Nonaqueous electrolyte and lithium secondary battery containing same

Abstract

To provide an electrolytic solution having an excellent cycle life, capable of suppressing deterioration of battery characteristics even under high temperature condition.SOLUTION: Disclosed is a nonaqueous electrolytic solution containing a compound which contains 5 to 20 wt.% nitrogen atom in a molecule, and 25 to 70 wt.% sulfur atom or oxygen atom, and has no disulfide bond in the molecule. The compound contains two or more sulfur atoms or oxygen atoms in the molecule.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a non-aqueous electrolyte solution and a lithium secondary battery containing the same. [Background technology]

[0002] Lithium secondary batteries are widely used not only in portable devices such as mobile phones and laptops, but also as storage batteries for automobiles and industrial use, and also for new applications such as drones. Although lithium secondary batteries have a relatively high energy density compared to other types of secondary batteries, the use of materials containing nickel as the positive electrode active material is being considered in order to produce lithium secondary batteries with even higher energy density.

[0003] Traditionally, lithium cobalt oxide (LCO) has been used as the positive electrode active material for lithium secondary batteries, but nickel-containing nickel-cobalt-manganese (NCM) is increasingly being used. In addition, the use of nickel-cobalt-aluminum (NCA) ternary materials is also being considered. These ternary materials are advantageous not only from the standpoint of high energy density, but also from the standpoint of cost competitiveness, as they can reduce the use of cobalt.

[0004] In addition, technology to use silicon-containing materials as negative electrode active materials is also being developed. Silicon-containing materials have a large theoretical capacity, and are therefore expected to be used in automobiles, where large capacity is required.

[0005] Research is also underway to find the best electrolyte for use with these positive and negative active materials. It is known that the electrolyte can deteriorate due to the influence of trace amounts of moisture contained in the electrolyte. For example, LiPF 6 When an electrolyte is used, the electrolyte decomposes and produces acid through the following reaction:

[0006] LiPF 6 +H 2 O → LiF + POF3 +2HF

[0007] It is known that the acid generated in this way reacts with the surface of the negative electrode material containing silicon such as SiO or the coating formed on the surface, causing an increase in impedance and degrading the battery characteristics. In addition, when a material containing nickel is used as the positive electrode active material, there is a risk that the reaction generating the acid will be accelerated due to the large amount of residual alkali in the material.

[0008] Japanese Patent Application Laid-Open No. 2019-40701 discloses that the high-temperature storage characteristics and cycle characteristics of a lithium secondary battery are improved by using a non-aqueous electrolyte containing a boric acid triester. - Although suppressing the effect on the components is disclosed, the effect on the acid content is not disclosed.

[0009] JP 2019-71302 A discloses that the life and high temperature stability of a lithium secondary battery are improved by using an electrolyte containing a specific silicon-containing compound. However, silicon-containing compounds are generally difficult to prepare, and their practical use is unclear.

[0010] Japanese Patent Application Laid-Open No. 2019-186078 describes that the generation of hydrogen fluoride is suppressed by adding at least one additive selected from the group consisting of compounds containing a nitrogen atom having a lone pair to a non-aqueous electrolyte and using a specific fluorinated acrylate as an electrolyte composition. However, although it has been demonstrated that the use of graphite as the negative electrode is effective, the effect of using a material containing silicon on the negative electrode and the coating on its surface has not been clarified. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] JP 2019-40701 A [Patent Document 2] JP 2019-71302 A [Patent Document 3] JP 2019-186078 A Summary of the Invention [Problem to be solved by the invention]

[0012] Therefore, there has been a demand for an electrolyte that can stabilize the characteristics of the electrolyte and has excellent battery characteristics and cycle life even when a nickel-containing material is used for the positive electrode and a silicon-containing material is used for the negative electrode.

[0013] The present invention has been made to solve the problems of the conventional technology described above, and has an object to provide an electrolyte solution that can suppress deterioration of battery characteristics even under high temperature conditions and has an excellent cycle life. [Means for solving the problem]

[0014] As a result of intensive research into the above-mentioned problems, the inventors unexpectedly discovered that by using a compound containing specific amounts of nitrogen atoms and sulfur atoms or oxygen atoms and having no disulfide bonds in the molecule as an additive to the electrolyte, it is possible to maintain excellent capacity density even under high temperature conditions, and thus arrived at the present invention.

[0015] The object of the present invention is to provide a non-aqueous electrolyte solution containing a compound having 5 to 20% by mass of nitrogen atoms and 25 to 70% by mass of sulfur atoms or oxygen atoms in the molecule and having no disulfide bond in the molecule, The compound is achieved by a non-aqueous electrolyte containing two or more sulfur or oxygen atoms in the molecule.

[0016] The compound preferably contains 5 to 20% by mass of nitrogen atoms and 25 to 70% by mass of sulfur atoms in the molecule and has no disulfide bonds in the molecule.

[0017] The compound preferably contains two or more sulfur atoms in the molecule. The compound preferably contains three or more sulfur atoms in the molecule.

[0018] The compound preferably includes a compound represented by the following chemical formulas 1 to 3 alone or two or more of these.

[0019] [ka]

[0020] (In the formula, R 1 is an alkyl group having 1 to 18 carbon atoms or a phenyl group, R 2 is an alkyl group having 1 to 18 carbon atoms or a phenyl group, R 3 is an alkyl group having 1 to 18 carbon atoms or a phenyl group, R 4 is an alkyl group having 1 to 18 carbon atoms or a phenyl group, R 5 is an alkylene group having 1 to 12 carbon atoms.

[0021] [ka]

[0022] (In the formula, R 6 is hydrogen, an alkyl group having 1 to 18 carbon atoms, or -SR 8 and R 7 is hydrogen, an alkyl group having 1 to 18 carbon atoms, or -SR 9 In this case, R 8 and R 9 are each independently a hydrogen atom or an alkyl group having 1 to 18 carbon atoms.

