Lithium ion secondary battery

Abstract

The purpose of the present invention is to provide a lithium ion secondary battery having improved capacity retention. The lithium ion secondary battery according to the present invention comprises: a positive electrode containing a positive electrode active material; a negative electrode containing a negative electrode active material; and a non-aqueous electrolyte containing an electrolyte additive. The positive electrode active material contains nickel. In addition, the electrolyte additive is represented by chemical formula (1), where R1, R2, and R3 may be identical to or different from one another and are each an alkyl group having 1 to 5 carbon atoms; R4 is an alkylene group having 1 to 5 carbon atoms; and R5 is a CN group, a NH2 group, an SH group, or a halogen atom.

Description

lithium-ion secondary battery

[0001] The present invention relates to a lithium-ion secondary battery.

[0002] This application claims the benefit of priority based on Japanese Patent Application No. 2024-232656 filed on December 27, 2024, and all contents disclosed in the document of the said Korean patent application are incorporated as part of this specification.

[0003] Recently, as lithium-ion rechargeable batteries are being used not only for electronic devices such as smartphones and PCs but also as power sources for transportation equipment such as automobiles, there is an even greater demand for higher capacity.

[0004] Currently, commercially available lithium-ion rechargeable batteries using graphite as the anode are close to their theoretical capacity, making it difficult to achieve significantly higher capacities. Consequently, the development of lithium-ion rechargeable batteries utilizing materials that alloy with Li, such as Si, as the anode is underway. However, such anodes exhibit significant volume expansion and contraction during charging and discharging. This volume change can lead to cracking in the SEI (electrolyte-electrolyte interface) film. If cracks form in the film, electrolyte decomposition reactions or lithium ion consumption may occur. These reactions cause a reduction in charge-discharge cycle life and lead to gas generation issues. In particular, for Si anodes, capacity and lifespan are in a trade-off relationship, making it a challenge to achieve both high capacity and long lifespan.

[0005] To solve this problem, several methods are being developed. One approach to stabilizing a robust solid electrolyte interphase (SEI) involves nanosizing the anode active material particles to suppress volume change (Non-patent Literature 1). Additionally, another approach involves using a Si-based carbon composite material as the anode active material (Non-patent Literature 2).

[0006] [Prior Art Literature]

[0007] [Non-patent literature]

[0008] Non-patent Document 1: Chen P, Xu J, Chen H, Zhou C. 2011. Hybrid silicon-carbon nanostructured composites as superior anodes for lithium ion batteries. Nano Res.. 4(3): 290-296

[0009] Non-patent literature 2: Park M, Kim MG, Joo J, Kim K, Kim J, Ahn S, Cui Y, Cho J. 2009. Silicon Nanotube Battery Anodes. Nano Lett. 9(11): 3844-3847.

[0010] However, the prior art described above had a certain effect on the stabilization of SEI, but the capacity retention rate was still insufficient.

[0011] The present invention was made to solve the problems of the prior art as described above, and aims to provide a lithium-ion secondary battery with improved capacity retention rate.

[0012] As a result of carefully examining the above problem, the inventors discovered that in the case of a lithium-ion secondary battery comprising a positive electrode containing a specific positive active material, a negative electrode, and an electrolyte containing a specific electrolyte additive, the capacity retention rate is improved, and thus reached the completion of the present invention.

[0013] To solve the above problem, the present invention includes the following configuration.

[0014] The lithium-ion secondary battery according to the present embodiment is,

[0015] Anode containing a positive electrode active material,

[0016] A cathode containing a cathode active material, and

[0017] A non-aqueous electrolyte containing an electrolyte additive is provided,

[0018] The above positive active material contains nickel, and

[0019] The above electrolyte additive is the following chemical formula (1):

[0020] [Chemical Formula (1)]

[0021]

[0022] It is an electrolyte additive represented by (wherein R1, R2 and R3 may be the same or different and are alkyl groups with 1 to 5 carbon atoms, R4 is an alkylene group with 1 to 5 carbon atoms, and R5 is a CN group, NH2 group, SH group, or halogen element).

