Nonaqueous electrolyte containing additive for nonaqueous electrolyte and lithium secondary battery containing the same

Abstract

The present invention provides a non-aqueous electrolyte containing an additive for a non-aqueous electrolyte represented by the following chemical formula 1: JPEG2024517274000009.jpg62170In the above chemical formula 1, R 1 ~R 5 may each independently be any one selected from the group consisting of H, an alkenyl group having 2 to 20 carbon atoms, an alkynyl group having 2 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, a cycloalkenyl group having 3 to 12 carbon atoms, and a nitrile group.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0129871 filed on September 30, 2021 and Korean Patent Application No. 10-2022-0125570 filed on September 30, 2022, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a non-aqueous electrolyte containing an additive for a non-aqueous electrolyte and a lithium secondary battery containing the same. [Background technology]

[0003] In recent years, the application areas of lithium secondary batteries have rapidly expanded from power supply for electronic devices such as electrical, electronic, communication, and computer equipment to power storage and supply for large-area devices such as automobiles and power storage devices. Accordingly, there has been an increasing demand for high-capacity, high-power, and highly stable secondary batteries.

[0004] In particular, high capacity, high power output, and long life are important characteristics for lithium secondary batteries for automotive applications. To achieve high capacity, secondary batteries often use positive electrode active materials with high nickel content, which have high energy density but low stability, or are operated at high voltages.

[0005] However, when a secondary battery is operated under the above conditions, as charging and discharging proceeds, side reactions caused by electrolyte degradation can cause deterioration of the coatings formed on the surfaces of the positive and negative electrodes or the structure of the electrode surfaces, leading to the elution of transition metal ions from the surface of the positive electrode.The eluted transition metal ions are then electro-deposited on the negative electrode, which reduces the passivation properties of the SEI, resulting in the degradation of the negative electrode.

[0006] Such deterioration of secondary batteries tends to be accelerated when the potential of the positive electrode increases or when the battery is exposed to high temperatures.

[0007] Furthermore, when lithium-ion batteries are used continuously for long periods of time or left at high temperatures, gas is generated and the battery thickness increases, a phenomenon known as swelling. It is known that the amount of gas generated at this time depends on the state of the SEI.

[0008] Therefore, in order to solve these problems, research and development efforts are being conducted to find a method that can suppress the elution of metal ions in the positive electrode, form a stable SEI film on the negative electrode, reduce the swelling phenomenon of secondary batteries, and improve their stability at high temperatures. Summary of the Invention [Problem to be solved by the invention]

[0009] As a result of extensive research into solving the above problems, the present invention aims to provide an additive for a non-aqueous electrolyte that can suppress deterioration of a positive electrode, reduce side reactions between a positive electrode and an electrolyte, and form a stable SEI film on a negative electrode.

[0010] Another object of the present invention is to provide a non-aqueous electrolyte that contains the additive for a non-aqueous electrolyte and thereby has improved stability at high temperatures.

[0011] Another object of the present invention is to provide a lithium secondary battery that contains the non-aqueous electrolyte, thereby improving high-temperature cycle characteristics and high-temperature storage characteristics, and thereby improving various performances. [Means for solving the problem]

[0012] According to one embodiment, in order to achieve the above object, the present invention provides a non-aqueous electrolyte including an additive for a non-aqueous electrolyte represented by the following Chemical Formula 1:

[0013] [ka]

[0014] In the above Chemical Formula 1, R1 to R5 may each independently be any one selected from the group consisting of H, an alkenyl group having 2 to 20 carbon atoms, an alkynyl group having 2 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, a cycloalkenyl group having 3 to 12 carbon atoms, and a nitrile group.

[0015] According to another embodiment, the present invention provides a lithium secondary battery including the non-aqueous electrolyte. [Effects of the Invention]

[0016] The compound represented by Formula 1, which is provided as an additive for a non-aqueous electrolyte according to the present invention, is a compound based on an imidazole structure fused with a cycloalkyl ring, and can minimize an increase in the resistance of a lithium secondary battery while forming a stable SEI (Solid Electrolyte Interphase) film on the surface of the negative electrode. Therefore, deterioration of the passivation characteristics of the SEI at high temperatures can be suppressed, thereby preventing deterioration of the negative electrode.

[0017] In addition, the compound represented by Chemical Formula 1, which is provided as an additive for a non-aqueous electrolyte of the present invention, has high binding energy with PF5, a by-product of LiPF6 used as a lithium salt during charging and discharging, and therefore has the effect of suppressing further decomposition of PF5 and increasing the durability of the battery.

