a thick active material layer per the same amount of carbon. Accordingly, the positive electrode according to an embodiment of the present invention can embody a lithium-sulfur battery with a high energy density.

Description

Technical Field

[0001] The present invention relates to a lithium-sulfur battery having a high energy density.

[0002] This application claims priority based on Korean Patent Application Nos. 10-2022-0159965 filed on November 25, 2022, 10-2022-0183586 and 10-2022-0183771 filed on December 23, 2022, 10-2022-0185613 filed on December 27, 2022, 10-2023-0063394 filed on May 16, 2023, 10-2023-0070299 filed on May 31, 2023, 10-2023-0073163 filed on June 7, 2023, and 10-2023-0075765 filed on June 13, 2023, and all of the content disclosed in the specifications and drawings of those applications is incorporated herein by reference.

Background Art

[0003] As interest in energy storage technologies has grown and the application fields have expanded to include mobile phones, tablets, notebook computers, and camcorders, and even the energy of electric vehicles (EVs) and hybrid electric vehicles (HEVs), research and development of electrochemical devices have been gradually increasing. Electrochemical devices are the most prominent fields in this regard, and in particular, interest has been focused on the development of secondary batteries such as lithium-sulfur batteries that can be charged and discharged. In the development of such batteries, in recent years, research and development have been conducted on new electrode and battery designs in order to improve the capacity density and specific energy.

[0004] Among such electrochemical devices, lithium-sulfur (LiS) batteries have attracted attention as next-generation secondary batteries that can replace lithium-ion batteries because they have a high energy density. Lithium sulfur is used as a positive electrode active material, and when discharging in a lithium-sulfur battery, a reduction reaction of sulfur and an oxidation reaction of lithium metal occur. At this time, sulfur forms lithium polysulfides (Li2S2, Li2S4, Li2S6, Li2S8) with a linear structure from S8 with a cyclic structure. Such a lithium-sulfur battery is characterized by showing a stepwise discharge voltage until polysulfide (PS) is completely reduced to LiS.

[0005] In a lithium-sulfur battery, when using a carbon material with a high specific surface area and a large porosity such as carbon nanotubes as a sulfur carrier, it is possible to achieve a high energy density and life characteristics. However, further research is needed to achieve an energy density and life characteristics that can be actually commercialized.

[0006] Therefore, there have been attempts to increase the loading amount of sulfur, which is a positive electrode active material, in order to improve the energy density. However, since sulfur has no conductivity, the problem has occurred that the reactivity decreases as the sulfur content increases, and the energy density rather decreases. Summary of the Invention Problems to be Solved by the Invention

[0007] Therefore, an object of the present invention is to provide a lithium-sulfur battery having a large sulfur loading amount and a high energy density.

[0008] Also, other objects and advantages of the present invention can be realized by the means or methods shown in the claims and combinations thereof. Means for Solving the Problems

[0009] To solve the above problems, according to one aspect of the present invention, a positive electrode of the following embodiment is provided.

[0010] The positive electrode according to the first embodiment includes 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 composite and a binder polymer, the sulfur-carbon composite includes a porous carbon material and a sulfur-based material, and the ratio of the thickness of the positive electrode active material layer to the carbon weight per unit area of the positive electrode active material layer is 80 μm / mg to 130 μm / mg.

[0011] According to the second embodiment, in the first embodiment, the porosity of the positive electrode active material layer can be 80 vol% or more.

[0012] According to the third embodiment, in the first embodiment or the second embodiment, the content of sulfur element (S) can be 60 wt% or more based on the total weight of the positive electrode active material layer.

[0013] According to the fourth embodiment, in any one of the first to third embodiments, the porous carbon material can be in the form of angular particles.

[0014] According to the fifth embodiment, in any one of the first to fourth embodiments, the porous carbon material can have a particle shape uniformity of 1.3 or less according to the following formula 1.

[0015] Particle shape uniformity = [(average diameter of the circumscribed circle of the particle) / (average diameter of the inscribed circle of the particle)]... Formula 1 According to the sixth embodiment, in any one of the first to fifth embodiments, the porous carbon material can be manufactured by pulverizing a porous carbon material as a raw material using a centrifugal pulverizer and sieving the pulverized porous carbon material with a sieve having a mesh size of 50 μm to 100 μm.

[0016] According to the seventh embodiment, in any one of the first to sixth embodiments, The tap density of the porous carbon material may be 0.09 g / cm 3 or less.

[0017] According to the eighth embodiment, in any one of the first to seventh embodiments, the porosity of the positive electrode active material layer may be 81 vol% to 85 vol%.

[0018] According to the ninth embodiment, in any one of the first to eighth embodiments, the porous carbon material may include a secondary structure formed by aggregation of a plurality of carbon nanotubes as a primary structure.

[0019] According to the tenth embodiment, in any one of the first to ninth embodiments, the tap density of the porous carbon material may be 0.07 g / cm 3 or less.

[0020] According to the eleventh embodiment, in any one of the first to tenth embodiments, the content of sulfur element (S) may be 65 wt% to 90 wt% based on the total weight of the positive electrode active material layer.

[0021] According to the twelfth embodiment, in any one of the first to eleventh embodiments, the loading amount of sulfur (S) may be 2.9 mgs / cm 2 or more.

[0022] According to another aspect of the present invention, a lithium-sulfur battery of the following embodiment is provided.

[0023] The lithium-sulfur battery according to the thirteenth embodiment includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte according to any one of the first to twelfth embodiments.

[0024] According to the fourteenth embodiment, in the thirteenth embodiment, The carbon weight per unit area of the positive electrode active material layer and the thickness of the positive electrode active material layer may each be measured after at least one discharge has been performed.

[0025] According to the 15th embodiment, in the 13th or 14th embodiment, The carbon weight per unit area of the positive electrode active material layer and the thickness of the positive electrode active material layer may each be measured at an SOC (State of Charge) of 97% to 100%.

[0026] According to the 16th embodiment, in any one of the 13th to 15th embodiments, The ratio (El / S weight ratio) of the weight of the electrolyte to the weight of sulfur (S) in the sulfur-carbon composite may be 3.5 g / g or less.

[0027] According to the 17th embodiment, in any one of the 13th to 16th embodiments, The energy density of the lithium-sulfur battery may be 400 Wh / kg or more.

Advantages of the Invention

[0028] According to one aspect of the present invention, a positive electrode for a lithium-sulfur battery having a large amount of sulfur supported as a positive electrode active material, and a lithium-sulfur battery including the positive electrode can be provided. In particular, according to one aspect of the present invention, a lithium-sulfur battery with improved energy density can be provided by maintaining and improving the electrochemical reactivity of sulfur while having a large amount of sulfur supported as a positive electrode active material.

Brief Description of the Drawings

[0029]

Figure 1

Figure 2

Figure 3

Figure 4a

Figure 4b

Figure 5

Mode for Carrying Out the Invention

[0030] Hereinafter, the present invention will be described in detail.

[0031] Throughout this specification, when a certain part includes, has, or comprises a certain component, unless otherwise specified, it does not exclude other components and may further include other components.

[0032] Also, terms such as "about" and "substantially" used throughout this specification are used as a meaning equal to or close to that numerical value when manufacturing and material tolerances inherent in the mentioned meaning are presented, in order to prevent unscrupulous infringers from improperly using the disclosed content where an exact or absolute numerical value is mentioned to assist in the understanding of this application.

[0033] Throughout this specification, the description of "A and / or B" means "A, B, or all of these".

[0034] As used herein, the term "composite" means a substance in which two or more materials are combined to form physically and chemically distinct phases while exhibiting a more effective function.

[0035] As used herein, the term "polysulfide" encompasses "polysulfide ion (Sx 2- , 1 ≦ x ≦ 8)" and "lithium polysulfide (Li2S x or LiS x - , 1 ≦ x ≦ 8)".

[0036] In the present invention, the "specific surface area" is measured by the BET method, and specifically, it can be calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77K) using BELSORP-mini II manufactured by BEL Japan, Inc.

[0037] In the present invention, "particle size D 10 " means the particle size at the 10% reference of the volume cumulative particle size distribution of the particles to be measured, "particle size D 50 " means the particle size at the 50% reference of the volume cumulative particle size distribution of the particles to be measured, and "particle size D 90 " means the particle size at the 90% reference of the volume cumulative particle size distribution of the particles to be measured.

[0038] The particle sizes D 10 , D 50 and D 90 can each be measured using the laser diffraction method. For example, after dispersing the particle powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT3000), irradiated with ultrasonic waves of about 28 kHz at an output of 60 W, and then a volume cumulative particle size distribution graph is obtained, and the particle sizes corresponding to 10%, 50%, and 90% of the volume cumulative distribution are determined for measurement. That is, for example, the average particle size D 50shows the median or median diameter in the particle size distribution graph and represents the particle size at the 50% point of the cumulative distribution. The particle size is the diameter of the particle, and the diameter of the particle means the longest length within the particle.

