Lithium-sulfur battery

Abstract

The present invention relates to a lithium-sulfur battery having sufficient energy density and capacity even at high-rate discharge, and provides new parameters for the lithium-sulfur battery having the above characteristics. A lithium-sulfur battery according to one aspect of the present invention is characterized in that the value according to formula 1 in claim 1 is 80% or more.

Description

[Technical Field]

[0001] The present invention relates to a lithium-sulfur battery, and more particularly to a lithium-sulfur battery that exhibits excellent capacity even at high discharge rates.

[0002] This application claims priority based on Korean Patent Application No. 2023-0066600, filed on May 23, 2023, the entire contents of which are incorporated herein by reference. [Background technology]

[0003] Lithium secondary batteries are being used in a wide range of applications, including not only portable electronic devices but also electric vehicles (EVs), electric storage systems (ESSs), etc., and there is an increasing demand for lithium secondary batteries with high capacity, high energy density, and long life.

[0004] There are various types of lithium secondary batteries, but lithium-sulfur batteries are a battery system that uses a sulfur-based material containing sulfur-sulfur bonds as the positive electrode active material and lithium metal, a carbon-based material into which lithium ions are inserted and 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 the advantages of being low in weight per atom, abundant in resources, easy to supply and demand, inexpensive, non-toxic, and environmentally friendly.

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

[0007] During discharge, sulfur (S8) accepts electrons at the positive electrode and undergoes a multi-step reduction reaction to form lithium polysulfide (LiPS, Li2S). x , x=2~8), and finally to lithium sulfide (Li2S). During this process, energy is released during the conversion into each substance.

[0008] On the other hand, lithium-sulfur batteries are a promising next-generation battery for applications where energy density is important, such as aviation. For lithium-sulfur batteries to exhibit high output characteristics, even at high discharge rates (C rates), the conversion of lithium polysulfide (LiPS) in all steps, specifically from Li2S8 to Li2S2, and the final step of conversion to lithium sulfide (Li2S) must be sufficient. In particular, considering the physical properties required for a drone's minimum usage time of approximately 30 minutes, it may be necessary for the battery to be able to release sufficient energy even when continuously discharged at a discharge rate of 2.0C.

[0009] However, it has been reported that currently developed lithium-sulfur batteries have problems such as insufficient stepwise conversion reactions when the discharge rate is increased, resulting in a significant decrease in capacity retention due to repeated charge and discharge, and a significant decrease in charge and discharge efficiency. As a result, the capacity of currently developed lithium-sulfur batteries is reduced compared to the theoretical capacity when the discharge rate is increased to increase the output.

[0010] Therefore, there is a need to develop lithium-sulfur batteries that have sufficient capacity even under high discharge rates. Summary of the Invention [Problem to be solved by the invention]

[0011] The present invention solves the above problems, The object of the present invention is to provide a lithium-sulfur battery that has an excellent capacity retention rate even under high power output conditions.

[0012] In particular, an object of the present invention is to provide a lithium-sulfur battery that has excellent capacity retention even at a discharge rate (C rate) of 1.0 C or more, for example, a discharge rate of 2.0 C. [Means for solving the problem]

[0013] In order to solve the above problems, According to one aspect of the present invention, there is provided a lithium-sulfur battery having the following configuration.

[0014] The lithium-sulfur battery according to the first aspect comprises: a positive electrode; a negative electrode; a separator interposed between the positive electrode and the negative electrode; and an electrolyte; The positive electrode includes a positive electrode active material containing a sulfur-carbon composite, and the lithium-sulfur battery is characterized in that the ratio R (1.0C / 0.5C) according to the following formula 1 is 80% or more. [Formula 1] R(1.0C / 0.5C)=[A(DOD100) 1.0C / A(DOD100) 0.5C ]×100(%) In the formula 1, The above A (DOD100) 1.0C is the amount of lithium sulfide (Li2S) present when discharged at 1.0 C and at DOD 100, The above A (DOD100) 0.5C is the amount of lithium sulfide (Li2S) present when discharged at 0.5C and in the state of DOD100.

[0015] According to the second aspect, in the first aspect, The R(1.0C / 0.5C) may be 85% or more.

[0016] According to the third aspect, in the first or second aspect, The DOD 100 may be in a state where it has a potential of 1.7V to 1.9V.

[0017] According to a fourth aspect, in any one of the first to third aspects, The DOD 100 may be in a state with a potential of 1.8V.

[0018] According to a fifth aspect, in any one of the first to fourth aspects, The amount of lithium sulfide (LiS) can be weight, volume, or moles of the lithium sulfide.

[0019] According to a sixth aspect, in any one of the first to fifth aspects, the ratio R(1.0C / 0.5C) is measured by a ratio of peak intensities of the lithium sulfide (LiS) on an X-ray diffraction spectrum of the lithium-sulfur battery; The lithium sulfide (LiS) has a scattering vector (q) of 1.85 to 1.92 Å in the X-ray diffraction spectrum. -1 It may have a characteristic peak in the region of

[0020] According to a seventh aspect, in any one of the first to sixth aspects, The weight ratio of sulfur (S) in the electrolyte and the sulfur-carbon composite (E1 / S weight ratio) may be 2.7 g / g or more.

[0021] According to an eighth aspect, in any one of the first to seventh aspects, The electrolyte may include a non-aqueous solvent, a lithium salt, and an additive.

[0022] According to a ninth aspect, in any one of the first to eighth aspects, The lithium-sulfur battery may have an energy density of 300 Wh / kg or more.

[0023] According to a tenth aspect, in any one of the first to ninth aspects, The sulfur (S) content in the sulfur-carbon composite may be 60 to 85% by weight.

[0024] According to an eleventh aspect, in any one of the first to tenth aspects, The weight of the sulfur-carbon composite may be 90 wt % or more based on the total weight of the positive electrode.

[0025] According to a twelfth aspect, in any one of the first to eleventh aspects, The lithium-sulfur battery can be a coin cell, a pouch cell, or a cylindrical cell.

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

[0027] The evaluation method according to the thirteenth aspect includes: A method for evaluating output characteristics of a lithium-sulfur battery comprising: a positive electrode; a negative electrode; a separator interposed between the positive electrode and the negative electrode; and an electrolyte; wherein the positive electrode comprises a positive electrode active material containing a sulfur-carbon composite, the method comprising: If the ratio R(1.0C / 0.5C) according to the following formula 1 is 80% or more, the battery is determined to be a high-power lithium-sulfur battery: [Formula 1] R(1.0C / 0.5C)=[A(DOD100) 1.0C / A(DOD100) 0.5C ]×100(%) In the formula 1, The above A (DOD100) 1.0C is the amount of lithium sulfide (Li2S) present when discharged at 1.0 C and at DOD 100, The above A (DOD100) 0.5C is the amount of lithium sulfide (Li2S) present when discharged at 0.5C and in the state of DOD100.

[0028] According to the fourteenth aspect, in the thirteenth aspect, The high-power lithium-sulfur battery may be a battery that maintains an energy density of 300 Wh / kg or more under discharge conditions of 1.0 C rate or more at room temperature.

