Cathode active material containing sulfur-carbon composite and lithium-sulfur secondary battery with high power output characteristics

Abstract

The present invention relates to a positive electrode active material for a lithium-sulfur battery, the positive electrode active material comprising a sulfur-carbon composite, the sulfur-carbon composite comprising a porous carbon material and a sulfur-based material, wherein the porous carbon material has a particle size D 10 and D 90 The sum of the particle diameter and the particle size D is 60 μm or less. 10 Particle size D 90 By satisfying at least one of the above points, a lithium-sulfur battery that achieves high power density and high capacity can be provided.

Description

[Technical Field]

[0001] The present invention relates to a positive electrode active material for a lithium-sulfur battery, and to a lithium-sulfur battery using the positive electrode active material and having high power density and high capacity characteristics.

[0002] This application is a Korean Patent Application No. 10-2022-0159965 filed on November 25, 2022, Korean Patent Application Nos. 10-2022-0183586 and 10-2022-0183771 filed on December 23, 2022, Korean Patent Application No. 10-2022-0185613 filed on December 27, 2022, Korean Patent Application No. 10-2023-0063394 filed on May 16, 2023, Korean Patent Application No. 10-2023 Priority is claimed based on Korean Patent Application No. 10-2023-0070299, filed on June 7, 2023, Korean Patent Application No. 10-2023-0073163, filed on June 13, 2023, Korean Patent Application No. 10-2023-0075765, filed on September 8, 2023, Korean Patent Application No. 10-2023-0119938, filed on November 24, 2023, and the contents disclosed in the specifications and drawings of these applications are incorporated herein in their entirety. [Background technology]

[0003] A lithium-sulfur battery is a battery system that uses a sulfur-based material with a sulfur-sulfur bond (SS bond) as the positive electrode active material and lithium metal as the negative electrode active material. Sulfur, the main material of the positive electrode active material, has the advantages of being abundant worldwide, non-toxic, and having a low atomic weight.

[0004] As the application areas of secondary batteries expand to electric vehicles (EVs) and energy storage systems (ESSs), lithium-sulfur battery technology is gaining attention due to its high theoretical energy storage density per weight (up to 2,500Wh / kg) compared to lithium-ion secondary batteries, which have a relatively low energy storage density per weight (up to 250Wh / kg).

[0005] During discharge, lithium, the negative electrode active material, releases electrons and is oxidized as it is ionized into lithium cations, while the positive electrode active material, a sulfur-based material, receives electrons and is reduced. Through the reduction reaction of the sulfur-based material, the S-S bond receives two electrons and is converted into sulfur anions. The lithium cations generated by the oxidation reaction of lithium are transferred to the positive electrode via the electrolyte, where they combine with sulfur anions generated by the reduction reaction of sulfur-based compounds to form salts. Specifically, sulfur before discharge has a cyclic S8 structure, which is converted into lithium polysulfide (Li2S) through a reduction reaction. x ) and is completely reduced to form lithium sulfide (LiS).

[0006] As sulfur (S8) used as a positive electrode active material is a non-conductor, porous carbon materials are being researched as sulfur supports to improve the reactivity of sulfur. In order to improve the dynamic activity of electrochemical reactions during charge and discharge in lithium-sulfur secondary batteries, there is a continuous need to develop technology for sulfur-carbon composite cathode materials in which the positive electrode active material is supported on porous carbon materials.

[0007] In particular, theoretically, loading sulfur onto a porous carbon material with a large specific surface area should increase the sulfur content, thereby improving the energy density and lifespan characteristics of the battery. However, experimental results have shown that loading sulfur onto a porous carbon material with a large specific surface area results in non-uniform battery capacity development, a low tap density during electrode formation, a low compression ratio during rolling, and swelling of the electrode, making the manufacture and commercialization of the electrode difficult.

[0008] Therefore, research and development is ongoing into sulfur-carbon composites with diverse properties that can be used in lithium-sulfur secondary batteries. Summary of the Invention [Problem to be solved by the invention]

[0009] In order to solve the above-mentioned problems, the present invention According to one aspect, an active material in which the particle size of a porous carbon material carrying sulfur is reduced to uniformize the electrochemical reactivity of sulfur, and an electrode and a battery using the active material are provided.

[0010] According to another aspect, the present invention provides an active material in which the particle size of the porous carbon material on which sulfur is supported is uniform, thereby uniforming the electrochemical reactivity of sulfur, and an electrode and a battery using the active material.

[0011] Specifically, the objective is to provide a lithium-sulfur battery that has improved energy density, battery capacity, and uniformity of electrochemical reaction by reducing the particle size of the porous carbon material that supports sulfur or adjusting the particle size distribution to a predetermined ratio. [Means for solving the problem]

[0012] To solve the above-mentioned problems, According to one aspect of the present invention, there is provided a positive electrode active material for a lithium-sulfur battery according to the following embodiment.

[0013] The positive electrode active material according to the first embodiment is A sulfur-carbon composite including a porous carbon material and a sulfur-based material, The porous carbon material satisfies at least one of the particle size conditions (1) and (2) below.

[0014] (1) Particle size D 10 and particle size D 90 The sum of these is 60 μm or less. (2) Particle size D according to the following formula 1 10 Particle size D 90 The distribution ratio (Broadness Factor, BF) is 7 or less.

[0015] [Formula 1] Broadness Factor(BF)=[(particle size D 90 ) / (particle size D 10 )]

[0016] According to the second embodiment, in the first embodiment, The sulfur-based material is inorganic sulfur (S8); Li2S n (n≧1); organic sulfur compounds including one or more of 2,5-dimercapto-1,3,4-thiadiazole and 1,3,5-trithiocyanic acid; carbon-sulfur polymers (C2S x ) n , x=2.5 to 50, n≧2); or a mixture of two or more thereof.

[0017] According to the third embodiment, in the first or second embodiment, The BET surface area of ​​the porous carbon material is 150 m 2 / g or more.

[0018] According to the fourth embodiment, in any one of the first to third embodiments, The porous carbon material may include carbon nanotubes, carbon black, graphite, activated carbon, graphene, or a mixture of two or more thereof.

[0019] According to the fifth embodiment, in any one of the first to fourth embodiments, The porous carbon material may include carbon nanotubes.

[0020] According to the sixth embodiment, in any one of the first to fifth embodiments, The sulfur (S) content may be 60 wt% or more relative to 100 wt% of the sulfur-carbon composite.

[0021] According to the seventh embodiment, in any one of the first to sixth embodiments, The porous carbon material is The porous carbon material as the raw material is pulverized using a centrifugal pulverizer. The porous carbon material is crushed and sieved to a desired particle size. The mesh size of the sieve is determined based on the particle size D of the porous carbon material produced. 50 It may be 2.8 to 4 times larger than the original size.

[0022] According to the eighth embodiment, in any one of the first to seventh embodiments, The particle diameter D of the porous carbon material 50 can be 100 μm or less.

[0023] According to the ninth embodiment, in any one of the first to eighth embodiments, The porous carbon material may have a BF value of 4 to 7 according to Equation 1 above.

[0024] According to another aspect of the present invention, there is provided a positive electrode according to the following embodiment.

[0025] The positive electrode according to the tenth embodiment is 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 the positive electrode active material for a lithium-sulfur battery according to any one of the first to ninth embodiments.

[0026] The positive electrode according to the eleventh embodiment is 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 contains a plurality of sulfur-carbon composites, With respect to a plane of the positive electrode active material layer parallel to the current collector as a reference, an error value of the area of ​​any 10 sulfur-carbon composites per 50 μm×50 μm area calculated by the following Equation 2 is 100% or less:

[0027] [Formula 2] Error(%)=[Standard deviation / Average]×100

[0028] According to the twelfth embodiment, in the tenth or eleventh embodiment, The positive electrode active material layer may have an average tortuosity of 1.7 or less.

[0029] According to the thirteenth embodiment, in any one of the tenth to twelfth embodiments, The positive electrode active material layer may further include at least one of a binder and a conductive material.

[0030] According to the 14th embodiment, in any one of the 10th to 13th embodiments, The content of sulfur (S) in the positive electrode active material layer (100 wt %) may be 60 wt % or more.

[0031] According to the fifteenth embodiment, in any one of the tenth to fourteenth embodiments, Sulfur loading: 1.67mg s / cm 2 ~2.92mg s / cm 2 It could be.

[0032] According to the 16th embodiment, in any one of the 10th to 15th embodiments, The sulfur-carbon composite includes a porous carbon material and a sulfur-based material, The porous carbon material may satisfy at least one of the particle size conditions (1) and (2) below.

[0033] (1) Particle size D 10 and particle size D 90 The sum of these is 60 μm or less. (2) Particle size D according to the following formula 1 10 Particle size D 90 The distribution ratio (Broadness Factor, BF) is 7 or less. [Formula 1] Broadness Factor(BF)=[(particle size D 90 ) / (particle size D 10 )]

[0034] According to yet another aspect of the present invention, there is provided a lithium-sulfur battery according to the following embodiment:

[0035] The lithium-sulfur battery according to the seventeenth embodiment is The battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte; The positive electrode is the positive electrode according to any one of the eleventh to sixteenth embodiments.

[0036] According to the eighteenth embodiment, in the seventeenth embodiment, The ratio (El / S) of the total weight of the electrolyte to the total weight of elemental sulfur (S) in the positive electrode may be 3.5 g / g or less.

[0037] According to the 19th embodiment, in the 17th or 18th embodiment, The 10-second power density may be 2.1 kW / kg or greater.

[0038] According to the 20th embodiment, in any one of the 17th to 19th embodiments, 1,000mAh / g per weight of sulfur (S) in the positive electrode s The discharge capacity may be greater than or equal to 1000 volts. [Effects of the Invention]

[0039] If the particles of the carbon material are large, the gaps between the carbon material particles become wider than necessary, which makes it difficult to realize the cell capacity.

[0040] Furthermore, if the particle size distribution of the carbonaceous material is wide, the reaction of the sulfur-based material, for example, sulfur (S8), supported on the carbonaceous material of non-uniform size will also be non-uniform, resulting in a decrease in cell capacity.

[0041] The present invention provides a porous carbon material with small and uniform particle size distribution to enhance reaction uniformity. When a carbon material with small and uniform particle size is used as a support for a sulfur-based material, superior cell capacity and power density can be achieved compared to cells using a carbon material with large and non-uniform particle size as a support.

[0042] For example, according to one embodiment of the present invention, a lithium-sulfur battery can be provided that has a power density of 2.1 kW / kg or more for 10 seconds throughout the entire discharge process.