[0039] The unit "mAh / g" used in this specification s ", unless otherwise specified, is for indicating the capacity per unit weight of sulfur (S) and can be used interchangeably with other expression methods such as mAh / g(s), mAh / gs, etc.

[0040] The unit "mg" used in this specification s / cm 2 ", unless otherwise specified, is for indicating the weight of sulfur (S) per unit area and can be used interchangeably with other expression methods such as mg(s) / cm 2 , mAh / gs, etc.

[0041] The term "porosity" used in this specification means the ratio of the volume occupied by pores to the total volume of a certain structure, uses vol% as the unit, and is interchangeable with terms such as void fraction and porosity. The porosity can be measured by the method of ISO 15901:2019 known in the art.

[0042] The present invention provides a positive electrode used in an electrochemical element and an electrochemical element including the positive electrode. In this specification, the electrochemical element may include any element that performs an electrochemical reaction. Specifically, it includes all types of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors such as supercapacitor elements. In particular, the electrochemical element may be a secondary battery, and the secondary battery may be a lithium-ion secondary battery. The lithium-ion secondary battery includes a lithium-metal battery, a lithium-sulfur battery, an all-solid-state battery, a lithium polymer battery, etc., and among them, a lithium-sulfur battery is preferably used.

[0043] Conventional lithium-sulfur batteries have been pointed out as having a problem of low energy density. Therefore, by using a carbon material with a high specific surface area and porosity, such as carbon nanotubes, as a carrier for sulfur-based materials, relatively high energy density and life characteristics have been realized, but it still has not reached a level that can be commercialized. In addition, in order to increase the energy density of a lithium-sulfur battery, it is necessary to increase the loading amount of the sulfur-based material in the sulfur-carbon composite contained in the positive electrode. However, since the sulfur-based material has no conductivity or extremely low conductivity, there is a problem that the reactivity of the positive electrode decreases as the loading amount increases.

[0044] According to one embodiment of the present invention, by supporting a sulfur-based material, such as sulfur (S8) or a sulfur compound, on a porous carbon material whose shape is modified so as to have excellent electric conductivity in the positive electrode while increasing the loading rate of the sulfur-based material, a positive electrode with improved electric conductivity and a lithium-sulfur battery with improved energy density are provided.

[0045] The 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. Specifically, the positive electrode active material layer includes a sulfur-carbon composite and a binder polymer. Further, the sulfur-carbon composite includes a porous carbon material and a sulfur-based material.

[0046] In one embodiment of the present invention, the porous carbon material can be particulate.

[0047] In one embodiment of the present invention, the porous carbon material includes irregular pores inside the particles (closed pores) and / or on the surface of the particles (open pores). At this time, the average diameter of the pores is, for example, in the range of 1 nm to 200 nm, and the porosity can be 10 vol% to 90 vol% of the total volume of the porous carbon material. The average diameter of the pores can be measured by a known method such as the BET measurement method using gas adsorption or the mercury intrusion method.

[0048] In one embodiment of the present invention, the porous carbon material may have a particle size within a specific range as described hereinafter.

[0049] In one embodiment of the present invention, the sulfur-carbon composite may be provided in a form in which the sulfur-based material is supported on all or at least a part of the inside and outside surfaces of the pores of the porous carbon material. Further, the sulfur-carbon composite may be provided in a form in which the sulfur-based material covers all or at least a part of the inside and outside surfaces of the pores of the porous carbon material.

[0050] In one embodiment of the present invention, since the positive electrode contains a porous carbon material as a carrier for the active material, it has a low tap density, and thus can exhibit the characteristic of a high porosity. In particular, by supporting the active material on the above-described porous carbon material, even if the active material is contained in a high content, a sufficient migration path for substances such as ions in the positive electrode is ensured, and the characteristics of low resistance and improved capacity can be realized.

[0051] Specifically, the positive electrode may have a ratio of the thickness of the positive electrode active material layer to the carbon weight per unit area of the positive electrode active material layer in the range of 80 μm / mg to 130 μm / mg.

[0052] In one embodiment of the present invention, the positive electrode is characterized in that the porosity of the active material layer is 80 vol% or more.

[0053] In one embodiment of the present invention, the positive electrode is characterized in that, based on the total weight of the active material layer, the content of the sulfur element (S) is 60 wt% or more, specifically 65 wt% or more. At this time, the sulfur element (S) is derived from the sulfur-based material, and may particularly be derived from the inorganic sulfur (S8) used in the production of the sulfur-carbon composite.

[0054] In one embodiment of the present invention, the positive electrode is characterized in that, based on the total weight of the active material layer, the content of the sulfur element (S) is 60 wt% or more, specifically 65 wt% or more, and the porosity is 80 vol% or more.

[0055] That is, according to one embodiment of the present invention, by using a porous carbon material with a modified shape, there is an advantage that not only the loading amount of the active material in the positive electrode active material can be increased, but also the porosity of the positive electrode can be ensured.

[0056] Sulfur-based materials used as active materials in lithium-sulfur batteries, such as inorganic sulfur (S8), are insulators. Therefore, in a lithium-sulfur battery according to the prior art, when the amount of the active material, that is, the sulfur-based material, in the positive electrode active material layer is excessively large, the resistance in the positive electrode increases, so the reactivity of the positive electrode decreases. Therefore, it is difficult to include 60 wt% or more of the sulfur-based material contained in the total 100 wt% of the positive electrode active material layer. Specifically, it is difficult to make the content of sulfur element (S) 60 wt% or more based on the total 100 wt% of the positive electrode active material layer.

[0057] However, the present invention can provide a positive electrode with improved reactivity while increasing the content of the active material (that is, the sulfur-based material) and the porosity of the active material layer by setting the ratio of the thickness of the positive electrode active material layer to the carbon weight per unit area of the positive electrode active material layer within a specific range.

[0058] As described above, in the positive electrode according to one embodiment of the present invention, the ratio of the thickness of the positive electrode active material layer to the carbon weight per unit area of the positive electrode active material layer is 80 μm / mg to 130 μm / mg. Here, "unit area" means 1 cm 2 (1 cm × 1 cm).

[0059] In one embodiment of the present invention, the ratio of the thickness of the positive electrode active material layer to the carbon weight per unit area of the positive electrode active material layer can be calculated by measuring the carbon weight per 1 cm 2 of the positive electrode active material layer and measuring the thickness of the positive electrode active material layer.

[0060] In this specification, the carbon weight per unit area of the positive electrode active material layer and the thickness of the positive electrode active material layer can each be measured based on the state where the positive electrode has not been used in an electrochemical reaction and immediately after being manufactured (un-used fresh cell). Alternatively, the carbon weight per unit area of the positive electrode active material layer and the thickness of the positive electrode active material layer can each be measured after the electrode has been discharged at least once. In this case, it is preferable that the electrode has a capacity retention rate of 97% or more of the initial capacity, but the present invention is not limited thereto.

[0061] Specifically, the thickness of the positive electrode active material layer is preferably measured in a charged state in terms of measurement accuracy. For example, it can be measured based on the state where it has been charged to SOC of 97% or more, for example, SOC of 97% to 100%, specifically SOC of 100% after being discharged at least once. Alternatively, the carbon weight per unit area of the positive electrode active material layer and the thickness of the positive electrode active material layer can be measured based on the cycle in which the thickness of the positive electrode active material layer is the thinnest.

[0062] In one embodiment of the present invention, the ratio of the thickness of the positive electrode active material layer to the carbon weight per unit area of the positive electrode active material layer can be calculated using the value obtained by calculating the weight of carbon per electrode loading and measuring the thickness of the positive electrode active material layer. Here, the electrode loading can be calculated from the content of sulfur (S) in the positive electrode by a known method.

[0063] In another embodiment of the present invention, the ratio of the thickness of the positive electrode active material layer to the carbon weight per unit area of the positive electrode active material layer can be calculated by a method of directly analyzing the carbon content per unit area of the positive electrode active material layer and a method of measuring the thickness of the electrode. Here, examples of the method of directly analyzing the carbon content per unit area include elemental analysis methods such as known ICP-OES analysis, EA analysis, and ICP analysis, but the measurement method is not limited thereto. Further, the method of measuring the thickness of the electrode can be, for example, a method of measuring the thickness of the entire positive electrode using a known thickness measuring instrument, such as a thickness measuring instrument manufactured by Mitutoyo Corporation, and subtracting the thickness of the current collector to measure the thickness of the positive electrode active material layer, but the measurement method is not limited thereto.