[0018] Therefore, when the nonaqueous electrolyte of the present invention containing the compound of Chemical Formula 1 is used, a stable and low-resistance electrode-electrolyte interface can be formed even at high temperatures, thereby improving the high-temperature cycle characteristics and high-temperature storage characteristics, and realizing a lithium secondary battery with improved performance. DETAILED DESCRIPTION OF THE INVENTION

[0019] The terms and words used in this specification and claims should not be interpreted in a limited way to their ordinary or dictionary meanings, but should be interpreted in a way that is consistent with the technical idea of ​​the present invention, based on the principle that the inventors can appropriately define the concepts of terms in order to best explain their inventions.

[0020] As used herein, the terms "comprises," "comprises," or "having" are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, and should be understood as not precluding the presence or possible addition of one or more other features, numbers, steps, components, or combinations thereof.

[0021] In addition, in the description of "number of carbon atoms a to b" herein, "a" and "b" refer to the number of carbon atoms contained in a specific functional group. That is, the functional group may contain "a" to "b" carbon atoms. For example, an "alkylene group having 1 to 5 carbon atoms" refers to an alkylene group containing 1 to 5 carbon atoms, i.e., -CH2-, -CH2CH2-, -CH2CH2CH2-, -CH2(CH3)CH-, -CH(CH3)CH2-, and -CH(CH3)CH2CH2-.

[0022] In addition, in this specification, the term "alkylene group" means a branched or unbranched divalent hydrocarbon group.

[0023] In this specification, an alkyl group or alkylene group may be substituted or unsubstituted. Unless otherwise defined, the term "substituted" means that at least one hydrogen atom bonded to a carbon atom is replaced with an element other than hydrogen, such as an alkyl group having 1 to 20 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, an alkynyl group having 2 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, a cycloalkenyl group having 3 to 12 carbon atoms, a heterocycloalkyl group having 3 to 12 carbon atoms, a heterocycloalkenyl group having 3 to 12 carbon atoms, an aryloxy group having 6 to 12 carbon atoms, a halogen atom, a fluoroalkyl group having 1 to 20 carbon atoms, a nitro group, an aryl group having 6 to 20 carbon atoms, a heteroaryl group having 2 to 20 carbon atoms, or a haloaryl group having 6 to 20 carbon atoms.

[0024] The present invention will now be described in more detail.

[0025] non-aqueous electrolyte A non-aqueous electrolyte according to one embodiment of the present invention contains, as an additive, a compound represented by the following Chemical Formula 1. A secondary battery containing the non-aqueous electrolyte of the present invention is inhibited from deterioration due to interfacial reactions at high temperatures, and can have excellent high-temperature cycle characteristics and high-temperature storage characteristics.

[0026] [ka]

[0027] The compound of Formula 1 is a compound based on an imidazole structure fused with a cycloalkyl ring, which minimizes an increase in the resistance of a lithium secondary battery and can form a stable SEI (Solid Electrolyte Interphase) film on the surface of the negative electrode. Therefore, it can prevent the deterioration of the passivation characteristics of the SEI at high temperatures and prevent the deterioration of the negative electrode.

[0028] In the above Chemical Formula 1, R1 to R5 may each independently represent any one selected from the group consisting of H, an alkenyl group having 2 to 20 carbon atoms, an alkynyl group having 2 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, a cycloalkenyl group having 3 to 12 carbon atoms, and a nitrile group. Preferably, R1 and R2 in the above Chemical Formula 1 are H, and R3 to R5 may each independently represent any one selected from the group consisting of H, an alkenyl group having 2 to 20 carbon atoms, an alkynyl group having 2 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, a cycloalkenyl group having 3 to 12 carbon atoms, and a nitrile group. Most preferably, R1 to R5 in the above Chemical Formula 1 may be H.

[0029] Specifically, the compound of Chemical Formula 1 may be a compound of Chemical Formula 1-1 below.

[0030] [ka]

[0031] The additive for a non-aqueous electrolyte according to the present invention may be contained in an amount of 0.01 to 5 parts by weight, preferably 0.05 to 0.9 parts by weight, more preferably 0.1 to 0.5 parts by weight, and most preferably 0.3 parts by weight, per 100 parts by weight of the non-aqueous electrolyte. When the content of the compound represented by Chemical Formula 1 satisfies the above range, a sufficient coating film is formed on the positive electrode, which inhibits the elution of transition metals from the positive electrode active material, and the viscosity of the electrolyte is maintained at an appropriate level, resulting in excellent rate characteristics and life characteristics during high-temperature storage.

[0032] The non-aqueous electrolyte according to the present invention may further contain a lithium salt, an organic solvent, or other electrolyte additives.

