High-energy-density lithium secondary batteries

Abstract

The present invention relates to a lithium-sulfur battery having a high energy density, and provides a lithium-sulfur battery containing a compound defined by a characteristic peak in an XRD pattern in a discharged state. The lithium-sulfur battery according to one embodiment of the present invention has a high energy density. In particular, the lithium-sulfur battery of the present invention may have an energy density of 300 Wh / kg or more, and even 430 Wh / kg or more.

Description

[Technical Field]

[0001] The present invention relates to a lithium secondary battery, and more particularly to a lithium-sulfur battery having a high energy density.

[0002] This application claims priority based on Korean Patent Application No. 10-2023-0074500 filed on June 9, 2023, and Korean Patent Application No. 10-2023-0155551 filed on November 10, 2023, the entire contents of which are incorporated herein by reference. [Background technology]

[0003] As the range of applications of lithium secondary batteries expands from portable electronic devices to electric vehicles (EVs) and electric storage systems (ESSs), there is an increasing demand for lithium secondary batteries with high capacity, high energy density, and long life.

[0004] Among various lithium secondary batteries, lithium-sulfur batteries are battery systems that use sulfur-based materials with sulfur-sulfur bonds as the positive electrode active material and lithium metal, carbon-based materials in which lithium ions are inserted / extracted, or silicon or tin that forms an alloy with lithium as the negative electrode active material.

[0005] Sulfur, the main positive electrode active material in lithium-sulfur batteries, has advantages such as being lightweight per atom, abundant in resources, easy to supply and demand, inexpensive, non-toxic, and environmentally friendly.

[0006] In addition, lithium-sulfur batteries utilize the conversion reaction between lithium ions and sulfur at the positive electrode (S8+16Li + +16e -The theoretical specific capacity of the lithium secondary battery (Li-FeS) is 1,675mAh / g, and when lithium metal is used as the anode, it exhibits a theoretical energy density of 2,600Wh / kg. This is significantly higher than the theoretical energy densities of other battery systems currently being researched (Ni-MH battery: 450Wh / kg, Li-FeS battery: 480Wh / kg, Li-MnO2 battery: 1,000Wh / kg, Na-S battery: 800Wh / kg) and lithium-ion batteries (250Wh / kg). Therefore, it is attracting attention as an environmentally friendly, high-capacity, and inexpensive lithium secondary battery among the secondary batteries currently being developed.

[0007] However, the amount of electrolyte is still large, or the theoretical capacity cannot be fully realized due to a decrease in the efficiency of the positive electrode and deterioration of the negative electrode, and the energy density cannot be sufficiently increased.

[0008] Therefore, research is ongoing to realize lithium-sulfur batteries with high energy density. Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention aims to solve the above-mentioned problems and provide a lithium-sulfur battery with high energy density.

[0010] In particular, the present invention seeks to provide a lithium-sulfur battery with high energy density by reducing the amount of electrolyte and improving the efficiency of the positive electrode to increase capacity. [Means for solving the problem]

[0011] In order to solve the above-mentioned problems, According to one aspect of the present invention, there is provided a lithium-sulfur battery according to the following embodiment:

[0012] The lithium-sulfur battery according to the first embodiment is A lithium-sulfur battery comprising a positive electrode and a negative electrode, each of which includes a sulfur-carbon composite, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, The compound contains three or more characteristic peaks selected from the following diffraction angles (2θ values) in an X-ray diffraction (XRD) pattern at a DOD (Depth Of Discharge) of 15% to 80%: 7.1±0.2°, 9.0±0.2°, 9.4±0.2°, 9.6±0.2°, 9.9±0.2°, 10.0±0.2°, 10.4±0.2°, 11.0±0.2°, 11.6±0.2°, 12.1±0.2°, 13.3±0.2°, 14.5±0.2°, and 15.0±0.2°.

[0013] According to the second embodiment, in the first embodiment, The DOD15% to DOD80% may be a state having a potential of 1.7V to 2.2V.

[0014] According to the third embodiment, in the first or second embodiment, The DOD 15% to DOD 80% may be a state in which the battery has a discharge capacity per sulfur (S) weight of 150 to 960 mAh / g(s).

[0015] According to the fourth embodiment, in any one of the first to third embodiments, The compound may have four or more characteristic peaks selected from the diffraction angles mentioned above.

[0016] According to the fifth embodiment, in any one of the first to fourth embodiments, The compound may have an X-ray diffraction (XRD) pattern with diffraction angles (2θ values) of 7.1±0.2°, 9.0±0.2°, 9.4±0.2°, 9.6±0.2°, 9.9±0.2°, 10.0±0.2°, 10.4±0.2°, 11.0±0.2°, 11.6±0.2°, 12.1±0.2°, 13.3±0.2°, 14.5±0.2°, and 15.0±0.2°.

[0017] According to the sixth embodiment, in any one of the first to fifth embodiments, The sulfur-carbon composite may have a sulfur to carbon weight ratio (S / C weight ratio) of 2.3 g / g or more.

[0018] According to the seventh embodiment, in any one of the first to sixth embodiments, the positive electrode includes a current collector and a positive electrode active material layer formed on at least one surface of the current collector and including the sulfur-carbon composite; The weight of the sulfur-carbon composite may be 90 wt % or more based on the total weight of the positive electrode.

[0019] According to the eighth embodiment, in any one of the first to seventh embodiments, The positive electrode has a capacity of 2 to 5 mAh / cm 2 may have a sulfur (S) loading of

[0020] According to the ninth embodiment, in any one of the first to eighth embodiments, The negative electrode may have a thickness of 40 to 80 μm.

[0021] According to the tenth embodiment, in any one of the first to ninth embodiments, The weight ratio (E1 / S weight ratio) of the electrolyte to the sulfur element (S) in the sulfur-carbon composite may be 2.5 g / g or less.

[0022] According to the eleventh embodiment, in any one of the first to tenth embodiments, The lithium-sulfur battery is S according to the following equation 1: X is 1.4mAh / cm 2 It could be more than that.

[0023] [Formula 1] S X =S PE / S EL / S In Formula 1, The above S PE is the sulfur (S) loading in the positive electrode, The above S EL / S is the weight ratio of the electrolyte to the sulfur element (S) in the sulfur-carbon composite.

[0024] According to the twelfth embodiment, in any one of the first to eleventh embodiments, The lithium-sulfur battery may have an energy density of 430 Wh / kg or more.

[0025] According to the thirteenth embodiment, in any one of the first to twelfth embodiments, The lithium-sulfur battery can be a pouch-type battery or a cylindrical battery.

[0026] According to another aspect of the present invention, there is provided an evaluation method according to the following embodiment.

[0027] The evaluation method according to the fourteenth embodiment is as follows: A method for evaluating the energy density of a lithium-sulfur battery including a positive electrode and a negative electrode each including a sulfur-carbon composite, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, comprising: The method includes determining that a lithium-sulfur battery containing a compound having three or more characteristic peaks selected from the group consisting of diffraction angles (2θ values) of 7.1±0.2°, 9.0±0.2°, 9.4±0.2°, 9.6±0.2°, 9.9±0.2°, 10.0±0.2°, 10.4±0.2°, 11.0±0.2°, 11.6±0.2°, 12.1±0.2°, 13.3±0.2°, 14.5±0.2°, and 15.0±0.2° in an X-ray diffraction (XRD) pattern at DOD 15% to DOD 80% is a battery having high energy density.

[0028] According to the fifteenth embodiment, in the fourteenth embodiment, The battery having a high energy density may be a battery having an energy density of 430 Wh / kg or more. [Effects of the Invention]

[0029] A lithium-sulfur battery according to one embodiment of the present invention has a high energy density.

