Lithium secondary battery

Abstract

The present invention relates to a battery comprising a negative electrode, a positive electrode, a separator, and a non-aqueous electrolyte, wherein the negative electrode comprises a negative electrode active material, the negative electrode active material comprises a silicon-based active material, and the silicon-based active material has an average particle size (D 50 ) is 1 μm to 20 μm, the non-aqueous electrolyte contains a lithium salt, an organic solvent, and an additive, the organic solvent contains fluoroethylene carbonate and diethyl carbonate in a volume ratio of 5:95 to 25:75, and the additive contains a compound represented by a specific chemical formula.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0182375, filed December 22, 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 lithium secondary battery, and more specifically to a lithium secondary battery that includes a nonaqueous electrolyte containing an additive capable of forming a strong SEI film on positive and negative electrodes, thereby suppressing an increase in initial resistance and improving output characteristics and life performance. [Background technology]

[0003] The development of the information society has led to the development of personal IT devices and computer networks, which has increased society's overall dependence on electrical energy. This has led to a demand for the development of technologies to efficiently store and utilize electrical energy.

[0004] Of the technologies currently being developed, secondary batteries are the most suitable for a variety of applications, and among these secondary batteries, interest is growing in lithium-ion batteries, which not only can be miniaturized to a degree suitable for use in personal IT devices, but also have the highest energy density.

[0005] Generally, a lithium secondary battery is manufactured by injecting or impregnating a non-aqueous electrolyte into an electrode assembly including a positive electrode, a negative electrode, and a porous separator.

[0006] Positive electrode active materials for such lithium secondary batteries include lithium-containing cobalt oxide, LiMnO2 with a layered crystal structure, LiMn2O4 with a spinel crystal structure, lithium-containing nickel oxide (LiNiO2), and lithium nickel-cobalt-manganese transition metal oxide.

[0007] On the other hand, carbon-based active materials such as graphite have been used as negative electrode active materials, but in recent years, the use of silicon-based active materials has been considered because they have higher capacity than carbon-based active materials.

[0008] While silicon-based active materials have the advantage of high capacity, they suffer from the problem of significant volume expansion / contraction during charge / discharge. This significant volume expansion / contraction significantly reduces the conductivity of the negative electrode and shortens its lifespan. Furthermore, during initial activation, a solid electrolyte interface layer (SEI) is formed on the surface of the negative electrode. Silicon-based active materials experience significant volume expansion, which can lead to cracking of the SEI layer and the continuous generation of new negative electrode surfaces. This can accelerate electrolyte side reactions due to the continuous generation of SEI layer formation reactions, resulting in an increased SEI layer thickness and increased resistance. Summary of the Invention [Problem to be solved by the invention]

[0009] An object of the present invention is to solve the above-mentioned problems, and to provide a lithium secondary battery that contains a silicon-based active material as a negative electrode active material, and that has improved output characteristics and life characteristics by forming a strong and low-resistance SEI film on the negative electrode. [Means for solving the problem]

[0010] The present invention relates to a battery comprising a negative electrode, a positive electrode, a separator, and a non-aqueous electrolyte, wherein the negative electrode comprises a negative electrode active material, the negative electrode active material comprises a silicon-based active material, and the silicon-based active material has an average particle size (D 50) is 1 μm to 20 μm, the non-aqueous electrolyte contains a lithium salt, an organic solvent, and an additive, the organic solvent contains fluoroethylene carbonate and diethyl carbonate in a volume ratio of 5:95 to 25:75, and the additive contains at least one compound selected from the group consisting of compounds represented by the following Chemical Formula 1 to Chemical Formula 3:

[0011] [ka]

[0012] In the above chemical formula 1, R1 is hydrogen or an alkyl group having 1 to 3 carbon atoms, and n is an integer of 1 to 10.

[0013] [ka]

[0014] In the above chemical formula 2, m is an integer of 0-18.

[0015] [ka]

[0016] In the above Chemical Formula 3, R2 and R3 are each independently an alkylene group having 1 to 10 carbon atoms, and R4 is an alkyl group having 1 to 20 carbon atoms substituted with one or more fluorine atoms. [Effects of the Invention]

[0017] The present invention provides a negative electrode with a specific average particle size (D 50), and the non-aqueous electrolyte contains fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) as organic solvents in a specific volume ratio, and contains at least one additive selected from the group consisting of compounds represented by Chemical Formulas 1 to 3. The silicon-based active material has a micron-sized average particle size, and the composition of the non-aqueous electrolyte allows an organic / inorganic composite SEI coating to be smoothly formed on the negative electrode, thereby preventing cracking of the SEI coating due to volume changes of the silicon-based active material and significantly improving the life performance at room temperature and high temperature. DETAILED DESCRIPTION OF THE INVENTION

[0018] First, before describing the present invention, the terms and words used in this specification and claims should not be interpreted in a limited manner to their ordinary or dictionary meanings, but should be interpreted in a manner that is consistent with the technical idea of ​​the present invention, in accordance with the principle that the inventors can appropriately define the concepts of terms in order to best explain their invention.

[0019] However, the terms used in this specification are merely used to describe exemplary embodiments and are not intended to limit the present invention. The singular expressions include the plural expressions unless the context clearly indicates otherwise.

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

[0021] In this specification, "%" means % by weight unless expressly indicated otherwise.

[0022] Before describing the present invention, in the description of "number of carbon atoms a to b" in the specification, "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.

[0023] In addition, in this specification, 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, for example, with an alkyl group having 1 to 5 carbon atoms or a fluorine atom.

[0024] In this specification, the average particle size (D 50 The average particle size (D) can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve. 50 ) can be measured, for example, by the laser diffraction method. The laser diffraction method is generally capable of measuring particle sizes from the submicron range to several mm, and can provide results with high reproducibility and high resolution.

[0025] The present invention will now be described in more detail.

