Positive electrode for lithium-sulfur batteries and lithium-sulfur batteries with 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 the applications is incorporated herein.

Background Art

[0003] As interest in energy storage technologies increases and the application fields expand to include mobile phones, tablets, laptop computers, and camcorders, as well as 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 rechargeable lithium-sulfur batteries. In the development of such batteries, in recent years, research and development have been conducted on new electrode and battery designs to improve the capacity density and specific energy.

[0004] Among these electrochemical elements, lithium-sulfur (LiS) batteries are attracting attention as a next-generation secondary battery that can replace lithium-ion batteries due to their high energy density. Lithium sulfur is used as the positive electrode active material, and when discharged within a lithium-sulfur battery, a reduction reaction of sulfur and an oxidation reaction of lithium metal occur. At this time, sulfur forms linear lithium polysulfides (Li2S2, Li2S4, Li2S6, Li2S8) from a cyclic structure S8. A characteristic of such lithium-sulfur batteries is that they exhibit a stepwise discharge voltage until the polysulfide (PS) is completely reduced to LiS.

[0005] In lithium-sulfur batteries, using carbon materials with a high specific surface area and high porosity, such as carbon nanotubes, as sulfur carriers can achieve high energy density and lifespan characteristics. However, further research is needed to achieve energy density and lifespan characteristics that are actually commercially viable.

[0006] Therefore, attempts were made to increase the amount of sulfur, which is the positive electrode active material, in order to improve the energy density. However, since sulfur is not conductive, the more sulfur content is increased, the lower the reactivity becomes, and the energy density actually decreases. [Overview of the project] [Problems that the invention aims to solve]

[0007] Therefore, the present invention aims to provide a lithium-sulfur battery with a large sulfur load and high energy density.

[0008] Furthermore, other objects and advantages of the present invention can be realized by means or methods and combinations thereof as set forth in the claims. [Means for solving the problem]

[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 in the first embodiment is, The current collector and the positive electrode active material layer formed on at least one surface of the current collector, The positive electrode active material layer comprises a sulfur-carbon composite and a binder polymer, the sulfur-carbon composite comprises 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 example, in the first example, The porosity of the positive electrode active material layer may be 80 vol% or higher.

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

[0013] According to the fourth example of manifestation, in any one of the first to third examples of manifestation, The porous carbon material may be in the form of angular particles.

[0014] According to the fifth example of manifestation, in any one of the first to fourth examples of manifestation, The porous carbon material may have a particle shape uniformity of 1.3 or less, as shown in the following formula 1.

[0015] Particle shape uniformity = [(average diameter of the circumscribed circle of the particles) / (average diameter of the inscribed circle of the particles)]... Equation 1 According to the sixth example, in any one of the first to fifth examples, The porous carbon material may be manufactured by crushing a porous carbon material as a raw material using a centrifugal mill, and then sieving the crushed porous carbon material with a sieve having a mesh size of 50 μm to 100 μm.

[0016] According to the 7th embodiment example, in any one of the 1st to 6th embodiment examples, The tap density of the porous carbon material is 0.09 g / cm³. 3 The following are possible:

[0017] According to the eighth example of implementation, in any one of the seventh examples of implementation, The porosity of the positive electrode active material layer may be 81 vol% to 85 vol%.

[0018] According to the 9th embodiment example, in any one of the 1st to 8th embodiment examples, The porous carbon material may include a secondary structure formed by the aggregation of multiple carbon nanotubes as a primary structure.

[0019] According to the 10th embodiment, in any one of the 1st to 9th embodiments, The tap density of the porous carbon material is 0.07 g / cm³. 3 The following are possible:

[0020] According to the 11th embodiment, in any one of the 1st to 10th embodiments, The sulfur (S) content can be 65% to 90% by weight based on the total weight of the positive electrode active material layer.

[0021] According to the 12th embodiment, in any one of the 1st to 11th embodiments, The loading amount of sulfur (S) is 2.9 mg s / cm³. 2 It could be any of the above.

[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 13th embodiment example is The invention includes a positive electrode, a negative electrode, a separation membrane 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 14th embodiment example, in the 13th embodiment example, 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 example, in the 13th or 14th example, The carbon weight per unit area of ​​the positive electrode active material layer and the thickness of the positive electrode active material layer may be measured at a State of Charge (SOC) of 97% to 100%.

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

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

[0028] According to one aspect of the present invention, a positive electrode for a lithium-sulfur battery with a large amount of sulfur supported as the positive electrode active material, and a lithium-sulfur battery containing said 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 the positive electrode active material. [Brief explanation of the drawing]

[0029] [Figure 1] This graph shows the specific capacity of lithium-sulfur batteries according to Comparative Examples 1, 2, and 4 described herein. [Figure 2] This graph shows the specific capacity of lithium-sulfur batteries according to Comparative Example 1, Example 1, and Example 2 in this specification. [Figure 3]This graph shows the relative energy density of lithium-sulfur batteries according to Example 1, Example 2, and Comparative Examples 1 to 3 as described herein. [Figure 4a] This is an SEM image of the porous carbon material used to measure the particle shape uniformity of the porous carbon material used in Comparative Example 4 of this specification. The intersecting arrows in the image indicate the major and minor axes used for length measurement, respectively. [Figure 4b] This is an SEM image of the porous carbon material used to measure the particle shape uniformity of the porous carbon material used in Example 1 of this specification. The intersecting arrows in the image indicate the major and minor axes used for length measurement, respectively. [Figure 5] The left image shows that the surface of the porous carbon material of Comparative Example 1 is relatively flat, and the right image shows that the surface of the porous carbon material of Example 1 is relatively rough. [Modes for carrying out the invention]

[0030] The present invention will be described in detail below.

[0031] Throughout this specification, when a part "includes," "has," or "companies" a component, unless otherwise specified, it does not exclude other components, but rather means that it may further include other components.

[0032] Furthermore, terms such as “about” and “substantially” used throughout this specification are used in the sense of, or nearly the same as, the manufacturing and material tolerances inherent to the meanings referred to, to help the understanding of this application. This is to prevent unscrupulous infringers from unfairly using disclosures that refer to precise or absolute numerical values.

[0033] Throughout this specification, the phrase "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, specifically, it can be calculated from the amount of nitrogen gas adsorbed 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 measurement target particles, "particle size D 50 " means the particle size at the 50% reference of the volume cumulative particle size distribution of the measurement target particles, and "particle size D 90 " means the particle size at the 90% reference of the volume cumulative particle size distribution of the measurement target particles.

