Acid-reducing or water-reducing agent for non-aqueous electrolyte solution, non-aqueous electrolyte solution comprising same, lithium secondary battery comprising non-aqueous electrolyte solution, and method for reducing acid or moisture in non-aqueous electrolyte solution

Abstract

The present invention provides a non-aqueous electrolyte solution which can reduce the generation of gas by reducing acid and / or moisture even under high-temperature conditions, thereby suppressing the deterioration of battery characteristics. This acid-reducing or water-reducing agent for a non-aqueous electrolyte solution contains a diisocyanate compound represented by formula (1), (2) or (3), and the non-aqueous electrolyte solution contains a cyclic carbonate containing a fluorine atom. # imgabs0 #

Description

Technical Field

[0001] The present invention relates to an acid or water reducing agent for non-aqueous electrolytes, a non-aqueous electrolyte containing the acid or water reducing agent, a lithium secondary battery including the non-aqueous electrolyte, and a method for reducing acid or moisture in a non-aqueous electrolyte.

[0002] This application claims the priority of Japanese Patent Application No. 2022-210485 filed on December 27, 2022, the disclosure of which is incorporated herein by reference. Background Art

[0003] Due to their high energy density and excellent charge and discharge cycle characteristics, lithium secondary batteries are widely used as storage batteries in portable devices (such as mobile phones or laptop computers) and automotive and industrial applications, and their applications are being extended to new industrial fields such as drones.

[0004] Lithium cobalt oxide (LCO) has been used as a positive electrode material for lithium secondary batteries, but recently, the use of materials with a higher nickel mixing ratio has been increasing. Materials with a higher nickel mixing ratio are advantageous not only from the perspective of high energy density but also from the perspective of cost competitiveness because they can reduce the use of cobalt.

[0005] In addition, technologies using silicon-containing materials as negative electrode active materials have been developed. Due to their high theoretical capacity, silicon-containing materials are expected to be used, especially for vehicle applications that require high capacity.

[0006] When using the positive electrode active material and the negative electrode active material as described above, the optimal electrolyte has been studied. The electrolyte undergoes reductive decomposition at the negative electrode, and the decomposition products accumulate on the surface of the negative electrode. In addition, a film (also called a solid electrolyte interface (SEI) layer) derived from the electrolyte components forms on the surface of the negative electrode. In order to effectively form the SEI layer to improve the battery life, electrolytes containing cyclic carbonates containing fluorine atoms have been developed.

[0007] However, when using an electrolyte containing a cyclic carbonate containing a fluorine atom, a large amount of gas is generated in the battery due to the decomposition reaction of the cyclic carbonate containing a fluorine atom. For example, it is known that when using fluoroethylene carbonate (FEC), carbon dioxide is generated due to the oxidative decomposition of FEC on the positive electrode.

[0008] In addition, it is known that the electrolyte deteriorates due to the influence of a small amount of moisture contained in the electrolyte material. For example, when LiPF 6 is used as the electrolyte, the following reaction occurs, and the decomposition of the electrolyte generates acid components.

[0009] LiPF 6 +H 2O → LiF + POF 3 + 2HF

[0010] It is known that acidic substances react with the surface of a silicon-containing negative electrode material or with a film on the surface, resulting in an increase in impedance and deterioration of battery characteristics. In addition, when a nickel-containing material is used as a positive electrode active material, a large amount of alkali remains in the material, which may accelerate the reaction to generate acidic substances. For example, when fluoroethylene carbonate (FEC) is used, FEC decomposes into ethylene carbonate (VC) and hydrofluoric acid (HF). When FEC is consumed by this reaction, the film-forming ability of the silicon-containing negative electrode decreases, and the battery characteristics deteriorate faster. Therefore, although the non-aqueous electrolyte contains a cyclic carbonate having a fluorine atom, a nickel-containing material is used in the positive electrode, and a silicon-containing material is used in the negative electrode, reducing acids and / or moisture holds promise for the development of an electrolyte with excellent characteristics that can suppress gas generation in the battery under high-temperature conditions, thereby suppressing deterioration of battery characteristics.

[0011] Patent Document 1 discloses that when a compound containing an isocyanate group is added to a non-aqueous solvent, the reduction decomposition reaction of the non-aqueous solvent during charging is suppressed. However, Patent Document 1 does not disclose the effects of the compound containing an isocyanate group on acids and moisture, and in particular, does not disclose the effects on acids and moisture when an electrolyte containing a cyclic carbonate having a fluorine atom is used.

[0012] Patent Document 2 discloses adding an isocyanate compound to a non-aqueous solvent, thereby suppressing the reduction decomposition reaction of the electrolyte and suppressing a decrease in surface activation and modification of the active material due to the reaction between the isocyanate group and the Si surface. However, Patent Document 2 does not disclose the effects of the isocyanate compound on acids and moisture.

[0013] Patent Document 3 discloses adding a compound having an isocyanate group to a non-aqueous electrolyte to reduce acids or moisture, thereby improving battery characteristics. However, when developing the solvent of the non-aqueous electrolyte of the battery and the active material of the battery, the structure of the isocyanate compound as the best additive for these materials still poses a challenge.

[0014] [Prior Art Documents]

[0015] [Patent Documents]

[0016] Patent Document 1: Japanese Patent Laid-Open No. 2002-008719

[0017] Patent Document 2: Japanese Patent Laid-Open No. 2022-103379

[0018] Patent Document 3: Japanese Patent Laid-Open No. 2022-102227 Summary of the Invention

[0019] Technical problem

[0020] Therefore, when using a non-aqueous electrolyte containing a cyclic carbonate having a fluorine atom, an acid-reducing and / or water-reducing agent for stabilizing the characteristics of the electrolyte, and an electrolyte having excellent battery characteristics due to a reduction in acid and / or moisture are required.

[0021] The present invention aims to solve the above problems of the prior art. Therefore, the present invention aims to provide an acid-reducing or water-reducing agent for a non-aqueous electrolyte, which is used to reduce gas generation under high-temperature conditions to suppress deterioration of battery characteristics.

[0022] Technical solution

[0023] After continuous efforts to solve this problem, the inventors unexpectedly found that in a secondary battery using a non-aqueous electrolyte containing a cyclic carbonate having a fluorine atom, an isocyanate compound having a specific chemical structure is used as an acid-reducing or water-reducing agent for the non-aqueous electrolyte, reducing gas generation under high-temperature conditions, thereby suppressing deterioration of battery characteristics, and finally completing the present invention.

