Electrochemical elements

Abstract

The present invention relates to an electrochemical device capable of preventing depletion of salts and additives in an electrolyte. The electrochemical device according to an embodiment of the present invention may include a positive electrode, a lithium metal negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte including tin chloride (SnCl2).

Description

[Technical Field]

[0001] The present invention relates to an electrochemical device, and more particularly to an electrochemical device having improved life characteristics by preventing depletion of salts and additives in an electrolyte.

[0002] This application claims priority based on Korean Patent Application No. 10-2022-0004176, filed on January 11, 2022, the entire contents of which are incorporated herein by reference in their entirety in the specification and drawings thereof. [Background technology]

[0003] As interest in energy storage technology grows, its application fields expand to include mobile phones, tablets, laptops, and video cameras, as well as the energy sources of electric vehicles (EVs) and hybrid electric vehicles (HEVs), and research and development on electrochemical devices is gradually increasing. Electrochemical devices are the field that has received the most attention in this regard, and recently, the development of such batteries has led to research and development on new electrode and battery designs to improve capacity density and specific energy.

[0004] Among these electrochemical devices, lithium metal secondary batteries, such as lithium-sulfur batteries (Li-S batteries), which use lithium metal as the anode, have a theoretical capacity of 3,862 mAh / g, making them garnering attention as next-generation high-capacity batteries due to their use of lightweight lithium metal as the anode active material. During discharge, a reduction reaction of sulfur and an oxidation reaction of lithium metal occur within a lithium-sulfur battery, during which sulfur transforms from a ring-shaped S8 to a linear lithium polysulfide (LiPS). These lithium-sulfur batteries are characterized by their gradual discharge voltage until the polysulfide is completely reduced to Li2S.

[0005] However, lithium metal secondary batteries such as lithium-sulfur batteries experience a decrease in charge / discharge efficiency during the charge / discharge process due to side reactions of the electrolyte (accumulation of by-products due to the decomposition of the electrolyte) and instability of the lithium metal (the occurrence of short circuits due to the growth of dendrites on the lithium metal anode), resulting in a shortened battery life.

[0006] In particular, lithium metal, which is the negative electrode active material, easily forms large dendrites and reacts with salts and additives in the electrolyte to form a solid electrolyte interphase (SEI), which continuously consumes the salts and additives in the electrolyte and ultimately accelerates battery degradation.

[0007] Therefore, the use of lithium metal as the negative electrode requires technological development to prevent the depletion of salts and additives in the electrolyte. Summary of the Invention [Problem to be solved by the invention]

[0008] Therefore, an object of the present invention is to provide an electrochemical device that can prevent depletion of salts and additives in an electrolyte. [Means for solving the problem]

[0009] In order to solve the above problems, according to one aspect of the present invention, there is provided an electrochemical device according to the following embodiment.

[0010] The first embodiment relates to an electrochemical device comprising a positive electrode, a lithium metal negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte containing tin chloride (SnCl).

[0011] In the second embodiment, in the first embodiment, the content of the tin chloride may be 0.5 wt % to 5 wt % with respect to 100 wt % of the total non-aqueous electrolyte solution.

[0012] In the third embodiment, in the first or second embodiment, the content of the tin chloride may be 1 wt % to 4 wt % with respect to 100 wt % of the total non-aqueous electrolyte solution.

[0013] A fourth embodiment is any one of the first to third embodiments, and may further include a Li—Cl and Li—Sn alloy protective layer on the surface of the lithium metal negative electrode.

[0014] In the fifth embodiment, in any one of the first to fourth embodiments, the nonaqueous electrolyte solution may further include a first solvent containing a heterocyclic compound which may or may not contain one or more double bonds and which contains one or more oxygen atoms and sulfur atoms; a second solvent containing one or more of an ether-based compound, an ester-based compound, an amide-based compound, and a carbonate-based compound; a lithium salt; and lithium nitrate.

[0015] The sixth embodiment is the fifth embodiment, wherein the lithium salt is LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 , LiPF6, LiCF3SO3, LiCF3CO2, LiC4BO8, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, (C2F5SO2)2NLi, (SO2F)2NLi, (CF3SO2)2NLi, (CF3SO2)3CLi, lithium chloroborane, lithium lower aliphatic carboxylates having 4 or less carbon atoms, lithium 4-phenylborate, lithium imide, or two or more of these.

[0016] In the seventh embodiment, in the fifth or sixth embodiment, the concentration of the lithium salt may be 0.2 to 2.0M.

[0017] In an eighth embodiment, in any of the fifth to seventh embodiments, the heterocyclic compound may be a 3- to 15-membered heterocyclic compound substituted or unsubstituted with one or more selected from the group consisting of an alkyl group having 1 to 4 carbon atoms, a cyclic alkyl group having 3 to 8 carbon atoms, an aryl group having 6 to 10 carbon atoms, a halogen group, a nitro group, an amine group, and a sulfonyl group, or may be a polycyclic compound of a heterocyclic compound and one or more of a cyclic alkyl group having 3 to 8 carbon atoms and an aryl group having 6 to 10 carbon atoms.

[0018] In the ninth embodiment, in any one of the fifth to eighth embodiments, the heterocyclic compound is 1,3-dioxolane, 4,5-diethyl-1,3-dioxolane, 4,5-dimethyl-1,3-dioxolane, 4-methyl-1,3-dioxolane, 4-ethyl-1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, 4-methyl-1,3-dioxane and 2-methyl-1,3-dioxane, furan, 2-methylfuran, 3-methylfuran, 2-ethylfuran, 2-propyl The alkylthiophene may include furan, 2-butylfuran, 2,3-dimethylfuran, 2,4-dimethylfuran, 2,5-dimethylfuran, pyran, 2-methylpyran, 3-methylpyran, 4-methylpyran, benzofuran, 2-(2-nitrovinyl)furan, thiophene, 2-methylthiophene, 2-ethylthiophene, 2-propylthiophene, 2-butylthiophene, 2,3-dimethylthiophene, 2,4-dimethylthiophene, 2,5-dimethylthiophene, or two or more thereof.