[0026] Lithium secondary battery The present invention relates to a battery comprising a negative electrode, a positive electrode, a separator, and a non-aqueous electrolyte, wherein the negative electrode comprises a negative electrode active material, the negative electrode active material comprises a silicon-based active material, and the silicon-based active material has an average particle size (D 50 ) is 1 μm to 20 μm, the non-aqueous electrolyte contains a lithium salt, an organic solvent, and an additive, the organic solvent contains fluoroethylene carbonate and diethyl carbonate in a volume ratio of 5:95 to 25:75, and the additive contains at least one compound selected from the group consisting of compounds represented by the following Chemical Formula 1 to Chemical Formula 3:

[0027] [ka]

[0028] In the above chemical formula 1, R1 is hydrogen or an alkyl group having 1 to 3 carbon atoms, and n is an integer of 1 to 10.

[0029] [ka]

[0030] In the above chemical formula 2, m is an integer of 0-18. [ka]

[0031] In the above chemical formula 3, R2 and R3 are each independently an alkylene group having 1 to 10 carbon atoms, and R4 is an alkyl group having 1 to 20 carbon atoms substituted with one or more fluorine atoms.

[0032] The present invention provides a negative electrode with a specific average particle size (D 50 ), and the non-aqueous electrolyte contains fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) as organic solvents in a specific volume ratio, and contains at least one additive selected from the group consisting of compounds represented by Chemical Formulas 1 to 3. The silicon-based active material has a micron-sized average particle size, and the non-aqueous electrolyte composition allows an organic / inorganic composite SEI coating to be smoothly formed on the negative electrode, thereby preventing cracking of the SEI coating due to volume changes of the silicon-based active material and significantly improving the life performance at room temperature and high temperature.

[0033] The lithium secondary battery includes a negative electrode, a positive electrode, a separator, and a non-aqueous electrolyte. Specifically, the lithium secondary battery includes a negative electrode, a positive electrode facing the negative electrode, a separator interposed between the negative electrode and the positive electrode, and a non-aqueous electrolyte. The lithium secondary battery can be manufactured by housing an electrode assembly including the negative electrode, a positive electrode facing the negative electrode, and a separator interposed between the negative electrode and the positive electrode in a battery case and then injecting a non-aqueous electrolyte.

[0034] (1) Negative electrode The negative electrode contains a silicon-based active material. The silicon-based active material exhibits a higher capacity compared to a carbon-based active material, but has a problem of a large degree of volume expansion / contraction due to charge and discharge. However, when the silicon-based active material and the non-aqueous electrolyte described below are used together, an SEI film with high flexibility and excellent durability can be formed on the negative electrode, so that electrolyte side reactions are prevented and a lithium secondary battery having high life performance and output characteristics can be realized.

[0035] The silicon-based active material may contain a compound represented by the following chemical formula A.

[0036] [Chemical formula A] SiOx (0≦x<2)

[0037] In the chemical formula A, since SiO2 does not react with lithium ions and thus cannot store lithium, x is preferably within the above range.

[0038] The silicon-based active material may be Si (silicon). Si is advantageous in that its capacity is about 2.5 to 3 times higher than that of silicon oxide (for example, SiOx (0<x<2)), but the degree of volume expansion / contraction of Si due to charge and discharge is much larger than that of silicon oxide, so it is not easy to commercialize. However, the lithium secondary battery of the present invention can have high life performance and output characteristics by applying the non-aqueous electrolyte described below.

[0039] The average particle size (D of the silicon-based active material50 The average particle diameter (D) of the silicon-based active material is 1 μm to 20 μm. 50 If the average particle diameter (D) of the silicon-based active material is less than 1 μm, the surface area is too high and the fluoroethylene carbonate described below is reacted and completely lost, resulting in a significant change in physical properties such as ionic conductivity, an imbalance in lithium ion transport, an increase in resistance, and a decrease in life performance. 50 If the thickness exceeds 20 μm, the volume expansion of the silicon-based active material becomes excessively large, making it difficult to maintain the conductive network, resulting in a significant decrease in life performance and resistance characteristics.

[0040] Specifically, the average particle size (D 50 ) may be 2 μm to 10 μm, specifically 3 μm to 8 μm. When the thickness is within the above range, an organic / inorganic composite SEI coating can be favorably formed when combined with a nonaqueous electrolyte described below, cracking of the SEI coating, consumption of the nonaqueous electrolyte, and the like can be prevented, and the life performance can be improved to a preferred level.

[0041] The negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the silicon-based active material may be included in the negative electrode active material layer.

[0042] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. Specifically, the negative electrode current collector may be made of copper, stainless steel, aluminum, nickel, titanium, baked carbon, copper or stainless steel whose surface is treated with carbon, nickel, titanium, silver, or the like, or an aluminum-cadmium alloy.

[0043] The negative electrode current collector usually has a thickness of 3 μm to 500 μm.

[0044] The negative electrode current collector may have a surface with fine irregularities to enhance the bonding strength of the negative electrode active material. For example, the negative electrode current collector may be used in various forms such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0045] The negative electrode active material layer may be disposed on at least one surface of the negative electrode current collector. Specifically, the negative electrode active material layer may be disposed on one or both surfaces of the negative electrode current collector.

[0046] The silicon-based active material may be contained in the negative electrode active material layer in an amount of 60 wt % to 99 wt %, preferably 70 wt % to 85 wt %, in order to minimize the influence of volume expansion / contraction on the battery and to fully realize the high capacity of the silicon-based active material in the secondary battery.

[0047] The negative electrode active material layer may further include a carbon-based active material in addition to the silicon-based active material.

[0048] The carbon-based active material may be, for example, graphite, hard carbon, soft carbon, etc. Specifically, the carbon-based active material may be graphite. The graphite may be artificial graphite, natural graphite, or a mixture thereof.

[0049] When the negative electrode active material layer contains the silicon-based active material and the carbon-based active material, the sum of the weights of the silicon-based active material and the carbon-based active material may be 60% by weight to 99% by weight, preferably 70% by weight to 98% by weight, based on the total weight of the negative electrode active material. When the negative electrode active material layer contains the silicon-based active material and the carbon-based active material, the weight ratio of the silicon-based active material to the carbon-based active material may be 1:99 to 30:70, specifically 2:98 to 20:80.

[0050] The negative electrode active material layer may further include a conductive material and / or a binder in addition to the silicon-based active material.

