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

Abstract

To provide an electrolyte in which the acid and / or water content is decreased to realize suppression of decrease in battery characteristics even under high temperature conditions and to have an excellent cycle life.SOLUTION: An agent for decreasing the acid or water content of a nonaqueous electrolyte comprises a (meth)acrylate comprising an isocyanate group or amide linkage.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an acid or moisture reducing agent for a non-aqueous electrolyte solution, a non-aqueous electrolyte solution containing the same, a lithium secondary battery containing a non-aqueous electrolyte solution, and a method for reducing the acid or moisture in a non-aqueous electrolyte solution. [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 a high ratio of nickel as the positive electrode active material is being considered in order to manufacture 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 materials in the electrolyte. For example, when LiPF6 is used as the electrolyte, the following reaction occurs, causing the electrolyte to decompose and produce acid.

[0006] LiPF6+H2O→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. 2019-186078 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. 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.

[0009] WO 2012 / 147502 and WO 2014 / 125946 disclose that a compound having an isocyanate group is added as an additive to a non-aqueous electrolyte for a secondary battery to improve charge / discharge characteristics from low to high temperatures. However, although these documents disclose the formation of a coating on the negative electrode, they do not disclose the effects of acid and moisture. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] JP 2019-186078 A [Patent Document 2] International Publication No. 2012 / 147502 [Patent Document 3] International Publication No. 2014 / 125946 Summary of the Invention [Problem to be solved by the invention]

[0011] Therefore, there has been a demand for an acid or moisture reducing agent that can stabilize the properties of an electrolyte even when a nickel-containing material is used for the positive electrode and a silicon-containing material is used for the negative electrode, as well as an electrolyte that has excellent battery properties and cycle life by reducing the acid and / or moisture.

[0012] The present invention has been made to solve the problems of the conventional technology, and aims to provide an electrolyte solution that can suppress deterioration of battery characteristics even under high temperature conditions by reducing acid and / or moisture, and has an excellent cycle life. [Means for solving the problem]

[0013] As a result of extensive research into the above-mentioned problems, the inventors unexpectedly discovered that by using a (meth)acrylate containing an isocyanate group or an amide bond as an acid or moisture reducing agent for the electrolyte, it is possible to maintain excellent capacity density even under high temperature conditions, and thus arrived at the present invention.

[0014] The object of the present invention is achieved by an acid or moisture reducing agent for a non-aqueous electrolyte solution, which comprises a (meth)acrylate containing an isocyanate group or an amide bond.

[0015] The (meth)acrylate containing an isocyanate group or an amide bond is preferably a (meth)acrylate containing an isocyanate group.

[0016] The (meth)acrylate containing an isocyanate group or an amide bond is selected from the group consisting of the following compounds: [ka] It is preferably selected from:

[0017] The (meth)acrylate containing an isocyanate group or an amide bond is preferably 2-isocyanatoethyl acrylate or 2-isocyanatoethyl methacrylate.

[0018] The present invention also relates to a non-aqueous electrolyte solution comprising the acid or moisture reducing agent of the present invention.

[0019] The (meth)acrylate containing an isocyanate group or an amide bond is preferably contained in an amount of 0.1 to 1% by mass based on the total mass of the nonaqueous electrolyte solution.

[0020] The nonaqueous electrolyte solution of the present invention preferably further contains a cyclic carbonate and a chain carbonate.

[0021] The non-aqueous electrolyte of the present invention preferably further contains a lithium salt, and the lithium salt preferably contains LiPF6.

[0022] The present invention also provides positive electrode, negative electrode, The nonaqueous electrolyte of the present invention is disposed between the positive electrode and the negative electrode. The present invention also relates to a lithium secondary battery comprising:

[0023] The positive electrode preferably comprises a nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminium (NCA) ternary material.

[0024] The negative electrode preferably contains a material containing silicon.