[0023] In one embodiment, the compound represented by the above chemical formula (1) is the following chemical formula (2):

[0024] [Chemical Formula (2)]

[0025]

[0026] (In the formula, R is a CN group, NH2 group, SH group, or halogen element) can be represented.

[0027] In one embodiment, the electrolyte additive represented by the above chemical formula (1) may be contained in an amount of 0.1 mass% or more and 5.0 mass% or less with respect to the total mass of the above non-aqueous electrolyte.

[0028] In one embodiment, the non-aqueous electrolyte may further contain cyclic carbonates and linear carbonates.

[0029] In one embodiment, the non-aqueous electrolyte may further contain a lithium salt.

[0030] In one embodiment, the nickel content contained in the positive electrode active material may be 40 mass% or more and 90 mass% or less with respect to the total amount of the positive electrode active material.

[0031] In one embodiment, the negative electrode active material may contain Si elements.

[0032] In one embodiment, the charging voltage of the lithium-ion secondary battery according to the present invention may be 4.3V or higher.

[0033] According to the present invention, a lithium-ion secondary battery with improved capacity retention rate can be provided.

[0034] However, the effects obtainable through the present invention are not limited to those described above, and other unmentioned technical effects will be clearly understood by those skilled in the art from the description of the invention below.

[0035] The present invention will be described in more detail below.

[0036] Terms and words used in this specification and claims shall not be interpreted as being limited to their ordinary or dictionary meanings, and shall be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe their invention.

[0037] A lithium-ion secondary battery according to one embodiment of the present invention comprises a positive electrode containing a positive active material, a negative electrode containing a negative active material, and a non-aqueous electrolyte containing an electrolyte additive, wherein the positive active material contains nickel and the electrolyte additive is represented by the following chemical formula (1).

[0038] [Chemical Formula (1)]

[0039]

[0040] (In the formula, R1, R2, and R3 may be the same or different and are alkyl groups having 1 to 5 carbon atoms, R4 is an alkylene group having 1 to 5 carbon atoms, and R5 is a CN group, NH2 group, SH group, or a halogen element.)

[0041] [Electrolyte]

[0042] A lithium-ion secondary battery according to the present invention comprises a non-aqueous electrolyte and contains a compound represented by the following chemical formula (1) in the non-aqueous electrolyte.

[0043] [Chemical Formula (1)]

[0044]

[0045] In chemical formula (1), R1, R2 and R3 may be the same or different from each other and are alkyl groups with 1 to 5 carbon atoms, R4 is an alkylene group with 1 to 5 carbon atoms, and R5 is a CN group, NH2 group, SH group, or halogen element.

[0046] Preferably, the compound represented by the above chemical formula (1) may also be the compound represented by the following chemical formula (2).

[0047] [Chemical Formula (2)]

[0048]

[0049] (In the formula, R is a CN group, NH2 group, SH group, or halogen element.)

[0050] Although not bound by theory, the lithium-ion secondary battery according to the present invention contains a compound represented by the above chemical formula (1) in the electrolyte, thereby forming a complex between the transition metal, particularly nickel, in the positive electrode active material and the compound represented by the above chemical formula (1), and promoting the formation of CEI (Cathode Electrolyte Interphase) on the positive electrode surface. As a result, the leaching of the transition metal from the positive electrode active material is suppressed. Accordingly, it is believed that suppressing the reaction between the transition metal and the solid electrolyte interphase (SEI) on the negative electrode surface leads to an improvement in the capacity retention rate or cycle life of the lithium-ion secondary battery.

[0051] In chemical formula (1), R1, R2, and R3 may be the same or different from each other and may be alkyl groups having 1 to 5 carbon atoms. Preferably, R1, R2, and R3 may be the same. Preferably, R1, R2, and R3 may be alkyl groups having 1 to 3 carbon atoms, and more preferably, R1, R2, and R3 may be ethyl groups. Although not bound by theory, when R1, R2, and R3 are alkyl groups having 1 to 5 carbon atoms, -OR1, -OR2, and -OR3 groups can be easily removed from the compound represented by chemical formula (1), which is advantageous for the formation of CEI.