[0064] In one embodiment of the present invention, the carbon weight per unit area of the positive electrode active material layer means the total carbon weight including all carbon derived from the sulfur-carbon composite contained in the positive electrode active material layer, carbon derived from a binder and / or a conductive material that may be contained in the positive electrode active material layer, excluding the current collector from the positive electrode to be measured.

[0065] Therefore, in one embodiment of the present invention, when the composition of the positive electrode and the content of the sulfur-based material in the sulfur-carbon composite are known, the carbon weight per unit area of the positive electrode active material layer can be calculated from the loading amount.

[0066] On the other hand, in a lithium-sulfur battery, the thickness of the positive electrode can change as the battery is repeatedly charged / discharged. Therefore, in order to measure the ratio of the thickness of the positive electrode active material layer to the carbon weight per unit area of the positive electrode active material layer, conditions for the number of charge / discharge cycles (cycle) and / or the state of charge (SOC) may be required. During discharge of the battery, discharge products are generated inside the structure of the porous carbon material present in the positive electrode active material layer. Therefore, it may be difficult to accurately measure the thickness of the positive electrode without removing such discharge products. Therefore, the thickness of the positive electrode active material layer can be measured based on the state of charge, for example, when the SOC is 97% to 100%, preferably when the SOC is 100%.

[0067] As described above, the positive electrode in which the ratio of the thickness of the positive electrode active material layer to the carbon weight per unit area of the positive electrode active material layer satisfies 80 μm / mg to 130 μm / mg may be, for example, one in which the content of sulfur element (S) is 65 wt% or more based on the total 100 wt% of the positive electrode active material layer, and the porosity is 80 vol% or more.

[0068] In one embodiment of the present invention, the ratio of the thickness of the positive electrode active material layer to the carbon weight per unit area of the positive electrode active material layer may be, for example, 80 μm / mg to 120 μm / mg, 80 μm / mg to 110 μm / mg, 80 μm / mg to 100 μm / mg, or 83 μm / mg to 98 μm / mg. Also, based on the electrode immediately after manufacturing, the ratio of the thickness of the positive electrode active material layer to the carbon weight per unit area of the positive electrode active material layer may be, for example, 90 μm / mg to 120 μm / mg or 95 μm / mg to 119 μm / mg.

[0069] In one embodiment of the present invention, as the sulfur-based material, any material that can provide sulfur (S8) as an active material of a lithium-sulfur battery can be used without particular limitation. For example, the sulfur-based material includes one or more of sulfur (S8) and sulfur compounds.

[0070] In one embodiment of the present invention, the sulfur-based material is inorganic sulfur (S8), Li2S n (n≧1), organic sulfur compounds such as 2,5-dimercapto-1,3,4-thiadiazole and 1,3,5-trithiocyanuric acid, carbon-sulfur polymer ((C2S x ) n , x = 2.5 to 50, n≧2), or may contain a mixture of two or more of these. Specifically, the sulfur-based material may contain inorganic sulfur (S8).

[0071] In one embodiment of the present invention, the sulfur-based material in the sulfur-carbon composite can be included by physical adsorption with a porous carbon material, or by chemical bonds such as covalent bonds or van der Waals bonds between sulfur element (S) and carbon in the porous carbon material. In particular, the sulfur-based material can be chemically bonded to the surface of the porous carbon material to form a composite.

[0072] In the sulfur-carbon composite according to the present invention, the sulfur-based material is located on at least one surface of the inner and outer surfaces of the pores of the carbon material. At this time, it can exist in an area of less than 100% of the total surface of the inside and outside of the carbon material, preferably 1% to 95%, more preferably 60% to 90%. When the sulfur (S) exists within the above range on the surface of the carbon material, the maximum effect can be achieved in terms of the electron transfer area and the wettability of the electrolyte. Specifically, since sulfur is thinly and uniformly impregnated on the surface of the carbon material in the area within the above range, the electron transfer contact area can be increased during the charge and discharge process. If the sulfur is located in an area of 100% of the total surface of the carbon material, the carbon material is completely covered with sulfur, the wettability of the electrolyte decreases, and the contact with the conductive material contained in the electrode decreases, resulting in no electron transfer and inability to participate in the reaction.

[0073] In one embodiment of the present invention, the content of the sulfur element (S) can be 60 wt% or more, 65 wt% or more, for example, 60 wt% to 100 wt%, 60 wt% to 90 wt%, 65 wt% to 80 wt%, 65 wt% to 75 wt%, 65 wt% to 70 wt%, or 70 wt% to 75 wt% based on 100 wt% of the total positive electrode active material layer. For example, the content of the sulfur element (S) can be 67.2 wt% to 72 wt% based on 100 wt% of the total positive electrode active material layer. If the content of the sulfur element (S) is within the above range, it not only improves the capacity of the battery but also has an advantageous effect on the stability of the battery. However, the present invention is not limited thereto.

[0074] In one embodiment of the present invention, the porous carbon material may have a modified shape of a normal porous carbon material used in a lithium-sulfur battery. Specifically, the porous carbon material may have a particulate shape, particularly an angular particulate shape. For example, the porous carbon material may be particulate having prismoidal sphericity.

[0075] As will be described later, the porous carbon material may be one having a modified particulate shape using a centrifugal grinder.

[0076] Referring to FIG. 5, it can be confirmed that the surface (left side) of the porous carbon material pulverized by a jet mill or the like is relatively flat, while the surface (right side) of the porous carbon material pulverized by a centrifugal grinder is relatively rough. It can be confirmed that the porous carbon material on the right side has an angular particulate shape due to its rough surface characteristics.

[0077] Specifically, the porous carbon material is a carbonaceous material having porosity and conductivity, and may include those 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, thermal black; carbon nanotubes (CNT) such as single-walled carbon nanotubes (SWCNT), multi-walled carbon nanotubes (MWCNT); carbon fibers such as graphite nanofibers (GNF), carbon nanofibers (CNF), activated carbon fibers (ACF); graphite such as natural graphite, artificial graphite, expanded graphite; carbon nanoribbons; carbon nanobelts, carbon nanorods, and activated carbon, and may include one or more selected from the group consisting of.

[0078] In one embodiment of the present invention, the porous carbon material may include carbon nanotubes. The carbon nanotubes are those in which carbon connected in a hexagonal shape forms a tube pattern. According to one embodiment of the present invention, the carbon nanotubes can be single-walled carbon nanotubes (SWCNT), multi-walled carbon nanotubes (MWCNT), or a combination thereof, depending on the number of carbon atom layers (also referred to as "carbon walls") constituting the same. Here, the length of individual carbon nanotubes is not particularly limited.

[0079] In one embodiment of the present invention, the porous carbon material may include carbon nanotubes in terms of improving the sulfur loading rate, and specifically may include multi-walled carbon nanotubes (MWCNT), but the present invention is not limited thereto.

[0080] In one embodiment of the present invention, the porous carbon material may include a secondary structure formed by aggregation of a plurality of carbon nanotubes as a primary structure.

[0081] In another embodiment of the present invention, the carbon nanotubes may exist in a form in which two or more carbon nanotubes are in close contact with each other and intertwined 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 liquid dispersed so as to exist as a single strand in a dispersion medium or the like, but the carbon nanotubes of the primary structure may be aggregated with each other and provided in the form of a secondary structure.

[0082] From such aspects, when the porous carbon material includes carbon nanotubes, the carbon nanotubes can be a bundle-like secondary structure, an entangled secondary structure, or include both of them.

[0083] The bundled secondary structure of the carbon nanotubes refers to a form in which a single carbon nanotube serves as the primary structure, and a plurality of the primary structures are oriented in the longitudinal direction of the carbon nanotubes by the cohesive force between carbons and the like, and are solidified together, and can also be referred to as bundled CNT (bundled CNT).

[0084] In one embodiment of the present invention, the carbon nanotubes may include, for example, entangled multi-walled carbon nanotubes (Entagled MWCNT).

[0085] In one embodiment of the present invention, the porous carbon material may have a BET specific surface area of, for example, 150 m 2 / g or more. In one embodiment of the present invention, the BET specific surface area of the porous carbon material is, for example, 150 m 2 / g to 2,500 m 2 / g, 150 m 2 / g to 2,000 m 2 / g, 150 m 2 / g to 1,500 m 2 / g, 150 m 2 / g to 1,000 m 2 / g, 130 m 2 / g to 300 m 2 / g, or 170 m 2 / g to 200 m 2 / g, but is not limited thereto. In the present invention, the "specific surface area" is measured by the BET method, and specifically, it can be calculated from the adsorption amount of nitrogen gas at liquid nitrogen temperature (77K) using BELSORP-mini II manufactured by BEL Japan, Inc.