[0023] [ka]

[0024] (In the formula, R 10 is hydrogen, an alkyl group having 1 to 18 carbon atoms, or -SR13 and R 11 is hydrogen, an alkyl group having 1 to 18 carbon atoms, or -SR 14 In this case, R 13 and R 14 are each independently a hydrogen atom or an alkyl group having 1 to 18 carbon atoms; R 12 Ha-SR 15 Or -N(R 16 )(R 17 ) and R 15 is hydrogen, an alkyl group having 1 to 18 carbon atoms, or -SR 18 In this case, R 18 is hydrogen or an alkyl group having 1 to 18 carbon atoms, and R 16 and R 17 are each independently a substituted or unsubstituted alkyl group having 1 to 18 carbon atoms.

[0025] The compounds include methylene bis(diethylthiocarbamate), ethylene bis(diethyldithiocarbamate), methylene bis(dipropylthiocarbamate), ethylene bis(dipropyldithiocarbamate), methylene bis(dibutyldithiocarbamate), ethylene bis(dibutyldithiocarbamate), methylene bis(dipentyldithiocarbamate), ethylene bis(dipentyldithiocarbamate), methylene bis(dihexyldithiocarbamate), ethylene bis(dihexyldithiocarbamate), 2,5-dimercapto-1,3,4-thiadiazole, 2-hydrocarbyldithio-5-mercapto and 6-(diisopropylamino)-1,3,5-triazine-2,4-dithiol, 6-(diisobutylamino)-1,3,5-triazine-2,4-dithiol, 6-diallylamino-1,3,5-triazine-2,4-dithiol, 6-diallylamino-1,3,5-triazine-2,4-dithiol, 6-di(2-ethylhexyl)amino-1,3,5-triazine-2,4-dithiol, or two or more thereof.

[0026] The compound preferably includes a compound represented by the above formula 1, a compound represented by the above formula 3, or two or more of these.

[0027] The compounds include methylene bis(diethylthiocarbamate), ethylene bis(diethyldithiocarbamate), methylene bis(dipropylthiocarbamate), ethylene bis(dipropyldithiocarbamate), methylene bis(dibutyldithiocarbamate), ethylene bis(dibutyldithiocarbamate), methylene bis(dipentyldithiocarbamate), ethylene bis(dipentyldithiocarbamate), methylene bis(dihexyldithiocarbamate), and ethylene bis(dihexyldithiocarbamate). Preferably, the compound contains at least one of the following: 1,3,5-triazine-2,4,6-trithiol, 2-(dibutylamino)-1,3,5-triazine-4,6-dithiol, 6-(diisopropylamino)-1,3,5-triazine-2,4-dithiol, 6-(diisobutylamino)-1,3,5-triazine-2,4-dithiol, 6-diallylamino-1,3,5-triazine-2,4-dithiol, 6-di(2-ethylhexyl)amino-1,3,5-triazine-2,4-dithiol, or two or more of these.

[0028] The compound is preferably contained in an amount of 0.1 to 1% by mass based on the total mass of the nonaqueous electrolyte solution.

[0029] The nonaqueous electrolyte solution of the present invention preferably further contains a cyclic carbonate and a chain carbonate.

[0030] The non-aqueous electrolyte of the present invention preferably further contains a lithium salt, and the lithium salt is LiPF 6 It is preferable that:

[0031] The present invention also provides positive electrode, negative electrode, The present invention also relates to a lithium secondary battery comprising the non-aqueous electrolyte of the present invention disposed between the positive electrode and the negative electrode.

[0032] The positive electrode preferably comprises a nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminium (NCA) ternary material.

[0033] The negative electrode preferably contains a material containing silicon.

[0034] The initial capacity density per positive electrode is preferably 185 mAh / g or more. Effect of the Invention

[0035] According to the present invention, by using a compound containing 5 to 20 mass % of nitrogen atoms and 25 to 70 mass % of sulfur atoms or oxygen atoms in the molecule and having no disulfide bonds in the molecule as an additive for a nonaqueous electrolyte solution, it is possible to make it difficult for acid to be generated even when water is mixed into a lithium secondary battery, and therefore it is possible to suppress deterioration of battery characteristics even under high temperature conditions and to provide an electrolyte solution having an excellent cycle life. [Brief description of the drawings]

[0036] [Figure 1] 1 shows a graph showing the relationship between the number of cycles and the capacity, obtained from the results of charge-discharge cycle tests of Examples 1 and 2 and Comparative Example 1. [Diagram 2] 1 shows a graph showing the relationship between the number of cycles and the capacity, obtained from the results of the charge-discharge cycle tests of Examples 3 and 4 and Comparative Example 1. [Diagram 3] 1 shows a graph showing the relationship between the number of cycles and the capacity, obtained from the results of the charge-discharge cycle tests of Examples 5 and 6 and Comparative Example 1. [Figure 4] 1 shows a graph showing the relationship between the number of cycles and the capacity, obtained from the results of the charge-discharge cycle tests of Examples 7 and 8, and Comparative Example 1. [Diagram 5] 1 shows a graph showing the relationship between the shelf life and the capacity obtained from the results of the high-temperature storage tests of Examples 3 and 4 and Comparative Example 1. [Figure 6]1 shows a graph showing the relationship between the shelf life and the capacity obtained from the results of the high-temperature storage tests of Examples 5 and 6 and Comparative Example 1. [Figure 7] 1 shows a graph showing the relationship between the shelf life and the capacity obtained from the results of the high-temperature storage tests of Examples 7 and 8, and Comparative Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0037] The nonaqueous electrolyte of the present invention contains, as an additive, a compound that contains 5 to 20 mass % of nitrogen atoms and 25 to 70 mass % of sulfur atoms or oxygen atoms in the molecule and has no disulfide bonds in the molecule.

[0038] The compound as an additive contained in the nonaqueous electrolyte of the present invention may be a compound containing 5 to 20 mass% of nitrogen atoms and 25 to 70 mass% of sulfur atoms in the molecule and having no disulfide bonds in the molecule, or a compound containing 5 to 20 mass% of nitrogen atoms and 25 to 70 mass% of oxygen atoms in the molecule and having no disulfide bonds in the molecule. A compound containing 5 to 20 mass% of nitrogen atoms and 25 to 70 mass% of sulfur atoms in the molecule and having no disulfide bonds in the molecule is preferred.