[0043] According to one embodiment of the present invention, the battery has a capacity of 1,000 mAh / g when discharged at 1.0 C. s It is possible to provide a lithium-sulfur battery having the above discharge capacity. [Brief explanation of the drawings]

[0044] [Figure 1] 1 is a graph showing the measurement results of particle size distribution in Comparative Example 1 and Examples 1 to 3. [Figure 2] 1 shows SEM images of the porous carbon material used in the preparation of the sulfur-carbon composite in Example 4. The left image is at 1,000x magnification, and the right image is at 10,000x magnification. [Figure 3] 1 shows SEM images of the porous carbon material used in the preparation of the sulfur-carbon composite of Comparative Example 2. The left image is at 1,000x magnification, and the right image is at 10,000x magnification. [Figure 4a]1 is a SEM image (magnification: 400) of a 200 μm×200 μm area of ​​the upper surface of a positive electrode active material layer of a positive electrode prepared using the sulfur-carbon composite of Example 1. [Figure 4b] 1 is a SEM image (magnification: 1,000) of a 70 μm×70 μm area of ​​the upper surface of a positive electrode active material layer of a positive electrode produced using the sulfur-carbon composite of Example 1. [Figure 4c] 10 is an SEM image (magnification: 400) of a 200 μm×200 μm area of ​​an upper surface of a positive electrode active material layer of a positive electrode prepared using the sulfur-carbon composite of Example 1, illustrating a process of measuring the degree of bending in the vertical and horizontal directions. [Figure 5a] 1 is a SEM image at 400x magnification of a 200 μm×200 μm area of ​​the upper surface of a positive electrode active material layer of a positive electrode prepared using the sulfur-carbon composite of Comparative Example 1. [Figure 5b] 1 is a 1,000-magnification SEM image of a 70 μm×70 μm area of ​​the upper surface of a positive electrode active material layer of a positive electrode produced using the sulfur-carbon composite of Comparative Example 1. [Figure 5c] 1 shows an SEM image (magnification: 400) of a 200 μm × 200 μm area of ​​the upper surface of the positive electrode active material layer in a positive electrode obtained from a lithium-sulfur battery disassembled after charge / discharge in Evaluation Example 2. Specifically, the positive electrode was prepared using the sulfur-carbon composite of Comparative Example 1. [Figure 5d] 1 shows an SEM image (magnification: 1,000) of a 70 μm × 70 μm area on the upper surface of the positive electrode active material layer in a positive electrode obtained from a lithium-sulfur battery disassembled after charge / discharge in Evaluation Example 2. Specifically, the positive electrode was prepared using the sulfur-carbon composite of Comparative Example 1. [Figure 5e] 10 is an SEM image (magnification: 400) of a 200 μm×200 μm area of ​​the upper surface of a positive electrode active material layer of a positive electrode prepared using the sulfur-carbon composite of Comparative Example 1, illustrating a process of measuring the degree of bending in the vertical and horizontal directions. [Figure 6a] 1 shows SEM images of a vertical cross section of a positive electrode prepared using the sulfur-carbon composite of Comparative Example 2. The left image is a 1,000x magnification image, and the right image is a 5,000x magnification image. [Figure 6b] 6A is an image showing a process of measuring the average degree of bending of a positive electrode active material layer using the left image of FIG. 6A. [Figure 7a] 1 shows SEM images of a vertical cross section of a positive electrode fabricated using the sulfur-carbon composite of Example 4. The left image is a 1,000x magnification, and the right image is a 5,000x magnification. [Figure 7b] 7A is an image illustrating a process of measuring the average degree of bending of a positive electrode active material layer using the left image of FIG. 7A. [Figure 8] 1 is a graph showing the change in discharge capacity according to the charge-discharge cycle in Comparative Example 1 and Examples 1 to 3. [Figure 9] 1 is a graph showing a comparison of relative capacities between Comparative Example 1 and Examples 1 to 3. [Figure 10] 1 is a graph showing a comparison of the relative nominal voltages of Comparative Example 1 and Examples 1 to 3. [Figure 11] 1 is a graph showing the 0.5 C discharge capacity evaluation of the batteries using the sulfur-carbon composites of Example 1 and Comparative Example 1. [Figure 12] 1 is a graph showing the 0.5 C discharge capacity evaluation of the batteries using the sulfur-carbon composites of Example 4 and Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0045] The present invention will be described in more detail below.

[0046] The terms and words used in this specification and claims should not be interpreted limited to their ordinary and dictionary meanings, but should be interpreted in terms and concepts that correspond to the technical idea of ​​the present invention, in accordance with the principle that the inventor himself can appropriately define the concept of the term in order to explain the invention in the best way.

[0047] Throughout this specification, when a part is described as "comprising" or "having" a certain component, it does not mean that other components are excluded, but that other components may also be included, unless otherwise specified.

[0048] Furthermore, the terms "about," "substantially," and the like used throughout this specification, when given manufacturing and material tolerances inherent in the stated meaning, are used to mean a numerical value or a value close to that numerical value, in order to prevent unconscionable infringers from unfairly using disclosure content in which precise or absolute numerical values ​​are stated to aid in the understanding of this application.

[0049] Throughout this specification, the phrase "A and / or B" means "A, B, or all of these."

[0050] In the present 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 (77 K) using a BELSORP-mini II manufactured by BEL Japan.

[0051] As used herein, the term "polysulfide" refers to "polysulfide ions (S x 2- , 1≦x≦8) and "Lithium polysulfide (Li2S x or LiS x - , 1≦x≦8).

[0052] The term "composite" as used herein means a material in which two or more materials are combined to form physically and chemically distinct phases, thereby exhibiting more effective functions.

[0053] In the present invention, "particle size D 10 " means the particle size at 10% of the volume cumulative particle size distribution of the particles to be measured, and "particle size D 50 " means the particle size at 50% of the volume cumulative particle size distribution of the particles to be measured, and "particle size D 90 " means the particle size at 90% of the volume cumulative particle size distribution of the particles to be measured.

[0054] The particle size D 10 , D 50and D 90 can be measured using the laser diffraction method. For example, the particle powder to be measured is dispersed in a dispersion medium, introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT3000), and irradiated with ultrasonic waves of about 28 kHz at an output of 60 W. 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. That is, for example, the average particle size D 50 indicates the median value or mean diameter on a particle distribution graph, and represents the particle size at the 50% point of the cumulative distribution. Particle size is the diameter of a particle, and the diameter of a particle means the longest length within the particle.

[0055] The unit used in this specification is "mAh / g s " is used to indicate the capacity per weight of sulfur (S), unless otherwise specified, and may be used in combination with other expression systems such as mAh / g(s) and mAh / gs.

[0056] The units used herein are "mg s / cm 2 " is intended to indicate the weight of sulfur (S) per unit area, mg(s) / cm unless otherwise specified. 2 It can be used in combination with other expression methods such as mAh / g, mAh / g, etc.

[0057] The term "porosity" as used herein means the ratio of the volume occupied by pores to the total volume of a structure, and is expressed in units of vol%. It can be used interchangeably with terms such as void ratio, porosity, etc. The porosity can be measured by the method of ISO 15901:2019, which is known in the art.

[0058] The present invention relates to a cathode active material for an electrochemical device, a cathode including the cathode active material, and a secondary battery including the cathode. The secondary battery may be a lithium-ion secondary battery. In particular, the cathode active material according to the present invention includes a sulfur-carbon composite, and the lithium-ion secondary battery may be a lithium-sulfur secondary battery.

[0059] According to an embodiment of the present invention, the positive electrode active material includes a sulfur-carbon composite including a porous carbon material and a sulfur-based material.

[0060] 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). The average pore diameter may be, for example, 1 to 200 nm, and the porosity may be 10 to 90 vol% of the total volume of the porous carbon material. The average pore diameter may be measured by a known method, such as a BET measurement method using gas adsorption or mercury intrusion porosimetry.

[0061] 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 portion of the interior and exterior pores of the porous carbon material, or in a form in which the sulfur-based material coats all or at least a portion of the interior and exterior pores of the porous carbon material.

[0062] According to one embodiment of the present invention, the porous carbon material satisfies at least one of the particle size conditions (1) and (2) below.

[0063] Condition (1) Particle size D 10 and particle size D 90 The sum of these is 60 μm or less.

[0064] Condition (2) Particle size D according to the following formula 1 10 Particle size D 90 The distribution ratio (Broadness Factor, BF) is 7 or less.

[0065] [Formula 1] Broadness Factor(BF)=[(particle size D 90 ) / (particle size D 10 )]

[0066] In one embodiment of the present invention, the porous carbon material has a particle size D10 and particle size D 90 The structural feature is that the sum of the above is 60 μm or less.

[0067] In another embodiment of the present invention, the porous carbon material has a particle size D 10 Particle size D 90 The broadness factor (BF) of the porous carbon material is 7 or less. 10 Particle size D 90 This means the particle size distribution ratio of the above formula 1 [(particle size D 90 ) / (particle size D 10 )].

[0068] In yet another embodiment of the present invention, the porous carbon material has a particle size D 10 and particle size D 90 The structural features are that the sum of the above is 60 μm or less and BF is 7 or less.

[0069] In one embodiment of the present invention, if the particle size of the porous carbon material is large or the particle size distribution is wide, i.e., if the size of the porous carbon material is not uniform, the reaction of the sulfur-based material supported on the porous carbon material will also be non-uniform. This will result in a problem of reduced capacity of the electrode and battery. Therefore, the present invention is characterized by improving the power density and capacity development of the electrode and battery by using a porous carbon material with a small particle size (particle size condition (1)) or a narrow particle size distribution (particle size condition (2)), or by using a porous carbon material with a small particle size and a narrow particle size distribution (particle size conditions (1) and (2)).

[0070] In this specification, the BF value may be measured based on the state before the porous carbon material is provided as a sulfur-based material by supporting the sulfur-based material. That is, it may be measured based on the raw material before the sulfur-carbon composite is prepared. The BF value may also be measured in the state of a final product, such as a cathode active material, a cathode, or a lithium-sulfur battery. For example, a lithium-sulfur battery with a SOC (State of Charge) of 70 to 100, preferably a lithium-sulfur battery with an SOC of 100, is disassembled under inactive conditions to obtain a cathode. The binder and sulfur-based material are extracted and removed from the obtained cathode using a known extraction method, and the remaining porous carbon material is then extracted into particles of the above-mentioned particle size D. n (n=10, 50 or 90) 90 and D 10 After measuring D 90 / D 10 It can be calculated and measured as the value of

[0071] In one embodiment of the present invention, a small porous carbon material is used, so that the particle size D of the porous carbon material is 10 and particle size D 90 The sum of the particle diameter D of the porous carbon material and the particle diameter D of the porous carbon material may be, for example, 10 μm to 60 μm, 20 μm to 55 μm, 30 μm to 55 μm, 35 μm to 55 μm, 40 μm to 55 μm, 45 μm to 55 μm, or 50 μm to 55 μm. 10 and particle size D 90 The sum of the particle size D and the particle size D may be 50 μm to 52 μm or 51 μm. 10 and particle size D 90 When the sum of (a) and (b) is within the above-mentioned range, the size of the porous carbon material is small, the content of the sulfur-based material supported per porous carbon material is uniform, and the gaps between the porous carbon materials in the positive electrode prepared using the sulfur-carbon composite formed therefrom are narrow, which is advantageous in achieving uniform reactivity of the lithium-sulfur battery using the same.

[0072] In one embodiment of the present invention, the particle size D n In the present invention, the particle diameter D of the porous carbon material is 10 is the particle size D90 At this time, the particle diameter D 10 Particle size D 90 The smaller the particle size distribution ratio, the more uniform the particle size. The present invention achieves the effect of uniforming the electrochemical reactivity of the active material by providing a porous carbon material with a BF of 7 or less, but the mechanism of the present invention is not limited thereto. The BF value of the porous carbon material may be, for example, greater than 1 and less than 7, greater than 1 and less than 6, 2 to 6, 3 to 6, 4 to 7, 4 to 6, or more specifically, 5.3 to 5.6.

