Non-aqueous electrolyte and electrochemical device containing the same

Abstract

The present invention relates to a non-aqueous electrolyte having improved stability. The non-aqueous electrolyte according to one embodiment of the present invention includes a first solvent including a heterocyclic compound having one or more double bonds or no double bonds and having at least one of oxygen atoms and sulfur atoms; a second solvent including at least one of ether-based compounds, ester-based compounds, amide-based compounds, and carbonate-based compounds; and a first lithium salt, the first lithium salt including lithium bis(nonafluorobutanesulfonyl)imide, and the lithium bis(nonafluorobutanesulfonyl)imide may be included in an amount of 2 to 5 wt % relative to 100 wt % of the total non-aqueous electrolyte.

Description

Technical Field

[0001] The present invention relates to a non-aqueous electrolyte and an electrochemical device including the same.

[0002] This application claims priority based on Korean Patent Application No. 2022-0003568 filed on January 10, 2022, and all of the content disclosed in the specification and drawings of the application is incorporated herein.

Background Art

[0003] As interest in energy storage technology is increasing, the application fields are expanding to mobile phones, tablets, laptops, video cameras, and even the energy of electric vehicles (EVs) and hybrid electric vehicles (HEVs), and research and development on electrochemical devices are gradually increasing. Electrochemical devices are the most spotlighted fields in this aspect, and among them, the development of secondary batteries such as rechargeable lithium-sulfur batteries has been the focus of interest. Recently, in developing such batteries, research and development on new electrode and battery designs have led to improve the capacity density and specific energy.

[0004] Among such electrochemical devices, lithium metal secondary batteries such as lithium-sulfur batteries (Li-S batteries) not only use light lithium metal as a negative electrode active material but also have a high energy density (theoretical capacity; 3,862 mAh / g), and are attracting attention as next-generation high-capacity secondary batteries that can replace existing secondary batteries such as lithium-ion batteries. In such a lithium-sulfur battery, a reduction reaction of sulfur and an oxidation reaction of lithium metal occur during discharge. At this time, sulfur forms lithium polysulfide (LiPS) having a linear structure from the S8 having a ring structure. Such a lithium-sulfur battery is characterized by showing a stepwise discharge voltage until the polysulfide is completely reduced to Li2S.

[0005] However, such lithium-sulfur batteries have a decrease in charge / discharge efficiency during the charge and discharge process and a degradation of battery life due to reasons such as side reactions of the electrolyte (deposition of by-products accompanying the decomposition of the electrolyte).

[0006] In particular, lithium, which is the negative electrode active material, easily forms dendritic crystals (dendrites) with a large area, reacts with salts and additives in the electrolyte to form a solid electrolyte interphase (SEI), and continuously consumes the salts and additives in the electrolyte without interruption. As a result, it promotes the degradation of the battery.

[0007] The decomposition of such an electrolyte becomes more intense and is accelerated at high temperatures. Therefore, at present, it is desired to develop an electrolyte composition that can enhance the stability of the electrolyte for driving the battery in a high-temperature environment.

Summary of the Invention

Problems to be Solved by the Invention

[0008] Therefore, the problems to be solved by the present invention are to provide a non-aqueous electrolyte with improved stability and an electrochemical element including the same.

[0009] Another problem to be solved by the present invention is to provide a non-aqueous electrolyte with improved life performance at high temperatures and an electrochemical element including the same.

Means for Solving the Problems

[0010] In order to solve the above problems, according to one aspect of the present invention, a non-aqueous electrolyte of the following embodiment is provided.

[0011] The first embodiment is a first solvent including a heterocyclic compound that may or may not include one or more double bonds and includes one or more of either an oxygen atom or a sulfur atom, A second solvent containing any one or more of an ether compound, an ester compound, an amide compound, and a carbonate compound, a first lithium salt, and comprising The first lithium salt includes lithium bis(nonafluorobutanesulfonyl)imide, The non-aqueous electrolyte is characterized in that the lithium bis(nonafluorobutanesulfonyl)imide is contained in an amount of 2 to 5% by weight based on 100% by weight of the whole non-aqueous electrolyte.

[0012] A second aspect is the non-aqueous electrolyte according to the first aspect, wherein the non-aqueous electrolyte further contains a second lithium salt, The second lithium salt may include 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 carboxylate having 4 or less carbon atoms, lithium 4-phenylborate, lithium imide, or two or more of these.

[0013] A third aspect is the non-aqueous electrolyte according to the second aspect, wherein the second lithium salt may contain (SO2F)2NLi.

[0014] A fourth aspect is the non-aqueous electrolyte according to the second aspect, wherein the concentration of the second lithium salt may be 0.2 to 2.0 M.

[0015] A fifth aspect is the non-aqueous electrolyte according to any one of the first to fourth aspects, The heterocyclic compound may be a 3- to 15-membered heterocyclic compound which is 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 may be a polycyclic compound of one or more of a cyclic alkyl group having 3 to 8 carbon atoms and an aryl group having 6 to 10 carbon atoms and a heterocyclic compound.

[0016] A sixth aspect is the non-aqueous electrolyte according to any one of the first to fifth aspects, The heterocyclic compound may 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, 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.

[0017] A seventh aspect is the non-aqueous electrolyte according to any one of the first to sixth aspects, 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 may include two or more of these.

[0018] The eighth aspect is in the non-aqueous electrolyte according to any one of the first aspect to the seventh aspect, The non-aqueous electrolyte may further contain lithium nitrate.