[0039] The mass ratio of nitrogen atoms to sulfur atoms or oxygen atoms in the molecule of the above compound is not particularly limited, but is preferably 5:1 to 1:10, more preferably 2:1 to 1:8, and most preferably 1:1 to 1:6.

[0040] The above compounds contain two or more sulfur atoms or oxygen atoms in the molecule, and may contain two or more sulfur atoms or two or more oxygen atoms in the molecule. It is preferable that the compound contains two or more sulfur atoms in the molecule.

[0041] In one embodiment, the compound contained as an additive in the nonaqueous electrolyte solution of the present invention may include compounds represented by the following chemical formulas 1 to 3, either alone or in combination of two or more of them.

[0042] [ka]

[0043] (In the formula, R 1 is an alkyl group having 1 to 18 carbon atoms or a phenyl group, R 2 is an alkyl group having 1 to 18 carbon atoms or a phenyl group, R 3 is an alkyl group having 1 to 18 carbon atoms or a phenyl group, R 4 is an alkyl group having 1 to 18 carbon atoms or a phenyl group, R 5 is an alkylene group having 1 to 12 carbon atoms.

[0044] [ka]

[0045] (In the formula, R 6 is hydrogen, an alkyl group having 1 to 18 carbon atoms, or -SR 8 and R 7 is hydrogen, an alkyl group having 1 to 18 carbon atoms, or -SR 9 In this case, R 8 and R 9 are each independently a hydrogen atom or an alkyl group having 1 to 18 carbon atoms.

[0046] [ka]

[0047] (In the formula, R 10 is hydrogen, an alkyl group having 1 to 18 carbon atoms, or -SR 13 and R 11 is hydrogen, an alkyl group having 1 to 18 carbon atoms, or -SR 14 In this case, R 13 and R 14are each independently a hydrogen atom or an alkyl group having 1 to 18 carbon atoms; R 12 Ha-SR 15 Or -N(R 16 )(R 17 ) and R 15 is hydrogen, an alkyl group having 1 to 18 carbon atoms, or -SR 18 In this case, R 18 is hydrogen or an alkyl group having 1 to 18 carbon atoms, and R 16 and R 17 are each independently a substituted or unsubstituted alkyl group having 1 to 18 carbon atoms.

[0048] In the above formula 1, R 1 R is preferably an alkyl group having 1 to 18 carbon atoms, and more preferably an alkyl group having 2 to 12 carbon atoms. 2 R is preferably an alkyl group having 1 to 18 carbon atoms, and more preferably an alkyl group having 2 to 12 carbon atoms. 3 R is preferably an alkyl group having 1 to 18 carbon atoms, and more preferably an alkyl group having 2 to 12 carbon atoms. 4 is preferably an alkyl group having 1 to 18 carbon atoms, and more preferably an alkyl group having 2 to 12 carbon atoms. 1 From R 4 are preferably identical to each other.

[0049] In the above formula 1, R 5 is preferably an alkylene group having 1 to 6 carbon atoms, and more preferably an alkylene group having 1 to 3 carbon atoms.

[0050] In the above formula 2, R 6 is hydrogen, an alkyl group having 1 to 18 carbon atoms, or -SR 8 (At this time, R 8 R is preferably hydrogen or an alkyl group having 1 to 18 carbon atoms, and more preferably hydrogen, an alkyl group having 2 to 12 carbon atoms, -SH, or an alkylthio group having 2 to 12 carbon atoms. 7 is hydrogen, an alkyl group having 1 to 18 carbon atoms, or -SR 9 (At this time, R9 is preferably hydrogen or an alkyl group having 1 to 18 carbon atoms, and more preferably hydrogen, an alkyl group having 2 to 12 carbon atoms, -SH, or an alkylthio group having 2 to 12 carbon atoms.

[0051] In the above formula 3, R 10 is hydrogen, an alkyl group having 1 to 18 carbon atoms, or -SR 13 (At this time, R 13 R is preferably hydrogen or an alkyl group having 1 to 18 carbon atoms, and more preferably hydrogen, an alkyl group having 2 to 12 carbon atoms, -SH, or an alkylthio group having 2 to 12 carbon atoms. 11 is hydrogen, an alkyl group having 1 to 18 carbon atoms, or -SR 14 (At this time, R 14 R is preferably hydrogen or an alkyl group having 1 to 18 carbon atoms, and more preferably hydrogen, an alkyl group having 2 to 12 carbon atoms, -SH, or an alkylthio group having 2 to 12 carbon atoms. 12 Ha-SR 15 Or -N(R 16 )(R 17 ) and then R 15 is hydrogen, an alkyl group having 1 to 18 carbon atoms, or -SR 18 In this case, R 18 is hydrogen or an alkyl group having 1 to 18 carbon atoms, and R 16 and R 17 are preferably each independently a substituted or unsubstituted alkyl group having 1 to 18 carbon atoms, and more preferably a thio group, an alkylthio group having 2 to 12 carbon atoms, a dialkylamino group having 2 to 12 carbon atoms, or a diallylalkylamino group having 2 to 12 carbon atoms.

[0052] Examples of the compound represented by the above chemical formula 1 include methylene bis(diethylthiocarbamate), ethylene bis(diethyldithiocarbamate), methylene bis(dipropylthiocarbamate), ethylene bis(dipropyldithiocarbamate), methylene bis(dibutyldithiocarbamate), ethylene bis(dibutyldithiocarbamate), methylene bis(dipentyldithiocarbamate), ethylene bis(dipentyldithiocarbamate), methylene bis(dihexyldithiocarbamate), and ethylene bis(dihexyldithiocarbamate).

[0053] In one embodiment, the compound contained as an additive in the nonaqueous electrolyte solution of the present invention is preferably a thiadiazole compound represented by the above chemical formula 2. The thiadiazole compound represented by the above chemical formula 2 is preferably 2,5-dimercapto-1,3,4-thiadiazole or a derivative thereof, such as 2-hydrocarbyldithio-5-mercapto-1,3,4-thiadiazole and 2,5-bis-(hydrocarbyldithio)-1,3,4-thiadiazole.

[0054] Preferably, the compound contained as an additive in the nonaqueous electrolyte of the present invention is methylene bis(dibutyldithiocarbamate) or 2,5-dimercapto-1,3,4-thiadiazole.