[0033] The lithium salt is used as an electrolyte salt in a lithium secondary battery and is used as a medium for transferring ions. Generally, the lithium salt contains, for example, Li as a cation.+ and as an anion, F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , B 10 Cl 10 - , AlCl4 - , AlO2 - , PF6 - , CF3SO3 - , CH3CO2 - , CF3CO2 - , AsF6 - , SbF6 - , CH3SO3 - , (CF3CF2SO2)2N - , (CF3SO2)2N - , (FSO2)2N - , BF2C2O4 - , BC4O8 - , PF4C2O4 - , PF2C4O8 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , C4F9SO3 - , CF3CF2SO3 - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , CF3(CF2)7SO3 - , and SCN - At least one selected from the group consisting of:

[0034] Specifically, the lithium salts include LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10, LiAlCl4, LiAlO2, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiN(SO2F)2 (lithium bis(fluorosulfonyl)imide; LiFSI), LiN(SO2CF2CF3)2 (lithium bis(perfluoroethanesulfonyl)imide; LiBETI), and LiN(SO2CF3)2 (lithium bis(trifluoromethanesulfonyl)imide; LiTFSI). In addition to these, any lithium salt commonly used in the electrolyte of a lithium secondary battery can be used without any limitation.

[0035] To obtain the optimum effect of forming a corrosion prevention coating on the electrode surface, the lithium salt may be contained in the electrolyte at a concentration of 0.5 M to 4 M, preferably 0.5 M to 3 M, and more preferably 0.8 M to 2 M. When the concentration of the lithium salt satisfies the above range, the effect of improving the cycle characteristics of the lithium secondary battery during high-temperature storage is sufficient, and the viscosity of the non-aqueous electrolyte is appropriate, thereby improving the electrolyte impregnation.

[0036] The nonaqueous electrolyte according to the present invention may contain LiPF as a lithium salt because of its excellent high-temperature stability. In this case, the compound represented by Chemical Formula 1 has high binding energy with PF, a by-product of LiPF used as the lithium salt during charging and discharging, thereby suppressing the further decomposition reaction of PF and increasing battery durability.

[0037] In addition, in order to produce an electrolyte having high ionic conductivity, the organic solvent may further contain at least one or more ester organic solvents selected from the group consisting of linear ester organic solvents and cyclic ester organic solvents in addition to at least one or more carbonate organic solvents selected from the group consisting of cyclic carbonate organic solvents and linear carbonate organic solvents.

[0038] The non-aqueous organic solvent may include at least one organic solvent selected from the group consisting of cyclic carbonate organic solvents, linear carbonate organic solvents, linear ester organic solvents, and cyclic ester organic solvents.

[0039] Specifically, the organic solvent may include a cyclic carbonate organic solvent, a linear carbonate organic solvent, or a mixed organic solvent thereof.

[0040] The cyclic carbonate organic solvent is a highly viscous organic solvent that has a high dielectric constant and therefore easily dissociates the lithium salt in the electrolyte. Specific examples of the cyclic carbonate organic solvent include at least one organic solvent selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, and vinylene carbonate, and among these, ethylene carbonate may be included.

[0041] The linear carbonate organic solvent is an organic solvent having low viscosity and low dielectric constant, and typical examples thereof include at least one organic solvent selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate, and ethyl propyl carbonate, and specifically, ethyl methyl carbonate (EMC) may be used.

[0042] Specific examples of such linear ester-based organic solvents include at least one organic solvent selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate.

[0043] The cyclic ester organic solvent may be at least one organic solvent selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0044] Meanwhile, the organic solvent may further include, as needed, any organic solvent commonly used in non-aqueous electrolytes, for example, at least one of an ether-based organic solvent, a glyme-based organic solvent, and a nitrile-based organic solvent.

[0045] The ether solvent may be any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, ethyl propyl ether, 1,3-dioxolane (DOL), and 2,2-bis(trifluoromethyl)-1,3-dioxolane (TFDOL), or a mixture of two or more of these, but is not limited thereto.

[0046] The glyme-based solvent has a higher dielectric constant and lower surface tension than linear carbonate-based organic solvents and is less reactive with metals, and may include at least one selected from the group consisting of dimethoxyethane (glyme, DME), diethoxyethane, diglyme, triglyme, and tetraglyme (TEGDME), but is not limited thereto.

[0047] The nitrile solvent may be one or more selected from the group consisting of acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile, but is not limited thereto.

[0048] In addition, the non-aqueous electrolyte of the present invention may further contain a known electrolyte additive, as needed, to prevent the non-aqueous electrolyte from being decomposed in a high-power environment, thereby causing the collapse of the negative electrode, or to further improve low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, and the effect of suppressing battery expansion at high temperatures.

