Lithium-ion battery

Abstract

The present invention provides a lithium secondary battery comprising a negative electrode, a positive electrode, a separator, and a non-aqueous electrolyte, wherein the negative electrode comprises a silicon-based active material, the non-aqueous electrolyte comprises a lithium salt, an organic solvent, and an additive, and the additive comprises a compound represented by a specific chemical formula.

Description

[Technical Field]

[0001] This application claims priority under Korean Patent Application No. 10-2022-0146436 dated November 4, 2022, and all content disclosed in the said Korean Patent Application is incorporated herein by reference.

[0002] The present invention relates to a lithium secondary battery, and more specifically to a lithium secondary battery that can suppress an increase in initial resistance and improve output characteristics and lifespan performance by including a non-aqueous electrolyte containing an additive that can form a strong SEI film on the positive electrode / negative electrode. [Background technology]

[0003] With the development of the information society, personal IT devices and computer networks have advanced, and as a result, society as a whole has become more dependent on electrical energy, there is a growing need for technologies to efficiently store and utilize electrical energy.

[0004] Rechargeable batteries are the most suitable technology among the developed technologies for a wide range of applications, and among these rechargeable batteries, there is growing interest in lithium-ion batteries, which not only can be miniaturized to a degree that makes them applicable to personal IT devices, but also have the highest energy density.

[0005] Generally, lithium secondary batteries are manufactured by injecting or impregnating an electrode assembly, which consists of a positive electrode, a negative electrode, and a porous separator, with a non-aqueous electrolyte.

[0006] Possible positive electrode active materials for such lithium secondary batteries include lithium-containing cobalt oxide, layered crystalline LiMnO2, spinel crystalline LiMn2O4, 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 recently, silicon-based active materials are being considered because they have a higher capacity compared to carbon-based active materials.

[0008] While the aforementioned silicon-based active material has the advantage of high capacity, it suffers from the problem of very large volume expansion / contraction during the charge / discharge process. Such large volume expansion / contraction significantly reduces the conductivity of the negative electrode, causing a decrease in lifespan performance. Furthermore, during initial activation, a solid electrolyte interface layer (SEI film) is formed on the surface of the negative electrode. However, the large volume expansion of the silicon-based active material leads to problems such as cracking of the SEI film and the continuous formation of new negative electrode surfaces. This, in turn, accelerates side reactions of the electrolyte, such as the continuous occurrence of the SEI film formation reaction, resulting in an increase in the thickness of the SEI film and thus an increase in resistance. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Korean Published Patent Publication No. 2017-0012308 [Overview of the project] [Problems that the invention aims to solve]

[0010] One objective of the present invention is to solve the above-mentioned problems and to provide a lithium secondary battery containing a silicon-based active material as the negative electrode active material, wherein a strong, low-resistance SEI film is formed on the negative electrode, thereby improving both output characteristics and lifespan characteristics simultaneously. [Means for solving the problem]

[0011] The present invention provides a lithium secondary battery comprising a negative electrode, a positive electrode, a separator, and a non-aqueous electrolyte, wherein the negative electrode comprises a silicon-based active material, and the non-aqueous electrolyte comprises a lithium salt, an organic solvent, and an additive, the additive comprising a compound represented by the following chemical formula 1. [ka] In the above chemical formula 1, R1 and R2 are each independently an alkylene group having 1 to 10 carbon atoms, and R3 is an alkyl group having 1 to 20 carbon atoms substituted with one or more fluorine atoms. [Effects of the Invention]

[0012] The present invention relates to a lithium secondary battery in which a silicon-based active material is included in the negative electrode, and the non-aqueous electrolyte contains a compound represented by the chemical formula 1 as an additive. The compound represented by the chemical formula 1 contains a fluorocarbon functional group in which a propargyl group (-C≡C-) and one or more fluorine elements are substituted in its structure, and is reduced before organic solvents, allowing a low-resistance SEI film containing fluorocarbon components to be formed on the surface of the negative electrode. The SEI film formed on the negative electrode by the compound represented by the chemical formula 1 is strong and has low resistance, thus preventing cracking of the SEI film due to volume expansion of the silicon-based active material, and by having low resistance, the life characteristics and output characteristics (specifically, room temperature output characteristics and low-temperature output characteristics) of the lithium secondary battery can be improved simultaneously. [Modes for carrying out the invention]

[0013] First, before describing the present invention, the terms and words used in this specification and in the claims should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather in a manner consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors may define the concepts of terms as appropriate to best describe their invention.

[0014] On the other hand, the terms used herein are used solely to describe exemplary embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

[0015] In this specification, terms such as “includes,” “equip,” or “have” indicate the presence of implemented features, figures, steps, components, or combinations thereof, but should be understood not to preclude the existence or possibility of adding one or more different features, figures, steps, components, or combinations thereof.