[0019] In a tenth embodiment, in any one of the fifth to ninth embodiments, the ether-based compound of the second solvent may include dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, ethyl propyl ether, dimethoxyethane, diethoxyethane, methoxyethoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, triethylene glycol methyl ethyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, tetraethylene glycol methyl ethyl ether, polyethylene glycol dimethyl ether, polyethylene glycol diethyl ether, polyethylene glycol methyl ethyl ether, or two or more of these.

[0020] In an eleventh embodiment, in any one of the first to tenth embodiments, the nonaqueous electrolyte solution may further include lanthanum nitrate, potassium nitrate, cesium nitrate, magnesium nitrate, barium nitrate, lithium nitrite, potassium nitrite, cesium nitrite, or two or more of these.

[0021] In a twelfth embodiment, in any one of the first to eleventh embodiments, the nonaqueous electrolyte solution may further include 1,3-dioxolane as a first solvent, dimethoxyethane as a second solvent, (CF3SO2)2NLi as a lithium salt, and lithium nitrate.

[0022] In a thirteenth embodiment, in any one of the first to twelfth embodiments, the electrochemical device may be a lithium-sulfur battery.

[0023] In a fourteenth embodiment, in any one of the first to twelfth embodiments, the electrochemical device may be a lithium-lithium symmetric cell. [Effects of the Invention]

[0024] The electrochemical device according to one embodiment of the present invention includes tin chloride in the non-aqueous electrolyte, which can improve lithium charge / discharge efficiency and suppress dendrite growth.

[0025] In addition, the electrochemical device according to an embodiment of the present invention includes tin chloride in the non-aqueous electrolyte, thereby improving lithium utilization efficiency and increasing the capacity and lifespan of the electrochemical device.

[0026] In an electrochemical device according to an embodiment of the present invention, the content of tin chloride in the non-aqueous electrolyte is 0.5 wt % to 4 wt % based on 100 wt % of the total non-aqueous electrolyte, thereby preventing a side reaction between tin chloride and the positive electrode active material and more easily improving the lifespan of the electrochemical device.

[0027] In an electrochemical device according to an embodiment of the present invention, tin chloride contained in a non-aqueous electrolyte reacts with a lithium metal anode during an initial charge / discharge process to form a lithophilic / highly ion-conductive Li—Cl and Li—Sn alloy protective layer on the surface of the lithium metal anode, thereby more easily improving the lifespan of the electrochemical device.

[0028] The following drawings attached to this specification illustrate preferred embodiments of the present invention and, together with the detailed description of the invention, serve to further understand the technical concepts of the present invention. Therefore, the present invention should not be interpreted as being limited to only the matters described in the drawings. [Brief explanation of the drawings]

[0029] [Figure 1] FIG. 2 is a graph showing the interface resistance of the lithium-lithium symmetric cell produced in Example 2-1. [Figure 2] FIG. 10 is a graph showing the interface resistance of the lithium-lithium symmetric cell produced in Example 2-2. [Figure 3] FIG. 10 is a graph showing the interface resistance of the lithium-lithium symmetric cell produced in Example 2-3. [Figure 4]FIG. 10 is a graph showing the interface resistance of the lithium-lithium symmetric cell produced in Example 2-4. [Figure 5] FIG. 10 is a graph showing the interface resistance of the lithium-lithium symmetric cell produced in Example 2-5. [Figure 6] FIG. 10 is a graph showing the interface resistance of the lithium-lithium symmetric cell produced in Example 2-6. [Figure 7] FIG. 10 is a graph showing the interface resistance of the lithium-lithium symmetric cell produced in Comparative Example 2-1. [Figure 8] FIG. 2 shows the cycle life performance of the lithium-lithium symmetric cell produced in Example 2-1. [Figure 9] FIG. 10 shows the cycle life performance of the lithium-lithium symmetric cell produced in Example 2-2. [Figure 10] FIG. 10 shows the cycle life performance of the lithium-lithium symmetric cell prepared in Example 2-3. [Figure 11] FIG. 10 shows the cycle life performance of the lithium-lithium symmetric cell prepared in Example 2-4. [Figure 12] FIG. 10 shows the cycle life performance of the lithium-lithium symmetric cell prepared in Example 2-5. [Figure 13] FIG. 10 shows the cycle life performance of the lithium-lithium symmetric cells prepared in Example 2-6. [Figure 14] FIG. 10 is a graph showing the cycle life performance of the lithium-lithium symmetric cell produced in Comparative Example 2-1. [Figure 15] FIG. 1 is a graph showing the cycle life performance of the lithium-sulfur batteries produced in Examples 3-1 to 3-6 and Comparative Example 3-1. [Figure 16] FIG. 10 is a photograph of the surface of the lithium metal negative electrode of the lithium-sulfur battery produced in Example 3-3 after 100 cycles of operation. DETAILED DESCRIPTION OF THE INVENTION

[0030] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, the terms and phrases used in the specification and claims should not be construed as being limited to their ordinary and dictionary meanings, but should be construed as having meanings and concepts corresponding to the technical ideas of the present invention, in accordance with the principle that the inventors themselves can appropriately define the concepts of terms in order to best describe the invention.

[0031] Therefore, it should be understood that the configurations shown in the embodiments described in this specification are merely the most desirable embodiments of the present invention and do not represent the entire technical idea of ​​the present invention, and that there may be various equivalents and modifications that can be substituted therefor at the time of this application.

[0032] An electrochemical device according to one aspect of the present invention includes a positive electrode, a lithium metal negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte containing tin chloride (SnCl).