[0051] The binder may be used to improve the adhesive strength between the negative electrode active material layer and a negative electrode current collector (described later) or to improve the binding strength between silicon-based active materials.

[0052] Specifically, the binder may include at least one selected from the group consisting of styrene butadiene rubber (SBR), nitrile butadiene rubber (NBR), acrylonitrile butadiene rubber, acrylic rubber, butyl rubber, fluororubber, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl alcohol (PVA), polyacrylic acid (PAA), polyethylene glycol (PEG), polyacrylonitrile (PAN), and polyacrylamide (PAM), and preferably includes nitrile butadiene rubber, in order to further improve electrode adhesive strength and provide sufficient resistance to volume expansion / contraction of the silicon-based active material.

[0053] The binder may be included in the negative electrode active material layer in an amount of 1 wt % to 30 wt %, preferably 7 wt % to 15 wt %. When the amount is within this range, the silicon-based active material can be better bound, minimizing the problem of volume expansion of the active material, and the binder can be easily dispersed during preparation of a slurry for forming the negative electrode active material layer, thereby improving the coatability and phase stability of the slurry.

[0054] The conductive material is used to assist and improve the conductivity of the secondary battery, and is not particularly limited as long as it does not cause chemical changes and is conductive. Specifically, the conductive material may include at least one selected from the group consisting of graphite such as natural graphite and artificial graphite; carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and polyphenylene derivatives. Preferably, the conductive material may include carbon black in order to achieve high conductivity.

[0055] The conductive material may be contained in the negative electrode active material layer in an amount of 1 wt % to 20 wt %, preferably 8 wt % to 15 wt %, and when the amount is within the above range, it is preferable because it can mitigate the increase in resistance caused by the binder and form an excellent conductive network.

[0056] The thickness of the negative electrode active material layer may be 5 μm to 500 μm, preferably 5 μm to 100 μm.

[0057] The loading amount of the negative electrode active material layer is 3 mAh / cm 2 ~15mAh / cm 2 , preferably 8mAh / cm 2 ~13mAh / cm 2 It may be.

[0058] The negative electrode may be fabricated by coating a negative electrode slurry containing a negative electrode active material, and optionally a binder, a conductive material, and a solvent for forming the negative electrode slurry, on the negative electrode current collector, followed by drying and rolling.

[0059] The solvent for forming the negative electrode slurry may include, for example, at least one selected from the group consisting of distilled water, ethanol, methanol, and isopropyl alcohol, preferably including distilled water, from the viewpoint of facilitating the dispersion of the negative electrode active material, binder, and / or conductive material.

[0060] The solvent for forming the negative electrode slurry may be included in the negative electrode slurry such that the concentration of the solid content including the negative electrode active material and optionally the binder and conductive material is 15% to 45% by weight, considering the viscosity, coating property, dispersibility, etc. of the negative electrode slurry.

[0061] (2) Positive electrode The positive electrode includes a positive electrode active material.

[0062] The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium. Specifically, it may include a lithium transition metal composite oxide containing at least one transition metal selected from nickel, cobalt, manganese, and aluminum and lithium, preferably a lithium transition metal composite oxide containing a transition metal containing nickel, cobalt, and manganese and lithium.

[0063] For example, as the lithium transition metal composite oxide, there are lithium-manganese-based oxides (such as LiMnO2, LiMn2O4, etc.), lithium-cobalt-based oxides (such as LiCoO2, etc.), lithium-nickel-based oxides (such as LiNiO2, etc.), lithium-nickel-manganese-based oxides (such as LiNi 1-Y Mn Y O2 (where 0 < Y < 1), LiMn 2-Z Ni Z O4 (where 0 < Z < 2), etc.), lithium-nickel-cobalt-based oxides (such as LiNi 1-Y1 Co Y1 O2 (where 0 < Y1 < 1), etc.), lithium-manganese-cobalt-based oxides (such as LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2-Z1 CoZ1 O4 (where 0 < Z1 < 2, etc.), lithium-nickel-manganese-cobalt-based oxides (e.g., Li(Ni p Co q Mn r1 )O2 (where 0 < p < 1, 0 < q < 1, 0 < r1 < 1, p + q + r1 = 1) or Li(Ni p1 Co q1 Mn r2 )O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r2 < 2, p1 + q1 + r2 = 2), etc.), or lithium-nickel-cobalt-transition metal (M) oxides (e.g., Li(Ni p2 Co q2 Mn r3 M S2 )O2 (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r3, and s2 are the atomic fractions of the respective independent elements, 0 < p2 < 1, 0 < q2 < 1, 0 < r3 < 1, 0 < s2 < 1, and p2 + q2 + r3 + s2 = 1), etc.), and any one or two or more of these compounds may be included. Among them, from the viewpoint of improving the capacity characteristics and stability of the battery, the lithium transition metal composite oxide is LiCoO2, LiMnO2, LiNiO2, lithium nickel-manganese-cobalt oxide (e.g., Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2, or Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, etc.), or lithium nickel cobalt aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 Al 0.05 )O2, etc.), and considering the significance of the improvement effect by controlling the types and content ratios of the constituent elements forming the lithium transition metal composite oxide, the lithium transition metal composite oxide is Li(Ni 0.6 Mn 0.2Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2, or Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, etc., and any one or a mixture of two or more of these can be used.

[0064] More specifically, the positive electrode active material may be a lithium transition metal composite oxide containing 60 mol% or more of nickel based on the total number of moles of transition metals contained in the lithium transition metal composite oxide. Specifically, the positive electrode active material may be a lithium transition metal composite oxide containing nickel and at least one selected from manganese, cobalt, and aluminum, and containing 60 mol% or more, specifically 60 mol% to 90 mol%, of the transition metals based on the total number of moles of the transition metals. When such a lithium transition metal composite oxide containing a high content of nickel is used together with the nonaqueous electrolyte solution, it is preferable because it can reduce by-products in the gas generated by structural collapse.

