Nonaqueous electrolyte and lithium secondary battery containing same

Abstract

The present invention provides a non-aqueous electrolyte comprising a lithium salt, an organic solvent, a compound represented by Chemical Formula 1 as a first additive, and a compound represented by Chemical Formula 2 as a second additive. TIFF2024540035000022.tif129158In chemical formula 1, A is a cyclic phosphate group having 2 or 3 carbon atoms, R is an alkylene group having 1 to 5 carbon atoms or an alkenylene group having 2 to 5 carbon atoms, and X is a perfluoroalkyl group having 1 to 5 carbon atoms. In Chemical Formula 2, R1 to R6 are each independently any one selected from the group consisting of H, F, a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 10 carbon atoms, a substituted or unsubstituted alkynyl group having 2 to 10 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 10 carbon atoms, a substituted or unsubstituted alkylcarbonyl group having 2 to 10 carbon atoms, a substituted or unsubstituted alkyl ester group having 1 to 10 carbon atoms, CN, SO3, and SO3CF3.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0059163, filed on May 13, 2022, and all contents disclosed in the documents of this Korean patent application are incorporated herein by reference.

[0002] The present invention relates to 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 may use positive electrode active materials with high nickel content, which have high energy density but low stability, or may be operated at high voltage.

[0005] However, when a secondary battery is operated under the above conditions, as charging and discharging proceeds, the coating formed on the surface of the positive and negative electrodes or the electrode surface structure deteriorates due to side reactions caused by electrolyte degradation, which can lead 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, reducing the passivation ability of the SEI, resulting in the degradation of the negative electrode.

[0006] Such deterioration of secondary batteries tends to accelerate when the potential of the positive electrode increases or when the battery is exposed to high temperatures, and this deterioration causes the problem of deterioration in the cycle characteristics of the secondary battery.

[0007] Furthermore, when a lithium-ion battery is used continuously for a long 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, an object of the present invention is to provide a non-aqueous electrolyte having improved stability at high temperatures by including an additive for a non-aqueous electrolyte that can suppress deterioration of the positive electrode, reduce side reactions between the positive electrode and the electrolyte, and form a stable SEI film on the negative electrode.

[0010] Another object of the present invention is to provide a lithium secondary battery containing the above non-aqueous electrolyte, which has improved high-temperature cycle characteristics and high-temperature storage characteristics, and thus improved performance. [Means for solving the problem]

[0011] In order to achieve the above object, one embodiment of the present invention provides a non-aqueous electrolyte comprising a lithium salt, an organic solvent, a compound represented by the following Chemical Formula 1 as a first additive, and a compound represented by the following Chemical Formula 2 as a second additive:

[0012] [ka]

[0013] In the above chemical formula 1, A is a cyclic phosphate group having 2 or 3 carbon atoms, R is an alkylene group having 1 to 5 carbon atoms or an alkenylene group having 2 to 5 carbon atoms, and X is a perfluoroalkyl group having 1 to 5 carbon atoms.

[0014] [ka]

[0015] In the above chemical formula 2, R1 to R6 are each independently any one selected from the group consisting of H, F, a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 10 carbon atoms, a substituted or unsubstituted alkynyl group having 2 to 10 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 10 carbon atoms, a substituted or unsubstituted alkylcarbonyl group having 2 to 10 carbon atoms, a substituted or unsubstituted alkylester group having 1 to 10 carbon atoms, CN, SO3, and SO3CF3.

[0016] Another embodiment of the present invention provides a lithium secondary battery including the non-aqueous electrolyte. [Effects of the Invention]

[0017] The compound represented by Formula 1, which is provided as the first additive for a non-aqueous electrolyte of the present invention, is a compound based on a cyclic phosphate structure. During the formation of the negative electrode SEI layer, a ring-opening reaction occurs, resulting in poly-phosphoesterification. This allows the formation of a resilient and strong SEI (Solid Electrolyte Interphase) coating on the surface of the negative electrode. This prevents the SEI from losing its passivation ability at high temperatures, thereby preventing negative electrode degradation.

[0018] The compound represented by Formula 2, which is provided as a second additive for a non-aqueous electrolyte according to the present invention, is a compound based on a coumarin structure and can be rapidly reductively decomposed during charge and discharge to form a stable SEI (Solid Electrolyte Interphase) coating on the surface of the negative electrode. This prevents the SEI from losing its passivation ability at high temperatures, thereby preventing negative electrode degradation. Furthermore, the coumarin structure contained in the compound represented by Formula 2 binds with reactive oxygen compounds generated at a positive electrode containing a high content of nickel positive electrode active material, thereby suppressing electrolyte decomposition and gas generation.