[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 measurement target particle powder 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 to measure. That is, for example, the average particle size D 50The particle distribution graph shows the median value or median diameter, representing the particle size at the 50% point of the cumulative distribution. Particle size is the diameter of the particle, and particle diameter refers to the longest length within the particle.

[0039] The unit used herein is "mAh / g". s Unless otherwise specified, mAh / g(s) is used to indicate the volume per unit weight of sulfur (S) and may be used interchangeably with other expressions such as mAh / g(s) and mAh / gs.

[0040] The unit used herein is "mg" s / cm 2 Unless otherwise specified, "mg(s) / cm²" indicates the weight of sulfur (S) per unit area. 2 It can be used in combination with other expression methods such as mAh / gs.

[0041] As used herein, the term "porosity" refers to the ratio of the volume occupied by pores to the total volume of a structure, using vol% as the unit, and is interchangeable with terms such as void ratio and porosity. The porosity may be measured by the method of ISO 15901:2019, which is known in the art.

[0042] The present invention provides a positive electrode for use 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, this 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. Examples of lithium-ion secondary batteries include lithium-metal batteries, lithium-sulfur batteries, all-solid-state batteries, and lithium polymer batteries, with lithium-sulfur batteries being preferred.

[0043] Conventional lithium-sulfur batteries have been criticized for their low energy density. While relatively high energy density and lifespan characteristics have been achieved by using carbon materials with high specific surface area and porosity, such as carbon nanotubes, as supports for sulfur-based materials, this has not yet reached a level suitable for commercialization. Furthermore, increasing the energy density of lithium-sulfur batteries requires increasing the amount of sulfur-based material supported in the sulfur-carbon composite within the positive electrode. However, because sulfur-based materials have little to no conductivity, increasing the amount actually decreases the reactivity of the positive electrode.

[0044] According to one embodiment of the present invention, a positive electrode with improved electrical conductivity and a lithium-sulfur battery with improved energy density are provided by supporting a sulfur-based material, such as sulfur (S8) or a sulfur compound, on a porous carbon material whose shape has been modified to increase the loading rate of sulfur-based materials, such as sulfur (S8) or a sulfur compound, while also improving the electrical conductivity within the positive electrode.

[0045] A positive electrode according to one embodiment of the present invention includes a current collector and a positive electrode active material layer formed on at least one surface of the current collector. Specifically, the positive electrode active material layer includes a sulfur-carbon composite and a binder polymer. The sulfur-carbon composite also includes a porous carbon material and a sulfur-based material.

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

[0047] In one embodiment of the present invention, the porous carbon material contains irregular pores inside the particles (closed pores) and / or on the surface of the particles (open pores). In this case, 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 known methods 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 later.

[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 part of the interior and exterior surfaces of the pores of the porous carbon material. Alternatively, the sulfur-carbon composite may be provided in a form in which the sulfur-based material covers all or at least part of the interior and exterior surfaces of the pores of the porous carbon material.

[0050] In one embodiment of the present invention, the positive electrode contains a porous carbon material as a support for the active material, resulting in a low tap density, which enables the realization of high porosity. In particular, by supporting the active material on the porous carbon material described above, even with a high content of the active material, sufficient pathways for the movement of ions and other substances within the positive electrode are ensured, resulting in low resistance and improved capacity.

[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 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 the sulfur element (S) content is 60% by weight or more, specifically 65 wt% or more, based on the total weight of the active material layer. In this case, the sulfur element (S) is derived from the sulfur-based material and may be derived from inorganic sulfur (S8) used in the production of sulfur-carbon composites.

[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 sulfur element (S) content is 60% by weight or more, specifically 65 wt% or more, and the porosity is 80 vol% or more.

[0055] In other words, according to one embodiment of the present invention, by using a porous carbon material with a modified shape, it is possible not only to increase the loading amount of active material within the positive electrode active material, but also to ensure the porosity of the positive electrode.

[0056] Sulfur-based materials used as active materials in lithium-sulfur batteries, such as inorganic sulfur (S8), are insulators. Therefore, in conventional lithium-sulfur batteries, if the amount of active material, i.e., sulfur-based material, in the positive electrode active material layer is excessively high, the resistance within the positive electrode increases, resulting in reduced reactivity of the positive electrode. Consequently, it is difficult to include more than 60 wt% of sulfur-based material in the total 100 wt% of the positive electrode active material layer. Specifically, it is difficult to achieve a sulfur element (S) content of more than 60 wt% based on the total 100 wt% of the positive electrode active material layer.

[0057] However, the present invention makes it possible to provide a positive electrode with improved reactivity while increasing the active material (i.e., sulfur-based material) content 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" refers to 1 cm². 2 This means (1cm x 1cm).

[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 is such that the thickness of the positive electrode active material layer is equal to the carbon weight per unit area of ​​the positive electrode active material layer. 2 This can be calculated by measuring the carbon weight per unit area and 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 may be measured based on the positive electrode immediately after manufacture (un-used fresh cell), when it has not been used in an electrochemical reaction. Alternatively, the carbon weight per unit area of ​​the positive electrode active material layer and the thickness of the positive electrode active material layer may be measured after the electrode has discharged at least once. In this case, it is preferable that the electrode has a capacity retention rate of 97% or more of its 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 for accuracy. For example, it can be measured based on the state of charge (SOC) of 97% or higher, for example, SOC 97% to 100%, specifically SOC 100%, after being discharged at least once and then charged. 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 positive electrode active material layer is thinnest.

[0062] In one embodiment of the present invention, the ratio of the thickness of the positive electrode active material layer to the weight of carbon per unit area of ​​the positive electrode active material layer can be calculated using the weight of carbon per electrode loading and the measured thickness of the positive electrode active material layer. Here, the electrode loading can be calculated from the sulfur (S) content 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, the method of directly analyzing the carbon content per unit area includes, for example, known elemental analysis methods such as ICP-OES analysis, EA analysis, and ICP analysis, but the measurement method is not limited to these. Furthermore, the method of measuring the thickness of the electrode may 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 determine the thickness of the positive electrode active material layer, but the measurement method is not limited to these.

