Electrolyte for lithium-sulfur battery and lithium-sulfur battery comprising same

Abstract

The present invention provides an electrolyte for a lithium-sulfur battery and a lithium-sulfur battery comprising same, the electrolyte exhibiting excellent capacity retention and lifespan characteristics by comprising a predetermined non-aqueous solvent. An electrolyte for a lithium sulfur battery according to an embodiment of the present invention comprises a lithium salt and a non-aqueous solvent, wherein the non-aqueous solvent includes a linear ether-based solvent but not a cyclic ether-based solvent. The linear ether-based solvent includes a compound having a structure of chemical formula 1, and the compound having a structure of chemical formula 1 is contained at 35-70 vol% relative to the total 100 vol% of the non-aqueous solvent. [Chemical formula 1] R1 and R1' are each independently a linear or branched alkylene group having 1 to 10 carbon atoms, a linear or branched alkenylene group having 1 to 10 carbon atoms, a cycloalkylene group having 3 to 10 carbon atoms, or an arylene group having 6 to 10 carbon atoms.

Description

Electrolyte for lithium-sulfur batteries and lithium-sulfur batteries containing the same

[0001] The present invention relates to an electrolyte for a lithium-sulfur battery and a lithium-sulfur battery including the same.

[0002] This application claims priority to Korean Application No. 10-2024-0021862, filed February 15, 2024, the entire disclosure of which is incorporated herein by reference.

[0003] A lithium-sulfur battery is a battery system that uses a sulfur-based material containing a sulfur-sulfur bond as a positive electrode active material, and lithium metal, a carbon-based material in which lithium ions can be inserted / deinserted, or silicon or tin that forms an alloy with lithium as a negative electrode active material.

[0004] Sulfur, the main material of the cathode active material in lithium-sulfur batteries, has the advantages of being a low atomic weight, abundant in resources, easy to supply, inexpensive, non-toxic, and environmentally friendly material.

[0005] In addition, lithium-sulfur batteries have a conversion reaction between lithium ions and sulfur (S8+16Li) at the cathode. + +16e - → The theoretical specific capacity from 8Li2S reaches 1,675 mAh / g, and when lithium metal is used as the negative electrode, it shows a theoretical energy density of 2,600 Wh / kg. This is a very high figure compared to the theoretical energy density of other battery systems currently being studied (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 lithium ion batteries (250 Wh / kg), and therefore, it is attracting attention as a high-capacity, eco-friendly, and low-cost lithium secondary battery among the secondary batteries being developed so far.

[0006] When discharging a lithium-sulfur battery, a reduction reaction occurs at the positive electrode where sulfur accepts electrons, and an oxidation reaction occurs at the negative electrode where lithium ionizes. Specifically, when discharging, lithium, the negative active material, is oxidized as it donates electrons and ionizes into lithium cations, and the sulfur-based material, the positive active material, is reduced as it accepts electrons. Here, through the reduction reaction of the sulfur-based material, the S-S bond accepts two electrons and is converted into a sulfur anion. The lithium cation generated by the lithium oxidation reaction is transferred to the positive electrode through the electrolyte, and this combines with the sulfur anion generated by the reduction reaction of the sulfur-based compound to form a salt. Specifically, before discharging, sulfur has a cyclic S8 structure, which is converted into lithium polysulfide (Li2Sx) through the reduction reaction, and is completely reduced to produce lithium sulfide (Li2S).

[0007] At this time, lithium-sulfur batteries are generally operated by a reaction in which the active material is dissolved into polysulfide from the cathode in the first discharge, and the dissolved polysulfide is deposited again on the cathode in a solid state in the second discharge.

[0008] However, polysulfides are easily dissolved into the electrolyte during the discharge process, and these polysulfides cause side reactions within the battery, promoting battery deterioration and shortening its lifespan. They also accelerate lithium deterioration, making long-term operation difficult.

[0009] Accordingly, the inventors of the present invention have conducted various studies to solve the above problems, and as a result, the purpose is to provide an electrolyte for a lithium-sulfur battery that can prevent deterioration of the negative electrode due to lithium polysulfide by introducing a predetermined solvent.

[0010] In addition, the purpose is to provide a lithium-sulfur battery with improved life characteristics due to increased capacity retention of the lithium-sulfur battery.

[0011] To achieve the above purpose, the present invention provides an electrolyte for a lithium-sulfur battery and a lithium-sulfur battery of the following embodiments.

[0012] According to the first implementation example,

[0013] An electrolyte for a lithium-sulfur battery containing a lithium salt and a non-aqueous solvent,

[0014] The above non-aqueous solvent includes a linear ether solvent, but does not include a cyclic ether solvent,

[0015] The linear ether solvent includes a compound having a structure represented by the following chemical formula 1:

[0016] The present invention relates to an electrolyte for a lithium-sulfur battery, wherein the compound having the structure of the above chemical formula 1 is included in an amount of 35 to 70% by volume based on 100% by volume of a total non-aqueous solvent.

[0017] [Chemical Formula 1]

[0018]

[0019] The above R1 and R1' are each independently a straight or branched alkylene group having 1 to 10 carbon atoms, a straight or branched alkenylene group having 1 to 10 carbon atoms, a cycloalkylene group having 3 to 10 carbon atoms, or an arylene group having 6 to 10 carbon atoms.

[0020] According to the second embodiment, in the first embodiment,

[0021] The compound having the structure of the above chemical formula 1 relates to an electrolyte for a lithium-sulfur battery, characterized in that R1 and R1' are each independently a straight-chain alkylene group having 1 to 10 carbon atoms.