[0029] According to the fifteenth aspect, in the thirteenth or fourteenth aspect, The room temperature may be a temperature of 23°C to 25°C.

[0030] According to a sixteenth aspect, in any one of the thirteenth to fifteenth aspects, The above A (DOD100) xC (x=0.5 or 1.0) is when the lithium-sulfur battery is discharged at a rate of xC to obtain an X-ray diffraction spectrum at DOD 100, and the scattering vector (q) on the obtained X-ray diffraction spectrum is 1.85 to 1.92 Å. -1 The ratio R (1.0C / 0.5C) can be determined by calculating the ratio of the peak intensities obtained above. [Effects of the Invention]

[0031] A lithium-sulfur battery according to one aspect of the present invention has the advantage of having sufficient energy density and capacity even when discharged at a high C-rate.

[0032] Specifically, even when the battery is discharged at a rate of 1.0 C or more, the same energy and maintenance effect as when the battery is discharged at 0.5 C can be achieved.

[0033] In particular, the lithium-sulfur battery of the present invention can have a specific capacity of 1,000 mAh / g or greater.

[0034] In particular, the lithium-sulfur battery of the present invention can have an energy density of 300 Wh / kg or greater.

[0035] The following drawings attached to this specification illustrate preferred embodiments of the present invention and are intended to facilitate a further understanding of the technical concepts of the present invention together with the above-described content of the invention, and therefore the present invention should not be construed as being limited to the matters depicted in the drawings. Meanwhile, the shape, size, scale, or ratio of elements in the drawings attached to this specification may be exaggerated to emphasize a clearer description. [Brief explanation of the drawings]

[0036] [Figure 1] 1 is a graph showing the discharge C rate-energy density of the lithium-sulfur batteries of Example 1, Example 2, and Comparative Example 1. [Figure 2] 1 is a graph showing the specific capacity-voltage relationship of the lithium-sulfur batteries of Example 1, Example 2, and Comparative Example 1. [Figure 3] 1 is a graph showing the nominal voltages of the lithium-sulfur batteries of Example 1, Example 2, and Comparative Example 1 at 0.5 C rate discharge and 1.0 C rate discharge. [Figure 4] 1 is a graph showing the amount of Li2S produced when the lithium-sulfur batteries of Example 1, Example 2, and Comparative Example 1 are discharged at a 0.5 C rate. [Figure 5] 1 is a graph showing the amount of Li2S produced when the lithium-sulfur batteries of Example 1, Example 2, and Comparative Example 1 are discharged at a 1.0 C rate. DETAILED DESCRIPTION OF THE INVENTION

[0037] The present invention will now be described in more detail.

[0038] The terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as having meanings and concepts corresponding to the technical ideas of the present invention, in accordance with the principle that the inventor can appropriately define the concepts of terms himself / herself in order to best explain the invention.

[0039] The terms used in this specification are merely used to describe specific embodiments and are not intended to limit the present invention. The singular expressions include the plural expressions unless the context clearly dictates otherwise. In this specification, the terms "comprise" or "have" and the like specify the presence of a feature, number, step, operation, component, part, or combination thereof described in the specification, and should be understood not to preclude the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0040] Also, throughout the specification, when a part is said to "include," "comprise," "have," or "have" a certain element, this means that it may further include other elements, without excluding other elements, unless otherwise specified.

[0041] Throughout this specification, the phrase "A and / or B" means "A or B or both."

[0042] Throughout this specification, the term "C rate" refers to the current rate, which indicates the rate at which a battery is charged or discharged. Throughout this specification, the term "C rate" may be abbreviated as "C."

[0043] Throughout this specification, unless otherwise specified, temperatures are in degrees Celsius and are expressed in °C.

[0044] As used herein, the term "composite" means a substance that combines two or more materials to form physically and chemically different phases while exhibiting a more effective function.

[0045] As used herein, the term "(poly)sulfide" includes both "(poly)sulfide ion (S x 2- , 1 ≦ x ≦ 8)" and "lithium (poly)sulfide (Li2S x or LiS x - , 1 ≦ x ≦ 8)".

[0046] As used herein, the term "polysulfide" includes both "polysulfide ion (S x 2- , 1 < x ≦ 8)" and "lithium (poly)sulfide (Li2S x or LiS x - , 1 < x ≦ 8)".

[0047] In a lithium-sulfur battery, during discharge of the positive electrode, sulfur (S8), which is the starting material, is converted to lithium sulfide (Li2S) via lithium polysulfide (LiPS), releasing energy.

[0048] According to one aspect of the present invention, there is provided a lithium-sulfur battery that stably realizes the above-described conversion reaction even when discharging at a high discharge rate.

[0049] A lithium-sulfur battery according to one aspect of the present invention is a lithium-sulfur battery including a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode includes a positive electrode active material containing a sulfur-carbon composite.

[0050] At this time, when the lithium-sulfur battery is discharged to a DOD (depth of discharge) of 100 at a rate of 1.0C, the amount of Li2S generated is 80% or more compared to the amount of Li2S generated when discharged to a DOD of 100 at a rate of 0.5C.

[0051] In one embodiment of the present invention, when the lithium-sulfur battery is discharged to a DOD (depth of discharge) of 100 at a rate of 1.0C, the amount of Li2S generated can be 85% or more compared to the amount of Li2S generated when discharged to a DOD of 100 at a rate of 0.5C.

[0052] In one embodiment of the present invention, the sulfur-carbon composite may contain at least one of sulfur and sulfur-based compounds. Here, sulfur-based compounds are a general term for substances containing sulfur element (S).

[0053] When the sulfur-carbon composite contains sulfur (S8), lithium polysulfide is formed at the positive electrode by a reduction reaction during discharge in the lithium-sulfur battery. When the formed lithium polysulfide is dissolved by the electrolyte and elutes from the positive electrode into the electrolyte, the amount of lithium polysulfide oxidized at the positive electrode during charging of the lithium-sulfur battery decreases, and as a result, the capacity of the lithium-sulfur battery may decrease.

[0054] The sulfur-based compound may include all sulfur-containing compounds that can be formed by, for example, a reduction reaction of inorganic sulfur (S8) or an oxidation reaction of lithium sulfide (Li2S). More specifically, lithium sulfide (Li2S), lithium polysulfide (Li2Sx, 1 < x ≤ 8), disulfide compounds, carbon-sulfur polymers ((C2S [[ID=I7]] y ) n , y = 2.5 to 50, |n| ≥ 2), or may include two or more of these.

[0055] Incidentally, when a lithium-sulfur battery contains inorganic sulfur (S8) as a positive electrode active material, during discharge of the lithium-sulfur battery, it becomes lithium polysulfide (Li2Sx, 1 < x ≤ 8) formed by the reduction reaction of sulfur at the positive electrode, and the lithium polysulfide is reduced again to become lithium sulfide (Li2S). However, when the lithium-sulfur battery discharges at a high C rate, the reduction reaction does not proceed well, and the amount of lithium polysulfide (Li2S) generated during discharge decreases, which causes a serious decrease in capacity.