[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, and carbon derived from the binder and / or 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, if 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 lithium-sulfur batteries, the thickness of the positive electrode can change as the battery is repeatedly charged and 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 regarding the number of charge / discharge cycles and / or state of charge (SOC) may be necessary. During battery discharge, discharge products are generated within the structure of the porous carbon material present in the positive electrode active material layer, and it may be difficult to accurately measure the thickness of the positive electrode unless such discharge products are removed. Therefore, the thickness of the positive electrode active material layer may 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, a positive electrode satisfying 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 being 80 μm / mg to 130 μm / mg may, for example, have a sulfur element (S) content of 65 wt% or more based on 100 wt% of the total positive electrode active material layer, and a porosity of 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. Furthermore, using the electrode immediately after manufacturing as a reference, 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, the sulfur-based material can be any substance capable of providing sulfur (S8) as an active material for a lithium-sulfur battery, without any particular limitations. 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), organosulfur compounds such as 2,5-dimercapto-1,3,4-thiadiazole and 1,3,5-trithiocyanuric acid, carbon-sulfur polymers ((C2S x ) n It may include x = 2.5 to 50, n ≥ 2, or 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 may be included by physical adsorption with the porous carbon material, or by chemical bonding such as covalent bonds or van der Waals bonds between the sulfur element (S) and the carbon in the porous carbon material. In particular, the sulfur-based material may be chemically bonded to the surface of the porous carbon material to form a composite.

[0072] In the sulfur-carbon composite according to the present invention, the sulfur-based material is located on at least one surface of the pores of the carbon material, both internally and externally, and can be present in a region of less than 100%, preferably 1% to 95%, and more preferably 60% to 90%, of the total internal and external surface of the carbon material. When the sulfur (S) is present on the surface of the carbon material within the above range, the maximum effect can be achieved in terms of electron transfer area and electrolyte wettability. Specifically, because the sulfur is thinly and uniformly impregnated into the surface of the carbon material within the above range, the electron transfer contact area can be increased during the charge and discharge process. If the sulfur is located in a region of 100% of the total surface of the carbon material, the carbon material will be completely covered with sulfur, reducing the wettability of the electrolyte and decreasing contact with the conductive material contained in the electrode, preventing electron transfer and preventing participation in the reaction.

[0073] In one embodiment of the present invention, the content of sulfur element (S) may be 60 wt% or more, 65 wt% or more, based on 100 wt% of the total positive electrode active material layer, 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%. For example, the content of sulfur element (S) may be 67.2 wt% to 72 wt% based on 100 wt% of the total positive electrode active material layer. If the content of sulfur element (S) is within the above range, it will have advantageous effects not only in terms of improving the capacity of the battery but also in terms of the stability of the battery, but the present invention is not limited thereto.

[0074] In one embodiment of the present invention, the porous carbon material may have a shape that is a modified version of a conventional porous carbon material used in lithium-sulfur batteries. Specifically, the porous carbon material has a granular shape, and may be particularly angular. For example, the porous carbon material may be granular with prismoidal sphericity.

[0075] As will be described later, the porous carbon material may be one whose particle shape has been modified using a centrifugal grinder.

[0076] Referring to Figure 5, it can be seen that the surface of the porous carbon material pulverized by a jet mill (left side) is relatively flat, while the surface of the porous carbon material pulverized by a centrifugal mill (right side) is relatively rough. The porous carbon material on the right side can be seen to have angular particles due to its rough surface characteristics.

[0077] Specifically, the porous carbon material may include one or more carbon-based substances having porosity and conductivity that are commonly used in the industry. For example, it may include graphite; graphene; carbon blacks such as Denka Black, Acetylene Black, Ketjen Black, Channel Black, Furnace Black, Lamp Black, and Thermal 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); graphite such as natural graphite, artificial graphite, and expanded graphite; carbon nanoribbons; carbon nanobelts, carbon nanorods, and activated carbon (activateDcarbon).

[0078] In one embodiment of the present invention, the porous carbon material may include carbon nanotubes. The carbon nanotubes are composed of hexagonally linked carbon atoms forming a tubular pattern. According to one embodiment of the present invention, the carbon nanotubes may be single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), or a combination thereof, depending on the number of carbon atom layers (also referred to as "carbon walls") that constitute them. Here, the length of the individual carbon nanotubes is not particularly limited.

[0079] In one embodiment of the present invention, the porous carbon material may contain carbon nanotubes in order to improve the sulfur loading rate, and specifically may contain multi-walled carbon nanotubes (MWCNTs), 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 the 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 tightly intertwined with each other due to cohesive forces 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 in which they exist as single tubes in a dispersion medium or the like, or they may be provided in the form of a secondary structure in which the primary carbon nanotubes aggregate with each other.

[0082] From this perspective, if the porous carbon material contains carbon nanotubes, the carbon nanotubes may contain bundled secondary structures, entangled secondary structures, or both.

[0083] The aforementioned bundled secondary structure of carbon nanotubes is a form in which a single carbon nanotube is used as the primary structure, and multiple such primary structures are oriented in the longitudinal direction of the carbon nanotube by cohesive forces between carbon atoms, and are solidified together. It can also be called a bundled CNT (bundled CNT).

[0084] In one embodiment of the present invention, the carbon nanotube may include, for example, an entangled multilayer carbon nanotube (Entagled MWCNT).

[0085] In one embodiment of the present invention, the porous carbon material has a BET specific surface area of, for example, 150 m². 2 It may be more than / g. In one embodiment of the present invention, the BET specific surface area of ​​the porous carbon material is, for example, 150m². 2 / g~2,500m 2 / g, 150m 2 / g~2,000m 2 / g, 150m 2 / g~1,500m 2 / g, 150m 2 / g~1,000m 2 / g, 130m 2 / g~300m 2 / g, or 170m 2 / g~200m 2 It may be, but is not limited to, / g. In this invention, the "specific surface area" is measured by the BET method, and specifically can be calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77K) using BELSORP-mini II manufactured by BEL Japan.

[0086] According to one embodiment of the present invention, the porous carbon material may be one whose shape has been modified by grinding. Specifically, the grinding may involve finely crushing or shearing the particles. For example, particles may be broken or scraped off when held between two blades. When particles are ground, the outer surface of the particles is stimulated, causing them to break or be scraped off. Also, when particles are ground, friction occurs between the rotating blades of the grinder and the particles, which may cause the particles to be torn or made coarser.