[0065] The positive electrode active material may include a lithium composite transition metal oxide represented by the following chemical formula B:

[0066] [Chemical formula B] Li 1+x (Ni a Co b Mn c M d )O2

[0067] In the chemical formula B, M is one or more selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and 1+x, a, b, c, and d are atomic fractions of each independent element, and 0≦x≦0.2, 0.50≦a<1, 0 <b≦0.25、0<c≦0.25、0≦d≦0.1、a+b+c+d=1である。

[0068] Preferably, a, b, c, and d may be in the ranges 0.70≦a≦0.95, 0.025≦b≦0.20, 0.025≦c≦0.20, and 0≦d≦0.05, respectively.

[0069] Furthermore, the a, b, c, and d may be in the ranges 0.80≦a≦0.95, 0.025≦b≦0.15, 0.025≦c≦0.15, and 0≦d≦0.05, respectively.

[0070] Furthermore, the a, b, c, and d may be 0.85≦a≦0.90, 0.05≦b≦0.10, 0.05≦c≦0.10, and 0≦d≦0.03, respectively.

[0071] The positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector. In this case, the positive electrode active material layer may include the positive electrode active material described above.

[0072] The positive electrode current collector usually has a thickness of 3 μm to 500 μm.

[0073] The positive electrode current collector may have a surface with fine irregularities to enhance the bonding strength of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0074] The positive electrode active material layer may be disposed on at least one surface of the positive electrode current collector. Specifically, the positive electrode active material layer may be disposed on one or both surfaces of the positive electrode current collector.

[0075] The positive electrode active material may be contained in the positive electrode active material layer in an amount of 80% by weight to 99% by weight, taking into consideration the sufficient capacity of the positive electrode active material.

[0076] The positive electrode active material layer may further contain a binder and / or a conductive material in addition to the positive electrode active material.

[0077] The binder is a component that assists in binding the active material and conductive material, etc., and in binding them to the current collector, and specifically may contain at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluororubber, and preferably polyvinylidene fluoride.

[0078] The binder may be contained in the positive electrode active material layer in an amount of 1 to 20% by weight, preferably 1.2 to 10% by weight, in order to ensure sufficient binding strength between components such as the positive electrode active material.

[0079] The conductive material is used to assist and improve the conductivity of the secondary battery, and is not particularly limited as long as it does not cause chemical changes and is conductive. Specifically, the positive electrode conductive material may include at least one selected from the group consisting of graphite such as natural graphite and artificial graphite; carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; fluorocarbons; metal powders such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and polyphenylene derivatives, and preferably includes carbon nanotubes in order to improve conductivity.

[0080] In order to ensure sufficient electrical conductivity, the conductive material may be contained in the positive electrode active material layer in an amount of 1 to 20% by weight, preferably 1.2 to 10% by weight.

[0081] The thickness of the positive electrode active material layer may be 5 μm to 500 μm, and preferably 100 μm to 200 μm.

[0082] The loading amount of the positive electrode active material layer is 2 mAh / cm 2 ~6mAh / cm 2 , preferably 4 mAh / cm 2 ~5mAh / cm 2 It may be.

[0083] The positive electrode may be fabricated by coating a positive electrode slurry containing a positive electrode active material, and optionally a binder, a conductive material, and a solvent for forming the positive electrode slurry, on the positive electrode current collector, followed by drying and rolling.

[0084] The solvent for forming the positive electrode slurry may include an organic solvent such as N-methyl-2-pyrrolidone (NMP), and the solid content of the positive electrode slurry may be 40% by weight to 90% by weight, specifically 50% by weight to 80% by weight.

[0085] (3) Separator The separator may be interposed between the positive electrode and the negative electrode.

[0086] 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. 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.

[0087] (4) Nonaqueous electrolyte 1) Lithium salt First, the lithium salt will be explained as follows. In the non-aqueous electrolyte for a lithium secondary battery according to one embodiment of the present invention, the lithium salt may be any of those commonly used in electrolytes for lithium secondary batteries, without any limitation. For example, Li + and as an anion, F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , AlO4 - , AlCl4 - , PF6 - , SbF6 - , AsF6 - , B 10 Cl 10 - , BF2C2O4 - , BC4O8 - , PF4C2O4 - , PF2C4O8 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 -, (CF3)5PF - , (CF3)6P - , CF3SO3 - , C4F9SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , CH3SO3 - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - , and (CF3CF2SO2)2N - Specifically, the lithium salt may be at least one selected from the group consisting of LiCl, LiBr, LiI, LiBF4, LiClO4, LiAlO4, LiAlCl4, LiPF6, LiSbF6, LiAsF6, LiB 10 Cl 10 , LiBOB (LiB(C2O4)2), LiCF3SO3, LiTFSI (LiN(SO2CF3)2), LiFSI (LiN(SO2F)2), LiCH3SO3, LiCF3CO2, LiCH3CO2, LiDFOB (LiB(C2O4)F2), and LiBETI (LiN(SO2CF2CF3)2). Specifically, the lithium salt may include a single substance or a mixture of two or more substances selected from the group consisting of LiBF4, LiClO4, LiPF6, LiBOB (LiB(C2O4)2), LiCF3SO3, LiTFSI (LiN(SO2CF3)2), LiFSI (LiN(SO2F)2), LiDFOB (LiB(C2O4)F2), and LiBETI (LiN(SO2CF2CF3)2), and more specifically, may include LiPF6.

[0088] The lithium salt may be varied as appropriate within a range that is normally usable, but in order to obtain the optimum effect of forming a corrosion prevention coating on the electrode surface, it may be contained in the electrolyte at a concentration of 0.8 M to 3.0 M, specifically 1.0 M to 3.0 M.

[0089] When the concentration of the lithium salt satisfies the above range, the viscosity of the nonaqueous electrolyte can be controlled to achieve optimal impregnation, improving the mobility of lithium ions and improving the capacity characteristics and cycle characteristics of the lithium secondary battery.

[0090] 2) Organic solvents The organic solvent includes fluoroethylene carbonate (FEC) and diethyl carbonate (DEC).

[0091] The volume ratio of the fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) is 5:95 to 25:75. The fluoroethylene carbonate (FEC) is decomposed to form an SEI film containing inorganic components such as LiF on the negative electrode. The inorganic components such as LiF are more easily adsorbed on the negative electrode than polymer-type organic SEI films, and are therefore highly effective in preventing electrolyte side reactions at the negative electrode. On the other hand, diethyl carbonate is preferred because it has low viscosity and a low dielectric constant and improves electrolyte impregnation when used together with the fluoroethylene carbonate.