[0019] The ninth aspect is in the non-aqueous electrolyte according to any one of the first aspect to the seventh aspect, The non-aqueous electrolyte may further contain lanthanum nitrate, potassium nitrate, cesium nitrate, magnesium nitrate, barium nitrate, lithium nitrite, potassium nitrite, cesium nitrite, or two or more of these.

[0020] The tenth aspect is in the non-aqueous electrolyte according to any one of the first aspect to the ninth aspect, The non-aqueous electrolyte may contain 2-methylfuran as the first solvent, dimethoxyethane as the second solvent, lithium bis(fluorosulfonyl)imide ((SO2F)2NLi, LiFSI), lithium nitrate, and lithium bis(nonafluorobutanesulfonyl)imide (LiFSI).

[0021] In order to solve the above problems, according to one aspect of the present invention, an electrochemical element of the following aspect is provided.

[0022] Aspect 11 is related to an electrochemical device, characterized by including a positive electrode, a negative electrode, a separator sandwiched between the positive electrode and the negative electrode, and a non-aqueous electrolyte according to any one of Aspects 1 to 10. Aspect 12 is related to the non-aqueous electrolyte according to Aspect 11, wherein the electrochemical device can be a lithium-sulfur battery.

[0023] Aspect 13 is related to the non-aqueous electrolyte according to Aspect 11, wherein the electrochemical device can be a lithium-sulfur battery. The non-aqueous electrolyte according to one embodiment of the present invention contains lithium bis(nonafluorobutanesulfonyl)imide at 2 to 5% by weight based on 100% by weight of the whole non-aqueous electrolyte, thereby suppressing the decomposition of the electrolyte and making it possible to improve the stability.

Advantages of the Invention

[0024] The non-aqueous electrolyte according to one embodiment of the present invention contains lithium bis(nonafluorobutanesulfonyl)imide at 2 to 5% by weight based on 100% by weight of the whole non-aqueous electrolyte, thereby making it possible to improve the life performance especially at high temperatures.

[0025] The non-aqueous electrolyte according to one embodiment of the present invention contains lithium bis(nonafluorobutanesulfonyl)imide at 2 to 5% by weight based on 100% by weight of the whole non-aqueous electrolyte, thereby making it possible to improve the life performance especially at high temperatures.

[0026] The drawings attached to this specification illustrate the preferred embodiments of the present invention and are for the purpose of further understanding the technical idea of the present invention together with the content of the invention. Therefore, the present invention is not construed as being limited only to the matters described in the drawings.

Brief Description of the Drawings

[0027]

Figure 1

Modes for Carrying Out the Invention

[0028] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, the terms and words used in this specification and the claims are not to be construed as being limited to ordinary or dictionary meanings. The inventor himself interprets them in accordance with the meaning and concept corresponding to the technical idea of the present invention in accordance with the principle that he can appropriately define the concept of the terms in order to explain the invention in the best way.

[0029] Therefore, it should be understood that the embodiments described in this specification and the configurations shown in the drawings are only the most preferred embodiments of the present invention and do not represent all of the technical ideas of the present invention. Therefore, there may be various equivalents and modifications that can replace them at the time of this application.

[0030] A non-aqueous electrolyte according to one aspect of the present invention includes a first solvent containing a heterocyclic compound that contains one or more double bonds or does not contain them and contains one or more of either an oxygen atom or a sulfur atom, a second solvent containing one or more of an ether compound, an ester compound, an amide compound, and a carbonate compound, and a first lithium salt. The first lithium salt contains lithium bis(nonafluorobutanesulfonyl)imide (LiNFSI), and the lithium bis(nonafluorobutanesulfonyl)imide is contained at 2 to 5% by weight based on 100% by weight of the entire non-aqueous electrolyte.

[0031] Hereinafter, each of the first solvent, the second solvent, and the lithium bis(nonafluorobutanesulfonyl)imide which is the first lithium salt contained in the non-aqueous electrolyte according to one embodiment of the present invention will be described in detail.

[0032] First Solvent The first solvent contains a heterocyclic compound that may or may not contain one or more double bonds and contains one or more of either an oxygen atom or a sulfur atom. Due to the characteristic that it is difficult to dissolve a salt by the delocalization of the lone pair electrons of the heteroatom (oxygen atom or sulfur atom), in the initial discharge stage of the battery, a polymer protective film (solid electrolyte interphase; SEI layer) is formed on the surface of the negative electrode by the ring opening reaction of the heterocyclic compound, thereby suppressing the generation of lithium dendrites. Furthermore, by reducing the decomposition of the electrolyte solution on the surface of the negative electrode and the accompanying side reactions, the life characteristics of the electrochemical device can be improved. In particular, when the negative electrode is a lithium-based metal, by forming a polymer protective film (solid electrolyte interphase; SEI layer) on the surface of the lithium-based metal, the generation of lithium dendrites can be suppressed. Furthermore, by reducing the decomposition of the electrolyte solution on the surface of the lithium-based metal and the accompanying side reactions, the life characteristics of the electrochemical device can be improved.

[0033] That is, the heterocyclic compound of the present invention may contain one or more double bonds in order to form a polymer protective film on the surface of the negative electrode, and necessarily contains one or more heteroatoms (oxygen atom or sulfur atom) so as to exhibit effects such as increasing the compatibility with other solvents in the electrolyte solution by making it polar.

