Nonaqueous electrolyte and lithium secondary battery containing same

Abstract

The present invention provides a lithium secondary battery including a negative electrode containing a silicon-based negative electrode active material, a positive electrode, a separator, and a non-aqueous electrolyte, wherein the non-aqueous electrolyte includes 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: In Chemical Formula 1, R is an alkylene group having 1 to 5 carbon atoms which may be substituted with fluorine, and R1 to R3 are each independently any one selected from the group consisting of H, an alkyl group having 1 to 5 carbon atoms, and a nitrile group. In Chemical Formula 2, R4 to R7 are each independently any one selected from the group consisting of alkyl groups having 1 to 10 carbon atoms which may be substituted with fluorine, and alkenyl groups having 2 to 10 carbon atoms which may be substituted with fluorine. JPEG2025534118000033.jpg57170

Description

[Technical Field]

[0001] This application claims priority based on Korean Patent Application No. 10-2023-0030216, filed with the Korean Intellectual Property Office on March 7, 2023, the entire contents of which 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 characteristics are important for lithium secondary batteries for automotive applications. To achieve high capacity secondary batteries, silicon-based negative electrode active materials, which have high energy density but low stability, can be used. Summary of the Invention [Problem to be solved by the invention]

[0005] As a result of extensive research into solving the above problems, the present invention has an object to provide a lithium secondary battery including a negative electrode using a silicon-based negative electrode active material with low stability, which includes a non-aqueous electrolyte capable of forming a stable SEI (Solid Electrolyte Interphase) film on a negative electrode that experiences significant volume changes, thereby providing a lithium secondary battery with excellent long-life characteristics, improved high-temperature storage characteristics and thermal stability, and other improved performances. [Means for solving the problem]

[0006] In order to achieve the above object, one embodiment of the present invention provides a lithium secondary battery including a negative electrode containing a silicon-based negative electrode active material, a positive electrode, a separator, and a non-aqueous electrolyte, wherein the non-aqueous electrolyte includes 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:

[0007] [ka]

[0008] In the above Chemical Formula 1, R is an alkylene group having 1 to 5 carbon atoms which may be substituted with fluorine, and R1 to R3 are each independently any one selected from the group consisting of H, an alkyl group having 1 to 5 carbon atoms, and a nitrile group.

[0009] [ka]

[0010] In the above Chemical Formula 2, R4 to R7 are each independently any one selected from the group consisting of an alkyl group having 1 to 10 carbon atoms which may be substituted with fluorine, and an alkenyl group having 2 to 10 carbon atoms which may be substituted with fluorine.

[0011] Another embodiment of the present invention provides a non-aqueous electrolyte including 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, R is an alkylene group having 1 to 5 carbon atoms which may be substituted with fluorine, and R1 to R3 are each independently any one selected from the group consisting of H, an alkyl group having 1 to 5 carbon atoms, and a nitrile group; [ka] In the above Chemical Formula 2, R4 to R7 are each independently any one selected from the group consisting of an alkyl group having 1 to 10 carbon atoms which may be substituted with fluorine, and an alkenyl group having 2 to 10 carbon atoms which may be substituted with fluorine. [Effects of the Invention]

[0014] The compound of Chemical Formula 1 provided as the first additive of the present invention can form a polyethylene oxide-based polymeric SEI layer having high elasticity upon reduction, and the compound of Chemical Formula 2 provided as the second additive can form a polysiloxane-structured SEI layer having a high shear modulus (the degree to which it can withstand shear stress) upon reduction.

[0015] In particular, the first additive contains a propargyl group, and the second additive contains a tetravinyl group, which allows for the formation of a stronger polymeric coating. Furthermore, because the second additive has a cyclic siloxane structure, the reduction reaction occurs more easily than with additives having a linear siloxane structure. Furthermore, the lone electron pair of the imidazole in the first additive structure promotes the ring-opening reaction of the second additive, facilitating the formation of a polymeric coating. In other words, the combination of the first additive and the second additive creates a synergistic effect, significantly improving the durability of the coating formed on the negative electrode.