[0086] According to an embodiment of the present invention, a porous carbon material whose shape is modified by grinding can be applied. Specifically, the grinding can be one that finely pulverizes or shears particles. For example, particles sandwiched between two blades can be broken or scraped off. When the particles are ground, stimuli are applied to the outer surface of the particles, causing the particles to be broken or scraped off. Also, when the particles are ground, since friction occurs between the rotating blade of the grinder and the particles, the particles can be torn or roughened.

[0087] Generally, carbon nanotubes such as single-walled carbon nanotubes (SWCNTs) or multi-walled carbon nanotubes (MWCNTs) are synthesized by a thermal chemical vapor deposition method or an arc discharge method, but an aggregation phenomenon occurs between carbon nanotube particles during the synthesis process. The aggregation phenomenon of carbon nanotubes can be classified into physical aggregation where nanotubes entangle with other particles as individual particles at the μm level, and chemical aggregation where they aggregate by surface attraction (~950 meV / nm) such as van der Waals force, which is an intermolecular force in the case of single-walled carbon nanotubes (SWCNTs) at the nm level. Such an aggregation phenomenon of carbon nanotubes may prevent the formation of a three-dimensional network structure that improves the mechanical strength and electrical conductivity characteristics. Such an aggregation phenomenon is a phenomenon common to linear conductive carbon materials such as carbon nanotubes. Therefore, in the present invention, after crushing a linear conductive carbon material by a pretreatment such as grinding, it is introduced into the manufacture of an electrode, so that a predetermined tap density range described later can be satisfied, and the filling rate of the sulfur-based material can be improved.

[0088] The porous carbon material of the conventional lithium-sulfur battery has been used after pretreatment by a jet mill. However, when pretreating the porous carbon material through a jet mill, due to the low particle shape uniformity and smooth particle surface of the porous carbon material, the effect of improving the tap density is insufficient. However, in the present invention, by pretreating the porous carbon material using a grinder, defects occur (for example, being torn) in each of the conductive carbon materials located on the surface of the porous carbon material, and gaps or coarseness are formed between the conductive carbon materials, further enhancing the particle shape uniformity of the porous carbon material while improving the surface roughness of the particles, further increasing the sulfur loading rate and further improving the tap density. However, the present invention is not limited thereto.

[0089] In one embodiment of the present invention, the pretreatment for the shape modification of the porous carbon material may further include a process of classifying by a sieve of a predetermined size after grinding.

[0090] In one embodiment of the present invention, the rotational speed of the grinder in the pretreatment process for the shape modification of the porous carbon material may be 10,000 rpm to 25,000 rpm or 15,000 rpm to 20,000 rpm. By the rotational speed of the grinder satisfying the above range, the porous carbon material can be efficiently ground. However, the rotational speed of the grinder is not limited to the above range, and an ordinary technician can adjust the rotational speed of the grinder so that the porous carbon material is ground to an appropriate degree. In a specific embodiment of the present invention, the grinding may be performed using a centrifugal mill, and for example, a ZM-200 device manufactured by RETSCH can be applied.

[0091] In one embodiment of the present invention, the pretreatment process for the shape modification of the porous carbon material includes a process of sieving and classifying the particles with a sieve of 50 μm to 100 μm, 60 μm to 100 μm, or 80 μm size after grinding and centrifugal pulverization at the above speed. Thereby, the porous carbon material is modified so that the particle size becomes small and uniform, the surface roughness of the particles is improved by grinding, and the ratio of the length of the major axis to the length of the minor axis converges to 1.3 or less, specifically 1.

[0092] In one embodiment of the present invention, the particle shape uniformity can be calculated by the following Mathematical Formula 1.

[0093] Particle shape uniformity = [(average diameter of the circumscribed circle of the particle) / (average diameter of the inscribed circle of the particle)]... Mathematical Formula 1 In Mathematical Formula 1, the "circumscribed circle of the particle" means the diameter of a virtual circumscribed circle having the major axis of any particle as the diameter. That is, it means the major axis of the particle.

[0094] In Mathematical Formula 1, the "inscribed circle of the particle" means the diameter of a virtual inscribed circle having the minor axis of any particle as the diameter. That is, it means the minor axis of the particle.

[0095] The particle shape uniformity can be calculated from the average value of the diameters of the circumscribed circles and the average value of the diameters of the inscribed circles of at least 10 particles.

[0096] In one embodiment of the present invention, the diameter of the circumscribed circle and the diameter of the inscribed circle of the particle can be measured through analysis such as an SEM image of the porous carbon material.

[0097] In one embodiment of the present invention, the porous carbon material can be one in which the particle shape is controlled to have a low tap density by the pretreatment method described later.

[0098] In one embodiment of the present invention, the porous carbon material can be produced by pulverizing a porous carbon material as a raw material using a centrifugal pulverizer and sieving the pulverized porous carbon material with a sieve having a target particle size. At this time, the mesh size of the sieve can be 2.8 to 4 times that of the particle size D 50 of the produced porous carbon material, and can be, for example, 50 μm to 100 μm.

[0099] Conventionally, in order to adjust the particle size of a porous carbon material, the porous carbon material has been pulverized using a ball mill or a blade. However, in such a conventional pulverization method, the porous carbon material comes into random contact with the ball or the blade, and a problem of a wide particle size distribution occurs because the porous carbon material having a large particle size and the porous carbon material having a small particle size coexist.

[0100] The present invention can be produced through a step (step 1) of pulverizing the porous carbon material using a centrifugal pulverizer and then (step 2) sieving the pulverized porous carbon material with a sieve.

[0101] In one embodiment of the present invention, step 1 may be pulverization by rotation at an angular velocity of 30 rad / s to 125 rad / s using a centrifugal pulverizer. Specifically, it may be a step of pulverization by rotation at an angular velocity of 30 rad / s to 95 rad / s. When the centrifugal pulverization speed in step 1 is the speed described above, it is advantageous in that while pulverizing the particle size of the porous carbon material to be small, it can be uniformly controlled and the tap density is not increased.

[0102] In one embodiment of the present invention, the centrifugal pulverizer may include a plurality of rotating teeth, and the porous carbon material may be pulverized while the rotating teeth rotate. Specifically, the centrifugal pulverizer 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.

[0103] Also, in one embodiment of the present invention, each of the plurality of rotating teeth may be triangular prism-shaped, and the plurality of rotating teeth may be arranged toward the rotation axis of the centrifugal pulverizer. Specifically, when viewed from above along the rotation axis of the centrifugal pulverizer, the vertical cross-sections of the triangular prisms may be arranged so as to intersect at the center of the centrifugal pulverizer.

[0104] In one embodiment of the present invention, the plurality of the rotating teeth can be made of, for example, stainless steel, titanium, or stainless steel material with a protective coating, but are not limited thereto.

[0105] In one embodiment of the present invention, a centrifuge mill equipped with rotating teeth can be used in the step 1, and for example, a ZM200 device manufactured by RETSCH can be used.

[0106] In one embodiment of the present invention, the centrifugal milling is performed at 6,000 rpm to 18,000 rpm, and the particle size of the porous carbon material can be adjusted within the above range. Specifically, the centrifugal milling can be performed at a speed of 6,000 rpm to 23,000 rpm, specifically 6,000 rpm to 18,000 rpm using a ZM200 device manufactured by RETSCH.

[0107] In one embodiment of the present invention, depending on the size of the centrifuge mill, even at the same rpm, the magnitude of the applied force can vary. Therefore, considering the size of the centrifuge mill, the rpm can be adjusted so that the grinding can be performed at an angular velocity of 30 rad / s to 125 rad / s according to the following formula 2.

[0108] Angular velocity = (RPM × Circumference) / 60 seconds... Formula 2 In Formula 2, "Circumference" indicates the distance traveled during one rotation of one rotating tooth.

[0109] The step 2 is a step of sieving the porous carbon material centrifugally milled in the step 1 with a sieve.

[0110] In one embodiment of the present invention, the sieve is provided in the centrifuge mill and can be provided at the outer edge of the centrifuge mill. Specifically, the sieve can be provided so as to surround a plurality of rotating teeth in the centrifuge mill.

[0111] In one embodiment of the present invention, the sieve may be cylindrical and may be arranged to surround a plurality of the rotating teeth. For example, as viewed from the upper surface of the centrifugal grinder, the shortest distance between the plurality of the rotating teeth and the sieve may be 0.1 mm to 5 mm or 0.5 mm to 2 mm, for example, 1 mm. The sieve may include a mesh having trapezoidal and / or circular holes.

[0112] In one embodiment of the present invention, when the rotating teeth rotate, the porous carbon material is pulverized, and the porous carbon material with the particle size controlled to the target size immediately passes through a sieve located at the outer edge where a series of rotating teeth are arranged under a centrifugal force, thereby solving the problems of further reduction of the particle size and / or surface damage. According to one embodiment of the present invention, by performing stage 1 and stage 2 simultaneously, the particle size is controlled to the target size, and a porous carbon material having a narrow particle size distribution is obtained.