[0056] Thus, in the case of a conventional lithium-sulfur battery discharging at a high C rate, the efficiency of the reduction reaction at the positive electrode is low, resulting in a decrease in the battery capacity.

[0057] However, the lithium-sulfur battery according to one aspect of the present invention shows that when discharging to DOD100 at 1.0C rate, the amount of Li2S generated is 80% or more, specifically 85% or more compared to when discharging to DOD100 at 0.5C rate. Therefore, even when discharging at a high C rate, there is an advantage that the decrease in capacity is less compared to when discharging at a low C rate.

[0058] In this specification, the DOD100 indicates a state of complete discharge, that is, a state where the depth of discharge is 100% based on the buffer state, i.e., the state of SOC (state of charge) 100%. In other words, it can be SOC0%.

[0059] In one embodiment of the present invention, the DOD100 may be, for example, a state having a potential of 1.7V to 1.9V, specifically, a state having a potential of 1.8V, but the present invention is not limited thereto.

[0060] Specifically, a lithium-sulfur battery in which the ratio R(1.0C / 0.5C) of lithium sulfide (Li2S) according to the following formula 1 is 80% or more can exhibit the effect of having high output characteristics. [Formula 1] R(1.0C / 0.5C)=[A(DOD100) 1.0C / A(DOD100) 0.5C ]×100(%) In the formula 1, The above A (DOD100) 1.0C is the amount of lithium sulfide present when discharged to DOD100 at 1.0 C, The above A (DOD100) 0.5C is the amount of lithium sulfide present when discharged to DOD 100 at 0.5C.

[0061] According to Equation 1, the ratio of the amount of lithium sulfide generated in the lithium-sulfur battery when fully discharged at a rate of 1.0 C, i.e., when discharged to DOD 100, to the amount of lithium sulfide generated in the lithium-sulfur battery when fully discharged at a rate of 0.5 C can be calculated. In this case, the higher the ratio, the more the positive electrode active material S8 → Li2S is converted in the high power state. x It can be seen that the conversion efficiency of (x=2~8) → Li2S (lithium sulfide) was maintained excellently.

[0062] In one embodiment of the present invention, the lithium sulfide (LiS) ratio R(1.0C / 0.5C) may be 88% or more, or 90% or more. For example, the lithium sulfide (LiS) ratio R(1.0C / 0.5C) may be 80% to 100%, 85% to 100%, 88% to 99%, 90% to 95%, 85% to 93%, 88% to 93%, 90% to 93%, or 91% to 93%.

[0063] In this specification, the amount of lithium sulfide (LiS) may be expressed by weight, volume, or moles. For measuring the ratio, the A(DOD100) 1.0C and A(DOD100) 0.5C is measured on the same basis, there is no particular limitation as to whether the "amount" is weight, volume, or moles.

[0064] In one embodiment of the present invention, the amount of LiS in the lithium-sulfur battery in the discharged state can be measured by disassembling the battery, i.e., by destructively analyzing the amount of LiS in the battery. However, it may be preferable to measure the amount of LiS in the battery in a non-destructive manner in order to prevent loss of LiS in the battery and shorten the analysis time.

[0065] For example, the amount of Li2S in the lithium-sulfur battery in the discharged state can be measured by non-destructive X-ray diffraction (XRD) analysis. Specifically, the Li2S has a scattering vector (q) of 1.85 to 1.92 Å in the spectrum obtained by XRD analysis. -1 Therefore, in the XRD patterns of the lithium-sulfur batteries discharged to DOD100 at different discharge rates, the scattering vector (q) is 1.85 to 1.92 Å. -1 The ratio of the amount of Li2S can be measured by the ratio of the peak intensities (i.e., scattering intensities) in the region.

[0066] Therefore, in one embodiment of the present invention, the ratio R (1.0C / 0.5C) is measured by the ratio of the peak intensities of the lithium sulfide (LiS) on the X-ray diffraction spectrum of the lithium-sulfur battery, and the lithium sulfide (LiS) has a scattering vector (q) of 1.85 to 1.92 Å on the X-ray diffraction spectrum. -1 It may have a characteristic peak in the region.

[0067] In one embodiment of the present invention, the A(DOD100) xC (x=0.5 or 1.0) is obtained by discharging the lithium-sulfur battery at a rate of xC and obtaining an X-ray diffraction spectrum at DOD 100, and the scattering vector (q) on the obtained X-ray diffraction spectrum is 1.85 to 1.92 Å. -1That is, the lithium-sulfur battery is discharged at a rate of 0.5 C to obtain an X-ray diffraction spectrum at DOD 100, and the scattering vector (q) on the obtained X-ray diffraction spectrum is measured by the peak intensity value in the range of 1.85 to 1.92 Å. -1 The peak intensity value in the region A(DOD100) 0.5C The lithium-sulfur battery was discharged at a rate of 1.0 C, and an X-ray diffraction spectrum was obtained at DOD 100. The scattering vector (q) on the obtained X-ray diffraction spectrum was 1.85 to 1.92 Å. -1 The peak intensity value in the region A(DOD100) 1.0C and calculate the ratio of the respective peak intensities obtained above, thereby determining the ratio R (1.0C / 0.5C).

[0068] In one embodiment of the present invention, the X-ray diffraction spectrum can be obtained by irradiating the lithium-sulfur battery with X-rays having a wavelength (λ) of 0.7 to 0.8 Å at room temperature.

[0069] In one embodiment of the present invention, the X-ray diffraction spectrum can be obtained by irradiating the lithium-sulfur battery with X-rays having a wavelength (λ) of 0.709 Å at room temperature.

[0070] Specifically, the XRD analysis can be performed by real-time X-ray diffraction (Operando XRD) analysis during operation. More specifically, the XRD pattern can be obtained by measuring the two-theta (2θ) range of 4 to 17° in transmission mode using Mo K-alpha X-rays (λ=0.709 Å) from an Empyrean XRD (PANalytical) at room temperature (23°C). In this case, one pattern can be obtained at 0.014° intervals for a total of one minute.

[0071] The ratio of the amount of Li2S in each discharge state measured by the above method is measured, and a lithium-sulfur battery with this ratio of 80% or more, specifically 85% or more, can be defined as a lithium-sulfur battery with high power characteristics.

[0072] Next, each component of the lithium-sulfur battery will be described in detail.

[0073] positive electrode In one embodiment of the present invention, the positive electrode may include the positive electrode current collector and a positive electrode active material layer coated on one or both sides of the positive electrode current collector.

[0074] The positive electrode current collector is not particularly limited as long as it supports the positive electrode active material, does not cause chemical changes in the battery, and has high conductivity, and examples thereof include copper, stainless steel, aluminum, nickel, titanium, palladium, baked carbon, copper or stainless steel surface-treated with carbon, nickel-silver, or the like, and aluminum-cadmium alloys.

[0075] 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, sheet, foil, mesh, net, porous material, foam, or nonwoven fabric.

[0076] The positive electrode active material layer may further include a conductive material, a binder, an additive, and the like in addition to the positive electrode active material.

[0077] In one embodiment of the present invention, the positive electrode active material includes a sulfur-carbon composite.