[0016] Therefore, in the present invention, due to the synergistic effect of the interaction between the first additive and the second additive, a stable and highly durable electrode-electrolyte interface can be formed even in a lithium secondary battery in which a silicon-based negative electrode active material that undergoes drastic volume changes during charge and discharge is used in the negative electrode, and unnecessary electrolyte decomposition side reactions can be suppressed, thereby realizing a lithium secondary battery with improved performance. DETAILED DESCRIPTION OF THE INVENTION

[0017] 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.

[0018] 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.

[0019] 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-.

[0020] In addition, in this specification, the term "alkylene group" means a branched or unbranched divalent saturated hydrocarbon group.

[0021] In addition, in this specification, any alkyl 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.

[0022] The present invention will now be described in more detail.

[0023] To achieve high energy density, lithium secondary batteries use lithium metal oxides based on transition metals such as nickel (Ni), cobalt (Co), and manganese (Mn) as the positive electrode and silicon-based negative electrode active materials such as silicon (Si) or silicon oxide (SiOx), which can be alloyed with lithium ions and have high theoretical capacity, as the negative electrode. However, when operating secondary batteries containing negative electrodes that use silicon-based negative electrode active materials, the durability of the coating (e.g., SEI film) formed on the surface of the negative electrode decreases due to drastic volume changes during repeated charging and discharging, resulting in a serious capacity loss.

[0024] This capacity reduction phenomenon of the secondary battery tends to be accelerated when the battery is exposed to high temperatures, and this reduction phenomenon causes a problem of deterioration in the cycle characteristics of the secondary battery.

[0025] Furthermore, when a lithium secondary battery is used continuously for a long period of time or left at a high temperature, gas is generated and the thickness of the battery increases, which is called a swelling phenomenon. It is known that the amount of gas generated in this case depends on the state of the SEI.

[0026] Therefore, the present invention provides a lithium secondary battery containing a non-aqueous electrolyte that can reduce the swelling phenomenon of the lithium secondary battery and improve its stability at high temperatures.

[0027] [Non-aqueous electrolyte] The non-aqueous electrolyte according to the present invention may include 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.

[0028] [ka]

[0029] In the above Chemical Formula 1, R is an alkylene group having 1 to 5 carbon atoms which may be substituted with fluorine, and R1 to R3 are each independently any one selected from the group consisting of H, an alkyl group having 1 to 5 carbon atoms, and a nitrile group.

[0030] [ka]

[0031] In the above Chemical Formula 2, R4 to R7 are each independently any one selected from the group consisting of an alkyl group having 1 to 10 carbon atoms which may be substituted with fluorine, and an alkenyl group having 2 to 10 carbon atoms which may be substituted with fluorine.

[0032] The lithium secondary battery according to the present invention includes a non-aqueous electrolyte containing a compound represented by Chemical Formula 1 below as a first additive. The compound represented by Chemical Formula 1 contains a propargyl group having a triple bond, which is known to have metal ion adsorption properties, and an oxygen atom. The propargyl group, which is separated by bond cleavage between the nitrogen (N) atom and the carbon (C) atom of the imidazole group, adsorbs metal impurities such as Fe, Co, Mn, and Ni that are eluted from the positive electrode during high-voltage charging of the lithium secondary battery. This effectively prevents negative electrode degradation caused by electrodeposition of these metal impurities on the negative electrode surface. Furthermore, the lone electron pair of the nitrogen (N) atom of the imidazole group in the compound represented by Chemical Formula 1 reacts with polyvinylene carbonate, a decomposition product of fluoroethylene carbonate (FEC), used as an organic solvent, and is reduced on the negative electrode surface, thereby forming a stable ion-conductive coating on the negative electrode surface. Therefore, not only can additional electrolyte decomposition reactions be suppressed during charge and discharge, but also intercalation and deintercalation of lithium ions from the negative electrode can be facilitated even during overcharge or high-temperature storage, thereby improving the cycle life characteristics and high-temperature storage performance of the secondary battery.