[0033] The positive electrode includes a positive electrode active material, a binder, and a conductive material. The positive electrode active material is a material commonly used in electrochemical devices, and may include, for example, a lithium nickel cobalt manganese-based compound (lithium NCM-based compound), elemental sulfur (S), a sulfur-based compound, or a mixture thereof. The sulfur-based compound may specifically be Li2Sn (n≧1), an organic sulfur compound, or a carbon-sulfur composite (C2S x ) n(x=2.5-50, n≧2). The positive electrode active material may include a sulfur-carbon composite. Because sulfur materials alone are not electrically conductive, they can be used in combination with a conductive material. The carbon material (or carbon source) constituting the sulfur-carbon composite may have a porous structure or a high specific surface area, and may be any carbon material commonly used in the art. For example, the porous carbon material may be, but is not limited to, graphite, graphene, carbon black such as denka black, acetylene black, ketjen black, channel black, furnace black, lamp black, or thermal black, carbon nanotubes (CNTs) such as single-walled carbon nanotubes (SWCNTs) or multi-walled carbon nanotubes (MWCNTs), carbon fibers such as graphite nanofibers (GNFs), carbon nanofibers (CNFs), or activated carbon fibers (ACFs), or activated carbon, or two or more of these. The shape of the porous carbon material is not particularly limited as long as it is spherical, rod-like, needle-like, plate-like, tubular, or bulk-like and applicable to electrochemical devices.

[0034] Furthermore, pores are formed in the carbon material, and the porosity of the pores may be 40 to 90%, or 60 to 80%. When the porosity of the pores is within the above-mentioned range, lithium ions are easily transmitted, and the problem of reduced mechanical strength is easily prevented. The pore diameter of the carbon material may be 10 nm to 5 μm, or 50 nm to 5 μm. When the pore diameter of the carbon material is within the above-mentioned range, lithium ions are easily transmitted, and the battery short circuit and safety issues due to contact between electrodes are easily prevented.

[0035] The binder is a component for binding the positive electrode active material and the conductive material, etc., and for binding to the current collector. Examples of the binder include, but are not limited to, polyvinylidene fluoride (PVdF), polyvinylidene fluoride-polyhexafluoropropylene copolymer (PVdF / HFP), polyvinyl acetate, polyvinyl alcohol, polyvinyl ether, polyethylene, polyethylene oxide, alkylated polyethylene oxide, polypropylene, polymethyl(meth)acrylate, polyethyl(meth)acrylate, polytetrafluoroethylene (PTFE), polyvinyl chloride, polyacrylonitrile, polyvinylpyridine, polyvinylpyrrolidone, styrene-butadiene rubber, acrylonitrile-butadiene rubber, ethylene-propylene-diene monomer (EPDM) rubber, sulfonated EPDM rubber, styrene-butylene rubber, fluororubber, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, or two or more of these.

[0036] The binder may be added in an amount of 1 to 50 parts by weight, or 3 to 15 parts by weight, based on 100 parts by weight of the total weight of the positive electrode. When the content of the binder satisfies the above range, the adhesive strength between the positive electrode active material and the current collector is easily ensured, and the battery capacity is easily ensured.

[0037] The conductive material contained in the positive electrode is not particularly limited as long as it does not cause side reactions in the internal environment of the electrochemical device, does not cause chemical changes in the battery, and has excellent electrical conductivity. Typical examples include graphite or conductive carbon. Examples include graphite such as natural graphite and artificial graphite, carbon black such as carbon black, acetylene black, ketjen black, denka black, thermal black, channel black, furnace black, lamp black, and thermal black, carbon-based materials with a graphene or graphite crystal structure, conductive fibers such as carbon fiber and metal fiber, fluorocarbon, metal powders such as aluminum powder and nickel powder, conductive whiskey such as zinc oxide and potassium titanate, conductive oxides such as titanium oxide, and conductive polymers such as polyphenylene derivatives, but are not necessarily limited to these.

[0038] The conductive material may be added in an amount of 0.5 to 50 parts by weight, or 1 to 30 parts by weight, based on 100 parts by weight of the total weight of the positive electrode. When the content of the conductive material satisfies the above range, it is easy to improve electrical conductivity, easy to prevent deterioration of electrochemical properties, and easy to ensure the capacity and energy density of the positive electrode.

[0039] The method for incorporating a conductive material into the positive electrode is not particularly limited, and any conventional method known in the art, such as coating the positive electrode active material, can be used. If necessary, the addition of the conductive material as described above can be replaced by adding a conductive second coating layer to the positive electrode active material.

[0040] In addition, a filler can be selectively added to the positive electrode of the present invention as a component for suppressing its expansion. Such a filler is not particularly limited as long as it can suppress the expansion of the electrode without causing chemical changes in the battery. For example, olefin polymers such as polyethylene and polypropylene, and fibrous materials such as glass fiber and carbon fiber can be used.

[0041] The positive electrode can be manufactured by dispersing and mixing a positive electrode active material, a binder, a conductive material, etc. in a dispersion medium (solvent) to prepare a slurry, applying the slurry to a positive electrode current collector, and then drying and rolling the slurry. The dispersion medium can be, but is not limited to, NMP (N-methyl-2-pyrrolidone), DMF (dimethyl formamide), DMSO (dimethyl sulfoxide), ethanol, isopropanol, water, or a mixture thereof.

[0042] The positive electrode current collector may be, but is not limited to, platinum (Pt), gold (Au), palladium (Pd), iridium (Ir), silver (Ag), ruthenium (Ru), nickel (Ni), stainless steel (STS), aluminum (Al), molybdenum (Mo), chromium (Cr), carbon (C), titanium (Ti), tungsten (W), ITO (In-doped SnO), FTO (F-doped SnO), alloys thereof, or aluminum (Al) or stainless steel surface-treated with carbon (C), nickel (Ni), titanium (Ti), or silver (Ag). The positive electrode current collector may be in the form of a foil, film, sheet, punched, porous, foam, or the like.

[0043] The negative electrode may be made of lithium metal and may further include a current collector on one side of the lithium metal. The current collector may be a negative electrode current collector. The negative electrode current collector may be any material that does not cause chemical changes in the battery and has high conductivity, and may be selected from the group consisting of copper, aluminum, stainless steel, zinc, titanium, silver, palladium, nickel, iron, chromium, alloys thereof, and combinations thereof. The stainless steel may be surface-treated with carbon, nickel, titanium, or silver, and the alloy may be an aluminum-cadmium alloy. In addition, calcined carbon, a non-conductive polymer or a conductive polymer surface-treated with a conductive material, etc. may also be used. Generally, a copper sheet is used as the negative electrode current collector.