[0030] In particular, the lithium-sulfur battery of the present invention can have an energy density of 300 Wh / kg or greater, and even 430 Wh / kg or greater. [Brief explanation of the drawings]

[0031] [Figure 1] 1 is a graph showing the results of discharge capacity evaluation for Example 1, Comparative Example 2, and Comparative Example 3. [Figure 2a] 1 shows the results of real-time charge / discharge XRD measurements on the lithium-sulfur battery of Example 1. [Figure 2b] FIG. 2a shows the XRD pattern in the discharged state (DOD 22%) in the real-time charge / discharge XRD graph obtained in FIG. 2a. [Figure 3a] 1 shows the results of real-time charge / discharge XRD measurements on the lithium-sulfur battery of Comparative Example 1. [Figure 3b] FIG. 3a shows the XRD pattern in the discharged state (DOD 22%) in the real-time charge / discharge XRD graph obtained in FIG. 3a. [Figure 4a] 1 shows the results of real-time charge / discharge XRD measurements on the lithium-sulfur battery of Comparative Example 2. [Figure 4b] FIG. 4a shows the XRD pattern in the discharged state (DOD 22%) in the real-time charge / discharge XRD graph obtained in FIG. 4a. [Figure 5a] 10 shows the results of real-time charge / discharge XRD measurements on the lithium-sulfur battery of Comparative Example 3. [Figure 5b] FIG. 5a shows the XRD pattern in the discharged state (DOD 22%) in the real-time charge / discharge XRD graph obtained in FIG. 5a. DETAILED DESCRIPTION OF THE INVENTION

[0032] The present invention will be described in more detail below.

[0033] Throughout this specification, when a part states that a certain component "includes", "has", or "comprises" a certain component, unless otherwise specified, it does not exclude other components, but means that it may further include other components.

[0034] Also, throughout this specification, terms such as "about" and "substantially" are used to mean the numerical value or a value close to it when manufacturing and material tolerances inherent in the mentioned meaning are presented, in order to prevent unscrupulous infringers from misusing the disclosed content where exact or absolute numerical values are mentioned to assist in the understanding of this application.

[0035] Throughout this specification, the description "A and / or B" means "A, B, or all of these".

[0036] Throughout this specification, unless otherwise specified, temperature means Celsius temperature and the unit is °C.

[0037] As used herein, the term "composite" means a substance in which two or more materials are combined to form physically and chemically distinct phases while exhibiting a more effective function.

[0038] As used herein, the term "(poly)sulfide" includes all of "(poly)sulfide ion (S x 2- , 1 ≤ x ≤ 8)" and "lithium (poly)sulfide (Li2S x or Li2S x - , 1 ≤ x ≤ 8)".

[0039] As used herein, the term "polysulfide" includes "polysulfide ion (S x 2- , 1 < x ≤ 8)" and "lithium polysulfide (Li2S x or Li2S x -It is a concept that includes all of "1 < x ≤ 8)".

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

[0041] The unit "mg" used in this specification s / cm 2 is, unless otherwise specified, for indicating the weight of sulfur (S) per unit area, and can be used in combination with other expression methods such as mg(s) / cm 2 , or mAh / cm as the loading amount 2 etc.

[0042] According to an embodiment of the present invention, a lithium-sulfur battery having a high energy density is provided.

[0043] The lithium-sulfur battery according to an embodiment of the present invention includes a positive electrode containing a sulfur-carbon composite, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte.

[0044] In one embodiment of the present invention, the lithium-sulfur battery may include an electrode assembly including the positive electrode, the negative electrode, and the separator, and a case for housing the electrolyte.

[0045] The lithium-sulfur battery includes, in a discharged state, particularly at DOD (Depth Of Discharge) of 15% to DOD 80%, a compound having three or more characteristic peaks selected from diffraction angles (2θ values) of 7.1 ± 0.2°, 9.0 ± 0.2°, 9.4 ± 0.2°, 9.6 ± 0.2°, 9.9 ± 0.2°, 10.0 ± 0.2°, 10.4 ± 0.2°, 11.0 ± 0.2°, 11.6 ± 0.2°, 12.1 ± 0.2°, 13.3 ± 0.2°, 14.5 ± 0.2° and 15.0 ± 0.2° in an X-ray diffraction (XRD) pattern.

[0046] In one embodiment of the present invention, the lithium-sulfur battery may contain a compound having three or more characteristic peaks selected from diffraction angles (2θ values) of 7.1°, 9.0°, 9.4°, 9.6°, 9.9°, 10.0°, 10.4°, 11.0°, 11.6°, 12.1°, 13.3°, 14.5°, and 15.0° in the X-ray diffraction pattern in the discharged state.

[0047] In one embodiment of the present invention, specifically, the lithium-sulfur battery may contain a compound having three or more characteristic peaks selected from diffraction angles (2θ values) of 7.1°, 9.0°, 9.4°, 9.6°, 9.9°, 10.0°, 10.4°, 11.0°, 11.6°, 12.1°, 13.3°, 14.5°, and 15.0° in the X-ray diffraction pattern at DOD 15% to DOD 80%.

[0048] The lithium-sulfur battery according to one embodiment of the present invention contains a compound having the XRD pattern in the discharged state.

[0049] The lithium-sulfur battery contains inorganic sulfur (S8) as a positive electrode active material. In the lithium-sulfur battery, lithium polysulfide is formed through a reduction reaction at the positive electrode during discharge. At this time, the compound may be a crystal form of lithium polysulfide formed through the reduction reaction of the inorganic sulfur (S8). The lithium-sulfur battery according to one embodiment of the present invention realizes a high energy density by including a crystal form of lithium polysulfide having the XRD pattern in the discharged state.

[0050] In one embodiment of the present invention, the compound may be a crystal form of lithium polysulfide, where the lithium polysulfide is Li2S x and Li2S x - and may be at least one of (1 < x ≤ 8).

[0051] In this specification, the compound may be defined as a crystalline form of lithium polysulfide having three or more characteristic peaks from among the diffraction angles (2θ values) of 7.1±0.2°, 9.0±0.2°, 9.4±0.2°, 9.6±0.2°, 9.9±0.2°, 10.0±0.2°, 10.4±0.2°, 11.0±0.2°, 11.6±0.2°, 12.1±0.2°, 13.3±0.2°, 14.5±0.2°, and 15.0±0.2°.

[0052] In one embodiment of the present invention, the compound may be a crystalline form of lithium polysulfide formed under high energy density conditions during discharge of a high energy density lithium-sulfur battery. For example, the high energy density lithium-sulfur battery may have a low El / S (electrolyte / sulfur) weight ratio, as described below. When the lithium-sulfur battery is operated, lithium polysulfide is dissolved in a small amount of electrolyte at a high concentration, forming a crystalline form that exhibits a characteristic peak in the diffraction angle of the XRD pattern. However, the mechanism of formation of the compound is not limited thereto.

[0053] In one embodiment of the present invention, the compound may have four or more, for example, five or more, characteristic peaks selected from the diffraction angles (2θ values), specifically, three, four, five, six, seven, eight, nine, ten, eleven, twelve, or thirteen characteristic peaks.

[0054] In one embodiment of the present invention, the compound may have an XRD pattern with diffraction angles (2θ values) of 7.1±0.2°, 9.0±0.2°, 9.4±0.2°, 9.6±0.2°, 9.9±0.2°, 10.0±0.2°, 10.4±0.2°, 11.0±0.2°, 11.6±0.2°, 12.1±0.2°, 13.3±0.2°, 14.5±0.2°, and 15.0±0.2°.

[0055] In one embodiment of the present invention, the compound may have an XRD pattern with diffraction angles (2θ values) of 7.1°, 9.0°, 9.4°, 9.6°, 9.9°, 10.0°, 10.4°, 11.0°, 11.6°, 12.1°, 13.3°, 14.5°, and 15.0°.

[0056] In one embodiment of the invention, the compound may comprise diffraction angles of an XRD pattern consisting of 7.1±0.2°, 9.0±0.2°, 9.4±0.2°, 9.6±0.2°, 9.9±0.2°, 10.0±0.2°, 10.4±0.2°, 11.0±0.2°, 11.6±0.2°, 12.1±0.2°, 13.3±0.2°, 14.5±0.2° and 15.0±0.2°.

[0057] In one embodiment of the present invention, the compound may have an XRD pattern with diffraction angles (2θ values) of 7.1°, 9.0°, 9.4°, 9.6°, 9.9°, 10.0°, 10.4°, 11.0°, 11.6°, 12.1°, 13.3°, 14.5° and 15.0°.

[0058] In one embodiment of the present invention, the compound may be contained in at least one of the positive electrode, negative electrode, separator, electrolyte, and inner surface of the case of the lithium-sulfur battery, and the XRD pattern may be obtained through non-destructive analysis of the lithium-sulfur battery, i.e., the XRD pattern may be measured without disassembling the lithium-sulfur battery.

[0059] In one embodiment of the present invention, the XRD pattern may be obtained from the lithium-sulfur battery through non-destructive analysis of the lithium-sulfur battery, for example, operando XRD analysis.