[0052] In chemical formula (1), R4 may be an alkylene group having 1 to 5 carbon atoms. Preferably, R4 may be an alkylene group having 1 to 3 carbon atoms. More preferably, R4 may be an ethylene group. Although not bound by theory, when R4 is an alkylene group having 1 to 5 carbon atoms, it is advantageous for CEI formation.

[0053] In chemical formula (1), R5 may be a CN group, an NH2 group, an SH group, or a halogen element. Preferably, the halogen element may be F, Cl, Br, or I. Preferably, R5 may be an SH group. Although not limited to theory, when R5 is a CN group, an NH2 group, an SH group, or a halogen element, the bonding strength between R5 and the transition metal in the positive electrode active material, particularly nickel, is high, which is advantageous for the formation of CEI and can suppress the leaching of the transition metal in the positive electrode active material.

[0054] The ratio of the mass of the compound represented by the above chemical formula (1) to the mass of the above non-aqueous electrolyte is calculated by the following mathematical formula 1.

[0055] [Mathematical Formula 1]

[0056] (Ratio of the mass of the compound represented by chemical formula (1) to the mass of the non-aqueous electrolyte) (mass%) = (Mass of the compound represented by chemical formula (1)) (g) / (Total mass of the non-aqueous electrolyte) (g)

[0057] Preferably, the ratio of the mass of the compound represented by Formula (1) to the mass of the non-aqueous electrolyte may be 0.01 mass% or more and 5.0 mass% or less. For example, the content of the compound represented by Formula (1) contained in the non-aqueous electrolyte can be identified by gas chromatography, nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FT-IR), etc. In one embodiment, the ratio of the mass of the compound represented by Formula (1) to the mass of the non-aqueous electrolyte may be 0.05 mass% or more and 3.0 mass% or less. The lower limit of this mass ratio may be 0.01 mass% or more, 0.05 mass% or more, 0.1 mass% or more, or 0.3 mass% or more. Additionally, the upper limit of the mass ratio may be 5.0 mass% or less, 3.0 mass% or less, 2.5 mass% or less, or 1 mass% or less.

[0058] The non-aqueous electrolyte used in the lithium-ion secondary battery according to the present invention preferably contains at least one type selected from cyclic carbonates and linear carbonates as a solvent. More preferably, the non-aqueous electrolyte contains cyclic carbonates and linear carbonates.

[0059] Cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate (VC), methyl vinylene carbonate, ethyl vinylene carbonate, 1,2-diethyl vinylene carbonate, vinyl ethylene carbonate (VEC), 1-methyl-2-vinyl ethylene carbonate, 1-ethyl-2-vinyl ethylene carbonate, 1-methyl-2-vinyl ethylene carbonate, 1,1-divinyl ethylene carbonate, 1,2-divinyl ethylene carbonate, 1,1-dimethyl-2-methylene ethylene carbonate, 1,1-diethyl-2-methylene ethylene carbonate, ethynyl ethylene carbonate, 1,2-diethynyl ethylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, Examples include 2,3-pentylene carbonate, chloroethylene carbonate, and combinations thereof.

[0060] Examples of linear carbonates 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.

[0061] The non-aqueous electrolyte may contain a carbonate containing fluorine atoms as a cyclic carbonate or a linear carbonate. Examples of carbonates containing fluorine atoms 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-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-dioxoran-2-one, trans or cis 4,5-difluoro-1,3-dioxoran-2-one, 4-ethynyl-1,3-dioxoran-2-one, methyl-2,2,2-trifluoroethyl carbonate, and combinations thereof. there is.