[0024] The object of the present invention is achieved by an acid-reducing or water-reducing agent for a non-aqueous electrolyte containing a diisocyanate compound represented by formula (1), (2), or (3):

[0025] [Chemical formula 1]

[0026]

[0027] Wherein, in formula (1), R 1 to R 4 are each independently hydrogen, an alkyl group having 1 to 4 carbon atoms, or a halogen atom, and R 5 and R 6 are each independently a bond or an alkylene group having 1 to 4 carbon atoms;

[0028] Wherein, in formula (2), R' 1 to R' 4 are each independently hydrogen, an alkyl group having 1 to 4 carbon atoms, or a halogen atom, and R' 5 and R' 6 are each independently a bond or an alkylene group having 1 to 4 carbon atoms or an alkylene group; and

[0029] Wherein, in formula (3), R'' 1 to R'' 4 are each independently hydrogen, an alkyl group having 1 to 4 carbon atoms, or a halogen atom, and R'' 5 and R'' 6 are each independently a bond or an alkylene group having 1 to 4 carbon atoms, and

[0030] Among them, the non-aqueous electrolyte contains a cyclic carbonate containing a fluorine atom.

[0031] Preferably, the diisocyanate compound is represented by the formula (1).

[0032] Preferably, the diisocyanate compound is selected from the group consisting of isophthalic acid dimethyl diisocyanate, toluene diisocyanate, and mixtures thereof.

[0033] In addition, the present invention relates to a non-aqueous electrolyte containing the acid-reducing or water-reducing agent of the present invention.

[0034] Preferably, based on the total mass of the non-aqueous electrolyte, the content of the diisocyanate compound is 0.1% by mass or more and 1% by mass or less.

[0035] Preferably, the non-aqueous electrolyte further contains a lithium salt and a linear carbonate.

[0036] Furthermore, the present invention relates to a lithium secondary battery, which includes a positive electrode, a negative electrode, and the non-aqueous electrolyte of the present invention between the positive electrode and the negative electrode.

[0037] Preferably, the positive electrode contains a material such as nickel cobalt manganese (NCM), nickel cobalt aluminum (NCA), or nickel cobalt manganese aluminum (NCMA).

[0038] Preferably, the positive electrode contains 50% by mass or more of nickel.

[0039] Preferably, the negative electrode contains 30% by mass or more of silicon.

[0040] In addition, the present invention relates to a method for reducing acid or moisture in a non-aqueous electrolyte, which includes adding a diisocyanate compound represented by the formula (1), (2), or (3) to a non-aqueous electrolyte containing a cyclic carbonate containing a fluorine atom.

[0041] Embodiments of the present invention are as follows:

[0042] (Embodiment 1)

[0043] An acid-reducing or water-reducing agent for a non-aqueous electrolyte, which contains a diisocyanate compound represented by the formula (1), (2), or (3), wherein the non-aqueous electrolyte contains a cyclic carbonate containing a fluorine atom:

[0044] [Chemical formula 2]

[0045]

[0046] Among them, in the formula (1), R 1 to R 4Each independently is hydrogen, an alkyl group having 1 to 4 carbon atoms, or a halogen atom, and R 5 and R 6 Each independently is a bond or an alkylene group having 1 to 4 carbon atoms;

[0047] Wherein, in formula (2), R' 1 to R' 4 Each independently is hydrogen, an alkyl group having 1 to 4 carbon atoms, or a halogen atom, and R' 5 and R' 6 Each independently is a bond or an alkylene group having 1 to 4 carbon atoms; and

[0048] Wherein, in formula (3), R'' 1 to R'' 4 Each independently is hydrogen, an alkyl group having 1 to 4 carbon atoms, or a halogen atom, and R'' 5 and R'' 6 Each independently is a bond or an alkylene group having 1 to 4 carbon atoms.

[0049] (Embodiment 2)

[0050] An acid-reducing or water-reducing agent for a non-aqueous electrolyte as defined in Embodiment 1, wherein the diisocyanate compound is represented by formula (1).

[0051] (Embodiment 3)

[0052] An acid-reducing or water-reducing agent for a non-aqueous electrolyte as defined in Embodiment 1 or 2, wherein the diisocyanate compound is selected from the group consisting of isophthalic dimethyl diisocyanate, toluene diisocyanate, and mixtures thereof.

[0053] (Embodiment 4)

[0054] A non-aqueous electrolyte containing an acid-reducing or water-reducing agent as defined in any one of Embodiments 1 to 3.

[0055] (Embodiment 5)

[0056] The non-aqueous electrolyte as defined in Embodiment 4, wherein the content of the diisocyanate compound is 0.1% by mass or more and 1% by mass or less based on the total mass of the non-aqueous electrolyte.

[0057] (Embodiment 6)

[0058] The non-aqueous electrolyte as defined in Embodiment 4 or 5, further comprising a lithium salt and a linear carbonate.

[0059] (Embodiment 7)

[0060] A lithium secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte defined in any one of Embodiments 4 to 6 between the positive electrode and the negative electrode.

[0061] (Embodiment 8)

[0062] A lithium secondary battery as defined in Embodiment 7, wherein the positive electrode comprises a nickel-cobalt-manganese (NCM), nickel-cobalt-aluminum (NCA), or nickel-cobalt-manganese-aluminum (NCMA) type material.

[0063] (Embodiment 9)

[0064] A lithium secondary battery as defined in Embodiment 7 or 8, wherein the positive electrode comprises 50 mass% or more of nickel.

[0065] (Embodiment 10)

[0066] A lithium secondary battery as defined in any one of Embodiments 7 to 9, wherein the negative electrode comprises 30 mass% or more of silicon.

[0067] (Embodiment 11)

[0068] A method for reducing acid or moisture in a non-aqueous electrolyte, comprising: adding a diisocyanate compound represented by Formula (1), (2), or (3) to a non-aqueous electrolyte containing a fluorine atom-containing cyclic carbonate:

[0069] [Chemical Formula 3]

[0070]

[0071] Wherein, in Formula (1), R 1 to R 4 are each independently hydrogen, an alkyl group having 1 to 4 carbon atoms, or a halogen atom, and R 5 and R 6 are each independently a bond or an alkylene group having 1 to 4 carbon atoms;

[0072] Wherein, in Formula (2), R' 1 to R' 4 are each independently hydrogen, an alkyl group having 1 to 4 carbon atoms, or a halogen atom, and R' 5 and R' 6 are each independently a bond or an alkylene group having 1 to 4 carbon atoms; and

[0073] Wherein, in Formula (3), R'' 1 to R'' 4 are each independently hydrogen, an alkyl group having 1 to 4 carbon atoms, or a halogen atom, and R'' 5 and R'' 6Each independently represents a key or an alkylene group having 1 to 4 carbon atoms.