[0049] Representative examples of such other electrolyte additives may include at least one SEI film-forming additive selected from the group consisting of cyclic carbonate-based compounds, halogen-substituted carbonate-based compounds, sultone-based compounds, sulfate-based compounds, phosphate-based compounds, borate-based compounds, nitrile-based compounds, benzene-based compounds, amine-based compounds, silane-based compounds, and lithium salt-based compounds.

[0050] Examples of the cyclic carbonate compounds include vinylene carbonate (VC) and vinylethylene carbonate.

[0051] The halogen-substituted carbonate compounds include fluoroethylene carbonate (FEC).

[0052] The sultone compound includes at least one compound selected from the group consisting of 1,3-propane sultone (PS), 1,4-butane sultone, ethene sultone, 1,3-propene sultone (PRS), 1,4-butene sultone, and 1-methyl-1,3-propene sultone.

[0053] Examples of the sulfate-based compounds include ethylene sulfate (Esa), trimethylene sulfate (TMS), and methyl trimethylene sulfate (MTMS).

[0054] The phosphate-based compound may be one or more compounds selected from the group consisting of lithium difluoro(bisoxalato)phosphate, lithium difluorophosphate, tetramethyltrimethylsilylphosphate, trimethylsilylphosphite, tris(2,2,2-trifluoroethyl)phosphate, and tris(trifluoroethyl)phosphite.

[0055] Examples of the borate-based compounds include tetraphenylborate, lithium oxalyldifluoroborate (LiODFB), and lithium bisoxalateborate (LiB(C2O4)2, LiBOB).

[0056] Examples of the nitrile compound include at least one compound selected from the group consisting of succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

[0057] The benzene-based compound may be fluorobenzene, the amine-based compound may be triethanolamine or ethylenediamine, and the silane-based compound may be tetravinylsilane.

[0058] The lithium salt-based compound is a compound different from the lithium salt contained in the non-aqueous electrolyte, and examples thereof include lithium difluorophosphate (LiDFP), LiPO2F2, and LiBF4.

[0059] Among these other electrolyte additives, when a combination of vinylene carbonate (VC), 1,3-propane sultone (PS), ethylene sulfate (Esa), and lithium difluorophosphate (LiDFP) is further included, a stronger SEI film can be formed on the surface of the negative electrode during the initial activation process of the secondary battery, and the generation of gas that may be generated by decomposition of the electrolyte at high temperatures can be suppressed, thereby improving the high-temperature stability of the secondary battery.

[0060] Meanwhile, the other electrolyte additives may be used in combination of two or more kinds, and may be contained in an amount of 0.05 to 20 wt %, specifically 0.1 to 15 wt %, and preferably 0.3 to 10 wt %, based on the total weight of the non-aqueous electrolyte. When the content of the other electrolyte additives satisfies the above range, better ionic conductivity and improved cycle characteristics can be obtained.

[0061] Lithium secondary battery The present invention also provides a lithium secondary battery containing the non-aqueous electrolyte.

[0062] Specifically, the lithium secondary battery includes a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, a separator interposed between the positive electrode and the negative electrode, and the non-aqueous electrolyte.

[0063] The lithium secondary battery of the present invention can be manufactured by a conventional method known in the art, for example, by forming an electrode assembly in which a positive electrode, a negative electrode, and a separator are sequentially stacked between the positive electrode and the negative electrode, inserting the electrode assembly into a battery case, and injecting the nonaqueous electrolyte according to the present invention into the battery case.

[0064] (1) Positive electrode The positive electrode may be prepared by coating a positive electrode mixture slurry containing a positive electrode active material, a binder, a conductive material, and a solvent on a positive electrode current collector.

[0065] The positive electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has conductivity. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or those obtained by surface treatment of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. may be used.