[0044] The negative electrode current collector may be in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric, with or without micro-irregularities on the surface. The negative electrode current collector may have a thickness ranging from 3 to 500 μm. When the thickness of the negative electrode current collector is within the above range, it is possible to ensure a current collecting effect and also to ensure ease of processability when assembling the cell by folding.

[0045] The lithium metal may be lithium or a lithium alloy, which includes an element capable of alloying with lithium, specifically, an alloy of lithium with at least one element selected from the group consisting of Si, Sn, C, Pt, Ir, Ni, Cu, Ti, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Sb, Pb, In, Zn, Ba, Ra, Ge, and Al.

[0046] The lithium metal may be in the form of a sheet or foil, and in some cases, may be in the form of lithium or a lithium alloy deposited or coated on a current collector by a dry process, or may be in the form of metal or alloy deposited or coated on particles by a wet process, etc.

[0047] A conventional separator may be interposed between the positive electrode and the negative electrode. The separator is a physical separator that physically separates the electrodes. Any conventional separator may be used, and it is particularly preferred that the separator has low resistance to ion migration of the electrolyte and excellent electrolyte humidification capacity. The separator separates or insulates the positive electrode and the negative electrode from each other while allowing lithium ions to be transported between the positive electrode and the negative electrode. Such a separator may be made of a porous, non-conductive, or insulating material. The separator may be an independent member such as a film, or a coating layer attached to the positive electrode and / or the negative electrode.

[0048] Examples of polyolefin-based porous membranes that can be used as the separation membrane include membranes formed from polyolefin-based polymers such as polyethylene (e.g., high-density polyethylene, linear low-density polyethylene, low-density polyethylene, and ultra-high molecular weight polyethylene), polypropylene, polybutylene, and polypentene, either alone or in combination. Examples of nonwoven fabrics that can be used as the separator include nonwoven fabrics made of polymers such as polyphenylene oxide, polyimide, polyamide, polycarbonate, polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, polyphenylene sulfide, polyacetal, polyethersulfone, polyetheretherketone, and polyester, either alone or in combination. Such nonwoven fabrics are in the form of fibers that form a porous web, and may be spunbond or meltblown, made of long fibers.

[0049] The thickness of the separator is not particularly limited, but may be 1 to 100 μm, or 5 to 50 μm. When the thickness of the separator is within the above range, the mechanical properties can be maintained and the problem of the separator acting as a resistance layer, which would reduce battery performance, can be easily prevented. The pore size and porosity of the separator are not particularly limited, but the pore size may be 0.1 to 50 μm, and the porosity may be 10 to 95%. When the pore size of the separator is within the above range, the separator is easily prevented from acting as a resistance layer and the mechanical properties of the separator can be easily maintained.

[0050] The tin chloride improves the lithium charge / discharge efficiency and inhibits the growth of dendrites, and improves the lithium utilization efficiency, thereby contributing to an increase in the capacity and lifespan of the battery.

[0051] Conventionally, lithium metal is supported in a solvent in which metal chloride is dissolved, and a lithium alloy / Li-Cl protective layer is formed on the surface of the lithium metal anode.

[0052] However, this ex-situ protective layer formation method has limitations such as low reactivity of metal chlorides due to the non-uniformity of the lithium metal surface and the presence of a native oxide layer on the lithium metal surface, and destruction of the protective layer during the initial charge / discharge process.

[0053] The inventors of the present invention have found that the life of a battery can be improved by using tin chloride as an electrolyte additive, and have completed the present invention.

[0054] When tin chloride is included in a non-aqueous electrolyte as an electrolyte additive, it can overcome the low reactivity between lithium and tin chloride due to the native oxide layer on the surface of the lithium metal negative electrode.

[0055] In one embodiment of the present invention, tin chloride can form a Li-Cl and Li-Sn alloy protective layer in situ on the surface of the lithium metal negative electrode during the initial charge / discharge process when the native oxide film on the surface of the lithium metal negative electrode is destroyed, thereby allowing the Li-Cl and Li-Sn alloy protective layer to be included on the surface of the lithium metal negative electrode.

[0056] The tin chloride contained in the nonaqueous electrolyte can etch the native oxide film on the lithium surface, which has high interfacial resistance during the initial charge / discharge process, thereby reducing the interfacial resistance between lithium and the electrolyte. At the same time, the tin chloride reacts with the lithium metal negative electrode to form a lithophilic Li-Cl and Li-Sn alloy protective layer on the surface of the lithium metal negative electrode, improving the lithium charge / discharge efficiency and more effectively suppressing dendrite growth. The Li-Cl and Li-Sn alloy protective layer functions as a stable electrode protective layer that prevents the depletion of salts and additives in the electrolyte. The inclusion of the Li-Cl and Li-Sn alloy protective layer on the surface of the lithium metal negative electrode can more easily improve the lifespan of electrochemical devices.

[0057] In one embodiment of the present invention, the tin chloride content may be 0.5 wt % to 5 wt %, 0.7 wt % to 5 wt %, 1 wt % to 5 wt %, 0.7 wt % to 4 wt %, 1 wt % to 4 wt %, 1 wt % to 3 wt %, or 1 wt % to 2 wt %, based on 100 wt % of the total non-aqueous electrolyte. When the tin chloride content satisfies the above range, the problem of accelerated battery degradation due to a side reaction between tin chloride and the positive electrode active material is prevented, and the life-span improvement effect is more easily achieved. In particular, when the tin chloride content is 1 wt % to 2 wt %, based on 100 wt % of the total non-aqueous electrolyte, the life of the electrochemical device can be most improved.