[0019] Furthermore, in a nonaqueous electrolyte containing a second additive along with a first additive of the present invention, the second additive promotes the ring-opening reaction of the first additive by generating free radicals during a reduction reaction at the negative electrode, thereby aiding in the film-forming reaction. The film formed by the interaction between the first additive and the second additive contains both a polymerizable ester structure with high physical durability and a polyphosphoester structure with excellent ion transport properties on the surface of the negative electrode, thereby improving the charge / discharge characteristics and output characteristics of the lithium secondary battery. Furthermore, the film formed by the interaction between the first additive and the second additive is highly durable and therefore highly resistant to volume expansion of the negative electrode that occurs during charge / discharge.

[0020] Therefore, by using the nonaqueous electrolyte of the present invention containing the first additive and the second additive, it is possible to form an electrode-electrolyte interface that is stable even at high temperatures and has high durability, 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

[0021] 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 inventor can appropriately define the concept of the term in order to best explain his / her invention.

[0022] 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.

[0023] 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-.

[0024] In addition, in this specification, the term "alkylene group" means a branched or unbranched divalent saturated hydrocarbon group, and the term "alkenylene group" means a branched or unbranched divalent unsaturated hydrocarbon group containing a double bond.

[0025] Furthermore, in this specification, both the alkyl group and the 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 substituted 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.

[0026] The present invention will now be described in more detail.

[0027] non-aqueous electrolyte The non-aqueous electrolyte according to the present invention may contain a second additive together with the first additive described below.

[0028] The nonaqueous electrolyte according to the present invention includes a compound represented by the following Chemical Formula 1 as a first additive. The compound represented by the following Chemical Formula 1 is a compound based on a cyclic phosphate structure, and undergoes a ring-opening reaction during the formation of the negative electrode SEI layer, resulting in poly-phosphoesterification. This allows the formation of a resilient and strong SEI (Solid Electrolyte Interphase) coating on the surface of the negative electrode.

[0029] [ka]

[0030] In the above chemical formula 1, A may be a cyclic phosphate group having 2 or 3 carbon atoms, R may be an alkylene group having 1 to 5 carbon atoms or an alkenylene group having 2 to 5 carbon atoms, and X may be a perfluoroalkyl group having 1 to 5 carbon atoms.

[0031] In the above formula 1, A may be a cyclic phosphate group having 2 or 3 carbon atoms, preferably a cyclic phosphate group having 2 carbon atoms. When A is a cyclic phosphate group having 2 carbon atoms, the ring strain is relatively high, and the ring-opening reaction occurs easily.

[0032] In the above chemical formula 1, R may be an alkylene group having 1 to 5 carbon atoms or an alkenylene group having 2 to 5 carbon atoms, preferably an alkylene group having 1 to 5 carbon atoms, and most preferably an alkylene group having 1 to 3 carbon atoms.

[0033] In Chemical Formula 1, X may be a perfluoroalkyl group having 1 to 5 carbon atoms, preferably CF3 or CF2CF3. The additive of Chemical Formula 1 contains a perfluoroalkyl group, which facilitates the production of inorganic LiF and allows the formation of a stable SEI layer based on a polymer-inorganic material. This allows the formation of a polymer-inorganic material coating rich in inorganic materials such as LiF, and has the effect of suppressing deterioration due to interfacial reactions.

[0034] The non-aqueous electrolyte according to the present invention contains a compound represented by the following chemical formula 2 as a second additive.

[0035] [ka]

[0036] In the above Chemical Formula 2, R1 to R6 may each independently be any one selected from the group consisting of H, F, a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 10 carbon atoms, a substituted or unsubstituted alkynyl group having 2 to 10 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 10 carbon atoms, a substituted or unsubstituted alkylcarbonyl group having 2 to 10 carbon atoms, a substituted or unsubstituted alkylester group having 1 to 10 carbon atoms, CN, SO3, and SO3CF3, and preferably, R2, R3, R4, and R6 in the above Chemical Formula 2 may be H. In the above Chemical Formula 2, the substituent may be a substituent such as F, CN, SO3, SO3CF3, or -C≡CH.