[0033] [ka]

[0034] In the above chemical formula 1, R may be an alkylene group having 1 to 5 carbon atoms which may be substituted with fluorine, for example, an alkylene group having 1 to 3 carbon atoms.

[0035] In the above Chemical Formula 1, R1 to R3 may each independently be any one selected from the group consisting of H, an alkyl group having 1 to 5 carbon atoms, and a nitrile group, for example, any one selected from the group consisting of H and an alkyl group having 1 to 3 carbon atoms.

[0036] For example, the compound of Formula 1 may be any one selected from the group consisting of the following Formulas 1-1 to 1-3.

[0037] [ka]

[0038] [ka]

[0039] [ka]

[0040] The lithium secondary battery according to the present invention includes a compound represented by the following chemical formula 2 as a second additive in a non-aqueous electrolyte. The compound of chemical formula 2 easily undergoes a reduction reaction through a ring-opening reaction, and can form an SEI layer containing polysiloxane on the negative electrode. The SEI layer containing the polysiloxane structure has a high shear modulus (the degree to which it can withstand shear stress), and can therefore withstand even severe volume changes in the negative electrode.

[0041] [ka]

[0042] In Chemical Formula 2, R4 to R7 may each independently be any one selected from the group consisting of an alkyl group having 1 to 10 carbon atoms which may be substituted with fluorine, and an alkenyl group having 2 to 10 carbon atoms which may be substituted with fluorine, for example, an alkyl group having 1 to 5 carbon atoms which may be substituted with fluorine, or an alkyl group having 1 to 3 carbon atoms which is substituted with fluorine. When the compound of Chemical Formula 2 is substituted with a fluorine group, a strong and elastic polymeric coating can be formed on an electrode, including an inorganic substance such as LiF.

[0043] As an example, the compound of the present invention represented by Chemical Formula 2 may be any one selected from the group consisting of the following Chemical Formulas 2-1 to 2-3.

[0044] [ka]

[0045] [ka]

[0046] [ka]

[0047] When the nonaqueous electrolyte of the present invention containing the first additive and the second additive is used, the radicals generated by the cleavage of the ring structure of the first additive promote the film-forming reaction of the second additive. The film formed by the interaction between the first additive and the second additive has an imidazole or structure derived therefrom present between the cyclic alkyl group-based film, forming a film morphology with excellent lithium ion transport properties, improving various performances of the lithium secondary battery, such as the charge / discharge characteristics and output characteristics. The film formed by the interaction between the first additive and the second additive has excellent oxidation resistance, thereby suppressing side reactions occurring in the positive and negative electrode films, even in the acidic electrolyte atmosphere. Furthermore, the film formed by the interaction between the first additive and the second additive has excellent durability against volume changes in the negative electrode that occur during charge / discharge. Therefore, the nonaqueous electrolyte of the present invention can form an electrode-electrolyte interface that is stable and highly durable even at high temperatures, suppressing unnecessary electrolyte decomposition side reactions, thereby realizing a lithium secondary battery with improved performance.

[0048] In the non-aqueous electrolyte according to the present invention, the first additive may be contained in an amount of 0.01 to 10 parts by weight, for example, 0.1 to 5.0 parts by weight, or 0.5 to 3.0 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.

[0049] In the non-aqueous electrolyte according to the present invention, the second additive may be contained in an amount of 0.01 to 10 parts by weight, for example, 0.1 to 5.0 parts by weight, or 0.5 to 3.0 parts by weight, per 100 parts by weight of the non-aqueous electrolyte. When the content of the second 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.

[0050] In the nonaqueous electrolyte of the present invention, the first additive and the second additive may be included in a weight ratio of 1:0.002 to 1:500, for example, a weight ratio of 1:0.1 to 1:10, or a weight ratio of 1:0.2 to 1:5. When the above range is satisfied, the elasticity of the SEI coating is in an appropriate range, and the SEI coating can be maintained strong during charge / discharge or at high temperatures.