[0058] In one embodiment of the present invention, the non-aqueous electrolyte may further include a first solvent including a heterocyclic compound having one or more double bonds and including one or more oxygen atoms and sulfur atoms; a second solvent including one or more of an ether-based compound, an ester-based compound, an amide-based compound, and a carbonate-based compound; a lithium salt; and lithium nitrate.

[0059] The first solvent, the second solvent, the lithium salt, and the lithium nitrate contained in the nonaqueous electrolyte according to one embodiment of the present invention will be specifically described below.

[0060] First Solvent The first solvent includes a heterocyclic compound containing one or more oxygen atoms and one or more sulfur atoms, with or without one or more double bonds. The first solvent has the property of being difficult to dissolve salt due to delocalization of lone pair electrons of the heteroatom (oxygen atom or sulfur atom). Therefore, during the initial discharge stage of the battery, a ring-opening polymerization reaction of the heterocyclic compound forms a polymer protective film (solid electrolyte interphase, SEI layer) on the surface of lithium metal, thereby suppressing the formation of lithium dendrites. Furthermore, decomposition of the electrolyte on the surface of lithium metal and the resulting side reactions are reduced, thereby improving the life characteristics of the electrochemical device.

[0061] That is, the heterocyclic compound of the present invention may contain one or more double bonds to form a polymer protective film on the surface of lithium metal, and must contain one or more heteroatoms (oxygen atoms or sulfur atoms) to have polarity and thereby exhibit effects such as increasing affinity with other solvents in the electrolyte solution.

[0062] The heterocyclic compound may be a 3- to 15-membered, 3- to 7-membered, or 5- to 6-membered heterocyclic compound. Furthermore, the heterocyclic compound may be a heterocyclic compound substituted or unsubstituted with one or more selected from the group consisting of an alkyl group having 1 to 4 carbon atoms, a cyclic alkyl group having 3 to 8 carbon atoms, an aryl group having 6 to 10 carbon atoms, a halogen group, a nitro group (-NO), an amine group (-NH), and a sulfonyl group (-SO). Furthermore, the heterocyclic compound may be a polycyclic compound of a heterocyclic compound and one or more of a cyclic alkyl group having 3 to 8 carbon atoms and an aryl group having 6 to 10 carbon atoms.

[0063] When the heterocyclic compound is substituted with an alkyl group having 1 to 4 carbon atoms, radicals can be stabilized, thereby suppressing side reactions in the electrolyte solution. Furthermore, when the heterocyclic compound is substituted with a halogen group or a nitro group, a functional protective film can be formed on the surface of lithium metal, and the formed functional protective film can be stabilized as a compact protective film. Furthermore, uniform deposition of lithium metal is possible. In particular, when the electrochemical device is a lithium-sulfur battery, side reactions between polysulfides and lithium metal can be suppressed.

[0064] Specific examples of the heterocyclic compound include 1,3-dioxolane, 4,5-diethyl-1,3-dioxolane, 4,5-dimethyl-1,3-dioxolane, 4-methyl-1,3-dioxolane, 4-ethyl-1,3-dioxolane, and 1,3-dioxane. ane, 1,4-dioxane, 4-methyl-1,3-dioxane, 2-methyl-1,3-dioxane, furan, 2-methylfuran, 3-methylfuran, 2-ethylfuran, 2-propylfuran, 2-butylfuran, 2,3-dimethylfuran Examples of thiophene include 2,3-dimethylfuran, 2,4-dimethylfuran, 2,5-dimethylfuran, pyran, 2-methylpyran, 3-methylpyran, 4-methylpyran, benzofuran, 2-(2-nitrovinyl)furan, thiophene, 2-methylthiophene, 2-ethylthiophene, 2-propylthiophene, 2-butylthiophene, 2,3-dimethylthiophene, 2,4-dimethylthiophene, and 2,5-dimethylthiophene.The first solvent containing such a heterocyclic compound may be included in a volume ratio of 5 to 50 with respect to 100 volume ratio of the total organic solvent (i.e., first solvent + second solvent) included in the nonaqueous electrolyte according to one embodiment of the present invention (the remainder corresponds to the second solvent). When the content of the first solvent satisfies the above range, it is easy to prevent the problem of a protective film not being completely formed on the lithium metal surface and the problem of reduced battery capacity and lifespan due to increased surface resistance of the electrolyte and lithium metal.

[0065] In particular, when the positive electrode active material is sulfur, the ability to reduce the amount of polysulfide elution decreases, making it difficult to suppress an increase in the resistance of the electrolyte solution.

[0066] Second Solvent The second solvent may include at least one of an ether-based compound, an ester-based compound, an amide-based compound, and a carbonate-based compound, and may dissolve a lithium salt to impart lithium ion conductivity to the electrolyte solution, and may also dissolve a positive electrode active material to facilitate an electrochemical reaction with lithium. In particular, when the positive electrode active material is sulfur, the second solvent may dissolve the sulfur, which is a positive electrode active material, to facilitate an electrochemical reaction with lithium.

[0067] The carbonate-based compound may be a linear carbonate-based compound or a cyclic carbonate-based compound.

[0068] Specific examples of the ether-based compound include dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, ethyl propyl ether, dimethoxyethane, diethoxyethane, methoxyethoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, triethylene glycol methyl ethyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, tetraethylene glycol methyl ethyl ether, polyethylene glycol dimethyl ether, polyethylene glycol diethyl ether, polyethylene glycol methyl ethyl ether, or two or more of these, but are not limited thereto.

[0069] Examples of the ester compound include, but are not limited to, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, ε-caprolactone, or two or more of these.

[0070] The amide-based compound may be a conventional amide-based compound used in the art.

[0071] Examples of the linear carbonate-based compound include, but are not limited to, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethylmethyl carbonate (EMC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), or two or more of these.

[0072] Examples of the cyclic carbonate compound include, but are not limited to, ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate, halides thereof (such as fluoroethylene carbonate (FEC)), or two or more of these.