[0037] The alkylcarbonyl group having 2 to 10 carbon atoms has a -COR' structure, where R' may be an alkyl group having 1 to 9 carbon atoms, an alkenyl group having 2 to 9 carbon atoms, or an alkynyl group having 2 to 9 carbon atoms. The alkylester group having 2 to 10 carbon atoms has a -COOR'' structure, where R'' may be an alkyl group having 1 to 9 carbon atoms, an alkenyl group having 2 to 9 carbon atoms, or an alkynyl group having 2 to 9 carbon atoms.

[0038] In addition, the compound of Formula 2 may contain at least one nitrile group or propargyl group. By including a nitrile group or propargyl group in addition to the coumarin structure, a dense coating can be formed on the electrode, thereby suppressing deterioration due to interfacial reactions at high temperatures.

[0039] Specifically, the compound represented by Chemical Formula 2 of the present invention may be any one of the compounds represented by Chemical Formulas 2a to 2j below.

[0040] [ka]

[0041] [ka]

[0042] [ka]

[0043] [ka]

[0044] [ka]

[0045] [ka]

[0046] [ka]

[0047] [ka]

[0048] [ka]

[0049] [ka]

[0050] In the non-aqueous electrolyte according to the present invention, the first additive may be contained in an amount of 0.01 to 5 parts by weight, preferably 0.05 to 3.0 parts by weight, and more preferably 0.10 to 2.0 parts by weight, per 100 parts by weight of the non-aqueous electrolyte. When the content of the first additive satisfies the above range, the effect of forming a coating on the negative electrode is sufficient, and excellent high-temperature life characteristics and high-temperature storage characteristics are achieved.

[0051] In the non-aqueous electrolyte according to the present invention, the second additive may be contained in an amount of 0.01 to 5 parts by weight, preferably 0.05 to 3.0 parts by weight, and more preferably 0.10 to 2.5 parts by weight, per 100 parts by weight of the non-aqueous electrolyte. When the content of the first additive satisfies the above range, the effect of forming a coating on the negative electrode is sufficient, and excellent high-temperature life characteristics and high-temperature storage characteristics are achieved.

[0052] In the nonaqueous electrolyte solution of the present invention, the first additive and the second additive may be contained in a weight ratio of 1:0.1 to 1:10, preferably 1:0.5 to 1:5, and most preferably 1:1 to 1:4, so that the elasticity of the formed SEI film falls within an appropriate range, and the SEI film can be maintained strong during charge / discharge or at high temperatures.

[0053] The non-aqueous electrolyte according to the present invention may contain a lithium salt. The lithium salt is used as an electrolyte salt in a lithium secondary battery and is used as a medium for transferring ions. Typically, 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:

[0054] 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.

[0055] The lithium salt can be varied as appropriate within a range that is normally usable, but to obtain the optimum effect of forming a corrosion-preventing coating on the electrode surface, it may be contained in the electrolyte at a concentration of 0.5 M to 5.0 M, preferably 1.0 M to 3.0 M, and more preferably 1.2 M to 2.0 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, allowing for improved electrolyte impregnation.

[0056] The nonaqueous electrolyte according to the present invention may include an organic solvent, which may include 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.

[0057] The additive of the present invention is particularly effective when a cyclic carbonate solvent is used. When a conventional electrolyte additive is used together with a cyclic carbonate solvent, the SEI film formed by decomposition of the cyclic carbonate solvent is difficult to maintain due to volume changes in the negative electrode that occur as cycling progresses, resulting in the problem of continued solvent decomposition. This causes problems such as a decrease in the ionic conductivity of the electrolyte and a decrease in cycle performance. However, when a combination of the additive of the present invention and a cyclic carbonate solvent is used, a strong SEI film can be formed, and high cycle performance can be maintained.

[0058] 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 thereof include at least one organic solvent selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, and vinylene carbonate, and among these, fluoroethylene carbonate (FEC) may be included.

[0059] 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 among these, diethyl carbonate (DEC) may be included.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] Examples of the cyclic carbonate compounds include vinylene carbonate (VC) and vinylethylene carbonate.

[0070] The halogen-substituted carbonate compounds include fluoroethylene carbonate (FEC).

[0071] 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.

[0072] Examples of the sulfate-based compounds include ethylene sulfate (Esa), trimethylene sulfate (TMS), and methyl trimethylene sulfate (MTMS).

[0073] 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.

[0074] Examples of the borate-based compounds include tetraphenylborate, lithium oxalyldifluoroborate (LiODFB), and lithium bisoxalateborate (LiB(C2O4)2, LiBOB).

[0075] 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.