[0016] In this specification, "%" means weight percent unless otherwise explicitly indicated.

[0017] Before describing the present invention, in the description of "carbon number 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.

[0018] Furthermore, in this specification, "substitution" means, unless otherwise defined, that at least one hydrogen atom bonded to a carbon atom is substituted with an element other than hydrogen, for example, by an alkyl group having 1 to 5 carbon atoms or by a fluorine element.

[0019] 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 The particle size can be measured, for example, using the laser diffraction method. This laser diffraction method can generally measure particle sizes from the submicron region to several millimeters in size, and can yield highly reproducible and high-resolution results.

[0020] The present invention will be described in more detail below.

[0021] [Lithium-ion secondary battery] The present invention provides a lithium secondary battery comprising a negative electrode, a positive electrode, a separator, and a non-aqueous electrolyte, wherein the negative electrode comprises a silicon-based active material, and the non-aqueous electrolyte comprises a lithium salt, an organic solvent, and an additive, the additive comprising a compound represented by the following chemical formula 1.

[0022] [ka]

[0023] In the above chemical formula 1, R1 and R2 are each independently an alkylene group having 1 to 10 carbon atoms, and R3 is an alkyl group having 1 to 20 carbon atoms substituted with one or more fluorine atoms.

[0024] The present invention relates to a lithium secondary battery in which a silicon-based active material is included in the negative electrode and a compound represented by chemical formula 1 is included as an additive in the non-aqueous electrolyte. The compound represented by chemical formula 1 contains a fluorocarbon functional group in which a propargyl group (-C≡C-) and one or more fluorine elements are substituted in its structure, and is reduced before organic solvents, allowing a low-resistance SEI film containing fluorocarbon components to be formed on the surface of the negative electrode. The SEI film formed on the negative electrode by the compound represented by chemical formula 1 is strong and has low resistance, thus preventing cracking of the SEI film due to volume expansion of the silicon-based active material and simultaneously improving the life characteristics and output characteristics (specifically, room temperature output characteristics and low-temperature output characteristics) of the lithium secondary battery.

[0025] 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.

[0026] (1) Negative electrode The negative electrode includes a silicon-based active material. The silicon-based active material exhibits a higher capacity than the carbon-based active material, but has a problem in that the degree of volume expansion / contraction due to charge / discharge is large. However, when the silicon-based active material and a non-aqueous electrolyte described later are used together, it is possible to form a strong and low-resistance SEI film on the negative electrode, prevent side reactions of the electrolyte, and realize a lithium secondary battery having high life performance and output characteristics.

[0027] The silicon-based active material can include a compound represented by the following chemical formula A.

[0028] [Chemical formula A] SiO x (0 ≦ x < 2)

[0029] In the chemical formula A, in the case of SiO2, since it does not react with lithium ions and cannot store lithium, x is preferably within the above range.

[0030] The silicon-based active material can 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, SiO [[ID=2,7]] x (0 < x < 2)), but the degree of volume expansion / contraction of Si due to charge / 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 a non-aqueous electrolyte described later.

[0031] The average particle size (D) of the silicon-based active material 50 The thickness of the active material can be 0.5 μm to 20 μm, preferably 1 μm to 8 μm, in order to ensure structural stability of the active material during charging and discharging, to more smoothly form a conductive network for maintaining electrical conductivity, or to facilitate access to the binder for bonding the active material and the current collector.

[0032] 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. Here, the silicon-based active material may be included in the negative electrode active material layer.

[0033] 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 can be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloy.

[0034] The negative electrode current collector can typically have a thickness of 3 μm to 500 μm.

[0035] The negative electrode current collector can also have fine irregularities formed on its surface to strengthen the bonding force of the negative electrode active material. For example, the negative electrode current collector can be used in various forms such as film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0036] The negative electrode active material layer is disposed on at least one surface of the negative electrode current collector. Specifically, the negative electrode active material layer can be disposed on one or both surfaces of the negative electrode current collector.

[0037] The silicon-based active material can be included in the negative electrode active material layer in an amount of 60% to 99% by weight, preferably 70% to 85% by weight, in order to minimize the effect of volume expansion / contraction on the battery and to fully realize the high capacity of the silicon-based active material in the secondary battery.

[0038] The negative electrode active material layer may further include a conductive material and / or a binder, together with the silicon-based active material.

[0039] The binder can be used to improve the adhesion between the negative electrode active material layer and the negative electrode current collector described later, or to improve the bonding force between silicon-based active materials.