[0055] In addition, examples of the triazine-based compound represented by the above chemical formula 3 include 1,3,5-triazine-2,4,6-trithiol, 2-(dibutylamino)-1,3,5-triazine-4,6-dithiol, 6-(diisopropylamino)-1,3,5-triazine-2,4-dithiol, and 6-(diisopropylamino)-1,3,5-triazine-2,4-dithiol. Examples of the thiolamine include 6-(diisobutylamino)-1,3,5-triazine-2,4-dithiol, 6-diallylamino-1,3,5-triazine-2,4-dithiol, and 6-di(2-ethylhexyl)amino-1,3,5-triazine-2,4-dithiol.

[0056] The compound as an additive contained in the nonaqueous electrolyte according to an embodiment of the present invention may include a compound represented by Formula 1, a compound represented by Formula 3, or two or more thereof.

[0057] The compound represented by the above chemical formula 1 has better electrolyte stability (acid content reduction effect) than the compound represented by the above chemical formula 2, and the compound represented by the above chemical formula 3 may be more advantageous than the compound represented by the above chemical formula 2 because of ease of synthesis and introduction of substituents.

[0058] The compounds include methylene bis(diethylthiocarbamate), ethylene bis(diethyldithiocarbamate), methylene bis(dipropylthiocarbamate), ethylene bis(dipropyldithiocarbamate), methylene bis(dibutyldithiocarbamate), ethylene bis(dibutyldithiocarbamate), methylene bis(dipentyldithiocarbamate), ethylene bis(dipentyldithiocarbamate), methylene bis(dihexyldithiocarbamate), and ethylene bis(dihexyldithiocarbamate). 1,3,5-triazine-2,4,6-trithiol, 2-(dibutylamino)-1,3,5-triazine-4,6-dithiol, 6-(diisopropylamino)-1,3,5-triazine-2,4-dithiol, 6-(diisobutylamino)-1,3,5-triazine-2,4-dithiol, 6-diallylamino-1,3,5-triazine-2,4-dithiol, 6-di(2-ethylhexyl)amino-1,3,5-triazine-2,4-dithiol, or two or more thereof.

[0059] The compound as an additive contained in the nonaqueous electrolyte of the present invention is preferably contained in an amount of 0.1 to 1 mass % based on the total mass of the nonaqueous electrolyte, more preferably contained in an amount of 0.2 to 0.9 mass %, and most preferably contained in an amount of 0.3 to 0.8 mass %. By containing the compound as an additive in an amount within the above range, the acid generation reaction in the battery can be effectively suppressed.

[0060] The compound contained in the nonaqueous electrolyte solution of the present invention as an additive may be used alone or in combination of two or more compounds. When two or more compounds are used, the total amount is preferably within the above range.

[0061] The non-aqueous electrolyte of the present invention preferably further contains an organic solvent such as a cyclic carbonate, a chain carbonate, an ether compound, an ester compound, and an amide compound. These organic solvents may be used alone or in combination. Preferably, the non-aqueous electrolyte of the present invention contains a cyclic carbonate and a chain carbonate as an organic solvent.

[0062] Examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate (VC), methylvinylene carbonate, ethylvinylene carbonate, 1,2-diethylvinylene carbonate, vinylethylene carbonate (VEC), 1-methyl-2-vinylethylene carbonate, 1-ethyl-2-vinylethylene carbonate, 1-methyl-2-vinylethylene carbonate, and 1,1-divinylethylene carbonate. Examples of the carbonate include ethylene carbonate, 1,2-divinylethylene carbonate, 1,1-dimethyl-2-methyleneethylene carbonate, 1,1-diethyl-2-methyleneethylene carbonate, ethynylethylene carbonate, 1,2-diethynylethylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, chloroethylene carbonate, and combinations thereof. Examples of the chain carbonate include dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), methyl isopropyl carbonate, methyl butyl carbonate, diethyl carbonate (DEC), ethyl propyl carbonate, ethyl butyl carbonate, dipropyl carbonate, propyl butyl carbonate, and combinations thereof.

[0063] The cyclic carbonate can also include the cyclic carbonate containing fluorine atom.The cyclic carbonate containing fluorine atom can include fluorovinylene carbonate, trifluoromethylvinylene carbonate, fluoroethylene carbonate, 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate, 4-fluoro-1,3-dioxolan-2-one, trans or cis-4,5-difluoro-1,3-dioxolan-2-one, 4-ethynyl-1,3-dioxolan-2-one, and combinations thereof.

[0064] In particular, among carbonates, the cyclic carbonates ethylene carbonate and propylene carbonate are suitable for use because they are high-viscosity organic solvents with high dielectric constants and can easily dissociate the lithium salt in the electrolyte. It is preferable to mix such cyclic carbonates with chain carbonates having low viscosity and low dielectric constants, such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, in an appropriate ratio, so that an electrolyte solution having high electrical conductivity can be prepared.

[0065] The non-aqueous electrolyte of the present invention may further include an ether compound such as a cyclic ether or a chain ether. Examples of the cyclic ether include tetrahydrofuran and 2-methyltetrahydrofuran. The non-aqueous electrolyte of the present invention may further include a chain ether. Examples of the chain ether include dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, and ethyl propyl ether.

[0066] The non-aqueous electrolyte of the present invention may further contain an ester compound such as a carboxylate. Examples of the carboxylate include methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, methyl valerate, ethyl valerate, propyl valerate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, ε-caprolactone, compounds in which a portion of the hydrogen of these carboxylates is replaced with fluorine, and combinations thereof.

[0067] In addition to the above, the nonaqueous electrolyte of the present invention may contain other solvents, such as polyethers, sulfur-containing solvents, and phosphorus-containing solvents, without particular limitation, as long as the object of the present invention is not impaired.

[0068] The nonaqueous electrolyte solution of the present invention may contain a mixture of a cyclic carbonate and a chain carbonate, and the volume ratio of the cyclic carbonate to the chain carbonate is preferably 1:9 to 9:1, and more preferably 2:8 to 8:2.

[0069] The non-aqueous electrolyte of the present invention may contain an electrolyte generally used in a secondary battery. The electrolyte acts as a medium for transporting ions involved in an electrochemical reaction in a secondary battery. In particular, the present invention is useful as an electrolyte for a lithium secondary battery, and in this case, the electrolyte contains a lithium salt.