[0113] Thus, in one embodiment of the present invention, it is preferable that stage 2 is performed with a centrifugal force applied to the pulverized porous carbon material.

[0114] Stage 2 is a stage in which the porous carbon material centrifugally pulverized in stage 1 moves to the sieve and is filtered, and stage 1 and stage 2 may be continuous processes performed simultaneously.

[0115] The sieve used in stage 2 can control the particle size of the porous carbon material by adjusting the mesh size. The mesh size of the sieve is 2.8 times to 4 times (2.8 ≤ mesh size / target D 50 (target D 50 ) with respect to 50 ≤ 4), and by limiting the range of the mesh size of the sieve as described above, the particle size D 50 of the target porous carbon material is obtained, and a porous carbon material having a narrow particle size distribution is obtained.

[0116] In one embodiment of the present invention, the particle size D 50 (target D50 ) is, for example, the particle size D of the porous carbon material produced according to an embodiment of the present invention 50 and can be, for example, 10 μm to 100 μm, 5 μm to 90 μm, 10 μm to 80 μm, 15 μm to 70 μm, 20 μm to 60 μm, 10 μm to 50 μm, 15 μm to 40 μm, or 20 μm to 40 μm.

[0117] In a lithium-sulfur battery according to an embodiment of the present invention, the porous carbon material has a tap density when tapped 1,000 times of, for example, 0.1 g / cm 3 or less or less than 0.1 g / cm 3 which is preferable. For example, in an embodiment of the present invention, the tap density of the porous carbon material can be 0.09 g / cm 3 or less. Specifically, the tap density of the porous carbon material can be 0.07 g / cm 3 or less. More specifically, the tap density of the porous carbon material can be 0.02 g / cm 3 to 0.09 g / cm 3 , 0.05 g / cm 3 to 0.09 g / cm 3 , or 0.05 g / cm 3 to 0.07 g / cm 3 and can be. When the tap density of the porous carbon material satisfies the above range, it is possible to increase the content of the sulfur-based material supported on the porous carbon material, improve the porosity of the positive electrode, and provide a lithium-sulfur battery having high energy density and excellent reactivity of the positive electrode, but the present invention is not limited thereto.

[0118] In the present invention, the tap density can be measured according to ASTM B527-06 and can be measured using TAP-2S (manufactured by LOGAN).

[0119] According to an embodiment of the present invention, the porous carbon material with modified shape is spherical particles having a large number of pores formed on the surface, and the particle shape uniformity according to the following mathematical formula 1 can be 1.3 or less. For example, the particle shape uniformity can be 1 to 1.3, 1 to 1.2, or 1 to 1.1.

[0120] Particle shape uniformity = [(average diameter of the circumscribed circle of the particle) / (average diameter of the inscribed circle of the particle)] … Equation 1 In the present specification, the particle shape uniformity can be numerically represented as the ratio of the length of the major axis to the length of the minor axis of the particle, that is, the ratio of the diameter of the circumscribed circle of the particle to the diameter of the inscribed circle of the particle as described above. At this time, the higher the uniformity, the closer the numerical value is to "1", and the lower the uniformity, the more the value deviates from 1.

[0121] In one embodiment of the present invention, the "major axis" means the longest length of the particle, and preferably can be measured by the diameter of the circumscribed circle of the particle. Also, the "minor axis" means the shortest length of the particle, and preferably can be measured by the diameter of the inscribed circle of the particle.

[0122] In the present invention, the length of the major axis (diameter of the circumscribed circle) and the length of the minor axis (diameter of the inscribed circle) of the particle can be measured using an image analysis device such as SEM (scanning electron microscope) or TEM (transmission electron microscope) for the particle, or may be measured by a known method for measuring the size of the particle.

[0123] In one embodiment of the present invention, the particle shape uniformity can be measured by photographing a sheet in which the particles are dispersed and fixed so as to be arranged in parallel to the sheet without piling up from directly above the sheet with a scanning electron microscope (S-4800, manufactured by Hitachi High-Tech Corporation), and analyzing the image with Azo-kun (registered trademark) (manufactured by Asahi Kasei Engineering Co., Ltd.). At this time, the particle shape uniformity of at least 5, at least 10, for example, 10 to 1,000, 100 to 1,000, 10 to 500 or 100 to 500, or 10 particles can be measured, and the average of the measured particle shape uniformities can be used as the particle shape uniformity of the particle. For example, the shape uniformity of 300 particles can be measured, and the average value of the measured particle shape uniformity values can be used as the shape uniformity of the entire particles. However, the number of particles used for measuring the particle shape uniformity is not limited to the above range, and an ordinary technician can select an appropriate number.

[0124] Figures 4a and 4b show SEM images (manufactured by Jeol, magnification of 1,000 times) used to measure the particle shape uniformity of the porous carbon material according to an embodiment of the present invention. According to an embodiment of the present invention, the ratio of the major axis length to the minor axis length of at least 5 particles on the image of the porous carbon material can be measured, and the average value of these can be calculated to calculate the particle shape uniformity.

[0125] In one embodiment of the present invention, the particle size D of the porous carbon material with modified shape 50 can be 120 μm or less, for example, 100 μm or less, 90 μm or less, or 80 μm or less. When the particle size of the porous carbon material satisfies the above range, the uniformity of the electrode surface increases, and the cycle life of the battery can be improved.

[0126] In another embodiment of the present invention, the porous carbon material with modified shape has a broadness factor (BF) of the particle size distribution with respect to the particle size D 10 of the particle size D 90 that can be 7 or less. The BF means the ratio of the particle size distribution of the porous carbon material with respect to the particle size D 10 of the particle size D 90 and can be calculated as [particle size D 90 / particle size D 10 .

[0127] In the present invention, "particle size D 10 " means the particle size at the 10% reference of the volume cumulative particle size distribution of the particles to be measured, "particle size D 50 " means the particle size at the 50% reference of the volume cumulative particle size distribution of the particles to be measured, and "particle size D 90 " means the particle size at the 90% reference of the volume cumulative particle size distribution of the particles to be measured.

[0128] The particle sizes D 10 , D 50 and D 90They can each be measured using the laser diffraction method. For example, after dispersing the particulate powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (for example, Microtrac MT3000), irradiated with ultrasonic waves of approximately 28 kHz at an output of 60 W to obtain a volume cumulative particle size distribution graph, and then measured by determining the particle sizes corresponding to 10%, 50%, and 90% of the volume cumulative distribution.

[0129] By using the porous carbon material as described above, the porosity of the positive electrode according to one embodiment of the present invention can be 80 vol% or more, but the mechanism of the present invention is not limited thereto.

[0130] In one embodiment of the present invention, the porosity of the positive electrode can be, for example, 80 vol% to 90 vol%, specifically 80 vol% to 85 vol%, 81 vol% to 85 vol%, or 82 vol% to 83 vol%. When the porosity of the positive electrode is within the above-described range, it has an advantageous effect in terms of improving the reactivity of the positive electrode, but the present invention is not limited thereto.

[0131] In the present invention, the porosity of the positive electrode can be measured, for example, by the commonly used mercury intrusion method (Hg porosimeter), and can be measured using, for example, a mercury porosimeter (manufactured by Micromeritics, AutoPore V). Further, the porosity of the positive electrode may be measured using the BET (Brunauer - Emmett - Teller) measurement method using an adsorbed gas such as nitrogen commonly used, and can be measured using, for example, an analytical instrument of the BELSORP series manufactured by BEL Japan, such as mini II, but the present invention is not limited thereto. The porosity measured by such a method can mean the total volume of pores formed in the positive electrode. Further, the porosity may be calculated from the true density of the material constituting the positive electrode, the apparent density of the manufactured positive electrode, and the thickness of the positive electrode. Specifically, it can be calculated by the value of [(true density - apparent density) / true density]×100 (%) of the positive electrode.

[0132] Hereinafter, the configuration of the positive electrode of the present invention will be described.

[0133] The sulfur-carbon composite may be simply mixed and compounded with the sulfur-based material and the carbon material, or may be in a coating form or a supported form of a core-shell structure. The coating form of the core-shell structure is a form in which one of the sulfur-based material and the carbon material coats the other, and as an example, the surface of the carbon material may be covered with sulfur or vice versa. Further, the supported form may be a form in which the sulfur-based material is filled inside the carbon material, particularly in the internal pores. The form of the sulfur-carbon composite may be any form as long as it satisfies the content ratio of sulfur and the carbon material described above, and is not limited in the present invention.

[0134] The method for producing the sulfur-carbon composite according to the present invention is not particularly limited and can be produced by a composite method comprising (S1) mixing a porous carbon material and a sulfur-based material and then (S2) compounding.