[0078] 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 pores inside the porous carbon material and the outer surface of the porous carbon material. In the case of sulfur acting as the positive electrode active material, since it has no electrical conductivity alone, it is used in combination with a conductive material such as a carbon material, and a porous carbon material can be used to support sulfur. Further, as the sulfur-based compound added as the positive electrode active material, for example, inorganic sulfur (S8), lithium sulfide (Li2S), lithium polysulfide (Li2Sx, 1 < x ≦ 8), disulfide compound, carbon-sulfur polymer ((C2S y ) n , y = 2.5 to 50, 2 ≦ n), lithium sulfide (Li2S) or may contain two or more of these. Preferably, the sulfur-based compound may be inorganic sulfur (S8).

[0079] 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 fixing the sulfur-based compound, and is for improving the conductivity of the positive electrode. As long as it is a porous carbon material substance, its type can be used without particular limitation.

[0080] The porous carbon material can generally be produced by carbonizing various carbonaceous precursors. The porous carbon material contains pores of non-uniform size inside, and the average diameter of the pores is in the range of 1 nm to 200 nm, and the porosity can be in the range of 10% to 90% by volume of the total volume of the porous carbon material. If the average diameter of the pores is less than the above range, since the pore diameter is only at the molecular level, sulfur impregnation cannot be performed. On the contrary, if it exceeds the above range, the mechanical strength of the porous carbon material becomes weak and it is not suitable for application in the electrode manufacturing process.

[0081] In one embodiment of the present invention, the "average pore diameter" can be measured according to a method known in the art for measuring the pore diameter of a porous material, but the measurement method is not particularly limited. For example, the pore diameter can be measured by a scanning electron microscope (SEM), a field emission electron microscope, a laser diffraction method, or the Brunauer-Emmett-Teller (BET) method. Measurement using the laser diffraction method can be performed, for example, using a commercially available Rayter diffraction particle size analyzer (e.g., Microtrac MT 3000). Measurement using the BET method can be performed, for example, using a BELSORP series analyzer manufactured by BEL Japan, but is not limited thereto.

[0082] 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 as a unit of % and can be used interchangeably with terms such as void ratio, porosity, etc. In the present invention, the measurement of the porosity is not particularly limited, and may be measured, for example, by the BET method using nitrogen gas or the mercury penetration method (Hg porosimeter) and according to ASTM D2873, depending on one embodiment of the present invention.

[0083] The shape of the porous carbon material may be spherical, rod-like, needle-like, plate-like, tubular or bulk, and any shape commonly used in lithium-sulfur batteries may be used without limitation.

[0084] The porous carbon material may have a porous structure or a large specific surface area, and may be any material commonly used in the art. Examples of the porous carbon material include, but are not limited to, one or more selected from the group consisting of graphite, graphene, carbon blacks such as denka black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black, carbon nanotubes (CNTs) such as single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs), carbon fibers such as graphite nanofibers (GNFs), carbon nanofibers (CNFs), and activated carbon fibers (ACFs), graphites such as natural graphite, artificial graphite, and expanded graphite, and activated carbon.

[0085] Preferably, the porous carbon material may be carbon nanotubes.

[0086] In one embodiment of the present invention, the porous carbon material may include, for example, carbon nanotubes (CNTs).

[0087] In one embodiment of the present invention, the sulfur-carbon composite may have a sulfur-to-carbon weight ratio (S / C weight ratio) of, for example, 5 g / g or less, more specifically, 2.5 g / g or less. For example, the sulfur-to-carbon composite may have a sulfur-to-carbon weight ratio of 2.4 g / g. The S / C ratio of the sulfur-carbon composite in this range may be advantageous in terms of ensuring the electron transfer ability (conductivity) and electrochemical specific surface area of ​​the sulfur-carbon composite. For example, the increased usable surface of the sulfur-carbon composite may be advantageous in suppressing sulfur elution from the positive electrode, but the present invention is not limited thereto.

[0088] The method for preparing the sulfur-carbon composite is not particularly limited in the present invention, and may be a method commonly used in the art, such as a method of simply mixing sulfur and a porous carbon material and then heat-treating the mixture to prepare a composite.

[0089] In addition to the above-described composition, the positive electrode active material may further include one or more selected from a transition metal element, a Group IIIA element, a Group VIA element, sulfur compounds of these elements, and alloys of these elements with sulfur.

[0090] Examples of the transition metal elements include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Os, Ir, Pt, Au, and Hg, examples of the elements include Al, Ga, In, and Ti, and examples of the VIA group elements include Ge, Sn, and Pb.

[0091] In one embodiment of the present invention, the sulfur-carbon composite may account for 50 wt % or more of the total weight of the positive electrode. Specifically, the sulfur-carbon composite may account for, for example, 80 wt % or more, 90 wt % or more, or 95 wt % or more of the total weight of the positive electrode active material layer. Specifically, the sulfur-carbon composite may be included 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 % of the total weight of the positive electrode active material layer. If the content of the sulfur-carbon composite is less than 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. Conversely, if the content exceeds the above range, the content of the conductive materials or binders described later is relatively insufficient, resulting in poor physical properties.

[0092] The conductive material electrically connects the electrolyte and the positive electrode active material and serves as a path for electrons to move from a current collector to the positive electrode active material. Any conductive material may be used without limitation as long as it is an electrode component physically distinct from the carbon contained in the sulfur-carbon composite and has electrical conductivity.

[0093] 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.

[0094] In one embodiment of the present invention, the content of the conductive material may be 0 to 10 wt %, for example, 1 to 10 wt %, based on the total weight of the positive electrode active material. If the content of the conductive material is less than this range, electron transfer between the positive electrode active material and the current collector may be difficult, which may result in a decrease in voltage and capacity. Conversely, if the content exceeds this range, the proportion of the positive electrode active material may be relatively reduced, which may result in a decrease in the total energy (charge amount) of the battery. Therefore, it is desirable to maintain an appropriate content within the above range.

[0095] In one embodiment of the present invention, the positive electrode may include a positive electrode active material and a binder polymer, but may not include a conductive material. That is, the positive electrode may not include a conductive material other than the porous carbon material of the sulfur-carbon composite included in the positive electrode active material. Since the positive electrode does not include a conductive material, it may include more positive electrode active material, thereby improving the energy density and / or capacity of the lithium-sulfur battery.

[0096] The binder polymer maintains the positive electrode active material on the positive electrode current collector and organically connects the positive electrode active materials together to further enhance the bonding strength therebetween, and any known binder can be used.

[0097] For example, the binder polymer may include a fluororesin-based binder such as polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); a rubber-based binder such as styrene butadiene rubber (SBR), acrylonitrile butadiene rubber, or styrene-isoprene rubber; a cellulose-based binder such as carboxyl methyl cellulose (CMC), starch, hydroxypropyl cellulose, or regenerated cellulose; a polyalcohol-based binder; a polyolefin-based binder such as polyethylene or polypropylene; a polyimide-based binder; a polyester-based binder; a polyacrylic binder such as polyacrylic acid (PAA); a silane-based binder; or a polyurethane-based binder; or a mixture of two or more of these. The binder polymer may also include a copolymer having repeating units derived from two or more of these binders.