[0087] Generally, carbon nanotubes such as single-walled carbon nanotubes (SWCNTs) or multi-walled carbon nanotubes (MWCNTs) are synthesized by thermochemical vapor deposition (VMP) or arc discharge, but aggregation occurs between carbon nanotube particles during the synthesis process. This aggregation can be divided into two types: physical aggregation, where nanotubes intertwine with other particles as individual particles at the μm level, and chemical aggregation, where, as in the case of single-walled carbon nanotubes (SWCNTs), aggregation occurs at the nm level due to surface attractive forces such as van der Waals forces (~950 meV / nm), which are intermolecular forces. Such aggregation of carbon nanotubes may hinder the formation of a three-dimensional network structure that improves mechanical strength and electrical conductivity. This aggregation phenomenon is common to linear conductive carbon materials such as carbon nanotubes. Therefore, in this invention, the linear conductive carbon material is crushed by pretreatment such as grinding before being introduced into electrode manufacturing, thereby satisfying the predetermined tap density range described later and improving the packing rate of sulfur-based material.

[0088] Conventional porous carbon materials for lithium-sulfur batteries are used after pretreatment with a jet mill. However, when porous carbon materials are pretreated with a jet mill, the low particle shape uniformity and smooth particle surface of the porous carbon material result in insufficient improvement of tap density. However, in the present invention, by pretreating the porous carbon material using a grinder, defects are created in each conductive carbon material located on the surface of the porous carbon material (for example, by tearing), creating gaps or roughness between the conductive carbon materials. This improves the particle surface roughness while further increasing the particle shape uniformity of the porous carbon material, thereby further increasing the sulfur loading rate and further improving the tap density. However, the present invention is not limited to this.

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

[0090] In one embodiment of the present invention, the rotational speed of the grinder during the pretreatment process for modifying the shape of the porous carbon material may be 10,000 rpm to 25,000 rpm or 15,000 rpm to 20,000 rpm. By satisfying the above range of rotational speed of the grinder, 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 grinder, for example, a ZM-200 device manufactured by Lechner may be used.

[0091] In one embodiment of the present invention, the pretreatment process for modifying the shape of the porous carbon material may include grinding at the above speed and centrifugal grinding, followed by a process of sieving and classifying the particles using sieves of 50 μm to 100 μm, 60 μm to 100 μm, or 80 μm size. As a result, the porous carbon material is modified to have smaller and more uniform particle sizes, the surface roughness of the particles is improved by grinding, and the shape is modified so that the ratio of the length of the long axis to the length of the short axis converges to 1.3 or less, specifically to 1.

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

[0093] Particle shape uniformity = [(average diameter of the circumscribed circle of the particles) / (average diameter of the inscribed circle of the particles)]... Equation 1 In Equation 1, the "circumscribed circle of the particle" refers to the diameter of a hypothetical circumscribed circle whose diameter is the major axis of any particle. In other words, it refers to the major axis of the particle.

[0094] In Equation 1, the "inscribed circle of the particle" refers to the diameter of a hypothetical inscribed circle whose diameter is the minor axis of any particle. In other words, it refers to the minor axis of the particle.

[0095] The aforementioned particle shape uniformity can be calculated from the average value of the circumcircle diameters and the average value of the incircle diameters of a minimum of 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 may be measured by analysis such as SEM imaging of the porous carbon material.

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

[0098] In one embodiment of the present invention, the porous carbon material may be manufactured by crushing a porous carbon material as a raw material using a centrifugal mill, and then sieving the crushed porous carbon material with a sieve of a desired particle size. In this case, the mesh size of the sieve is the particle size D of the manufactured porous carbon material. 50 This can be 2.8 to 4 times larger in comparison, for example, 50 μm to 100 μm.

[0099] Conventionally, porous carbon materials are ground using ball mills or blades to adjust their particle size. However, this conventional grinding method has the problem of a wide particle size distribution, as the porous carbon material comes into random contact with the balls or blades, resulting in the coexistence of large and small particle sizes.

[0100] The present invention may be manufactured by first crushing the porous carbon material using a centrifugal mill (step 1), and then sieving the crushed porous carbon material with a sieve (step 2).

[0101] In one embodiment of the present invention, step 1 is performed using a centrifugal grinder 30 m / s ~125 m / s of linear velocity ( linear It may be a device that rotates at a velocity to pulverize. Specifically, 30 m / s ~95 m / s of linear velocity This can be a stage in which the material is rotated and crushed. When the centrifugal crushing speed in step 1 is the speed described above, it is advantageous in that it uniformly controls the particle size of the porous carbon material while crushing it to a small size, and does not increase the tap density.

[0102] In one embodiment of the present invention, the centrifugal grinder may be equipped with a plurality of rotating teeth, which pulverize a porous carbon material while rotating. Specifically, the centrifugal grinder may be equipped with, for example, 2 to 20, 4 to 18, 6 to 16, 8 to 14, 10 to 14, or 10 to 12 rotating teeth.

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

[0104] In one embodiment of the present invention, the plurality of rotating teeth may be, but are not limited to, stainless steel, titanium, or stainless steel with a protective coating.

[0105] In one embodiment of the present invention, a centrifugal grinder equipped with rotating teeth may be used in step 1, for example, a ZM200 device manufactured by Lechner may be used.

[0106] In one embodiment of the present invention, the centrifugal grinding is performed at a speed of 6,000 rpm to 18,000 rpm, and the particle size of the porous carbon material can be adjusted within this range. Specifically, the centrifugal grinding 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 apparatus manufactured by Lechner.

[0107] In one embodiment of the present invention, the magnitude of the force applied may change even at the same rpm depending on the size of the centrifugal grinder, so taking the size of the centrifugal grinder into consideration, 30 is calculated using the following formula 2. m / s ~125 m / s of linear velocity The rpm can be adjusted so that it can be ground.

[0108] linear velocity =(RPM × circumference) / 60 seconds … Formula 2

[0109] Step 2 is the step of sieving the porous carbon material that was centrifuged in Step 1 using a sieve.

[0110] In one embodiment of the present invention, the sieve is provided in a centrifugal grinder and may be provided on the outer edge of the centrifugal grinder. Specifically, the sieve may be provided so as to surround a plurality of rotating teeth inside the centrifugal grinder.