[0025] The present invention also relates to a method for reducing the acid or moisture content of a non-aqueous electrolyte solution, comprising adding the above-mentioned (meth)acrylate containing an isocyanate group or an amide bond to the non-aqueous electrolyte solution. Effect of the Invention

[0026] According to the present invention, by using a (meth)acrylate containing an isocyanate group or an amide bond as an acid or moisture reducing agent 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, so that deterioration of battery characteristics can be suppressed even under high temperature conditions, and an electrolyte solution having an excellent cycle life can be provided. [Brief description of the drawings]

[0027] [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. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] The acid or moisture reducing agent for the non-aqueous electrolyte solution of the present invention contains a (meth)acrylate containing an isocyanate group or an amide bond. Preferably, the acid or moisture reducing agent for the non-aqueous electrolyte solution of the present invention contains a (meth)acrylate containing an isocyanate group.

[0029] The (meth)acrylate containing an isocyanate group or an amide bond contained in the acid or moisture reducing agent of the nonaqueous electrolyte of the present invention may contain one isocyanate group or amide bond in the molecule, or may contain two or more isocyanate groups or amide bonds in the molecule. In addition, the groups and bonds contained in the molecule are not particularly limited.

[0030] In one embodiment, the (meth)acrylate containing an isocyanate group or an amide bond contained in the acid or moisture reducing agent for the nonaqueous electrolyte solution of the present invention is the following compound: [ka] is selected from.

[0031] In particular, (meth)acrylates containing an isocyanate group at the end of the molecule are preferably used, and are represented by the following general formula (1): [ka] (In the formula, R1 is a hydrogen atom or a methyl group, and R2 is a divalent organic group.) It is preferable that the compound is represented by the following formula:

[0032] In the general formula (1), R2 is a divalent organic group, such as an alkylene group, an arylene group, or an alkenylene group. R2 is preferably an alkylene group having 1 to 6 carbon atoms, and more preferably an alkylene group having 1 to 3 carbon atoms.

[0033] Preferably, the (meth)acrylate containing an isocyanate group or an amide bond contained in the acid or moisture reducing agent of the non-aqueous electrolyte of the present invention is 2-isocyanatoethyl methacrylate, 2-isocyanatoethyl acrylate, 1,1-(bisacryloyloxymethyl)ethyl isocyanate, 2-[0-(1'-methylpropylideneamino)carboxyamino]ethyl methacrylate or 2-[0-(1'-methylpropylideneamino)carboxyamino]ethyl acrylate. More preferably, the (meth)acrylate containing an isocyanate group or an amide bond contained in the acid or moisture reducing agent of the non-aqueous electrolyte of the present invention is 2-isocyanatoethyl acrylate or 2-isocyanatoethyl methacrylate.

[0034] The (meth)acrylate containing an isocyanate group or an amide bond contained in the acid or moisture reducing agent for the nonaqueous electrolyte solution of the present invention may be used alone or in combination of two or more compounds.

[0035] The present invention also relates to a non-aqueous electrolyte solution containing the acid or moisture reducing agent of the present invention. The (meth)acrylate containing an isocyanate group or an amide bond contained in the non-aqueous electrolyte solution is preferably contained in an amount of 0.1 to 1 mass %, more preferably in an amount of 0.2 to 0.9 mass %, and most preferably in an amount of 0.3 to 0.8 mass %, based on the total mass of the non-aqueous electrolyte solution. By containing the (meth)acrylate containing an isocyanate group or an amide bond as the acid or moisture reducing agent in an amount within the above range, acid or moisture generating reactions in the battery can be effectively suppressed.

[0036] 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.

[0037] 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.

[0038] The cyclic carbonate may also include a cyclic carbonate containing a fluorine atom.The cyclic carbonate containing a fluorine atom may 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] Examples of the lithium salt contained in the nonaqueous electrolyte of the present invention include LiPF6, LiBF4, and LiB 12 F 12, LiAsF6, LiFSO3, Li2SiF6, LiCF3CO2, LiCH3CO2, LiCF3SO3, LiC4F9SO3, LiCF3CF2SO3, LiCF3(CF2)7SO3, LiCF3CF2(CF3)2CO, Li(CF3 SO2)2CH, LiNO3, LiN(CN)2, LiN(FSO2)2, LiN(F2SO2)2, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiC(CF3SO2)3, LiP(CF3)6, LiPF(CF3)5, LiP F2(CF3)4, LiPF3(CF3)3, LiPF4(CF3)2, LiPF4(CF3)2, LiPF4(CF3SO2)2, LiPF4(C2F5SO2)2, LiBF2C2O4, LiBC4O8, LiBF2(CF3)2, LiBF2(C2F5)2, LiBF2(CF3SO2)2, LiBF2(C2F5SO2)2, LiSbF6, LiAlO4, LiAlF4, LiSCN, LiClO4, LiCl, LiF, LiBr, LiI, and LiAlCl4. In particular, inorganic salts such as LiPF6, LiBF4, LiAsF6, and LiClO4 are preferred, and LiPF6 is more preferred. The lithium salt can be used alone or in combination with multiple lithium salts.