[0073] In one embodiment of the present invention, the particle size D of the porous carbon material 50 can be, for example, 100 μm or less, 70 μm or less, or 50 μm or less. 50 The particle diameter D of the porous carbon material may be, for example, 1 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. 50 When the particle size D is within the above range, it is advantageous in improving the tap density of the cathode used therewith, thereby improving the energy density of the battery, but the present invention is not limited thereto. For example, if the particle size of the porous carbon material is large, the pores between the particles of the carbon material become large, which may result in a decrease in battery capacity. Therefore, another structural feature of the present invention is that the particle size of the porous carbon material is controlled within an appropriate range to have a small and uniform particle size distribution. When a porous carbon material with such a small and uniform particle size distribution is used as a support for a sulfur-based material, it can achieve more uniform electrochemical performance and further improved battery capacity compared to carbon materials with large particle sizes and non-uniform particle size distribution. The particle size D 50 The method for measuring is as described above.

[0074] In one embodiment of the present invention, the porous carbon material serves as a support that provides a framework for uniformly and stably immobilizing sulfur, and compensates for the low electrical conductivity of sulfur, thereby enabling a smooth electrochemical reaction. The porous carbon material may be used without any particular limitation as long as it satisfies the above particle size requirements.

[0075] 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). The average pore diameter may be, for example, 1 nm to 200 nm, and the porosity may be 10 vol% to 90 vol% of the total volume of the porous carbon material. The average pore diameter may be measured by a known method, such as a BET measurement method using gas adsorption or mercury intrusion porosimetry.

[0076] In one embodiment of the present invention, the BET specific surface area of ​​the porous carbon material is not particularly limited, but is, for example, 150 m 2 / g or more. The use of a porous carbon material with a large specific surface area is advantageous in that it increases the loading rate of sulfur-based materials and improves the electrochemical performance of cathodes and lithium-sulfur batteries using the same, but the present invention is not limited thereto. The sulfur-carbon composite according to the present invention has a high loading amount of sulfur but a low irreversible capacity and a high energy density because the carbon material serving as the sulfur support has a large BET specific surface area and an appropriate particle size range. That is, the composite has a structure that improves the utilization rate of sulfur during electrochemical reactions, but the present invention is not limited thereto.

[0077] In one embodiment of the present invention, the BET specific surface area of ​​the porous carbon material is, for example, 150 m 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 / g, but is not limited thereto. The BET specific surface area is measured by the BET method and may be a value measured by a known method for measuring BET specific surface area. For example, the BET specific surface area may be a value calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77K) using a BELSORP-max manufactured by BEL Japan.

[0078] In one embodiment of the present invention, the porous carbon material may be in any shape, including, without limitation, a sphere, a rod, a needle, a plate, a tube, or a bulk.

[0079] The porous carbon material may be any material having a porous structure or a large specific surface area, and may include, for example, carbon nanotubes, carbon black, graphite, activated carbon, graphene, or a mixture of two or more thereof, preferably carbon nanotubes.

[0080] The carbon nanotubes may include, but are not limited to, one or more selected from the group consisting of single-walled carbon nanotubes and multi-walled carbon nanotubes. The carbon black may include, but is not limited to, one or more selected from the group consisting of denka black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black. The porous carbon material may include carbon nanofibers, which may include, but are not limited to, one or more selected from the group consisting of graphite nanofibers, carbon nanofibers, and activated carbon fibers. The graphite may include, but is not limited to, one or more selected from the group consisting of natural graphite, artificial graphite, and expanded graphite.

[0081] In one embodiment of the present invention, the porous carbon material may include porous and conductive carbon-based materials commonly used in the art, such as graphite; graphene; carbon black, 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 (GNFs), carbon nanofibers (CNFs), and activated carbon fibers (ACFs); graphite, such as natural graphite, artificial graphite, and expanded graphite; carbon nanoribbons; carbon nanobelts; carbon nanorods; and activated carbon.

[0082] In one embodiment of the present invention, the porous carbon material may include carbon nanotubes. The carbon nanotubes are formed of hexagonally connected carbon atoms in a tube-like 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 the carbon nanotubes. Here, the length of each carbon nanotube is not particularly limited.

[0083] In one embodiment of the present invention, the porous carbon material may include carbon nanotubes to improve sulfur loading, specifically multi-walled carbon nanotubes, but the present invention is not limited thereto.

[0084] In another embodiment of the present invention, the carbon nanotubes may be present in a form in which two or more carbon nanotubes are closely entangled with each other due to their cohesive force. Specifically, in one embodiment of the present invention, the carbon nanotubes may be provided in the form of a carbon nanotube dispersion in which the carbon nanotubes are dispersed as single strands in a dispersion medium or the like, or may be provided in the form of a secondary structure in which primary structure carbon nanotubes are aggregated with each other.

[0085] In view of this, when the porous carbon material contains carbon nanotubes, the carbon nanotubes may have a bundled secondary structure, an entangled secondary structure, or both.

[0086] The bundled secondary structure of carbon nanotubes has a configuration in which a single carbon nanotube is used as the primary structure, and multiple primary structures are aligned in the longitudinal direction of the carbon nanotube due to the cohesive force between carbon atoms, and are solidified together, and can also be called a bundled CNT.

[0087] In one embodiment of the present invention, the carbon nanotubes may include, for example, entangled multi-walled carbon nanotubes (MWCNTs).

[0088] In one embodiment of the present invention, the porous carbon material has a BET specific surface area of, for example, 100 m 2 / g~2,500m 2 / g,100m 2 / g~400m 2 / g, 150m 2 / g~350m 2 / g, specifically 200m 2 / g of carbon nanotubes, but is not limited thereto.

[0089] In one embodiment of the present invention, the graphene may be a carbon layer composed of only carbon, or may be graphene oxide, reduced graphene oxide, or a mixture thereof depending on its form, but the present invention is not limited thereto.

[0090] Meanwhile, in another embodiment of the present invention, the carbon material may be prepared by carbonizing various carbon precursors.

[0091] In one embodiment of the present invention, the porous carbon material may be prepared by a pretreatment process in which the porous carbon material is pulverized using a centrifugal pulverizer to have the above-described particle size, and then classified using a sieve according to the particle size, but the method for preparing the porous carbon material of the present invention is not limited thereto.

[0092] In one embodiment of the present invention, the porous carbon material may be prepared by controlling the particle size to satisfy the particle size condition (1) and / or the particle size condition (2) through a pretreatment method described below.

[0093] In one embodiment of the present invention, the porous carbon material may be prepared by pulverizing a porous carbon material as a raw material using a centrifugal pulverizer and sieving the pulverized porous carbon material through a sieve having a desired particle size. In this case, to satisfy the particle size condition (1) and / or the particle size condition (2), the mesh size of the sieve may be set to a value equal to or larger than the particle size D of the prepared porous carbon material. 50 It may be 2.8 to 4 times larger than the above.

[0094] Conventionally, in order to control the particle size of a porous carbon material, the porous carbon material is pulverized using a ball mill or a blade, etc. However, such a conventional pulverization method has a problem in that the porous carbon material comes into random contact with the ball or blade, resulting in the coexistence of porous carbon materials with large particle sizes and porous carbon materials with small particle sizes, resulting in a wide particle size distribution.

[0095] The present invention may be prepared by pulverizing the porous carbon material using a centrifugal pulverizer (step (1)) and then sieving the pulverized porous carbon material (step (2)).

[0096] In one embodiment of the present invention, step (1) may be a step of rotating and pulverizing the porous carbon material using a centrifugal pulverizer at a linear velocity of 30 m / s to 125 m / s. Specifically, it may be a step of rotating and pulverizing the porous carbon material at a linear velocity of 30 m / s to 95 m / s. When the centrifugal pulverization speed in step (1) is within the above range, it is advantageous in that the particle size of the porous carbon material can be uniformly controlled while being pulverized to a small size, and the tap density can be prevented from increasing.

[0097] In one embodiment of the present invention, the centrifugal crusher may have a plurality of rotating teeth that crush the porous carbon material as the rotating teeth rotate. Specifically, the centrifugal crusher may have, for example, 2 to 20, 4 to 18, 6 to 16, 8 to 14, 10 to 14, or 10 to 12 rotating teeth.

[0098] In one embodiment of the present invention, each of the plurality of rotary teeth may be triangular prism-shaped and may be arranged toward the rotation axis of the centrifugal crusher. Specifically, when viewed from above along the rotation axis of the centrifugal crusher, the plurality of rotary teeth may be arranged such that the vertical cross sections of the triangular prisms intersect at the center of the centrifugal crusher.

[0099] In one embodiment of the present invention, the plurality of rotating teeth may be made of a material such as, but not limited to, stainless steel, titanium, or stainless steel with a protective coating.

[0100] In one embodiment of the present invention, the centrifugal crusher used in step (1) may be one equipped with a rotary tooth, such as a ZM200 machine manufactured by Retsch.

[0101] 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 the above range. Specifically, the centrifugal grinding can be performed using a ZM200 machine manufactured by Retsch at a speed of 6,000 rpm to 23,000 rpm, specifically 6,000 rpm to 18,000 rpm.

[0102] In one embodiment of the present invention, the magnitude of the applied force may vary depending on the size of the centrifugal grinder even at the same rpm. Therefore, taking the size of the centrifugal grinder into consideration, the rpm may be adjusted so that grinding can be performed at a linear velocity of 30 m / s to 125 m / s according to the following Equation 3:

[0103] [Formula 3] Linear velocity=(RPM×circumference) / 60 seconds

[0104] In the above formula 3, the "circumference" indicates the distance traveled by one rotary tooth during one rotation. Specifically, when the radius of rotation of one rotary tooth is r, the circumference is expressed as 2πr.

[0105] The step (2) is a step of sieving the porous carbon material centrifuged in the step (1).

[0106] In one embodiment of the present invention, the sieve may be provided in a centrifugal crusher and may be provided on the outer periphery of the centrifugal crusher. Specifically, the sieve may be provided to surround a plurality of rotating teeth in the centrifugal crusher.

[0107] In one embodiment of the present invention, the sieve may be cylindrical and may be disposed so as to surround the plurality of rotary teeth. For example, the shortest distance between the plurality of rotary teeth and the sieve, as viewed from above the centrifugal grinder, may be 0.1 mm to 5 mm or 0.5 mm to 2 mm, e.g., 1 mm. The sieve may include a mesh with trapezoidal and / or circular holes.

[0108] In one embodiment of the present invention, the porous carbon material is pulverized by the rotation of the rotary teeth, and the porous carbon material having a particle size controlled to a desired size is immediately passed through a sieve located on the outer edge of a series of rotary teeth under centrifugal force, thereby solving the problems of further particle size reduction and / or surface damage. According to one embodiment of the present invention, steps (1) and (2) are performed simultaneously, thereby controlling the particle size to a desired size and obtaining a porous carbon material having a narrow particle size distribution.

[0109] As such, in one embodiment of the present invention, the step (2) is preferably performed while centrifugal force is applied to the pulverized porous carbon material.

[0110] The step (2) is a step in which the porous carbon material centrifugally pulverized in the step (1) is transferred to a sieve and filtered, and the steps (1) and (2) may be a continuous process carried out simultaneously.

[0111] The mesh size of the sieve used in step (2) can be adjusted to control the particle size of the porous carbon material. The mesh size of the sieve is determined based on the desired particle size D of the porous carbon material. 50 (Target D 50 ) 2.8 to 4 times (2.8≦Mesh size / Target D 50 ≦4), and by limiting the mesh size range of the sieve as described above, the particle size D of the porous carbon material to be targeted can be 50 As a result, a porous carbon material with a narrow particle size distribution can be obtained.