[0022] According to the third embodiment, in the first embodiment or the second embodiment,

[0023] The compound having the structure of the above chemical formula 1 relates to an electrolyte for a lithium-sulfur battery, which comprises 40 to 60 volume% of the compound based on 100 volume% of the total non-aqueous solvent.

[0024] According to the fourth embodiment, in any one of the first to third embodiments,

[0025] The present invention relates to an electrolyte for a lithium-sulfur battery, characterized in that the non-aqueous solvent further comprises a linear ether solvent such as dimethoxyethane (DME), dimethoxymethane, dimethoxyethane, dimethoxypropane, ethylene glycol ethyl methyl ether, or a mixture of two or more thereof.

[0026] According to the fifth embodiment, in any one of the first to fourth embodiments,

[0027] The present invention relates to an electrolyte for a lithium-sulfur battery, characterized in that the non-aqueous solvent further comprises a linear ether solvent, dimethoxyethane (DME).

[0028] According to the sixth embodiment, in any one of the first to fifth embodiments,

[0029] The present invention relates to an electrolyte for a lithium-sulfur battery, characterized in that the non-aqueous solvent is composed of a linear ether solvent.

[0030] According to the seventh embodiment, in any one of the first to sixth embodiments,

[0031] The electrolyte for a lithium-sulfur battery is characterized in that it further includes an additive.

[0032] According to the eighth embodiment, in the seventh embodiment,

[0033] The above additive relates to an electrolyte for a lithium sulfur battery, characterized in that it contains a nitric acid compound.

[0034] According to the ninth embodiment, in the eighth embodiment,

[0035] The above-mentioned nitric acid compound relates to an electrolyte for a lithium sulfur battery, characterized in that it is lithium nitrate (LiNO3).

[0036] According to the 10th implementation example,

[0037] A lithium-sulfur battery comprising a positive electrode; a negative electrode; and a separator interposed between the positive electrode and the negative electrode; and an electrolyte,

[0038] The above electrolyte relates to a lithium-sulfur battery, characterized in that it is an electrolyte for a lithium-sulfur battery according to any one of the first to ninth embodiments.

[0039] According to the 11th embodiment, in the 10th embodiment,

[0040] The above positive electrode relates to a lithium sulfur battery characterized in that it includes a sulfur-containing compound as a positive electrode active material.

[0041] According to the 12th embodiment, in the 10th embodiment or the 11th embodiment,

[0042] The above negative electrode relates to a lithium-sulfur battery characterized in that it includes lithium metal, lithium alloy or a mixture thereof as a negative electrode active material.

[0043] The present invention can prevent degradation of a negative electrode due to polysulfide by utilizing predetermined non-aqueous solvents with different solubilities for polysulfide. Specifically, by including a compound having a specific structural formula with relatively low solubility in polysulfide, degradation of the negative electrode can be prevented.

[0044] Accordingly, the electrolyte for a lithium-sulfur battery of the present invention and the lithium-sulfur battery including the same can exhibit improved life characteristics due to increased capacity retention.

[0045] The following drawings attached to this specification illustrate preferred embodiments of the present invention, and serve to further understand the technical idea of ​​the present invention together with the contents of the invention described above, and therefore the present invention should not be interpreted as being limited to matters described in such drawings.

[0046] Figure 1 is a graph showing the energy density measured according to the number of cycles of lithium sulfur batteries of Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3.

[0047] Figure 2 is a graph measuring the coulombic efficiency according to the number of cycles of the lithium sulfur batteries of Example 2 and Comparative Example 4.

[0048] Figure 3 is a graph measuring the energy density according to the number of cycles of the lithium sulfur batteries of Example 1, Example 3, Comparative Example 5, and Comparative Example 5.

[0049] Figure 4 is a graph measuring the energy density according to the number of cycles of the lithium sulfur batteries of Example 3, Comparative Example 7, and Comparative Example 8.

[0050] Figure 5 is a graph showing the energy density measured according to the number of cycles of the lithium sulfur batteries of Example 4, Comparative Example 9, and Comparative Example 10.

[0051] Hereinafter, the present invention will be described in more detail.

[0052] Terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0053] The terminology used in this invention is used solely to describe specific embodiments and is not intended to limit the invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

[0054] Throughout this specification, whenever a part is said to “include” or “have” a component, this does not mean that other components are excluded, but rather that other components may be included, unless otherwise specifically stated.

[0055] The terms "about," "substantially," etc., used throughout this specification are used in the sense of, or close to, the numerical values ​​when manufacturing and material tolerances inherent to the meanings stated, and are used to prevent unscrupulous infringers from unfairly exploiting disclosures that state exact or absolute values ​​to aid understanding of this specification.

[0056] Throughout this specification, the description of “A and / or B” means “A or B or both.”

[0057] The term "composite" used in this specification refers to a material in which two or more materials are combined to form physically and chemically different phases and exhibit more effective functions.

[0058] The term “polysulfide” used in this specification means “polysulfide ion (S x 2- , x= 8, 6, 4, 2) and 「lithium polysulfide (Li2S x or Li2S x - = 8, 6, 4, 2) is a concept that includes all of them.

[0059]

[0060] Lithium secondary batteries, particularly lithium-sulfur batteries, suffer from the following problems: During charging and discharging, the lithium anode and electrolyte continuously react, resulting in the deterioration of the anode due to lithium sulfide and / or polysulfide. Lithium sulfide accumulates on the surface of the anode, which is detrimental to its lifespan. Furthermore, the continuous reaction between the anode and electrolyte accelerates the decomposition of lithium salts, resulting in poor stability. Therefore, one aspect of the present invention seeks to address the aforementioned problems.