[0051] 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:

[0052] For example, the lithium salt may be LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10 , LiAlCl4, LiAlO2, LiPF6, LiSO3CF3, LiCO2CH3, LiCO2CF3, LiAsF6, LiSbF6, LiSO3CH3, 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, lithium salts commonly used in electrolytes for lithium secondary batteries can be used without any restrictions.

[0053] 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, for example, 1.0 M to 3.0 M, or 1.2 M to 2.0 M. When the lithium salt concentration 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.

[0054] The nonaqueous electrolyte according to the present invention may contain an organic solvent, which 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.

[0055] 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.

[0056] The cyclic carbonate organic solvent is a highly viscous organic solvent that has a high dielectric constant and thus 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), fluoroethylene carbonate (FEC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, and vinylene carbonate. In particular, the cyclic carbonate organic solvent may include fluoroethylene carbonate (FEC). When fluoroethylene carbonate is used as the organic solvent, the excellent reducing properties of FEC and the interaction with the first and second additives allow for the formation of a stronger coating on the silicon-based negative electrode, which undergoes significant volume changes during charge and discharge.

[0057] 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 particularly, ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) may be used.

[0058] 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 including one or more 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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 and causing the collapse of the negative electrode in a high-power environment, 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.

[0066] 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.

[0067] Examples of the cyclic carbonate compounds include vinylene carbonate (VC) and vinylethylene carbonate.

[0068] The halogen-substituted carbonate compounds include fluoroethylene carbonate (FEC).

[0069] 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.

[0070] Examples of the sulfate-based compounds include ethylene sulfate (Esa), trimethylene sulfate (TMS), and methyl trimethylene sulfate (MTMS).

[0071] The phosphate-based compound may be one or more compounds selected from the group consisting of lithium difluoro(bisoxalato)phosphate, lithium difluorophosphate, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite, tris(2,2,2-trifluoroethyl)phosphate, and tris(2,2,2-trifluoroethyl)phosphite.

[0072] Examples of the borate-based compounds include tetraphenylborate, lithium difluoro(oxalate)borate (LiODFB), and lithium bisoxalateborate (LiB(C2O4)2, LiBOB).

[0073] 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.

[0074] The benzene-based compound may be fluorobenzene, the amine-based compound may be triethanolamine or ethylenediamine, and the silane-based compound may be tetravinylsilane.

[0075] 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.

[0076] 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, the generation of gas that may be generated by decomposition of the electrolyte at high temperatures can be suppressed, and the high-temperature stability of the secondary battery can be improved compared to conventional secondary batteries.

[0077] Meanwhile, the other electrolyte additives may be used in combination of two or more kinds, and may be included in an amount of 0.050 wt % to 20 wt %, for example, 0.10 wt % to 15 wt %, or 0.30 wt % 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 compared to conventional lithium-ion batteries.

[0078] [Lithium secondary battery] The present invention also provides a lithium secondary battery containing the above-mentioned non-aqueous electrolyte.

[0079] For example, a lithium secondary battery according to the present invention includes a negative electrode containing a silicon-based negative electrode active material, a positive electrode, a separator, and the non-aqueous electrolyte described above.

[0080] 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.

[0081] The positive electrode included in the lithium secondary battery of the present invention can be produced by coating a positive electrode current collector with a positive electrode mixture slurry containing a positive electrode active material, a binder, a conductive material, a solvent, and the like.

[0082] The positive electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and is conductive, and may be, for example, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel whose surface has been surface-treated with carbon, nickel, titanium, silver, etc. Furthermore, the bonding force of the positive electrode active material may be strengthened by forming fine irregularities on the surface, and the positive electrode current collector may be used in various forms such as a film, sheet, foil, net, porous body, foam, or nonwoven fabric.