[0046] 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.

[0047] The non-aqueous electrolyte of the present invention may further contain at least one additive, such as a flame retardant, a wetting agent, a stabilizer, an anticorrosive agent, a gelling agent, an overcharge inhibitor, and a negative electrode film-forming additive.

[0048] The present invention also provides positive electrode, negative electrode, The nonaqueous electrolyte of the present invention is disposed between the positive electrode and the negative electrode. It also relates to a lithium secondary battery including the same.

[0049] The lithium battery containing the non-aqueous electrolyte of the present invention can use a positive electrode and a negative electrode that can be used in a known lithium secondary battery without limitation, and can be configured by being housed in a container together with the non-aqueous electrolyte of the present invention. Also, a separator can be interposed between the positive electrode and the negative electrode.

[0050] The positive electrode used in the lithium secondary battery of the present invention can be manufactured, for example, by coating a positive electrode slurry 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.

[0051] The positive electrode current collector is not particularly limited as long as it has conductivity without inducing a chemical change in the lithium secondary battery of the present invention. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or a material obtained by surface-treating the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. can be used.

[0052] The positive electrode active material is a compound capable of reversibly occluding and releasing lithium. Specifically, it may include a lithium composite metal oxide containing one or more metals such as cobalt, manganese, nickel, or aluminum and lithium. More specifically, the lithium composite metal oxide is a lithium-manganese-based oxide (for example, LiMnO2, LiMn2O4, etc.), a lithium-cobalt-based oxide (for example, LiCoO2, etc.), a lithium-nickel-based oxide (for example, LiNiO2, etc.), a lithium-nickel-manganese-based oxide (for example, LiNi 1-y1 Mn y1 O2 (where 0 < y1 < 1), LiMn 2-z1 Ni z O4 (where 0 < Z1 < 2), etc.), a lithium-nickel-cobalt-based oxide (for example, LiNi 1-y2 Co y2 O2 (where 0 < y2 < 1), etc.), a lithium-manganese-cobalt-based oxide (for example, LiCo 1-y3Mn y3 O2 (where 0 < y3 < 1), LiMn 2-z2 Co z2 O4 (where 0 < Z2 < 2), etc.), lithium-nickel-manganese-cobalt oxide (e.g., Li(Ni p1 Co q1 Mn r1 )O2 (where 0 < p1 < 1, 0 < q1 < 1, 0 < r1 < 1, p1 + q1 + r1 = 1), or Li(Ni p2 Co q2 Mn r2 )O4 (where 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 )O2 (where 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, 0 < p3 < 1, 0 < q3 < 1, 0 < r3 < 1, 0 < s3 < 1, p3 + q3 + r3 + s3 = 1), etc.), etc. These may be included alone or in combination of two or more.

[0053] Preferably, from the viewpoint of enhancing 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 oxide (e.g., LiNiO2, etc.), lithium-nickel-manganese-cobalt oxide (e.g., Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, or Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, etc.), or lithium-nickel-cobalt-aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 Al 0.05)O2, etc.) can be used, and in particular, it is preferable to use lithium-nickel-manganese-cobalt oxide or lithium-nickel-cobalt-aluminum oxide, which are nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) ternary materials, from the standpoint of cost.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] Examples of conductive materials include carbon powders such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, single-walled carbon nanotubes (SWCNT), and multi-walled carbon nanotubes (MWCNT); 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] The negative electrode active material may contain at least one selected from the group consisting of lithium metal, a carbon material capable of reversibly occluding and releasing lithium ions, a metal, an alloy of these metals and lithium, a metal composite oxide, a material capable of doping and dedoping lithium, and a transition metal oxide.