[0061]

[0062] The electrolyte for a lithium sulfur battery of the present invention

[0063] An electrolyte for a lithium-sulfur battery containing a lithium salt and a non-aqueous solvent,

[0064] The above non-aqueous solvent includes a linear ether solvent, but does not include a cyclic ether solvent,

[0065] The linear ether solvent includes a compound having a structure represented by the following chemical formula 1:

[0066] An electrolyte for a lithium-sulfur battery comprising 35 to 70% by volume of a compound having the structure of the above chemical formula 1 based on 100% by volume of a total non-aqueous solvent:

[0067] [Chemical Formula 1]

[0068]

[0069] The above R1 and R1' are each independently a straight or branched alkylene group having 1 to 10 carbon atoms, a straight or branched alkenylene group having 1 to 10 carbon atoms, a cycloalkylene group having 3 to 10 carbon atoms, or an arylene group having 6 to 10 carbon atoms.

[0070]

[0071] The above chemical formula can also be expressed as CH3-(R1)-O-CH2CH2-O-(R1')-CH3.

[0072]

[0073] The electrolyte for the lithium-sulfur battery may be a solid electrolyte, a polymer electrolyte, a gel electrolyte, or a liquid electrolyte, and preferably, it may be an electrolyte solution that is a liquid electrolyte.

[0074]

[0075] lithium salt

[0076] In the present invention, the lithium salt is a compound capable of providing lithium ions, and is not particularly limited as long as it is used in the electrolyte of a lithium-sulfur battery.

[0077] These lithium salts include LiCl, LiBr, LiI, LiClO4, LiBF4, and LiB 10 Cl 10 , LiPF6, LiCF3SO3, LiCF3CO2, LiC4BO8, LiAsF6, LiSbF6, LiAl04, LiAlCl4, LiCH3SO3, LiCF3SO3, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiN(SO2F)2, (CF3SO2)3CLi, LiB(C2O4)2 or LiC4F9SO3 can be used.

[0078] In the present invention, in order to increase the usability of sulfur and to realize a high-capacity and high-voltage battery, the lithium salt may include Li-FSI and / or Li-BETI. The lithium salt may include Li-FSI (LiN(SO2F)2) and / or Li-BETI (LiN(C2F5SO2)2) in an amount of 80 wt% or more, or 90 wt% or more, or 100%, based on 100 wt% of the total lithium salt.

[0079] The concentration of the lithium salt is in the range of 0.1 to 2.0 M, preferably 0.5 to 1 M, and more preferably 0.5 to 0.75 M. When the concentration of the lithium salt is within the range, the electrolyte has appropriate conductivity and viscosity, so that it can exhibit excellent electrolyte performance, and lithium ions can move effectively. When the concentration of the lithium salt is below the range, it may be difficult to secure ionic conductivity suitable for battery operation, and when it exceeds the range, the viscosity of the electrolyte may increase, so that the mobility of lithium ions may decrease, or the decomposition reaction of the lithium salt itself may increase, so that the performance of the battery may deteriorate.

[0080]

[0081] non-aqueous solvents

[0082] The above non-aqueous solvent can be used to dissolve components included in the electrolyte, such as lithium salts and / or additives described below.

[0083] The above non-aqueous solvent includes a linear ether solvent, but does not include a cyclic ether solvent. Since the boiling point of a cyclic ether solvent is relatively low, while the boiling point of a linear ether solvent is relatively high, the inclusion of a linear ether solvent increases the boiling point of the electrolyte, enabling stable operation even at high temperatures, thus providing an advantage in terms of thermal stability.

[0084] The linear ether solvent includes a compound having a structure represented by the following chemical formula 1.

[0085] [Chemical Formula 1]

[0086]

[0087] The above R1 and R1' are each independently a straight-chain or branched-chain alkylene group having 1 to 10 carbon atoms, a straight-chain or branched-chain alkenylene group having 1 to 10 carbon atoms, a cycloalkylene group having 3 to 10 carbon atoms, or an arylene group having 6 to 10 carbon atoms.

[0088] Specifically, R1 and R1' may each independently be a straight-chain alkylene group having 1 to 10 carbon atoms, 1 to 3 carbon atoms, or 1 carbon atoms. For example, the compound having the structure of the chemical formula 1 may be ethylene glycol diethyl ether (EGDEE).

[0089] In particular, a compound having a structure of chemical formula 1 may exhibit non-solvent characteristics due to its relatively poor ability to participate in coordination due to the alkyl group that acts as electron withdrawing and steric hindrance around the oxygen (O) atom, which is an atom that coordinates to lithium ions, and thus its solubility in polysulfide may be reduced.

[0090]

[0091] The compound having the structure of the above chemical formula 1 may be included in an amount of 35 to 70% by volume, or 40 to 60% by volume, based on 100% by volume of the total non-aqueous solvent.

[0092] When the compound having the structure of the above chemical formula 1 is included in the above-described amount, it can exhibit advantageous effects in that it can increase the boiling point of the electrolyte and lower the solubility properties for sulfur.

[0093]

[0094] According to one embodiment of the present invention, the non-aqueous solvent may be composed of a linear ether solvent. That is, the non-aqueous solvent may further include a compound having a structure of chemical formula 1 and a linear ether solvent other than the compound having a structure of chemical formula 1.