[0040] Specifically, the binder can further improve electrode adhesion and provide sufficient resistance to the expansion / contraction of the silicon-based active material's volume. It can contain at least one selected from the group consisting of styrene butadiene rubber (SBR), nitrile butadiene rubber (NBR), acrylonitrile butadiene rubber, acrylic rubber, butyl rubber, fluoro rubber, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinyl alcohol (PVA), polyacrylic acid (PAA), polyethylene glycol (PEG), polyacrylonitrile (PAN), and polyacrylamide (PAM). Preferably, it can contain nitrile butadiene rubber.

[0041] The binder can be contained in the negative electrode active material layer at 1 wt% to 30 wt%, preferably 7 wt% to 15 wt%. When it is within the above range, it can better bind the silicon-based active material, minimize the problem of volume expansion of the active material, and facilitate the dispersion of the binder during the production of the slurry for forming the negative electrode active material layer, improving the coating property and the phase stability of the slurry.

[0042] In the secondary battery, the conductive material can be used to assist and improve conductivity. It is not particularly limited as long as it does not cause chemical changes and has conductivity. Specifically, the conductive material can 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, thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, nickel powder; conductive whiskers such as zinc oxide, potassium titanate; conductive metal oxides such as titanium oxide; and polyphenylene derivatives. Preferably, in terms of achieving high conductivity, it can include carbon black.

[0043] The conductive material can be contained in the negative electrode active material layer at 1 wt% to 20 wt%, preferably 8 wt% to 15 wt%. When it is within the above range, it is preferable in terms of relaxing the increase in resistance caused by the binder and forming an excellent conductive network.

[0044] The thickness of the negative electrode active material layer can be 5 μm to 500 μm, preferably 5 μm to 100 μm.

[0045] The loading amount of the negative electrode active material layer is 3 mAh / cm 2 ~15 mAh / cm 2 Preferably, it is 8 mAh / cm 2 ~13 mAh / cm 2 and can be such that.

[0046] The negative electrode can be manufactured by coating the negative electrode current collector with a negative electrode slurry containing a negative electrode active material and selectively a binder, a conductive material, and a solvent for forming the negative electrode slurry, followed by drying and rolling.

[0047] 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 distilled water, in terms of facilitating the dispersion of the negative electrode active material, binder, and / or conductive material.

[0048] The solvent for forming the negative electrode slurry can be included in the negative electrode slurry such that the concentration of the negative electrode active material and solid components, selectively containing a binder and conductive material, is 15% to 45% by weight, taking into consideration the viscosity, coating properties, and dispersibility of the negative electrode slurry.

[0049] (2) Positive electrode The positive electrode includes a positive electrode active material.

[0050] The positive electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium, specifically a lithium transition metal composite oxide containing lithium and at least one transition metal consisting of nickel, cobalt, manganese, and aluminum, preferably a lithium transition metal composite oxide containing lithium and a transition metal including nickel, cobalt, and manganese.

[0051] For example, the lithium transition metal composite oxides include lithium-manganese oxides (e.g., LiMnO2, LiMn2O4, etc.), lithium-cobalt oxides (e.g., LiCoO2, etc.), lithium-nickel oxides (e.g., LiNiO2, etc.), and lithium-nickel-manganese oxides (e.g., LiNi 1-Y Mn Y O2(where 0 <Y<1)、LiMn 2-z Ni zO4 (where 0 < Z < 2, etc.), lithium-nickel-cobalt-based oxides (e.g., LiNi 1-Y1 Co Y1 O2 (where 0 < Y1 < 1, etc.), lithium-manganese-cobalt-based oxides (e.g., LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2-z1 Co z1 O4 (where 0 < Z1 < 2, etc.), lithium-nickel-manganese-cobalt-based oxides (e.g., Li(Ni p Co q Mn 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 one or more of these compounds can be included. Among them, in terms of being able to enhance 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[[ID=3�]] 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 [[ID=SO]]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 It can be Li(Ni)(O2, etc.), and considering the remarkable improvement effect of controlling the type and content ratio of constituent elements that form the lithium transition metal composite oxide, the lithium transition metal composite oxide is Li(Ni)(O2, etc.). 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 ) These can be O2, etc., and one or more of these, or a mixture of two or more, can be used.

[0052] More specifically, the positive electrode active material may contain 60 mol% or more of nickel relative to the total number of moles of transition metal contained in the lithium transition metal composite oxide. Specifically, the positive electrode active material is a lithium transition metal composite oxide, and the transition metal comprises nickel and at least one selected from manganese, cobalt, and aluminum, and the nickel may be contained in an amount of 60 mol% or more, specifically 60 mol% to 90 mol%, relative to the total number of moles of transition metal. When such a lithium transition metal composite oxide with a high nickel content is used together with the above-mentioned non-aqueous electrolyte, it is preferable in that by-products in the gas generated by structural collapse can be reduced.