[0034] The heterocyclic compound can be a 3- to 15-membered, preferably 3- to 7-membered, more preferably 5- to 6-membered heterocyclic compound. Further, such a heterocyclic compound can 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 (-NO2), an amine group (-NH2), and a sulfonyl group (-SO2). Furthermore, the heterocyclic compound can be a polycyclic compound of one or more of a cyclic alkyl group having 3 to 8 carbon atoms and an aryl group having 6 to 10 carbon atoms and a heterocyclic compound.

[0035] When the heterocyclic compound is substituted with an alkyl group having 1 to 4 carbon atoms, the radical can be stabilized to suppress side reactions between electrolytes. Also, when substituted with a halogen group or a nitro group, a functional protective film can be formed on the surface of the negative electrode. At this time, the formed functional protective film can be a protective film in a compressed (compact) form and can be stable. In particular, when the negative electrode is a lithium-based metal, a functional protective film can be formed on the surface of the lithium-based metal. Furthermore, it may be possible to deposit the lithium-based metal uniformly. Moreover, when the electrochemical device is a lithium-sulfur battery, side reactions between polysulfide and the lithium-based metal can be suppressed.

[0036] 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, 1,3-dioxane, 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, 2,4-dimethylfuran, 2,5-dimethylfuran, pyran, 2-methylpyran, 3-methylpyran, 4-methylpyran, benzofuran, 2-(2-Nitrovinyl)furan, thiophene, 2-methylthiophene, 2-ethylthiphene, 2-propylthiophene, 2-butylthiophene, 2,3-dimethylthiophene, 2,4-dimethylthiophene, and 2,5-dimethylthiophene, etc.In particular, when the positive electrode active material is sulfur, 2-methylfuran has a low solubility in polysulfide. Therefore, when 2-methylfuran is used as the first solvent, the elution amount of polysulfide in the non-aqueous electrolyte can be reduced, and an increase in the resistance of the non-aqueous electrolyte can be suppressed, which is advantageous. Further, even when the non-aqueous electrolyte contains lithium bis(nonafluorobutanesulfonyl)imide having a high molecular weight, it is easier to compensate for the increase in resistance. Furthermore, when the negative electrode is a lithium-based metal, 2-methylfuran can form a protective film on the surface of the lithium-based metal by a ring-opening polymerization reaction.

[0037] The first solvent containing such a heterocyclic compound may be contained in a volume ratio of 5 to 50, or 10 to 30, with respect to 100 volume ratios of the total organic solvents (i.e., the sum of the first solvent and the second solvent) contained in the non-aqueous electrolyte according to an embodiment of the present invention (the remainder corresponds to the second solvent). When the content of the first solvent satisfies the above-described range, it is easy to prevent the problem that the protective film is not perfectly formed on the surface of the negative electrode, and it is easy to prevent the problem that the capacity and life of the battery are reduced due to an increase in the surface resistance of the electrolyte and the negative electrode.

[0038] In particular, when the positive electrode active material is sulfur, it is easy to prevent the problem that the ability to reduce the elution amount of polysulfide is reduced and it becomes difficult to suppress an increase in the resistance of the electrolyte. When the negative electrode active material is a lithium-based metal, it is easy to prevent the problem that the protective film is not perfectly formed on the surface of the lithium-based metal, and it is easy to prevent the problem that the capacity and life of the battery are reduced due to an increase in the surface resistance of the electrolyte and the lithium-based metal.

[0039] [[ID=ll]] Second solvent The second solvent contains any one or more of an ether-based compound, an ester-based compound, an amide-based compound, and a carbonate-based compound, and not only dissolves a lithium salt to give the electrolyte lithium ion conductivity, but also plays a role of eluting the positive electrode active material to smoothly perform an electrochemical reaction with lithium. In particular, when the positive electrode active material is sulfur, it can play a role of eluting sulfur as the positive electrode active material to smoothly perform an electrochemical reaction with lithium.

[0040] The carbonate compound may be a linear carbonate compound, a cyclic carbonate compound, or a mixture thereof.

[0041] Specific examples of the ether 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. In particular, when the positive electrode active material is sulfur, when dimethoxyethane is used as the second solvent, the solubility in polysulfide is high, which is advantageous for the reaction to proceed smoothly.

[0042] Examples of the ester compound include 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, but are not limited thereto.

[0043] The amide compound can be a normal amide compound used in the art.

[0044] Examples of the linear carbonate 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 thereof.

[0045] 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, vinyl ethylene carbonate, halides thereof (such as fluoroethylene carbonate (FEC)), or two or more thereof.

[0046] The second solvent may be contained in a volume ratio of 50 to 95, or 70 to 90, based on 100 volume ratios of the total organic solvents (i.e., the sum of the first solvent and the second solvent) contained in the non-aqueous electrolyte according to an embodiment of the present invention. When the content of the second solvent satisfies the above-described range, it is easy to prevent the problem that the lithium salt cannot be sufficiently dissolved and the lithium ion conductivity drops, and it is easy to prevent the problem that the positive electrode active material precipitates exceeding the soluble concentration. In particular, when the positive electrode active material is sulfur, it is easy to prevent the problem that sulfur, which is the positive electrode active material, precipitates exceeding the soluble concentration, and it is easy to prevent the problem that sulfur is eluted excessively and the shuttle phenomenon between the lithium polysulfide and the lithium negative electrode becomes intense, reducing the lifespan.