[0074] (Embodiment 12)

[0075] The method as defined in Embodiment 11, wherein the diisocyanate compound is selected from the group consisting of isophthalic diisocyanate, toluene diisocyanate, and mixtures thereof.

[0076] Beneficial effect

[0077] According to the present invention, in a lithium secondary battery using a non-aqueous electrolyte containing a cyclic carbonate having a fluorine atom, a non-aqueous electrolyte using a diisocyanate compound having a specific chemical structure as an acid or water reducing agent for the non-aqueous electrolyte can be provided to suppress the generation reaction of acid or moisture in the battery, thereby reducing gas generation under high temperature conditions and suppressing deterioration of battery characteristics. Description of the Drawings

[0078] Figure 1 It is a graph showing the measurement results of the remaining capacity and the restored capacity after high-temperature storage in Examples 1 and 2 and Comparative Example 1.

[0079] Figure 2 It is a graph showing the measurement results of the remaining capacity and the restored capacity after high-temperature storage in Comparative Examples 1 and 2.

[0080] Figure 3 It is a graph showing the measurement results of the remaining capacity and the restored capacity after high-temperature storage in Comparative Examples 1 and 3.

[0081] Figure 4 It is a graph showing the measurement results of the early AC impedance in Examples 1 and 2 and Comparative Example 1.

[0082] Figure 5 It is a graph showing the measurement results of the AC impedance after 2 weeks in Examples 1 and 2 and Comparative Example 1.

[0083] Figure 6 It is a graph showing the measurement results of the AC impedance after 4 weeks in Examples 1 and 2 and Comparative Example 1.

[0084] Figure 7 It is a graph showing the measurement results of the battery volume after high-temperature storage in Examples 1 and 2 and Comparative Example 1.

[0085] Figure 8 It is a graph showing the measurement results of the battery volume after high-temperature storage in Comparative Examples 1 and 2.

[0086] Figure 9 It is a graph showing the measurement results of the battery volume after high-temperature storage in Comparative Examples 1 and 3. Detailed Description of the Invention

[0087] [Acid or water reducing agent for non-aqueous electrolyte]

[0088] The acid or water reducing agent for non-aqueous electrolyte of the present invention contains a diisocyanate compound represented by formula (1), (2) or (3):

[0089] [Chemical formula 4]

[0090]

[0091] (In the above formula (1), R 1 to R 4 are each independently hydrogen, an alkyl group having 1 to 4 carbon atoms or a halogen atom, and R 5 and R 6 are each independently a bond or an alkylene group having 1 to 4 carbon atoms;

[0092] In the above formula (2), R' 1 to R' 4 are each independently hydrogen, an alkyl group having 1 to 4 carbon atoms or a halogen atom, and R' 5 and R' 6 are each independently a bond or an alkylene group having 1 to 4 carbon atoms; and

[0093] In the above formula (3), R'' 1 to R'' 4 are each independently hydrogen, an alkyl group having 1 to 4 carbon atoms or a halogen atom, and R'' 5 and R'' 6 are each independently a bond or an alkylene group having 1 to 4 carbon atoms).

[0094] In this specification, "alkyl group" refers to a straight-chain or branched-chain monovalent saturated hydrocarbon group, unless otherwise defined herein.

[0095] In this specification, "alkylene group" refers to a straight-chain or branched-chain divalent saturated hydrocarbon group, unless otherwise defined herein.

[0096] In this specification, "halogen atom" refers to a fluorine atom, a chlorine atom, a bromine atom, an iodine atom and an astatine atom, unless otherwise defined herein. The halogen atom is preferably a fluorine atom, a chlorine atom, a bromine atom or an iodine atom.

[0097] In the above formula (1), preferably, R 1 to R 4 are each independently hydrogen or an alkyl group having 1 to 4 carbon atoms, more preferably hydrogen, methyl or ethyl, and even more preferably hydrogen or methyl. In the above formula (1), preferably, R 5 and R 6 are each independently a bond, a methylene group or an ethylene group, and more preferably a bond or a methylene group.

[0098] In the above formula (2), preferably, R' 1 to R' 4 are each independently hydrogen or an alkyl group having 1 to 4 carbon atoms, more preferably hydrogen, methyl or ethyl, and still more preferably hydrogen or methyl. In the above formula (2), preferably, R' 5 and R' 6 are each independently a bond, methylene or ethylene, and more preferably a bond or methylene.

[0099] In the above formula (3), preferably, R'' 1 to R'' 4 are each independently hydrogen or an alkyl group having 1 to 4 carbon atoms, more preferably hydrogen, methyl or ethyl, and still more preferably hydrogen or methyl. In the above formula (3), preferably, R'' 5 and R'' 6 are each independently a bond, methylene or ethylene, and more preferably a bond or methylene.

[0100] In one embodiment, the diisocyanate compound contained in the acid-reducing or water-reducing agent for non-aqueous electrolytes of the present invention is preferably represented by formula (1). More preferably, the diisocyanate compound contained in the acid-reducing or water-reducing agent for non-aqueous electrolytes of the present invention is represented by formula (1), wherein R 1 to R 4 are each independently hydrogen or methyl, and R 5 and R 6 are each independently a bond or methylene. By using the diisocyanate compound having the above structure, the production reaction of acid or moisture in the battery can be more effectively inhibited.

[0101] In one embodiment, more preferably, the diisocyanate compound contained in the acid-reducing or water-reducing agent for non-aqueous electrolytes of the present invention is selected from the group consisting of isophthalic acid dimethyl diisocyanate, toluene diisocyanate and mixtures thereof. In particular, the diisocyanate compound contained in the acid-reducing or water-reducing agent for non-aqueous electrolytes of the present invention is preferably isophthalic acid dimethyl diisocyanate or toluene diisocyanate. When using the diisocyanate compound having the above structure, the production reaction of acid or moisture in the battery can be more effectively inhibited.

[0102] These diisocyanate compounds contained in the acid-reducing or water-reducing agent for non-aqueous electrolytes of the present invention can be used alone or in combination.

[0103] [Non-aqueous electrolyte]

[0104] The present invention also relates to a non-aqueous electrolyte containing the acid-reducing or water-reducing agent of the present invention. The non-aqueous electrolyte of the present invention contains a cyclic carbonate containing a fluorine atom.