[0053] Furthermore, the positive electrode active material may include a lithium composite transition metal oxide represented by the following chemical formula B.

[0054] [Chemical formula B] Li 1+x (Ni a Co b Mn c M d)O2

[0055] 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 the atomic fractions of independent elements, with 0≦x≦0.2 and 0.50≦a<1, 0 <b≦0.25、0<c≦0.25、0≦d≦0.1、a+b+c+d=1である。

[0056] Preferably, a, b, c, and d can be 0.70 ≤ a ≤ 0.95, 0.025 ≤ b ≤ 0.20, 0.025 ≤ c ≤ 0.20, and 0 ≤ d ≤ 0.05, respectively.

[0057] Furthermore, a, b, c, and d can satisfy the following inequalities: 0.80 ≤ a ≤ 0.95, 0.025 ≤ b ≤ 0.15, 0.025 ≤ c ≤ 0.15, and 0 ≤ d ≤ 0.05, respectively.

[0058] Furthermore, a, b, c, and d can satisfy the following conditions, respectively: 0.85 ≤ a ≤ 0.90, 0.05 ≤ b ≤ 0.10, 0.05 ≤ c ≤ 0.10, and 0 ≤ d ≤ 0.03.

[0059] 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. Here, the positive electrode active material layer may include the positive electrode active material described above.

[0060] The positive 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 positive electrode current collector can be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloy.

[0061] The positive electrode current collector can typically have a thickness of 3 μm to 500 μm.

[0062] The positive electrode current collector can also have fine irregularities formed on its surface to strengthen the bonding force of the positive electrode active material. For example, the positive electrode current collector can be used in various forms such as film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0063] The positive electrode active material layer is disposed on at least one surface of the positive electrode current collector. Specifically, the positive electrode active material layer can be disposed on one or both surfaces of the positive electrode current collector.

[0064] The positive electrode active material can be included in the positive electrode active material layer at an amount of 80% to 99% by weight, taking into consideration the sufficient capacity exertion of the positive electrode active material.

[0065] The positive electrode active material layer may further include a binder and / or a conductive material along with the positive electrode active material described above.

[0066] The binder is a component that helps in binding the active material to conductive materials and to the current collector, and specifically includes at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluororubber, preferably polyvinylidene fluoride.

[0067] The binder can be included 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 force between components such as the positive electrode active material.

[0068] The conductive material can be used in a secondary battery to assist and improve conductivity, 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 or 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. Preferably, carbon nanotubes can be included in terms of improving conductivity.

[0069] The conductive material can be included 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 electrical conductivity.

[0070] The thickness of the positive electrode active material layer can be 5 μm to 500 μm, preferably 100 μm to 200 μm.

[0071] The loading amount of the positive electrode active material layer is 2 mAh / cm². 2 ~6mAh / cm 2 Preferably 4mAh / cm² 2 ~5mAh / cm 2 It can be.

[0072] The positive electrode can be manufactured by coating the positive electrode current collector with a positive electrode slurry containing a positive electrode active material and selectively a binder, conductive material, and solvent for forming the positive electrode slurry, followed by drying and rolling.

[0073] The solvent for forming the positive electrode slurry may include organic solvents such as NMP (N-methyl-2-pyrrolidone). The solid content of the positive electrode slurry can be 40% to 90% by weight, specifically 50% to 80% by weight.

[0074] (3) Separator The separator can be interposed between the positive electrode and the negative electrode.

[0075] As the separator, conventional porous polymer films that have been used as separators, such as porous polymer films made from polyolefin polymers such as ethylene monopolymer, propylene monopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, can be used alone or in laminated form. Alternatively, conventional porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers, can be used, but are not limited to these. Furthermore, to ensure heat resistance or mechanical strength, coated separators containing ceramic components or polymeric substances may be used, and can be selectively used in single-layer or multi-layer structures.

[0076] (4) Non-aqueous electrolytes 1) Lithium salt First, let me explain lithium salts as follows:

[0077] In a non-aqueous electrolyte for a lithium secondary battery according to one embodiment of the present invention, the lithium salt can be any one that is commonly used in lithium secondary battery electrolytes, for example, Li as a cation. + It contains, 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 - At least one selected from the group consisting of is mentioned. Specifically, the lithium salt is LiCl, LiBr, LiI, LiBF4, LiClO4, LiAlO4, LiAlCl4, LiPF6, LiSbF6, LiAsF6, LiB 10 Cl 10The lithium salt may be at least one selected from the group consisting of LiBOB(LiB(C2O4)2), LiCF3SO3, LiTFSI(LiN(SO2CF3)2), LiFSI(LiN(SO2F)2), LiCH3SO3, LiCF3CO2, LiCH3CO2, 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), and LiBETI(LiN(SO2CF2CF3)2), and more specifically, it may include LiPF6.