[0073] The second solvent may be included in a volume ratio of 50 to 95 with respect to 100 volume ratio of the total organic solvent (i.e., first solvent + second solvent) included in the nonaqueous electrolyte according to one embodiment of the present invention. When the content of the second solvent satisfies the above range, it can sufficiently dissolve the lithium salt, thereby easily preventing the problem of reduced lithium ion conductivity and the problem of precipitation of the positive electrode active material exceeding its solubility concentration. In particular, when the positive electrode active material is sulfur, it can easily prevent the problem of sulfur precipitation exceeding its solubility concentration and the problem of reduced lifespan due to the severe shuttle phenomenon between lithium polysulfide and lithium metal anode caused by excessive sulfur elution.

[0074] Meanwhile, the organic solvents including the first solvent and the second solvent may be included in an amount of 60 to 99.5 wt %, 60 to 99 wt %, 60 to 98 wt %, or 60 to 95 wt %, based on 100 wt % of the total weight of the nonaqueous electrolyte according to one embodiment of the present invention. When the content of the organic solvent satisfies the above range, it is easy to prevent problems such as an increase in viscosity of the electrolyte solution, a decrease in ionic conductivity, or problems such as lithium salt or additives not being completely dissolved in the electrolyte solution, and it is easy to prevent problems such as a decrease in the concentration of lithium salt in the electrolyte solution, a decrease in ionic conductivity.

[0075] lithium salts The lithium salt is an electrolyte salt used to increase ionic conductivity, and examples thereof include LiCl, LiBr, LiI, LiClO4, LiBF4, and LiB 10 Cl 10 , LiPF6, LiCF3SO3, LiCF3CO2, LiC4BO8, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, (C2F5SO2)2NLi, (SO2F)2NLi (i.e., LiFSI), (CF3SO2)2NLi (i.e., LiTFSI), (CF3SO2)3CLi, lithium chloroborane, lithium lower aliphatic carboxylates having 4 or less carbon atoms, lithium 4-phenylborate, lithium imide, or two or more of these. In particular, using (CF3SO2)2Nli or (SO2F2)Nli as the lithium salt can be advantageous in that it has high solubility in the first solvent and / or second solvent and high lithium ion conductivity.

[0076] The concentration of the lithium salt can be determined in consideration of ionic conductivity, for example, 0.2 to 2 M, or 0.5 to 1 M. When the concentration of the lithium salt satisfies the above range, it is easy to ensure ionic conductivity suitable for driving the battery, and it is possible to prevent an increase in the viscosity of the electrolyte, which would reduce the mobility of lithium ions, or an increase in the decomposition reaction of the lithium salt itself.

[0077] Lithium nitrate The non-aqueous electrolyte according to one embodiment of the present invention may include lithium nitrate (LiNO3), which reacts with the lithium metal negative electrode to form a lithophilic protective film, such as lithium nitride (Li3N) or lithium oxynitride (LiON), on the surface of the lithium metal negative electrode, thereby inhibiting the growth of lithium dendrites and preventing decomposition of the electrolyte components, thereby improving battery life and efficiency.

[0078] If necessary, the non-aqueous electrolyte may further contain lanthanum nitrate (La(NO3)3), potassium nitrate (KNO3), cesium nitrate (CsNO3), magnesium (MgNO3), barium nitrate (BaNO3), lithium nitrite (LiNO2), potassium nitrite (KNO2), cesium nitrite (CsNO2), or two or more of these.

[0079] The lithium nitrate may be contained in a content of 0.1 to 7 wt %, or 0.5 to 5 wt %, or 0.5 to 1.5 wt %, based on 100 wt % of the total non-aqueous electrolyte. When the lithium nitrate content satisfies the above range, it is easy to prevent the problem of a sudden decrease in coulomb efficiency and the phenomenon of an increase in the viscosity of the electrolyte.

[0080] A non-aqueous electrolyte according to one embodiment of the present invention may include a first solvent, 1,3-dioxolane, a second solvent, dimethoxyethane, a lithium salt, (CF3SO2)2NLi, lithium nitrate, and tin chloride. 1,3-dioxolane and dimethoxyethane have high lithium polysulfide solubility and can stabilize a lithium metal anode. Therefore, when the non-aqueous electrolyte contains the above-mentioned materials, optimal electrochemical device performance can be achieved.

[0081] The electrochemical device of the present invention includes all devices that perform electrochemical reactions, and specific examples thereof include all types of primary and secondary batteries, fuel cells, solar cells, and capacitors such as supercapacitors.

[0082] In one embodiment of the present invention, the electrochemical device may be any lithium secondary battery commonly used in the art that uses lithium metal as a negative electrode, and may be a lithium-sulfur battery or a lithium-lithium symmetric cell.

[0083] An electrochemical device according to an embodiment of the present invention, including the above-described positive electrode, negative electrode, separator, and electrolyte, may be manufactured by interposing a separator between the positive electrode and the negative electrode, and then injecting a nonaqueous electrolyte according to an embodiment of the present invention.

[0084] Meanwhile, a lithium secondary battery according to an embodiment of the present invention can be applied not only to a battery cell used as a power source for a small device, but also particularly suitably used as a unit battery of a battery module, which is a power source for a medium- to large-sized device. In this regard, the present invention also provides a battery module including two or more electrochemical devices electrically connected (in series or parallel). The number of electrochemical devices included in the battery module can be adjusted in various ways depending on the application and capacity of the battery module. The present invention also provides a battery pack in which the battery modules are electrically connected according to conventional techniques in the art. The battery module and battery pack can be used as a power source for one or more medium- to large-sized devices, including, but not limited to, power tools, electric vehicles (EVs), hybrid electric vehicles (HEVs), and electric vehicles including plug-in hybrid electric vehicles (PHEVs), electric trucks, electric commercial vehicles, and power storage systems.

[0085] The present invention will be described in detail below with reference to examples to aid in understanding the present invention. However, the examples according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the following examples. The embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

[0086] Example 1-1 First, 1 wt% of lithium nitrate and 0.5 wt% of tin chloride (based on the total weight of the electrolyte) were added to an organic solvent, which was a mixture of 1,3-dioxolane (first solvent) and dimethoxyethane (second solvent) in a 1:1 volume ratio (v / v), and dissolved to a concentration of 1M (CF3SO2)2NLi(LiTFSI) (lithium salt), to prepare a non-aqueous electrolyte.