[0070] The lithium salt contained in the nonaqueous electrolyte of the present invention is, for example, LiPF 6 , LiBF 4 , LiB 12 F 12 , LiAsF 6 , LiFSO 3 , Li 2 SiF 6 , LiCF 3 CO 2 , LiCH 3 CO 2 , LiCF 3 SO3 、LiC 4 F 9 SO 3 、LiCF 3 CF 2 SO 3 、LiCF 3 (CF 2 ) 7 SO 3 、LiCF 3 CF 2 (CF 3 ) 2 CO、Li(CF 3 SO 2 ) 2 CH, LiNO 3 、LiN(CN) 2 、LiN(FSO 2 ) 2 、LiN(F 2 SO 2 ) 2 、LiN(CF 3 SO 2 ) 2 、LiN(C 2 F 5 SO 2 ) 2 、LiC(CF 3 SO 2 ) 3 、LiP(CF 3 ) 6 、LiPF(CF 3 ) 5 、LiPF 2 (CF 3 ) 4 、LiPF 3 (CF 3 ) 3 、LiPF 4 (CF 3 ) 2 、LiPF 4 (C 2 F 5 ) 2 、LiPF 4 (CF 3 SO 2 ) 2 、LiPF 4 (C 2 F 5 SO 2 ) 2 、LiBF 2 C2 O 4 , LiBC 4 O 8 , LiBF 2 (CF 3 ) 2 , LiBF 2 (C 2 F 5 ) 2 , LiBF 2 (CF 3 SO 2 ) 2 , LiBF 2 (C 2 F 5 SO 2 ) 2 , LiSbF 6 , LiAlO 4 , LiAlF 4 , LiSCN, LiClO 4 , LiCl, LiF, LiBr, LiI, LiAlCl 4 In particular, LiPF 6 , LiBF 4 , LiAsF 6 , and LiClO 4 and inorganic salts such as LiPF 6 The lithium salt may be used alone or in combination of two or more kinds.

[0071] The content of the electrolyte is not particularly limited, but is preferably 0.1 mol / L to 5 mol / L or less, more preferably 0.5 mol / L to 3 mol / L or less, and more preferably 0.5 mol / L to 2 mol / L or less, based on the total mass of the non-aqueous electrolyte. By setting the amount of the electrolyte within the above range, sufficient battery characteristics can be obtained.

[0072] The non-aqueous electrolyte of the present invention may contain at least one additional additive, such as a flame retardant, a wetting agent, a stabilizer, a corrosion inhibitor, a gelling agent, an overcharge inhibitor, and a negative electrode film-forming additive.

[0073] The present invention also provides positive electrode, negative electrode, The present invention also relates to a lithium secondary battery comprising the non-aqueous electrolyte of the present invention disposed between the positive electrode and the negative electrode.

[0074] The lithium battery containing the non-aqueous electrolyte solution of the present invention can be constructed by using any positive and negative electrodes that can be used in known lithium secondary batteries without any restrictions, and housing them in a container together with the non-aqueous electrolyte solution of the present invention. A separator can also be interposed between the positive and negative electrodes.

[0075] The positive electrode used in the lithium secondary battery of the present invention can be produced, for example, by coating a positive electrode current collector with a positive electrode slurry containing a positive electrode active material, a binder, a conductive material, a solvent, etc., followed by drying and rolling.

[0076] The positive electrode current collector is not particularly limited as long as it does not induce a chemical change in the lithium secondary battery of the present invention and has conductivity. For example, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel whose surface has been surface-treated with carbon, nickel, titanium, silver, or the like can be used.

[0077] The positive electrode active material is a compound capable of reversibly absorbing and releasing lithium, and may specifically include a lithium composite metal oxide containing lithium and one or more metals such as cobalt, manganese, nickel, or aluminum. More specifically, the lithium composite metal oxide may be a lithium-manganese-based oxide (e.g., LiMnO 2 , LiMn 2 O 4 ), lithium-cobalt oxides (e.g., LiCoO 2 etc.), lithium-nickel oxides (e.g., LiNiO 2 etc.), lithium-nickel-manganese oxides (e.g., LiNi 1-y1 Mn y1 O 2 (where 0 <y1<1)、LiMn 2-z1 Ni z O 4(Here, 0 < Z1 < 2), etc., lithium-nickel-cobalt-based oxide (e.g., LiNi 1-y2 Co y2 O 2 (Here, 0 < y2 < 1), etc., lithium-manganese-cobalt-based oxide (e.g., LiCo 1-y3 Mn y3 O 2 (Here, 0 < y3 < 1), LiMn 2-z2 Co z2 O 4 (Here, 0 < Z2 < 2), etc., lithium-nickel-manganese-cobalt-based oxide (e.g., Li(Ni p1 Co q1 Mn r1 )O 2 (Here, 0 < p1 < 1, 0 < q1 < 1, 0 < r1 < 1, p1 + q1 + r1 = 1), or Li(Ni p2 Co q2 Mn r2 )O 4 (Here, 0 < p2 < 2, 0 < q2 < 2, 0 < r2 < 2, p2 + q2 + r2 = 2), etc., or lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni p3 Co q3 Mn r3 M S3 )O 2 (Here, M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p3, q3, r3, and s3 are atomic fractions of independent elements, where 0 < p3 < 1, 0 < q3 < 1, 0 < r3 < 1, 0 < s3 < 1, and p3 + q3 + r3 + s3 = 1), etc., and these may be included alone or two or more of them may be included.

[0078] Preferably, from the viewpoint of being able to improve the capacity characteristics and stability of the battery, the lithium composite metal oxide is preferably a lithium composite metal oxide containing a nickel-containing metal and lithium. Specifically, lithium-nickel-based oxide (e.g., LiNiO 2 etc.), lithium-nickel-manganese-cobalt oxide (e.g., Li(Ni 0.6 Mn 0.2 Co0.2 )O 2 , Li(Ni 0.5 Mn 0.3 Co 0.2 )O 2 , or Li(Ni 0.8 Mn 0.1 Co 0.1 )O 2 etc.), or lithium-nickel-cobalt-aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 Al 0.05 )O 2 In particular, it is preferable to use nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) ternary materials such as lithium-nickel-manganese-cobalt oxide or lithium-nickel-cobalt-aluminum oxide from the viewpoint of cost.