[0083] The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and may include a lithium metal oxide containing one or more metals such as cobalt, manganese, nickel, or aluminum and lithium. For example, 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 Y O2 (where 0 < Y < 1), LiMn 2-Z Ni Z O4 (where 0 < Z < 2), etc.), a lithium-nickel-cobalt-based oxide (e.g., LiNi 1-Y1 Co Y1 O2 (where 0 < Y1 < 1), etc.), a lithium-manganese-cobalt-based oxide (e.g., LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2-Z1 Co Z1 O4 (where 0 < Z1 < 2), etc.), a lithium-nickel-manganese-cobalt-based oxide (e.g., Li(Ni p Co[[ID=***]] 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 a lithium-nickel-cobalt-transition metal (M) oxide (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, and p2 + q2 + r2 + s2 = 1), etc.). Among these, any one or two or more of these compounds may be included.

[0084] Among these, nickel-cobalt-manganese oxides may be used as the lithium metal oxide, since they can improve the capacity characteristics and stability of the battery.

[0085] For example, the lithium nickel cobalt manganese-based oxide may have a composition represented by the following Chemical Formula 3:

[0086] [Chemical formula 3] Li x Ni a Co b M 1 c M 2 d O2

[0087] In the above Chemical Formula 3, the M 1 may be Mn or a combination of Mn and Al, for example, may be a combination of Mn and Al from the viewpoint of enhancing structural stability.

[0088] In the above Chemical Formula 3, the M 2 may be one or more selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta, and Nb.

[0089] The x represents the atomic fraction of lithium in the lithium nickel cobalt manganese-based oxide, and may be 0.90≦x≦1.1, for example, 0.95≦x≦1.08, or 1.0≦x≦1.08.

[0090] The a represents the atomic fraction of nickel among the metal elements excluding lithium in the lithium nickel cobalt manganese-based oxide, and may be 0.80≦a<1.0, for example, 0.80≦a≦0.95 or 0.80≦a≦0.90. When the nickel content satisfies the above range, high capacity characteristics can be achieved.

[0091] The b represents the atomic fraction of cobalt among the metal elements excluding lithium in the lithium nickel cobalt manganese oxide, and is 0. <b<0.2、0<b≦0.15、または0.01≦b≦0.10であってよい。

[0092] The c is M among the metal elements other than lithium in the lithium nickel cobalt manganese oxide. 1 represents the atomic fraction of 0 <c<0.2、0<c≦0.15、または0.01≦c≦0.10であってよい。

[0093] The d is M among the metal elements other than lithium in the lithium nickel cobalt manganese oxide. 2 and may be 0≦d≦0.1, or 0≦d≦0.05.

[0094] The positive electrode active material may be contained in an amount of 60 to 99 wt %, for example, 70 to 99 wt %, or 80 to 98 wt %, based on the total weight of solids in the positive electrode mixture slurry excluding the solvent.

[0095] The binder is a component that assists in binding the active material and the conductive material and in binding them to the current collector.

[0096] 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.

[0097] Typically, the binder may be included in an amount of 1 wt % to 20 wt %, for example, 1 wt % to 15 wt %, or 1 wt % to 10 wt %, based on the total weight of the solid content excluding the solvent in the positive electrode mixture slurry.

[0098] 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 wt % to 20 wt % based on the total weight of the solid content in the negative electrode 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 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.

[0099] Typically, the conductive material may be contained in an amount of 1 wt % to 20 wt %, for example, 1 wt % to 15 wt %, or 1 wt % to 10 wt %, based on the total weight of solids in the positive electrode mixture slurry excluding the solvent.

[0100] The solvent may include 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 included so that the concentration of the solids including the positive electrode active material, and optionally a binder, a conductive material, etc. is 50% by weight to 95% by weight, e.g., 70% by weight to 95% by weight, or 70% by weight to 90% by weight.

[0101] The negative electrode included in the lithium secondary battery of the present invention can be produced by coating a negative electrode current collector with a negative electrode mixture slurry containing a negative electrode active material, a binder, a conductive material, a solvent, and the like.

[0102] For example, when manufacturing a negative electrode by coating a negative electrode binder slurry on the negative electrode current collector, the negative electrode current collector generally has a thickness of 3 μm to 500 μm. Such a negative electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, those with a surface treatment of carbon, nickel, titanium, silver, etc. on the surface of copper or stainless steel, aluminum-cadmium alloy, etc. may be used. Also, similar to the positive electrode current collector, the binding force of the negative electrode active material may be strengthened by forming fine irregularities on the surface, and it may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven fabric bodies, etc.