[0135] The mixing in the step (S1) is for increasing the mixing degree of 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.

[0136] The compounding in the step (S2) is not particularly limited in the present invention and can be performed by a method commonly used in the art. As an example, it can be performed by a method commonly used in the art such as dry compounding or wet compounding such as spray coating. As an example, a method can be used in which the mixture of sulfur and the carbon material obtained by mixing is ball-milled and pulverized, and then left in an oven at 120°C to 160°C for 20 minutes to 1 hour so that the molten sulfur is uniformly coated on the inside and outside of the first carbon material.

[0137] In one embodiment of the present invention, the sulfur-carbon composite can be produced by sequentially mixing a porous carbon material and a sulfur-based material and heat-treating the mixture of the porous carbon material and the sulfur-based material at 120°C, but the production method is not limited thereto.

[0138] In one embodiment of the present invention, the content of the sulfur element (S) in the sulfur-carbon composite can be 60 wt% or more, 70 wt% or more, or 75 wt% or more based on 100 wt% of the sulfur-carbon composite. For example, the content of the sulfur element (S) in the sulfur-carbon composite is preferably 60 wt% to 99 wt%, 65 wt% to 99 wt%, 70 wt% to 99 wt%, 75 wt% to 90 wt%, 70 wt% to 85 wt%, 70 wt% to 80 wt%, or 70 wt% to 75 wt% based on 100 wt% of the sulfur-carbon composite.

[0139] In one embodiment of the present invention, the positive electrode active material layer contains a binder polymer together with the sulfur-carbon composite. Further, the positive electrode active material layer may further contain 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, the positive electrode active material layer preferably contains 70 wt% or more, 85 wt% or more, 90 wt% or more, or 95 wt% or more of the positive electrode active material, specifically the sulfur-carbon composite, based on 100 wt% of the positive electrode active material layer.

[0140] In one embodiment of the present invention, the loading amount of the active material in the positive electrode, specifically the loading amount of sulfur (S), is 2.9 mgs / cm 2 or more, specifically 3.1 mgs / cm 2 or more, but the present invention is not limited thereto. According to one embodiment of the present invention, it is advantageous for realizing a high-loading electrode due to the characteristics of the porous carbon material and the positive electrode described above.

[0141] In one embodiment of the present invention, when converting the loading amount of the positive electrode to volume, for example, the loading amount is 3.5 mAh / cm 2 or more, specifically 3.5 mAh / cm 2~10 mAh / cm 2 , more specifically 3.5 mAh / cm 2 ~5 mAh / cm 2 , or 3.5 mAh / cm 2 ~4.5 mAh / cm 2 It can be, but the present invention is not limited thereto.

[0142] The binder polymer serves to improve the adhesion between the positive electrode active material particles and the adhesive force between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM) rubber, sulfonated-EPDM, styrene butadiene rubber (SBR), fluorine rubber, or various copolymers thereof. Among these, one alone or a mixture of two or more can be used. The binder resin can be contained in an amount of 1 wt% to 30 wt%, preferably 1 wt% to 20 wt%, more preferably 1 wt% to 10 wt% based on the total weight of the positive electrode active material layer.

[0143] The conductive material is used to impart conductivity to the electrode, and can be used without particular limitation as long as it has electron conductivity without causing chemical changes in the battery being formed. 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, thermal 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. One of these alone or a mixture of two or more thereof can be used. When the conductive material is used, the conductive material can usually be contained in an amount of 1 wt% to 30 wt%, preferably 1 wt% to 20 wt%, more preferably 1 wt% to 10 wt% based on the total weight of the positive electrode active material layer.

[0144] In one embodiment of the present invention, as the positive electrode current collector, various positive electrode current collectors used in the art can be used. For example, as the positive electrode current collector, stainless steel, aluminum, nickel, titanium, fired carbon, or those obtained by surface treatment with carbon, nickel, titanium, silver, etc. on the surface of aluminum or stainless steel can be used. The positive electrode current collector can usually have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the positive electrode current collector to enhance the adhesive force of the positive electrode active material. The positive electrode current collector can be used in various forms such as a film, sheet, foil, net, porous body, foam, non-woven fabric body, etc.

[0145] According to another embodiment of the present invention, a lithium-sulfur battery including the above-described positive electrode is provided.

[0146] Specifically, the lithium-sulfur battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and is characterized in that the above-described positive electrode is used as the positive electrode.

[0147] A unit including the positive electrode, negative electrode, and separator is defined as an electrode assembly. The electrode assembly may be laminated, for example, with the separator interposed between the negative electrode and the positive electrode to form a laminated or laminated / folded structure, or wound to form a jelly-roll structure. Further, when a jelly-roll structure is formed, a separator may be further disposed on the outside to prevent contact between the negative electrode and the positive electrode.

[0148] The negative electrode includes a negative electrode current collector and a negative electrode active material layer formed on at least one surface of the negative electrode current collector. The negative electrode active material layer may further include a negative electrode active material, and optionally a conductive material and / or a binder.

[0149] The current collector, active material, conductive material, and binder of the negative electrode can be those commonly used in lithium-sulfur batteries and are not particularly limited in the present invention.

[0150] The separator is disposed within the electrode assembly in a manner interposed between the negative electrode and the positive electrode. The separator can be used without particular limitation as long as it separates the negative electrode and the positive electrode and provides a migration path for lithium ions, such as those commonly used as separators in normal lithium secondary batteries.

[0151] The electrolyte can be various electrolytes usable in lithium-sulfur batteries, such as 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.

[0152] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0153] As the organic solvent, an ether-based solvent may be included in terms of enhancing the charge-discharge performance of the battery. Such ether-based solvents include cyclic ethers (e.g., 1,3-dioxolane, tetrahydrofuran, tetrahydropyran, etc.), linear ether compounds (e.g., 1,2-dimethoxyethane, etc.), and low-viscosity fluorinated ethers (e.g., 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, 1H,1H,2’H,3H-decafluorodipropyl ether, pentafluoroethyl 2,2,2-trifluoroethyl ether, 1H,1H,2’H-perfluorodipropyl ether). A mixture of one or more of these may be included as the non-aqueous solvent.

[0154] In one embodiment of the present invention, the organic solvent may include a mixture of 2-methylfuran and dimethoxyethane. For example, it may include a mixture in which 2-methylfuran and dimethoxyethane are mixed at a volume ratio (v / v) of 1:9 to 5:5, but is not limited thereto.

[0155] The lithium salt can be used without particular limitation as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2, etc. The concentration of the lithium salt may be in the range of 0.1 M to 5.0 M, preferably 0.1 M to 3.0 M. If the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, exhibits excellent electrolyte performance, and lithium ions can move effectively.

[0156] In addition to the constituent components of the electrolyte, the electrolyte may further contain additives for the purpose of improving the life characteristics of the battery, suppressing a decrease in battery capacity, improving the discharge capacity of the battery, and the like. For example, as the additive, a haloalkylene carbonate-based compound such as LiNO3 or difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexamethylphosphoric triamide, nitrobenzene derivative, sulfur, quinoneimine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride, etc. may be used alone or in combination, but is not limited thereto. The additive may be contained in an amount of 0.1 wt% to 10 wt%, preferably 0.1 wt% to 5 wt% based on the total weight of the electrolyte. In one embodiment of the present invention, the additive may contain LiNO3.

[0157] On the other hand, in one embodiment of the present invention, in the lithium-sulfur battery of the present invention, the ratio (El / S) of the total weight of the electrolyte to the total weight of sulfur element (S) in the positive electrode, specifically, the total weight of sulfur element (S) contained in the sulfur-carbon composite in the positive electrode, is preferably, for example, 3.5 g / g or less, 3.3 g / g or less, 3.2 g / g or less, or 3.0 g / g or less. Further, in the lithium-sulfur battery, 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 2.0 g / g to 3.0 g / g, for example, 2.3 g / g. When using the sulfur-carbon composite according to the present invention, a lithium-sulfur battery with an El / S ratio within the above-described range can also be realized, and thereby the effect of improving the energy density can be achieved. However, a lithium-sulfur battery with an El / S ratio higher than the above-described range can also be realized for the lithium-sulfur battery using the sulfur-carbon composite, and the present invention is not limited thereto.

[0158] The shape of the lithium-sulfur battery is not particularly limited and may be various shapes such as cylindrical, laminated, coin-shaped, etc.

[0159] In addition, 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 and large-sized devices that require high-temperature stability, long cycle characteristics, and high capacity characteristics, etc.

[0160] According to an embodiment of the present invention, by using the above-described positive electrode, the lithium-sulfur battery can have a discharge capacity of 1,000 mAh / g or more, s and further 1,100 mAh / g or more, s per unit weight of sulfur (S), but the present invention is not limited thereto.