[0079] The positive electrode active material is preferably contained in an amount of 80 to 99% by mass based on the total mass of the solid content in the positive electrode slurry. By setting the content of the positive electrode active material within the above range, high energy density and capacity can be obtained.

[0080] The binder is a component that aids in bonding the positive electrode active material to the conductive material and the current collector, and is preferably contained in an amount of 1 to 30% by mass based on the total mass of the solid content in the positive electrode slurry. Examples of the binder include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluororubber.

[0081] The conductive material is a substance that imparts electrical conductivity to the lithium secondary battery of the present invention without inducing chemical changes, and is preferably contained in an amount of 0.5 to 50 mass %, more preferably 1 to 20 mass %, based on the total mass of the solid content in the positive electrode slurry. By containing the conductive material in the above range, electrical conductivity is improved, and high energy density and capacity can be obtained.

[0082] Examples of conductive materials include carbon powders such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; graphite powders such as natural graphite, artificial graphite, and graphite with a developed crystal structure; conductive fibers such as carbon fiber and metal fiber; metal powders such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0083] The solvent is not limited as long as it can make the positive electrode active material, binder, conductive material, etc. into a slurry as the positive electrode material, and for example, organic solvents such as NMP (N-methyl-2-pyrrolidone), DMF (dimethylformamide), acetone, dimethylacetamide, water, etc. can be used. In addition, it can be used in an amount that gives the positive electrode slurry a suitable viscosity, for example, in an amount that gives the slurry a solid content concentration of 10% by mass to 60% by mass, preferably 20% by mass to 50% by mass.

[0084] The negative electrode used in the lithium secondary battery of the present invention can be manufactured, for example, by coating a negative electrode current collector with a negative electrode slurry containing a negative electrode active material, a binder, a conductive material, a solvent, etc., followed by drying and rolling.

[0085] The negative electrode current collector generally has a thickness of 3 to 500 μm. The negative electrode current collector is not particularly limited as long as it does not induce a chemical change in the lithium secondary battery of the present invention and has high conductivity, and for example, copper, stainless steel, aluminum, nickel, titanium, baked carbon, copper or stainless steel surface treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, as with the positive electrode current collector, the binding force of the negative electrode active material may be strengthened by forming fine irregularities on the surface, and it may be used in various forms such as a film, sheet, foil, net, porous body, foam, and nonwoven fabric.

[0086] The negative electrode active material may include at least one selected from the group consisting of lithium metal, a carbon material capable of reversibly absorbing and releasing lithium ions, a metal or an alloy of such a metal and lithium, a metal composite oxide, a material capable of doping and dedoping lithium, and a transition metal oxide.

[0087] The carbonaceous material capable of reversibly absorbing and releasing lithium ions can be any carbonaceous negative electrode active material commonly used in lithium secondary batteries, and can be, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of crystalline carbon include graphite such as amorphous, plate-like, scaly (flake)-like, spherical, or fibrous natural graphite and artificial graphite. Examples of amorphous carbon include soft carbon (low-temperature calcined carbon) or hard carbon, mesophase pitch carbide, and calcined coke.

[0088] As the metal or the alloy of these metals and lithium, a metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn, or an alloy of these metals and lithium can be used.

[0089] Metal composite oxides include PbO, PbO 2 , Pb 2 O3 , Pb 3 O 4 , Sb 2 O 3 , Sb 2 O 4 , Sb 2 O 5 , GeO, GeO 2 , Bi 2 O 3 , Bi 2 O 4 , Bi 2 O 5 , Li x , Fe 2 O 3 (0 ≦ x ≦ 1), Li x , WO 2 (0 ≦ x ≦ 1), and Sn x , Me 1-x , Me’ y O z (Me: Mn, Fe, Pb, Ge; Me’: Al, B, P, Si, elements of Group 1, Group 2, Group 3 of the periodic table, halogen; 0 < x ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8) selected from the group consisting of can be used.

[0090] Substances that can dope and undope lithium include Si, SiO x (0 < x < 2), Si - Y alloy (where Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, and is not Si), Sn, SnO 2 , Sn - Y (where Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, and is not Sn), etc., and at least one of these and SiO 2They may be used in combination. As the element Y, it may be selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

[0091] Examples of the transition metal oxide include lithium-containing titanium composite oxide (LTO), vanadium oxide, lithium vanadate, and the like.

[0092] As the negative electrode active material of the lithium secondary battery of the present invention, it is preferable to use a material containing silicon, for example, Si, SiO x (0 < x < 2), Si-Y alloy (where Y is an element selected from the group consisting of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a transition metal, a rare earth element, and combinations thereof, and is not Si), and at least one of these and SiO 2 and a mixture thereof can be used. In particular, it is more preferable to use SiO.

[0093] The negative electrode active material is preferably contained in an amount of 80 to 99% by mass based on the total mass of the solid content in the negative electrode slurry.

[0094] The binder is a component that helps bind the conductive material, the negative electrode active material, and the current collector, and is preferably contained in an amount of 1 to 30% by mass based on the total mass of the solid content in the negative electrode slurry. Examples of the binder include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluororubber, etc.

[0095] The conductive material is a component for further improving the conductivity of the negative electrode active material, and is preferably contained in an amount of 1 to 20 mass% based on the total mass of the solid content in the negative electrode slurry. The conductive material is not particularly limited as long as it has conductivity without inducing a chemical change in the lithium secondary battery, and examples thereof include graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; metal powders such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0096] The solvent is not limited as long as it can make the negative electrode active material, binder, conductive material, etc. into a slurry state as the negative electrode material, and for example, water, organic solvents such as NMP and alcohol can be used. Also, it can be used in an amount that gives the negative electrode slurry a suitable viscosity, for example, in an amount that gives the slurry a solid content concentration of 50% by mass to 75% by mass, preferably 50% by mass to 65% by mass.