[0105] Cyclic carbonates containing fluorine atoms may include vinylene carbonate fluoride, (trifluoromethyl) vinylene carbonate, fluoroethylene carbonate, 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, tetrafluoroethylene carbonate, 1-fluoro-2-methyl ethylene carbonate, 1-fluoro-1-methyl ethylene carbonate, 1,2-difluoro-1-methyl ethylene carbonate, 1,1,2-trifluoro-2-methyl ethylene carbonate, (trifluoromethyl) ethylene 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. More preferably, the cyclic carbonate containing fluorine atoms may be selected from fluoroethylene carbonate, 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1-fluoro-2-methyl ethylene carbonate, 1-fluoro-1-methyl ethylene carbonate, or 1,2-difluoro-1-methyl ethylene carbonate, more preferably selected from fluoroethylene carbonate, 1,2-difluoroethylene carbonate, or 1,1-difluoroethylene carbonate, and particularly preferably fluoroethylene carbonate. By using the cyclic carbonate containing fluorine atoms, a fluorine-containing SEI layer can be effectively formed on the surface of the negative electrode, thereby suppressing the deterioration of battery characteristics.

[0106] Generally, when the non-aqueous electrolyte contains a cyclic carbonate containing fluorine atoms, the decomposition reaction of the cyclic carbonate containing fluorine atoms is a troublesome problem. For example, it is considered that the cyclic carbonate containing fluorine atoms decomposes into a cyclic carbonate (such as VC) and an acidic substance (such as hydrofluoric acid). As a result, gas is generated due to the oxidative decomposition of the cyclic carbonate at the positive electrode. In addition, the acidic substance causes the dissociation of metal ions in the positive electrode.

[0107] On the contrary, the inventors surprisingly found that using an isocyanate compound having a specific chemical structure as an acid-reducing or water-reducing agent for the non-aqueous electrolyte can effectively inhibit the generation reaction of acids and / or moisture in the battery.

[0108] After high-temperature storage, the content of acidic substances in the non-aqueous electrolyte of the present invention is preferably 0.1 ppm or more and 100 ppm or less, more preferably 60 ppm or less, more preferably 50 ppm or less, still more preferably 40 ppm or less, even more preferably 30 ppm or less, still more preferably 20 ppm or less, and particularly preferably 15 ppm or less. After high-temperature storage, the amount of acidic substances contained in the non-aqueous electrolyte is measured by neutralization titration after storing the non-aqueous electrolyte at 60 °C for 1 week.

[0109] Based on the total mass of the non-aqueous electrolyte, the content of the diisocyanate compound contained in the non-aqueous electrolyte of the present invention is preferably 0.1% by mass or more and 1% by mass or less, more preferably 0.2% by mass or more and 0.9% by mass or less, and still more preferably 0.3% by mass or more and 0.7% by mass or less. When the content of the diisocyanate compound as an acid or water reducing agent in the non-aqueous electrolyte is within the above range, the generation reaction of acid or moisture in the battery can be effectively inhibited.

[0110] Based on the total volume of the non-aqueous electrolyte, the content of the fluorine atom-containing cyclic carbonate contained in the non-aqueous electrolyte of the present invention is preferably 5% by volume or more and 30% by volume or less, more preferably 8% by volume or more and 25% by volume or less, and still more preferably 10% by volume or more and 20% by volume or less. When the content of the fluorine atom-containing cyclic carbonate in the non-aqueous electrolyte is within the above range, the film-forming ability on the surface of the negative electrode of the battery is higher.

[0111] Preferably, the non-aqueous electrolyte of the present invention further comprises a linear carbonate. The linear carbonate may include dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), isopropyl methyl carbonate, methyl butyl carbonate, diethyl carbonate (DEC), ethyl propyl carbonate, ethyl butyl carbonate, dipropyl carbonate, propyl butyl carbonate, and combinations thereof.

[0112] The non-aqueous electrolyte of the present invention may contain a mixture of a cyclic carbonate and a linear carbonate. The volume ratio of the cyclic carbonate to the linear carbonate is preferably 0.5:9.5 to 5:5, more preferably 0.5:9.5 to 3:7, and still more preferably 1:9 to 2:8.

[0113] The non-aqueous electrolyte of the present invention may further comprise an organic solvent, such as an ether compound, an ester compound, or an amide compound.

[0114] The ether compound may include a cyclic ether or a linear ether. Examples of the cyclic ether may include tetrahydrofuran and 2-methyltetrahydrofuran. Examples of the linear ether may include dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, and ethyl propyl ether.

[0115] The ester compound may include a carboxylic acid ester. Examples of the carboxylic acid ester may 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, a compound in which a hydrogen of a carboxylic acid ester is partially substituted by fluorine, and combinations thereof.

[0116] Examples of the amide compound include dimethylacetamide (DMA) and dimethylformamide.

[0117] In addition, without departing from the object of the present invention, the non-aqueous electrolyte of the present invention may include, but is not limited to, any other solvents, such as polyethers, sulfur-containing solvents, and phosphorus-containing solvents.

[0118] The non-aqueous electrolyte of the present invention may include electrolytes commonly used in secondary batteries. The electrolyte serves as a medium for transporting ions participating in the electrochemical reactions in the secondary battery. In particular, the present invention can be used for electrolytes for lithium secondary batteries, and in this case, it includes a lithium salt as the electrolyte.

[0119] The lithium salt contained in the non-aqueous electrolyte of the present invention may include, 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 SO 3 、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 SO2 ) 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 C 2 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 、LiFSI、LiTFSI. In particular, the lithium salt preferably includes, such as LiPF 6 、LiBF 4 、LiAsF 6 and LiClO 4Inorganic salts such as... In one embodiment, most preferably, the lithium salts contained in the non-aqueous electrolyte of the present invention include LiPF 6 These lithium salts can be used alone or in combination.

[0120] In one embodiment, the lithium salts contained in the non-aqueous electrolyte of the present invention may include lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). In one embodiment, the lithium salts contained in the non-aqueous electrolyte of the present invention may include LiFSI and LiPF 6 ...

[0121] The amount of the electrolyte is not limited to a specific range, but based on the total mass of the non-aqueous electrolyte, the content of the electrolyte is 0.1 to 5 mol / L, preferably 0.5 to 3 mol / L, and more preferably 0.5 to 2 mol / L. When the amount of the electrolyte is within the above range, sufficient battery characteristics can be obtained.

[0122] The non-aqueous electrolyte of the present invention may further contain at least one additive. The additive may include, for example, a flame retardant, a wetting agent, a stabilizer, a corrosion inhibitor, a gelling agent, an overcharge inhibitor, and a negative electrode film-forming additive.

[0123] [Lithium secondary battery]

[0124] The present invention also relates to a lithium secondary battery, which includes a positive electrode, a negative electrode, and the non-aqueous electrolyte of the present invention between the positive electrode and the negative electrode.