[0062] In particular, among carbonates, cyclic carbonates such as ethylene carbonate, propylene carbonate, and fluoroethylene carbonate are high-viscosity organic solvents. Ethylene carbonate and propylene carbonate have high dielectric constants, which facilitate the dissociation of lithium salts in the electrolyte. By mixing these cyclic carbonates with linear carbonates of low viscosity and low dielectric constant, such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, in appropriate proportions, an electrolyte with high electrical conductivity can be produced.

[0063] The non-aqueous electrolyte of the present invention may contain a mixture of cyclic carbonates and linear carbonates. The ratio of cyclic carbonates to the total of cyclic carbonates and linear carbonates is preferably 1 volume% or more and 95 volume% or less, more preferably 1 volume% or more and 50 volume% or less, and more preferably 5 volume% or more and 30 volume% or less.

[0064] The non-aqueous electrolyte of the present invention may further contain an ester compound. Examples of ester compounds include carboxylic acid esters. Examples of carboxylic acid esters 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 some of the hydrogens of the carboxylic acid esters are substituted with fluorine, and combinations thereof.

[0065] In addition to the above, the non-aqueous electrolyte of the present invention may contain other solvents without particular limitation, such as ether compounds such as cyclic ethers or linear ethers, polyethers, sulfur-containing solvents and phosphorus-containing solvents, as long as it does not impede the purpose of the present invention.

[0066] Examples of cyclic ethers include tetrahydrofuran and 2-methyltetrahydrofuran. Additionally, the non-aqueous electrolyte of the present invention may further contain linear ethers. Examples of linear ethers include dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, and ethyl propyl ether.

[0067] The non-aqueous electrolyte used in the lithium-ion secondary battery according to the present invention may contain an electrolyte generally used in lithium-ion secondary batteries. The electrolyte acts as a medium for transporting ions involved in electrochemical reactions within the lithium-ion secondary battery. Preferably, the non-aqueous electrolyte used in the lithium-ion secondary battery according to the present invention contains a lithium salt as the electrolyte.

[0068] The lithium salt contained in the non-aqueous electrolyte used in the lithium-ion secondary battery according to the present invention is, for example, LiPF6, LiBF4, LiB12 F 12 , LiAsF6, LiFSO3, Li2SiF6, LiCF3CO2, LiCH3CO2, LiCF3SO3, LiC4F9SO3, LiCF3CF2SO3, LiCF3(CF2)7SO3, LiCF3CF2(CF3)2CO, Li(CF3SO2)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, LiPF2(CF3)4, LiPF3(CF3)3, LiPF4(CF3)2, LiPF4(C2F5)2, LiPF4(CF3SO2)2, LiPF4(C2F5SO2)2, LiBF2C2O4, LiBC4O8, It may include LiBF2(CF3)2, LiBF2(C2F5)2, LiBF2(CF3SO2)2, LiBF2(C2F5SO2)2, LiSbF6, LiAlO4, LiAlF4, LiSCN, LiClO4, LiCl, LiF, LiBr, LiI, LiAlCl4, lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), etc. In one embodiment, the electrolyte used in the lithium-ion secondary battery according to the present invention contains LiTFSI as a lithium salt. A single type of lithium salt may be used alone, or a combination of multiple lithium salts may be used.

[0069] The content of the electrolyte is not particularly limited, but it may be contained in an amount of 0.1 mol / L or more and 5 mol / L or less, preferably 0.5 mol / L or more and 3 mol / L or less, and more preferably 0.5 mol / L or more and 2 mol / L or less, with respect to the total amount of the non-aqueous electrolyte. By setting the amount of the electrolyte to the above range, sufficient battery characteristics can be obtained.

[0070] In the lithium-ion secondary battery according to the present invention, the non-aqueous electrolyte may contain at least one other additive. Examples of other additives include flame retardants, wetting agents, stabilizers, rust inhibitors, gelling agents, overcharge inhibitors, and negative electrode film forming additives.

[0071] [cathode]

[0072] The negative electrode used in the lithium-ion secondary battery of the present invention can be manufactured, for example, by coating a negative electrode slurry containing a negative electrode active material, a binder, a conductive material, and a solvent onto a negative electrode current collector, and then drying and rolling.