[0098] The content of the binder polymer may be 0.5 to 30 wt% relative to the total amount (100 wt%) of the positive electrode active material layer. When the content of the binder polymer satisfies this range, the physical properties of the positive electrode are improved, the active material and conductive material in the positive electrode are prevented from falling off, and the ratio of the active material and conductive material in the positive electrode is appropriately controlled, thereby ensuring battery capacity.

[0099] In the present invention, the method for manufacturing the positive electrode for the lithium secondary battery is not particularly limited, and any method known to ordinary skilled artisans or various modified methods thereof can be used.

[0100] For example, the positive electrode for a lithium secondary battery may be manufactured by preparing a positive electrode slurry composition containing 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.

[0101] The positive electrode slurry composition may further include a binder, a conductive material, and a solvent in addition to the positive electrode active material.

[0102] The solvent used can uniformly disperse the positive electrode active material. Water is the most preferred aqueous solvent, and the water may be distilled water or deionized water. However, the solvent is not limited thereto, and a lower alcohol that is easily miscible with water can be used as needed. Examples of the lower alcohol include methanol, ethanol, propanol, isopropanol, and butanol, and these are preferably mixed with water.

[0103] The content of the solvent may be a concentration that allows easy coating, and the specific content varies depending on the application method and device.

[0104] The positive electrode slurry composition may further contain, as needed, substances commonly used in the art for the purpose of improving its performance, etc. Examples thereof include a viscosity modifier, a fluidizing agent, and a filler.

[0105] The method for applying the positive electrode slurry composition is not particularly limited in the present invention, and examples thereof include bar coating, doctor blade, die casting, comma coating, screen printing, dipping, reverse roll, direct roll, gravure, and extrusion. Alternatively, the positive electrode active material layer may be formed by applying the slurry to a separate substrate, and then the positive electrode active material layer may be attached to the positive electrode current collector by pressing or lamination.

[0106] The amount of the positive electrode slurry composition to be applied onto the current collector is not particularly limited, and can be adjusted in consideration of the final thickness of the positive electrode active material layer.

[0107] After the coating, a drying process can be performed to remove the solvent. The drying process is performed at a temperature and time that allows the solvent to be sufficiently removed. The conditions may vary depending on the type of solvent, and are not particularly limited in the present invention. For example, drying methods using warm air, hot air, hot air, or low-humidity air, vacuum drying, or drying by irradiation with (far) infrared rays or electron beams, etc., can be used. The drying speed is usually adjusted so that the solvent can be removed as quickly as possible within a speed range that does not cause cracks in the positive electrode active material layer due to stress concentration or peeling of the positive electrode active material layer from the positive electrode current collector.

[0108] Furthermore, after the drying, the current collector can 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.

[0109] The positive electrode manufactured by the above-described composition and manufacturing method, specifically the positive electrode active material layer, may have a porosity of 50 to 80% by volume, specifically 60 to 75% by volume.

[0110] When the porosity of the positive electrode satisfies 50 to 80% by volume, the filling degree of the positive electrode active material layer including the positive electrode active material, the conductive material, and the binder is appropriately maintained, and therefore, a sufficient amount of electrolyte for realizing ionic conduction and / or electrical conduction can be maintained between the positive electrode active materials, thereby improving the output characteristics and cycle characteristics of the battery, preventing problems of overvoltage and reduction in discharge capacity of the battery, and ensuring physical and electrical connection with the current collector to improve adhesion, thereby improving the energy density of the battery.

[0111] In one embodiment of the present invention, the positive electrode has a capacity of 2 to 5 mAh / cm 2 For example, the sulfur (S) loading of the positive electrode may be 、 2~4mAh / cm 2 , 2.5~4mAh / cm 2 , 2.5~3.5mAh / cm 2 , or 2.5 to 3.0 mAh / cm 2However, the present invention is not limited to this.

[0112] negative electrode In one embodiment of the present invention, the negative electrode may be a current collector-free type including only a negative electrode active material layer without including a current collector, or may include a negative electrode current collector and a negative electrode active material layer formed on at least one surface of the negative electrode current collector.

[0113] In one embodiment of the present invention, 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.

[0114] The negative electrode current collector is for supporting the negative electrode active material layer, and is the same as that described for the positive electrode current collector.

[0115] 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.

[0116] The negative electrode active material is lithium (Li + The lithium ion-containing compound may include a material capable of reversibly intercalating and deintercalating lithium ions, a material capable of reacting with lithium ions to form a reversible lithium-containing compound, and lithium metal.

[0117] 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 reversibly forming a lithium-containing compound by reacting with lithium (Li) may be, for example, tin oxide, titanium nitrate, or silicon. The lithium alloy may be, for example, an alloy of lithium (Li) and a metal selected from 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).

[0118] According to one embodiment of the present invention, the negative electrode active material may be lithium metal, specifically, in the form of a lithium metal thin film or lithium metal powder.

[0119] Preferably, the negative electrode active material may be lithium metal, specifically in the form of a lithium metal thin film or lithium metal powder.

[0120] In one embodiment of the present invention, the negative electrode may have a thickness of 40 to 80 μm. For example, the thickness of the negative electrode may be 50 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, such as, but not limited to, a thickness measuring instrument manufactured by Mitutoyo Corporation.

[0121] Separator The separator separates or insulates the positive electrode and the negative electrode from each other and allows lithium ions to be transported between the positive electrode and the negative electrode. Any separator commonly used in lithium-sulfur batteries can be used without any particular limitations. For example, the separator can be made of a porous, non-conductive or insulating material. In particular, the separator can be an independent member such as a film, or a coating layer attached to the positive electrode and / or the negative electrode.

[0122] In one embodiment of the present invention, the separator may preferably have low resistance to ion migration of the electrolyte and excellent moisture absorption ability for the electrolyte.

[0123] In one embodiment of the present invention, the separator may include a porous substrate. The porous substrate may be any porous substrate commonly used in secondary batteries. A porous polymer film may be used alone or in combination. For example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, or the like, or a polyolefin-based porous film may be used, but is not limited thereto.

[0124] The material of the porous substrate is not particularly limited in the present invention, and any porous substrate generally used in electrochemical devices can be used. For example, the porous substrate can be made of polyolefin (polyethylene, polypropylene, etc.), polyester (polyethylene terephthalate, polybutylene terephthalate, etc.), polyamide, polyacetal, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, polyethylene naphthalate, polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl chloride, etc. The adhesive layer may include one or more materials selected from the group consisting of polyparaphenylene benzobisoxazole (P-phenylene), polyacrylonitrile, cellulose, nylon, and polyarylate.

[0125] In one embodiment of the present invention, the thickness of the porous substrate is not particularly limited, but may be 1 to 100 μm, preferably 5 to 50 μm. Although the thickness of the porous substrate is not limited to the above range, if the thickness is smaller than the lower limit, the mechanical properties may be reduced, and the separator may be easily damaged during use of the battery.

[0126] 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 to 50 μm and 10 to 95% by volume, respectively.

[0127] 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.