[0066] The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium. Specifically, it may include a lithium metal oxide containing one or more metals such as cobalt, manganese, nickel, or aluminum and lithium. More specifically, the lithium metal oxide includes lithium-manganese-based oxides (e.g., LiMnO2, LiMn2O4, etc.), lithium-cobalt-based oxides (e.g., LiCoO2, etc.), lithium-nickel-based oxides (e.g., LiNiO2, etc.), lithium-nickel-manganese-based oxides (e.g., LiNi 1-Y Mn Y O2 (where 0 < Y < 1), LiMn 2-Z Ni Z O4 (where 0 < Z < 2), etc.), lithium-nickel-cobalt-based oxides (e.g., LiNi 1-Y1 Co Y1 O2 (where 0 < Y1 < 1), etc.), lithium-manganese-cobalt-based oxides (e.g., LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2-Z1 Co Z1 O4 (where 0 < Z1 < 2), etc.), lithium-nickel-manganese-cobalt-based oxides (e.g., Li(Ni p Co q Mn r )O2 (where 0 < p < 1, 0 < q < 1, 0 < r < 1, p + q + r = 1) or Li(Ni p1 Co q1 Mn r1 )O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r1 < 2, p1 + q1 + r1 = 2), etc.), or lithium-nickel-cobalt-transition metal (M) oxides (e.g., Li(Ni p2 Co q2 Mnr2 M S2 )O2 (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r2, and s2 are atomic fractions of independent elements, respectively, where 0 < p2 < 1, 0 < q2 < 1, 0 < r2 < 1, 0 < s2 < 1, and p2 + q2 + r2 + s2 = 1), etc.) etc. may be mentioned, and one or more of these compounds may be included.

[0067] Among them, from the point of view of being able to enhance the capacity characteristics and stability of the battery, the lithium metal oxide is LiCoO2, LiMnO2, LiNiO2, lithium nickel manganese cobalt oxide (for example, Li(Ni 1 / 3 Mn 1 / 3 Co 1 / 3 )O2, Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2 and Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, etc.), or lithium nickel cobalt aluminum oxide (for example, Li(Ni 0.8 Co 0.15 Al 0.05 )O2, etc.), etc. may be used, and one or more mixtures of these may be used.

[0068] Among them, from the point of view of being able to enhance the capacity characteristics of the battery the most, a positive electrode active material with a nickel content of 80 atm% or more can be used. For example, the lithium transition metal oxide may include those represented by the following Chemical Formula 2.

[0069] [Chemical Formula 2] Li x Ni a Co b M 1 c M 2d O2

[0070] In the above Chemical Formula 2, the M 1 is one or more selected from Mn and Al, and may be preferably Mn or a combination of Mn and Al.

[0071] M 2 may be one or more selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S.

[0072] The x represents the atomic fraction of lithium in the lithium transition metal oxide, and may be 0.90≦x≦1.1, preferably 0.95≦x≦1.08, and more preferably 1.0≦x≦1.08.

[0073] The a represents the atomic fraction of nickel among the metal elements excluding lithium in the lithium transition metal oxide, and may be 0.80≦a<1.0, preferably 0.80≦a≦0.95, and more preferably 0.80≦a≦0.90. When the nickel content satisfies the above range, high capacity characteristics can be achieved.

[0074] The b represents the atomic fraction of cobalt among the metal elements excluding lithium in the lithium transition metal oxide, and is 0. <b<0.2、0<b≦0.15、または0.01≦b≦0.10であってもよい。

[0075] The c is M among the metal elements other than lithium in the lithium transition metal oxide. 1 represents the atomic fraction of 0 <c<0.2、0<c≦0.15、または0.01≦c≦0.10であってもよい。

[0076] The d is the number of metal elements other than lithium in the lithium transition metal oxide. 2 and may be 0≦d≦0.1, or 0≦d≦0.05.

[0077] The positive electrode active material may be contained in the positive electrode mixture slurry in an amount of 60 to 99 wt %, preferably 70 to 99 wt %, and more preferably 80 to 98 wt %, based on the total weight of solids excluding the solvent.

[0078] The binder is a component that assists in binding the active material and the conductive material and in binding them to the current collector.

[0079] Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene (PE), polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluororubber, and various copolymers.

[0080] Generally, the binder may be contained in the positive electrode mixture slurry in an amount of 1 to 20% by weight, preferably 1 to 15% by weight, and more preferably 1 to 10% by weight, based on the total weight of solids excluding the solvent.

[0081] The conductive material is a component for further improving the conductivity of the positive electrode active material and may be added in an amount of 1 to 20 wt % based on the total weight of the solid content in the positive electrode mixture slurry. The conductive material is not particularly limited as long as it does not cause chemical changes in the battery and has conductivity, and examples of such 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 highly developed crystalline structures; conductive fibers such as carbon fiber and metal fiber; conductive powders such as carbon fluoride powder, 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.

[0082] Generally, the conductive material may be contained in the positive electrode mixture slurry in an amount of 1 to 20% by weight, preferably 1 to 15% by weight, and more preferably 1 to 10% by weight, based on the total weight of solids excluding the solvent.

[0083] The solvent may contain an organic solvent such as NMP (N-methyl-2-pyrrolidone), and may be used in an amount that provides a suitable viscosity when containing the positive electrode active material, and optionally a binder, a conductive material, etc. For example, the solvent may be contained so that the concentration of the solids including the positive electrode active material, and optionally a binder and a conductive material, is 50 to 95 wt %, preferably 70 to 95 wt %, and more preferably 70 to 90 wt %.