[0103] Further, the negative electrode of the present invention is characterized by containing a silicon-based negative electrode active material. When using a silicon-based negative electrode active material, a lithium secondary battery having a high energy density can be provided. The silicon-based negative electrode active material may be Si or SiO x (0 < x ≤ 2), and for example, when the negative electrode active material is made of Si, the highest energy density can be provided. When using a negative electrode active material based on Si, if a strong SEI layer is not formed on the surface of the negative electrode during initial activation, the decrease in life characteristics is promoted due to the intense volume expansion - contraction during cycling. However, the lithium secondary battery of the present invention has elasticity and forms a strong SEI layer, so that excellent life characteristics and storage characteristics can be provided while using a negative electrode active material based on Si.

[0104] The negative electrode active material may be contained at 60% by weight to 99% by weight, for example, 70% by weight to 99% by weight, or 80% by weight to 98% by weight based on the total weight of the solid content in the negative electrode binder slurry.

[0105] Examples of the binder 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. Styrene-butadiene rubber (SBR)-carboxymethyl cellulose (CMC) can be used because of its high viscosity.

[0106] Typically, the binder may be included in an amount of 1 wt % to 20 wt %, for example, 1 wt % to 15 wt %, or 1 wt % to 10 wt %, based on the total weight of solids in the negative electrode mixture slurry excluding the solvent.

[0107] 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 wt % to 20 wt % based on the total weight of the solid content in the negative 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 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.

[0108] The conductive material may be contained in an amount of 1 wt % to 20 wt %, for example, 1 wt % to 15 wt %, or 1 wt % to 10 wt %, based on the total weight of solids in the negative electrode mixture slurry excluding the solvent.

[0109] 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 solids including the negative electrode active material, and optionally a binder and a conductive material, is 50 wt % to 95 wt %, e.g., 70 wt % to 90 wt %.

[0110] 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, a polyethylene terephthalate fiber, etc., 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.

[0111] For example, the separator may include a porous separator substrate and a porous coating layer that is coated on one or both sides of the separator substrate, and 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.

[0112] 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.

[0113] The external shape of the lithium secondary battery of the present invention is not particularly limited, and may be, for example, a cylindrical shape having a circular or rectangular cross section, a rectangular shape, a pouch shape, or a coin shape.

[0114] 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.

[0115] [Example] Example 1 (Production of non-aqueous electrolyte) A non-aqueous solvent was prepared by dissolving LiPF in an organic solvent (fluoroethylene carbonate (FEC): ethyl methyl carbonate (EMC): diethyl carbonate (DEC) = 20:70:10 volume ratio) to a concentration of 1.3 M, and 0.1 g of a compound represented by the following Formula 1-1 and 0.1 g of a compound represented by the following Formula 2-1 were added to 99.8 g of the non-aqueous solvent to prepare a non-aqueous electrolyte.

[0116] [ka]

[0117] [ka]

[0118] (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.

[0119] 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.

[0120] 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.

[0121] 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 0.1 g of the compound of Chemical Formula 1-1 and 5 g of the compound of Chemical Formula 2-1 to 94.9 g of the non-aqueous solvent prepared in Example 1.

[0122] Example 3 A secondary battery was manufactured in the same manner as in Example 1, except that 5 g of the compound of Formula 1-1 and 0.1 g of the compound of Formula 2-1 were added to 94.9 g of the nonaqueous solvent manufactured in Example 1 to prepare a nonaqueous electrolyte.

[0123] Example 4 A secondary battery was manufactured in the same manner as in Example 1, except that 2 g of the compound of Chemical Formula 1-1 and 2 g of the compound of Chemical Formula 2-1 were added to 96 g of the nonaqueous solvent manufactured in Example 1 to prepare a nonaqueous electrolyte.