[0047] On the one hand, the organic solvent containing the first solvent and the second solvent can be contained in an amount of 60 to 95% by weight, preferably 60 to 92% by weight, and more preferably 60 to 90% by weight, based on 100% by weight of the non-aqueous electrolyte according to an embodiment of the present invention. When the content of the organic solvent satisfies the above-mentioned range, it is easy to prevent problems such as an increase in the viscosity of the electrolyte and a decrease in ionic conductivity, or problems such as incomplete dissolution of the lithium salt and additives in the electrolyte, and it is easy to prevent problems such as a decrease in the concentration of the lithium salt in the electrolyte and a decrease in ionic conductivity.

[0048] Lithium bis(nonafluorobutanesulfonyl)imide (LiNFSI) (first lithium salt) The decomposition of the electrolyte becomes intense and is accelerated at high temperatures. In particular, the decomposition of the salt becomes intense and is accelerated.

[0049] Lithium bis(nonafluorobutanesulfonyl)imide has a longer carbon chain length than commonly used lithium salts, so it is stable even at high temperatures and is difficult to decompose. As a result, it is possible to continuously supply the lithium salt to the electrolyte even at high temperatures, and it is possible to improve the life performance of the electrochemical element at high temperatures.

[0050] In an embodiment of the present invention, when the non-aqueous electrolyte further contains a second lithium salt described later, even if the second lithium salt such as lithium bis(fluorosulfonyl)imide (LiFSI) is decomposed at high temperatures, lithium bis(nonafluorobutanesulfonyl)imide can continuously supply the lithium salt to the electrolyte, and it is possible to improve the life performance of the electrochemical element at high temperatures.

[0051] The lithium bis(nonafluorobutanesulfonyl)imide is contained in an amount of 2 to 5% by weight based on 100% by weight of the non-aqueous electrolyte. When the content of the lithium bis(nonafluorobutanesulfonyl)imide satisfies the above-mentioned range, the decomposition of the electrolyte can be suppressed and the stability of the electrolyte can be improved. In addition, the life performance of the electrolyte at high temperatures can be improved.

[0052] When lithium bis(nonafluorobutanesulfonyl)imide is contained in an amount of less than 2% by weight based on 100% by weight of the entire non-aqueous electrolyte, the effect of improving stability becomes negligible. When lithium bis(nonafluorobutanesulfonyl)imide is contained in an amount exceeding 5% by weight based on 100% by weight of the entire non-aqueous electrolyte, there is a risk of increased resistance due to the long carbon chain length. In addition, overvoltage occurs and it is difficult to drive at a high rate, and moreover, the life performance is not improved.

[0053] In one embodiment of the present invention, the non-aqueous electrolyte may further contain a second lithium salt.

[0054] The second lithium salt is an electrolyte salt used to increase ionic conductivity. Examples of this include LiCl, LiBr, LiI, LiClO4, LiBF4, 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 carboxylate having 4 or less carbon atoms, lithium 4-phenylborate, lithium imide, or two or more of these. In particular, when (SO2F)2NLi is used as the second lithium salt, it is advantageous because a protective film can be formed on the electrode.

[0055] In the non-aqueous electrolyte according to one aspect of the present invention, the second lithium salt may contain LiFSI.

[0056] The concentration of the second lithium salt can be determined in consideration of ion conductivity and the like, and can be, for example, 0.2 to 2 M, or 0.5 to 1 M. When the concentration of the second lithium salt satisfies the above-described range, it is easy to ensure an ion conductivity suitable for driving the battery, and it is possible to prevent the viscosity of the electrolytic solution from increasing and the mobility of lithium ions from decreasing, or the decomposition reaction of the second lithium salt itself from increasing.

[0057] In one embodiment of the present invention, the non-aqueous electrolytic solution may further contain lithium nitrate (LiNO3).

[0058] When the negative electrode is a lithium-based metal, lithium nitrate reacts with the lithium-based metal to form a lithiumophilic protective film such as lithium nitride (Li3N) or lithium oxynitride (LiON) on the surface of the lithium-based metal, suppressing the growth of lithium dendrites, preventing the decomposition of the electrolytic solution components, and improving the battery life and efficiency.

[0059] Also, when the positive electrode active material is sulfur, it is advantageous in suppressing the shuttle reaction in which polysulfide moves to the negative electrode side and reacts with the negative electrode.

[0060] Furthermore, if necessary, in addition to lithium nitrate, lanthanum nitrate (La(NO3)3), potassium nitrate (KNO3), cesium nitrate (CsNO3), magnesium nitrate (Mg(NO3)2), barium nitrate (Ba(NO3)2), lithium nitrite (LiNO2), potassium nitrite (KNO2), cesium nitrite (CsNO2), or two or more of these may be further contained.

[0061] The lithium nitrate may be contained in an amount of 0.1 to 7% by weight, preferably 0.5 to 5% by weight, based on 100% by weight of the entire non-aqueous electrolytic solution. When the content of lithium nitrate satisfies the above-described range, it is easy to prevent the problem that the Coulomb efficiency rapidly decreases, and it is easy to prevent the phenomenon that the viscosity of the electrolytic solution becomes high.