[0084] (2) Negative electrode The negative electrode may be prepared by coating a negative electrode mixture slurry containing a negative electrode active material, a binder, a conductive material, and a solvent on a negative electrode current collector, or a graphite electrode made of carbon (C) or a metal itself may be used as the negative electrode.

[0085] For example, when a negative electrode is manufactured by coating a negative electrode mixture slurry onto the negative electrode current collector, the negative electrode current collector generally has a thickness of 3 to 500 μm. Such a negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, aluminum-cadmium alloy, etc. may be used. Furthermore, as with the positive electrode current collector, the bonding strength of the negative electrode active material may be strengthened by forming fine irregularities on the surface, and the negative electrode current collector may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0086] Further, the negative electrode active material may contain at least one or more selected from the group consisting of lithium metal, a carbon material capable of reversibly intercalating / deintercalating lithium ions, a metal or an alloy of these metals and lithium, a metal composite oxide, a material capable of doping and undoping lithium, and a transition metal oxide.

[0087] The carbon material capable of reversibly intercalating / deintercalating lithium ions can be used without particular limitation as long as it is a carbon-based negative electrode active material generally used in lithium ion secondary batteries. Representative examples thereof include crystalline carbon, amorphous carbon, or both of these may be used. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon (low-temperature fired carbon) or hard carbon, mesophase pitch carbide, fired coke, and the like.

[0088] 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.

[0089] 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.

[0090] 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. Also, at least one of these may be mixed with SiO2 and used. The element Y 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, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

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

[0092] The negative electrode active material may be contained in an amount of 60 to 99% by weight, preferably 70 to 99% by weight, more preferably 80 to 98% by weight, based on the total weight of the solid content in the negative electrode binder slurry.

[0093] The binder is a component that helps bind the conductive material, active material, and current collector together. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluororubber, and various copolymers thereof. Specifically, styrene-butadiene rubber (SBR)-carboxymethyl cellulose (CMC) can be used because of its high viscosity.

[0094] Generally, the binder may be contained in the negative electrode mixture slurry in an amount of 1 to 20% by weight, preferably 1 to 15% by weight, and more preferably 1 to 10% by weight, based on the total weight of solids excluding the solvent.

[0095] The conductive material is a component for further improving the conductivity of the negative electrode active material and may be added in an amount of 1 to 20 wt % based on the total weight of the solid content in the negative electrode mixture slurry. Such a conductive material is not particularly limited as long as it does not cause chemical changes in the battery and has conductivity, and examples thereof 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 highly developed crystalline structures; conductive fibers such as carbon fiber and metal fiber; conductive powders such as carbon fluoride powder, 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.

[0096] The conductive material may be contained in the negative electrode mixture slurry in an amount of 1 to 20% by weight, preferably 1 to 15% by weight, and more preferably 1 to 10% by weight, based on the total weight of solids excluding the solvent.

[0097] The solvent may include water or an organic solvent such as NMP (N-methyl-2-pyrrolidone), and may be used in an amount that provides a suitable viscosity when containing the negative electrode active material, and optionally a binder and a conductive material, etc. For example, the solvent may be included so that the concentration of the solids including the negative electrode active material, and optionally a binder and a conductive material, is 50% by weight to 95% by weight, preferably 70% by weight to 90% by weight.

[0098] When a metal is used as the anode, the anode can be fabricated by physically bonding, rolling, or depositing a metal on a metal thin film or the anode current collector. The deposition method can be electrochemical deposition or chemical vapor deposition.

[0099] For example, the metal thin film itself or the metal bonded / rolled / deposited on the negative electrode current collector may include one metal or an alloy of two metals selected from the group consisting of lithium (Li), nickel (Ni), tin (Sn), copper (Cu), and indium (In).

[0100] (3) Separator The separator may be a conventional porous polymer film, such as a porous polymer film made of a polyolefin polymer such as an ethylene homocopolymer, a propylene homocopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, either alone or in a laminate, or a conventional porous nonwoven fabric, such as a nonwoven fabric made of a high-melting point glass fiber or polyethylene terephthalate fiber, but is not limited to these. Furthermore, to ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer material may be used, and may be selectively used as a single-layer or multi-layer structure.

[0101] Specifically, the separator included in the electrode assembly of the present invention may be a safety reinforced separator (SRS) having a coating layer containing a ceramic component or a polymer material formed thereon to ensure heat resistance or mechanical strength.