[0112] In one embodiment of the present invention, the particle size D of the desired porous carbon material 50 (Target D 50 ) is the particle size D of the porous carbon material produced, for example, according to one embodiment of the present invention. 50 For example, it may be 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.

[0113] In one embodiment of the present invention, the sulfur-based material may be any material capable of providing sulfur (S) as an active material for a lithium-sulfur battery, for example, the sulfur-based material may include at least one of sulfur (S) and a sulfur compound.

[0114] In one embodiment of the present invention, the sulfur-based material is inorganic sulfur (S), LiS n (n≧1), organic sulfur compounds containing one or more of 2,5-dimercapto-1,3,4-thiadiazole and 1,3,5-trithiocyanuric acid; carbon-sulfur polymers ((CS x ) n , x=2.5 to 50, n≧2); or two or more of these.

[0115] In one embodiment of the present invention, the sulfur-based material in the sulfur-carbon composite may be contained by physical adsorption with the porous carbon material or by chemical bonding, such as covalent bonding or van der Waals bonding, between sulfur element (S) and carbon in the porous carbon material. In particular, the sulfur-based material may be chemically bonded to the surface of the porous carbon material to form a composite.

[0116] In one embodiment of the present invention, the sulfur-carbon composite preferably has a sulfur (S) content of 60 wt% or more, 70 wt% or more, or 75 wt% or more to 99 wt% or less, relative to 100 wt% of the sulfur-carbon composite. For example, the sulfur-carbon composite preferably has a sulfur (S) content of 60 wt% to 99 wt%, 70 wt% to 99 wt%, 60 wt% to 90 wt%, 75 wt% to 90 wt%, 70 wt% to 85 wt%, 70 wt% to 80 wt%, 75 wt% to 80 wt%, or 70 wt% to 75 wt% relative to 100 wt% of the sulfur-carbon composite.

[0117] In one embodiment of the sulfur-carbon composite, the sulfur-based material is located within the pores of the porous carbon material and at least part of the outer surface thereof. The sulfur-based material may be present in an area of ​​less than 100%, preferably 1% to 95%, and more preferably 60% to 90% of the entire inner and outer surface of the porous carbon material. When the sulfur is located within the above-described range on the surface of the porous carbon material, it can maximize the electron transfer area and electrolyte wettability. Specifically, within the above-described range, the sulfur is thinly and uniformly impregnated on the surface of the porous carbon material, thereby increasing the electron transfer contact area during charge and discharge. If the sulfur is located over 100% of the surface of the porous carbon material, the porous carbon material is completely covered with sulfur, reducing the electrolyte wettability and contact with the conductive material contained in the electrode, making it unable to transfer electrons and participate in the reaction.

[0118] The sulfur-carbon composite may be a composite formed by simply mixing the sulfur-based material and the carbon material, or may be in a core-shell structure, coated, or supported form. The core-shell structure may be a coating form in which either the sulfur-based material or the carbon material coats the other, for example, the surface of the carbon material may be covered with sulfur, or vice versa. The supported form may be a form in which the interior, particularly the pores, of the carbon material are filled with the sulfur-based material. The form of the sulfur-carbon composite may be any form that satisfies the above-mentioned sulfur to carbon material content ratio, and is not limited in the present invention.

[0119] Another embodiment of the present invention provides a method for preparing the sulfur-carbon composite. The method for preparing the sulfur-carbon composite according to this embodiment is not particularly limited and may be a composite method well known in the art, comprising (S1) mixing a porous carbon material with a sulfur-based material and (S2) composite formation.

[0120] The mixing in step (S1) is for increasing the degree of mixing of the sulfur-based material and the porous carbon material and may be carried out using a stirrer commonly used in the art. Here, the mixing time and speed may be selectively adjusted depending on the content and conditions of the raw materials.

[0121] The compounding in step (S2) is not particularly limited and may be performed by a method commonly used in the art. For example, it may be performed by a method commonly used in the art, such as dry compounding or wet compounding such as spray coating. For example, the mixture of sulfur and carbon material obtained by mixing may be pulverized using a ball mill, 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.

[0122] The sulfur-carbon composite prepared by the above-described preparation method has a large specific surface area and a large amount of sulfur loaded therein, resulting in an improved sulfur utilization rate. This not only improves the electrochemical reactivity of sulfur but also improves the accessibility and contactability of the electrolyte, thereby improving the capacity and lifespan characteristics of lithium-sulfur batteries.

[0123] Yet another embodiment of the present invention provides a positive electrode formed using the sulfur-carbon composite.

[0124] A positive electrode for a lithium-sulfur battery 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, wherein the positive electrode active material layer includes the above-described positive electrode active material for a lithium-sulfur battery as an active material.

[0125] The positive electrode for the lithium-sulfur battery 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. The sulfur-carbon composite includes a porous carbon material and a sulfur-based material supported on all or at least a portion of the interior and exterior pores of the porous carbon material.

[0126] In this case, the positive electrode active material layer is characterized in that it contains the above-mentioned positive electrode active material.

[0127] That is, the positive electrode active material includes a sulfur-carbon composite, and the sulfur-carbon composite includes a porous carbon material that satisfies at least one of the particle size conditions (1) and (2) described above. Specifically, the porous carbon material satisfies the particle size condition (1): particle size D 10 and particle size D 90 and the sum of the particle size is 60 μm or less, particle size condition (2): particle size D according to the following formula 1 10 Particle size D 90 The broadness factor (BF) of the distribution ratio of the above-mentioned polymorphism may be 7 or less.

[0128] [Formula 1] Broadness Factor(BF)=[(particle size D 90 ) / (particle size D 10 )]

[0129] In one embodiment of the present invention, the particle size D of the porous carbon material 50 can be, for example, 100 μm or less.

[0130] A positive electrode according to an 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.

[0131] According to an embodiment of the present invention, the positive electrode active material layer may include a plurality of sulfur-carbon composites, and the positive electrode may satisfy the following Equation 4:

[0132] [Formula 4] X L / X S ≦15

[0133] In Formula 4, the X L is the average value of the lengths of the longest axes of the top five sulfur-carbon composites in terms of area in the top view of the positive electrode active material layer, and X S is the average length of the longest axis among the five sulfur-carbon composites in the bottom area in the top view of the positive electrode active material layer.

[0134] In a positive electrode that satisfies the above formula 4, the sulfur-carbon composite contained in the positive electrode active material layer can have a small and / or uniform particle size, and the gaps between the sulfur-carbon composites in the positive electrode active material layer can be narrow, resulting in the effect that the reactivity of a lithium-sulfur battery using the positive electrode can be uniform.

[0135] Specifically, according to one embodiment of the present invention, the X L / X S The value of X may be, for example, 15 or less, 10 or less, or 5 or less. L / X S The value of X may be 1 or more, 1.5 or more, 2 or more, 2.5 or more, 3 or more, or 3.5 or more within the range satisfying the upper limit described above. L / X S The value of X may be 1 to 15, 1.5 to 10, 2.0 to 5, 2.5 to 5.0, 3.0 to 5.0, 3.0 to 4.0, or 3.0 to 4.5. L / X S When the value of is within the above range, the gaps between the sulfur-carbon composites in the positive electrode active material layer are narrow, which can be advantageous in terms of uniformity of the electrochemical reaction in the positive electrode.

[0136] In this specification, when the stacking direction of the current collector and the positive electrode active material layer in the positive electrode is defined as the "vertical direction," the surface of the positive electrode active material layer facing the current collector is defined as the "lower surface of the positive electrode active material layer," and the surface behind the surface facing the current collector is defined as the "upper surface of the positive electrode active material layer."

[0137] In an embodiment of the present invention, when an electrode assembly including a positive electrode, a negative electrode, and a separator is manufactured using the positive electrode, the top surface of the positive electrode active material layer may refer to the surface in contact with the separator.

[0138] In this specification, the "top view of the positive electrode active material layer" refers to an image for confirming the area and the length of the major axis of the sulfur-carbon composite distributed on the surface and inside of the positive electrode active material layer, and may be, for example, an SEM image obtained on the top surface of the positive electrode active material layer.

[0139] According to an embodiment of the present invention, in a top view of the positive electrode active material layer, gaps between the sulfur-carbon composites, grain boundaries, and grain surfaces of the sulfur-carbon composites can be distinguished by contrast.

[0140] In this case, to measure the longest axes of the top five sulfur-carbon composites and the bottom five sulfur-carbon composites based on the area of ​​the sulfur-carbon composites, it is preferable to use an image of the top view of the cathode active material layer having a magnification of, for example, 400 times or more. For example, the top view of the cathode active material layer may be an image of 400 times, 1,000 times, 2,000 times, or 5,000 times.

[0141] In one embodiment of the present invention, the top five sulfur-carbon composites and the bottom five sulfur-carbon composites based on the area of ​​the sulfur-carbon composites may be selected from images at the same magnification. However, they may also be selected from images at different magnifications to facilitate measurement of the length of the longest axis within each sulfur-carbon composite.

[0142] For example, based on the area of ​​the sulfur-carbon composites, the top five sulfur-carbon composites may be selected from SEM images at 400x magnification, and the bottom five sulfur-carbon composites may be selected from SEM images at 1,000x magnification.

[0143] In an embodiment of the present invention, the top five and bottom five sulfur-carbon composites may be selected from the entire region of the positive electrode active material layer. However, for ease of measurement, a portion of the positive electrode active material layer may be selected and the top five and bottom five sulfur-carbon composites may be selected from the same selected region.

[0144] In an embodiment of the present invention, the top five sulfur-carbon composites and the bottom five sulfur-carbon composites may be selected within the same area of ​​the positive electrode active material layer or may be selected within different areas.

[0145] For example, the top five sulfur-carbon composites and the bottom five sulfur-carbon composites may be selected from an area of ​​50 μm×50 μm to 1,000 μm×1,000 μm on the upper surface of the positive electrode active material layer.

[0146] In an embodiment of the present invention, the top five sulfur-carbon composites may be selected from an area of ​​150 μm×150 μm to 1,000 μm×1,000 μm on the upper surface of the positive electrode active material layer.

[0147] In an embodiment of the present invention, the bottom five sulfur-carbon composites may be selected from an area of ​​50 μm×50 μm to 100 μm×100 μm on the upper surface of the positive electrode active material layer.

[0148] For example, the top five and bottom five sulfur-carbon composites may be selected within a 200 μm×200 μm area on the top surface of the positive electrode active material layer.

[0149] In this case, when the top five and bottom five sulfur-carbon composites are selected from images of different magnifications, as described above, the top five sulfur-carbon composites may be selected within a 200 μm×200 μm area on the top surface of the positive electrode active material layer, and the bottom five sulfur-carbon composites may be selected within a 70 μm×70 μm area located within the 200 μm×200 μm area.

[0150] In one embodiment of the present invention, the area of ​​the sulfur-carbon composite may be determined from the pixel area occupied by the sulfur-carbon composite in a top view of the cathode active material layer. That is, the top five sulfur-carbon composites based on the area of ​​the sulfur-carbon composite may refer to the top five sulfur-carbon composites in order of the largest pixel area occupied by the particle surface in the top view of the cathode active material layer. Furthermore, the bottom five sulfur-carbon composites based on the area of ​​the sulfur-carbon composite may refer to the bottom five sulfur-carbon composites in order of the smallest pixel area occupied by the particle surface in the top view of the cathode active material layer.