[0062] A non-aqueous electrolyte according to an embodiment of the present invention may contain 2-methylfuran as the first solvent, dimethoxyethane as the second solvent, (SO2F)2NLi, lithium nitrate, and lithium bis(nonafluorobutanesulfonyl)imide. In particular, when the positive electrode active material is sulfur, when the non-aqueous electrolyte contains the substances described above, the reaction proceeds smoothly, and polysulfide is more preferably dissolved so that a large resistance does not occur.

[0063] By containing lithium bis(nonafluorobutanesulfonyl)imide at 2 to 5% by weight based on 100% by weight of the whole non-aqueous electrolyte, a non-aqueous electrolyte according to an embodiment of the present invention can suppress the decomposition of the electrolyte at high temperatures, particularly at 45°C or higher, and it becomes possible to improve the stability and the life performance at high temperatures. Thereby, it becomes possible to improve the life performance at high temperatures of an electrochemical element containing such a non-aqueous electrolyte.

[0064] Next, an electrochemical element according to an embodiment of the present invention will be described.

[0065] An electrochemical element according to an embodiment of the present invention includes a positive electrode, a negative electrode, a separator sandwiched between the positive electrode and the negative electrode, and the non-aqueous electrolyte. The above-described matters regarding the non-aqueous electrolyte shall apply mutatis mutandis.

[0066] The electrochemical element of the present invention encompasses all elements that undergo an electrochemical reaction. Specific examples include capacitors such as all types of primary batteries, secondary batteries, fuel cells, solar cells, or supercapacitor elements.

[0067] In one embodiment of the present invention, the electrochemical element can be any lithium secondary battery commonly used in the art, and among them, it can be a lithium-sulfur battery. When the electrochemical element is a lithium-sulfur battery, the non-aqueous electrolyte according to an embodiment of the present invention is even more advantageous in extracting a suitable solubility of polysulfide.

[0068] The positive electrode includes a positive electrode active material, a binder, a conductive material, etc. The positive electrode active material can be one applied to a normal electrochemical device. For example, it may include a lithium nickel cobalt manganese-based compound (lithium NCM-based compound), and may also include elemental sulfur (Elemental sulfur; S8), a sulfur-based compound, or a mixture thereof. Specifically, the sulfur-based compound can be Li2Sn (n≧1), an organic sulfur compound, or a carbon-sulfur complex ((C2S x ) n : x = 2.5~50, n≧2), etc. Further, the positive electrode active material may include a sulfur-carbon complex. Since the sulfur substance has no electrical conductivity in its single form, it can be used in combination with a conductive material. The carbon material (or carbon source) constituting the sulfur-carbon complex may have a porous structure or a high specific surface area, and can be any material as long as it is commonly used in the art. For example, the porous carbon material may be graphite; graphene; carbon black such as Denka black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; carbon nanotubes (CNT) such as single-walled carbon nanotubes (SWCNT), multi-walled carbon nanotubes (MWCNT); carbon fibers such as graphite nanofibers (GNF), carbon nanofibers (CNF), activated carbon fibers (ACF); activated carbon; or two or more of these, but is not limited thereto. Its shape can be spherical, rod-shaped, needle-shaped, plate-shaped, tube-shaped, or bulk-shaped, and there is no particular limitation as long as it is applicable to an electrochemical device.

[0069] In addition, pores are formed in the carbon material, and the porosity of the pores can be 40 to 90 vol% or 60 to 80 vol%. When the porosity of the pores satisfies the above-described range, the transfer of lithium ions is likely to occur normally, and it is easy to prevent the problem of a decrease in mechanical strength. The pore diameter of the carbon material can be 10 nm to 5 μm or 50 nm to 5 μm. When the pore diameter of the carbon material satisfies the above-described range, it is easy to permeate lithium ions, and it is easy to prevent problems such as short circuit of the battery due to contact between electrodes and safety problems.

[0070] The binder is a component that assists in binding the positive electrode active material and the conductive material, etc., and binding to the current collector. For example, polyvinylidene fluoride (PVdF), polyvinylidene fluoride - hexafluoropropylene 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, polyvinyl pyridine, polyvinyl pyrrolidone, styrene - butadiene rubber, acrylonitrile - butadiene rubber, ethylene - propylene - diene monomer (EPDM) rubber, sulfonated EPDM rubber, styrene - butylene rubber, fluorine rubber, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, or two or more of these can be used, but it is not necessarily limited to these.

[0071] The binder can usually 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-described range, it is easy to ensure the adhesive force between the positive electrode active material and the current collector, and it is also easy to ensure the capacity of the battery.

[0072] 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 element and does not induce chemical changes in the battery, while having excellent electrical conductivity. Typically, graphite or conductive carbon can be used. For example, 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 substances with a crystal structure of graphene or graphite; conductive fibers such as carbon fibers and metal fibers; carbon fluoride; metal powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive oxides such as titanium oxide; conductive polymers such as polyphenylene derivatives; or two or more of these can be used, but it is not necessarily limited to these.

[0073] The conductive material can usually 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-mentioned range, it is easy to improve the electrical conductivity, prevent the degradation of electrochemical properties, and ensure the capacity and energy density of the positive electrode.

[0074] The method of including the conductive material in the positive electrode is not particularly limited, and known ordinary methods in the art such as coating on the positive electrode active material can be used. Also, if necessary, a conductive second coating layer may be added to the positive electrode active material to replace the addition of the conductive material as described above.

[0075] 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 inducing chemical changes in the battery. For example, olefin polymers such as polyethylene and polypropylene; fibrous substances such as glass fibers and carbon fibers; etc. can be used.