[0125] The lithium secondary battery containing the non-aqueous electrolyte of the present invention may include, but is not limited to, any type of positive electrode and negative electrode commonly used in lithium secondary batteries, and may include a container for accommodating the positive electrode, the negative electrode, and the non-aqueous electrolyte of the present invention. In addition, a separator may be provided between the positive electrode and the negative electrode.

[0126] <Positive electrode>

[0127] The positive electrode used in the lithium secondary battery of the present invention can be manufactured, for example, by coating a positive electrode paste containing a positive electrode active material, a binder, a conductive material, and a solvent on a positive electrode current collector, and then drying and rolling.

[0128] The positive electrode current collector is not limited to a specific type, and may include a positive electrode current collector having conductivity and not causing any chemical changes in the lithium secondary battery of the present invention, such as stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel treated with carbon, nickel, titanium, and silver on the surface.

[0129] The positive electrode active material is a compound capable of reversibly inserting and extracting lithium, and specifically, may include a lithium composite metal oxide containing lithium and at least one metal among cobalt, manganese, nickel, or aluminum. More specifically, the lithium composite metal oxide may include: lithium manganese oxides (such as LiMnO 2 , LiMn 2 O 4 ), lithium cobalt oxides (such as, LiCoO 2 ), lithium nickel oxides (such as, LiNiO 2 ), lithium nickel manganese oxides (such as LiNi 1-y1 Mn y1 O 2 (where 0 < y1 < 1), LiMn 2-z1 Ni z1 O 4 (where 0 < Z1 < 2)), lithium nickel cobalt oxides (such as LiNi 1-y2 Co y2 O 2 (where 0 < y2 < 1)), lithium manganese cobalt oxides (such as LiCo 1-y3 Mn y3 O 2 (where 0 < y3 < 1), LiMn 2-z2 Co z2 O 4 (where 0 < Z2 < 2)), lithium nickel manganese cobalt oxides (such as Li(Ni p1 Co q1 Mn r1 )O 2 (where 0 < p1 < 1, 0 < q1 < 1, 0 < r1 < 1, p1 + q1 + r1 = 1) or Li(Ni p2 Co q2 Mn r2 )O 4 (where 0 < p2 < 2, 0 < q2 < 2, 0 < r2 < 2, p2 + q2 + r2 = 2)), or lithium nickel cobalt manganese transition metal (M) oxides (such as Li(Ni p3 Co q3 Mn r3 M S3 )O 2 (where M is selected from Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p3, q3, r3, and s3 are each independently the atomic fractions of these elements, 0 < p3 < 1, 0 < q3 < 1, 0 < r3 < 1, 0 < s3 < 1, p3 + q3 + r3 + s3 = 1)), and these materials can be used alone or in combination.

[0130] In the lithium secondary battery of the present invention, a lithium composite metal oxide containing a metal containing nickel and lithium is preferably included. In terms of the capacity characteristics and stability of the battery, more preferably, the positive electrode contains a material of the nickel-cobalt-manganese (NCM), nickel-cobalt-aluminum (NCA), or nickel-cobalt-manganese-aluminum (NCMA) type.

[0131] The positive electrode used in the lithium secondary battery of the present invention preferably contains 50% by mass or more of nickel, more preferably 60% by mass or more of nickel, still more preferably 75% by mass or more of nickel, even more preferably 80% by mass or more of nickel, and yet more preferably 85% by mass or more of nickel.

[0132] Based on the total mass of the solids in the positive electrode slurry, the content of the positive electrode active material is preferably 80 to 99% by mass, and more preferably 90 to 98% by mass. When the amount of the positive electrode active material is within the above range, high energy density and capacity can be achieved.

[0133] The binder is a component that helps to hold the positive electrode active material and the conductive material together and bind them to the current collector, and based on the total mass of the solids in the positive electrode slurry, the content of the binder is preferably 1 to 30% by mass, and more preferably 1.5% to 10% by mass. Examples of the binder can include polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluororubber.

[0134] The conductive material is a material that provides conductivity and does not cause any chemical changes in the lithium secondary battery of the present invention, and based on the total mass of the solids in the positive electrode slurry, the content of the conductive material is preferably 0.5 to 50% by mass, and more preferably 1 to 20% by mass. When the content of the conductive material is within the above range, the conductivity can be improved and high energy density and capacity can be achieved.

[0135] The conductive material can include, for example: carbon powders such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, pyrolytic carbon black, single-walled carbon nanotubes (SWCNT), and multi-walled carbon nanotubes (MWCNT); graphite powders having a well-grown crystal structure such as natural graphite, artificial graphite, and graphite; conductive fibers such as carbon fibers and metal fibers; metal powders such as aluminum powder 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.

[0136] The solvent may include, but is not limited to, any solvent that makes the positive electrode active material, binder, and conductive material into a slurry as the positive electrode material, and may include, for example, organic solvents such as N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), acetone, dimethylacetamide, and water. Additionally, the amount of the solvent may be such that the positive electrode slurry has an optimal viscosity, and for example, the solid concentration in the slurry is 10% to 60% by mass, preferably 20% to 50% by mass.

[0137] <Negative electrode>

[0138] The negative electrode used in the lithium secondary battery of the present invention can be manufactured, for example, by coating a negative electrode slurry containing a negative electrode active material, binder, conductive material, and solvent on a negative electrode current collector, and then drying and rolling.

[0139] The thickness of the negative electrode current collector is generally 3 to 500 μm. The negative electrode current collector is not limited to a specific type and may include a negative electrode current collector having high conductivity and not causing any chemical changes in the lithium secondary battery of the present invention, such as copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel treated with carbon, nickel, titanium, and silver on the surface, and aluminum-cadmium alloy. In addition, similar to the positive electrode current collector, the negative electrode current collector may have fine textures on the surface to increase the bonding strength of the negative electrode active material and may be in various forms such as a film, sheet, foil, grid or mesh, porous body, foam, and nonwoven material.

[0140] The negative electrode active material may include at least one selected from the group consisting of lithium metal, a carbon material capable of reversibly inserting or extracting lithium ions, a metal or an alloy of these metals with lithium, a metal composite oxide, a material capable of doping and dedoping lithium, and a transition metal oxide.

[0141] The carbon material capable of reversibly inserting or extracting lithium ions may include, but is not limited to, any carbon-based negative electrode active material commonly used in lithium secondary batteries, such as crystalline carbon, amorphous carbon, or a combination thereof. Examples of crystalline carbon may include graphite, such as natural graphite and artificial graphite in amorphous, plate-like, flake-like, spherical, or fibrous forms. Examples of amorphous carbon may include soft carbon (low-temperature sintered carbon) or hard carbon, mesophase pitch carbide, and sintered coke.