[0060] More specifically, the XRD pattern can be obtained by measuring the 2θ range of 7-17° in transmission mode using MoK-α X-rays (λ=0.709 Å) on an Empyrean XRD (manufactured by PANalytical) at room temperature (23°C). Therefore, the XRD pattern can be measured using X-rays with a wavelength of 0.709 Å. One pattern can be obtained at 0.014° intervals for a total of 3 minutes. The error range of the 2θ values ​​measured by XRD can be ±0.2°, more specifically ±0.1°.

[0061] According to one embodiment of the present invention, since the compound having the XRD pattern is present in the discharged state of the lithium-sulfur battery, the XRD measurement and the charge / discharge of the lithium-sulfur battery can be performed simultaneously. Specifically, the XRD measurement can be performed continuously while the charge / discharge of the lithium-sulfur battery is in progress.

[0062] More specifically, the XRD pattern can be obtained from the results of real-time charge / discharge XRD measurements using operando X-ray diffraction.

[0063] In one embodiment of the present invention, when the lithium-sulfur battery is a pouch-type battery, a pressure jig equipped with a Be-window may be used to measure XRD during operation of the lithium-sulfur battery, but the present invention is not limited thereto.

[0064] As described above, the XRD pattern of the compound is obtained when the lithium-sulfur battery is in a discharged state, and the discharged state for obtaining the XRD pattern is between DOD 15% and DOD 80%.

[0065] In this specification, the DOD 15% to DOD 80% state refers to a state in which 15% to 80% of the total capacity is discharged from a fully charged state of a lithium-sulfur battery, that is, a 100% SOC (State of Charge) state.

[0066] In one embodiment of the present invention, the XRD peak of the compound can be detected at any discharge state of the lithium-sulfur battery, for example, at a DOD of 20% to 60% or at a DOD of 20% to 50%. For example, the XRD peak of the compound can be detected when the lithium-sulfur battery is at a DOD of 22%, but the present invention is not limited to a specific discharge state.

[0067] In one embodiment of the present invention, the DOD 15% may be a state having a potential of 2.2 V or less, and the state of DOD 15% to DOD 80% may be a state having a potential of, for example, 1.7 V to 2.2 V, but the present invention is not limited thereto.

[0068] In one embodiment of the present invention, the total discharge capacity of the lithium-sulfur battery may be 1,000 mAh / g(s) or more based on the discharge capacity per weight of sulfur (S). For example, the total discharge capacity of the lithium-sulfur battery may be 1,000 mAh / g(s) to 1,300 mAh / g(s), specifically 1,100 mAh / g(s) to 1,200 mAh / g(s), e.g., 1,180 mAh / g(s), based on the discharge capacity per weight of sulfur (S). The DOD 15% state may be 15% of the total discharge capacity, and the DOD 80% state may be 80% of the total discharge capacity. For example, the DOD 15% to DOD 80% state may be 150 to 960 mAh / g(s), based on the discharge capacity per weight of sulfur (S).

[0069] As described above, a lithium-sulfur battery containing a compound having the above-described characteristic peaks in the XRD pattern at a DOD of 15% to 80% can exhibit the effect of having a high energy density.

[0070] In one embodiment of the present invention, the lithium-sulfur battery is a lithium-sulfur battery having a capacity of S according to the following Equation 1: X Value is 1.4mAh / cm 2 It could be more than that.

[0071] [Formula 1] S X =S PE / S EL / S In Formula 1, The above S PE is the sulfur (S) loading in the positive electrode, The above S EL / S is the weight ratio of the electrolyte to the sulfur element (S) in the sulfur-carbon composite.

[0072] Specifically, the above-mentioned S PE is mAh / cm 2 It may have units of

[0073] Also, the above S EL / S is a dimensionless value, similar to the weight ratio (El / S) of the electrolyte to the sulfur element (S) in the sulfur-carbon composite, which will be described later.

[0074] In one embodiment of the present invention, S according to Equation 1 above X The value is 1.4mAh / cm 2 For example, 1.4mAh / cm 2 ~10mAh / cm 2 , specifically 1.5mAh / cm 2 ~6mAh / cm 2 , more specifically 1.6mAh / cm 2 ~4mAh / cm 2 , e.g., 1.7mAh / cm 2 ~2.5mAh / cm 2 In one embodiment of the present invention, when the value of Equation 1 satisfies the above range, the lithium-sulfur battery contains a compound having the above XRD peak, thereby exhibiting the effect of having high energy density, but the present invention is not limited thereto.

[0075] Each component of the lithium-sulfur battery will now be described in detail.

[0076] <Positive electrode> In one embodiment of the present invention, the positive electrode may include a positive electrode current collector and a positive electrode active material layer coated on one or both surfaces of the positive electrode current collector.

[0077] The positive electrode current collector is not particularly limited as long as it supports the positive electrode active material, does not induce chemical changes in the battery, and has high conductivity, and may be made of, for example, copper, stainless steel, aluminum, nickel, titanium, palladium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, silver, or the like, or an aluminum-cadmium alloy.

[0078] The positive electrode current collector may have fine irregularities on its surface to strengthen the bonding force with the positive electrode active material, and may be in various forms such as a film, a sheet, a foil, a mesh, a net, a porous material, a foam, or a nonwoven fabric.

[0079] The positive electrode active material layer includes a positive electrode active material, and may further include a conductive material, a binder, an additive, and the like.

[0080] In one embodiment of the present invention, the positive electrode active material includes a sulfur-carbon composite.

[0081] In one embodiment of the present invention, the sulfur-carbon composite may include a porous carbon material and a sulfur-based compound supported on at least one of the interior of the pores of the porous carbon material and the outer surface of the porous carbon material. Sulfur, which acts as the positive electrode active material, does not have electrical conductivity by itself, so it may be used in combination with a conductive material such as a carbon material, and the porous carbon material may be used to support the sulfur. The sulfur-based compound is added as a positive electrode active material, and examples thereof include inorganic sulfur (S), lithium sulfide (LiS), and lithium (poly)sulfide (LiS). x , an integer 1≦x≦8), disulfide compounds, carbon-sulfur polymers ((CS y ) n , y=2.5-50, n≧2), or two or more of these. Preferably, the sulfur-based compound may be inorganic sulfur (S8).

[0082] In one embodiment of the present invention, the porous carbon material supports a sulfur-based compound as a positive electrode active material, provides a framework for uniformly and stably immobilizing the sulfur-based compound, and improves the conductivity of the positive electrode. Any porous carbon material may be used without particular limitation as long as it is a porous carbon material.

[0083] The porous carbon material can generally be prepared by carbonizing various carbon precursors. The porous carbon material contains irregular pores, with an average pore diameter of 1 nm to 200 nm and a porosity of 10 to 90% by volume of the total volume of the porous carbon material. If the average pore diameter is below the above range, the pore size is merely at the molecular level and cannot be impregnated with sulfur. If the average pore diameter exceeds the above range, the mechanical strength of the porous carbon material is weakened, making it difficult to apply to electrode manufacturing processes.

[0084] In one embodiment of the present invention, the "average pore diameter" may be measured by any known method for measuring the pore diameter of a porous material in the art, and the measurement method is not particularly limited. For example, the pore diameter may be measured by a scanning electron microscope (SEM), a field emission electron microscope, a laser diffraction method, or a Brunauer-Emmett-Teller (BET) method. Measurement using the laser diffraction method may be performed using, for example, a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT3000). Measurement using the BET method may be performed using, for example, a BELSORP series analyzer manufactured by BEL Japan, but is not limited thereto.

[0085] In one embodiment of the present invention, the "porosity" refers to the ratio of the volume occupied by pores to the total volume of a structure, and is expressed in units of "%." The term may be used interchangeably with terms such as void ratio, porosity, etc. In one embodiment of the present invention, the measurement of the porosity is not particularly limited, and may be measured by, for example, the BET method using nitrogen gas, mercury intrusion porosimetry (Hg porosimeter), or ASTM D2873.

[0086] The shape of the porous carbon material may be any shape commonly used in lithium-sulfur batteries, such as spheres, rods, needles, plates, tubes, or bulks, without limitation.

[0087] The porous carbon material may be any material commonly used in the art, having a porous structure or a large specific surface area. For example, the porous carbon material may be at least one selected from the group consisting of graphite, graphene, carbon black (e.g., denka black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black), carbon nanotubes (CNTs) (e.g., single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs)), carbon fibers (e.g., graphite nanofibers (GNFs), carbon nanofibers (CNFs), and activated carbon fibers (ACFs), graphite (e.g., natural graphite, artificial graphite, and expanded graphite), and activated carbon. Preferably, the porous carbon material is carbon nanotubes.