[0151] In an embodiment of the present invention, the longest axis in the sulfur-carbon composite refers to the longest straight line in one sulfur-carbon composite in a top view of the cathode active material layer.

[0152] In one embodiment of the present invention, the longest axis of the sulfur-carbon composite may pass through the center of gravity of one sulfur-carbon composite. However, if the shape of the sulfur-carbon composite in the top view of the cathode active material layer is not spherical or elliptical, the longest axis may not pass through the center of gravity of the sulfur-carbon composite. Therefore, the longest axis of the sulfur-carbon composite is not limited to a line passing through the center of gravity of the sulfur-carbon composite.

[0153] In an embodiment of the present invention, the length of the longest axis in the sulfur-carbon composite may be determined by the longest distance between pixels where the longest axis is located in a top view of the cathode active material layer.

[0154] In the above formula 4, the X L is the average value of the lengths of the longest axes of the top five sulfur-carbon composites in terms of area in the top view of the positive electrode active material layer, and X S is the average length of the longest axis among the five sulfur-carbon composites in the bottom area in the top view of the positive electrode active material layer.

[0155] In this specification, the term "average value" means the arithmetic mean. L can be measured by measuring the length of the longest axis of each of the top five sulfur-carbon composites based on the area in a top view of the positive electrode active material layer and then calculating the average. S can be measured by measuring the length of the longest axis of each of the five sulfur-carbon composites in the bottom area in a top view of the positive electrode active material layer and then calculating the average.

[0156] In one embodiment of the present invention, particles having a length of less than 1 μm along their longest axis may appear in a top view of the positive electrode active material layer. In this case, the particles having a length of less than 1 μm along their longest axis are not sulfur-carbon composites carrying sulfur on their outer surfaces and / or inside their pores, but are porous carbon materials or other impurities crushed during the preparation of the positive electrode. Therefore, the X STo measure the area of ​​the sulfur-carbon composites, the bottom five sulfur-carbon composites are selected from the top view of the positive electrode active material layer. Particles with a longest axis length of 1 μm or more are not selected, and only particles with a longest axis length of 1 μm or more are selected.

[0157] In one embodiment of the present invention, whether the positive electrode satisfies Equation 4 can be measured immediately after manufacturing the positive electrode or after charging and discharging.

[0158] For example, immediately after the positive electrode is manufactured and before activation, a top view of the positive electrode active material layer is obtained, and X L and X S can be measured using the method described above to confirm whether Equation 4 is satisfied.

[0159] In addition, a lithium-sulfur battery assembled using the positive electrode was disassembled to obtain the positive electrode, and X was obtained from a top view of the positive electrode active material layer of the obtained positive electrode. L and X S can be measured using the method described above to confirm whether Equation 4 is satisfied.

[0160] Specifically, when disassembling the lithium-sulfur battery to determine whether Formula 4 is satisfied, the lithium-sulfur battery may be disassembled in a charged state. Specifically, the lithium-sulfur battery may be disassembled in a charged state under a non-active atmosphere to obtain a positive electrode, and the electrolyte impregnated in the obtained positive electrode may be extracted using an appropriate solvent, washed, and dried, and then a top view of the positive electrode active material layer may be obtained to determine whether Formula 4 is satisfied.

[0161] In one embodiment of the present invention, the state of charge of the lithium-sulfur battery may be, for example, 50% to 90% SOC, specifically 60% to 80% SOC, but the present invention is not limited thereto. Also, the inert atmosphere may be, for example, an Ar atmosphere, but the present invention is not limited thereto.

[0162] In one embodiment of the present invention, repeated charge and discharge of a lithium-sulfur battery can cause the active material to be separated from the positive electrode active material layer due to external pressure, or the positive electrode can be deformed due to repeated expansion and contraction of the positive electrode active material. Therefore, when disassembling an assembled lithium-sulfur battery to obtain a positive electrode, it is preferable to check whether Equation 4 is satisfied from a lithium-sulfur battery that exhibits a capacity retention rate of 80% or more compared to the capacity immediately after manufacture (initial capacity).

[0163] In an embodiment of the present invention, the positive electrode active material layer may include a plurality of sulfur-carbon composites, and the positive electrode may satisfy the following Equation 5:

[0164] [Formula 5] X L / X A ≦2

[0165] In Formula 5, the X L is the average value of the lengths of the longest axes of the top five sulfur-carbon composites in terms of area in the top view of the positive electrode active material layer, and X A is the average length of the longest axis in all sulfur-carbon composites observed from the top view of the positive electrode active material layer.

[0166] X L and X A The method for measuring X L and X S The above-mentioned method is used as the measurement method.

[0167] At this time, the X A is calculated as the average value of the lengths of the longest axes of all sulfur-carbon composites observed in the top view of the positive electrode active material layer.

[0168] In one embodiment of the present invention, the positive electrode active material layer may have an average tortuosity of 1.7 or less, specifically, 1.6 or less, for example, 1.3 to 1.6.

[0169] In one embodiment of the present invention, the "tortuosity" may refer to the degree of tortuosity of the transport path of ions, etc. in the positive electrode active material layer. That is, the smaller the tortuosity, the shorter the transport path of ions, etc. in the positive electrode active material layer, which may improve the electrochemical activity of the electrode and the battery using the electrode, and may have a beneficial effect on high-power characteristics in particular.

[0170] In one embodiment of the present invention, the average degree of tortuosity of the positive electrode active material layer can be measured by the following method. For example, first, an image of a vertical cross section of the current collector-positive electrode active material layer is obtained along the stacking direction (vertical direction) of the current collector and the positive electrode to be measured. A point on the surface of the current collector is selected from the image, and the vertical distance (L) is measured by connecting the edge of the electrode in the vertical direction from the point to the surface of the positive electrode. Next, the minimum distance (C) is measured along the boundary between particles (sulfur-carbon composites) located between the selected point and the edge of the electrode. The measured L and C values ​​are used to calculate the degree of tortuosity (C / L). The above process is repeated for at least three different points on the surface of the current collector, and the average of the obtained C / L values ​​is calculated to measure the average degree of tortuosity.

[0171] That is, the tortuosity can be calculated by the following Equation 6 after measuring the vertical distance (L) from any point on the surface of the current collector to the end point of the positive electrode located in the vertical direction and the minimum distance (C) of the curve along the particle (sulfur-carbon composite) interface.

[0172] [Formula 6] Curvature = [Minimum curve distance (C) / Vertical distance (L)]

[0173] In one embodiment of the present invention, the vertical cross-sectional image of the positive electrode may be, for example, a SEM image. For example, Figs. 6b and 7b show SEM images of the vertical distance (L) and the minimum distance (C) of the curve for evaluating the curvature of the positive electrode active material layer for the positive electrodes using the sulfur-carbon composites of Comparative Example 2 and Example 4, respectively. The SEM images may be images magnified 1,000 times, but the method for measuring the curvature is not limited thereto.

[0174] In an embodiment of the present invention, the positive electrode active material layer may have an average degree of curvature in the vertical and vertical directions of 1.7 or less in a top view.

[0175] For example, in a top view of the positive electrode active material layer, the value of [(vertical bending degree + vertical bending degree) / 2] may be 1.7 or less. Specifically, the average bending degrees in the horizontal and vertical directions may be 1 to 1.7.

[0176] In this case, the degree of bending in each of the horizontal and vertical directions can be calculated as [minimum distance of the curve (C) / vertical distance (L)] as described above.

[0177] In one embodiment of the present invention, the longitudinal and average longitudinal tortuosity in a top view of the positive electrode active material layer can be measured as follows: Two lines extending in the longitudinal and vertical directions and intersecting each other are drawn on the top view of the positive electrode active material layer. The linear distance (L) between each line is measured. The minimum distance (C) along the boundary between particles (sulfur-carbon composites) located between each point is measured, and then the C / L value is calculated to calculate the average transverse and longitudinal tortuosity.

[0178] For example, SEM images showing the vertical distance and the minimum distance of the curve to evaluate the curvature of the upper surface of the cathode active material layer for the cathodes using the sulfur-carbon composites of Example 1 and Comparative Example 1 are shown in Figure 4c (Example 1) and Figure 5e (Comparative Example 1), respectively.

[0179] In one embodiment of the present invention, the positive electrode active material layer may further include at least one of a binder and a conductive material. Specifically, the positive electrode active material layer may further include a binder resin together with the sulfur-carbon composite. Furthermore, the positive electrode active material layer may further include a conductive material, if necessary, in addition to the positive electrode active material and the binder resin. In this regard, in one embodiment of the present invention, the positive electrode active material layer preferably contains 70 wt% or more, 85 wt% or more, or 90 wt% or more of the positive electrode active material relative to 100 wt% of the positive electrode active material layer.

[0180] The positive electrode active material includes the sulfur-carbon composite. In one embodiment of the present invention, the sulfur (S) element in the sulfur-carbon composite is preferably contained in an amount of 60 wt% or more, 65 wt% or more, 70 wt% or more, or 75 wt% or more, based on 100 wt% of the positive electrode active material layer.

[0181] If the sulfur (S) content in the positive electrode is less than 60 wt%, it may be difficult to improve the energy density of the battery due to a lack of electrode active material, but the present invention is not limited thereto. In addition, in one embodiment of the present invention, the positive electrode active material layer may contain 50 wt% or more, 70 wt% or more, 90 wt% or more, or 95 wt% or more of the sulfur-carbon composite having the above-described characteristics relative to 100 wt% of the positive electrode active material. In one embodiment of the present invention, the positive electrode active material may consist solely of the sulfur-carbon composite.

[0182] In one embodiment of the present invention, the loading amount of the positive electrode is, for example, 1.67 mg s / cm 2 The above, specifically 1.67 mg s / cm 2 ~2.92mg s / cm 2 , more specifically 1.67 mg s / cm 2 ~2.08mg s / cm 2 The loading amount can be calculated from the content of the active material in the positive electrode and the content of sulfur (S) in the active material.

[0183] In one embodiment of the present invention, the loading amount of the positive electrode is converted into a capacity, for example, the loading amount is 2.0 mAh / cm 2 Specifically, 2.0mAh / cm 2 ~3.5mAh / cm 2 , more specifically 2.0mAh / cm 2 ~2.5mAh / cm 2 However, the present invention is not limited to this.