[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 top surface of the centrifugal grinder, the shortest distance between the plurality of 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, the porous carbon material is crushed by the rotation of the rotating teeth, and the porous carbon material, whose particle size is controlled to a desired size, immediately passes through a sieve located on the outer edge where a series of rotating teeth are arranged under centrifugal force, thereby solving the problem of further reduction in particle size and / or surface damage. According to one embodiment of the present invention, by performing steps 1 and 2 simultaneously, a porous carbon material is obtained in which the particle size is controlled to a desired size and has a narrow distribution of particle sizes.

[0113] Thus, in one embodiment of the present invention, it is preferable that step 2 is performed while centrifugal force is applied to the crushed porous carbon material.

[0114] Step 2 is a step in which the porous carbon material that was centrifuged in Step 1 is moved to a sieve and filtered, and Steps 1 and 2 may be a continuous process that is performed simultaneously.

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

[0116] In one embodiment of the present invention, the particle size D of the target porous carbon material 50 (Target D)50 ) is, for example, the particle size D of a porous carbon material manufactured by one embodiment of the present invention. 50 These 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 one embodiment of the present invention, the porous carbon material has a tap density of, for example, 0.1 g / cm³ after 1,000 taps. 3 The following or 0.1 g / cm³ 3 It is preferable that it be less than 0.09 g / cm³. For example, in one embodiment of the present invention, the tap density of the porous carbon material is 0.09 g / cm³. 3 The following is possible. Specifically, the tap density of the porous carbon material is 0.07 g / cm³. 3 The following may be true. More specifically, the tap density of the porous carbon material is 0.02 g / cm³. 3 ~0.09 g / cm³ 3 , 0.05 g / cm³ 3 ~0.09 g / cm³ 3 , or 0.05 g / cm³ 3 ~0.07 g / cm³ 3 This is possible. If the tap density of the porous carbon material satisfies the above range, the content of the sulfur-based material supported on the porous carbon material can be increased, improving the porosity of the positive electrode and providing a lithium-sulfur battery with high energy density and excellent reactivity of the positive electrode; however, the present invention is not limited thereto.

[0118] In this invention, tap density can be measured in accordance with ASTM B527-06 and may be measured using TAP-2S (manufactured by LOGAN).

[0119] According to one embodiment of the present invention, the modified porous carbon material is a spherical particle with numerous pores formed on its surface, and the particle shape uniformity according to the following formula 1 may be 1.3 or less. For example, the particle shape uniformity may 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 particles) / (average diameter of the inscribed circle of the particles)] ... Equation 1 In this specification, the particle shape uniformity can be expressed numerically 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 circumcircle of the particle to the diameter of the incircle of the particle, in which case the higher the uniformity, the closer the numerical value will be to "1", and the lower the uniformity, the further the value will be from 1.

[0121] In one embodiment of the present invention, the "major axis" refers to the longest length of the particle, which is preferably measured by the diameter of the circumcircle of the particle. The "minor axis" refers to the shortest length of the particle, which is preferably measured by the diameter of the incircle 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 may be measured using an image analysis device such as an SEM (scanning electron microscope) or TEM (transmission electron microscope), respectively, or they may be measured by known methods for measuring particle size.

[0123] In one embodiment of the present invention, the particle shape uniformity can be measured by photographing a sheet, in which particles are dispersed and fixed so as to be arranged parallel to the sheet without accumulating, from directly above the sheet using 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 Corporation). In this case, the particle shape uniformity of a minimum of 5 particles, a minimum of 10 particles, for example, 10 to 1,000 particles, 100 to 1,000 particles, 10 to 500 particles, or 100 to 500 particles, or 10 particles, can be measured, and the average of the measured particle shape uniformity values ​​can be taken as the particle shape uniformity of the entire particle. For example, the shape uniformity of 300 particles can be measured, and the average of the measured particle shape uniformity values ​​can be taken as the shape uniformity of the entire particle. However, the number of particles used to measure the particle shape uniformity is not limited to the above range, and an appropriate number can be selected by an ordinary technician.

[0124] Figures 4a and 4b show SEM images (Jeol, 1,000x magnification) used to measure the particle shape uniformity of a porous carbon material according to one embodiment of the present invention. According to one embodiment of the present invention, the ratio of the length of the major axis to the length of the minor axis of a minimum of five particles on the image of the porous carbon material can be measured, and the average value of these can be calculated to determine the particle shape uniformity.

[0125] In one embodiment of the present invention, the particle size D of a porous carbon material whose shape has been modified. 50 The particle size may 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 battery cycle life can be improved.

[0126] In another embodiment of the present invention, the porous carbon material with modified shape has a particle size D 10 Particle size D 90 The ratio of the particle size distribution (Broadness Factor, BF) may be 7 or less. The BF is the particle size D of the porous carbon material. 10 Particle size D 90 This refers to the ratio of particle size distributions, [particle size D 90 / particle size D 10 It can be calculated using ].

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

[0128] The particle size D 10 , D 50 and D 90Each of these can be measured using the laser diffraction method. For example, the particle size can be measured by dispersing the target particle powder in a dispersion medium, introducing it into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT3000), irradiating it with ultrasound at approximately 28 kHz at an output of 60 W to obtain a volume cumulative particle size distribution graph, and then determining the particle sizes corresponding to 10%, 50%, and 90% of the volume cumulative distribution, respectively.

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

[0130] In one embodiment of the present invention, the porosity of the positive electrode may 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%. While having the porosity of the positive electrode within the above range provides advantageous effects in terms of improving the reactivity of the positive electrode, 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 a mercury porosimeter (Micromeristics, AutoPore V). Alternatively, the porosity of the positive electrode may be measured using the BET (Brunauer-Emmett-Teller) measurement method using an adsorbed gas such as nitrogen, and can be measured using an analytical instrument from the BELSORP series manufactured by BEL Japan, such as the mini II, but the present invention is not limited thereto. The porosity measured by such methods may represent the total volume of pores formed in the positive electrode. Alternatively, 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 as the value of [(true density - apparent density) / true density] × 100 (%) for the positive electrode.

[0132] The configuration of the positive electrode of the present invention will be described below.