[0097] The separator of the lithium secondary battery of the present invention serves to block internal short circuits between the two electrodes and to impregnate the electrolyte. The separator composition may be prepared by mixing a polymer resin, a filler, and a solvent to prepare a separator composition, and then the separator composition may be directly coated on the upper part of an electrode and dried to form a separator film, or the separator composition may be cast on a support and dried, and then the separator film peeled off from the support is laminated on the upper part of an electrode to form a separator film.

[0098] As the separator, a typical porous polymer film conventionally used as a separator, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, may be used alone or in a laminate thereof, or a typical porous nonwoven fabric such as a nonwoven fabric made of a high melting point glass fiber or a polyethylene terephthalate fiber may be used, but is not limited thereto.

[0099] The pore size of the porous separator may generally be 0.01 to 50 μm, and the porosity may be 5 to 95%, and the thickness of the porous separator may generally be in the range of 5 to 300 μm.

[0100] The charging voltage of the lithium secondary battery of the present invention is preferably 4.0 V or higher, and more preferably 4.1 V or higher. The positive electrode potential of the lithium secondary battery of the present invention when fully charged is preferably 4.0 V or higher.

[0101] In addition, the initial capacity density per positive electrode of the lithium secondary battery of the present invention is preferably 185 mAh / g or more.

[0102] The external shape of the lithium secondary battery of the present invention is not particularly limited, and may be cylindrical, rectangular, pouch-shaped, coin-shaped, or the like. EXAMPLES

[0103] The present invention will be described in more detail below using examples and comparative examples, but the scope of the present invention is not limited to the examples.

[0104] Example 1 <Production of positive electrodes> A nickel-cobalt-manganese (NCM) ternary material (Li(Ni 0.8 Mn 0.1 Co 0.1 )O 2A positive electrode slurry was prepared by dispersing 96.5 parts by mass of the above, 1.5 parts by mass of acetylene black as a conductive material, and 2 parts by mass of polyvinylidene fluoride as a binder in the above. The positive electrode slurry thus prepared was uniformly applied onto an aluminum foil, heated and vacuum dried, and then pressed to produce a positive electrode.

[0105] <Production of negative electrodes> A negative electrode slurry was prepared by dispersing 96 parts by mass of a 9:1 mixture of graphite and SiO as a negative electrode active material, 1.0 part by mass of acetylene black as a conductive material, and 3.0 parts by mass of styrene-butadiene rubber and carboxymethyl cellulose as a binder in water. The prepared negative electrode slurry was uniformly applied onto copper foil, heated and vacuum dried, and then pressed to produce a negative electrode.

[0106] <Production of non-aqueous electrolyte> A solvent containing 30 parts by volume of ethylene carbonate (EC) and 70 parts by volume of ethyl methyl carbonate (EMC) was used, and LiPF 6 A solution was prepared by dissolving the above to a salt concentration of 1 M. To 100 parts by mass of the obtained solution, 0.5 parts by mass of methylene bis(dibutyldithiocarbamate) (A1) (manufactured by Sanyo Chemical Industries, Ltd.) and 0.5 parts by mass of vinylene carbonate were added to obtain a nonaqueous electrolyte solution of the present invention.

[0107] <Manufacturing lithium secondary batteries> The positive and negative electrodes and non-aqueous electrolyte prepared by the above method were used, and a polyolefin film was used as a separator to form a 12 cm 2 A pouch-type battery was fabricated.

[0108] Example 2 A nonaqueous electrolyte solution and a lithium secondary battery containing the same were prepared in the same manner as in Example 1, except that 2,5-dimercapto-1,3,4-thiadiazole (manufactured by Sanyo Chemical Industries, Ltd.) (A2) was added to the nonaqueous electrolyte solution instead of methylene bis(dibutyldithiocarbamate).

[0109] Example 3 A nonaqueous electrolyte solution and a lithium secondary battery containing the same were produced in the same manner as in Example 1, except that 1,3,5-triazine-2,4,6-trithiol (manufactured by Sanyo Chemical Industries, Ltd.) (A3) was added to the nonaqueous electrolyte solution instead of methylene bis(dibutyldithiocarbamate).

[0110] Example 4 A nonaqueous electrolyte solution and a lithium secondary battery containing the same were prepared in the same manner as in Example 1, except that 2-(dibutylamino)-1,3,5-triazine-4,6-dithiol (manufactured by Sanyo Chemical Industries, Ltd.) (A4) was added to the nonaqueous electrolyte solution instead of methylene bis(dibutyldithiocarbamate).

[0111] Example 5 A nonaqueous electrolyte solution and a lithium secondary battery containing the same were prepared in the same manner as in Example 1, except that 6-(diisopropylamino)-1,3,5-triazine-2,4-dithiol (manufactured by Sanyo Chemical Industries, Ltd.) (A5) was added to the nonaqueous electrolyte solution instead of methylene bis(dibutyldithiocarbamate).

[0112] Example 6 A nonaqueous electrolyte solution and a lithium secondary battery containing the same were produced in the same manner as in Example 1, except that 6-(diisobutylamino)-1,3,5-triazine-2,4-dithiol (manufactured by Sanyo Chemical Industries, Ltd.) (A6) was added to the nonaqueous electrolyte solution instead of methylene bis(dibutyldithiocarbamate).

[0113] Example 7 A nonaqueous electrolyte solution and a lithium secondary battery containing the same were produced in the same manner as in Example 1, except that 6-diallylamino-1,3,5-triazine-2,4-dithiol (manufactured by Sanyo Chemical Industries, Ltd.) (A7) was added to the nonaqueous electrolyte solution instead of methylene bis(dibutyldithiocarbamate).

[0114] Example 8 A nonaqueous electrolyte solution and a lithium secondary battery containing the same were produced in the same manner as in Example 1, except that 6-di(2-ethylhexyl)amino-1,3,5-triazine-2,4-dithiol (manufactured by Sanyo Chemical Industries, Ltd.) (A8) was added to the nonaqueous electrolyte solution instead of methylene bis(dibutyldithiocarbamate).

[0115] Comparative Example 1 A non-aqueous electrolyte solution and a lithium secondary battery containing the same were produced in the same manner as in Example 1, except that methylene bis(dibutyldithiocarbamate) was not added to the non-aqueous electrolyte solution.