[0087] Example 1-2 A non-aqueous electrolyte solution was prepared in the same manner as in Example 1-1, except that 1 wt % of tin chloride was added instead of 0.5 wt % of tin chloride.

[0088] Examples 1-3 A non-aqueous electrolyte solution was prepared in the same manner as in Example 1-1, except that 2 wt % of tin chloride was added instead of 0.5 wt % of tin chloride.

[0089] Examples 1-4 A non-aqueous electrolyte solution was prepared in the same manner as in Example 1-1, except that 3 wt % of tin chloride was added instead of 0.5 wt % of tin chloride.

[0090] Examples 1-5 A non-aqueous electrolyte solution was prepared in the same manner as in Example 1-1, except that 4 wt % of tin chloride was added instead of 0.5 wt % of tin chloride.

[0091] Examples 1-6 A non-aqueous electrolyte solution was prepared in the same manner as in Example 1-1, except that 5 wt % of tin chloride was added instead of 0.5 wt % of tin chloride.

[0092] Comparative Example 1-1 A non-aqueous electrolyte solution was prepared in the same manner as in Example 1-1, except that tin chloride was not added.

[0093] Examples 2-1 to 2-6 and Comparative Example 2-1: Fabrication of Lithium-Lithium Symmetric Cell Two electrodes were fabricated by cross-rolling lithium to a thickness of 35 μm onto a copper current collector, respectively, to form a positive electrode and a negative electrode, with the lithium facing each other. A porous polyethylene (PE) separator having a thickness of 16 μm was then interposed between the positive electrode and the negative electrode, and the nonaqueous electrolytes prepared in Examples 1-1 to 1-6 and Comparative Example 1-1 were injected and sealed to fabricate coin cell-type lithium-lithium symmetric cells.

[0094] Examples 3-1 to 3-6 and Comparative Example 3-1: Fabrication of Lithium-Sulfur Battery First, 87.5 parts by weight of a sulfur-carbon (CNT) composite (S / C 75:25 weight ratio) as a positive electrode active material, 5 parts by weight of Denka Black as a conductive material, and 7.5 parts by weight of styrene butadiene rubber / carboxymethyl cellulose (SBR / CMC 7:3) as a binder were mixed to prepare a positive electrode slurry composition, which was then applied to one side of a current collector (Al foil), dried at 80°C, and rolled using a roll press to prepare a positive electrode (at this time, the loading amount was 4 mg / cm). 2 (I did that).

[0095] Next, the prepared positive electrode and a negative electrode in which lithium having a thickness of 35 μm was cross-rolled onto a copper current collector were disposed opposite each other, and a porous polyethylene (PE) separator was interposed between them. Then, the non-aqueous electrolytes prepared in Examples 1-1 to 1-6 and Comparative Example 1-1 were injected into the negative electrode and sealed to prepare coin cell-type lithium-sulfur batteries.

[0096] Evaluation example 1: Evaluation of interface resistance and cycle life of lithium-lithium symmetric cells The interface resistance and cycle life of the lithium-lithium symmetric cells fabricated in Examples 2-1 to 2-6 and Comparative Example 2-1 were evaluated and are shown in Table 1 and FIGS. 1 to 14 below.

[0097] The interfacial resistance of the lithium-lithium symmetric cells was determined by measuring the impedance of the lithium-lithium symmetric cells prepared in Examples 2-1 to 2-6 and Comparative Example 2-1 at a temperature of 25°C in the frequency range of 0.1 Hz to 1 MHz using electrochemical impedance spectroscopy (EIS), and defining the radius of the first semicircle as the interfacial resistance (R).

[0098] The cycle life of the lithium-lithium symmetric cells was 1.5 mA / cm at 25°C for the lithium-lithium symmetric cells manufactured in Examples 2-1 to 2-6 and Comparative Example 2-1. 2 The potential was measured over time (cycles) by repeating discharge (lower limit -1V) and charge (upper limit +1V) cycles at a current density of 1000 kJ / s.

[0099] [Table 1]

[0100] As can be seen from Table 1 and Figures 1 to 7, the lithium-lithium symmetric cells prepared in Examples 2-1 to 2-6, in which the electrolyte contained tin chloride, exhibited reduced interfacial resistance compared to the lithium-lithium symmetric cell prepared in Comparative Example 2-1, in which the electrolyte did not contain tin chloride. This is because the native oxide film on the surface of the lithium metal anode, which has high interfacial resistance, was etched by tin chloride, forming lithophilic Li-Cl and Li-Sn alloy protective layers on the surface of the lithium metal anode.

[0101] Furthermore, as can be seen from Table 1 and Figures 8 to 14, the lithium-lithium symmetric cells prepared in Examples 2-1 to 2-6, which contained tin chloride in the electrolyte, exhibited improved lifespans compared to the lithium-lithium symmetric cell prepared in Comparative Example 2-1, which did not contain tin chloride in the electrolyte. In particular, the lithium-lithium symmetric cells prepared in Examples 2-1 to 2-5, which contained tin chloride in an amount of 0.5 wt % to 4 wt % relative to 100 wt % of the total electrolyte, exhibited even improved lifespans.

[0102] Evaluation example 2: Evaluation of cycle life of lithium-sulfur battery The lithium-sulfur batteries prepared in Examples 3-1 to 3-6 and Comparative Example 3-1 were subjected to 0.2C charge / 0.3C discharge cycles in the voltage range of 1.8V to 2.5V in CC mode at a temperature of 25°C to measure the capacity-potential relationship (after initial stabilization processes of 2.5 cycles at 0.1C / 0.1C and 3 cycles at 0.2C / 0.2C, the batteries were driven at 0.3C / 0.5C from the 7th cycle). The results are shown in Table 2 and FIG. 15.