[0128] 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 that are commonly used in porous coating layers of separators, and the manufacturing method thereof is not particularly limited.

[0129] electrolyte The electrolyte is a medium in which ions involved in the electrochemical reaction of the lithium-sulfur battery can move, and may include a non-aqueous solvent and a lithium salt as an electrolyte.

[0130] 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.

[0131] In one embodiment of the present invention, the electrolyte may include a non-aqueous solvent, a lithium salt, and an additive.

[0132] In one embodiment of the present invention, the non-aqueous solvent may be any solvent that can be used in a lithium-sulfur battery, and examples of such solvents include ether solvents, esters, amides, linear carbonates, and cyclic carbonates.

[0133] 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, α-valerolactone, and ε-caprolactone, or a mixture of two or more thereof, but is not limited thereto.

[0134] In one embodiment of the present invention, the linear carbonate may be, for example, any one selected from the group consisting of dimethyl 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.

[0135] 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. Examples of halides thereof include, but are not limited to, fluoroethylene carbonate.

[0136] In one embodiment of the present invention, the non-aqueous solvent may include an ether-based solvent.

[0137] 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. When the amount of the ether-based solvent is within the above range, based on the total volume of the non-aqueous solvent, it can exhibit advantageous effects in terms of the solubility of electrolyte components such as lithium salt, but the present invention is not limited thereto.

[0138] In one embodiment of the present invention, the ether solvent may include an acyclic ether, a cyclic ether, or a mixture thereof.

[0139] In one embodiment of the present invention, the acyclic ether may include at least one 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 at least one 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.

[0140] 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, tetrahydropyran, 1,4-dioxane, 1,2-dimethoxybenzene, 1,3-dimethoxybenzene, 1,4-dimethoxybenzene, and isosobide 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.

[0141] In one embodiment of the present invention, the non-aqueous solvent may comprise a mixture of an acyclic ether and a cyclic ether.

[0142] In one embodiment of the present invention, the non-aqueous solvent may include dimethoxyethane (DME) and 2-methylfuran (2-MeF).

[0143] In one embodiment of the present invention, the volume ratio (v / v) of the acyclic ether to the cyclic ether can be 5:95 to 95:5, specifically 95:5 to 50:50, more specifically 90:10 to 50:50, 90:10 to 70:30, 85:15 to 75:25, or 80:20. In the present invention, the volume ratio corresponds to the ratio of the "volume % of the acyclic ether" to the "volume % of the cyclic ether" in the ether-based solvent.

[0144] In one embodiment of the present invention, the non-aqueous solvent may be free of a carbonate-based solvent in terms of electrolyte solubility, or may contain a small amount of carbonate-based solvent to the extent that the carbonate-based solvent 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-based 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.

[0145] In one embodiment of the present invention, the lithium salt is not particularly limited as long as it 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 4-phenylborate, lithium imide, or two or more thereof.

[0146] 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 to 4 M, preferably 0.2 to 2 M, 0.2 to 1 M, 0.5 to 2 M, 0.6 to 1 M, or 0.6 to 0.9 M. When the concentration of the lithium salt is within the above range, advantageous effects can be exhibited in terms of ensuring ionic conductivity suitable for battery operation, providing an appropriate viscosity of the electrolyte, improving the mobility of lithium ions, and suppressing the decomposition reaction of the lithium salt itself, but the present invention is not limited thereto.

[0147] In one embodiment of the present invention, the additive may include, in addition to the lithium salt, a nitrogen compound to improve the electrical conductivity of the electrolyte and extend the life of the lithium-sulfur battery.

[0148] Specifically, the nitrogen compound may inhibit the reduction reaction of polysulfides that occurs during the charge and discharge process of a lithium-sulfur battery, thereby preventing irreversible consumption of polysulfides, thereby improving the performance of the lithium-sulfur battery, although the effect is not limited thereto.

[0149] 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 exhibits the effect of improving charge / discharge efficiency. For example, the nitrogen compound may be a nitrate compound, a nitrite compound, or a mixture thereof.

[0150] 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 nitrate, propyl nitrate, butyl nitrate, pentyl nitrate, and octyl nitrate; organic nitro compounds such as nitromethane, nitropropane, nitrobutane, nitrobenzene, dinitrobenzene, nitropyridine, dinitropyridine, nitrotoluene, and dinitrotoluene; and combinations thereof, preferably lithium nitrate.

[0151] In one embodiment of the present invention, the nitrogen compound may be contained in an amount of, for example, 1 wt % to 10 wt %, specifically 1 wt % to 7 wt %, or 1 wt % to 5 wt %, based on the total weight of the electrolyte, but is not limited thereto. When the nitrogen compound is contained in the amount described above, more advantageous effects can be achieved in terms of improving the electrical conductivity of the electrolyte due to the nitrogen compound and suppressing the reduction of polysulfides when used in a lithium-sulfur battery, but the present invention is not limited thereto.

[0152] In one embodiment of the present invention, the lithium-sulfur battery has a sulfur (S) weight ratio (El / S weight ratio) in the electrolyte and the sulfur-carbon composite of 2.7 g / g or more, 2.8 g / g or more, 2.9 g / g or more, or 3.0 g / g or more. For example, the El / S ratio may be 2.7 g / g to 4.0 g / g, 2.8 g / g to 3.7 g / g, 2.9 g / g to 3.5 g / g, 3.0 g / g to 3.5 g / g, 2.8 g / g to 3.4 g / g, 2.9 g / g to 3.4 g / g, or 3.0 g / g to 3.4 g / g. Here, El is the weight of the electrolyte, and S is the weight of sulfur (S) contained in the positive electrode.

[0153] When the weight of electrolyte per weight of elemental sulfur contained in the positive electrode of the lithium-sulfur battery (El / S) satisfies the above range, the reduction reaction of the positive electrode active material can be smoothly carried out even when the lithium-sulfur battery is discharged at a high C rate, and the capacity when discharged at a high C rate can be significantly improved, and the capacity decrease can be smaller than when discharged at a low C rate.

[0154] In an embodiment of the present invention, the El / S ratio of the lithium-sulfur battery can be calculated by the ratio of the weight of sulfur in the sulfur-carbon composite cathode added in a manufacturing step immediately after the fabrication of the lithium-sulfur battery to the weight of the electrolyte added.

[0155] In another embodiment of the present invention, the El / S ratio of the lithium-sulfur battery can be calculated by disassembling the battery and calculating the weight ratio of sulfur in the sulfur-carbon composite cathode to the weight of the electrolyte.

[0156] For example, to analyze the El / S ratio of a lithium-sulfur battery by disassembling the battery, the total weight of the lithium-sulfur battery is measured in a charged state, and then the battery is disassembled. The cathode, anode, separator, and case are washed and dried with a solvent to determine the sum of their respective weights. The weight of the electrolyte can be measured by subtracting the weights of the cathode, anode, separator, and case from the total battery weight. Preferably, the washing solvent is capable of extracting the electrolyte attached to the cathode, anode, separator, and case. Next, the cathode active material layer and current collector are separated from the dried cathode, and the weight of sulfur derived from the sulfur-carbon composite present in the cathode active material layer is measured to determine the weight of sulfur in the cathode. The El / S ratio of the lithium-sulfur battery can be calculated from the ratio of the weight of sulfur in the sulfur-carbon composite of the cathode to the weight of the added electrolyte.