[0116] Evaluation of non-aqueous electrolytes and lithium secondary batteries (1) Acid content measurement The electrolytes of Examples 1 and 2 were measured for acid content before and after storage at 60° C. for one week, and the results are shown in Table 1. The acid content was measured by adding 10 g of electrolyte sample to 100 g of pure water, neutralizing titration was performed using 0.1 mol / L NaOH reagent, and the concentration was calculated on the assumption that all the acid generated was HF (hydrogen fluoride).

[0117] [Table 1]

[0118] As can be seen from the results in Table 1, the amount of acid generated was suppressed in Examples 1 and 2, which used an electrolyte solution containing methylene bis(dibutyldithiocarbamate) or 2,5-dimercapto-1,3,4-thiadiazole as the non-aqueous electrolyte solution. In particular, in Example 1, which used methylene bis(dibutyldithiocarbamate), the acid content was greatly reduced after storage, demonstrating the effect of reducing the acid content.

[0119] (2) Charge / discharge cycle test Using the lithium secondary batteries manufactured in Examples 1 to 8 and Comparative Example 1, charge / discharge cycle tests were performed at 45° C. with a constant current of 0.5 C, a charge upper limit voltage of 4.20 V, and a discharge lower limit voltage of 2.50 V. However, in order to confirm the accurate capacity at the 50th, 100th, and 200th cycles, the tests were performed using a constant current of 0.1 C.

[0120] Graphs showing the relationship between the number of cycles and the capacity obtained from the above test are shown in Figures 1 to 4. In Figure 1, there is a large difference between Examples 1 and 2 and Comparative Example 1 in terms of capacity retention from a relatively early stage, and in the case of Comparative Example 1 in which no additive was added to the non-aqueous electrolyte, the capacity was significantly reduced. On the other hand, in the cases of Examples 1 and 2 in which the non-aqueous electrolyte contains bis(dibutyldithiocarbamate)methylene (A1) or 2,5-dimercapto-1,3,4-thiadiazole (A2), it was found that the capacity was retained for a long period of time. 2 to 4, in the case of Comparative Example 1 in which no additive was added to the nonaqueous electrolyte solution, the capacity was significantly reduced, whereas in the cases of Examples 3 to 8 in which the nonaqueous electrolyte solution contained 1,3,5-triazine-2,4,6-trithiol, 2-(dibutylamino)-1,3,5-triazine-4,6-dithiol, 6-(diisopropylamino)-1,3,5-triazine-2,4-dithiol, 6-(diisobutylamino)-1,3,5-triazine-2,4-dithiol, 6-diallylamino-1,3,5-triazine-2,4-dithiol, and 6-di(2-ethylhexyl)amino-1,3,5-triazine-2,4-dithiol, respectively, the capacity was maintained for a long period of time.

[0121] (3) 60℃ storage test The lithium secondary batteries manufactured in Examples 3 to 8 and Comparative Example 1 were used, and the discharge capacity was confirmed by setting the upper limit charge voltage to 4.2 V and the lower limit discharge voltage to 2.50 V at a constant current of 0.5 C at 25° C., and the upper limit charge voltage was set to 4.35 V at a constant current of 0.5 C, and the batteries were stored in an oven at 60° C. in a fully charged state, and the remaining capacity of the lithium secondary batteries was measured after 2 weeks and 4 weeks to evaluate the degree of deterioration. Graphs showing the relationship between the number of cycles and capacity obtained as a result of the test are shown in Figures 5 to 7.

[0122] In Figures 5 to 7, the drop in capacity immediately after 2 weeks and 4 weeks is the "remaining capacity." The reason why the 2-week remaining capacity rises again is because the battery was charged again at 4.2 V. In other words, the 4-week remaining capacity is the capacity after measuring the 2-week remaining capacity, charging again at 4.2 V, and then storing the battery at 60°C for 2 weeks. [Industrial Applicability]

[0123] The non-aqueous electrolyte solution of the present invention is useful because it can suppress the generation of acid and thereby retain capacity even under high temperature conditions and after repeated charge and discharge cycles.

Claims

1. positive electrode, negative electrode, A lithium secondary battery comprising a non-aqueous electrolyte solution disposed between the positive electrode and the negative electrode, the positive electrode comprises a nickel-containing material; the negative electrode comprises a material containing silicon; the nonaqueous electrolyte solution contains a compound that does not have a disulfide bond in its molecule, The compound includes a compound represented by the following chemical formula 1. 【Chemistry 1】 (In the formula, R １ is an alkyl group having 1 to 18 carbon atoms or a phenyl group, R ２ is an alkyl group having 1 to 18 carbon atoms or a phenyl group, R ３ is an alkyl group having 1 to 18 carbon atoms or a phenyl group, R ４ is an alkyl group having 1 to 18 carbon atoms or a phenyl group, R ５ is an alkylene group having 1 to 12 carbon atoms.

2. 2. The lithium secondary battery of claim 1, wherein the compound comprises methylene bis(diethylthiocarbamate), ethylene bis(diethyldithiocarbamate), methylene bis(dipropylthiocarbamate), ethylene bis(dipropyldithiocarbamate), methylene bis(dibutyldithiocarbamate), ethylene bis(dibutyldithiocarbamate), methylene bis(dipentyldithiocarbamate), ethylene bis(dipentyldithiocarbamate), methylene bis(dihexyldithiocarbamate), ethylene bis(dihexyldithiocarbamate), or two or more thereof.

3. 2. The lithium secondary battery according to claim 1, wherein the compound is contained in an amount of 0.1 to 1% by mass based on the total mass of the non-aqueous electrolyte solution.

4. The lithium secondary battery according to claim 1 , wherein the non-aqueous electrolyte further contains a cyclic carbonate and a chain carbonate.

5. 2. The lithium secondary battery according to claim 1, wherein the non-aqueous electrolyte further comprises a lithium salt.

6. The lithium salt is LiPF ６ The lithium secondary battery according to claim 5 .

7. 2. The lithium secondary battery of claim 1, wherein the positive electrode comprises a nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) ternary material.

8. 2. The lithium secondary battery according to claim 1, wherein the initial capacity density per positive electrode is 185 mAh / g or more.

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