[0092] Meanwhile, as described below, the lithium secondary battery according to the present invention must use, together with the organic solvent, an additive containing the compound represented by Chemical Formula 1. Without the additive, it is difficult to effectively form an inorganic SEI coating containing an inorganic component such as LiF on the negative electrode, and the decomposition of FEC continues, causing an imbalance in lithium ion transport in the negative electrode, increasing resistance and potentially resulting in a decrease in lifespan performance due to permanent lithium loss.

[0093] When the volume content of fluoroethylene carbonate is less than 5% by volume and the volume content of diethyl carbonate is more than 95% in the total volume of the fluoroethylene carbonate and diethyl carbonate, the inorganic SEI coating by fluoroethylene carbonate is insufficient, and the aforementioned effects of the present invention cannot be achieved.On the other hand, when the volume content of fluoroethylene carbonate is more than 25% by volume and the volume content of diethyl carbonate is less than 75% in the total volume of the fluoroethylene carbonate and diethyl carbonate, the fluoroethylene carbonate has a solvated structure that makes it difficult to effectively generate inorganic components such as LiF, and it is difficult to smoothly form the aforementioned inorganic SEI coating.

[0094] Specifically, the volume ratio of the fluoroethylene carbonate and diethyl carbonate may be 7:93 to 20:80.

[0095] As the organic solvent, an organic solvent that is commonly used in non-aqueous electrolytes may be added as needed without any restrictions.

[0096] The organic solvent may further include at least one of a cyclic carbonate organic solvent, a linear carbonate organic solvent, an ester organic solvent, an ether organic solvent, a glyme organic solvent, and a nitrile organic solvent.

[0097] The cyclic carbonate organic solvent is one other than fluoroethylene carbonate (FEC), and specifically may include at least one organic solvent selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, and vinylene carbonate.

[0098] Furthermore, the linear carbonate organic solvent is one other than diethyl carbonate (DEC), and specifically may include at least one selected from the group consisting of dimethyl carbonate (DMC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate, and ethyl propyl carbonate.

[0099] The ester-based organic solvent may include at least one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0100] 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.

[0101] 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.

[0102] 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.

[0103] On the other hand, in the non-aqueous electrolyte, the remainder excluding the lithium salt and the additive is an organic solvent unless otherwise specified.

[0104] (3) Additives The non-aqueous electrolyte of the present invention contains an additive.

[0105] The additive includes at least one compound selected from the group consisting of compounds represented by the following chemical formulas 1 to 3.

[0106] [ka]

[0107] In the above chemical formula 1, R1 is hydrogen or an alkyl group having 1 to 3 carbon atoms, and n is an integer of 1 to 10.

[0108] [ka]

[0109] In the above chemical formula 2, m is an integer of 0-18.

[0110] [ka]

[0111] In the above chemical formula 3, R2 and R3 are each independently an alkylene group having 1 to 10 carbon atoms, and R4 is an alkyl group having 1 to 20 carbon atoms substituted with one or more fluorine atoms.

[0112] Specifically, at least one of the compounds represented by Chemical Formulas 1 to 3, when used with the organic solvent, more effectively forms an inorganic SEI coating containing an inorganic component such as LiF. Furthermore, at least one of the compounds represented by Chemical Formulas 1 to 3 prevents continued decomposition of fluoroethylene carbonate and allows a sufficient inorganic SEI coating to be formed on the negative electrode, thereby balanced lithium ion transport in the negative electrode and significantly improving the life performance of the lithium secondary battery.

[0113] Furthermore, at least one of the compounds represented by Chemical Formulas 1 to 3 contains a vinyl or propargyl-containing functional group within its structure, which allows it to be easily reductively decomposed on the surface of a negative electrode containing a silicon-based active material, thereby forming an SEI film with low resistance and high passivation ability. Therefore, when a nonaqueous electrolyte containing at least one of the compounds represented by Chemical Formulas 1 to 3 is used as an electrolyte additive, it is possible to prevent a self-discharge reaction of the negative electrode due to additional reductive decomposition of the electrolyte caused by the instability of the SEI film.

[0114] Furthermore, at least one of the compounds represented by Chemical Formulas 1 to 3 contains a fluorocarbon functional group substituted with one or more fluorine elements at the structural terminal, thereby forming a coating that ensures oxidation resistance on the surface of the positive electrode, thereby suppressing the elution of transition metals from the positive electrode and suppressing the electrodeposition and precipitation of the eluted transition metals on the negative electrode, thereby preventing internal short circuits.

[0115] As described above, at least one of the compounds represented by Chemical Formulas 1 to 3 contains a fluorine-containing alkyl group, which has excellent flame retardancy and non-flammability, and a vinyl group or a propargyl group. This allows a low-resistance, strong SEI coating to be formed on the negative electrode, which not only suppresses the additional reductive decomposition reaction of the electrolyte but also prevents the self-discharge reaction of the negative electrode. This improves the life performance, suppresses an increase in initial resistance, and provides a lithium secondary battery with improved room-temperature and low-temperature output characteristics.

[0116] In the above Chemical Formula 1, R1 may be hydrogen or an alkyl group having 1 to 3 carbon atoms, and specifically may be hydrogen.

[0117] In Chemical Formula 1, n may be an integer of 1 to 10, specifically an integer of 3 to 8. When n is 0, it acts as a non-solvent, making it difficult to effectively form an inorganic SEI coating containing an inorganic component such as LiF. When n is an integer greater than 10, miscibility with organic solvents and the like decreases, making it difficult to effectively form an inorganic SEI coating, making it difficult to effectively form the desired inorganic SEI coating.

[0118] The compound represented by Chemical Formula 1 may specifically include at least one selected from the group consisting of compounds represented by the following Chemical Formulas 1-1 to 1-3, and more specifically, may include a compound represented by the following Chemical Formula 1-1.