[0078] The lithium salt can be appropriately modified within a range of normal use, but in order to obtain the optimal effect of forming a corrosion-preventive coating on the electrode surface, it can be included in the electrolyte at a concentration of 0.8 M to 3.0 M, specifically 1.0 M to 3.0 M.

[0079] When the concentration of the lithium salt satisfies the aforementioned range, the viscosity of the non-aqueous electrolyte can be controlled to achieve optimal impregnation, thereby improving the mobility of lithium ions and obtaining an improvement in the capacity characteristics and cycle characteristics of the lithium secondary battery.

[0080] 2) Organic solvents The aforementioned organic solvent is not particularly limited as long as it is a non-aqueous solvent commonly used in lithium secondary batteries that can minimize decomposition due to oxidation reactions during the charging and discharging process of the secondary battery.

[0081] Specifically, the organic solvent may include cyclic carbonate organic solvents and linear carbonate organic solvents.

[0082] The cyclic carbonate-based organic solvent is a highly viscous organic solvent that has a high dielectric constant and can effectively dissociate lithium salts in the electrolyte. Specifically, it can 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. More specifically, it can include ethylene carbonate.

[0083] Furthermore, the linear carbonate-based organic solvent is an organic solvent having low viscosity and low dielectric constant, and specifically includes at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate, and ethyl propyl carbonate. Specifically, the linear carbonate-based organic solvent may include dimethyl carbonate and ethyl methyl carbonate, and more specifically, it may contain dimethyl carbonate and ethyl methyl carbonate in a volume ratio of 60:40 to 90:10.

[0084] The organic solvent may be a mixture of a cyclic carbonate organic solvent and a linear carbonate organic solvent. Here, the cyclic carbonate organic solvent and the linear carbonate organic solvent may be mixed in a volume ratio of 10:90 to 40:60, specifically, in a volume ratio of 15:85 to 35:65.

[0085] On the other hand, the organic solvent may be further used without limitation by adding any organic solvents commonly used for non-aqueous electrolytes, as needed. For example, it may further contain at least one or more organic solvents from among ester-based organic solvents, ether-based organic solvents, glyme-based solvents, and nitrile-based organic solvents.

[0086] 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, and butyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0087] As the ether-based solvent, 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, may be used, but is not limited thereto.

[0088] The aforementioned glyme-based solvent has a higher dielectric constant and lower surface tension compared to linear carbonate-based organic solvents, and is less reactive with metals. It may include, but is not limited to, at least one selected from the group consisting of dimethoxyethane (Gleim, DME), diethoxyethane, digylme, triglyme, and tetraglyme (TEGDME).

[0089] The nitrile solvent may be one or more selected from the group consisting of acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonile, cyclohexanecarbonile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile, but is not limited thereto.

[0090] On the other hand, the remainder of the non-aqueous electrolyte, excluding the lithium salt and additives, may be organic solvents unless otherwise specified.

[0091] (3) Additives The non-aqueous electrolyte of the present invention contains additives.

[0092] The aforementioned additive contains a compound represented by the following chemical formula 1.

[0093] [ka]

[0094] In the aforementioned chemical formula 1, R1 and R2 are each independently alkylene groups having 1 to 10 carbon atoms. R3 is an alkyl group having 1 to 20 carbon atoms, with one or more fluorine atoms substituted on it.

[0095] Specifically, the compound represented by chemical formula 1, by containing a propargyl functional group in its structure, is readily reductively decomposed on the surface of the negative electrode containing a silicon-based active material, thereby forming an SEI film with low resistance and high passivation capacity. Therefore, when using a non-aqueous electrolyte containing the compound represented by chemical formula 1 as an electrolyte additive, it is possible to prevent the self-discharge reaction of the negative electrode caused by further reductive decomposition of the electrolyte due to the instability of the SEI film.

[0096] Furthermore, the compound represented by chemical formula 1 contains a fluorocarbon functional group in which one or more fluorine elements are substituted at the ends of the structure, thereby forming a coating on the surface of the positive electrode that ensures oxidation resistance, suppressing the elution of transition metals from the positive electrode, suppressing the electrodeposition and deposition of the eluted transition metals on the negative electrode, and preventing internal short circuits.