[0124] 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 0.1 g of a compound represented by the following Formula 1-2 and 0.1 g of a compound represented by the following Formula 2-1 to 99.8 g of the non-aqueous solvent prepared in Example 1.

[0125] [ka]

[0126] Example 6 A secondary battery was manufactured in the same manner as in Example 1, except that a non-aqueous electrolyte was prepared by adding 0.1 g of a compound represented by the following Formula 1-3 and 0.1 g of a compound represented by the following Formula 2-1 to 99.8 g of the non-aqueous solvent prepared in Example 1.

[0127] [ka]

[0128] Example 7 A secondary battery was manufactured in the same manner as in Example 1, except that a non-aqueous electrolyte was prepared by adding 0.1 g of the compound of Chemical Formula 1-1 and 0.1 g of the compound of Chemical Formula 2-2 below to 99.8 g of the non-aqueous solvent prepared in Example 1.

[0129] [ka]

[0130] Example 8 A secondary battery was manufactured in the same manner as in Example 1, except that a non-aqueous electrolyte was prepared by adding 0.1 g of the compound of Chemical Formula 1-1 and 0.1 g of the compound of Chemical Formula 2-3 below to 99.8 g of the non-aqueous solvent prepared in Example 1.

[0131] [ka]

[0132] Comparative Example 1 A secondary battery was manufactured in the same manner as in Example 1, except that 0.1 g of the compound of Formula 1-1 was added to 99.9 g of the non-aqueous solvent prepared in Example 1 to prepare a non-aqueous electrolyte.

[0133] Comparative Example 2 A secondary battery was manufactured in the same manner as in Example 1, except that 5 g of the compound of Formula 1-1 was added to 95 g of the non-aqueous solvent prepared in Example 1 to prepare a non-aqueous electrolyte.

[0134] Comparative Example 3 A secondary battery was manufactured in the same manner as in Example 1, except that 0.1 g of the compound of Formula 2-1 was added to 99.9 g of the nonaqueous solvent prepared in Example 1 to prepare a nonaqueous electrolyte.

[0135] Comparative Example 4 A secondary battery was manufactured in the same manner as in Example 1, except that 5 g of the compound of Formula 2-1 was added to 95 g of the non-aqueous solvent manufactured in Example 1 to prepare a non-aqueous electrolyte.

[0136] [Experimental Example 1 - Evaluation of High-Temperature Cycle Characteristics] The cycle characteristics of each of the secondary batteries produced in Examples 1 to 8 and Comparative Examples 1 to 4 were evaluated.

[0137] For example, each of the batteries manufactured in Examples 1 to 8 and Comparative Examples 1 to 4 was charged at 45°C under constant current / constant voltage conditions (0.05C cutoff) at a 0.33C rate to 4.2V and then discharged at a constant current of 0.33C to 3.0V, with one cycle being defined as 200 charge / discharge cycles. After that, the capacity retention rate after 200 cycles relative to the initial capacity after one cycle was measured. The resistance increase rate after 200 cycles relative to the initial resistance after one cycle was also measured. The results are shown in Table 1 below.

[0138] [Table 1]

[0139] [Experimental Example 2 - Evaluation of high temperature storage characteristics] The secondary batteries produced in Examples 1 to 8 and Comparative Examples 1 to 4 were evaluated for high-temperature storage characteristics.

[0140] For example, each of the secondary batteries of Examples 1 to 8 and Comparative Examples 1 to 4 was fully charged to 4.2 V and then stored at 60° C. for 8 weeks.

[0141] Before storage, the capacity of the fully charged secondary battery was measured and set as the initial capacity of the secondary battery.

[0142] 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. In addition, the percentage of the increased resistance relative to the initial resistance of the secondary battery was calculated to determine the resistance increase rate after 8 weeks. The results are shown in Table 2 below.

[0143] [Table 2]

[0144] Experimental Example 3: Evaluation of Thermal Stability The thermal stability of each of the secondary batteries produced in Examples 1 to 8 and Comparative Examples 1 to 4 was evaluated.