[0119] [ka]

[0120] [ka]

[0121] [ka]

[0122] In the above Chemical Formula 2, m may be an integer of 0 to 18, specifically an integer of 1 to 10, and more specifically an integer of 2 to 8.

[0123] When m is within the above range, the thermal properties of the compound itself can be improved, and the stability of the coating formed therefrom can be expected. In Formula 2, when m is greater than 18, the fluorine element is contained in an excessive amount, which increases the viscosity and non-polarity of the material and reduces the solubility in the electrolyte, thereby reducing ionic conductivity and possibly resulting in deterioration of battery performance.

[0124] Preferably, the compound represented by Chemical Formula 2 may include at least one selected from the group consisting of compounds represented by the following Chemical Formulas 2-1 to 2-4, and more preferably, may include at least one selected from the group consisting of compounds represented by Chemical Formulas 2-1 to 2-2.

[0125] [ka]

[0126] [ka]

[0127] [ka]

[0128] [ka]

[0129] In the above chemical formula 3, R2 and R3 may each independently be an alkylene group having 1 to 5 carbon atoms, and R4 may be an alkyl group having 3 to 20 carbon atoms substituted with one or more fluorine atoms.

[0130] In addition, in the above chemical formula 3, R2 and R3 may each independently be an alkylene group having 1 to 3 carbon atoms, and R4 may be an alkyl group having 3 to 15 carbon atoms substituted with one or more fluorine atoms.

[0131] Specifically, in the above Chemical Formula 3, R4 may be an alkyl group having 4 to 8 carbon atoms substituted with one or more fluorine atoms.

[0132] Preferably, the compound represented by Chemical Formula 3 may include a compound represented by the following Chemical Formula 3-1.

[0133] [ka]

[0134] At least one compound selected from the compounds represented by Chemical Formulas 1 to 3 may be contained in the non-aqueous electrolyte in an amount of 0.01% by weight to 10.0% by weight.

[0135] When the content of at least one of the compounds represented by Chemical Formulas 1 to 3 is within the above range, defects such as side reactions, capacity reduction, and resistance increase due to additives can be minimized, and an inorganic SEI coating containing an inorganic component such as LiF can be effectively formed on the surface of the negative electrode, thereby improving the lithium migration effect in the coating, suppressing further reduction decomposition reactions of the electrolyte, and preventing self-discharge reactions of the negative electrode.

[0136] Specifically, when the content of at least one of the compounds represented by Chemical Formulas 1 to 3 is 0.01 wt % or more, a stable coating is formed during battery operation, forming a low-resistance SEI coating on the surface of the negative electrode, thereby improving battery output performance. Furthermore, when the content of at least one of the compounds represented by Chemical Formulas 1 to 3 is 10.0 wt % or less, the viscosity of the nonaqueous electrolyte can be controlled to achieve optimal impregnation, effectively suppressing an increase in battery resistance due to decomposition of additives, further increasing ionic conductivity within the battery, and preventing a decrease in output characteristics.

[0137] Specifically, at least one of the compounds represented by Chemical Formulas 1 to 3 may be contained in the non-aqueous electrolyte solution in an amount of 0.05% by weight to 6.0% by weight, specifically 0.1% by weight to 5.0% by weight.

[0138] Meanwhile, the non-aqueous electrolyte may further include an additional additive. When the non-aqueous electrolyte further includes an additional additive, at least one compound among the compounds represented by Formulas 1 to 3 may be referred to as a "first additive," and the additional additive may be referred to as a "second additive."

[0139] Specifically, the additive may contain other additional additives in addition to the compound represented by Formula 1, 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.

[0140] Examples of such additional additives include at least one selected from the group consisting of cyclic carbonate compounds, halogen-substituted carbonate compounds, sultone compounds, sulfate compounds, phosphate or phosphite compounds, borate compounds, nitrile compounds, benzene compounds, amine compounds, silane compounds, and lithium salt compounds.

[0141] The cyclic carbonate compound may be, for example, vinylene carbonate (VC) or vinylethylene carbonate.

[0142] The halogen-substituted carbonate compound may be, for example, fluoroethylene carbonate (FEC).

[0143] The sultone compound may be, for example, 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.

[0144] The sulfate compound may be, for example, ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS).

[0145] The phosphate-based or phosphite-based compound may be, for example, 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(trifluoroethyl)phosphite.

[0146] Examples of the borate-based compounds include tetraphenylborate, lithium difluoro(oxalato)borate (LiDFOB, LiB(C2O4)F2), and lithium bisoxalatoborate (LiB(C2O4)2, LiBOB).

[0147] The nitrile compound may be, for example, 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.

[0148] The benzene-based compound may be, for example, fluorobenzene, the amine-based compound may be, for example, triethanolamine or ethylenediamine, and the silane-based compound may be, for example, tetravinylsilane.

[0149] 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 (LiPO2F2) and LiBF4.

[0150] When at least one selected from the group consisting of vinyl ethylene carbonate, 1,3-propane sultone, vinylene carbonate, succinonitrile, and lithium difluoro(oxalato)borate is contained among these additional additives, a stronger SEI coating can be formed on the surface of the negative electrode during the initial activation process of the secondary battery.

[0151] The additional additive may be a combination of two or more compounds, and the total content of the compound represented by Formula 1 and the additional additive may be 50 wt % or less, specifically 0.05 wt % to 20 wt %, more specifically 0.05 wt % to 10 wt %, based on the total weight of the non-aqueous electrolyte. When the total content of the additives satisfies the above range, the low-temperature output characteristics, high-temperature storage characteristics, and high-temperature life characteristics of the battery may be improved more effectively, and side reactions in the battery due to residual additives after the reaction may be prevented.

[0152] The lithium secondary battery according to the present invention can be usefully used in portable devices such as mobile phones, notebook computers, and digital cameras, and in electric vehicles such as hybrid electric vehicles (HEVs).

[0153] Therefore, according to another embodiment of the present invention, there is provided a battery module including the lithium secondary battery as a unit cell, and a battery pack including the same.

[0154] The battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, such as power tools; electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); and power storage systems.

[0155] 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.

[0156] The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for small devices, but also as a unit battery in a medium- to large-sized battery module containing a large number of battery cells.