[0095] Specifically, the linear ether solvent other than the compound having the structure of Chemical Formula 1 may be, for example, dimethoxyethane (DME), dimethoxymethane, dimethoxyethane, dimethoxypropane, ethylene glycol ethyl methyl ether, diethylene glycol dimethyl ether (DGDME), or a mixture of two or more thereof.

[0096] According to one embodiment of the present invention, the non-aqueous solvent may further include dimethoxyethane (DME) or diethylene glycol dimethyl ether (DGDME) as a linear ether solvent.

[0097] According to one embodiment of the present invention, the non-aqueous solvent may include a combination of ethylene glycol diethyl ether (EDGEE) and dimethoxyethane (DME). According to the combination, dimethoxyethane (DME), which has a relatively high solubility in polysulfides, and ethylene glycol diethyl ether (EDGEE), which has a structure of chemical formula 1 and has a relatively low solubility in polysulfides, are mixed, thereby preventing deterioration of the negative electrode.

[0098] Using only solvents with low polysulfide solubility results in low discharge capacity and high overvoltage, resulting in a loss in energy density. Therefore, to ensure adequate solubility, it is crucial to appropriately mix solvents with high polysulfide solubility and solvents with low polysulfide solubility.

[0099]

[0100] Meanwhile, according to the present invention, the non-aqueous solvent does not include a cyclic ether solvent.

[0101] The specific type of the cyclic ether solvent is not limited within the present specification, but includes, for example, 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, It may refer to 1,4-dioxane, isosorbide dimethyl ether, etc.

[0102]

[0103] As described above, by using the composition of an electrolyte for a lithium-sulfur battery according to one aspect of the present invention, it is possible to suppress the dissolution of lithium polysulfide, improve the passivation phenomenon caused by the accumulation of lithium sulfide on the negative electrode, and thereby achieve the effect of improving the operating stability of a lithium-sulfur battery, as well as improving the capacity retention rate.

[0104]

[0105] additives

[0106] In one embodiment of the present invention, the electrolyte for a lithium sulfur battery may further include an additive.

[0107] The above additives are not particularly limited as long as they do not participate in the electrochemical reaction of the battery and can play a role in improving the efficiency of the negative electrode and the performance of the battery.

[0108] The above additive may include a nitric acid compound. The nitric acid compound can improve the electrical conductivity of a lithium-sulfur battery by dissolving in the electrolyte of the lithium secondary battery in addition to the lithium salt and providing ions, and can also prevent irreversible consumption of polysulfides by inhibiting the reduction reaction of polysulfides generated during the charge and discharge process of the lithium-sulfur battery, thereby improving the performance of the lithium-sulfur battery.

[0109] The above nitric acid compound may be used without particular limitations as long as it forms a stable film on the negative electrode of a lithium-sulfur battery and exhibits the effect of improving charge / discharge efficiency.

[0110] For example, the nitric acid compound may be an inorganic nitric acid or nitrous acid compound such as lithium nitrate (LiNO3), potassium nitrate (KNO3), cesium nitrate (CsNO3), barium nitrate (Ba(NO3)2), ammonium nitrate (NH4NO3), lithium nitrite (LiNO2), potassium nitrite (KNO2), cesium nitrite (CsNO2), ammonium nitrite (NH4NO2); an organic nitric acid or nitrous acid compound such as methyl nitrate, dialkyl imidazolium nitrate, guanidine nitrate, imidazolium nitrate, pyridinium nitrate, ethyl nitrite, propyl nitrite, butyl nitrite, pentyl nitrite, or octyl nitrite; It may be selected from the group consisting of organic nitro compounds such as nitromethane, nitropropane, nitrobutane, nitrobenzene, dinitrobenzene, nitropyridine, dinitropyridine, nitrotoluene, dinitrotoluene, and combinations thereof, and preferably may include lithium nitrate.

[0111]

[0112] In one embodiment of the present invention, the content of the additive may be included in an amount of 1 wt% to 10 wt%, 2 wt% to 9 wt%, 3 wt% to 8 wt%, or 3 wt% to 5 wt% based on 100 wt% of the total electrolyte for a lithium-sulfur battery, but is not limited thereto. When the additive is included in the above-described amount, it is advantageous in terms of improving the electrical conductivity of the electrolyte and suppressing the reduction of polysulfide when used in a lithium-sulfur battery.

[0113]

[0114] lithium-sulfur battery

[0115] In addition, according to another aspect of the present invention, a lithium-sulfur battery comprising the electrolyte for a lithium-sulfur battery described above is provided.

[0116] The above lithium-sulfur battery relates to a lithium secondary battery including a positive electrode; a negative electrode; a separator interposed between the positive electrode and the negative electrode; and an electrolyte, wherein the electrolyte is the same as the electrolyte for the lithium-sulfur battery of the present invention described above.

[0117]

[0118] anode

[0119] The above positive electrode may include a positive electrode current collector and a positive electrode active material layer applied to one or both sides of the positive electrode current collector.

[0120] The above-mentioned positive electrode current collector supports the positive electrode active material and is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, the positive electrode active material layer includes the positive electrode active material and may further include a conductive agent, a binder, an additive, and the like.

[0121] The above-described positive electrode active material comprises a sulfur-carbon composite. The sulfur-carbon composite may comprise sulfur in a porous carbon material and at least a portion of the inner and outer surfaces of the porous carbon material. Since the sulfur contained in the positive electrode active material does not have electrical conductivity on its own, it is used in a composite with a conductive material such as a carbon material. The sulfur may comprise at least one selected from the group consisting of elemental sulfur (S8) and sulfur compounds.