[0161] According to an embodiment of the present invention, by using the above-described positive electrode, the lithium-sulfur battery can have an energy density of 350 Wh / kg or more, but the present invention is not limited thereto. Specifically, the lithium-sulfur battery can have an energy density of 400 Wh / kg or more or 430 Wh / kg or more, for example, 350 Wh / kg to 500 Wh / kg or 430 Wh / kg to 480 Wh / kg. However, since the higher the energy density of the lithium-sulfur battery, the better the performance of the battery, the upper limit of the energy density is not particularly limited.

[0162] In an embodiment of the present invention, the lithium-sulfur battery can be used not only for small devices such as mobile phones but also for medium and large-sized devices. Examples of the medium and large-sized devices include power tools powered by an electric motor; electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), etc.; electric two-wheel vehicles including electric bicycles (E-bikes) and electric scooters (E-scooters); electric golf carts; power storage systems, etc., but are not limited thereto.

[0163] In one embodiment of the present invention, the lithium-sulfur battery can be a pouch-type, coin-type, or cylindrical lithium-sulfur battery, but the form of the lithium-sulfur battery is not limited thereto.

[0164] Hereinafter, the present invention will be described in more detail with reference to examples. However, the following examples are for illustrative purposes only, and the scope of the present invention is not limited thereto.

[0165] <Manufacture of Lithium-Sulfur Battery> [Example 1] Preparation of Porous Carbon Material Aggregates formed by intertwining a plurality of multi-walled carbon nanotubes (manufactured by Cnano, MWCNT, tap density 0.14 g / cm 3 , particle shape uniformity 1.52) were prepared. Then, the aggregates were pulverized at 18,000 rpm (angular velocity 94.2 rad / s) using a centrifugal pulverizer (ZM-200 manufactured by RETSCH), and then sieved through a sieve with a mesh size of 80 μm to prepare a porous carbon material with a modified shape.

[0166] The modified porous carbon material had a measured tap density of 0.07 g / cm 3 and a measured particle shape uniformity of 1.07.

[0167] At this time, the tap density was measured based on tapping the porous carbon material into a container 1,000 times, and the particle shape uniformity was the ratio of the average diameter of the circumscribed circle to the average diameter of the inscribed circle of 5 particles calculated from the SEM image (Figure 4b) of the porous carbon material, which is the value of [average diameter of circumscribed circle (major axis) / average diameter of inscribed circle (minor axis)]. (Measurement 1: 1.01, Measurement 2: 1.06, Measurement 3: 1.02, Measurement 4: 1.18, Measurement 5: 1.07) Manufacture of Sulfur-Carbon Composite The porous carbon material with the modified shape obtained as described above and sulfur (S8) were uniformly mixed at a weight ratio of 30:70 (CNT:S8). Then, heat treatment was performed in an oven at 155 °C for 30 minutes to impregnate the porous carbon material with sulfur, thereby manufacturing a sulfur-carbon composite.

[0168] Manufacture of the positive electrode The sulfur-carbon composite obtained as described above and polyacrylic acid as a binder polymer were put into water and mixed to produce a positive electrode slurry. At this time, the weight ratio of the sulfur-carbon composite to the binder polymer was 96:4. The solid content in the slurry was 27 wt%.

[0169] The slurry was coated on an aluminum foil (thickness: 20 μm) using a Mathis coater, dried at a temperature of 50 °C for 24 hours, and then rolled to produce a positive electrode. The porosity of the produced positive electrode active material layer was 83 vol%, and the loading amount of the active material was 3.1 mg / cm 2 At this time, the porosity was calculated as the percentage of the value obtained by subtracting the density (apparent density) of the positive electrode active material layer excluding the current collector from the true density of the material constituting the positive electrode active material layer and dividing by the true density.

[0170] Porosity (vol%) = [(true density - apparent density) / true density] × 100 Manufacture of the lithium-sulfur battery A 45-μm-thick lithium metal thin film was prepared as the negative electrode, and a mixed solution in which 3 wt% of LiNO3 and 0.75 M of LiFSI were dissolved in an organic solvent in which 2-methylfuran and dimethoxyethane were mixed at a volume ratio of 3:7 was prepared as the electrolyte.

[0171] The manufactured and prepared positive electrode and negative electrode were placed facing each other, and after interposing a polyethylene separator with a thickness of 16 μm and a porosity of 46 vol% therebetween, the electrolyte was injected so as to be 2.3 times that of the weight of sulfur (S) in the sulfur-carbon composite used for the positive electrode, and a lithium-sulfur battery was manufactured (El / S 2.3 g / g).

[0172] [Example 2] A lithium-sulfur battery was manufactured in the same manner as in Example 1, except that the weight ratio of the porous carbon material to sulfur was changed to 25:75 (CNT:S8) during the production of the sulfur-carbon composite. At this time, the porosity of the positive electrode produced was 82 vol%, and the loading amount of the active material was 3.1 mg / cm 2 .

[0173] [Comparative Example 1] Preparation of Porous Carbon Material An aggregate formed by intertwining a plurality of multi-walled carbon nanotubes (manufactured by Cnano, MWCNT, tap density 0.14 g / cm 3 , particle shape uniformity 1.52) was prepared. Then, the aggregate was jet milled to prepare a carbon nanotube aggregate with a tap density of 0.1 g / cm 3 and a particle shape uniformity of 1.44.

[0174] Manufacture of Sulfur-Carbon Composite The porous carbon material and sulfur obtained as described above were uniformly mixed at a weight ratio of 30:70 (CNT:S8). Then, heat treatment was performed in an oven at 155 °C for 30 minutes to impregnate the porous carbon material with sulfur, thereby manufacturing a sulfur-carbon composite.

[0175] Manufacture of Positive Electrode and Battery A lithium-sulfur battery was manufactured in the same manner as in Example 1, except that the sulfur-carbon composite manufactured as described above was used. At this time, the porosity of the positive electrode produced was 79 vol%, and the loading amount of the active material was 3.1 mg / cm 2 .

[0176] [Comparative Example 2] A lithium-sulfur battery was manufactured in the same manner as in Comparative Example 1, except that the weight ratio of the porous carbon material to sulfur was changed to 25:75 (CNT:S8) during the production of the sulfur-carbon composite. At this time, the porosity of the positive electrode produced was 78 vol%, and the loading amount of the active material was 3.1 mg / cm 2 .

[0177] [Comparative Example 3] A lithium-sulfur battery was manufactured in the same manner as in Comparative Example 1, except that the weight ratio of the porous carbon material to sulfur was changed to 35:65 (CNT:S8) during the production of the sulfur-carbon composite. At this time, the porosity of the produced positive electrode was 80 vol%, and the loading amount of the active material was 3.1 mg / cm 2 was obtained.

[0178] [Comparative Example 4] Preparation of Porous Carbon Material Without any separate pretreatment (grinding), a carbon nanotube aggregate with a tap density of 0.2 / cm 3 and a particle shape uniformity of 1.44 was prepared.

[0179] The SEM image of the porous carbon material is shown in Fig. 4a. The value of [average diameter of the circumscribed circle (major axis) / average diameter of the inscribed circle (minor axis)] of 5 particles was calculated from the image. (Measurement 1: 2.06, Measurement 2: 1.26, Measurement 3: 1.37, Measurement 4: 1.36, Measurement 5: 1.16) Manufacture of Sulfur-Carbon Composite The porous carbon material obtained as described above and sulfur (S8) were uniformly mixed at a weight ratio of 25:75 (CNT:S8). Then, it was heat-treated in an oven at 155 °C for 30 minutes to impregnate the porous carbon material with sulfur, and a sulfur-carbon composite was manufactured.

[0180] Manufacture of Positive Electrode and Battery Next, a lithium-sulfur battery was manufactured in the same manner as in Comparative Example 1, except that the sulfur-carbon composite manufactured as described above was used. At this time, the porosity of the produced positive electrode was 77 vol%, and the loading amount of the active material was 3.1 mg / cm 2 was obtained.

[0181] [Physical Property Evaluation of Lithium-Sulfur Battery] The characteristics of the lithium-sulfur battery manufactured as described above are summarized and shown in Tables 1 and 2 below.

[0182] Tap Density In accordance with the ASTM B527 standard method, after placing the porous carbon material used in the production of the sulfur-carbon composite in a test container and tapping it 1,000 times using a tapping device, the volume (Vomune, V) (cm 3 ) per mass (Mass, M) (g) of the porous carbon material was measured to determine the tap density.