[0076] 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 produce a slurry, applying this onto a positive electrode current collector, and then drying and rolling. As the dispersion medium, N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), ethanol, isopropanol, water, and mixtures thereof can be used, but are not necessarily limited thereto.

[0077] As the positive electrode current collector, 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), indium-doped tin oxide (ITO: In doped SnO2), fluorine-doped tin oxide (FTO: F doped SnO2), and alloys thereof, and those obtained by surface-treating the surface of aluminum (Al) or stainless steel with carbon (C), nickel (Ni), titanium (Ti), or silver (Ag) can be used, but are not necessarily limited thereto. The form of the positive electrode current collector can be in the form of a foil, film, sheet, punched-out piece, porous body, foam, etc.

[0078] The negative electrode contains a negative electrode active material, a binder, a conductive material, etc. As the negative electrode active material, ordinary negative electrode active materials that can be used for the negative electrode of conventional electrochemical elements can be used, such as lithium metal or lithium alloys, carbon, petroleum coke, activated carbon, graphite, or other carbonaceous materials such as lithium adsorbing substances.

[0079] The binder is a component that assists in binding the negative electrode active material and the conductive material, etc., and binding to the current collector. For example, polyvinylidene fluoride (PVdF), polyvinylidene fluoride - hexafluoropropylene 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, polyvinyl pyridine, polyvinyl pyrrolidone, styrene - butadiene rubber, acrylonitrile - butadiene rubber, ethylene - propylene - diene monomer (EPDM) rubber, sulfonated EPD, rubber, styrene - butylene rubber, fluorine rubber, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, or two or more of these can be used, but it is not necessarily limited to these.

[0080] The binder can usually 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 negative electrode. When the content of the binder satisfies the above - mentioned range, it is easy to ensure the adhesive force between the negative electrode active material and the current collector, and it is also easy to ensure the capacity of the battery.

[0081] The conductive material contained in the negative electrode is not particularly limited as long as it does not cause side reactions in the internal environment of the electrochemical element and does not induce chemical changes in the battery, while having excellent electrical conductivity. Typically, graphite or conductive carbon can be used. For example, 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, thermal black; carbon-based substances with a crystal structure of graphene or graphite; conductive fibers such as carbon fibers and metal fibers; carbon fluoride; metal powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive oxides such as titanium oxide; conductive polymers such as polyphenylene derivatives; or two or more of these can be used, but it is not necessarily limited to these.

[0082] The conductive material can usually 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 negative electrode. When the content of the conductive material satisfies the above-mentioned range, it is easy to improve the electrical conductivity, prevent the degradation of electrochemical properties, and ensure the capacity and energy density of the negative electrode.

[0083] The method of including the conductive material in the negative electrode is not particularly limited, and known ordinary methods in the art such as coating on the negative electrode active material can be used. Also, if necessary, by adding a conductive second coating layer to the negative electrode active material, it may replace the addition of the conductive material as described above.

[0084] In addition, a filler can be selectively added to the negative 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 inducing chemical changes in the battery. For example, olefin polymers such as polyethylene and polypropylene; fibrous substances such as glass fibers and carbon fibers; etc. can be used.

[0085] The negative electrode can be manufactured by dispersing and mixing a negative electrode active material, a binder, a conductive material, etc. in a dispersion medium (solvent), producing a slurry, applying this onto a negative electrode current collector, and then drying and rolling. As the dispersion medium, N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), ethanol, isopropanol, water, and mixtures thereof can be used, but are not necessarily limited thereto.

[0086] The negative electrode current collector can be used without particular limitation as long as it has high conductivity without causing a chemical change in the battery, and can 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. As the alloy, an aluminum-cadmium alloy can be used. In addition to these, fired carbon, a non-conductive polymer or a conductive polymer surface-treated with a conductive material may also be used. Generally, a copper foil plate is employed as the negative electrode current collector.

[0087] Also, as its form, various forms such as a film, sheet, foil, net, porous body, foam, non-woven fabric body, etc. with or without fine irregularities formed on the surface can be used. Further, the negative electrode current collector can have a thickness in the range of 3 to 500 μm. When the thickness of the negative electrode current collector satisfies the above-described range, workability can be easily ensured even when the cell is folded and assembled while ensuring the current collection effect.

[0088] The lithium-based metal can be lithium or a lithium alloy. At this time, the lithium alloy contains an element that can be alloyed with lithium. Specifically, the lithium alloy can be an alloy with one or more selected from the group consisting of lithium and 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.

[0089] The lithium-based metal can be in the form of a sheet or a foil. In some cases, it can be in a form where lithium or a lithium alloy is vapor-deposited or coated on the current collector by a dry process, or it can be in a form where particulate metals and alloys are vapor-deposited or coated by a wet process or the like.

[0090] A normal separator can be sandwiched between the positive electrode and the negative electrode. The separator is a physical separator having a function of physically separating the electrodes, and can be used without particular limitation as long as it is a separator commonly used. In particular, it is preferably one that has a low resistance to the movement of ions in the electrolytic solution and is excellent in the moisture retention ability of the electrolytic solution. Further, the separator enables the transport of lithium ions between the positive electrode and the negative electrode while separating or insulating the positive electrode and the negative electrode from each other. Such a separator can be made of a porous, non-conductive or insulating substance. The separator can be an independent member such as a film, or can be a coating layer added to the positive electrode and / or the negative electrode.