[0062] As the carbon material capable of reversibly occluding and releasing lithium ions, any carbon-based negative electrode active material generally used in lithium secondary batteries can be used without particular limitation. For example, crystalline carbon, amorphous carbon, or a combination thereof can be used. Examples of crystalline carbon include graphite such as amorphous, plate-like, 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.

[0063] As the metal or an 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.

[0064] Examples of the metal composite oxide include PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, Bi2O5, Li x Fe2O3 (0 ≦ x ≦ 1), Li x WO2 (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) can be used.

[0065] Examples of substances capable of doping and undoping lithium include Si, SiO x (0 < x < 2), Si-Y alloys (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, SnO2, 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. At least one of these may be mixed with SiO2 and used. 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.

[0066] Examples of transition metal oxides include lithium-containing titanium composite oxide (LTO), vanadium oxide, lithium vanadium oxide, etc.

[0067] 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 alloys (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), and mixtures of at least one of these with SiO2 can be used. In particular, it is more preferable to use SiO.

[0068] 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.

[0069] The binder is a component that aids in bonding between 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 relative to 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] Moreover, the initial capacity density per positive electrode of the lithium secondary battery of the present invention is preferably 180 mAh / g or more, and more preferably 185 mAh / g or more.

[0077] 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.

[0078] The present invention also relates to a method for reducing the acid or moisture content of a non-aqueous electrolyte solution, comprising adding a (meth)acrylate containing an isocyanate group or an amide bond to the non-aqueous electrolyte solution. The above-mentioned compounds can be used as the (meth)acrylate containing an isocyanate group or an amide bond. EXAMPLES

[0079] 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.

[0080] Example 1 (1) Manufacture of lithium secondary batteries <Production of positive electrodes> A nickel-cobalt-manganese (NCM) ternary material (Li(Ni 0.8 Mn 0.1 Co 0.1 A positive electrode slurry was prepared by dispersing 96.5 parts by mass of 1,024,048,050, 1.5 parts by mass of acetylene black as a conductive material, and 2 parts by mass of polyvinylidene fluoride as a binder. 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.

[0081] <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.

[0082] <Production of non-aqueous electrolyte> A solution was prepared by dissolving LiPF6 in a solvent containing 30 parts by volume of ethylene carbonate (EC) and 70 parts by volume of ethyl methyl carbonate (EMC) to a salt concentration of 1 M. 0.5 parts by mass of 2-isocyanatoethyl methacrylate (manufactured by Showa Denko K.K.) (A1) was added to 100 parts by mass of the obtained solution as an acid or moisture reducing agent to obtain a nonaqueous electrolyte solution of the present invention.

[0083] <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.

[0084] Example 2 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 2-isocyanatoethyl acrylate (manufactured by Showa Denko K.K.) (A2) was added to the non-aqueous electrolyte solution instead of 2-isocyanatoethyl methacrylate.

[0085] Example 3 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 1,1-(bisacryloyloxymethyl)ethyl isocyanate (manufactured by Showa Denko K.K.) was added to the non-aqueous electrolyte solution instead of 2-isocyanatoethyl methacrylate.

[0086] 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-[0-(1'-methylpropylideneamino)carboxyamino]ethyl methacrylate (manufactured by Showa Denko K.K.) was added to the nonaqueous electrolyte solution instead of 2-isocyanatoethyl methacrylate.

[0087] Example 5 A nonaqueous electrolyte solution and a lithium secondary battery containing the same were produced in the same manner as in Example 1, except that 2-[0-(1'-methylpropylideneamino)carboxyamino]ethyl acrylate (manufactured by Showa Denko KK) was added to the nonaqueous electrolyte solution.

[0088] 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 2-isocyanatoethyl methacrylate was not added to the non-aqueous electrolyte solution.

[0089] (2) Acid content measurement The electrolyte solutions of Examples 1 to 5 and Comparative Example 1 prepared in (1) were subjected to measurement of the acid content before and after storage at 60° C. for one week. The results are shown in Table 1 below.