[0076] The benzene-based compound may be fluorobenzene, the amine-based compound may be triethanolamine or ethylenediamine, and the silane-based compound may be tetravinylsilane.

[0077] 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.

[0078] 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.

[0079] Meanwhile, the other electrolyte additives may be used in combination of two or more kinds, and may be contained in an amount of 0.050 to 20 wt %, specifically 0.10 to 15 wt %, and preferably 0.30 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 improvements in ionic conductivity and cycle characteristics can be obtained.

[0080] Lithium secondary battery The present invention also provides a lithium secondary battery containing the non-aqueous electrolyte.

[0081] 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 nonaqueous electrolyte.

[0082] 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.

[0083] (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.

[0084] The positive electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. For example, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, or the like may be used.

[0085] The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and may specifically include a lithium metal oxide containing lithium and one or more metals such as cobalt, manganese, nickel, or aluminum. More specifically, the lithium metal oxide may be 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.), a lithium-nickel-manganese-based oxide (e.g., LiNi 1-Y Mn YO2 (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 Mn r2 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 the atomic fractions of the respective independent elements, 0 < p2 < 1, 0 < q2 < 1, 0 < r2 < 1, 0 < s2 < 1, p2 + q2 + r2 + s2 = 1), etc.), and any one or two or more of these compounds may be included.

[0086] 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 (e.g., 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 Co0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2, and Li(Ni 0.8 Mn 0.1 Co 0.1 )O2), or lithium nickel cobalt aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 Al 0.05 ) O2, etc.), and a mixture of any one or more of these may be used.

[0087] The positive electrode active material may be contained 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 in the positive electrode mixture slurry excluding the solvent.

[0088] The binder is a component that assists in binding the active material and the conductive material and in binding them to the current collector.

[0089] 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.

[0090] Generally, the binder may be contained 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 in the positive electrode mixture slurry excluding the solvent.

[0091] 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 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 fibers and metal fibers; carbon fluoride powders; conductive powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0092] Generally, the conductive material may be contained 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 in the positive electrode mixture slurry excluding the solvent.

[0093] 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 %.

[0094] (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.

[0095] 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.

[0096] The negative electrode active material may include at least one selected from the group consisting of lithium metal, a carbon material capable of reversibly intercalating / deintercalating lithium ions, a metal or an alloy of such a metal and lithium, a metal composite oxide, a material capable of doping and dedoping lithium, and a transition metal oxide.

[0097] The carbonaceous material capable of reversibly intercalating / deintercalating lithium ions may be any carbonaceous negative electrode active material commonly used in lithium ion secondary batteries, and representative examples thereof include crystalline carbon, amorphous carbon, or a combination of these. Examples of crystalline carbon include graphite, such as amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite. Examples of amorphous carbon include soft carbon (low-temperature calcined carbon), hard carbon, mesophase pitch carbide, and calcined coke.

[0098] 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.

[0099] As the metal composite oxide, 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) selected from the group consisting of can be used.

[0100] As the substance capable of doping and undoping lithium, Si, SiO x (0<x≦2), Si-Y alloy (where Y is an element selected from the group consisting of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a transition metal, a rare earth element, and a combination thereof, and is not Si), Sn, SnO2, Sn-Y (where Y is an element selected from the group consisting of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a transition metal, a rare earth element, and a combination thereof, and is not Sn), etc. can be mentioned, and at least one of these and SiO2 may be mixed 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 a combination thereof.

[0101] Examples of the transition metal oxide include lithium-containing titanium composite oxide (LTO), vanadium oxide, lithium vanadium oxide, and the like.

[0102] The additive according to the present invention is particularly effective when Si or SiO x (0 < x ≤ 2) is used as the negative electrode active material. Specifically, when a Si-based negative electrode active material is used, if a strong SEI layer is not formed on the surface of the negative electrode during initial activation, the life characteristics will be deteriorated due to intense volume expansion and contraction during cycling. However, the additive according to the present invention can form a strong SEI layer while having elasticity, so that a secondary battery using a Si-based negative electrode active material can have excellent life characteristics and storage characteristics.

[0103] The negative electrode active material may be contained at 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.

[0104] Examples of the binder include polyvinylidene fluoride (PVDF), polyvinyl alcohol, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluorine rubber, various copolymers thereof, and the like. Specifically, styrene-butadiene rubber (SBR)-carboxymethyl cellulose (CMC) can be used because of its high thickening property.