[0157] In one embodiment of the present invention, a method for measuring the weight of sulfur derived from the sulfur-carbon composite present in the positive electrode active material layer may be, for example, to measure the amount of sulfur (S) derived from the active material by scraping off the obtained positive electrode active material layer and subjecting the resulting product to thermogravimetric analysis (TGA). However, the measuring method is not limited thereto.

[0158] In one embodiment of the present invention, the state of charge at which the lithium-sulfur battery is disassembled may be a fully charged state, i.e., SOC 100%.

[0159] In another embodiment of the present invention, the state of charge for disassembling the lithium-sulfur battery may be SOC 95% to SOS 100%.

[0160] In one embodiment of the present invention, disassembly of the charged lithium-sulfur battery must be carried out in an inert atmosphere for safety reasons, for example, in an Ar atmosphere.

[0161] In one embodiment of the present invention, the lithium-sulfur battery may have an energy density of 300 Wh / kg or more. For example, the energy density of the lithium-sulfur battery may be 300 Wh / kg to 500 Wh / kg, or 300 Wh / kg to 400 Wh / kg.

[0162] In one embodiment of the present invention, the lithium-sulfur battery can exhibit an excellent effect of maintaining the energy density exhibited when discharging at a high discharge rate at the same level as the energy density exhibited when discharging at a low discharge rate.

[0163] For example, the lithium-sulfur battery may have an energy density measured when discharged at a 1.0 C rate that is 90% or more of the energy density measured when discharged at a 0.5 C rate.

[0164] Furthermore, the lithium-sulfur battery may have an energy density measured when discharged at a 2.0 C rate that is 90% or more of the energy density measured when discharged at a 1.0 C rate.

[0165] In one embodiment of the present invention, the energy density of the lithium-sulfur battery may be measured according to a known method, and the measurement method is not particularly limited. For example, the energy density of the lithium-sulfur battery may be measured by discharging the battery from 2.5 V to 1.8 V at a 0.5 C rate at room temperature once, charging the battery to 2.5 V at a 1.0 C rate once, and discharging the battery at a constant rate selected from a 0.5 C rate to a 2.0 C rate, according to the following formula:

[0166] [formula] Energy density (Wh / kg) = {[(discharge capacity (mAh) x driving voltage (V)) / 1000] / (cell weight (kg))}.

[0167] 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.

[0168] In one embodiment of the present invention, the specific capacity of the lithium-sulfur battery can be, for example, 1,000 mAh / g or more.

[0169] In one embodiment of the present invention, the specific capacity of the lithium-sulfur battery can be measured by, for example, discharging once at a 0.5C rate in the range of 1.8V to 2.5V at room temperature, and then charging and discharging at a 0.5C rate.

[0170] In one embodiment of the present invention, the room temperature may be a temperature of 23°C to 25°C.

[0171] In one embodiment of the present invention, the lithium-sulfur battery may be, but is not limited to, a coin-type battery, a pouch-type battery, or a cylindrical battery.

[0172] According to another aspect of the present invention, there is provided a method for evaluating the high-power characteristics of a lithium-sulfur battery using Equation 1.

[0173] The evaluation method includes a step of determining that a lithium-sulfur battery having a lithium sulfide ratio R(1.0C / 0.5C) according to the formula 1 of 85% or more is a high-power battery.

[0174] In one embodiment of the present invention, the high-power battery may be a battery that maintains an energy density of 300 Wh / kg or more under discharge conditions of, for example, 1.0 C rate or more at room temperature, where the room temperature may be a temperature of 23°C to 25°C.

[0175] The present invention will be described in more detail below with reference to examples. However, the following examples are for the purpose of illustrating the present invention and are not intended to limit the scope of the present invention.

[0176] [Manufacturing lithium-sulfur batteries] Example 1 A sulfur-carbon composite (S / C weight ratio = 2.3 g / g) in which sulfur (S8) was supported on carbon nanotubes (MWCNT) was prepared as a positive electrode active material. The prepared sulfur-carbon composite and polyacrylic acid (PAA) as a binder were mixed in a ratio of 96:4 and added to water 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 loading of the prepared positive electrode was 2.7 mAh / cm. 2 It was.

[0177] A 60 μm thick lithium metal was prepared as the negative electrode.

[0178] The negative electrode and the positive electrode were arranged to face each other, and a polyethylene separator having a thickness of 16 μm and a porosity of 46 vol % was interposed therebetween to prepare an electrode assembly.

[0179] The prepared electrode assembly was placed in a pouch-type case, and an electrolyte solution consisting of 0.75M lithium salt (LiTFSI) and 3 wt% lithium nitrate (LiNO3) dissolved in a solvent of a mixture of dimethoxyethane and 2-methylfuran (2-MeF) in a volume ratio of 8:2 was injected so that the El / S ratio was 3.0 g / g to fabricate a lithium-sulfur battery.

[0180] Example 2 A lithium-sulfur battery was produced in the same manner as in Example 1, except that the electrolyte solution was poured so that the El / S ratio was 3.4 g / g.

[0181] Comparative Example 1 A lithium-sulfur battery was produced in the same manner as in Example 1, except that the electrolyte solution was poured so that the El / S ratio was 2.6 g / g.

[0182] [Analysis of Li2S production and battery performance evaluation] The lithium-sulfur batteries of Example 1, Example 2, and Comparative Example 1 were charged to 2.4 V at a 0.5 C rate at room temperature (23° C.), and then discharged to 1.8 V at a 0.5 C rate, a 1.0 C rate, or a 2.0 C rate. The battery capacity (mAh) and energy (Wh) at this time were measured and then divided by the respective battery capacities to evaluate the specific capacity (mAh / g) and energy density (Wh / kg) of the batteries. The results are shown in FIGS. 1 and 2 below.

[0183] FIG. 3 shows a graph comparing the average discharge voltage, ie, the nominal voltage, of the battery at 0.5 C rate discharge and 1.0 C rate discharge.

[0184] Referring to FIG. 1, it was confirmed that when discharged at a 2.0 C rate, the energy density of the lithium-sulfur batteries of Examples 1 and 2 decreased slightly (both maintained at 300 wh / kg or more), but the energy density of the lithium-sulfur battery of Comparative Example 1 decreased significantly.

[0185] 2 is a graph showing the results when the battery was discharged to 1.8 V at a 2.0 C rate. The lithium-sulfur batteries of Examples 1 and 2 exhibited specific capacities of 1,000 mAh / g or more, while the lithium-sulfur battery of Comparative Example 1 exhibited a significantly lower specific capacity.

[0186] The lithium-sulfur battery of Comparative Example 1 had an El / S of 2.6, and it was confirmed that when discharged at 2.0C, the capacity and energy density decreased significantly.

[0187] 1 and 3, it was confirmed that, during 1.0 C discharge, the energy density of Comparative Example 1 was maintained at 300 Wh / kg or more, but the nominal voltage was significantly inferior to that of Examples 1 and 2.