[0091] Examples of polyolefin-based porous membranes that can be used as the separator include membranes formed by using, individually, polyolefin-based polymers such as polyethylene such as high-density polyethylene, linear low-density polyethylene, low-density polyethylene, and ultra-high molecular weight polyethylene, polypropylene, polybutylene, polypentene, etc., or membranes formed from polymers obtained by mixing these. Examples of nonwoven fabrics that can be used as the separator include nonwoven fabrics formed by using, individually, polyphenylene oxide, polyimide, polyamide, polycarbonate, polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, polyphenylene sulfide, polyacetal, polyether sulfone, polyether ether ketone, polyester, etc., or nonwoven fabrics formed from polymers obtained by mixing these. Such nonwoven fabrics are fibrous materials that form a porous web and may include the shape of spun bond or melt blown composed of long fibers.

[0092] The thickness of the separator is not particularly limited, but can be 1 to 100 μm, or 5 to 50 μm. When the thickness of the separator satisfies the above-described range, while maintaining mechanical physical properties, it is easy to prevent the problem that the separator acts as a resistance layer and the performance of the battery deteriorates. The pore diameter and porosity of the separator are not particularly limited, but the pore diameter can be 0.1 to 50 μm, and the porosity can be 10 to 95 vol%. When the pore diameter of the separator satisfies the above-described range, it is easy to prevent the separator from acting as a resistance layer and easy to maintain the mechanical physical properties of the separator.

[0093] An electrochemical element according to an embodiment of the present invention including the positive electrode, negative electrode, separator, and electrolytic solution as described above can be manufactured through a process of facing the positive electrode to the negative electrode, sandwiching a separator therebetween, and then injecting a non-aqueous electrolytic solution according to an embodiment of the present invention.

[0094] On the other hand, it goes without saying that a lithium secondary battery according to an embodiment of the present invention is applicable to a battery cell used as a power source for a small device, and can be particularly preferably used as a unit cell of a battery module that is a power source for a medium- to large-sized device. From such an aspect, the present invention also provides a battery module in which two or more electrochemical elements are electrically connected (in series or in parallel). Needless to say, the number of electrochemical elements included in the battery module can be variously adjusted in consideration of the use and capacity of the battery module. Further, the present invention provides a battery pack in which the battery module is electrically connected according to ordinary techniques in the art. The battery module and battery pack can be used as a power source for any one or more of medium- to large-sized devices including power tools; electric vehicles including electric vehicles (EV), hybrid electric vehicles (HEV), and plug-in hybrid electric vehicles (PHEV); electric trucks; electric commercial vehicles; or energy storage systems, but are not necessarily limited thereto.

[0095] Hereinafter, in order to deepen the understanding of the present invention, examples will be given to explain the present invention in more detail. However, the examples according to the present invention can be deformed into various other forms, and it should not be construed that the scope of the present invention is limited to the following examples. The examples of the present invention are provided to more fully explain the present invention to those having average knowledge in the art.

[0096] Example 1 Manufacture of non-aqueous electrolyte First, 5% by weight of lithium nitrate and 2% by weight of lithium bis(nonafluorobutanesulfonyl)imide (LiNFSI) based on the total weight of the electrolyte were added to an organic solvent obtained by mixing 2-methylfuran (first solvent) and dimethoxyethane (second solvent) at a volume ratio (v / v) of 20:80, and dissolved so that the concentration of (SO2F)2NLi (LiFSI) became 0.75 M to produce a non-aqueous electrolyte.

[0097] Manufacture of electrochemical device First, a sulfur-carbon (CNT) complex (S / C = 75:25 weight ratio) as a positive electrode active material and styrene-butadiene rubber / carboxymethyl cellulose (SBR / CMC = 7:3) as a binder were mixed at a weight ratio of 95:5 to produce a positive electrode slurry composition. After that, this was applied onto a current collector (Al foil) and dried, and then rolled with a roll press device to produce a positive electrode (at this time, the loading amount was 4.5 mg / cm 2 and the porosity was adjusted to 68 vol%).

[0098] Next, the positive electrode manufactured as described above and a negative electrode in which lithium was cross-rolled with a thickness of 45 μm on a copper current collector were positioned so as to face each other, and a porous polyethylene (PE) separator was sandwiched therebetween. Then, the electrolyte manufactured as described above was enclosed to produce a coin cell type lithium-sulfur battery.

[0099] Example 2 A non-aqueous electrolyte and an electrochemical device were produced in the same manner as in Example 1, except that 3% by weight of lithium bis(nonafluorobutanesulfonyl)imide was added instead of 2% by weight of lithium bis(nonafluorobutanesulfonyl)imide.

[0100] Example 3 A non-aqueous electrolyte and an electrochemical device were produced in the same manner as in Example 1, except that 5% by weight of lithium bis(nonafluorobutanesulfonyl)imide was added instead of 2% by weight of lithium bis(nonafluorobutanesulfonyl)imide.

[0101] Comparative Example 1 A non-aqueous electrolyte and an electrochemical device were produced in the same manner as in Example 1, except that lithium bis(nonafluorobutanesulfonyl)imide was not added.

[0102] Comparative Example 2 A non-aqueous electrolyte and an electrochemical device were produced in the same manner as in Example 1, except that 1% by weight of lithium bis(nonafluorobutanesulfonyl)imide was added instead of 2% by weight of lithium bis(nonafluorobutanesulfonyl)imide.