[0184] In addition to the sulfur-carbon composite, the positive electrode active material layer may further include a common positive electrode active material that can be used in lithium secondary batteries. Examples of such common positive electrode active materials include, but are not limited to, lithium transition metal oxides; lithium metal iron phosphate; lithium nickel-manganese-cobalt oxide; and oxides in which a portion of lithium nickel-manganese-cobalt oxide is substituted with another transition metal; or two or more of these. Specifically, the positive electrode active material may include layered compounds such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), or compounds substituted with one or more transition metals; and compounds having the chemical formula Li 1+x Mn 2-x O4 (where x is 0 to 0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, and Cu2V2O7; and the chemical formula LiNi 1-x M x O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, x = 0.01 to 0.3); Ni-site type lithium nickel oxide; chemical formula LiMn 2-x M x Lithium manganese composite oxides represented by Li2Mn3MO8 (where M = Co, Ni, Fe, Cr, Zn, or Ta, x = 0.01 to 0.1) or Li2Mn3MO8 (where M = Fe, Co, Ni, Cu, or Zn); lithium metal phosphate oxide LiMPO4 (where M = Fe, CO, Ni, or Mn); lithium nickel-manganese-cobalt oxide Li 1+x (Ni a Co b Mn c ) 1-x O2 (x=0~0.03, a=0.3~0.95, b=0.01~0.35, c=0.01~0.5, a+b+c=1); Lithium nickel-manganese-cobalt oxide, in which a portion of the oxide is replaced by aluminum a [Ni b Co c Mn d Al e ] 1-f M1f O2 (M1 is one or more selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, 0.8 ≦ a ≦ 1.2, 0.5 ≦ b ≦ 0.99, 0 < c < 0.5, 0 < d < 0.5, 0.01 ≦ e ≦ 0.1, 0 ≦ f ≦ 0.1); an oxide in which a part of lithium nickel-manganese-cobalt oxide is substituted with another transition metal Li 1+x (Ni a Co b Mn c M d ) 1-x O2 (x = 0 to 0.03, a = 0.3 to 0.95, b = 0.01 to 0.35, c = 0.01 to 0.5, d = 0.001 to 0.03, a + b + c + d = 1, M is any one selected from the group consisting of Fe, V, Cr, Ti, W, Ta, Mg, and Mo), a disulfide compound; examples include Fe2(MoO4)3, but are not limited thereto.

[0185] On the other hand, as the positive electrode current collector, various positive electrode current collectors used in the art can be used. For example, the positive electrode current collector can be stainless steel, aluminum, nickel, titanium, fired carbon, or a surface-treated product of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. 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 films, sheets, foils, nets, porous bodies, foams, non-woven fabrics, etc.

[0186] The binder resin, which functions to improve adhesion between positive electrode active material particles and between the positive electrode active material and the positive electrode current collector, may be 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 rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, either alone or in combination. The binder resin may be present in an amount of 1 to 30 wt%, preferably 1 to 20 wt%, and more preferably 1 to 10 wt%, based on the total weight of the positive electrode active material layer.

[0187] The conductive material is used to impart conductivity to the electrode and can be any material that is conductive and does not induce chemical changes in the battery. 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 powder or fiber, such as copper, nickel, aluminum, or silver; conductive whiskers, such as zinc oxide or potassium titanate; conductive metal oxides, such as titanium oxide; and conductive polymers, such as polyphenylene derivatives. These materials may be used alone or in combination. When a conductive material is used, the conductive material is typically present in an amount of 1 wt% to 30 wt%, preferably 1 wt% to 20 wt%, and more preferably 1 wt% to 10 wt% of the total weight of the positive electrode active material layer.

[0188] The positive electrode can be prepared by conventional methods well known in the art.

[0189] Specifically, in the method for producing a positive electrode of the present invention, the binder resin is first dissolved in a solvent for producing a slurry, and then a conductive material is dispersed therein. As the solvent for producing the slurry, it is preferable to use one that can uniformly disperse the positive electrode active material, the binder resin, and the conductive material used as needed, and that is easily evaporated. Typical examples include acetonitrile, methanol, ethanol, tetrahydrofuran, water, and isopropyl alcohol.

[0190] The positive electrode active material, optionally together with an additive, is then uniformly dispersed in the solvent containing the conductive material to prepare a positive electrode slurry. The amounts of the solvent, positive electrode active material, and optional additives contained in the slurry are not particularly important in the present invention, and the slurry only needs to have an appropriate viscosity to be easily coated.

[0191] The slurry thus prepared is applied to a current collector and dried under vacuum to form a positive electrode. The slurry may be coated on the current collector to an appropriate thickness depending on the viscosity of the slurry and the thickness of the positive electrode to be formed.

[0192] The coating may be performed by a conventional method known in the art, for example, by applying the positive electrode active material slurry to one surface of the positive electrode current collector and then uniformly dispersing the slurry using a doctor blade, etc. Alternatively, the coating may be performed by die casting, comma coating, screen printing, etc.

[0193] The drying is not particularly limited, but can be carried out in a vacuum oven at 50°C to 200°C within one day.

[0194] According to yet another embodiment of the present invention, there is provided a lithium-sulfur battery including the above-described positive electrode.

[0195] 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.

[0196] According to an embodiment of the present invention, the positive electrode may include the positive electrode active material described above.

[0197] According to an embodiment of the present invention, the positive electrode may include a positive electrode active material layer containing a plurality of sulfur-carbon composites. In a top view of the positive electrode active material layer, a ratio of an average length of the longest axis among the top five sulfur-carbon composites based on area to an average length of the longest axis among the bottom five sulfur-carbon composites based on area may satisfy Equation 4.

[0198] In one embodiment of the present invention, the unit structure of the positive electrode / separator / negative electrode may be referred to as an electrode assembly, and the electrode assembly may be stacked, for example, with the separator interposed between the negative electrode and the positive electrode to form a stacked or stack / folded structure, or may be wound up to form a jelly roll structure. Furthermore, when a jelly roll structure is formed, a separator may be further disposed on the outside to prevent the negative electrode and the positive electrode from coming into contact with each other.

[0199] 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 includes a negative electrode active material, a conductive material, and a binder.

[0200] The negative electrode will be described in detail below.

[0201] The negative electrode may have a structure in which a negative electrode active material layer is formed on one or both sides of a long sheet-like negative electrode current collector, and the negative electrode active material layer may include a negative electrode active material and a binder resin. The negative electrode active material layer may further include a conductive material, if necessary.

[0202] Specifically, the negative electrode may be manufactured by coating one or both sides of a long, sheet-shaped negative electrode current collector with a negative electrode slurry prepared by dispersing a negative electrode active material, a conductive material, and a binder in a solvent such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and then drying the negative electrode slurry to remove the solvent, followed by rolling. Meanwhile, a negative electrode including a non-coated portion may be manufactured by not coating a portion of the negative electrode current collector, for example, one end of the negative electrode current collector, with the negative electrode slurry during coating.

[0203] The negative electrode active material is lithium (Li + The material may include a material capable of reversibly intercalating or deintercalating lithium ions, a material capable of reversibly forming a lithium-containing compound by reacting with lithium ions, lithium metal, or a lithium alloy. The material capable of reversibly intercalating or deintercalating lithium ions may be, for example, crystalline carbon, amorphous carbon, or a mixture thereof, and specific examples include, but are not limited to, artificial graphite, natural graphite, graphitized carbon fiber, amorphous carbon, soft carbon, and hard carbon.

[0204] The material capable of reacting with lithium ions to reversibly form a lithium-containing compound may be, for example, tin oxide, titanium nitride, or a silicon-based compound.

[0205] The lithium alloy may be, for example, an alloy of lithium (Li) and a metal selected from the group consisting of sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), radium (Ra), aluminum (Al), and tin (Sn). Preferably, the negative electrode active material may be lithium metal, specifically, in the form of a lithium metal thin film or lithium metal powder.

[0206] The silicon-based compound is Si, Si-Me alloy (where Me is one or more selected from the group consisting of Al, Sn, Mg, Cu, Fe, Pb, Zn, Mn, Cr, Ti, and Ni), SiO y (where 0 < y < 2), Si-C composite, or a combination thereof, and preferably SiO y (where 0 < y < 2). Since the silicon-based compound has a high theoretical capacity, when the silicon-based compound is included as a negative electrode active material, the capacity characteristics can be improved.

[0207] As the negative electrode current collector, a negative electrode current collector generally used in the art can be used. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, those surface-treated with carbon, nickel, titanium, silver, etc. on the surface of copper or stainless steel, aluminum-cadmium alloy, etc. can be used. The negative electrode current collector usually can have a thickness of 3 μm to 500 μm. Similar to the positive electrode current collector, fine irregularities may be formed on the surface of the current collector to enhance the binding force of the negative electrode active material. For example, it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven fabrics, etc.

[0208] The binder resin serves to improve the adhesion between the negative electrode active material particles and the adhesion force between the negative electrode active material and the negative electrode current collector. Specifically, 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 rubber (EPDM rubber), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluorine rubber, or various copolymers thereof, etc. can be mentioned, and one of these alone or a mixture of two or more can be used. The binder resin can be included at 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 negative electrode active material layer.

[0209] The optional conductive material is used to impart conductivity to the negative electrode. Any conductive material can be used as long as it does not induce chemical changes in the battery. 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 fibers, such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and conductive polymers, such as polyphenylene derivatives. These materials may be used alone or in combination. When a conductive material is used, it is typically present in an amount of 1 wt% to 30 wt%, preferably 1 wt% to 20 wt%, and more preferably 1 wt% to 10 wt% of the total weight of the negative electrode active material layer.

[0210] The separator is disposed within the electrode assembly between the negative electrode and the positive electrode. The separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used. Specifically, the separator may be a porous polymer film, such as a porous polymer film made from a polyolefin polymer, such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof. Conventional porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. Separators coated with ceramic components or polymeric materials may also be used to ensure heat resistance or mechanical strength.

[0211] In yet another embodiment of the present invention, there is provided an electrochemical device including the electrode assembly. The electrochemical device includes an electrode assembly and an electrolyte housed together in a battery case, and the battery case may be of any type commonly used in the art, such as a pouch type, metal can type, cylindrical type, stack type, or coin type, without any particular limitation.

[0212] The electrolyte used in the present invention is not particularly limited, and may be any of various electrolytes that can be used in lithium secondary batteries, such as organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes.

[0213] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0214] The organic solvent may be any organic solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specific examples of the organic solvent that can be used include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether and tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (R is a C2-C20 linear, branched, or cyclic hydrocarbon group that may contain a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; and sulfolanes.

[0215] On the other hand, in one embodiment of the present invention, in order to form a polymer protective film that suppresses the formation of lithium dendrites and reduces decomposition and side reactions of the electrolyte on the surface of the lithium-based metal, it is preferable to include a heterocyclic compound containing an oxygen atom or a sulfur atom. The heterocyclic compound may be a 3- to 15-membered heterocyclic compound, preferably a 3- to 7-membered heterocyclic compound, and more preferably a 5- or 6-membered heterocyclic compound.

[0216] The heterocyclic compound may be a heterocyclic compound unsubstituted or substituted with one or more selected from the group consisting of an alkyl group having 1 to 4 carbon atoms, a cyclic alkyl group having 3 to 8 carbon atoms, an aryl group having 6 to 10 carbon atoms, a halogen group, a nitro group (-NO2), an amine group (-NH2), and a sulfonyl group (-SO2); or a multi-ring compound of a heterocyclic compound and one or more selected from the group consisting of a cyclic alkyl group having 3 to 8 carbon atoms and an aryl group having 6 to 10 carbon atoms.

[0217] When the heterocyclic compound is a heterocyclic compound substituted with an alkyl group having 1 to 4 carbon atoms, the radicals are stabilized, thereby suppressing side reactions between the additive and the electrolyte. Furthermore, when the heterocyclic compound is substituted with a halogen group or a nitro group, a functional protective film can be formed on the surface of the lithium-based metal. The functional protective film is a stable and compact protective film that allows for uniform deposition of the lithium-based metal and suppresses side reactions between the polysulfide and the lithium-based metal.

[0218] Specifically, the heterocyclic compound may include one or more compounds selected from the group consisting of furan, 2-methylfuran, 3-methylfuran, 2-ethylfuran, 2-propylfuran, 2-butylfuran, 2,3-dimethylfuran, 2,4-dimethylfuran, 2,5-dimethylfuran, pyran, 2-methylpyran, 3-methylpyran, 4-methylpyran, benzofuran, 2-(2-nitrovinyl)furan, thiophene, 2-methylthiophene, 2-ethylthiophene, 2-propylthiophene, 2-butylthiophene, 2,3-dimethylthiophene, 2,4-dimethylthiophene, and 2,5-dimethylthiophene, and preferably includes one or more compounds selected from the group consisting of 2-methylfuran and 2-methylthiophene.