[0133] The sulfur-carbon composite may be formed by simply mixing the sulfur-based material and the carbon material, or it may be in the form of a core-shell coating or supported structure. The core-shell coating structure is a form in which one of the sulfur-based material and the carbon material coats the other, for example, the surface of the carbon material may be covered with sulfur or vice versa. The supported structure may be a form in which the sulfur-based material fills the interior of the carbon material, particularly the pores inside. The form of the sulfur-carbon composite may be any form as long as it satisfies the above-mentioned sulfur-to-carbon material content ratio, and is not limited in this invention.

[0134] The method for producing the sulfur-carbon composite according to the present invention is not particularly limited and may be produced by a composite method commonly known in the art, which consists of (S1) mixing a porous carbon material and a sulfur-based material, and (S2) compounding them.

[0135] The mixing in step (S1) is intended to increase the degree of mixing between the sulfur-based material and the porous carbon material, and can be carried out using a stirring device commonly used in this industry. 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 step (S2) is not particularly limited in the present invention and can be carried out by methods commonly used in the industry. For example, it can be carried out by methods commonly used in the industry, such as dry compounding or wet compounding such as spray coating. For example, a method can be used in which the mixture of sulfur and carbon material obtained by mixing is ball-milled 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 surface 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 then 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 sulfur-carbon composite may have a sulfur element (S) content of 60 wt% or more, 70 wt% or more, or 75 wt% or more relative to 100 wt% of the sulfur-carbon composite. For example, it is preferable that the sulfur element (S) content of the sulfur-carbon composite is 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% relative to 100 wt% of the sulfur-carbon composite.

[0139] In one embodiment of the present invention, the positive electrode active material layer includes a binder polymer together with the sulfur-carbon composite. In addition, 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. In this embodiment of the present invention, it is preferable that the positive electrode active material layer 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, per 100 wt% of the positive electrode active material layer.

[0140] In one embodiment of the present invention, the positive electrode has a loading amount of active material, specifically a loading amount of sulfur (S), of 2.9 mg s / cm³. 2 Specifically, the above is 3.1 mg s / cm³. 2 The present invention may be limited to the above. According to one embodiment of the present invention, the characteristics of the porous carbon material and the cathode described above are advantageous for realizing a high-loading electrode.

[0141] In one embodiment of the present invention, when the loading amount of the positive electrode is converted to capacity, for example, the loading amount is 3.5 mAh / cm². 2 Specifically, 3.5mAh / cm² 2~10mAh / cm 2 More specifically, 3.5mAh / cm² 2 ~5mAh / cm 2 , or 3.5mAh / cm² 2 ~4.5mAh / cm 2 This is possible, but the present invention is not limited thereto.

[0142] The binder polymer plays a role in improving the adhesion between positive electrode active material particles and the adhesion 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, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM) rubber, sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one or more of these may be used individually or in mixtures of two or more. The binder resin may be included in an amount of 1 wt% to 30 wt%, preferably 1 wt% to 20 wt%, and more preferably 1 wt% to 10 wt%, relative to the total weight of the positive electrode active material layer.

[0143] The conductive material is used to impart conductivity to the electrodes and is not particularly limited as long as it does not cause chemical changes to the battery and has electronic conductivity. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, and carbon nanotubes; 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 or more of these may be used individually or in mixtures of two or more. When the conductive material is used, it is usually included in an amount of 1 wt% to 30 wt%, preferably 1 wt% to 20 wt%, and more preferably 1 wt% to 10 wt%, relative to the total weight of the positive electrode active material layer.

[0144] In one embodiment of the present invention, various positive electrode current collectors used in the art may be used as the positive electrode current collector. For example, the positive electrode current collector may be stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. The positive electrode current collector may typically 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 increase the adhesion strength of the positive electrode active material. The positive electrode current collector may be used in various forms such as film, sheet, foil, net, porous body, foam, nonwoven fabric, 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 comprises a positive electrode, a negative electrode, a separation membrane interposed between the positive electrode and the negative electrode, and an electrolyte, and is characterized in that the positive electrode is the positive electrode described above.

[0147] The unit comprising the positive electrode, negative electrode, and separator membrane is defined as an electrode assembly, which can be formed by stacking the electrode assemblies with the separator membrane interposed between the negative electrode and the positive electrode to form a stacked or stacked / folded structure, or by winding them up to form a jelly roll structure. Furthermore, when a jelly roll structure is formed, an additional separator membrane may be placed on the outside to prevent contact between the negative electrode and the positive electrode.

[0148] The negative electrode comprises 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 comprise 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 this invention.

[0150] The separation membrane is positioned within the electrode assembly, interposed between the negative electrode and the positive electrode. The separation membrane separates the negative electrode and the positive electrode and provides a pathway for lithium ions to move. Therefore, any separation membrane commonly used in lithium-ion secondary batteries can be used without any particular limitations.

[0151] The electrolyte can be a variety of electrolytes usable in lithium-sulfur 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.

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

[0153] The aforementioned organic solvent may include ether-based solvents in order to improve the charge and discharge performance of the battery. Examples of such ether-based solvents include cyclic ethers (e.g., 1,3-dioxolane, tetrahydrofuran, tetrohydropyran, etc.), linear ether compounds (e.g., 1,2-dimethoxyethane, etc.), and low-viscosity fluoride ethers (e.g., 1H,1H,2'H,3H-decafluorodipropyl ether, difluoromethyl 2,2,2-trifluoroethyl ether, 1,2,2,2-tetrafluoroethyltrifluoromethyl ether, 1,1,2,3,3,3-hexafluoropropyldifluoromethyl ether, 1H,1H,2'H,3H-decafluorodipropyl ether, pentafluoroethyl 2,2,2-trifluoroethyl ether, 1H,1H,2'H-perfluorodipropyl ether), and a mixture of one or more of these may be included as a non-aqueous solvent.

[0154] In one embodiment of the present invention, the organic solvent may include a mixture of 2-methylfuran and dimethoxyethane, for example, a mixture of 2-methylfuran and dimethoxyethane in a volume ratio (v / v) of 1:9 to 5:5.

[0155] The lithium salt can be any compound capable of providing lithium ions for use in lithium secondary batteries, without any particular limitations. Specifically, the lithium salt can 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 0.1M to 5.0M, preferably 0.1M to 3.0M. If the concentration of the lithium salt falls within the above range, the electrolyte will have appropriate conductivity and viscosity, exhibiting excellent electrolyte performance and allowing lithium ions to move effectively.