[0103] [Table 2]

[0104] As can be seen from Table 2 and Figure 15, the lithium-sulfur batteries prepared in Examples 3-1 to 3-6, which contained tin chloride in the electrolyte, exhibited improved lifespans compared to the lithium-sulfur battery prepared in Comparative Example 3-1, which did not contain tin chloride in the electrolyte. In particular, the lithium-sulfur batteries prepared in Examples 3-1 to 3-5, in which the tin chloride content was 0.5 wt% to 4 wt% based on 100 wt% of the total electrolyte, exhibited even improved lifespans. Among these, the lithium-sulfur battery prepared in Example 3-2, in which the tin chloride content was 1 wt% based on 100 wt% of the total electrolyte, exhibited a significant improvement in lifespan, and the lithium-sulfur battery prepared in Example 3-3, in which the tin chloride content was 2 wt% based on 100 wt% of the total electrolyte, exhibited the longest lifespan.

[0105] Evaluation example 3: Analysis of the surface of the lithium metal anode of a lithium-sulfur battery The lithium-sulfur battery prepared in Example 3-3 was operated for 100 cycles, and then the surface of the lithium metal anode of the lithium-sulfur battery was analyzed using a transmission electron microscope (SEM) EDS (energy dispersive spectroscopy). The results are shown in FIG. 16.

[0106] As can be seen in Figure 16, Sn and Cl were detected on the surface of the lithium metal anode even after the battery was operated. This confirmed that Li-Cl and Li-Sn alloy protective layers were present on the surface of the lithium metal anode even after the battery was operated.

Claims

1. A positive electrode, a lithium metal negative electrode, a separator interposed between the positive electrode and the negative electrode, and tin chloride (SnCl ２ and a non-aqueous electrolyte solution containing the nonaqueous electrolyte solution comprises a first solvent containing a heterocyclic compound which may or may not contain one or more double bonds and which contains one or more oxygen atoms and / or sulfur atoms; a second solvent containing at least one of an ether-based compound, an ester-based compound, an amide-based compound, and a carbonate-based compound; A lithium salt, lithium nitrate, The content of the tin chloride is 0.5 wt % to 5 wt % relative to 100 wt % of the total weight of the nonaqueous electrolyte solution, The electrochemical device is a lithium-sulfur battery.

2. 2. The electrochemical element according to claim 1, wherein the content of said tin chloride is 1 to 4% by weight with respect to 100% by weight of the total weight of said non-aqueous electrolyte.

3. 3. The electrochemical device according to claim 1, further comprising a Li-Cl and Li-Sn alloy protective layer on the surface of the lithium metal negative electrode.

4. The lithium salts include LiCl, LiBr, LiI, and LiClO. ４ , LiBF ４ , LiB １０ Cl １０ , LiPF ６ , LiCF ３ SO ３ , LiCF ３ CO ２ , LiC ４ BO ８ , LiAsF ６ , LiSbF ６ , LiAlCl ４ , C.H. ３ SO ３ Li, CF ３ SO ３ Li, (C ２ F ５ SO ２ ) ２ NLi, (SO ２ F) ２ NLi, (CF ３ SO ２ ) ２ NLi, (CF ３ SO ２ ) ３ 2. The electrochemical element according to claim 1, comprising C11, lithium chloroborane, lithium lower aliphatic carboxylate having 4 or less carbon atoms, lithium 4-phenylborate, lithium imide, or two or more of these.

5. 2. The electrochemical device according to claim 1, wherein the concentration of the lithium salt is 0.2 to 2.0M.

6. 2. The electrochemical element according to claim 1, wherein the heterocyclic compound is a 3- to 15-membered heterocyclic compound unsubstituted or substituted with one or more selected from the group consisting of an alkyl group having 1 to 4 carbon atoms, a cyclic alkyl group having 3 to 8 carbon atoms, an aryl group having 6 to 10 carbon atoms, a halogen group, a nitro group, an amine group, and a sulfonyl group, or a polycyclic compound of a heterocyclic compound and one or more selected from the group consisting of a cyclic alkyl group having 3 to 8 carbon atoms and an aryl group having 6 to 10 carbon atoms.

7. The heterocyclic compounds include 1,3-dioxolane, 4,5-diethyl-1,3-dioxolane, 4,5-dimethyl-1,3-dioxolane, 4-methyl-1,3-dioxolane, 4-ethyl-1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, 4-methyl-1,3-dioxane, and 2-methyl-1,3-dioxane, furan, 2-methylfuran, 3-methylfuran, 2-ethylfuran, 2-propylfuran, 2-butylfuran, and 2,3-dimethylfuran. 2,4-dimethylfuran, 2,5-dimethylfuran, pyran, 2-methylpyran, 3-methylpyran, 4-methylpyran, benzofuran, 2-(2-nitrovinyl)furan, thiophene, 2-methylthiophene, 2-ethylthiophene, 2-propylthiophene, 2-butylthiophene, 2,3-dimethylthiophene, 2,4-dimethylthiophene, 2,5-dimethylthiophene, or two or more thereof. The electrochemical element according to claim 1,

8. 2. The electrochemical element according to claim 1, wherein the ether-based compound of the second solvent includes dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, ethyl propyl ether, dimethoxyethane, diethoxyethane, methoxyethoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, triethylene glycol methyl ethyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, tetraethylene glycol methyl ethyl ether, polyethylene glycol dimethyl ether, polyethylene glycol diethyl ether, polyethylene glycol methyl ethyl ether, or two or more thereof.

9. 3. The electrochemical element according to claim 1, wherein the non-aqueous electrolyte further contains lanthanum nitrate, potassium nitrate, cesium nitrate, magnesium nitrate, barium nitrate, lithium nitrite, potassium nitrite, cesium nitrite, or two or more of these.

10. The non-aqueous electrolyte solution contains 1,3-dioxolane as a first solvent, dimethoxyethane as a second solvent, and a lithium salt (CF ３ SO ２ ) ２ 3. The electrochemical element according to claim 1, further comprising NLi and lithium nitrate.

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