[0219] Meanwhile, in one embodiment of the present invention, the non-aqueous solvent of the electrolyte solution may include an ether-based solvent to improve the charge / discharge performance of the battery. Examples of 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, and 1H,1H,2'H-perfluorodipropyl ether). A mixture of one or more of these may be used as the non-aqueous solvent.

[0220] The lithium salt may be any compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the lithium salt may be LiPF, LiClO, LiAsF, LiBF, LiSbF, LiAlO, LiAlCl, LiCF, SO, LiCF, SO, LiN(CF, SO), LiN(CF, SO), LiN(CF, SO), LiCl, LiI, or LiB(C, O) . 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. When the lithium salt concentration is within the above range, the electrolyte has appropriate conductivity and viscosity, exhibiting excellent electrolyte performance and allowing for efficient lithium ion migration.

[0221] In addition to the electrolyte components, the electrolyte may further contain additives for purposes such as improving battery life characteristics, suppressing battery capacity loss, and improving battery discharge capacity. Examples of additives include, but are not limited to, LiNO3, haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, and aluminum trichloride, which may be used alone or in combination. The additives may be present 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.

[0222] In one embodiment of the present invention, 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 elemental sulfur (S) in the positive electrode of, for example, 3.5 g / g or less, for example, 3.3 g / g or less, or preferably 3.2 g / g or less. Also, the lithium-sulfur battery may have a ratio (El / S) of the total weight of the electrolyte to the total weight of elemental sulfur (S) in the positive electrode of 3.0 g / g to 3.5 g / g, for example, 3.1 g / g to 3.2 g / g.

[0223] The use of the sulfur-carbon composite according to the present invention makes it possible to realize a lithium-sulfur battery having an El / S ratio in the above-mentioned range, thereby improving the energy density. However, the present invention is not limited to this, and lithium-sulfur batteries using the sulfur-carbon composite with an El / S ratio higher than the above-mentioned range can also be realized.

[0224] The shape of the lithium-sulfur battery is not particularly limited, and may be various shapes such as a cylindrical type, a stacked type, a coin type, etc.

[0225] The present invention also provides a battery module including the lithium-sulfur battery as a unit cell, which can be used as a power source for medium- to large-sized devices that require high-temperature stability, long cycle characteristics, and high capacity characteristics.

[0226] According to one embodiment of the present invention, the lithium-sulfur battery can maintain a high power density during discharge by using the above-described positive electrode active material or the above-described positive electrode, specifically, a power density of 2.1 kW / kg or more for 10 seconds during discharge.

[0227] In one embodiment of the present invention, the 10-second power density can be calculated by applying a current to a lithium-sulfur battery under test for 10 seconds using Equation 7. However, the measurement method is not limited thereto. Here, the measurement can be performed under a discharge condition of 1.5 V and 5 C.

[0228] [Formula 7] Power density (kW / kg) = [(Vmin) × (MaxC rate) × (discharge capacity)] / (battery weight)

[0229] According to one embodiment of the present invention, the lithium-sulfur battery has a discharge capacity per weight of sulfur (S) of 1,000 mAh / g by using the above-mentioned positive electrode active material or the above-mentioned positive electrode. s The present invention is not limited to the above capacity.

[0230] Examples of the medium- to 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 two-wheeled vehicles including electric bicycles (E-bikes) and electric scooters; electric golf carts; and power storage systems.

[0231] In one embodiment of the present invention, the lithium-sulfur battery may be a pouch-type, coin-type, or cylindrical battery, for example, a pouch-type battery, but the present invention is not limited thereto.

[0232] In order to facilitate understanding of the present invention, preferred examples are presented below. However, the following examples are merely illustrative of the present invention, and it will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the present invention and the technical concept thereof. It goes without saying that such changes and modifications also fall within the scope of the claims.

[0233] [Production of sulfur-carbon composite] Preparation Example 1. Preparation of porous carbon material Carbon nanotubes (CNT) (Entagled MWCNT, BET specific surface area 200m 2The carbon nanotubes (D) were put into a centrifugal crusher (Retsch ZM200) equipped with a sieve and crushed. The crushed carbon nanotubes were sieved under centrifugal force to control the particle size. 50 Particle size (target D 50 In order to obtain carbon nanotubes of the above particle size, the mesh size of the sieve and the rotation speed were adjusted to obtain carbon nanotubes with controlled particle size. The particle size conditions of the obtained porous carbon material are listed in Table 1 below.

[0234] Preparation Example 2. Preparation of porous carbon material Carbon nanotubes (CNTs) (Entagled MWCNTs, BET specific surface area 200m 2 / g) was pulverized by jet milling to obtain pulverized carbon nanotubes.

[0235] Production of sulfur-carbon composites The carbon nanotubes obtained in Preparation Example 1 or Preparation Example 2 were used as a porous carbon material. The porous carbon material and sulfur (S8) were mixed in the weight ratios shown in Table 1 below, followed by ball milling. The mixture was then placed in an oven at 155°C for 30 minutes to prepare a sulfur-carbon composite.

[0236] [Table 1]

[0237] [Table 2]

[0238] [Measurement of shape and particle size of porous carbon material] The D of the porous carbon material obtained by the dry method using a particle size analyzer (model: Bluewave, manufacturer: Microtrac) 10 , D 50 and D 90 When the carbon material had formed secondary particles due to aggregation, the primary particle size was observed and measured using a scanning electron microscope (model: SEM, manufacturer: JEOL).

[0239] The BF value is the particle size D 10 Particle size D 90 The ratio of D 90 / D 10 1 shows the results of measuring the particle size distribution of the porous carbon materials used in Examples 1 to 3 and Comparative Example 1.

[0240] 2 and 3 show SEM images of the porous carbon materials used in Example 4 (FIG. 2) and Comparative Example 2 (FIG. 3), respectively.

[0241] [Cathode manufacturing] The sulfur-carbon composites obtained in Examples 1 to 4 and Comparative Examples 1 and 2 were used to manufacture positive electrodes for lithium-sulfur batteries as follows.

[0242] A positive electrode slurry composition was prepared by mixing 90 wt% of sulfur-carbon composite as a positive electrode active material, 5 wt% of Denka black as a conductive material, and 5 wt% of styrene butadiene rubber / carboxymethyl cellulose (SBR:CMC = 7:3 weight ratio) as a binder in a solvent.

[0243] The prepared positive electrode slurry composition was applied to a thickness of 350 μm on an aluminum current collector having a thickness of 20 μm, dried at 50° C. for 12 hours, and pressed with a roll press to prepare a positive electrode.

[0244] The sulfur (S) content in the positive electrodes using the sulfur-carbon composites of Examples 1 to 3 and Comparative Example 1 was 67.5 wt%, and the sulfur (S) content in the positive electrodes using the sulfur-carbon composites of Example 4 and Comparative Example 2 was 63.0 wt%.

[0245] [Evaluation of whether the positive electrode satisfies Equation 4] Evaluation example 1 SEM images were taken of the upper surfaces of the positive electrode active material layers of the positive electrodes prepared using the sulfur-carbon composites of Example 1 and Comparative Example 1. The SEM images were taken at a magnification of 400x to a size of 200 μm × 200 μm and at a magnification of 1,000x to a size of 70 μm × 70 μm, based on the center of each positive electrode.

[0246] Next, the top five sulfur–carbon composites were selected from the 200 μm × 200 μm images based on the area of ​​the sulfur–carbon composites, and the bottom five sulfur–carbon composites were selected from the 70 μm × 70 μm images based on the area of ​​the sulfur–carbon composites.

[0247] The length of the longest axis in each selected sulfur-carbon composite was measured, and the average value was calculated using Equation 4 below. The results are shown in Table 3 below.

[0248] [Formula 4] X L / X S ≦15

[0249] In formula 4, the X L is the average value of the lengths of the longest axes of the top five sulfur-carbon composites in terms of area in the top view of the positive electrode active material layer, and X S is the average length of the longest axis among the five sulfur-carbon composites in the bottom area in the top view of the positive electrode active material layer.

[0250] Figures 4a and 4b show SEM images of the cathode of Example 1. Figure 4a shows the longest axes of the top five selected sulfur-carbon composites, and Figure 4b shows the longest axes of the bottom five selected sulfur-carbon composites. Figures 5a and 5b show SEM images of the cathode of Comparative Example 1. Figure 5a shows the longest axes of the top five selected sulfur-carbon composites, and Figure 5b shows the longest axes of the bottom five selected sulfur-carbon composites.

[0251] In each SEM image, particles with a longest axis length of less than 1 μm were confirmed to be not porous carbon materials supporting sulfur, i.e., sulfur-carbon composites, and were therefore excluded from selection.

[0252] [Table 3]

[0253] Evaluation example 2 After manufacturing a lithium-sulfur battery using the positive electrode, the following experiment was carried out to evaluate how the fulfillment of Equation 4 changes with repeated charge and discharge.

[0254] First, a lithium-sulfur battery was fabricated as follows.

[0255] An electrode assembly was fabricated using the cathode fabricated using the sulfur-carbon composite of Comparative Example 1, a cathode, and an anode, with a separator interposed between the cathode and anode. The electrode assembly was placed in a pouch-type case and filled with an electrolyte to fabricate a lithium-sulfur battery. A 35 μm-thick lithium metal thin film was used as the anode. A 16 μm-thick porous polyethylene was used as the separator. The electrolyte was prepared by adding 3 wt% LiNO3 and 1M LiPF6 to an organic solvent mixture of 2-methylfuran and dimethoxyethane in a volume ratio of 33:77. Pouch cells containing the cathode and anode fabricated in this manner were fabricated. The El / S ratio of each battery was controlled at 3.1 g / g.

[0256] Each lithium-sulfur battery was discharged at 25°C in a CC (Constant Current) mode at 0.5 C to 1.8 V, and then charged at a constant current of 0.3 C to 2.5 V, and then discharged and charged 200 times at 1.0 C. Using a charge-discharge tester, it was confirmed that the discharge capacity was maintained at 80% or more, based on the initial capacity of 100%.

[0257] After the final charge, the lithium-sulfur battery at 75% SOC was disassembled in a glove box under an Ar atmosphere, and the positive electrode was separated. The surface of the separated positive electrode was washed with DME and dried, and then the satisfaction of Equation 4 was evaluated in the same manner as in Evaluation Example 1.

[0258] Figures 5c and 5d show the SEM images obtained. Figure 5c shows the longest axes of the top five selected sulfur-carbon composites, and Figure 5d shows the longest axes of the bottom five selected sulfur-carbon composites. Equation 4 was calculated and the results are shown in Table 4 below.

[0259] [Table 4]

[0260] From Tables 3 and 4, it was confirmed that the positive electrode prepared using the sulfur-carbon composite of Comparative Example 1 failed to satisfy Equation 4 immediately after preparation and after repeated charge-discharge cycles after application to a battery.

[0261] Through subsequent experiments, it was confirmed that lithium-sulfur batteries using cathodes that do not satisfy Equation 4 are inferior in terms of battery capacity, power density, and high-speed output performance. This is presumably because sulfur (S) is not uniformly dispersed within the cathode, resulting in reduced reactivity.