[0156] The electrolyte may further contain additives in addition to the constituent components of the electrolyte, for the purpose of improving the battery's lifespan characteristics, suppressing the decrease in battery capacity, and improving the battery's discharge capacity. For example, the additives may be LiNO3, haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexamethyl phosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, either alone or in combination, but are not limited thereto. The additives may be present in an amount of 0.1 wt% to 10 wt%, preferably 0.1 wt% to 5 wt%, relative to the total weight of the electrolyte. In one embodiment of the present invention, the additives may include LiNO3.

[0157] On the other hand, in one embodiment of the present invention, it is preferable that the lithium-sulfur battery of the present invention has a ratio (El / S) of the total weight of the electrolyte to the total weight of the sulfur element (S) contained in the sulfur-carbon composite in the positive electrode, specifically, a ratio of 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. Furthermore, the lithium-sulfur battery may have a ratio (El / S) of 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 range can also be realized, thereby achieving the effect of improving energy density. However, lithium-sulfur batteries using the sulfur-carbon composite may also have an El / S ratio higher than the above range, and the present invention is not limited thereto.

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

[0159] Furthermore, the present invention provides a battery module that includes 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.

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

[0161] According to one embodiment of the present invention, the lithium-sulfur battery can have an energy density of 350 Wh / kg or more by using the positive electrode described above, but the present invention is not limited thereto. Specifically, the lithium-sulfur battery has 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, but since a higher energy density of the lithium-sulfur battery corresponds to a better performing battery, the upper limit of the energy density is not particularly limited.

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

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

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

[0165] <Manufacturing of lithium-sulfur batteries> [Example 1] Preparation of porous carbon material Multiple multi-walled carbon nanotubes (Cnano, MWCNT, tap density 0.14 g / cm³) 3 Agglomerates were prepared, formed by the intertwining of particles with a uniform particle shape (1.52). These aggregates were then subjected to pulverization at 18,000 rpm using a centrifugal grinder (ZM-200, manufactured by Retsch). linear velocity 94.2 m / s After being crushed using ), a porous carbon material with a modified shape was prepared by sieving it through an 80 μm mesh sieve.

[0166] The modified porous carbon material has a tap density of 0.07 g / cm³. 3 The particle shape uniformity was measured to be 1.07.

[0167] In this case, the tap density was measured based on the amount of tapping performed 1,000 times when the porous carbon material was placed in a container. The particle shape uniformity was calculated from an SEM image (Figure 4b) of the porous carbon material, using the ratio of the average diameter of the circumscribed circle to the average diameter of the inscribed circle of five particles, and 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) Production of sulfur-carbon composites As described above, the modified porous carbon material and sulfur (S8) were uniformly mixed in a weight ratio of 30:70 (CNT:S8). Subsequently, the porous carbon material was heat-treated in an oven at 155°C for 30 minutes to impregnate it with sulfur, thereby producing a sulfur-carbon composite.

[0168] Manufacturing of positive electrodes The sulfur-carbon composite obtained as described above, and polyacrylic acid as a binder polymer, were added to water and mixed to produce a cathode 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 onto aluminum foil (thickness: 20 μm) using a Mathis coater, dried at 50°C for 24 hours, and then rolled to produce a cathode. The porosity of the produced cathode active material layer was 83 vol%, and the loading amount of active material was 3.1 mg / cm³. 2 In this case, porosity was calculated as a percentage of the value obtained by subtracting the density of the positive electrode active material layer (apparent density) excluding the current collector in the manufactured positive electrode from the true density of the material constituting the positive electrode active material layer, and then dividing by the true density.

[0170] Porosity (vol%) = [(True density - Apparent density) / True density] × 100 Manufacturing of lithium-sulfur batteries A 45 μm thick lithium metal thin film was prepared as the negative electrode, and a mixture of 2-methylfuran and dimethoxyethane in a 3:7 volume ratio organic solvent was prepared, in which 3 wt% LiNO3 and 0.75 M LiFSI were dissolved.

[0171] A lithium-sulfur battery was manufactured by positioning the manufactured and prepared positive and negative electrodes facing each other, interposing a polyethylene separation membrane with a thickness of 16 μm and a porosity of 46 vol% between them, and then injecting the electrolyte in an amount 2.3 times the weight of sulfur (S) in the sulfur-carbon composite used in the positive electrode (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 porous carbon material to sulfur was changed to 25:75 (CNT:S8) during the production of the sulfur-carbon composite. In this case, the porosity of the manufactured positive electrode was 82 vol%, and the loading amount of active material was 3.1 mg / cm³. 2 That was the case.

[0173] [Comparative Example 1] Preparation of porous carbon material Multiple multi-walled carbon nanotubes (Cnano, MWCNT, tap density 0.14 g / cm³) 3 Agglomerates were prepared, formed by the intertwining of particles with a uniform particle shape (1.52). Subsequently, these aggregates were jet-milled to achieve a tap density of 0.1 g / cm³. 3 Carbon nanotube aggregates with a particle shape uniformity of 1.44 were prepared.

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

[0175] Manufacturing of positive electrodes and batteries 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. In this case, the porosity of the manufactured positive electrode was 79 vol%, and the loading amount of the active material was 3.1 mg / cm³. 2 That was the case.

[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 porous carbon material to sulfur was changed to 25:75 (CNT:S8) during the production of the sulfur-carbon composite. In this case, the porosity of the manufactured positive electrode was 78 vol%, and the loading amount of active material was 3.1 mg / cm³. 2 That was the case.

[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 porous carbon material to sulfur was changed to 35:65 (CNT:S8) during the production of the sulfur-carbon composite. In this case, the porosity of the manufactured positive electrode was 80 vol%, and the loading amount of active material was 3.1 mg / cm³. 2 That was the case.

[0178] [Comparative Example 4] Preparation of porous carbon material Without any separate pre-treatment (grinding), tap density of 0.2 / cm 3 Carbon nanotube aggregates with a particle shape uniformity of 1.44 were prepared.

[0179] Figure 4a shows an SEM image of the porous carbon material. The values ​​of [average diameter of circumscribed circle (major axis) / average diameter of inscribed circle (minor axis)] for five particles were calculated from the image. (Measurement 1: 2.06, Measurement 2: 1.26, Measurement 3: 1.37, Measurement 4: 1.36, Measurement 5: 1.16) Production of sulfur-carbon composites The porous carbon material obtained as described above and sulfur (S8) were uniformly mixed in a weight ratio of 25:75 (CNT:S8). Subsequently, the porous carbon material was heat-treated in an oven at 155°C for 30 minutes to impregnate it with sulfur, thereby producing a sulfur-carbon composite.