[0157] The present invention will be specifically described below with reference to examples.

[0158] In this regard, the embodiments of the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

[0159] The present invention will be specifically described below with reference to specific examples.

[0160] Examples and Comparative Examples Example 1 (Production of non-aqueous electrolyte) An organic solvent was prepared by mixing fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) in a volume ratio of 10:90.

[0161] Lithium salts LiPF and LiFSI were dissolved in the organic solvent to a molar concentration of 1.0 M in the non-aqueous electrolyte, and LiFSI was dissolved in the non-aqueous electrolyte to a molar concentration of 0.5 M.

[0162] In addition, the compound represented by Formula 1-1 and vinylene carbonate were added to the organic solvent in which the lithium salt was dissolved to prepare a non-aqueous electrolyte.

[0163] The compound represented by Chemical Formula 1-1 was contained in the non-aqueous electrolyte at 2 wt %. The vinylene carbonate was contained in the non-aqueous electrolyte at 2 wt %.

[0164] (Secondary battery manufacturing) Cathode active material (LiNi 0.86 Co 0.05 Mn 0.07 Al 0.02 A cathode mixture slurry (solid content 78 wt%) was prepared by adding the cathode mixture slurry (O2), conductive material (carbon nanotubes), and binder (polyvinylidene fluoride) in a weight ratio of 97:1:2 to the solvent N-methyl-2-pyrrolidone (NMP). The cathode mixture slurry was applied to one side of a 12 μm-thick cathode current collector (Al thin film) at a rate of 4.5 mAh / cm. 2 The coating was then dried and roll pressed to prepare a positive electrode.

[0165] As the negative electrode active material, Si (average particle size (D 50 Anode slurry (solid content: 48 wt%) was prepared by adding anode slurry (5 μm thick), nitrile butadiene rubber (NBR) as a binder, and carbon black as a conductive material to water as a solvent in a weight ratio of 80:10:10. The cathode slurry was applied to a copper (Cu) thin film as an anode current collector with a thickness of 15 μm, and the resulting current was 10.7 mAh / cm. 2 After drying, the coating was roll-pressed to prepare a negative electrode.

[0166] The positive electrode, a polyolefin-based porous separator coated with inorganic particles (Al2O3), and a negative electrode were sequentially stacked to prepare an electrode assembly.

[0167] The assembled electrode assembly was placed in a battery case, and the prepared non-aqueous electrolyte was injected into the battery case to manufacture a lithium secondary battery.

[0168] Example 2 A non-aqueous electrolyte and a lithium secondary battery were prepared in the same manner as in Example 1, except that the compound represented by Chemical Formula 1-2 was added to the non-aqueous electrolyte at a content of 2 wt % instead of the compound represented by Chemical Formula 1-1.

[0169] Example 3 A non-aqueous electrolyte and a lithium secondary battery were prepared in the same manner as in Example 1, except that the compound represented by Chemical Formula 1-3 was added to the non-aqueous electrolyte at a content of 2 wt % instead of the compound represented by Chemical Formula 1-1.

[0170] Example 4 A non-aqueous electrolyte and a lithium secondary battery were prepared in the same manner as in Example 1, except that the compound represented by Chemical Formula 2-1 was added to the non-aqueous electrolyte at a content of 2 wt % instead of the compound represented by Chemical Formula 1-1.

[0171] Example 5 A non-aqueous electrolyte and a lithium secondary battery were prepared in the same manner as in Example 1, except that the compound represented by Chemical Formula 2-2 was added to the non-aqueous electrolyte at a content of 2 wt % instead of the compound represented by Chemical Formula 1-1.

[0172] Example 6 A non-aqueous electrolyte and a lithium secondary battery were prepared in the same manner as in Example 1, except that the compound represented by Chemical Formula 2-3 was added to the non-aqueous electrolyte at a content of 2 wt % instead of the compound represented by Chemical Formula 1-1.

[0173] Example 7 A non-aqueous electrolyte and a lithium secondary battery were prepared in the same manner as in Example 1, except that the compound represented by Chemical Formula 2-4 was added to the non-aqueous electrolyte at a content of 2 wt % instead of the compound represented by Chemical Formula 1-1.

[0174] Example 8 A non-aqueous electrolyte and a lithium secondary battery were prepared in the same manner as in Example 1, except that the compound represented by Chemical Formula 3-1 was added to the non-aqueous electrolyte at a content of 2 wt % instead of the compound represented by Chemical Formula 1-1.

[0175] Comparative Example 1 A lithium secondary battery was produced in the same manner as in Example 1, except that the average particle size of the silicon-based active material (Si) used in the negative electrode was 0.05 μm (=50 nm).

[0176] Comparative Example 2 A lithium secondary battery was produced in the same manner as in Example 1, except that the average particle size of the silicon-based active material (Si) used in the negative electrode was 0.7 μm (=700 nm).

[0177] Comparative Example 3 A lithium secondary battery was produced in the same manner as in Example 1, except that the average particle size of the silicon-based active material (Si) used in the negative electrode was 40 μm.

[0178] Comparative Example 4 A non-aqueous electrolyte and a lithium secondary battery were produced in the same manner as in Example 1, except that a mixture of fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) in a volume ratio of 3:97 was used as the organic solvent.

[0179] Comparative Example 5 A non-aqueous electrolyte and a lithium secondary battery were produced in the same manner as in Example 1, except that a mixture of fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) in a volume ratio of 30:70 was used as the organic solvent.

[0180] Comparative Example 6 A non-aqueous electrolyte and a lithium secondary battery were produced in the same manner as in Example 1, except that the compound represented by Chemical Formula 1-1 was not added to the non-aqueous electrolyte.

[0181] Comparative Example 7 A non-aqueous electrolyte and a lithium secondary battery were produced in the same manner as in Example 1, except that a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 10:90 was used as the organic solvent.

[0182] Experimental Example Experimental Example 1: Evaluation of room temperature cycle capacity retention rate The lithium secondary batteries of Examples 1 to 8 and Comparative Examples 1 to 7 manufactured as described above were charged to 4.25 V, 0.05 C under CC / CV conditions at 25° C. and 0.33 C, and then discharged to 2.5 V under CC conditions at 0.33 C using an electrochemical charger / discharger. 100 charge / discharge cycles were performed, and the capacity retention rate was measured.