[0105] Usually, the binder may be contained at 1 to 20% by weight, preferably 1 to 15% by weight, more preferably 1 to 10% by weight, based on the total weight of the solid matter excluding the solvent in the negative electrode binder slurry.

[0106] 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; carbon fluoride powder; conductive powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0107] The conductive material may be contained 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 in the negative electrode mixture slurry excluding the solvent.

[0108] 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.

[0109] 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.

[0110] 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).

[0111] (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 homopolymer, a propylene homopolymer, 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.

[0112] 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 polymeric material formed thereon to ensure heat resistance or mechanical strength.

[0113] Specifically, the separator included in the electrode assembly of the present invention includes 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.

[0114] 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.

[0115] 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.

[0116] 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.

[0117] Example Example 1 (Production of non-aqueous electrolyte) A non-aqueous solvent was prepared by dissolving LiPF in an organic solvent (fluoroethylene carbonate (FEC):diethyl carbonate (DEC) = 10:90 volume ratio) to a concentration of 1.5M. 1 g of a compound represented by the following Formula 1a and 1 g of a compound represented by the following Formula 2a were added to 98 g of the non-aqueous solvent to prepare a non-aqueous electrolyte.

[0118] [ka]

[0119] [ka]

[0120] (Lithium secondary battery manufacturing) Cathode active material (LiNi 0.85 Co 0.05 Mn 0.08 Al 0.02 A cathode slurry (solid content 75.5 wt%) was prepared by adding O2, a conductive material (carbon nanotubes), and a binder (polyvinylidene fluoride) to a solvent, N-methyl-2-pyrrolidone (NMP), in a weight ratio of 97.74:0.7:1.56. The cathode slurry was applied to one side of a 15 μm-thick cathode current collector (Al thin film), dried, and roll-pressed to prepare a cathode.

[0121] Anode active material (silicon; Si), conductive material (carbon black), and binder (styrene-butadiene rubber (SBR)-carboxymethyl cellulose (CMC)) were mixed in a weight ratio of 70:20.3:9.7 with N-methyl-2-pyrrolidone (NMP) as a solvent to prepare anode slurry (solid content 26 wt%). The anode slurry was applied to one side of a 15 μm-thick anode current collector (Cu thin film), dried, and roll-pressed to prepare anode.

[0122] 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.

[0123] Example 2 A secondary battery was manufactured in the same manner as in Example 1, except that a non-aqueous electrolyte was prepared by adding 0.2 g of the compound of Chemical Formula 1a and 2 g of the compound of Chemical Formula 2a to 97.8 g of the non-aqueous solvent prepared in Example 1.

[0124] Example 3 A secondary battery was manufactured in the same manner as in Example 1, except that a non-aqueous electrolyte was prepared by adding 1.5 g of the compound of Formula 1a and 0.2 g of the compound of Formula 2a to 98.3 g of the non-aqueous solvent prepared in Example 1.

[0125] Example 4 A secondary battery was manufactured in the same manner as in Example 1, except that a non-aqueous electrolyte was prepared by adding 0.5 g of the compound of Chemical Formula 1a and 2 g of the compound of Chemical Formula 2a to 97.5 g of the non-aqueous solvent prepared in Example 1.

[0126] Example 5 A secondary battery was manufactured in the same manner as in Example 1, except that a non-aqueous electrolyte was prepared by adding 1.5 g of the compound of Formula 1a and 2 g of the compound of Formula 2a to 96.5 g of the non-aqueous solvent prepared in Example 1.

[0127] 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.

[0128] Comparative Example 2 A secondary battery was manufactured in the same manner as in Example 1, except that 2 g of the compound of Formula 1a was added to 98 g of the non-aqueous solvent prepared in Example 1 to prepare a non-aqueous electrolyte.

[0129] Comparative Example 3 A secondary battery was manufactured in the same manner as in Example 1, except that 2 g of the compound of Formula 2a was added to 98 g of the non-aqueous solvent prepared in Example 1 to prepare a non-aqueous electrolyte.

[0130] Experimental Example 1: Evaluation of high-temperature cycle characteristics The cycle characteristics of each of the secondary batteries produced in Examples 1 to 5 and Comparative Examples 1 to 3 were evaluated.

[0131] Specifically, each of the batteries manufactured in Examples 1 to 5 and Comparative Examples 1 to 3 was charged at 45° C. with a constant current of 1 C to 4.2 V and then discharged at a constant current of 0.5 C to 3.0 V, and after 250 charge-discharge cycles, the capacity retention rate relative to the initial capacity after the first cycle was measured. The results are shown in Table 1 below.