[0142] The metal or the alloy of these metals with lithium may include 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 with lithium.

[0143] The metal composite oxide may be selected from the group consisting of: PbO, PbO 2 、Pb2 O 3 、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), 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 and Group 3 in the periodic table, halogens; 0 < x ≤ 1; 1 ≤ y ≤ 3; 1 ≤ z ≤ 8).

[0144] Materials capable of doping and undoping lithium can 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), and mixtures of at least one of them with SiO 2 The element Y can 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.

[0145] Transition metal oxides can include lithium-containing titanium composite oxide (LTO), vanadium oxide, and lithium vanadium oxide.

[0146] The negative electrode active material of the lithium secondary battery of the present invention may preferably contain a silicon-containing material, such as Si, SiO x (0 < x < 2), Si-Y alloy (where Y is an element selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements, transition metals, rare earth elements, and combinations thereof, and is not Si), and a mixture of at least one of them and SiO 2 . In particular, more preferably, the negative electrode active material may include a Si material, such as Si microparticles.

[0147] The negative electrode used in the lithium secondary battery of the present invention preferably contains 30% by mass or more of silicon, more preferably 50% by mass or more of silicon, more preferably 65% by mass or more of silicon, and even more preferably 80% by mass or more of silicon.

[0148] Based on the total mass of the solids in the negative electrode slurry, the content of the negative electrode active material is preferably 80 to 99% by mass, and more preferably 90 to 99% by mass.

[0149] The binder is a component that helps to hold the conductive material, the negative electrode active material, and the current collector together, and based on the total mass of the solids in the negative electrode slurry, the content of the binder is preferably 1 to 30% by mass, and more preferably 1 to 10% by mass. Examples of the binder include polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber. These binders can be used alone or in combination.

[0150] The conductive material is a component for improving the conductivity of the negative electrode active material, and based on the total mass of the solids in the negative electrode slurry, the content of the conductive material is preferably 1 to 20% by mass. The conductive material is not limited to a specific type, and may include conductive materials having conductivity and not causing any chemical changes in the lithium secondary battery, such as graphite, such as natural graphite and artificial graphite; carbon black, such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and pyrolytic carbon black; conductive fibers, such as carbon fibers and metal fibers; metal powders, such as aluminum powder 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.

[0151] The solvent may include, but is not limited to, any solvent that makes the negative electrode active material, binder, and conductive material into a slurry as the negative electrode material, and may include, for example, organic solvents such as water, NMP, and alcohol. Additionally, the amount of the solvent may be such that the negative electrode slurry has an optimal viscosity, and for example, the solid concentration in the slurry is 50% to 75% by mass, preferably 50% to 65% by mass.

[0152] The separator of the lithium secondary battery of the present invention serves to prevent internal short circuits between the two electrodes and electrolyte wetting, and a separator composition can be prepared by mixing a polymer resin, a filler, and a solvent. The separator composition can be directly coated on the electrode and dried to form a separator, or the separator composition can be cast on a carrier and dried, and the separator can be peeled off from the carrier and laminated on the electrode.

[0153] The separator may include a porous polymer membrane commonly used as a separator, such as a porous polymer membrane made of polyolefin polymers (such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer), and these materials can be used alone or in a laminated manner, or a commonly used porous non-woven fabric, such as a non-woven fabric made of high melting point glass fibers and polyethylene terephthalate fibers, but is not limited thereto.

[0154] The pore size of the porous separator can generally be 0.01 to 50 μm, and the porosity can generally be 5 to 95%. Additionally, the thickness of the porous separator can generally be 5 to 300 μm.

[0155] The lithium secondary battery of the present invention is not limited to a specific shape, and the shape can be cylindrical, prismatic, laminated, pouch-type, or coin-type.

[0156] [Method for reducing acid or moisture in non-aqueous electrolyte]

[0157] The present invention also relates to a method for reducing acid or moisture in a non-aqueous electrolyte, which includes adding a diisocyanate compound represented by formula (1), (2), or (3) to a non-aqueous electrolyte containing a cyclic carbonate containing a fluorine atom:

[0158] [Chemical formula 5]

[0159]

[0160] (In the above formula (1), R 1 to R 4 are each independently hydrogen, an alkyl group having 1 to 4 carbon atoms, or a halogen atom, and R 5 and R 6 are each independently a bond or an alkylene group having 1 to 4 carbon atoms;

[0161] In the above formula (2), R' 1 to R' 4 are each independently hydrogen, an alkyl group having 1 to 4 carbon atoms, or a halogen atom, and R' 5 and R' 6 are each independently a bond or an alkylene group having 1 to 4 carbon atoms; and

[0162] In the above formula (3), R'' 1 to R'' 4 are each independently hydrogen, an alkyl group having 1 to 4 carbon atoms, or a halogen atom, and R'' 5 and R'' 6 are each independently a bond or an alkylene group having 1 to 4 carbon atoms).

[0163] The diisocyanate compound represented by formula (1), (2), or (3) may include the above compounds.

[0164] In the method for reducing acid or moisture in the non-aqueous electrolyte of the present invention, the diisocyanate compound is preferably the compound represented by formula (1), more preferably the compound represented by formula (1), wherein R 1 to R 4 are each independently hydrogen or methyl, and R 5 and R 6 are each independently a bond or a methylene group. In particular, isophthalic dimethyl diisocyanate or toluene diisocyanate is preferred. When a diisocyanate compound having the above structure is selected, the generation reaction of acid or moisture in the battery can be more effectively inhibited. Examples

[0165] Hereinafter, the present invention will be described in more detail using examples and comparative examples. However, the scope of the present invention is not limited to the examples.

[0166] (Example 1)

[0167] (1) Manufacture of a lithium secondary battery

[0168] (Manufacture of the positive electrode)

[0169] 96.5 parts by mass of nickel cobalt manganese aluminum-based oxide (NCMA, nickel content 85%) as the positive electrode active material, 1.5 parts by weight of acetylene black as the conductive material, and 2 parts by weight of polyvinylidene fluoride as the binder are dispersed in N-methyl-2-pyrrolidone as the solvent to prepare a positive electrode paste. The positive electrode paste is uniformly coated on an aluminum foil, dried by heating and vacuum, and pressed to manufacture a positive electrode.