[0183] The capacity retention rate was calculated using the following formula, and the results are shown in Table 1 below.

[0184] Capacity retention rate (%) = {(discharge capacity after 100 cycles / discharge capacity after 1 cycle)} × 100

[0185] Experimental Example 2: Evaluation of high-temperature cycle capacity retention The lithium secondary batteries of Examples 1 to 8 and Comparative Examples 1 to 7 manufactured as described above were charged to 4.25 V, 0.05 C under CC / CV conditions at 45° C. and 0.33 C, and then discharged to 2.5 V under CC conditions at 0.33 C using an electrochemical charger / discharger. 100 charge / discharge cycles were performed, and the capacity retention rate was measured.

[0186] The capacity retention rate was calculated using the following formula, and the results are shown in Table 1 below.

[0187] Capacity retention rate (%) = {(discharge capacity after 100 cycles / discharge capacity after 1 cycle)} × 100

[0188] [Table 1]

[0189] Referring to Table 1, it can be seen that the lithium secondary batteries of Examples 1 to 8 according to the present invention exhibit superior room temperature life performance and high temperature life performance compared to Comparative Examples 1 to 6.

[0190] Reference example Reference example 1 A non-aqueous electrolyte and a lithium secondary battery were produced in the same manner as in Comparative Example 1, except that a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 10:90 was used as the organic solvent.

[0191] Reference Experiment Example 1: Evaluation of Room Temperature Cycle Capacity Retention Rate The 100-cycle capacity retention rates of the lithium secondary batteries of Comparative Example 1 and Reference Example 1 were measured in the same manner as in Experimental Example 1 above.

[0192] Reference Experiment Example 2: Evaluation of High-Temperature Cycle Capacity Retention Rate The 100-cycle capacity retention rates of the lithium secondary batteries of Comparative Example 1 and Reference Example 1 were measured in the same manner as in Experimental Example 2 above.

[0193] [Table 2]

[0194] Referring to Table 2, it can be seen that Reference Example 1, which used EC instead of FEC, had higher room temperature and high temperature cycle capacity retention rates than Comparative Example 1. That is, the silicon-based active material (Si) had an average particle size (D) of less than 1 μm. 50 ), it can be confirmed that using FEC as an organic solvent adversely affects the performance of the lithium secondary battery.

Claims

1. a negative electrode, a positive electrode, a separator, and a non-aqueous electrolyte; the negative electrode includes a negative electrode active material, the negative electrode active material includes a silicon-based active material, The average particle size (D ５０ ) is 1 μm to 20 μm, the non-aqueous electrolyte contains a lithium salt, an organic solvent, and an additive; the organic solvent comprises fluoroethylene carbonate and diethyl carbonate in a volume ratio of 5:95 to 25:75; The additive includes at least one compound selected from the group consisting of compounds represented by the following Chemical Formulas 1 to 3: 【Chemistry 1】 In the above formula 1, R １ is hydrogen or an alkyl group having 1 to 3 carbon atoms, and n is an integer from 1 to 10; 【Chemistry 2】 In the above Chemical Formula 2, m is an integer of 0 to 18; 【Transformation 3】 In the above chemical formula 3, R ２ and R ３ are each independently an alkylene group having 1 to 10 carbon atoms, and R ４ is an alkyl group having 1 to 20 carbon atoms substituted with one or more fluorine atoms.

2. 2. The lithium secondary battery according to claim 1, wherein n is an integer of 3 to 7 in Chemical Formula 1.

3. In the above formula 1, R １ The lithium secondary battery according to claim 1 , wherein is hydrogen.

4. The lithium secondary battery according to claim 1, wherein the compound represented by Chemical Formula 1 includes at least one selected from the group consisting of compounds represented by the following Chemical Formulas 1-1 to 1-3: 【Chemistry 4】 【Transformation 5】 【Transformation 6】

5. 2. The lithium secondary battery according to claim 1, wherein m in Chemical Formula 2 is an integer of 2 to 8.

6. The lithium secondary battery according to claim 1, wherein the compound represented by Chemical Formula 2 includes at least one selected from the group consisting of compounds represented by the following Chemical Formulas 2-1 to 2-4: 【Transformation 7】 【Transformation 8】 【Chemistry 9】 【Chemistry 10】

7. In the above chemical formula 3, R ２ and R ３ are each independently an alkylene group having 1 to 5 carbon atoms, and R ４ 2. The lithium secondary battery according to claim 1, wherein is an alkyl group having 3 to 20 carbon atoms substituted with one or more fluorine atoms.

8. In the above chemical formula 3, R ４ 2. The lithium secondary battery according to claim 1, wherein is an alkyl group having 4 to 8 carbon atoms substituted with one or more fluorine atoms.

9. The lithium secondary battery of claim 1, wherein the compound represented by Chemical Formula 3 includes a compound represented by Chemical Formula 3-1: 【Chemistry 11】

10. 10. The lithium secondary battery according to claim 1, wherein the non-aqueous electrolyte contains 0.01% by weight to 10% by weight of at least one compound selected from the group consisting of compounds represented by Chemical Formulas 1 to 3.

11. The lithium salt is LiBF ４ , LiClO ４ , LiPF ６ , LiBOB(LiB(C ２ O ４ ) ２ ), LiCF ３ SO ３ , LiTFSI (LiN(SO ２ CF ３ ) ２ ), LiFSI (LiN(SO ２ F) ２ ), and LiBETI (LiN(SO ２ CF ２ CF ３ ) ２ 10. The lithium secondary battery according to claim 1, comprising at least one selected from the group consisting of:

12. 10. The lithium secondary battery according to claim 1, wherein the lithium salt is contained in the non-aqueous electrolyte at a concentration of 0.8 M to 3.0 M.

13. The lithium secondary battery according to claim 1 , wherein the silicon-based active material comprises a compound represented by the following chemical formula A: [Chemical formula A] Yes ｘ (0≦+<2)

14. The lithium secondary battery according to claim 1 , wherein the silicon-based active material is Si.

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