[0102] Specifically, the separator included in the electrode assembly of the present invention may include a porous separator substrate and a porous coating layer that is entirely coated on one or both sides of the separator substrate. The coating layer may include a mixture of inorganic particles selected from metal oxides, metalloid oxides, metal fluorides, metal hydroxides, and combinations thereof, and a binder polymer that binds and fixes the inorganic particles to each other.

[0103] The coating layer may contain inorganic particles selected from one or more of Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, YO3, SrTiO3, BaTiO3, Mg(OH)2, and MgF. The inorganic particles can improve the thermal stability of the separator. That is, the inorganic particles can prevent the separator from shrinking at high temperatures. The binder polymer can fix the inorganic particles and improve the mechanical stability of the separator.

[0104] The external shape of the lithium secondary battery of the present invention is not particularly limited, and may be a cylindrical shape using a can, a square shape, a pouch shape, a coin shape, or the like.

[0105] The present invention will be described in more detail below with reference to specific examples. However, the following examples are merely illustrative for understanding the present invention and are not intended to limit the scope of the present invention. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the present description and technical concept, and it goes without saying that such changes and modifications fall within the scope of the appended claims.

[0106] Example Example 1 (Production of non-aqueous electrolyte) A non-aqueous solvent was prepared by dissolving LiPF6 at 1.0 M and vinylene carbonate (VC) at 0.5 wt % in an organic solvent (ethylene carbonate (EC): ethyl methyl carbonate (EMC) = 30:70 volume ratio), and 0.1 g of a compound represented by the following Formula 1-1 was added to 99.9 g of the non-aqueous solvent to prepare a non-aqueous electrolyte.

[0107] [ka]

[0108] (Lithium secondary battery manufacturing) Cathode active material (LiNi 0.9 Co 0.06 Mn 0.03 Al 0.01 A cathode slurry (solid content 60 wt%) was prepared by adding O2, a conductive material (carbon black), and a binder (polyvinylidene fluoride) in a weight ratio of 97.6:0.8:1.6 to a solvent, N-methyl-2-pyrrolidone (NMP). The cathode slurry was applied to one side of a 13.5 μm-thick cathode current collector (Al thin film), dried, and roll-pressed to prepare a cathode.

[0109] Anode active material (graphite:SiO = 90.0:10.0 weight ratio), conductive material (carbon black), and binder (styrene-butadiene rubber (SBR)-carboxymethyl cellulose (CMC)) were mixed in a weight ratio of 97.6:0.8:1.6 to N-methyl-2-pyrrolidone (NMP) as a solvent to prepare anode slurry (solid content 60 wt%). The anode slurry was applied to one side of a 6 μm-thick anode current collector (Cu thin film), dried, and roll-pressed to prepare anode.

[0110] In a dry room, a polyolefin-based porous separator coated with inorganic particles Al2O3 was interposed between the positive electrode and negative electrode prepared above, and the non-aqueous electrolyte prepared above was then injected to prepare a secondary battery.

[0111] Example 2 A secondary battery was fabricated in the same manner as in Example 1, except that 0.3 g of the compound of Formula 1-1 was added to 99.7 g of the non-aqueous solvent prepared in Example 1 to prepare a non-aqueous electrolyte.

[0112] Example 3 A secondary battery was fabricated in the same manner as in Example 1, except that 0.5 g of the compound of Formula 1-1 was added to 99.5 g of the non-aqueous solvent prepared in Example 1 to prepare a non-aqueous electrolyte.

[0113] Comparative Example 1 A secondary battery was manufactured in the same manner as in Example 1, except that the non-aqueous electrolyte was prepared using 100 g of the non-aqueous solvent prepared in Example 1.

[0114] Experimental Example 1: Evaluation of high-temperature cycle characteristics The cycle characteristics of each of the secondary batteries produced in Examples 1 to 3 and Comparative Example 1 were evaluated.

[0115] Specifically, each of the batteries manufactured in Examples 1 to 3 and Comparative Example 1 was charged at 45° C. with a constant current of 0.33 C up to 4.2 V and discharged at a constant current of 0.33 C down to 2.8 V, and then subjected to 100 charge-discharge cycles, after which the rate of increase in resistance relative to the initial resistance after 100 cycles was measured. The results are shown in Table 1 below.

[0116] [Table 1]

[0117] As shown in Table 1, Examples 1 to 3, which used the additive for non-aqueous electrolytes of the present invention, had a lower resistance increase rate and better life characteristics than Comparative Example 1, which did not use the additive.

[0118] Experimental Example 2 - Evaluation of high-temperature storage characteristics The secondary batteries produced in Examples 1 to 3 and Comparative Example 1 were evaluated for high-temperature storage characteristics.