[0097] Thus, the compound represented by chemical formula 1 contains a fluorocarbon functional group and a propargyl group substituted with one or more fluorine elements, which have excellent flame retardancy and non-flammability. This allows for the formation of a strong, low-resistance SEI film on the negative electrode, which not only suppresses additional reductive decomposition reactions of the electrolyte but also prevents self-discharge reactions of the negative electrode. This results in improved lifespan, suppression of increased initial resistance, and improved output characteristics at room temperature and low temperatures, providing a lithium secondary battery with enhanced performance.

[0098] On the other hand, in the above chemical formula 1, R1 and R2 are each independently an alkylene group having 1 to 5 carbon atoms, and R3 can be an alkyl group having 3 to 20 carbon atoms substituted with one or more fluorine atoms.

[0099] Furthermore, in the above chemical formula 1, R1 and R2 are each independently an alkylene group having 1 to 3 carbon atoms, and R3 can be an alkyl group having 3 to 15 carbon atoms substituted with one or more fluorine atoms.

[0100] Specifically, in the above chemical formula 1, R3 can be an alkyl group having 4 to 8 carbon atoms substituted with one or more fluorine atoms.

[0101] Preferably, the compound represented by chemical formula 1 may be the compound represented by the following chemical formula 1a.

[0102] [ka]

[0103] On the other hand, the compound represented by chemical formula 1 can be included in the non-aqueous electrolyte in an amount of 0.01% to 10.0% by weight.

[0104] When the content of the compound represented by chemical formula 1 is within the range described above, drawbacks such as side reactions due to additives, decrease in capacity, and increase in resistance can be suppressed to the greatest extent possible, and a low-resistance SEI film can be formed on the surface of the negative electrode, improving the lithium transfer effect in the film, suppressing additional reductive decomposition reactions of the electrolyte, and preventing self-discharge reactions of the negative electrode.

[0105] Specifically, when the content of the compound represented by chemical formula 1 is 0.01% by weight or more, a stable film is formed during the battery's operating time, forming a low-resistance SEI film on the negative electrode surface, thereby improving battery output performance. Furthermore, when the content of the compound represented by chemical formula 1 is 10.0% by weight or less, the viscosity of the non-aqueous electrolyte can be controlled to achieve optimal impregnation, effectively suppressing the increase in battery resistance due to the decomposition of additives, further increasing the ionic conductivity within the battery, and preventing a decrease in output characteristics.

[0106] Specifically, the compound represented by chemical formula 1 can be included in the non-aqueous electrolyte in an amount of 0.05% to 6.0% by weight, more specifically 0.1% to 5.0% by weight, and more specifically 0.5% to 2% by weight.

[0107] On the other hand, the additive may, if necessary, include additional additives in addition to the compound represented by Chemical Formula 1, in order to prevent the non-aqueous electrolyte from decomposing in a high-power environment and causing negative electrode collapse, or to further improve low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, and suppression of battery swelling at high temperatures.

[0108] 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.

[0109] The cyclic carbonate compound may be, for example, vinylene carbonate (VC) or vinylethylene carbonate.

[0110] The halogen-substituted carbonate compound can be, for example, fluoroethylene carbonate (FEC).

[0111] The sultone compound can be, for example, at least one compound selected from the group consisting of 1,3-propanesultone (PS), 1,4-butanesultone, ethensultone, 1,3-propensultone (PRS), 1,4-butensultone, and 1-methyl-1,3-propensultone.

[0112] The sulfate compound may be, for example, ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS).

[0113] The phosphate or phosphite compound can be, for example, one or more compounds selected from the group consisting of lithium difluoro(bisoxalate) phosphate, lithium difluorophosphate, tris(trimethylsilyl) phosphate, tris(trimethylsilyl) phosphite, tris(2,2,2-trifluoroethyl) phosphate, and tris(trifluoroethyl) phosphite.

[0114] Examples of the borate compounds include tetraphenyl borate, lithium difluoro(oxalate) borate (LiODFB), or lithium bisoxalate borate (LiB(C2O4)2, LiBOB).

[0115] The nitrile compound can be, for example, at least one compound selected from the group consisting of succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonile, cyclohexanecarbonile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

[0116] The benzene-based compound may be, for example, fluorobenzene, the amine-based compound may be triethanolamine or ethylenediamine, and the silane-based compound may be tetravinylsilane.

[0117] The lithium salt compound is a compound different from the lithium salt contained in the non-aqueous electrolyte, and examples include lithium difluorophosphate (LiPO2F2) or LiBF4.

[0118] If such additional additives include at least one selected from the group consisting of vinylethylene carbonate, 1,3-propanesultone, fluoroethylene carbonate, succinonitrile, and lithium difluoro(oxalate) borate, a stronger SEI film can be formed on the surface of the negative electrode during the initial activation process of the secondary battery.