[0262] [Evaluation of average bending degree of positive electrode] SEM images of vertical cross sections of the cathodes prepared using the sulfur-carbon composites of Comparative Example 2 and Example 2 are shown in Fig. 6a (Comparative Example 2) and Fig. 7a (Example 2), respectively. The average tortuosity of the cathode active material layer was evaluated from the obtained SEM images as follows.

[0263] First, 1) a point on the surface of the current collector was randomly selected from the obtained SEM image, and the vertical distance (L) from that point to the surface of the positive electrode was measured by connecting the edge of the electrode in the vertical direction. Next, 2) the minimum distance (C) was measured along the boundary between particles (sulfur-carbon composites) located between the random point selected in step 1) and the edge of the electrode. 3) The tortuosity (C / L) was calculated using the measured L and C values. 4) At least three different points were selected on the surface of the current collector, and steps 1) to 3) were repeated. The average of the obtained C / L values ​​was then calculated to evaluate the average tortuosity.

[0264] [Formula 6] Curvature = [Minimum curve distance (C) / Vertical distance (L)]

[0265] 6b and 7b, the degrees of bending measured at three points A, B, and C and the average degree of bending at the three points are shown in Table 5 below.

[0266] [Table 5]

[0267] [Lithium-sulfur battery manufacturing] Using the positive electrodes using the sulfur-carbon composites obtained in Examples 1 to 4 and Comparative Examples 1 and 2, positive electrodes for lithium-sulfur batteries were produced as follows.

[0268] An electrode assembly was fabricated using the cathode prepared as described above, a cathode, and an anode, with a separator interposed between the cathode and the anode. The electrode assembly was placed in a pouch-type case, and an electrolyte was filled therein to fabricate a lithium-sulfur battery.

[0269] The negative electrode was a 35 μm-thick lithium metal thin film. The separator was a 16 μm-thick porous polyethylene. The electrolyte was prepared by adding 3 wt% LiNO3 and 1M LiPF6 to an organic solvent made by mixing 2-methylfuran and dimethoxyethane in a volume ratio of 33:77.

[0270] Pouch cells containing the positive and negative electrodes prepared in this way were fabricated. In each of the fabricated batteries, the El / S was controlled at 3.1 g / g.

[0271] [Electrochemical performance evaluation] 1.0C discharge capacity evaluation Each lithium-sulfur battery fabricated as described above was discharged at 25°C in CC mode at 0.5C to 1.8V, charged at a constant current of 0.3C to 2.5V, and then discharged at 1.0C to measure and compare the discharge capacity. The discharge capacity was measured based on the weight of sulfur (S). (mAh / g s ) A graph showing the change in discharge capacity due to repeated charge and discharge is shown in Fig. 8. The relative capacities of Examples 1 to 3 when the discharge capacity of Comparative Example 1 is set to 1 are shown in Fig. 9, and the relative nominal voltages of Examples 1 to 3 when the voltage of Comparative Example 1 is set to 1 are shown in Fig. 10.

[0272] The capacity measured at the first discharge after charging is shown in Table 6 below.

[0273] [Table 6]

[0274] Evaluation of 0.5C discharge capacity and energy density Each lithium-sulfur battery fabricated as described above was discharged at 25°C in CC mode at 0.5C to 1.8V, and then charged at a constant current of 0.5C to 2.5V. The discharge capacity was measured and compared. The results are shown in Table 6. The discharge capacity was measured based on the weight of sulfur (mAh / g). s ) The 0.5C discharge capacities of the batteries using the sulfur-carbon composites of Example 1, Example 4, Comparative Example 1, and Comparative Example 2 were evaluated. The results are shown in FIGS. 11 and 12, respectively, and the measured discharge capacities are shown in Table 7 below.

[0275] The energy density was measured using the measured 0.5C discharge capacity value according to the following Equation 8. The relative value of the energy density of Example 1 based on the energy density of Comparative Example 1, and the relative value of the energy density of Example 2 based on the energy density of Comparative Example 2 are shown in Table 7.

[0276] [Formula 8] Energy density = [(discharge capacity x driving voltage)] / (cell weight)

[0277] [Table 7]

[0278] 10-second power density evaluation After a current was applied to each of the lithium-sulfur batteries fabricated as described above for 10 seconds (1.5 V, 5 C discharge condition), the power density was calculated using Equation 7, and the results are shown in Table 8 below.

[0279] [Formula 7] Power density (kW / kg) = [(Vmin) × (MaxC rate) × (discharge capacity)] / (battery weight)

[0280] [Table 8]

[0281] [evaluation] Referring to Table 2, Figures 2 and 3, the BF value (D 90 / D 10 It can be seen that porous carbon materials with a BF value of 7 or less (Fig. 2) not only have more uniform particle sizes but also have narrower gaps between the particles than porous carbon materials with a larger BF value (Fig. 3).

[0282] Furthermore, referring to Table 3, Table 4, FIGS. 4a, 4b, 5a, 5b, 6a, and 7a, it can be seen that when a positive electrode is fabricated using a sulfur-carbon composite in which sulfur (S8) is loaded on a porous carbon material having a small BF value or a small size, the sulfur-carbon composite is uniformly distributed in the positive electrode active material layer and the gaps between the sulfur-carbon composites are narrow, thereby improving the sulfur utilization efficiency in the positive electrode.

[0283] 8 to 12, the lithium-sulfur battery according to an embodiment of the present invention has a discharge capacity of 1,000 mAh / g even at a high rate of 1.0 C. s It was confirmed that not only was it possible to realize the above-mentioned large discharge capacity, but also that it was possible to realize a higher energy density than in Comparative Examples 1 and 2, even if the amount of active material in the positive electrode was the same.

[0284] In particular, referring to Tables 6 to 8, when the sulfur (S) content was low, the pores between the porous carbon materials were large, and the sulfur-carbon composite was not uniformly distributed in the cathode (Comparative Example 2), the output density was low and the cathode was not suitable for high-power performance. However, when the discharge capacities of the batteries using Examples 1 and 2 were compared, it was confirmed that, according to one embodiment of the present invention, the electrochemical activity was sufficiently improved without increasing the sulfur loading rate, thereby increasing the battery capacity.

[0285] Through the above series of experiments, it was confirmed that by using a porous carbon material with small particle size or uniform particle size distribution as an active material support for a lithium-sulfur battery, sulfur (S) is uniformly dispersed, and therefore the oxidation-reduction reaction between sulfur (S) and LiS occurs uniformly during charging and discharging of the battery, improving the capacity and charge density of the battery and providing excellent high-speed output performance.

Claims

1. A sulfur-carbon composite including a porous carbon material and a sulfur-based material, The porous carbon material is selected from the following (1) and (2): (1) Particle size D １０ and particle size D ９０ The sum of these is 60 μm or less, (2) The following equation 1: [Formula 1] Broadness Factor (BF) = [(particle size D)] ９０ ) / (particle size D) １０ )] Particle size D １０ Particle size D ９０ The distribution ratio (BF) is 7 or less, A positive electrode active material for a lithium-sulfur battery, which satisfies at least one of the particle size conditions above.

2. The sulfur-based material is inorganic sulfur (S ８ ); Li ２ S ｎ (n≧1); organic sulfur compounds containing one or more of 2,5-dimercapto-1,3,4-thiadiazole and 1,3,5-trithiocyanic acid; carbon-sulfur polymers ((C ２ S ｘ ) ｎ , x=2.5-50, n≧2); or a mixture of two or more thereof.

3. The BET surface area of ​​the porous carbon material is 150 m ２ / g or more.

4. 2. The positive electrode active material for a lithium-sulfur battery according to claim 1, wherein the porous carbon material comprises carbon nanotubes, carbon black, graphite, activated carbon, graphene, or a mixture of two or more thereof.

5. The positive electrode active material for a lithium-sulfur battery according to claim 4 , wherein the porous carbon material comprises carbon nanotubes.

6. 2. The positive electrode active material for a lithium-sulfur battery according to claim 1, wherein the sulfur-carbon composite has a sulfur (S) content of 60 wt % or more based on 100 wt % of the sulfur-carbon composite.

7. The porous carbon material is The porous carbon material as the raw material is pulverized using a centrifugal pulverizer. The porous carbon material is crushed and sieved to a desired particle size. The mesh size of the sieve is determined based on the particle size D of the porous carbon material produced. ５０ The positive electrode active material for a lithium-sulfur battery according to claim 1, wherein the positive electrode active material has a size 2.8 to 4 times larger than that of the positive electrode active material for a lithium-sulfur battery.

8. The particle diameter D of the porous carbon material ５０ 2. The positive electrode active material for a lithium-sulfur battery according to claim 1, wherein the particle size is 100 μm or less.

9. 2. The positive electrode active material for a lithium-sulfur battery according to claim 1, wherein the porous carbon material has a BF value of 4 or more and 7 or less according to Equation 1.

10. a current collector and a positive electrode active material layer formed on at least one surface of the current collector, A positive electrode for a lithium-sulfur battery, wherein the positive electrode active material layer comprises the positive electrode active material for a lithium-sulfur battery according to any one of claims 1 to 9.

11. 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 contains a plurality of sulfur-carbon composites, The following equation 4: [Formula 4] X Ｌ / X Ｓ ≦15 Fulfilling In Equation 4, The X Ｌ is the average value of the lengths of the longest axes of the top five sulfur-carbon composites in terms of area in the top view of the positive electrode active material layer, The X Ｓ is the average value of the lengths of the longest axes of the five sulfur-carbon composites in the bottom area in a top view of the positive electrode active material layer.

12. 12. The positive electrode for a lithium-sulfur battery according to claim 11, wherein the positive electrode active material layer has an average degree of tortuosity of 1.7 or less.

13. 12. The positive electrode for a lithium-sulfur battery according to claim 11, wherein the positive electrode active material layer further comprises at least one of a binder and a conductive material.

14. 12. The positive electrode for a lithium-sulfur battery according to claim 11, wherein the content of elemental sulfur (S) relative to 100 wt% of the positive electrode active material layer is 60 wt% or more.

15. Sulfur loading: 1.67 mg ｓ / cm ２ More than 2.92 mg ｓ / cm ２ The positive electrode for a lithium-sulfur battery according to claim 11, wherein:

16. The sulfur-carbon composite includes a porous carbon material and a sulfur-based material, The porous carbon material is selected from the following (1) and (2): (1) Particle size D １０ and particle size D ９０ The sum of these is 60 μm or less, (2) The following equation 1: [Formula 1] Broadness Factor (BF) = [(particle size D)] ９０ ) / (particle size D) １０ )] Particle size D １０ Particle size D ９０ The distribution ratio (BF) is 7 or less, The positive electrode for a lithium-sulfur battery according to claim 11, which satisfies at least one particle size condition of the above.

17. The battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte; A lithium-sulfur battery, wherein the positive electrode is the positive electrode according to any one of claims 11 to 16.

18. 18. The lithium-sulfur battery of claim 17, wherein the ratio of the total weight of the electrolyte to the total weight of elemental sulfur (S) in the positive electrode (El / S) is 3.5 g / g or less.

19. 18. The lithium-sulfur battery of claim 17, wherein the power density for 10 seconds is 2.1 kW / kg or more.

20. 1,000 mAh / g per weight of sulfur (S) in the positive electrode ｓ 18. The lithium-sulfur battery of claim 17, having a discharge capacity of at least 1000 volts.

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