[0119] Specifically, each of the secondary batteries of Examples 1 to 3 and Comparative Example 1 was fully charged to 4.2 V and then stored at 60° C. for 4 weeks.

[0120] Before storage, the volume of the body of the fully charged secondary battery was measured and set as the initial volume of the secondary battery.

[0121] After 4 weeks, the volume of the body of the secondary battery was measured again, and the volume increase during the 4-week storage period was calculated. The volume increase rate after 4 weeks was calculated by calculating the percentage of the increased volume relative to the initial volume of the secondary battery. The results are shown in Table 2 below.

[0122] [Table 2]

[0123] As shown in Table 2, the secondary batteries of Examples 1 to 3 had a smaller volume increase rate after 4 weeks than the secondary battery of Comparative Example 1, and generated less gas at high temperatures.

Claims

1. A non-aqueous electrolyte for a lithium secondary battery, comprising an additive for a non-aqueous electrolyte represented by the following chemical formula 1: 【Chemical 1】 (In the above chemical formula 1, R １ ~R ５ are each independently any one selected from the group consisting of H, an alkenyl group having 2 to 20 carbon atoms, an alkynyl group having 2 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, a cycloalkenyl group having 3 to 12 carbon atoms, and a nitrile group.

2. R of Formula 1 １ and R ２ The nonaqueous electrolyte for a lithium secondary battery according to claim 1 , wherein is H.

3. R of Formula 1 １ ~R ５ The nonaqueous electrolyte for a lithium secondary battery according to claim 1 , wherein is H.

4. 2. The non-aqueous electrolyte for a lithium secondary battery according to claim 1, wherein the additive for the non-aqueous electrolyte is contained in an amount of 0.01 to 5 parts by weight based on 100 parts by weight of the non-aqueous electrolyte.

5. LiCl, LiBr, LiI, LiBF ４ , LiClO ４ , LiB １０ Cl １０ , LiAlCl ４ , LiAlO ２ , LiPF ６ , LiCF ３ SO ３ , LiCH ３ CO ２ , LiCF ３ CO ２ , LiAsF ６ , LiSbF ６ , LiCH ３ SO ３ , LiN(SO ２ F) ２ , LiN(SO ２ CF ２ CF ３ ) ２ , and LiN(SO ２ CF ３ ) ２ 2. The nonaqueous electrolyte for a lithium secondary battery according to claim 1, further comprising at least one lithium salt selected from the group consisting of:

6. LiPF as a lithium salt ６ The nonaqueous electrolyte for a lithium secondary battery according to claim 5 , comprising:

7. The LiPF ６ The nonaqueous electrolyte for a lithium secondary battery according to claim 6, wherein the nonaqueous electrolyte is contained at a concentration of 0.5 M to 4 M.

8. The nonaqueous electrolyte for a lithium secondary battery according to claim 1 , further comprising an organic solvent.

9. 9. The nonaqueous electrolyte for a lithium secondary battery according to claim 8, wherein the organic solvent comprises at least one organic solvent selected from the group consisting of a cyclic carbonate organic solvent, a linear carbonate organic solvent, a linear ester organic solvent, and a cyclic ester organic solvent.

10. 10. The nonaqueous electrolyte for a lithium secondary battery according to claim 9, wherein the cyclic carbonate organic solvent includes at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, and vinylene carbonate.

11. 10. The nonaqueous electrolyte for a lithium secondary battery according to claim 9, wherein the linear carbonate organic solvent includes at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate, and ethyl propyl carbonate.

12. 10. The nonaqueous electrolyte for a lithium secondary battery according to claim 9, wherein the linear ester-based organic solvent includes at least one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate.

13. 10. The nonaqueous electrolyte for a lithium secondary battery according to claim 9, wherein the cyclic ester organic solvent contains at least one selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

14. 9. The nonaqueous electrolyte for a lithium secondary battery according to claim 8, wherein the organic solvent comprises a cyclic carbonate organic solvent, a linear carbonate organic solvent, or a mixed organic solvent of a cyclic carbonate organic solvent and a linear carbonate organic solvent.

15. 2. The nonaqueous electrolyte for a lithium secondary battery according to claim 1, further comprising, as an additive, one or more compounds selected from the group consisting of cyclic carbonate compounds, halogen-substituted carbonate compounds, sultone compounds, sulfate compounds, phosphate compounds, borate compounds, nitrile compounds, benzene compounds, amine compounds, silane compounds, and lithium salt compounds.

16. 16. A lithium secondary battery comprising: a positive electrode containing a positive electrode active material; a negative electrode containing a negative electrode active material; a separator interposed between the positive electrode and the negative electrode; and the nonaqueous electrolyte for a lithium secondary battery according to claim 1.

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