[0170] (Manufacture of the negative electrode)

[0171] 80 parts by mass of Si fine particles to be used as a negative electrode active material, 10 parts by weight of graphite as a conductive material, and 10 parts by weight of styrene-butadiene rubber and carboxymethyl cellulose as binders are dispersed in water as a solvent to prepare a negative electrode slurry. The negative electrode slurry is uniformly coated on a copper foil, dried by heating and vacuum, and pressed to manufacture a negative electrode.

[0172] <Manufacture of non-aqueous electrolyte>

[0173] A mixture of 10 parts by volume of fluoroethylene carbonate (FEC) and 90 parts by volume of diethyl carbonate (DEC) is used as a solvent, and 1.2 M of LiPF as an electrolyte 6 is dissolved in the solvent to prepare a solution. 0.5 part by mass of m-xylene diisocyanate represented by the following formula (A) (available from Mitsui Chemicals) as an acid reducing or water reducing agent is added to 100 parts by mass of the obtained solution to obtain the non-aqueous electrolyte of the present invention.

[0174] [Chemical formula 6]

[0175]

[0176] <Manufacture of lithium secondary battery>

[0177] A pouch-type battery having a relative area of 12 cm is manufactured using the positive electrode, negative electrode, and non-aqueous electrolyte prepared by the above method and a polyolefin film as a separator. 2

[0178] (Example 2)

[0179] A non-aqueous electrolyte and a lithium secondary battery containing the non-aqueous electrolyte are manufactured by the same method as in Example 1, except that toluene diisocyanate (a mixture of 80% 2,4-isomer and 20% 2,6-isomer, available from Mitsui Chemicals) represented by the following formula (B) is added to the non-aqueous electrolyte in place of m-xylene diisocyanate.

[0180] [Chemical formula 7]

[0181]

[0182] (Comparative Example 1)

[0183] A non-aqueous electrolyte and a lithium secondary battery containing the non-aqueous electrolyte are manufactured by the same method as in Example 1, except that m-xylene diisocyanate is not added to the non-aqueous electrolyte.

[0184] (Comparative Example 2) ​

[0185] A non-aqueous electrolyte and a lithium secondary battery including the non-aqueous electrolyte were manufactured by the same method as in Example 1, except that hexane-1,6-diisocyanate represented by the following formula (C) (available from Mitsui Chemicals) was added to the non-aqueous electrolyte in place of isophthalic acid diisocyanate.

[0186] [Chemical formula 8]

[0187]

[0188] (Comparative Example 3)

[0189] A non-aqueous electrolyte and a lithium secondary battery including the non-aqueous electrolyte were manufactured by the same method as in Example 1, except that cyclohexane-1,3-dimethyl diisocyanate represented by the following formula (D) (available from Mitsui Chemicals) was added to the non-aqueous electrolyte in place of isophthalic acid diisocyanate.

[0190] [Chemical formula 9]

[0191]

[0192] (2) Measurement of acidic substances

[0193] Each of the non-aqueous electrolytes of Example 1 and 2 and Comparative Example 1 prepared in (1) was placed in an aluminum bottle and stored at 60 °C for 1 week. The amount of acidic substance (HF) in the electrolyte after storage was measured by neutralization titration. The results are shown in Table 1 below.

[0194] [Table 1] Results of measurement of acidic substances

[0195] Acid reducing agent or water reducing agent Acidic substance (ppm) Example 1 Isophthalic diisocyanate 11 Example 2 Toluene diisocyanate 48 Comparative Example 1 None 119

[0196] From the results in Table 1, it can be seen that the amount of acidic substances decreased after high-temperature storage in the non-aqueous electrolyte containing isophthalic acid diisocyanate or the non-aqueous electrolyte containing toluene diisocyanate. Therefore, it was confirmed that the degradation of the electrolyte itself was suppressed by using the acid-reducing or water-reducing agent of the present invention.

[0197] (3) 60 °C storage test (measurement of remaining and recovered capacity, measurement of AC impedance, measurement of battery volume)

[0198] For each lithium secondary battery prepared in (1), the lithium secondary battery in the charged state was left as it was at 60 °C for 1 week or 2 weeks. After storage at 60 °C, the remaining capacity was measured at 25 °C, the lower limit of the discharge voltage was 2.50 V, and after recharging (the upper limit of the charging voltage was 4.20 V), the recovery capacity was measured. Subsequently, the battery voltage was stabilized to 3.6 V corresponding to SOC50%, the AC impedance was measured at an amplitude voltage of 5 mV, and the battery volume was measured by the Archimedes method.

[0199] <Residual · Recovery Capacity Measurement>

[0200] Figure 1 The measurement results of the remaining capacity and the recovery capacity obtained by the above operation method using the lithium secondary batteries of Example 1 and Example 2 and Comparative Example 1 prepared in (1) are shown.

[0201] Figure 2 The measurement results of the remaining capacity and the recovery capacity obtained by the above operation method using the lithium secondary batteries of Comparative Example 1 and Comparative Example 2 prepared in (1) are shown.

[0202] Figure 3 The measurement results of the remaining capacity and the recovery capacity obtained by the above operation method using the lithium secondary batteries of Comparative Example 1 and Comparative Example 3 prepared in (1) are shown.

[0203] From Figure 1 the results, it can be seen that it was confirmed that in the lithium secondary battery of Example 1 using a non-aqueous electrolyte containing isophthaloyl diisocyanate or the lithium secondary battery of Example 2 using a non-aqueous electrolyte containing tolylene diisocyanate, the remaining capacity and the recovery capacity after 4 weeks were higher than those of the lithium secondary battery of Comparative Example 1, and the remaining capacity and the recovery capacity after 6 weeks were much higher than those of the lithium secondary battery of Comparative Example 1. Therefore, it was proved that in the lithium secondary batteries using the non-aqueous electrolytes of Example 1 and Example 2, the deterioration of the battery characteristics after high-temperature storage was effectively suppressed.

[0204] In contrast, from Figure 2 and Figure 3 the results, it can be seen that it was confirmed that in the lithium secondary battery of Comparative Example 2 using a non-aqueous electrolyte containing hexane-1,6-diisocyanate or the lithium secondary battery of Comparative Example 3 using a non-aqueous electrolyte containing cyclohexane-1,3-dimethyl diisocyanate, there was no significant difference in the remaining capacity and the recovery capacity after 4 to 6 weeks compared with the lithium secondary battery of Comparative Example 1, indicating that the deterioration of the battery characteristics after high-temperature storage could not be sufficiently suppressed.