[0132] [Table 1]

[0133] As shown in Table 1, Examples 1 to 5, which used a combination of the first additive and the second additive, had higher capacity retention rates and better life characteristics than Comparative Example 1, which used no additive, Comparative Example 2, which used only the first additive, and Comparative Example 3, which used only the second additive.

[0134] Experimental Example 2 - Evaluation of high-temperature storage characteristics The high-temperature storage characteristics of each of the secondary batteries produced in Examples 1 to 5 and Comparative Examples 1 to 3 were evaluated.

[0135] Specifically, each of the secondary batteries of Examples 1 to 5 and Comparative Examples 1 to 3 was fully charged to 4.2 V and then stored at 60° C. for 8 weeks.

[0136] Before storage, the capacity of the fully charged secondary battery was measured and set as the initial capacity of the secondary battery.

[0137] After 8 weeks, the capacity of the stored secondary battery was measured, and the capacity loss during the 8-week storage period was calculated. The percentage of the lost capacity relative to the initial capacity of the secondary battery was calculated to determine the capacity retention rate after 8 weeks. The results are shown in Table 2 below.

[0138] [Table 2]

[0139] As shown in Table 2, Examples 1 to 5, which used a combination of the first additive and the second additive, showed higher capacity retention rates after 8 weeks and more stable performance at high temperatures than the secondary batteries of Comparative Example 1, which used no additive, Comparative Example 2, which used only the first additive, and Comparative Example 3, which used only the second additive.

Claims

1. A lithium salt, an organic solvent; A compound represented by the following chemical formula 1 as a first additive; A non-aqueous electrolyte comprising, as a second additive, a compound represented by the following chemical formula 2: 【Chemistry 1】 In the above Chemical Formula 1, A is a cyclic phosphate group having 2 or 3 carbon atoms; R is an alkylene group having 1 to 5 carbon atoms or an alkenylene group having 2 to 5 carbon atoms, X is a perfluoroalkyl group having 1 to 5 carbon atoms, 【Chemistry 2】 In the above Chemical Formula 2, R １ and one of R 5 is F, a propargyl group, a substituted or unsubstituted alkoxy group having 1 to 4 carbon atoms, a substituted or unsubstituted alkylcarbonyl group having 2 to 4 carbon atoms, a substituted or unsubstituted alkylester group having 1 to 4 carbon atoms, CN, SO ３ , and S.O. ３ CF ３ and the other is H, and R 2 , R 3 , R 4 , and R 6 are H.

2. The non-aqueous electrolyte according to claim 1 , wherein A in Chemical Formula 1 is a cyclic phosphate group having two carbon atoms.

3. 2. The non-aqueous electrolyte according to claim 1, wherein R in Chemical Formula 1 is an alkylene group having 1 to 3 carbon atoms.

4. X in Formula 1 is CF ３ or CF ２ CF ３ The non-aqueous electrolyte according to claim 1 ,

5. The non-aqueous electrolyte of claim 1 , wherein the compound represented by Chemical Formula 2 contains at least one nitrile group.

6. The non-aqueous electrolyte according to claim 1 , wherein the compound represented by Chemical Formula 2 includes at least one propargyl group.

7. The non-aqueous electrolyte of claim 1 , wherein the first additive is contained in an amount of 0.01 to 5 parts by weight based on 100 parts by weight of the non-aqueous electrolyte.

8. The non-aqueous electrolyte of claim 1 , wherein the second additive is contained in an amount of 0.01 to 5 parts by weight based on 100 parts by weight of the non-aqueous electrolyte.

9. 2. The non-aqueous electrolyte according to claim 1, wherein the first additive and the second additive are contained in a weight ratio of 1:0.1 to 1:

10.

10. The lithium salts include LiCl, LiBr, LiI, and 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 The non-aqueous electrolyte according to claim 1 , wherein the non-aqueous electrolyte is one or more selected from the group consisting of:

11. 2. The non-aqueous electrolyte according to claim 1, wherein the lithium salt is contained at a concentration of 0.5M to 5.0M.

12. 2. The nonaqueous electrolyte according to claim 1, 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.

13. A positive electrode and a negative electrode; A lithium secondary battery comprising the nonaqueous electrolyte according to claim 1 .

14. The negative electrode contains SiO as a negative electrode active material. ｘ 14. The lithium secondary battery according to claim 13, comprising: (0≦x≦2).

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