[0122] The above sulfur-carbon composite not only provides a framework in which the aforementioned sulfur can be uniformly and stably fixed, but also includes a porous carbon material to complement the low electrical conductivity of sulfur so that an electrochemical reaction can proceed smoothly.

[0123] The above porous carbon material can generally be manufactured by carbonizing precursors of various carbon materials. The porous carbon material includes pores that are not uniform in size, and the average diameter of the pores ranges from 1 to 200 nm, and the porosity can range from 10 to 90% of the total volume of the porous carbon material. If the average diameter of the pores is less than the above range, the pore size is only at the molecular level, making sulfur impregnation impossible. Conversely, if it exceeds the above range, the mechanical strength of the porous carbon material is weakened, making it undesirable for application to the electrode manufacturing process.

[0124] 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, and the measurement method is not particularly limited. For example, the pore diameter can be measured according to a scanning electron microscope (SEM), a field emission electron microscope (laser diffraction method), or a laser diffraction method. The measurement using the laser diffraction method can be, for example, using a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000).

[0125] In one embodiment of the present invention, the 'porosity' refers to the ratio of the volume occupied by pores to the total volume in a certain structure, and uses % as its unit, and can be used interchangeably with terms such as porosity, porosity, etc. In the present invention, the measurement of the porosity is not particularly limited, and according to one embodiment of the present invention, for example, it can be measured according to the BET (Brunauer-Emmett-Teller) measurement method using nitrogen gas or the mercury penetration method (Hg porosimeter) and ASTM D2873.

[0126] The shape of the above porous carbon material may be spherical, rod-shaped, needle-shaped, plate-shaped, tubular or bulk-shaped, and can be used without limitation as long as it is a shape commonly used in lithium-sulfur batteries.

[0127] The porous carbon material may be any material commonly used in the art that has a porous structure or a high specific surface area. For example, the porous carbon material may be at least one selected from the group consisting of graphite; graphene; carbon black such as Denka black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer 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); and graphite and activated carbon such as natural graphite, artificial graphite, and expanded graphite, but is not limited thereto. Preferably, the porous carbon material may be a carbon nanotube.

[0128] In the sulfur-carbon composite according to the present invention, the sulfur is located on at least one of the inner and outer surfaces of the porous carbon material, and for example, may be present in an area less than 100%, preferably 1 to 95%, and more preferably 40 to 96% of the entire inner and outer surfaces of the porous carbon material. When the sulfur is present on the inner and outer surfaces of the porous carbon material within the above range, it can exhibit the maximum effect in terms of electron transfer area and wettability with the electrolyte. Specifically, since the sulfur is thinly and evenly impregnated on the inner and outer surfaces of the porous carbon material within the above-described range, the electron transfer contact area can be increased during the charge and discharge process. If the sulfur is located in an area of ​​100% of the entire inner and outer surfaces of the porous carbon material, the porous carbon material is completely covered with sulfur, and the wettability and contact with the electrolyte are reduced, so that electron transfer is not possible and the porous carbon material cannot participate in the electrochemical reaction.

[0129] The above sulfur-carbon complex may contain sulfur in an amount of, for example, 65 wt% or more, specifically 65 to 90 wt%, 70 to 85 wt%, or 72 to 80 wt%, based on 100 wt% of the sulfur-carbon complex. When the sulfur content is within the above-described range, it may exhibit advantageous effects in terms of improving battery performance and securing battery capacity, but the present invention is not limited thereto.

[0130] The method for manufacturing the sulfur-carbon composite of the present invention is not particularly limited, and any method commonly used in the art may be used. For example, a method of simply mixing the sulfur and porous carbon material and then heat-treating to form a composite may be used.

[0131] In addition to the composition described above, the positive electrode active material may further include one or more selected from among a transition metal element, a group ⅢA element, a group ⅣA element, a sulfur compound of these elements, and an alloy of these elements and sulfur.

[0132] The above 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 or Hg, and the above group ⅢA elements include Al, Ga, In, Ti, and the above group ⅣA elements may include Ge, Sn, Pb, and the like.

[0133] In the positive electrode of the lithium-sulfur battery of the present invention, the positive electrode active material may be included in an amount of, for example, 80 wt% or more, specifically 80 wt% to 100 wt%, more specifically 85 wt% to 98 wt%, or 80 wt% to 95 wt%, based on the total weight of the positive electrode active material layer. The content of the positive electrode active material may have a lower limit of 70 wt% or more or 85 wt% or more, and an upper limit of 99 wt% or less or 90 wt%, based on 100 wt% of the total positive electrode active material layer. The content of the positive electrode active material may be set by a combination of the lower limit and the upper limit. When the content of the positive electrode active material is less than the above range, the relative content of auxiliary materials such as conductive materials and binders increases and the content of the positive electrode active material decreases, making it difficult to realize a battery with high capacity and high energy density. On the contrary, when it exceeds the above range, the content of the conductive material or binder described later is relatively insufficient, which causes a problem in that the physical properties of the electrode deteriorate.

[0134] The above conductive material is a material that 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. Any conductive material that is physically distinct from the carbon contained in the sulfur-carbon complex and is a component of the electrode can be used without limitation.