[0073] The negative electrode current collector can generally have a thickness of 3 μm or more and 500 μm or less. The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the lithium-ion secondary battery of the present invention and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel with a surface treatment such as carbon, nickel, titanium, and silver, and aluminum-cadmium alloys can be used as negative electrode current collectors. In addition, the negative electrode current collector may strengthen the bonding strength of the negative active material by forming fine irregularities on its surface, similar to the positive electrode current collector, and may be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0074] In the lithium-ion secondary battery according to the present invention, it is preferable that the negative electrode active material contains silicon (Si). Examples of Si-containing materials include Si and SiO. x (0 < x < 2), a Si-A alloy (wherein A 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 a mixture of at least one of these and SiO2 may be used. Preferably, the silicon-containing material is Si or SiO2x (0 < x < 2) may be the case. Most preferably, the silicon-containing material may be Si. Although not bound by theory, when Si is contained as a negative electrode active material, the expansion and contraction of the negative electrode volume are large, making it easy for the SEI on the negative electrode surface to be damaged. Therefore, if a compound represented by the chemical formula (1) according to the present invention is contained in the electrolyte, the outflow of transition metal from the anode is suppressed, thereby allowing for effects such as significantly improved capacity retention rate and improved cycle life.

[0075] It is preferable that the cathode active material be contained in an amount of 80 mass% or more and 99 mass% or less with respect to the total mass of solids in the cathode slurry, and it is more preferable that it be contained in an amount of 90 mass% or more and 99 mass% or less.

[0076] A binder is a component that helps bond between a conductive material, a cathode active material, and a current collector. It is preferable that the binder be contained in an amount of 1 mass% or more and 30 mass% or less relative to the total mass of solids in the cathode slurry, and more preferable that it be contained in an amount of 1 mass% or more and 10 mass% or less. Examples of binders 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 (SBR), and fluororubber. A single type of binder may be used alone, or a combination of multiple compounds may be used.

[0077] A conductive material is a component for further improving the conductivity of the negative electrode active material. The conductive material may be contained in an amount of 0.1 mass% or more and 20 mass% or less, for example, 0.5 mass% or more and 10 mass% or less, for example, 1 mass% or more and 3 mass% or less, based on the total mass of the solids in the negative electrode slurry. As for the conductive material, it is not particularly limited as long as it does not cause chemical changes in the lithium-ion secondary battery and possesses conductivity, and examples 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 powders; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0078] The solvent used in the cathode slurry is not particularly limited as long as it can be formed into a slurry using the cathode active material, binder, and conductive material as the cathode material, and for example, water or organic solvents such as NMP and alcohol can be used. In addition, the solvent can be used in an amount such that the cathode slurry has an appropriate viscosity, for example, in an amount such that the solid content concentration in the slurry is 50 mass% or more and 75 mass% or less, preferably 50 mass% or more and 65 mass% or less.

[0079] [anode]

[0080] The positive electrode used in the lithium-ion 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 onto a positive electrode current collector, and then drying and rolling.

[0081] As for the positive current collector, it is not particularly limited as long as it does not cause chemical changes in the lithium-ion secondary battery of the present invention and has conductivity. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. can be used as the positive current collector.

[0082] The cathode active material is a compound capable of reversibly absorbing and releasing lithium, and specifically, may contain a lithium composite metal oxide comprising lithium and one or more metals such as cobalt, manganese, nickel, or aluminum. More specifically, the lithium composite metal oxide is a lithium-manganese-based oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt-based oxide (e.g., LiCoO2, etc.), a lithium-nickel-based oxide (e.g., LiNiO2, etc.), or a lithium-nickel-manganese-based oxide (e.g., LiNi 1-y1 Mn y1 O2 (where, 0 < y1 < 1), LiMn 2-z1 Ni z O4 (where 0 < Z1 < 2), etc.), lithium-nickel-cobalt oxides (e.g., LiNi 1-y2 Co y2 O2 (where 0 < y2 < 1), etc.), lithium-manganese-cobalt oxides (e.g., LiCo 1-y3 Mn y3 O2 (where, 0 < y3 < 1), LiMn 2-z2 Co z2 O4 (where 0 < Z2 < 2), etc.), lithium-nickel-manganese-cobalt oxides (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 Examples include )O2(wherein M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, p3, q3, r3 and s3 are each atomic fractions of independent elements, 0<p3<1, 0<q3<1, 0<r3<1, 0<s3<1, p3+q3+r3+s3=1), etc., and these may be included individually or two or more.