[0088] In one embodiment of the present invention, the porous carbon material may include, for example, carbon nanotubes (CNTs).

[0089] In one embodiment of the present invention, the sulfur-carbon composite has a weight ratio of sulfur to carbon (S / C For example, the sulfur-to-carbon weight ratio (S / C weight ratio) of the sulfur-carbon composite may be, for example, 2.3 g / g or more. For example, the sulfur-to-carbon weight ratio of the sulfur-carbon composite may be 2.3 g / g. The S / C ratio of the sulfur-carbon composite in the above range is preferable in terms of ensuring the electron transfer ability (conductivity) and electrochemical specific surface area of ​​the sulfur-carbon composite. For example, the usable surface of the sulfur-carbon composite is increased, which makes it easier to suppress sulfur elution from the positive electrode, but the present invention is not limited thereto.

[0090] In one embodiment of the present invention, the S / C ratio can be calculated from the weight (g) of sulfur and the weight (g) of carbon present in the sulfur-carbon composite. Alternatively, it can be calculated from the weight (wt%) of sulfur and the weight (wt%) of carbon based on the total weight of the sulfur-carbon composite. Thus, the S / C ratio can be a unitless value.

[0091] In one embodiment of the present invention, the S / C weight ratio may be, for example, 0.5 to 5.0, 0.5 to 4.0, 1.0 to 3.0, 1.5 to 2.5, 2.0 to 2.45, 2.25 to 2.35, or 2.3 to 3. For example, the S / C ratio may be calculated from the ratio of the weight of the inorganic sulfur (S8) to the weight of the porous carbon material. For example, the S / C ratio may be calculated from the weight ratio of S8 to CNT.

[0092] The method for preparing the sulfur-carbon composite is not particularly limited, and may be a method commonly used in the art. For example, the sulfur and the porous carbon material may be simply mixed and then heat-treated to form a composite.

[0093] In addition to the above-mentioned composition, the positive electrode active material may further include one or more selected from a transition metal element, a Group 13 element, a Group 14 element, a sulfur compound of these elements, and an alloy of these elements with sulfur.

[0094] The transition metal elements may include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Os, Ir, Pt, Au, or Hg, the Group 13 elements may include Al, Ga, In, or Ti, and the Group 14 elements may include Ge, Sn, or Pb.

[0095] In one embodiment of the present invention, the sulfur-carbon composite may be present in an amount of 50 wt % or more based on the total weight of the positive electrode. Specifically, the sulfur-carbon composite may be present in an amount of, for example, 80 wt % or more, 90 wt % or more, or 95 wt % or more based on the total weight of the positive electrode active material layer. Specifically, the sulfur-carbon composite may be present in an amount of 80 wt % to 100 wt %, more specifically, 85 wt % to 99 wt %, 90 wt % to 99 wt %, 95 wt % to 98 wt %, 95 wt % to 97 wt %, or 96 wt % based on the total weight of the positive electrode active material layer. If the content of the sulfur-carbon composite is below the above range, the relative contents of auxiliary materials such as conductive materials and binders increase, while the content of the sulfur-carbon composite decreases, making it difficult to achieve a high-capacity, high-energy density battery. If the content exceeds the above range, the content of the conductive materials or binders described below may be relatively insufficient, resulting in a problem of degraded physical properties of the electrode.

[0096] The conductive material electrically connects the electrolyte and the positive electrode active material and serves as a path for electrons to move from the current collector to the positive electrode active material. The conductive material is a component of the electrode that is physically distinct from the carbon contained in the sulfur-carbon composite, and may be any conductive material.

[0097] In one embodiment of the present invention, the conductive material may be, for example, carbon black such as Super P, Denka Black, acetylene black, Ketjen Black, channel black, furnace black, lamp black, thermal black, or carbon black; carbon derivatives such as carbon nanotubes or fullerenes; conductive fibers such as carbon fibers or metal fibers; metal powders such as carbon fluoride, aluminum, or nickel powder; or conductive polymers such as polyaniline, polythiophene, polyacetylene, or polypyrrole, which may be used alone or in combination.

[0098] In one embodiment of the present invention, the content of the conductive material may be 0 to 40 wt %, for example, 1 to 40 wt %, 15 to 40 wt %, 20 to 40 wt %, 25 to 35 wt %, or 0 to 10 wt %, for example, 1 to 10 wt %, based on the total weight of the positive electrode active material layer. If the content of the conductive material is below the above range, electron transfer between the positive electrode active material and the current collector may be difficult, resulting in a decrease in voltage and capacity. If the content of the conductive material is above the above range, the proportion of the positive electrode active material may be relatively reduced, resulting in a decrease in the total energy (charge) of the battery. Therefore, it is preferable to determine the appropriate content within the above range.

[0099] In an embodiment of the present invention, the binder supports the positive electrode active material on the positive electrode current collector and organically connects the positive electrode active materials to further enhance the binding strength therebetween. Any binder known in the art may be used.

[0100] For example, the binder may be one or a mixture of two or more selected from the group consisting of polyvinylidene fluoride (PVdF), polyvinylidene fluoride-based polymers containing at least one vinylidene fluoride repeating unit, polytetrafluoroethylene (PTFE), or a fluororesin-based binder including a mixture of two or more of these; rubber-based binders including styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, and styrene-isoprene rubber; acrylic binders; cellulose-based binders including carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, and regenerated cellulose; polyalcohol-based binders; polyolefin-based binders including polyethylene and polypropylene; polyimide-based binders; polyester-based binders; silane-based binders; polyacrylic acid-based binders; and polyacrylonitrile-based binders.

[0101] In one embodiment of the present invention, the content of the binder may be 1 to 10 wt % based on the total weight of the positive electrode active material layer. If the content of the binder is less than the above range, the physical properties of the positive electrode may be deteriorated, causing the positive electrode active material and the conductive material to fall off. If the content of the binder exceeds the above range, the ratio of the positive electrode active material to the conductive material in the positive electrode may be relatively reduced, causing a decrease in battery capacity. Therefore, it is preferable to determine the appropriate content within the above range.

[0102] In one embodiment of the present invention, the method for manufacturing the positive electrode for a lithium secondary battery is not particularly limited, and any method known to those skilled in the art or various methods modified therefrom may be used.

[0103] For example, the positive electrode for the lithium secondary battery may be manufactured by preparing a positive electrode slurry composition including the above-described composition and then applying the same to at least one surface of the positive electrode current collector to form the positive electrode active material layer.

[0104] The positive electrode slurry composition may include the above-described positive electrode active material, and may further include a binder, a conductive material, and a solvent.

[0105] The solvent used is one that allows the positive electrode active material to be uniformly dispersed. The most preferred solvent is water, which may be distilled water or deionized water. However, the solvent is not limited thereto. If necessary, a lower alcohol that is easily miscible with water may be used. Examples of the lower alcohol include methanol, ethanol, propanol, isopropanol, and butanol. These may be preferably mixed with water.

[0106] The solvent may be contained in an amount that allows easy coating, and the specific amount may vary depending on the application method and device.

[0107] The positive electrode slurry composition may further contain, as needed, substances commonly used in the art for the purpose of improving performance, etc. For example, a viscosity modifier, a fluidizing agent, a filler, etc.

[0108] The method for applying the positive electrode slurry composition is not particularly limited, and examples thereof include a doctor blade, die casting, comma coating, screen printing, etc. Alternatively, the positive electrode slurry may be formed on a separate substrate and then applied to the positive electrode current collector by pressing or laminating.

[0109] After coating, a drying process may be performed to remove the solvent. The drying process is performed at a temperature and time sufficient to sufficiently remove the solvent, and the conditions are not particularly limited as they may vary depending on the type of solvent. Examples include drying with warm air, hot air, or low-humidity air, vacuum drying, and drying by irradiation with (far) infrared rays or electron beams. The drying rate is usually adjusted to remove the solvent as quickly as possible without causing cracks in the positive electrode active material layer due to stress concentration or causing the positive electrode active material layer to peel off from the positive electrode current collector.

[0110] Furthermore, after drying, the current collector may be pressed to increase the density of the positive electrode active material in the positive electrode. Examples of pressing methods include die pressing and roll pressing.