[0103] Comparative Example 3 A non-aqueous electrolyte and an electrochemical device were produced in the same manner as in Example 1, except that 7% by weight of lithium bis(nonafluorobutanesulfonyl)imide was added instead of 2% by weight of lithium bis(nonafluorobutanesulfonyl)imide.

[0104] Comparative Example 4 A non-aqueous electrolyte and an electrochemical device were produced in the same manner as in Example 1, except that 3% by weight of lithium tetrafluoroborate (LiBF4) was added instead of 2% by weight of lithium bis(nonafluorobutanesulfonyl)imide.

[0105] Evaluation Example: Evaluation of Life Characteristics In Examples 1 to 3 and Comparative Examples 1 to 4, the manufactured electrochemical devices were first discharged at 0.1C in a constant current (CC) mode at 45°C, and then charged and discharged at 0.1C for 2 cycles. Next, after driving the charge and discharge at 0.2C for 3 cycles to go through the stabilization process, high-rate charge and discharge at 0.3C / 0.5C were performed to evaluate the life characteristics of the electrochemical devices, which are shown in Table 1 and Figure 1. At this time, the lower limit of discharge was set to 1.8V, and the upper limit of charge was set to 2.5V. The number of cycles showing a capacity retention rate of 80% based on the initial discharge capacity at a high rate of 0.5C was measured.

[0106]

Table 1

[0107] As is clear from Table 1 and Figure 1, compared with Comparative Examples 1 to 2 that do not contain lithium bis(nonafluorobutanesulfonyl)imide or contain it at less than 2% by weight based on 100% by weight of the whole non-aqueous electrolyte, the life characteristics of the electrochemical devices containing the non-aqueous electrolyte manufactured in Examples 1 to 3 that contain lithium bis(nonafluorobutanesulfonyl)imide at 2 to 5% by weight based on 100% by weight of the whole non-aqueous electrolyte were further significantly improved.

[0108] Also, it was confirmed that Comparative Example 3 containing more than 5% by weight of lithium bis(nonafluorobutanesulfonyl)imide based on 100% by weight of the whole non-aqueous electrolyte has a large resistance and cannot show the effect of improving the life.

[0109] Furthermore, even if two types of lithium salts are used together with LiFSI, it was confirmed that when LiBF4 and LiFSI, which are not lithium bis(nonafluorobutanesulfonyl)imide, are used in combination, the effects confirmed above are not exhibited.

Claims

1. A first solvent containing a heterocyclic compound that may or may not contain one or more double bonds and contains one or more of either oxygen atoms or sulfur atoms, a second solvent containing one or more of any one of an ether compound, an ester compound, an amide compound, and a carbonate compound, a first lithium salt, and the organic solvent contained in the non-aqueous electrolyte is composed only of the first solvent and the second solvent, the first lithium salt contains lithium bis(nonafluorobutanesulfonyl)imide, the non-aqueous electrolyte in which the lithium bis(nonafluorobutanesulfonyl)imide is contained at 2 to 5% by weight based on 100% by weight of the whole non-aqueous electrolyte.

2. The non-aqueous electrolyte further contains a second lithium salt, The second lithium salt is LiCl, LiBr, LiI, 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 , CH 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 CLi, lithium chloroborane, lithium lower aliphatic carboxylate having 4 or less carbon atoms, lithium 4-phenylborate, lithium imide, or a non-aqueous electrolyte according to claim 1 containing two or more of these.

3. The second lithium salt is (SO ２ F) ２ NLi, and the non-aqueous electrolyte according to claim 2.

4. The non-aqueous electrolyte according to Claim 2, wherein the concentration of the second lithium salt is 0.2 to 2.0 M.

5. The heterocyclic compound is a 3- to 15-membered heterocyclic compound that is 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 one or more of a cyclic alkyl group having 3 to 8 carbon atoms and an aryl group having 6 to 10 carbon atoms and a heterocyclic compound. The non-aqueous electrolyte according to Claim 1.

6. 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-propylfuran, 2-butylfuran, 2,3-dimethylfuran, 2,4-dimethylfuran, 2,5-dimethylfuran, pyran, 2-methylpyran, 3-methylpyran, 4-methylpyran, benzofuran, 2-(2-nitrovinyl)furan, thiophene, 2-methylthiophene, 2-ethylthiophene, 2-propylthiophene, 2-butylthiophene, 2,3-dimethylthiophene, 2,4-dimethylthiophene, 2,5-dimethylthiophene, or a combination of two or more thereof. The non-aqueous electrolyte according to Claim 1.

7. The ether-based compound of the second solvent is 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 a non-aqueous electrolyte according to claim 1 containing two or more of these.

8. The non-aqueous electrolyte according to claim 1, further comprising lithium nitrate.

9. The non-aqueous electrolyte according to claim 8, further comprising 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 is 2-methylfuran as the first solvent, dimethoxyethane as the second solvent, (SO ２ F) ２ NLithium, lithium nitrate, and lithium bis(nonafluorobutanesulfonyl)imide, the non-aqueous electrolyte according to claim 1.

11. An electrochemical element comprising a positive electrode, a negative electrode, a separator sandwiched between the positive electrode and the negative electrode, and the non-aqueous electrolyte according to any one of claims 1 to 10.

12. The electrochemical element according to claim 11, wherein the electrochemical element is a lithium-sulfur battery.

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