[0135] For example, the conductive material may include carbon black such as Super-P, Denka Black, Acetylene Black, Ketjen Black, Channel Black, Furnace Black, Lamp Black, Summer Black, and carbon black; carbon derivatives such as carbon nanotubes or fullerene; conductive fibers such as carbon fibers or metal fibers; metal powders such as fluorocarbon, aluminum, and nickel powder; or conductive polymers such as polyaniline, polythiophene, polyacetylene, and polypyrrole, which may be used alone or in combination.

[0136] The content of the conductive agent may be 1 to 10 wt% based on the total weight of the positive electrode active material. If the content of the conductive agent is below the above range, electron transfer between the positive electrode active material and the current collector is not easy, resulting in decreased voltage and capacity. Conversely, if the content exceeds the above range, the proportion of the positive electrode active material may relatively decrease, thereby reducing the total energy (charge) of the battery. Therefore, it is preferable to determine an appropriate content within the above-mentioned range.

[0137] The above binder maintains the positive electrode active material on the positive electrode current collector and organically connects the positive electrode active materials to further increase the bonding strength between them, and any binder known in the industry can be used.

[0138] For example, the binder may be a fluororesin binder including polyvinylidene fluoride (PVdF), a polyvinylidene fluoride polymer including at least one vinylidene fluoride as a repeating unit, polytetrafluoroethylene (PTFE), or a mixture of two or more thereof; a rubber binder including styrene butadiene rubber (SBR), acrylonitrile-butidiene rubber, or styrene-isoprene rubber; an acrylic binder; a cellulose binder including carboxyl methyl cellulose (CMC), starch, hydroxy propyl cellulose, or regenerated cellulose; a polyalcohol binder; a polyolefin binder including polyethylene or polypropylene; a polyimide binder; a polyester binder; and a silane-based binder; a mixture or copolymer of one or more selected from the group consisting of;

[0139] The content of the above 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 deteriorate, causing the positive electrode active material and conductive material to fall off. If the content of the binder is more than the above range, the ratio of the positive electrode active material and conductive material in the positive electrode may relatively decrease, resulting in a decrease in battery capacity. Therefore, it is preferable to determine an appropriate content within the above-described range.

[0140] In the present invention, the method for manufacturing the positive electrode of the lithium sulfur battery is not particularly limited, and various methods known to those skilled in the art or modified methods thereof can be used.

[0141] For example, the positive electrode of the lithium sulfur battery may be manufactured by forming the positive electrode active material layer by preparing a positive electrode slurry composition including the composition described above and then applying the same to at least one surface of the positive electrode current collector.

[0142] The above positive electrode slurry composition includes the positive electrode active material described above, and may further include a binder, a conductive material, and a solvent.

[0143] The above solvent is one that can uniformly disperse the positive electrode active material. Water is most preferably an aqueous solvent, and the water may be distilled or deionized water. However, this is not necessarily limited to this, and if necessary, a lower alcohol that is easily mixed with water may be used. Examples of the lower alcohol include methanol, ethanol, propanol, isopropanol, and butanol, and preferably, these can be mixed with water and used.

[0144] The content of the above solvent may be contained at a level that has a concentration that can facilitate coating, and the specific content varies depending on the application method and device.

[0145] The above-mentioned positive electrode slurry composition may additionally contain, as necessary, substances commonly used in the relevant technical field for purposes such as improving its function. Examples thereof include viscosity modifiers, fluidizing agents, and fillers.

[0146] The method for applying the positive electrode slurry composition is not particularly limited in the present invention, and examples thereof include methods such as doctor blade, die casting, comma coating, and screen printing. In addition, the positive electrode slurry may be applied onto the positive electrode current collector by molding it on a separate substrate and then pressing or lamination.

[0147] After the above application, a drying process for solvent removal can be performed. The drying process is performed at a temperature and time that can sufficiently remove the solvent, and the conditions may vary depending on the type of solvent and are therefore not particularly limited to the present invention. Examples include drying using warm air, hot air, low-humidity air, vacuum drying, and drying using irradiation with (far) infrared rays and electron beams. The drying speed is usually adjusted to remove the solvent 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 cause the positive electrode active material layer to peel off from the positive electrode current collector.

[0148] Additionally, the density of the positive electrode active material within the positive electrode can be increased by pressing the entire body after drying. Pressing methods include mold pressing and roll pressing.

[0149] The porosity of the positive electrode manufactured by the composition and manufacturing method described above, specifically, the positive electrode active material layer, may be 50 to 80%, specifically, 60 to 75%. If the porosity of the positive electrode is less than 50%, the filling degree of the positive electrode slurry composition including the positive electrode active material, the conductive agent, and the binder becomes excessively high, so that sufficient electrolyte capable of exhibiting ionic and / or electrical conductivity cannot be maintained between the positive electrode active materials, which may result in a deterioration in the output characteristics or cycle characteristics of the battery, and a serious problem of a decrease in overvoltage and discharge capacity of the battery. On the other hand, if the porosity of the positive electrode exceeds 80% and has excessively high porosity, there is a problem in that the physical and electrical connection with the current collector is lowered, resulting in a decrease in adhesive strength and difficulty in reaction. In addition, the increased porosity may be filled with electrolyte, which may result in a problem in that the energy density of the battery may be lowered, and therefore, the porosity is appropriately controlled within the above range.

[0150]

[0151] cathode

[0152] The above negative electrode may include a negative electrode current collector and a negative electrode active material layer applied to one or both surfaces of the negative electrode current collector. Alternatively, the negative electrode may be a lithium metal plate.

[0153] The above negative electrode current collector is for supporting the negative electrode active material layer, as described in the positive electrode current collector.