[0083] Preferably, in order to improve the capacity characteristics and stability of the battery, the lithium composite metal oxide may be a lithium composite metal oxide containing a nickel-containing metal and lithium. Specifically, lithium-nickel-based oxides (e.g., LiNiO2, etc.) and lithium-nickel-manganese-cobalt (NCM) oxides (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.), lithium-nickel-cobalt-aluminum (NCA) oxide (e.g., Li(Ni 0.8 Co 0.15 Al 0.05 )O2, etc.), or lithium-nickel-cobalt-manganese-aluminum (NCMA) oxide (e.g., Li[Ni 0.90 Co 0.045 Mn 0.045 Al 0.01]O2) etc. can be used. In particular, it is desirable 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, in terms of cost.

[0084] It is preferable that the positive active material be contained in an amount of 80 mass% or more and 99 mass% or less with respect to the total mass of solids in the positive slurry, and more preferable that it be contained in an amount of 90 mass% or more and 99 mass% or less. By making the content of the positive active material within the above range, high energy density and capacity can be obtained.

[0085] A binder is a component that helps bond the positive active material and the conductive material, and also helps bond to the current collector. It is preferable that the binder be contained in an amount of 1 mass% or more and 30 mass% or less relative to the total mass of the solids in the positive slurry. Examples of binders include polyvinylidene fluoride (PVdF), 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.

[0086] The conductive material is a substance that imparts conductivity to the lithium-ion secondary battery of the present invention without causing chemical changes. It is preferable that the conductive material be contained in an amount of 0.5 mass% or more and 50 mass% or less with respect to the total mass of the solids in the anode slurry, and more preferable that it be contained in an amount of 1 mass% or more and 20 mass% or less, for example, 1 mass% or more and 5 mass% or less. By containing the conductive material in the above range, the electrical conductivity of the anode is improved. In addition, by containing the conductive material in the above range, a lithium-ion secondary battery with high energy density and capacity can be obtained.

[0087] Examples of conductive materials include carbon powders such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; graphite powders such as natural graphite, artificial graphite, and graphite with developed crystal structures; conductive fibers such as carbon fibers and metal fibers; metal powders such as aluminum and nickel powders; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0088] The solvent of the anode slurry is not limited to any solvent that can be formed into a slurry using an anode active material, a binder, and a conductive material as the anode material, and for example, organic solvents such as NMP (N-methyl-2-pyrrolidone), DMF (dimethylformamide), acetone, dimethylacetamide, and water may be used. In addition, the anode slurry may be used in an amount such that the viscosity of the anode slurry is appropriate, for example, in an amount such that the solid content concentration in the slurry is 10 mass% or more and 60 mass% or less, preferably 20 mass% or more and 50 mass% or less.

[0089] [Separator]

[0090] In the lithium-ion secondary battery according to the present invention, a separator may be interposed between the positive electrode and the negative electrode.

[0091] The separator of the lithium-ion secondary battery of the present invention serves to block internal short circuits between two electrodes and impregnate the electrolyte. The separator can be formed by preparing a separator composition by mixing a polymer resin, a filler, and a solvent, and then directly coating and drying the separator composition on the upper surface of the electrode. Alternatively, the separator can be formed by casting and drying the separator composition onto a support, and then laminating the separator film peeled from the support onto the upper surface of the electrode.