[0205] <AC Impedance Measurement>

[0206] When measuring the AC impedance of the lithium secondary batteries of Example 1 and Example 2 and Comparative Example 1 prepared in (1) by the above operation method, Figure 4 The results in the early stage (week 0) are shown, Figure 5 The results after being left as it is for 2 weeks are shown, Figure 6 The results after being left as it is for 4 weeks are shown. In the obtained graphs, large arcs indicate high battery resistance.

[0207] According to Figure 4 the results, it was confirmed that in the early stage (week 0), when compared with the battery of Comparative Example 1 without an acid-reducing or water-reducing agent, the lithium secondary batteries of Example 1 and Example 2 using the acid-reducing or water-reducing agent of the present invention showed large arcs in the obtained graphs, indicating high battery resistance. This is because when a compound containing an isocyanate group is added to a non-aqueous electrolyte, the resistance generally increases. However, from Figure 5 the results, it can be seen that in a high-temperature (60 °C) environment, after the battery was left as it is for 2 weeks, in the obtained graphs, there was no or almost no difference in the arc size between Example 1 and Example 2 and Comparative Example 1, indicating that the battery resistance was at the same level. In addition, from Figure 6 the results, it can be seen that after being left as it is for 4 weeks in a high-temperature (60 °C) environment, in the obtained graphs, the batteries of Example 1 and Example 2 showed smaller arc sizes compared with Comparative Example 1. Therefore, it was confirmed that when stored for a long time in a high-temperature environment, using the acid-reducing or water-reducing agent of the present invention can effectively inhibit the increase in internal resistance.

[0208] <Battery volume measurement>

[0209] Figure 7 The battery volume measurement results obtained by using the lithium secondary batteries of Example 1 and Example 2 and Comparative Example 1 prepared in (1) by the above operation method are shown.

[0210] Figure 8 The battery volume measurement results obtained by using the lithium secondary batteries of Comparative Example 1 and Comparative Example 2 prepared in (1) by the above operation method are shown.

[0211] Figure 9 The battery volume measurement results obtained by using the lithium secondary batteries of Comparative Example 1 and Comparative Example 3 prepared in (1) by the above operation method are shown.

[0212] From Figure 7 the results, it was confirmed that in the lithium secondary battery of Example 1 using a non-aqueous electrolyte containing isophthalic acid dimethyl diisocyanate or the lithium secondary battery of Example 2 using a non-aqueous electrolyte containing toluene diisocyanate, the increase in battery volume after high-temperature storage was inhibited, indicating that gas generation in the battery was significantly inhibited.

[0213] In contrast, fromFigure 8 and Figure 9 As can be seen from the results of Figure 8 and Figure 9 , in the lithium secondary battery of Comparative Example 2 using a non-aqueous electrolyte containing hexane-1,6-diisocyanate or the lithium secondary battery of Comparative Example 3 using a non-aqueous electrolyte containing cyclohexane-1,3-dimethyl diisocyanate, when compared with the lithium secondary battery of Comparative Example 1, there is no significant difference in the increase in battery volume after high-temperature storage, indicating that gas generation after high-temperature storage is not sufficiently suppressed.

Claims

1. A deacidifying or water-reducing agent for non-aqueous electrolytes, which contains a diisocyanate compound represented by formula (1), (2) or (3). Wherein, The non-aqueous electrolyte contains a cyclic carbonate containing a fluorine atom. [Chemical formula 1] Among them, in formula (1), R 1 to R 4 are each independently hydrogen, an alkyl group having 1 to 4 carbon atoms, or a halogen atom, and R 5 and R 6 are each independently a bond or an alkylene group having 1 to 4 carbon atoms; Among them, in formula (2), R' 1 to R' 4 are each independently hydrogen, an alkyl group having 1 to 4 carbon atoms or a halogen atom, and R' 5 and R' 6 are each independently a bond or an alkylene group having 1 to 4 carbon atoms; and Among them, in formula (3), R” 1 to R” 4 are each independently hydrogen, an alkyl group having 1 to 4 carbon atoms, or a halogen atom, and R” 5 and R” 6 are each independently a bond or an alkylene group having 1 to 4 carbon atoms.

2. The deacidifying or water-reducing agent for non-aqueous electrolytes according to claim 1. Wherein, The diisocyanate compound is represented by formula (1).

3. The deacidifying or water-reducing agent for non-aqueous electrolytes according to claim 1. Wherein, The diisocyanate compound is selected from the group consisting of isophthalic acid dimethyl diisocyanate, toluene diisocyanate and mixtures thereof.

4. A non-aqueous electrolyte, which contains the deacidifying or water-reducing agent according to any one of claims 1 to 3.

5. The non-aqueous electrolyte according to claim 4. Wherein, Based on the total mass of the non-aqueous electrolyte, the content of the diisocyanate compound is 0.1% by mass or more and 1% by mass or less.

6. The non-aqueous electrolyte according to claim 4, which further contains: a lithium salt and a linear carbonate.

7. A lithium secondary battery, which contains: A positive electrode, A negative electrode; and The non-aqueous electrolyte according to claim 4 between the positive electrode and the negative electrode.

8. The lithium secondary battery according to claim 7. Wherein, The positive electrode contains a material such as nickel cobalt manganese (NCM), nickel cobalt aluminum (NCA) or nickel cobalt manganese aluminum (NCMA).

9. The lithium secondary battery according to claim 7. Wherein, The positive electrode contains 50% by mass or more of nickel.

10. The lithium secondary battery according to claim 7. Wherein, The negative electrode contains 30% by mass or more of silicon.

11. A method for reducing acid or moisture in a non-aqueous electrolyte, which Comprises: Adding a diisocyanate compound represented by formula (1), (2) or (3) to a non-aqueous electrolyte containing a cyclic carbonate containing a fluorine atom. [Chemical formula 2] Among them, in formula (1), R 1 to R 4 are each independently hydrogen, an alkyl group having 1 to 4 carbon atoms, or a halogen atom, and R 5 and R 6 are each independently a bond or an alkylene group having 1 to 4 carbon atoms; Among them, in formula (2), R' 1 to R' 4 are each independently hydrogen, an alkyl group having 1 to 4 carbon atoms, or a halogen atom, and R' 5 and R' 6 are each independently a bond or an alkylene group having 1 to 4 carbon atoms; and Among them, in formula (3), R” 1 to R” 4 are each independently hydrogen, an alkyl group having 1 to 4 carbon atoms, or a halogen atom, and R” 5 and R” 6 are each independently a bond or an alkylene group having 1 to 4 carbon atoms.

12. The method according to claim 11. Wherein, The diisocyanate compound is selected from the group consisting of isophthalic acid dimethyl diisocyanate, toluene diisocyanate and mixtures thereof.

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