[0111] The positive electrode manufactured using the above-described composition and manufacturing method, specifically the porosity of the positive electrode active material layer, may be 50% to 80% by volume, specifically 60% to 75% by volume. If the positive electrode porosity is less than 50% by volume, the filling rate of the positive electrode slurry composition containing the positive electrode active material, conductive material, and binder becomes too high, preventing sufficient electrolyte for ionic and / or electrical conduction from being maintained between the positive electrode active materials. This leads to reduced battery output and cycle characteristics, and serious problems such as overvoltage and reduced discharge capacity. On the other hand, if the positive electrode porosity is excessively high, exceeding 80% by volume, the physical and electrical connection with the current collector may be weakened, reducing adhesion and reaction difficulty. Furthermore, excessive pores may be filled with electrolyte, resulting in reduced battery energy density. Therefore, the porosity should be appropriately adjusted within the above range.

[0112] In one embodiment of the present invention, the sulfur (S) loading of the positive electrode is 2 to 5 mAh / cm 2 For example, the sulfur (S) loading of the positive electrode may be 2.5 to 5 mAh / cm 2 , 3~4mAh / cm 2 , 3.5~4mAh / cm 2 , 3.5~5mAh / cm 2 , 3.6~5mAh / cm 2 , or 3.7~4.5mAh / cm 2 More specifically, 3.7 to 4.0 mAh / cm 2 When the sulfur loading amount in the positive electrode is within the above range, it is advantageous in providing a lithium-sulfur battery having a high energy density, but the present invention is not limited thereto.

[0113] The sulfur loading amount may be a value calculated from the capacity value of the electrode calculated by measuring the total weight of sulfur (S) contained as a positive electrode active material in the positive electrode.

[0114] In an embodiment of the present invention, the weight of sulfur in the positive electrode may be measured from the positive electrode active material added during manufacturing.

[0115] In another embodiment of the present invention, the weight of sulfur in the positive electrode can be measured by thermogravimetric analysis (TGA) of the positive electrode after fabrication. Meanwhile, when disassembling a fabricated lithium-sulfur battery, a charged lithium-sulfur battery is disassembled in a non-active atmosphere to obtain a positive electrode, and the positive electrode is washed and dried using an appropriate washing solvent. The positive electrode active material layer is then scraped off to obtain a resultant product, and the sulfur (S) content derived from the active material can be measured and calculated by thermogravimetric analysis (TGA), but the measurement method is not limited thereto.

[0116] <Negative electrode> The negative electrode may include a negative electrode current collector and a negative electrode active material layer coated on one or both sides of the negative electrode current collector, or may be a lithium metal plate.

[0117] The negative electrode current collector is for supporting the negative electrode active material layer, and is the same as that described above for the positive electrode current collector.

[0118] The negative electrode active material layer may include, in addition to the negative electrode active material, a conductive material, a binder, etc. In this case, the conductive material and the binder are as described above.

[0119] The negative electrode active material is lithium (Li + The lithium ion-containing compound may include a material capable of reversible intercalation or deintercalation of lithium ions, a material capable of reversibly reacting with lithium ions to form a lithium-containing compound, lithium metal, or a lithium alloy.

[0120] The lithium ion (Li + The material capable of reversibly inserting or desorbing lithium ions (Li) can be, for example, crystalline carbon, amorphous carbon, or a mixture thereof. +The material capable of reacting with lithium (Li) to reversibly form a lithium-containing compound may be, for example, tin oxide, titanium nitride, or silicon. 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).

[0121] Preferably, the negative electrode active material may be lithium metal, specifically in the form of a lithium metal thin film or lithium metal powder.

[0122] In one embodiment of the present invention, the thickness of the negative electrode may be 40 μm to 80 μm. For example, the thickness of the negative electrode may be 50 μm to 70 μm, or 60 μm. The thickness of the negative electrode may be measured by a known method for measuring the thickness of each component of a battery, for example, but not limited to, a thickness gauge manufactured by Mitutoyo Corporation. For example, the thickness of the negative electrode may be measured in accordance with ASTM D374.

[0123] <Separation membrane> The separator separates or insulates the positive electrode and the negative electrode and transports lithium ions between them. The separator may include a porous, non-conductive or insulating material. Any material commonly used as a separator for lithium secondary batteries may be used without any particular limitation. The separator may be an independent member such as a film, or a coating layer applied to the positive electrode and / or the negative electrode.

[0124] The separation membrane preferably has low resistance to ion migration of the electrolyte and excellent wettability with respect to the electrolyte.

[0125] In one embodiment of the present invention, the separator may include a porous substrate, which may be any porous substrate commonly used in secondary batteries, such as a porous polymer film alone or in combination with other porous polymer films, including, but not limited to, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, or a polyolefin-based porous membrane.

[0126] The material of the porous substrate is not particularly limited, and any porous substrate commonly used in electrochemical devices can be used. For example, the porous substrate may include at least one selected from the group consisting of polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyamides, polyacetals, polycarbonates, polyimides, polyether ether ketones, polyether sulfones, polyphenylene oxides, polyphenylene sulfides, polyethylene naphthalate, polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl chloride, polyacrylonitrile, cellulose, nylon, polyparaphenylene benzobisoxazole, and polyarylates.

[0127] In one embodiment of the present invention, the thickness of the porous substrate is not particularly limited, but may be 1 μm to 100 μm, preferably 5 μm to 50 μm. The thickness of the porous substrate is not limited to the above range, but if it is thinner than the above lower limit, the mechanical properties may be reduced, and the separator may be easily damaged during use of the battery.

[0128] In one embodiment of the present invention, the average diameter and porosity of the pores present in the porous substrate are not particularly limited, but may be 0.001 μm to 50 μm and 10 vol % to 95 vol %, respectively.

[0129] In an embodiment of the present invention, the separator may further include a porous coating layer formed on at least one surface of the porous substrate and including inorganic particles and a binder.

[0130] In one embodiment of the present invention, the inorganic particles and binder contained in the porous coating layer may be any inorganic particles and binder commonly used in porous coating layers of separators, and the manufacturing method thereof is not particularly limited.

[0131] <Electrolyte> The electrolyte is a medium in which ions involved in the electrochemical reaction of the lithium-sulfur battery can move, and includes a non-aqueous solvent and a lithium salt as an electrolyte.

[0132] The electrolyte solution is not particularly limited as long as it has a composition that can be used in lithium secondary batteries, specifically lithium-sulfur batteries.

[0133] In one embodiment of the present invention, the electrolyte may include a non-aqueous solvent, a lithium salt, and an additive.

[0134] In an embodiment of the present invention, the non-aqueous solvent may be any solvent that can be used in a lithium-sulfur battery, without any particular limitation. For example, an ether solvent, an ester, an amide, a chain carbonate, a cyclic carbonate, etc. may be used.

[0135] In one embodiment of the present invention, the ester may be, for example, any one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone, or a mixture of two or more thereof, but is not limited thereto.

[0136] In one embodiment of the present invention, the chain carbonate may be, for example, any one selected from the group consisting of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate, or a mixture of two or more thereof, but is not limited thereto.

[0137] In one embodiment of the present invention, the cyclic carbonate may be any one or a mixture of two or more selected from the group consisting of ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate, and halides thereof, and examples of halides thereof include, but are not limited to, fluoroethylene carbonate.

[0138] In one embodiment of the present invention, the non-aqueous solvent may include an ether-based solvent.

[0139] In one embodiment of the present invention, the ether-based solvent may be present in an amount of 60% by volume or more, for example, 60% to 100% by volume, 70% to 100% by volume, 80% to 100% by volume, 85% to 100% by volume, 90% to 100% by volume, 95% to 100% by volume, 98% to 100% by volume, 90% to 98% by volume, or 90% to 95% by volume, based on the total volume of the non-aqueous solvent. The above-described range of the amount of the ether-based solvent, based on the total volume of the non-aqueous solvent, is advantageous in terms of the solubility of electrolyte components such as lithium salt, but the present invention is not limited thereto.

[0140] In one embodiment of the present invention, the ether solvent may include an acyclic ether, a cyclic ether, or a mixture thereof.