[0154] The above-mentioned negative electrode active material layer may include a conductive material, a binder, etc. in addition to the negative electrode active material. In this case, the conductive material and the binder follow the above-mentioned.

[0155] The above negative active material is lithium (Li + ) can be reversibly intercalated or deintercalated, a material that can react with lithium ions to form a reversibly lithium-containing compound, lithium metal, a lithium alloy, or a mixture thereof.

[0156] The above lithium ion (Li + ) can be reversibly inserted or de-inserted, for example, crystalline carbon, amorphous carbon, or a mixture thereof. The lithium ion (Li + ) can be, for example, tin oxide, titanium nitrate or silicon. The lithium alloy can 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).

[0157] Preferably, the negative active material may include lithium metal, a lithium alloy, or a mixture thereof, and specifically, the lithium metal may be in the form of a lithium metal thin film or lithium metal powder.

[0158]

[0159] membrane

[0160] The separator separates or insulates the positive and negative electrodes from each other and enables lithium ion transport between the positive and negative electrodes. It may be made of a porous non-conductive or insulating material, and can be used without any special restrictions as long as it is commonly used as a separator in a lithium secondary battery. The separator may be an independent member such as a film, or may be a coating layer added to the positive and / or negative electrodes.

[0161] It is preferable that the above separator have low resistance to ion movement of the electrolyte and excellent moisture absorption capacity for the electrolyte.

[0162] The above separator may be formed of a porous substrate. Any porous substrate commonly used in secondary batteries may be used as the porous substrate. A porous polymer film may be used alone or in a laminated manner. For example, a nonwoven fabric or a polyolefin porous film made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used, but is not limited thereto.

[0163] The material of the porous substrate is not particularly limited in the present invention, and any porous substrate commonly used in electrochemical devices can be used. For example, the porous substrate may be a polyolefin such as polyethylene, polypropylene, etc., a polyester such as polyethyleneterephthalate, polybutyleneterephthalate, polyamide, polyacetal, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfide, polyethylenenaphthalate, polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl chloride, polyacrylonitrile, cellulose, nylon, It may include at least one material selected from the group consisting of poly(p-phenylene benzobisoxazole) and polyarylate.

[0164] The thickness of the porous substrate is not particularly limited, but may be 1 to 100 μm, preferably 5 to 50 μm. The thickness range of the porous substrate is not limited to the aforementioned range, but if the thickness is excessively thinner than the aforementioned lower limit, the mechanical properties may deteriorate, and the separator may be easily damaged during battery use.

[0165] The average diameter and porosity of the pores present in the porous substrate are not particularly limited, but may be 0.001 to 50 ㎛ and 10 to 95%, respectively.

[0166] The lithium-sulfur battery according to the present invention can be manufactured by laminating (stacking) and folding a separator and electrode in addition to the general winding process.

[0167] The shape of the above lithium sulfur battery is not particularly limited, and can be made into various shapes such as cylindrical, stacked, coin-shaped, and pouch-shaped.

[0168]

[0169] Hereinafter, preferred examples are presented to help understand the present invention, but the following examples are only illustrative of the present invention, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and technical idea of ​​the present invention, and it is also natural that such changes and modifications fall within the scope of the appended patent claims.

[0170]

[0171] <Manufacturing of electrolyte for lithium-sulfur batteries>

[0172] Examples 1 to 4 and Comparative Examples 1 to 10

[0173] An electrolyte for a lithium-sulfur battery was manufactured with the composition shown in Table 1 below.

[0174] Lithium salt solvent 1 solvent 2 additive type concentration type volume ratio (vol%) type volume ratio (vol%) type concentration (wt%) Example 1 LiFSI 0.5 MDME 60 EGDEE 40 LiNO 3 5 Example 2 LiFSI 0.33 MDME 60 EGDEE 40 LiNO 3 5 LiBE TI 0.17 M Example 3 LiFSI 0.5 MDG DME 60 EGDEE 40 LiNO 3 5 Example 4 LiFSI 0.5 MDME 40 EGDEE 60 LiNO 3 5 Comparative Example 1 LiFSI 0.5 MDME 80 2-MeF 20 LiNO 3 5 Comparative Example 2 LiFSI 0.5 MDME 80 EGDEE 20 LiNO 3 5 Comparative Example 3 LiFSI 0.5 MDME 70 EGDEE 30 LiNO35Comparative Example 4LiFSI0.33MDME802-MeF20LiNO35LiBETI0.17MComparative Example 5LiFSI0.5MTHF60EGDEE40LiNO35Comparative Example 6LiFSI0.5MTHP60EGDEE40LiNO35Comparative Example 7LiFSI0.5MDGDME602-MeF40LiNO35Comparative Example 8LiFSI0.5MDGDME70EGDEE30LiNO35Comparative Example 9LiFSI0.5MDME20EGDEE80LiNO35Comparative Example 10LiFSI0.5MDME60DGDEE40LiNO35

[0175] In Table 1 above,

[0176] LiFSI is Lithium bis(fluorosulfonyl)imide, LiN(SO2F)2

[0177] LiBETI is lithium bisperfluoroethanesulfonimide, LiN(SO2CF2CF3)2

[0178] DME is dimethoxyethane,

[0179] DGDME is diethylene glycol dimethyl ether

[0180] THF is tetrahydrofuran,

[0181] THP is tetrahydropyran,

[0182] EGDEE is ethylene glycol diethyl ether,

[0183] DGDEE is diethylene glycol diethyl ether,

[0184] 2-MeF is 2-methylfuran.