[0188] 4 and 5 are graphs showing the analysis of the amount of Li2S in the lithium-sulfur batteries of Example 1, Example 2, and Comparative Example 1 after discharging them at 0.5 C or 1.0 C to 1.8 V (DOD100), respectively.

[0189] To measure the amount of Li2S in each discharge state, XRD patterns were obtained for the lithium-sulfur batteries in the discharged state by the following method.

[0190] First, XRD patterns were acquired for each battery while discharging at a 0.5C or 1.0C rate between 2.4V and 1.8V at room temperature (23°C). Specifically, measurements were taken in transmission mode using Mo K-alpha X-rays (λ = 0.709Å) from a PANalytical Empyrean XRD in the 4-17° 2θ range, with each pattern acquired at 0.014° intervals for a total of 1 minute. XRD was performed using a pressure jig equipped with a Be-window. In Figures 4 and 5, peak scattering intensities were measured in arbitrary units (au).

[0191] In the XRD pattern, Li2S has a characteristic peak at a scattering vector (q) of 1.85 to 1.92 / Å. The amount of Li2S can be determined using the peak intensity (i.e., scattering intensity) at this time.

[0192] The characteristic peak of Li2S can also be confirmed in the scattering vector (q) range of 1.4 to 1.6 / Å. However, since there is a possibility that this region overlaps with the scattering vector of S8, in this experiment, the characteristic peak value in the range of 1.85 to 1.92 / Å was used to quantify Li2S.

[0193] The graphs showing the measured LiS peak intensity at 0.5 C discharge (FIG. 4) and 1.0 C discharge (FIG. 5) are shown in FIGS. 4 and 5, respectively. Using the results of FIGS. 4 and 5, the lithium sulfide ratio R(1.0 C / 0.5 C) was calculated according to the following Equation 1 and is shown in Table 1 below. [Formula 1] R(1.0C / 0.5C)=[A(DOD100) 1.0C / A(DOD100) 0.5C ]×100(%) In the formula 1, The above A (DOD100) 1.0C is the amount of lithium sulfide present when discharged to DOD100 at 1.0 C, The above A (DOD100) 0.5C is the amount of lithium sulfide present when discharged to DOD 100 at 0.5C.

[0194] At this time, the A (DOD100) 1.0C and A (DOD100) 1.0C was measured using the peak intensity values ​​of the XRD pattern.

[0195] [Table 1]

[0196] 4, 5 and Table 1, it can be seen that the lithium-sulfur battery of Comparative Example 1 produced significantly less Li2S when discharged at 1.0 C.

[0197] From the above results, it was confirmed that Examples 1 and 2, in which the lithium sulfide ratio R (1.0C / 0.5C) was 85% or more, had high output characteristics, while Comparative Example 1, in which the ratio was low, did not have high output characteristics.

[0198] Although the present invention has been described above using limited embodiments and drawings, it goes without saying that the present invention is not limited to these, and that various modifications and variations can be made by a person having ordinary knowledge in the technical field to which the present invention pertains within the technical spirit of the present invention and the equivalent scope of the appended claims.

Claims

1. A lithium-sulfur battery including a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, the positive electrode comprises a positive electrode active material containing a sulfur-carbon composite; The lithium-sulfur battery has a ratio R (1.0C / 0.5C) of 80% or more according to the following formula 1: [Formula 1] R(1.0C / 0.5C)=[A(DOD100) １．０Ｃ / A(DOD100) ０．５Ｃ ]×100(%) In the formula 1, The above A (DOD100) １．０Ｃ is discharged at 1.0 C, and lithium sulfide (Li ２ S), The above A (DOD100) ０．５Ｃ is discharged at 0.5 C, and lithium sulfide (Li ２ S).

2. 2. The lithium-sulfur battery according to claim 1, wherein the R(1.0C / 0.5C) is 85% or more.

3. 2. The lithium-sulfur battery of claim 1, wherein the DOD 100 is in a state having a potential of 1.7V to 1.9V.

4. 2. The lithium-sulfur battery of claim 1, wherein the DOD 100 is in a state having a potential of 1.8V.

5. The lithium sulfide (Li ２ 2. The lithium-sulfur battery of claim 1, wherein the amount of lithium sulfide is weight, volume, or moles of lithium sulfide.

6. The ratio R (1.0C / 0.5C) is such that the lithium sulfide (Li ２ S) and The lithium sulfide (Li ２ S) has a scattering vector (q) of 1.85 to 1.92 Å on the X-ray diffraction spectrum. －１ 2. The lithium-sulfur battery of claim 1, having a characteristic peak in the region

7. 7. The lithium-sulfur battery according to claim 1, wherein a weight ratio (El / S weight ratio) of sulfur (S) in the electrolyte solution and the sulfur-carbon composite is 2.7 g / g or more.

8. 2. The lithium-sulfur battery of claim 1, wherein the electrolyte solution comprises a non-aqueous solvent, a lithium salt, and an additive.

9. 2. The lithium-sulfur battery according to claim 1, wherein the energy density of the lithium-sulfur battery is 300 Wh / kg or more.

10. 2. The lithium-sulfur battery according to claim 1, wherein the sulfur-carbon composite has a sulfur element (S) content of 60 to 85% by weight.

11. 2. The lithium-sulfur battery according to claim 1, wherein a weight of the sulfur-carbon composite is 90 wt % or more based on a total weight of the positive electrode.

12. 10. The lithium-sulfur battery of claim 1, wherein the lithium-sulfur battery is a coin-type battery, a pouch-type battery, or a cylindrical battery.

13. A method for evaluating output characteristics of a lithium-sulfur battery comprising a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode comprises a positive electrode active material containing a sulfur-carbon composite, An evaluation method including a step of determining that the battery is a high-power lithium-sulfur battery when the ratio R (1.0C / 0.5C) according to the following formula 1 is 80% or more: [Formula 1] R(1.0C / 0.5C)=[A(DOD100) １．０Ｃ / A(DOD100) ０．５Ｃ ]×100(%) In the formula 1, The above A (DOD100) １．０Ｃ is discharged at 1.0 C, and lithium sulfide (Li ２ S), The above A (DOD100) ０．５Ｃ is discharged at 0.5 C, and lithium sulfide (Li ２ S).

14. The evaluation method according to claim 13, wherein the high-power lithium-sulfur battery is a battery that maintains an energy density of 300 Wh / kg or more under discharge conditions of 1.0 C rate or more at room temperature.

15. The evaluation method according to claim 14, wherein the room temperature is a temperature of 23°C to 25°C.

16. The above A (DOD100) ｘＣ (x=0.5 or 1.0) The lithium-sulfur battery was discharged at a rate of xC to obtain an X-ray diffraction spectrum at a DOD of 100. In the obtained X-ray diffraction spectrum, the scattering vector (q) was 1.85 to 1.92 Å. －１ measured by the peak intensity value in the region, The ratio R (1.0C / 0.5C) is The evaluation method according to claim 15, wherein the measurement is performed by calculating the ratio of the obtained peak intensities.

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