[0092] As a separator, a porous polymer film made of a polyolefin-based polymer, such as a conventional porous polymer film used as a separator, for example, an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, may be used alone or in a laminate thereof, or a conventional porous nonwoven fabric, for example, a nonwoven fabric such as a high melting point glass fiber or a polyethylene terephthalate fiber, may be used, but is not limited to these.

[0093] The pore diameter of the porous separator is generally 0.01 µm or more and 50 µm or less, and the porosity may be 5% or more and 95% or less. In addition, the thickness of the porous separator may generally be in the range of 5 µm or more and 300 µm or less.

[0094] [Lithium-ion secondary battery]

[0095] The external shape of the lithium-ion secondary battery of the present invention is not particularly limited, but may be cylindrical, prismatic, pouch-type, or coin-type.

[0096]

[0097] The present invention will be described in more detail below through examples, but the following examples are intended to illustrate the invention and the scope of the invention is not limited thereto.

[0098] <1. Production of the Battery>

[0099] (1) Examples 1 to 8 and Comparative Example 1

[0100] (i) Fabrication of the anode plate

[0101] As a positive active material, NCM (811) ternary cathode material (Li(Ni) 0.8 Co 0.1 Mn 0.1An anode slurry was prepared by dispersing 96.5 mass% of O2, 1.5 mass% of acetylene black as a conductive material, and 2 mass% of polyvinylidene fluoride (PVdF) as a binder in an N-methyl-2-pyrrolidone solvent. The prepared anode slurry was uniformly coated onto an Al foil, heated and vacuum dried, and then pressed to achieve a predetermined film thickness and composite density to obtain an anode plate.

[0102] (ii) Fabrication of the cathode plate

[0103] A cathode slurry was prepared by dispersing 97.0 mass% of a mixture of graphite and Si in a mass ratio of 90:10 as a cathode active material, and 3.0 mass% of styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) as binders in water. The prepared cathode slurry was uniformly coated onto a Cu foil, heated and vacuum dried, and then pressed to achieve a predetermined film thickness and composite density to obtain a cathode plate.

[0104] (iii) Preparation of electrolyte

[0105] As a solvent, a mixture of EC (cyclic carbonate) and EMC (linear carbonate) in a volume ratio of 10:90 was used, and LiFSI was dissolved therein as a solute to a salt concentration of 1 M to form a base electrolyte. To the base electrolyte, an electrolyte additive represented by the following chemical formula (1) having the structure shown in Table 1 was added at the concentration shown in Table 1 to obtain an electrolyte.

[0106] [Chemical Formula (1)]

[0107]

[0108] (iv) Assembly of the battery

[0109] A pouch cell with an opposing area of ​​approximately 12 cm² was fabricated using the above positive plate, negative plate, electrolyte, and a polyolefin film (polyethylene separator) as a separator. The fabricated cells were designated as Examples 1 to 8 and Comparative Example 1.

[0110] (2) Comparative Example 2

[0111] LiCo as a positive electrode active material 0.5 Mn 0.5 A battery was manufactured in the same manner as in Example 2, except that O2 was used.

[0112] (3) Comparative Example 3

[0113] LiCo as a positive electrode active material 0.5 Mn 0.5 A battery was manufactured in the same manner as Comparative Example 1, except that O2 was used.

[0114] <2. Battery Evaluation>

[0115] (1) 45℃ charge / discharge cycle test

[0116] Using the lithium-ion secondary batteries of Examples 1 to 8 and Comparative Examples 1 to 3 prepared, a charge-discharge cycle test was conducted at 45°C with an upper charge limit voltage of 4.3V and a lower discharge limit voltage of 2.8V. The initial discharge capacity was measured under conditions of 0.1C before the start of the cycle. In addition, at 300 cycles, a test was conducted using a constant current of 0.1C to verify the accurate capacity. From the measured capacity, the capacity retention rate was calculated according to the following Equation 2.

[0117] [Mathematical Formula 2]

[0118] (Capacity retention rate)(%) = (Discharge capacity after 300 cycles (mAh·g) -1 ) / Initial discharge capacity (mAh·g -1 ))×100

[0119] In addition, the initial resistance and the resistance after 300 cycles were measured under the condition of SOC 50%, and the resistivity was calculated according to the following mathematical formula 3.