[0141] In one embodiment of the present invention, the acyclic ether may include one or more selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, dibutyl ether, diisobutyl ether, ethyl methyl ether, ethyl propyl ether, ethyl tert-butyl ether, dimethoxymethane, trimethoxymethane, dimethoxyethane, diethoxyethane, dimethoxypropane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, dipropylene glycol dimethylene ether, butylene glycol ether, diethylene glycol ethyl methyl ether, diethylene glycol isopropyl methyl ether, diethylene glycol butyl methyl ether, diethylene glycol tert-butyl ethyl ether, and ethylene glycol ethyl methyl ether. Preferably, the acyclic ether may include one or more selected from the group consisting of dimethyl ether, dimethoxyethane, diethoxyethane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether, and more preferably dimethoxyethane.

[0142] In one embodiment of the present invention, the cyclic ether may include, for example, one or more selected from the group consisting of 2-methylfuran, 1,3-dioxolane, 4,5-dimethyl-dioxolane, 4,5-diethyl-dioxolane, 4-methyl-1,3-dioxolane, 4-ethyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, 2,5-dimethoxytetrahydrofuran, 2-ethoxytetrahydrofuran, 2-methyl-1,3-dioxolane, 2-vinyl-1,3-dioxolane, 2,2-dimethyl-1,3-dioxolane, 2-methoxy-1,3-dioxolane, 2-ethyl-2-methyl-1,3-dioxolane, tetrahydrofuran, 1,4-dioxane, 1,2-dimethoxybenzene, 1,3-dimethoxybenzene, 1,4-dimethoxybenzene, and isosorbide dimethyl ether. Preferably, it may contain one or more selected from the group consisting of 2-methylfuran, 1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, and 2,5-dimethyltetrahydrofuran, and more preferably it may contain 2-methylfuran.

[0143] In one embodiment of the present invention, the non-aqueous solvent may comprise a mixture of an acyclic ether and a cyclic ether.

[0144] In one embodiment of the present invention, the non-aqueous solvent may include dimethoxyethane (DME) and 2-methylfuran (2-MeF).

[0145] In one embodiment of the present invention, the volume ratio of the acyclic ether to the cyclic ether may be 5:95 to 95:5 (v / v), specifically 95:5 to 50:50, more specifically 90:10 to 70:30, 85:15 to 75:25, or 80:20 (v / v). In the present invention, the volume ratio corresponds to the ratio of "volume % of acyclic ether" to "volume % of cyclic ether" in the ether-based solvent.

[0146] In one embodiment of the present invention, the non-aqueous solvent may not contain a carbonate-based solvent in terms of electrolyte solubility, or may contain a small amount of carbonate-based solvent that does not affect the solubility of the lithium salt. For example, when the non-aqueous solvent contains a carbonate-based solvent, the content of the carbonate solvent may be 3 wt % or less, 2 wt % or less, 1 wt % or less, 0.5 wt % or less, or 0 wt % (i.e., no content) based on the total weight of the lithium secondary battery electrolyte.

[0147] In one embodiment of the present invention, the lithium salt may be any suitable lithium salt that can be used as an electrolyte for a lithium secondary battery. Examples of the lithium salt include LiCl, LiBr, LiI, LiClO4, LiBF4, and LiB 10 Cl 10 , LiPF6, LiCF3SO3, LiCF3CO2, LiC4BO8, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, (CF3SO2)2NLi, (C2F5SO2)2NLi, (SO2F)2NLi, (CF3SO2)3CLi, lithium chloroborane, lithium lower aliphatic carboxylate, lithium tetraphenylborate, lithium imide, or two or more thereof.

[0148] In one embodiment of the present invention, the concentration of the lithium salt may be appropriately determined in consideration of ionic conductivity, solubility, etc., and may be, for example, 0.1 M to 4 M, preferably 0.5 M to 2 M. When the concentration of the lithium salt is within the above range, it is easy to ensure ionic conductivity suitable for battery operation, or the electrolyte has an appropriate viscosity, which is advantageous in terms of improving the mobility of lithium ions and suppressing the decomposition reaction of the lithium salt itself, but the present invention is not limited thereto.

[0149] In one embodiment of the present invention, the electrolyte may further contain a nitrogen compound in addition to the lithium salt to improve the electrical conductivity of the electrolyte and extend the life of the lithium-sulfur battery.

[0150] Specifically, the nitrogen compound has, but is not limited to, an effect of suppressing the reduction reaction of polysulfide that occurs during the charge / discharge process of a lithium-sulfur battery, thereby preventing irreversible consumption of polysulfide, and thereby improving the performance of the lithium-sulfur battery.

[0151] In one embodiment of the present invention, the nitrogen compound is not particularly limited as long as it stably forms a solid electrolyte membrane (SEI) of the negative electrode and improves charge / discharge efficiency, and may be, for example, a nitrate compound, a nitrite compound, or a mixture thereof.

[0152] In one embodiment of the present invention, the nitrogen compound may be selected from the group consisting of inorganic nitric acid or nitrite compounds such as lithium nitrate (LiNO), potassium nitrate (KNO), cesium nitrate (CsNO), barium nitrate (Ba(NO)), ammonium nitrate (NHNO), lithium nitrite (LiNO), potassium nitrite (KNO), cesium nitrite (CsNO), and ammonium nitrite (NHNO); organic nitric acid or nitrite compounds such as methyl nitrate, dialkylimidazolium nitrate, guanidine nitrate, imidazolium nitrate, pyridinium nitrate, ethyl nitrite, propyl nitrite, butyl nitrite, pentyl nitrite, and octyl nitrite; organic nitro compounds such as nitromethane, nitropropane, nitrobutane, nitrobenzene, dinitrobenzene, nitropyridine, dinitropyridine, nitrotoluene, and dinitrotoluene, and combinations thereof, and preferably includes lithium nitrate.

[0153] In one embodiment of the present invention, the nitrogen compound may be present in an amount of, for example, 1 wt % to 10 wt %, 2 wt % to 10 wt %, or 3 wt % to 10 wt %, specifically 3 wt % to 8 wt %, 3 wt % to 6 wt %, or 3 wt % to 5 wt %, based on the total weight of the electrolyte, but is not limited thereto. When the nitrogen compound is present in the above amounts, it is advantageous in terms of improving the electrical conductivity of the electrolyte and suppressing the reduction of polysulfides when applied to a lithium-sulfur battery, but the present invention is not limited thereto.

[0154] In an embodiment of the present invention, the lithium-sulfur battery may have a weight ratio of the electrolyte to sulfur (S) in the sulfur-carbon composite of the positive electrode (E1 / S weight ratio) of 2.5 g / g or less to achieve high energy density.

[0155] In one embodiment of the present invention, the lithium-sulfur battery has an El / S weight ratio of 1.5 to 2.5 g / g, specifically 2 to 2.5 g / g, 2 to 2.3 g / g, 2.0 to 2.2 g / g, or 2.0 to 2.15 g / g.

[0156] In an embodiment of the present invention, the El / S weight ratio of the lithium-sulfur battery can be calculated immediately after the fabrication of the lithium-sulfur battery by the ratio of the weight of sulfur in the sulfur-carbon composite of the positive electrode added during the fabrication process to the weight of the electrolyte added.

[0157] In another embodiment of the present invention, the El / S weight ratio of the lithium-sulfur battery can be calculated by disassembling the battery and calculating the ratio of the weight of sulfur in the sulfur-carbon composite cathode to the weight of the electrolyte.

[0158] For example, to analyze the El / S weight ratio of a lithium-sulfur battery by disassembling the battery, the total weight of the lithium-sulfur battery can be measured in a charged state, disassembled, and washed and dried with a solvent to determine the sum of the weights of the cathode, anode, separator, and case. The weight of the electrolyte can be determined by subtracting the weights of the cathode, anode, separator, and case from the total weight of the battery. Preferably, the washing solvent can extract the electrolyte attached to the cathode, anode, separator, and case. The cathode active material layer and current collector are then separated from the dried cathode, and the weight of sulfur in the cathode active material layer derived from the sulfur-carbon composite can be measured to determine the weight of sulfur in the cathode. The El / S weight ratio of the lithium-sulfur battery can be calculated based on the ratio of the weight of sulfur in the sulfur-carbon composite of the cathode to the weight of the added electrolyte.

[0159] In one embodiment of the present invention, the weight of sulfur originating from the sulfur-carbon composite present in the positive electrode active material layer may be measured by, for example, scraping the positive electrode active material layer and subjecting the resultant to thermogravimetric analysis (TGA) to measure the content of sulfur (S) originating from the active material, but the measuring method is not limited thereto.

[0160] In one embodiment of the present invention, the state of charge for disassembling the lithium-sulfur battery may be a fully charged state, i.e., SOC 100%.