[0185]

[0186] Performance evaluation of lithium-sulfur batteries

[0187] A positive electrode slurry composition was prepared by mixing 96 wt% of a sulfur-carbon composite (S:C = 75:25 (weight ratio)) as a positive electrode active material and 4 wt% of a binder. The positive electrode slurry composition was applied to an aluminum current collector and then dried to prepare a positive electrode. The porosity of the prepared positive electrode was about 75%, and the loading amount was about 3.0 mAh / cm. 2 It was.

[0188] Lithium metal with a thickness of 35 ㎛ was used as the cathode.

[0189] The positive and negative electrodes were positioned so as to face each other, and a polyethylene separator with a thickness of 12 ㎛ and a porosity of approximately 40% was interposed between them. Then, the pouch cell was assembled by stacking, and then the electrolyte was injected and sealed to complete the lithium-sulfur pouch cell.

[0190] The lithium-sulfur pouch cell manufactured as described above was subjected to an initial discharge of 0.1 C, two 0.1 C / 0.1 C charge / discharge cycles, and then 0.2 C / 0.5 C charge / discharge cycles at 25°C under cut-off conditions of 1.8 V-2.5 V to evaluate the energy density and / or coulombic efficiency according to the number of cycles. The results are shown in Figs. 1 to 5.

[0191] At this time, the Coulombic efficiency (%) was calculated by dividing the discharge capacity of the pouch cell by the charge capacity, and the energy density (Wh / kg) was calculated by dividing the pouch cell capacity (Wh) by the pouch cell weight (kg).

[0192]

[0193] Referring to Figures 1 to 5,

[0194] In Comparison 1, Comparative Example 4 and Comparative Example 7, it can be confirmed that the energy density and Coulomb efficiency are low due to the application of cyclic ether.

[0195] Comparative Examples 2, 3, and 8 can be confirmed to have low energy densities due to a low content of the compound having the structure of Chemical Formula 1.

[0196] Comparative Examples 5 and 6 contain a compound having the structure of Chemical Formula 1 in an appropriate amount, but it can be confirmed that the energy density is significantly low because it contains a cyclic ether.

[0197] Comparative Example 9 shows that the energy density is rapidly reduced at a low cycle number due to the excessive content of the compound having the structure of chemical formula 1.

[0198] Comparative Example 10 did not use a cyclic ether as a non-aqueous solvent, but only used a linear ether. However, it was confirmed that the energy density was rapidly reduced at a small number of cycles because the compound having the structure of Chemical Formula 1 was not applied.

Claims

1. An electrolyte for a lithium-sulfur battery containing a lithium salt and a non-aqueous solvent, The above non-aqueous solvent includes a linear ether solvent, but does not include a cyclic ether solvent, The linear ether solvent includes a compound having a structure represented by the following chemical formula 1: An electrolyte for a lithium-sulfur battery, comprising a compound having the structure of the above chemical formula 1 in an amount of 35 to 70% by volume based on 100% by volume of a total non-aqueous solvent: [Chemical Formula 1] The above R1 and R1' are each independently a straight or branched alkylene group having 1 to 10 carbon atoms, a straight or branched alkenylene group having 1 to 10 carbon atoms, a cycloalkylene group having 3 to 10 carbon atoms, or an arylene group having 6 to 10 carbon atoms.

2. In paragraph 1, An electrolyte for a lithium-sulfur battery, wherein the compound having the structure of the above chemical formula 1 is characterized in that R1 and R1' are each independently a straight-chain alkylene group having 1 to 10 carbon atoms.

3. In paragraph 1, An electrolyte for a lithium-sulfur battery, comprising a compound having the structure of the above chemical formula 1 in an amount of 40 to 60% by volume based on 100% by volume of a total non-aqueous solvent.

4. In paragraph 1, An electrolyte for a lithium-sulfur battery, characterized in that the non-aqueous solvent further comprises a linear ether solvent such as dimethoxyethane (DME), dimethoxymethane, dimethoxyethane, dimethoxypropane, ethylene glycol ethyl methyl ether, or a mixture of two or more thereof.

5. In paragraph 1, An electrolyte for a lithium-sulfur battery, characterized in that the non-aqueous solvent further comprises a linear ether solvent, dimethoxyethane (DME).

6. In paragraph 1, An electrolyte for a lithium-sulfur battery, characterized in that the non-aqueous solvent is composed of a linear ether solvent.

7. In paragraph 1, An electrolyte for a lithium-sulfur battery, characterized in that the electrolyte for the lithium-sulfur battery further comprises an additive.

8. In paragraph 7, An electrolyte for a lithium sulfur battery, characterized in that the additive comprises a nitric acid compound.

9. In paragraph 8, An electrolyte for a lithium-sulfur battery, characterized in that the above nitric acid compound is lithium nitrate (LiNO3).

10. A lithium-sulfur battery comprising a positive electrode; a negative electrode; and a separator interposed between the positive electrode and the negative electrode; and an electrolyte, A lithium-sulfur battery, characterized in that the electrolyte is an electrolyte for a lithium-sulfur battery according to any one of claims 1 to 9.

11. In paragraph 10, A lithium-sulfur battery, characterized in that the positive electrode includes a sulfur-containing compound as a positive electrode active material.

12. In paragraph 10, A lithium-sulfur battery, characterized in that the negative electrode comprises lithium metal, lithium alloy or a mixture thereof as a negative electrode active material.

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