[0119] The aforementioned additional additive can be used by mixing two or more compounds, and the total content of the compound represented by chemical formula 1 and the additional additive may be 50% by weight or less, specifically 0.05 to 20% by weight, or specifically 0.05 to 10% by weight, relative to the total weight of the non-aqueous electrolyte. When the total content of the additive satisfies the above range, the low-temperature power characteristics of the battery can be improved, the high-temperature storage characteristics and high-temperature life characteristics can be improved more effectively, and the occurrence of side reactions of the battery due to additives remaining after the reaction can be prevented.

[0120] The lithium secondary battery according to the present invention, as described above, can be usefully used in portable devices such as mobile phones, notebook computers, and digital cameras, as well as in the field of electric vehicles such as hybrid electric vehicles (HEVs).

[0121] Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

[0122] The aforementioned battery module or battery pack can be used as a power source for one or more medium-to-large devices, including power tools; electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0123] The external shape of the lithium secondary battery of the present invention is not particularly limited, but may be cylindrical, rectangular, pouch-type, or coin-type, using a can.

[0124] 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 suitably as a unit battery in medium- and large-sized battery modules containing a large number of battery cells.

[0125] The present invention will be specifically described below with reference to examples.

[0126] Herein, the embodiments of the present invention can be modified in various other forms, and the scope of the invention should not be construed as being limited to the embodiments detailed below. The embodiments of the present invention are provided to give a more complete explanation of the invention to a person of average skill in the art.

[0127] The present invention will be described in detail below with reference to specific examples.

[0128] [Examples] Example 1 (Manufacturing of non-aqueous electrolytes) An organic solvent was prepared by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 30:10:60.

[0129] LiPF6 was dissolved in the aforementioned organic solvent to a molar concentration of 1.0 M as a lithium salt.

[0130] Furthermore, a non-aqueous electrolyte was produced by adding the compound represented by chemical formula 1a and additional additives to the organic solvent in which the lithium salt was dissolved.

[0131] The compound represented by chemical formula 1a was present in the non-aqueous electrolyte at a concentration of 0.1% by weight.

[0132] The aforementioned additional additives used were vinylethylene carbonate (VEC), 1,3-propanesultone (PS), fluoroethylene carbonate (FEC), succinonitrile (SN), and LiODFB. The non-aqueous electrolyte was to be mixed with 0.5% by weight of vinylethylene carbonate (VEC), 1.0% by weight of 1,3-propanesultone (PS), 5.0% by weight of fluoroethylene carbonate (FEC), 1.0% by weight of succinonitrile (SN), and 0.5% by weight of LiODFB.

[0133] (Manufacturing of secondary batteries) Cathode active material (LiNi 0.85 Co 0.05 Mn 0.07 Al 0.03A cathode mixture slurry (78% solids by weight) was prepared by adding a conductive material (carbon nanotubes) and a binder (polyvinylidene fluoride) in a weight ratio of 97:1:2 to the solvent N-methyl-2-pyrrolidone (NMP). The cathode mixture slurry was then applied to one surface of a 12 μm thick cathode current collector (a thin film of Al) at a rate of 4.5 mAh / cm². 2 The positive electrode was manufactured by applying the material in the specified loading amount, followed by drying and roll pressing.

[0134] A negative electrode slurry (solid content: 48% by weight) was prepared by adding Si as the negative electrode active material, nitrile butadiene rubber (NBR) as the binder, and carbon black as the conductive material in a weight ratio of 80:10:10 to water as the solvent. This negative electrode slurry was then applied to a copper (Cu) thin film, which served as a 15 μm thick negative electrode current collector, to a current discharge rate of 10.7 mAh / cm². 2 After coating and drying with the specified loading amount, the negative electrode was manufactured by roll pressing.

[0135] An electrode assembly was manufactured by sequentially stacking the positive electrode, a polyolefin-based porous separator coated with inorganic particles (Al2O3), and the negative electrode.

[0136] After placing the assembled electrode assembly inside the battery case, the manufactured non-aqueous electrolyte was poured in to produce a lithium secondary battery.

[0137] Example 2 A non-aqueous electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the compound represented by chemical formula 1a was added at a content of 1.0% by weight based on the weight of the non-aqueous electrolyte to produce the non-aqueous electrolyte.

[0138] Example 3 A non-aqueous electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the compound represented by chemical formula 1a was added at a content of 5.0% by weight based on the weight of the non-aqueous electrolyte to produce the non-aqueous electrolyte.

[0139] Comparative Example 1 A non-aqueous electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the compound represented by chemical formula 1a was not added to produce the non-aqueous electrolyte.

[0140] Comparative Example 2 A non-aqueous electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the compound represented by Chemical Formula 2 below was added to the non-aqueous electrolyte at a content of 0.1% by weight, based on the weight of the non-aqueous electrolyte, instead of the compound represented by Chemical Formula 1a.