[0090] [Table 1]

[0091] As can be seen from the results in Table 1, in Examples 1 to 5 in which an electrolyte solution containing 2-isocyanatoethyl methacrylate, 2-isocyanatoethyl acrylate, 1,1-(bisacryloyloxymethyl)ethyl isocyanate, 2-[0-(1'-methylpropylideneamino)carboxyamino]ethyl methacrylate, or 2-[0-(1'-methylpropylideneamino)carboxyamino]ethyl acrylate was used as the non-aqueous electrolyte solution, the amount of acid generated was suppressed, and the amount of acid did not increase after storage. In particular, in the non-aqueous electrolyte solution containing 2-isocyanatoethyl acrylate, no acid was detected before or after storage.

[0092] (3) Charge / discharge cycle test Using the lithium secondary batteries of Examples 1 and 2 and Comparative Example 1 produced in (1), a charge-discharge cycle test was 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 2.80 V. However, in order to confirm the accurate capacity at the 50th, 100th, and 200th cycles, the test was performed using a constant current of 0.1 C.

[0093] A graph showing the relationship between the number of cycles and the capacity obtained from the above test is shown in Figure 1. 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 2-isocyanatoethyl methacrylate (A1) or 2-isocyanatoethyl acrylate (A2) was included in the non-aqueous electrolyte, it was found that the capacity was retained for a long period of time.

[0094] (4) Battery resistance increase rate The lithium secondary batteries of Examples 1 to 5 and Comparative Example 1 produced in (1) were used, and the lithium secondary batteries in a charged state were left at 60° C. for 4 weeks to measure the rate of increase in battery resistance. The results of the measurement of the rate of increase in battery resistance of the lithium secondary batteries after 200 cycles of charge-discharge cycle test are shown in Table 2 below.

[0095] [Table 2]

[0096] As can be seen from the results in Table 2, in particular in Examples 1 and 2 in which an electrolyte solution containing 2-isocyanatoethyl methacrylate or 2-isocyanatoethyl acrylate was used as the non-aqueous electrolyte solution, the increase in the resistance of the battery after high-temperature storage and after the cycle test was kept low, and it was found that the battery had excellent stability.

[0097] In addition, for the lithium secondary batteries of Example 2 and Comparative Example 1 that were tested, the amounts of metals detected from the negative electrode active materials after the tests were measured by ICP atomic emission spectrometry. The results are shown in Table 3 below.

[0098] [Table 3]

[0099] The metal amount measurement results shown in Table 3 indicate the influence of metal elution from the positive electrode. As can be seen from the results in Table 3, it was revealed that the elution of metals, particularly cobalt, was suppressed at high temperatures, particularly in Example 2, which used an electrolyte solution containing 2-isocyanatoethyl acrylate as the non-aqueous electrolyte solution. [Industrial Applicability]

[0100] The acid or moisture reducing agent of the present invention and the nonaqueous electrolyte solution containing the same are useful because they can suppress the generation of acid, thereby suppressing the elution of the positive electrode metal even under high temperature conditions, can retain capacity even after repeated charging and discharging many times, and can suppress an increase in battery resistance.

Claims

1. A (meth)acrylate containing an amide bond, The (meth)acrylate containing an amide bond is the following compound: 【Chemistry 1】 An additive that removes acid or both acid and water from the non-aqueous electrolyte solution, selected from the following:

2. A non-aqueous electrolyte solution comprising the additive according to claim 1.

3. The non-aqueous electrolyte solution according to claim 2, wherein the (meth)acrylate containing an amide bond is contained in an amount of 0.1 to 1 mass % based on the total mass of the non-aqueous electrolyte solution.

4. The nonaqueous electrolyte solution according to claim 2 or 3, further comprising a cyclic carbonate and a chain carbonate.

5. The non-aqueous electrolyte solution according to claim 2 , further comprising a lithium salt.

6. The lithium salt is LiPF ６ The non-aqueous electrolyte solution according to claim 5 .

7. positive electrode, negative electrode, The nonaqueous electrolyte according to any one of claims 2 to 6, which is disposed between the positive electrode and the negative electrode. A lithium secondary battery comprising:

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

9. 9. The lithium secondary battery according to claim 7 or 8, wherein the negative electrode comprises a material containing silicon.

10. The method includes adding an amide bond-containing (meth)acrylate to a non-aqueous electrolyte solution, The (meth)acrylate containing an amide bond is the following compound: 【Chemistry 2】 The method for removing an acid or both an acid and water from a non-aqueous electrolyte solution, comprising the steps of:

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