[0180] Manufacturing of positive electrodes and batteries 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. In this case, the porosity of the manufactured positive electrode was 77 vol%, and the loading amount of the active material was 3.1 mg / cm³. 2 That was the case.

[0181] <Evaluation of the physical properties of lithium-sulfur batteries> The characteristics of the lithium-sulfur batteries manufactured as described above are summarized in Tables 1 and 2 below.

[0182] Tap density In accordance with the ASTM B527 standard method, the porous carbon material used in the production of the sulfur-carbon composite was placed in a test container and tapped 1,000 times using a tapping device. After that, 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 long and short axes of five sulfur-carbon composites were measured from the SEM image to determine the particle shape uniformity. At this time, the long axis is the same as the diameter of the virtual circumcircle of the particle, and the short axis is the same as the diameter of the virtual incircle of the particle.

[0184] Particle shape uniformity = [(diameter of the circumcircle of the particle) / (diameter of the incircle 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) relative 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 a 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 substances constituting the positive electrode active material layer and then 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 the ratios based on the battery during driving while repeating charge and discharge were measured respectively.

[0187] First, the thickness of the positive electrode was measured using a thickness measuring instrument (Mitutoyo Corporation) on a fresh cell immediately after manufacturing. The thickness of the positive electrode active material layer was then determined by subtracting the thickness of the current collector from the measured thickness. Furthermore, the carbon weight within the positive electrode active material layer was calculated from the composition of the positive electrode used in the manufacturing process, and then divided by the loading amount of the active material to determine the unit area (1 cm²) of the active material layer. 2 Carbon weight per unit (mg / cm³) 2 The carbon weight was measured. At this time, the calculated value was cross-validated by measuring the carbon weight using 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, the area (cm²) of the positive electrode active material layer to be measured was measured. 2 Divide by (1cm²) to obtain the unit area of ​​the active material layer. 2 Carbon weight per unit (mg / cm³) 2 ) was measured.

[0188] Next, for a battery in operation, the thickness of the positive electrode active material layer was measured in the cycle during which the thickness of the positive electrode active material layer was minimized while maintaining a capacity of 90% or more compared to the initial capacity, in the fully charged state (SOC 100%) state. Then, 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] <Evaluation of specific capacity of lithium-sulfur batteries> Figure 1 shows performance evaluation graphs of lithium-sulfur batteries for Comparative Example 1, Comparative Example 2, and Comparative Example 4, and Figure 2 shows performance evaluation graphs of lithium-sulfur batteries for 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 CC (Constant Current) mode at 0.1C (C rate) until the voltage reached 1.8V, and then charged to 2.5V at a constant current of 0.1C to measure their discharge capacity. The discharge capacity was measured as the discharge capacity per unit of sulfur (S) content in the positive electrode (specific capacity, mAh / g(s)).

[0193] Referring to Figure 1, it can be confirmed that in lithium-sulfur batteries using porous carbon material with high tap density and low particle shape uniformity, as in conventional technology, the reactivity decreases and the discharge capacity decreases as the sulfur content increases (Comparative Examples 1 and 2). Furthermore, 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 Examples 1 and 4).

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

[0195] <Comparison of energy densities> The capacities of lithium-sulfur batteries in Example 1, Example 2, and Comparative Examples 1 to 3 were measured. The measured capacities were multiplied by the voltage, and then divided by the weight of each lithium-sulfur battery to calculate the energy density. The results are shown in Table 3 and Figure 3 below.

[0196] Figure 3 is a graph showing the relative energy densities of lithium-sulfur batteries from Example 1, Example 2, and Comparative Examples 1 to 3, with the energy density of Comparative Example 1 as the baseline.

[0197] [Table 3]

[0198] In Comparative Examples 1 to 3, which are lithium-sulfur batteries using porous carbon material with high tap density and low particle shape uniformity, similar to conventional technology, it was confirmed that as the sulfur content increased, the reactivity decreased, the discharge capacity decreased, and the energy density decreased (Comparative Examples 1 and 2). In Comparative Example 3, although the sulfur load was low and the reactivity was high, it was confirmed that the positive electrode active material content was low and the energy density was low.

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

[0200] As described above, the present invention has been explained with limited embodiments and drawings, but the present invention is not limited thereto, and it goes without saying that various modifications and variations are possible within the equivalent scope of the technical concept and claims of the present invention by persons with ordinary skill in the art to which the present invention pertains.

Claims

1. The current collector comprises a current collector and a positive electrode active material layer formed on at least one surface of the current collector, The positive electrode active material layer comprises a sulfur-carbon composite and a binder polymer. The sulfur-carbon composite comprises a porous carbon material and a sulfur-based material. A 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 is 80 μm / mg or more and 130 μm / mg or less.

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

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

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

5. The tap density of the porous carbon material is 0.09 g / cm³. ３ The positive electrode according to claim 1, which is as follows:

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

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

8. The tap density of the porous carbon material is 0.07 g / cm³. ３ The positive electrode according to claim 1, which is as follows:

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

10. The loading amount of sulfur (S) is 2.9 mg / cm³. ２ The positive electrode described in claim 1 is as described above.

11. A lithium-sulfur battery comprising a positive electrode, a negative electrode, a separation membrane interposed between the positive electrode and the negative electrode, and an electrolyte, according to any one of claims 1 to 10.

12. The lithium-sulfur battery according to claim 11, wherein the carbon weight per unit area of ​​the positive electrode active material layer and the thickness of the positive electrode active material layer are each measured after at least one discharge has been performed.

13. The lithium-sulfur battery according to claim 11, wherein the carbon weight per unit area of ​​the positive electrode active material layer and the thickness of the positive electrode active material layer were measured at a SOC of 97% to 100%, respectively.

14. The lithium-sulfur battery according to claim 12, wherein the ratio of the weight of the electrolyte to the weight of sulfur (S) in the sulfur-carbon composite ((weight of electrolyte) / (weight of sulfur (S) in the sulfur-carbon composite)) is 3.5 g / g or less.

15. The lithium-sulfur battery according to claim 11, wherein the energy density of the lithium-sulfur battery is 400 Wh / kg or more.

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