[0145] For example, after the activation process was performed on the lithium secondary batteries manufactured in the examples and comparative examples, they were charged at 25°C at a rate of 0.33C up to 4.2V under constant current / constant voltage conditions (0.05C cut-off) and fully charged to 100% SOC. The fully charged batteries were heated to 140°C at a rate of 5°C / min and then left for one hour, after which a hot box evaluation test was conducted to check for the presence or absence of ignition. A case in which no ignition occurred was evaluated as Pass, and a case in which ignition occurred was evaluated as Fail. The results are shown in Table 3 below.

[0146] [Table 3]

Claims

1. A lithium secondary battery including a negative electrode containing a silicon-based negative electrode active material, a positive electrode, a separator, and a non-aqueous electrolyte, The non-aqueous electrolyte includes 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. 【Chemical 1】 (In the above chemical formula 1, R is an alkylene group having 1 to 5 carbon atoms which may be substituted with fluorine; R １ ~R ３ are each independently any one selected from the group consisting of H, an alkyl group having 1 to 5 carbon atoms, and a nitrile group; 【Chemistry 2】 In the above Chemical Formula 2, R ４ ~R ７ are each independently any one selected from the group consisting of an alkyl group having 1 to 10 carbon atoms which may be substituted with fluorine, and an alkenyl group having 2 to 10 carbon atoms which may be substituted with fluorine.

2. 2. The lithium secondary battery of claim 1, wherein the compound of Formula 1 is any one selected from the group consisting of the following Formulas 1-1 to 1-3: 【Chemistry 3】 【Chemistry 4】 【Chemistry 5】

3. 2. The lithium secondary battery of claim 1, wherein the compound of Formula 2 is any one selected from the group consisting of the following Formulas 2-1 to 2-3: 【Chemistry 6】 【Chemistry 7】 【Chemistry 8】

4. 2. The lithium secondary battery of claim 1, wherein the first additive is contained in an amount of 0.01 to 10 parts by weight based on 100 parts by weight of the non-aqueous electrolyte.

5. 2. The lithium secondary battery of claim 1, wherein the second additive is contained in an amount of 0.01 to 10 parts by weight based on 100 parts by weight of the non-aqueous electrolyte.

6. 2. The lithium secondary battery according to claim 1, wherein the first additive and the second additive are contained in a weight ratio of 1:0.002 to 1:

500.

7. The lithium salts include LiCl, LiBr, LiI, and LiBF. ４ , LiClO ４ , LiB １０ Cl １０ , LiAlCl ４ , LiAlO ２ , LiPF ６ , LiSO ３ CF ３ , LiCO ２ CH ３ , LiCO ２ CF ３ , LiAsF ６ , LiSbF ６ , LiSO ３ CH ３ , LiN(SO ２ F) ２ , LiN(SO ２ CF ２ CF ３ ) ２ , and LiN(SO ２ CF ３ ) ２ 2. The lithium secondary battery according to claim 1, wherein the lithium secondary battery is one or more selected from the group consisting of:

8. 2. The lithium secondary battery according to claim 1, wherein the lithium salt is contained at a concentration of 0.5M to 5.0M.

9. 2. The lithium secondary battery 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.

10. 2. The lithium secondary battery according to claim 1, wherein the silicon-based negative electrode active material is made of Si.

11. 2. The lithium secondary battery according to claim 1, wherein the positive electrode contains a lithium nickel cobalt manganese oxide as a positive electrode active material.

12. The lithium secondary battery according to claim 11, wherein the lithium nickel cobalt manganese-based oxide has a composition represented by the following Chemical Formula 3: [Chemical formula 3] Li ｘ Ni ａ Co ｂ M １ ｃ M ２ ｄ O ２ (In the above chemical formula 3, M １ is Mn or a combination of Mn and Al, and M ２ is one or more elements selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta, and Nb, and 0.90≦x≦1.1, 0.80≦a<1.0, 0<b<0.2, 0<c<0.2, 0≦d≦0.1).

13. An electronic device comprising the lithium secondary battery according to claim 10.

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