[0120] [Mathematical Formula 3]

[0121] (Resistivity)(%) = (Resistance after 300 cycles (Ω) / Initial resistance (Ω)) × 100

[0122] In addition, the volume change of the pouch cell before and after the test was measured, the volume expansion rate was calculated according to the following mathematical formula 4, and the effect of gas generation due to side reactions was evaluated. The volume of the pouch cell was measured by the Archimedes method.

[0123] [Mathematical Formula 4]

[0124] (Volume Expansion Rate)(%) = (Pouch Cell Volume After 300 Cycles (cm³) / Pouch Cell Volume Before Cycle Test (cm³)) × 100

[0125] (2) High temperature storage test

[0126] For the batteries of Examples 1 to 8 and Comparative Examples 1 to 3 charged under conditions of 0.1C, the resistance was measured in the charged state. After the measurement, the batteries were left in a 60°C environment for 2 weeks, and then the resistance was measured again to conduct a high-temperature storage test. Based on the measured resistance values, the resistivity was calculated according to the following Equation 5.

[0127] [Mathematical Formula 5]

[0128] (Resistivity)(%) = (Resistance after high-temperature storage (Ω) / Initial resistance (Ω)) × 100

[0129] The results obtained from each evaluation are shown in Table 1.

[0130]

[0131] From Table 1, it can be seen that the batteries of Examples 1 to 8 have a higher capacity retention rate, lower resistivity, and lower volume expansion rate after the cycle test than the battery of Comparative Example 1. In addition, it can be seen that the resistivity after the high-temperature storage test is also low.

[0132] In addition, from Comparative Examples 2 and 3 of Table 1, it can be seen that even if an additive represented by chemical formula (1) is contained in the electrolyte, the effect of improving capacity retention rate does not appear when Ni is not contained in the positive active material.

[0133] The lithium-ion secondary battery according to the present invention is useful because it suppresses the leakage of transition metals from the positive electrode active material, thereby improving the capacity retention rate and charge / discharge cycle characteristics of the lithium-ion secondary battery.

Claims

1. Anode containing a positive active material, A cathode containing a cathode active material, and A non-aqueous electrolyte containing an electrolyte additive is provided, The above positive active material contains nickel, and The above electrolyte additive is the following chemical formula (1): [Chemical Formula (1)] (In the formula, R1, R2, and R3 may be the same or different, and are alkyl groups having 1 to 5 carbon atoms, and R4 is an alkylene group with 1 to 5 carbon atoms, and R5 is a CN group, NH2 group, SH group, or halogen element. A lithium-ion secondary battery, which is an electrolyte additive indicated by 2. In Paragraph 1, A compound represented by the above chemical formula (1) is the following chemical formula (2): [Chemical Formula (2)] (In the formula, R is a CN group, NH2 group, SH group, or halogen element) A lithium-ion secondary battery, indicated by.

3. In Paragraph 1, A lithium-ion secondary battery in which an electrolyte additive represented by the above chemical formula (1) is contained in an amount of 0.1 mass% or more and 5.0 mass% or less with respect to the total mass of the above non-aqueous electrolyte.

4. In Paragraph 1, A lithium-ion secondary battery in which the above-mentioned non-aqueous electrolyte further contains cyclic carbonate and linear carbonate.

5. In Paragraph 1, A lithium-ion secondary battery in which the above-mentioned non-aqueous electrolyte further contains a lithium salt.

6. In any one of paragraphs 1 through 5, A lithium-ion secondary battery in which the nickel content contained in the positive electrode active material is 40 mass% or more and 90 mass% or less with respect to the total amount of the positive electrode active material.

7. In any one of paragraphs 1 through 5, A lithium-ion secondary battery in which the above-mentioned negative electrode active material contains Si elements.

8. In any one of paragraphs 1 through 5, A lithium-ion secondary battery with a charging voltage of 4.3V or higher.

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