[0161] In another embodiment of the present invention, the state of charge for disassembling the lithium-sulfur battery may be SOC 95% to SOC 100%.

[0162] In one embodiment of the present invention, disassembly of the charged lithium-sulfur battery is performed in an inert atmosphere for safety reasons, for example, in an Ar atmosphere.

[0163] In one embodiment of the present invention, the energy density of the lithium-sulfur battery may be, for example, 400 Wh / kg or more. Specifically, the energy density of the lithium-sulfur battery may be 420 Wh / kg or more, more specifically, 430 Wh / kg or more. For example, the energy density of the lithium-sulfur battery may be 400 Wh / kg to 1,000 Wh / kg, specifically, 410 Wh / kg to 800 Wh / kg, 420 Wh / kg to 600 Wh / kg, specifically, 430 Wh / kg to 550 Wh / kg.

[0164] In an embodiment of the present invention, the energy density of the lithium-sulfur battery may be measured by a known method and is not particularly limited by the measurement method. For example, the energy density of the lithium-sulfur battery may be calculated by the following Equation 2 based on the specific capacity measured by discharging and charging at a rate of 0.1 C after one or more cycles of discharging and charging at room temperature in the range of 1.8 V to 2.7 V:

[0165] In one embodiment of the present invention, the initial discharge and charge may each be performed at a rate of 0.1 to 0.3 C. Specifically, the initial discharge and charge may each be performed at a rate of 0.1 to 0.2 C, for example, 0.1 C.

[0166] In addition, in one embodiment of the present invention, the initial discharge and charge may each be repeated three times at a 0.1 C rate.

[0167] In Equation 2 below, the discharge capacity may be measured in mAh, the driving voltage in V, and the cell weight in kg.

[0168] [Formula 2] Energy density (Wh / kg) = {[(discharge capacity (mAh) x driving voltage (V)) / 1000] / (cell weight (kg))} In one embodiment of the present invention, the room temperature may be, for example, a temperature of 23°C to 25°C, and specifically, 23°C.

[0169] In one embodiment of the present invention, the charge and discharge rate may be 0.1C rate to 0.5C rate, for example, 0.3C rate, but is not particularly limited thereto as long as charge and discharge are performed within the above-mentioned rate range.

[0170] In one embodiment of the present invention, the lithium-sulfur battery may have various shapes, such as, but not limited to, a pouch shape or a cylindrical shape.

[0171] According to another embodiment of the present invention, there is provided a method for evaluating the energy density of a lithium-sulfur battery through the diffraction angle of an XRD pattern for the lithium-sulfur battery.

[0172] In one embodiment of the present invention, the lithium-sulfur battery to be evaluated includes a cathode and an anode each including a sulfur-carbon composite, a separator interposed between the cathode and the anode, and an electrolyte. The lithium-sulfur battery may also include an electrode assembly including the cathode, the anode, and the separator, and a case containing the electrolyte.

[0173] The evaluation method includes a step of determining that a lithium-sulfur battery containing a compound having three or more characteristic peaks selected from the following diffraction angles (2θ values) in an X-ray diffraction (XRD) pattern at DOD 15% to DOD 80%: 7.1±0.2°, 9.0±0.2°, 9.4±0.2°, 9.6±0.2°, 9.9±0.2°, 10.0±0.2°, 10.4±0.2°, 11.0±0.2°, 11.6±0.2°, 12.1±0.2°, 13.3±0.2°, 14.5±0.2°, and 15.0±0.2°, is a battery having a high energy density.

[0174] In one embodiment of the present invention, the XRD pattern can be obtained from the results of real-time charge / discharge XRD measurements on a lithium-sulfur battery.

[0175] Specifically, in one embodiment of the present invention, the evaluation method may involve charging the lithium-sulfur battery to a fully charged state (SOC 100%) at 0.1C to 0.3C, for example, 0.2C, and then discharging at 0.05C to 0.2C, for example, 0.1C, while acquiring and evaluating XRD results in real time.

[0176] In one embodiment of the present invention, the DOD15% to DOD80% may be a state having a potential of 1.7V to 2.2V.

[0177] In one embodiment of the present invention, the DOD 15% to DOD 80% may be a state in which the battery has a discharge capacity per sulfur (S) weight of 150 to 960 mAh / g(s).

[0178] In one embodiment of the present invention, the battery having a high energy density may be, for example, a battery having an energy density of 300 Wh / kg or more, specifically 430 Wh / kg or more. For example, the lithium-sulfur battery may have an energy density of 400 Wh / kg to 1,000 Wh / kg, specifically 410 Wh / kg to 800 Wh / kg, or 420 Wh / kg to 600 Wh / kg, specifically 430 Wh / kg to 550 Wh / kg.

[0179] 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.

[0180] [Lithium-sulfur battery manufacturing] Example 1 A sulfur-carbon composite (S / C weight ratio = 2.33) was prepared as a positive electrode active material by mixing inorganic sulfur (S8) and carbon nanotubes (CNTs). 96 wt% of the prepared sulfur-carbon composite was mixed with 4 wt% of polyacrylate (PAA) as a binder to prepare a positive electrode slurry composition. The positive electrode slurry composition was applied to an aluminum current collector and dried to prepare a positive electrode. The sulfur (S) loading of the prepared positive electrode was 3.7 mAh / cm. 2 It was.

[0181] A 60 μm thick lithium metal was used as the negative electrode.

[0182] The positive electrode and the negative electrode were positioned facing each other, and a polyethylene separator having a thickness of 12 μm and a porosity of 46 vol% was interposed therebetween to prepare an electrode assembly.

[0183] The prepared electrode assembly was placed in a pouch-type case, and an electrolyte solution containing 0.75M lithium salt (LiTFSI) and 3 wt% lithium nitrate (LiNO3) dissolved in a solvent of a mixture of dimethoxyethane (DME) and 2-methylfuran (2-MeF) in a volume ratio of 8:2 was injected so that the El / S weight ratio was 2.15 g / g to fabricate a lithium-sulfur battery.

[0184] Comparative Example 1 The sulfur (S) loading of the positive electrode is 2.7 mAh / cm 2 A lithium-sulfur battery was fabricated in the same manner as in Example 1, except that the El / S weight ratio was adjusted to 2.9 g / g.

[0185] Comparative Example 2 Cathode sulfur (S) loading is 3.5mAh / cm 2 A lithium-sulfur battery was fabricated in the same manner as in Example 1, except that the El / S weight ratio was adjusted to 2.60 g / g.

[0186] Comparative Example 3 Cathode sulfur (S) loading is 3.5mAh / cm 2A lithium-sulfur battery was fabricated in the same manner as in Example 1, except that the El / S weight ratio was adjusted to 3.00 g / g.

[0187] [Battery performance evaluation] The lithium-sulfur batteries of Example 1 and Comparative Examples 1 to 3 were each discharged and charged three times at room temperature (23°C), in the range of 1.8 V to 2.7 V, and at 0.1 C. The specific capacity of the battery was then measured under the 0.1 C discharge condition, and the energy density (Wh / kg) of the battery was evaluated using the measured specific capacity.

[0188] For each of the batteries manufactured in Example 1 and Comparative Examples 1 to 3, the values ​​calculated using the following Equation 1 are shown in Table 1.

[0189] [Formula 1] S X =S PE / S EL / S In Formula 1, The above S PE is the sulfur (S) loading in the positive electrode, The above S EL / S is the weight ratio of the electrolyte to the sulfur element (S) in the sulfur-carbon composite.

[0190] FIG. 1 shows the results of evaluating the capacity of the batteries of Example 1, Comparative Example 2, and Comparative Example 3. The energy density was calculated using the following equation 2, and the energy densities of Example 1, and Comparative Examples 1 to 3 are shown in Table 1.

[0191] [Formula 2] Energy density (Wh / kg) = {[(discharge capacity (mAh) x driving voltage (V)) / 1000] / (cell weight (kg))}

[0192] [Table 1]

[0193] [Evaluation of XRD patterns of batteries] For each of the fabricated lithium-sulfur batteries of Example 1 and Comparative Examples 1 to 3, real-time charge / discharge XRD patterns were obtained through operando XRD analysis as follows.

[0194] First, the batteries of Example 1 and Comparative Example 1 were activated by discharging at 0.1 C to 1.8 V at room temperature (23°C), then charged at 0.2 C to 2.7 V, and discharged from 2.7 V to 1.8 V at a 0.1 C rate, and real-time charge / discharge XRD patterns were obtained.