[0183] Tap density (TD) = [M / V] Particle shape uniformity After obtaining a 1,000-fold magnification SEM image (S-4800, manufactured by Hitachi High-Tech Corporation) of the porous carbon material used in the production of the sulfur-carbon composite, the lengths of the major and minor axes of five sulfur-carbon composites were measured from the SEM image to determine the particle shape uniformity. At this time, the major axis is the same as the diameter of the virtual circumscribed circle of the particle, and the minor axis is the same as the diameter of the virtual inscribed circle of the particle.

[0184] Particle shape uniformity = [(diameter of the circumscribed circle of the particle) / (diameter of the inscribed circle of the particle)] Content of sulfur (S8) in the positive electrode active material From the mass of sulfur (S8) used in the production of the sulfur-carbon composite and the mass of the sulfur-carbon composite used in the production of the positive electrode active material layer, the mass of sulfur (S8) with respect to the total weight of the positive electrode active material layer was calculated.

[0185] Porosity For the positive electrode manufactured as described above, it was calculated as the percentage of the value obtained by subtracting the density (apparent density) of the positive electrode active material layer excluding the current collector from the true density of the material constituting the positive electrode active material layer and dividing by the true density.

[0186] Porosity (vol%) = [(true density - apparent density) / true density] × 100 Ratio of the thickness of the positive electrode active material layer to the carbon weight per unit area The ratios based on immediately after manufacturing and based on the battery during driving while repeating charge and discharge were measured respectively.

[0187] First, for a freshly manufactured battery (fresh cell), the thickness of the positive electrode was measured using a thickness measuring instrument (manufactured by Mitutoyo Corporation). The thickness of the current collector was subtracted from the measured thickness to measure the thickness of the positive electrode active material layer. Also, after calculating the carbon weight in the positive electrode active material layer from the composition of the positive electrode used in the manufacturing stage, it was divided by the loading amount of the active material to measure the carbon weight per unit area (1 cm 2 ) of the active material layer (mg / cm 2 ). At this time, the calculated value was mutually verified by measuring the carbon weight by the following method. The current collector was removed from the positive electrode, and the positive electrode active material layer was subjected to ICP-OES (Inductively Coupled Plasma Optical Emission Spectrometry) analysis using an elemental analyzer to measure the carbon weight relative to the total weight of the active material layer. Then, it was divided by the area (cm 2 ) of the positive electrode active material layer to be measured to measure the carbon weight per unit area (1 cm 2 ) of the active material layer (mg / cm 2 ).

[0188] Next, for the battery during operation, in the cycle where the thickness of the positive electrode active material layer becomes minimum while maintaining a capacity of 90% or more of the initial capacity ratio during operation, after measuring the thickness of the positive electrode active material layer in the fully charged (SOC 100%) state, the value of the ratio of the thickness of the positive electrode active material layer to the carbon weight per unit area measured above was calculated.

[0189]

Table 1

[0190]

Table 2

[0191] <Specific Capacity Evaluation of Lithium-Sulfur Battery> Figure 1 is a performance evaluation graph of lithium-sulfur batteries according to Comparative Example 1, Comparative Example 2, and Comparative Example 4, and Figure 2 is a performance evaluation graph of lithium-sulfur batteries according to Example 1, Example 2, and Comparative Example 1.

[0192] The lithium-sulfur batteries manufactured in the examples and comparative examples were discharged at 25°C in the CC (Constant Current) mode at 0.1C (C rate) until a voltage of 1.8V was reached, and then charged at a constant current of 0.1C to 2.5V to measure the discharge capacity. The discharge capacity was measured as the discharge capacity per unit content of sulfur element (S) in the positive electrode (specific capacity, mAh / g(s)).

[0193] Referring to FIG. 1, in a lithium-sulfur battery using a porous carbon material with a high tap density and a low particle shape uniformity as in the prior art, it can be confirmed that when the sulfur content increases, the reactivity decreases and the discharge capacity becomes smaller (Comparative Example 1 and Comparative Example 2). Also, it can be confirmed that the higher the density of the porous carbon material, the lower the reactivity and the smaller the discharge capacity (Comparative Example 1 and Comparative Example 4).

[0194] Referring to FIG. 2, it can be confirmed that a lithium-sulfur battery using a porous carbon material with a low tap density and a high particle shape uniformity through shape modification has improved reactivity compared to a lithium-sulfur battery using a porous carbon material with a high tap density and a low particle shape uniformity, although the sulfur content is the same (Example 1 and Comparative Example 1). Also, when using a porous carbon material with a modified surface, it can be confirmed that the reactivity is maintained even when the sulfur loading increases (Example 1 and Example 2).

[0195] <Comparison of Energy Density> The capacities of the lithium-sulfur batteries according to Example 1, Example 2, and Comparative Examples 1 to 3 were measured. After multiplying the measured capacity by the voltage, the energy density was calculated by dividing by the weight of each lithium-sulfur battery. The results are shown in Table 3 and FIG. 3 below.

[0196] FIG. 3 is a graph relatively showing the energy densities of the lithium-sulfur batteries according to Example 1, Example 2, and Comparative Examples 1 to 3 based on the energy density of Comparative Example 1.

[0197]

Table 3

[0198] In the case of Comparative Examples 1 to 3, which are lithium-sulfur batteries using a porous carbon material with a high tap density and a low particle shape uniformity as in the prior art, it was confirmed that as the sulfur content increased, the reactivity decreased, the discharge capacity decreased, and the energy density was low (Comparative Examples 1 and 2). In Comparative Example 3, although the sulfur loading amount was small and the reactivity was high, it was confirmed that the content of the positive electrode active material was small and the energy density was low.

[0199] On the other hand, it was confirmed that the lithium-sulfur battery according to Example 1 had improved reactivity, an increased discharge capacity, and an increased energy density. In Example 2, although the sulfur content increased compared to Example 1, the discharge capacity did not decrease, so the effect of increasing the energy density was confirmed.

[0200] As described above, although the present invention has been described with reference to the limited embodiments and drawings, the present invention is not limited thereto, and it goes without saying that various modifications and variations can be made within the equivalent scope of the technical idea and the claims of the present invention by those having ordinary knowledge in the technical field to which the present invention pertains.

Claims

1. A positive electrode comprising 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 contains a sulfur-carbon composite and a binder polymer, the sulfur-carbon composite contains a porous carbon material and a sulfur-based material, and a ratio of a thickness of the positive electrode active material layer to a carbon weight per unit area of the positive electrode active material layer is 80 µm / mg or more and 130 µm / mg or less.

2. The positive electrode according to claim 1, wherein a porosity of the positive electrode active material layer is 80 vol% or more.

3. The positive electrode according to claim 1, wherein a content of sulfur element (S) is 60% by weight or more based on a total weight of the positive electrode active material layer.

4. The positive electrode according to claim 1, wherein the porous carbon material is in a shape of angular particles.

5. The porous carbon material is represented by the following formula (1): Particle shape uniformity = [(average diameter of circumscribed circle of particle) / (average diameter of inscribed circle of particle)]... Formula (1) The positive electrode according to claim 1, wherein a particle shape uniformity calculated by the formula (1) is 1.3 or less.

6. The positive electrode according to claim 1, wherein the porous carbon material is manufactured by pulverizing a porous carbon material as a raw material using a centrifugal grinder and sieving the pulverized porous carbon material with a sieve having a mesh size of 50 µm or more and 100 µm or less.

7. The tap density of the porous carbon material is 0.09 g / cm ３ The positive electrode according to claim 1, wherein the tap density is 0.09 g / cm or less.

8. The positive electrode according to claim 1, wherein a porosity of the positive electrode active material layer is 81 vol% or more and 85 vol% or less.

9. The positive electrode according to claim 1, wherein the porous carbon material contains a secondary structure formed by aggregation of a plurality of carbon nanotubes as a primary structure.

10. The tap density of the porous carbon material is 0.07 g / cm ３ The positive electrode according to claim 1, which is as follows.

11. The positive electrode according to claim 1, wherein a content of sulfur element (S) is 65% by weight to 90% by weight based on a total weight of the positive electrode active material layer.

12. The loading amount of sulfur (S) is 2.9 mgs / cm ２ or more, the positive electrode according to claim 1.

13. A lithium-sulfur battery including the positive electrode according to any one of claims 1 to 12, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte.

14. The lithium-sulfur battery according to claim 13, wherein a carbon weight per unit area of the positive electrode active material layer and a thickness of the positive electrode active material layer are each measured after at least one discharge is performed.

15. The lithium-sulfur battery according to claim 13, wherein a carbon weight per unit area of the positive electrode active material layer and a thickness of the positive electrode active material layer are each measured at SOC 97% to 100%.

16. The lithium-sulfur battery according to claim 14, wherein a ratio of a weight of the electrolyte to a weight of sulfur (S) in the sulfur-carbon composite is 3.5 g / g or less.

17. The lithium-sulfur battery according to claim 13, wherein an energy density of the lithium-sulfur battery is 400 Wh / kg or more.

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