[0141] [ka]

[0142] Comparative Example 3 A non-aqueous electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the compound represented by chemical formula 2 was added at a content of 1.0% by weight, based on the weight of the non-aqueous electrolyte, instead of the compound represented by chemical formula 1a.

[0143] Comparative Example 4 A non-aqueous electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the compound represented by Chemical Formula 3 below was added at a content of 0.1% by weight, based on the weight of the non-aqueous electrolyte, instead of the compound represented by Chemical Formula 1a.

[0144] [ka]

[0145] [Experimental Example] Experimental Example 1: Evaluation of initial capacity and cycle capacity retention rate The lithium secondary batteries of Examples 1-3 and Comparative Examples 1-4, manufactured as described above, were charged to 4.25V and 0.05C at 25°C under CC / CV and 0.33C conditions using an electrochemical charger / discharger. One cycle consisted of charging to 2.5V under CC and 0.33C conditions, and 200 charge-discharge cycles were performed to measure the capacity retention rate.

[0146] The capacity retention rate was calculated using the following formula, and the results are shown in Table 1 below.

[0147] Capacity retention rate (%) = {(Discharge capacity after 200 cycles / Discharge capacity after 1 cycle)} × 100

[0148] The discharge capacity (initial capacity) after 1 cycle and the capacity retention rate after 200 cycles are shown in Table 1 below.

[0149] Experimental Example 2: Evaluation of Initial Resistance The lithium secondary batteries of Examples 1-3 and Comparative Examples 1-4, manufactured as described above, were charged to 4.25V and 0.05C at 25°C under CC / CV and 0.33C conditions, and then discharged to 2.5V under CC and 0.33C conditions, with each cycle being considered a charge-discharge cycle.

[0150] After one charge-discharge cycle, the discharge capacity after one cycle was measured using an electrochemical charger. After adjusting the SOC to 50%, a 2.5C pulse was applied for 10 seconds, and the initial resistance was calculated from the difference between the voltage before and after pulse application. The results are shown in Table 1 below.

[0151] [Table 1]

[0152] Referring to Table 1 above, it can be confirmed that the lithium secondary batteries of Examples 1 to 3 according to the present invention have superior initial capacity, capacity retention rate, and resistance characteristics compared to Comparative Examples 1 to 4.

Claims

1. It comprises a negative electrode, a positive electrode, a separator, and a non-aqueous electrolyte. The aforementioned negative electrode contains a silicon-based active material, The non-aqueous electrolyte comprises a lithium salt, an organic solvent, and an additive. The aforementioned additive is a lithium secondary battery containing a compound represented by the following chemical formula 1. 【Chemistry 1】 In the aforementioned chemical formula 1, R １ and R ２ Each of these is an alkylene group having 1 to 10 carbon atoms, R ３ This is an alkyl group having 1 to 20 carbon atoms, with one or more fluorine atoms substituted.

2. In the above chemical formula 1, R １ and R ２ Each of these is independently an alkylene group having 1 to 5 carbon atoms, and R ３ 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.

3. In the above Chemical Formula 1, R １ and R ２ are each independently an alkylene group having 1 to 3 carbon atoms, and R ３ is an alkyl group having 3 to 15 carbon atoms substituted with one or more fluorines. The lithium secondary battery according to claim 1.

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

5. The lithium secondary battery according to claim 1, wherein the compound represented by the chemical formula 1 is the compound represented by the following chemical formula 1a. 【Chemistry 2】

6. The lithium secondary battery according to claim 1, wherein the compound represented by chemical formula 1 is contained in the non-aqueous electrolyte in an amount of 0.01% to 10.0% by weight.

7. The lithium secondary battery according to claim 1, wherein the compound represented by chemical formula 1 is contained in an amount of 0.05% to 6.0% by weight relative to the total weight of the non-aqueous electrolyte for the lithium secondary battery.

8. The lithium secondary battery according to claim 1, wherein the additive comprises at least one additional additive selected from the group consisting of halogen-substituted or unsubstituted carbonate compounds, sultone compounds, sulfate compounds, phosphate or phosphite compounds, borate compounds, nitrile compounds, amine compounds, silane compounds, and lithium salt compounds.

9. The lithium secondary battery according to claim 1, wherein the organic solvent includes a cyclic carbonate organic solvent and a linear carbonate organic solvent.

10. The cyclic carbonate-based organic solvent includes ethylene carbonate. The lithium secondary battery according to claim 9, wherein the linear carbonate-based organic solvent comprises ethyl methyl carbonate and dimethyl carbonate.

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

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

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