[0195] In addition, the batteries of Comparative Examples 2 and 3 were activated by discharging at 0.1 C to 1.8 V at room temperature (23°C), then charged at 0.1 C to 2.7 V, and discharged from 2.7 V to 1.8 V at a 0.1 C rate, and real-time charge / discharge XRD patterns were obtained.

[0196] Specifically, measurements were performed in the 2θ range of 7-17° in transmission mode using MoK-α X-rays (λ=0.709Å) on an Empyrean XRD (manufactured by PANalytical), and one pattern was acquired at 0.014° intervals for a total of 3 minutes. XRD measurements were performed using a pressure jig equipped with a Be-window.

[0197] The obtained real-time charge / discharge XRD measurement results are shown in Figure 2a (Example 1), Figure 3a (Comparative Example 1), Figure 4a (Comparative Example 2), and Figure 5a (Comparative Example 3). The left side of the measurement result images in Figures 2a, 3a, 4a, and 5a shows the change from the start of charge (SOC 0%) to the fully charged state (SOC 100%), and from the start of discharge (DOD 0%) to the fully discharged state (DOD 100%).

[0198] 2a, 3a, 4a, 5a and Table 1, it was confirmed that in the discharged state, a characteristic peak not detected in Comparative Examples 1 to 3 appeared in Example 1. Specifically, it was confirmed that a characteristic peak not detected in Comparative Examples 1 to 3 appeared in Example 1 in the region of DOD 15% (Index about 130) to DOD 80% (Index about 230).

[0199] Specifically, in order to confirm the characteristic peaks observed only in Example 1 (the XRD measurement results in FIG. 2a), XRD patterns at DOD 22% were obtained from the results of real-time charge / discharge XRD measurements on the batteries of Comparative Examples 1 to 3, and are shown in FIG. 2b (Example 1), FIG. 3b (Comparative Example 1), FIG. 4b (Comparative Example 2), and FIG. 5b (Comparative Example 3).

[0200] 3b to 5b, the diffraction angles of characteristic peaks observed in the discharge state of Example 1, typically only at DOD 22%, were as follows:

[0201] Example 1 (2θ values): 7.1°, 9.0°, 9.4°, 9.6°, 9.9°, 10.0°, 10.4°, 11.0°, 11.6°, 12.1°, 13.3°, 14.5°, 15.0° Referring to Figure 3b (Comparative Example 1), Figure 4b (Comparative Example 2), and Figure 5b (Comparative Example 3), less than three characteristic peaks were observed in the region where the characteristic peaks of Example 1 were observed.

[0202] According to Figure 1, which compares the discharge profiles of Example 1, Comparative Example 2, and Comparative Example 3, no significant difference in discharge capacity was observed among them, but the XRD patterns shown in Figures 2 to 5 confirmed that a specific crystalline reactant was detected only in Example 1. Comparing the energy densities of the cells in Table 1, Example 1 had a discharge capacity of 440 Wh / kg, while Comparative Examples 2 and 3 had discharge capacities of 420 Wh / kg and 400 Wh / kg, respectively, confirming that there were differences in energy density despite the similar levels of discharge capacity.

[0203] That is, as shown in Equation 2 for calculating energy density, the cell weight and driving voltage are taken into account together to calculate the energy density, and it has been confirmed that it is inappropriate to estimate the energy density from only the discharge capacity.

[0204] Furthermore, to realize a lithium-sulfur battery with high energy density, it must have the characteristic of being able to maintain high reactivity even when a solid-state reaction occurs within the battery. x Value is 1.4mAh / cm 2 The characteristic XRD peak was detected only in Example 1. This confirmed that the battery according to Example 1 was able to exhibit a high energy density by maintaining high reactivity despite the occurrence of a solid-state reaction within the battery.

[0205] As described above, the present invention has been described using limited embodiments and drawings, but the present invention is not limited thereto, and it goes without saying that various modifications and variations can be made by a person having ordinary skill in the art to which the present invention pertains within the technical spirit of the present invention and the equivalent scope of the claims.

Claims

1. a positive electrode including a sulfur-carbon composite; a negative electrode; a separator interposed between the positive electrode and the negative electrode; An electrolyte; 1. A lithium-sulfur battery comprising: A lithium-sulfur battery comprising a compound having, in an X-ray diffraction pattern, three or more characteristic peaks selected from the group consisting of diffraction angles (2θ values) of 7.1±0.2°, 9.0±0.2°, 9.4±0.2°, 9.6±0.2°, 9.9±0.2°, 10.0±0.2°, 10.4±0.2°, 11.0±0.2°, 11.6±0.2°, 12.1±0.2°, 13.3±0.2°, 14.5±0.2°, and 15.0±0.2° when the depth of discharge (DOD) is 15% or more and 80% or less.

2. 2. The lithium-sulfur battery according to claim 1, wherein the DOD of 15% or more and 80% or less is a state in which the potential is 1.7 V or more and 2.2 V or less.

3. 2. The lithium-sulfur battery according to claim 1, wherein the DOD of 15% or more and 80% or less is a state in which the battery has a discharge capacity per sulfur weight of 150 mAh / g(s) or more and 960 mAh / g(s) or less.

4. 2. The lithium-sulfur battery according to claim 1, wherein the compound has four or more characteristic peaks selected from among the diffraction angles.

5. 2. The lithium-sulfur battery of claim 1, wherein the compound has an X-ray diffraction pattern with diffraction angles (2θ values) of 7.1±0.2°, 9.0±0.2°, 9.4±0.2°, 9.6±0.2°, 9.9±0.2°, 10.0±0.2°, 10.4±0.2°, 11.0±0.2°, 11.6±0.2°, 12.1±0.2°, 13.3±0.2°, 14.5±0.2°, and 15.0±0.2°.

6. 2. The lithium-sulfur battery according to claim 1, wherein the sulfur-carbon composite has a weight ratio of sulfur to carbon of 2.3 g / g or more.

7. the positive electrode includes a current collector and a positive electrode active material layer formed on at least one surface of the current collector and including the sulfur-carbon composite; 2. The lithium-sulfur battery according to claim 1, wherein the weight of the sulfur-carbon composite is 90 wt % or more based on the total weight of the positive electrode active material layer.

8. The sulfur loading of the positive electrode is 2 mAh / cm ２ Above, 5mAh / cm ２ 2. The lithium-sulfur battery of claim 1, wherein:

9. 2. The lithium-sulfur battery according to claim 1, wherein the thickness of the negative electrode is 40 μm or more and 80 μm or less.

10. 2. The lithium-sulfur battery according to claim 1, wherein a weight ratio of the electrolyte to elemental sulfur in the sulfur-carbon composite is 2.5 g / g or less.

11. The lithium-sulfur battery is represented by the following formula 1: [Formula 1] S Ｘ =S ＰＥ / S ＥＬ／Ｓ by S Ｘ is 1.4mAh / cm ２ That's all, In Equation 1, The S ＰＥ is the sulfur loading in the cathode, The S ＥＬ／Ｓ is the weight ratio of the electrolyte to the sulfur element in the sulfur-carbon composite.

12. 2. The lithium-sulfur battery of claim 1, wherein the energy density of the lithium-sulfur battery is 430 Wh / kg or greater.

13. The lithium-sulfur battery according to any one of claims 1 to 12, wherein the lithium-sulfur battery is a pouch-type battery or a cylindrical battery.

14. a positive electrode including a sulfur-carbon composite; a negative electrode; a separator interposed between the positive electrode and the negative electrode; an electrolyte; and a method for evaluating the energy density of a lithium-sulfur battery comprising: The evaluation method includes a step of determining that a lithium-sulfur battery containing a compound has three or more characteristic peaks selected from the group consisting of diffraction angles (2θ values) of 7.1±0.2°, 9.0±0.2°, 9.4±0.2°, 9.6±0.2°, 9.9±0.2°, 10.0±0.2°, 10.4±0.2°, 11.0±0.2°, 11.6±0.2°, 12.1±0.2°, 13.3±0.2°, 14.5±0.2°, and 15.0±0.2° in an X-ray diffraction pattern at a depth of discharge (DOD) of 15% to 80%, as a battery having a high energy density.

15. The evaluation method according to claim 14 , wherein the battery having a high energy density is a battery having an energy density of 430 Wh / kg or more.

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