Nonaqueous electrolyte composition and lithium secondary battery containing same

Abstract

The present invention relates to an electrolyte composition for a lithium secondary battery, which comprises an electrolyte represented by Chemical Formula 1 and has an oxidation potential window of 4.5 V or more, and thus has the advantage of being able to inhibit oxidative decomposition of the electrolyte composition during charging and discharging of the battery under high voltage conditions.

Description

[Technical Field]

[0001] The present invention relates to a non-aqueous electrolyte composition, and more particularly to a non-aqueous liquid electrolyte composition that enables the production of a battery having an improved oxidation potential window, excellent oxidation stability, and high energy density, and a lithium secondary battery containing the same.

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0107593, filed on August 26, 2022, and all contents disclosed in the documents of said Korean patent application are incorporated herein by reference. [Background technology]

[0003] BACKGROUND ART In recent years, secondary batteries have been widely used not only in small devices such as portable electronic devices but also in medium to large devices such as battery packs for hybrid cars and electric cars or power storage devices.

[0004] Such secondary batteries are manufactured by applying a composition containing an electrode active material to a current collector in a suitable thickness and length, and drying the composition, or by forming the electrode active material itself into a film to form a cathode and an anode. These are then wound or stacked together with an insulating separator between them to form an electrode assembly, which is then placed in a can or a similar container and filled with an electrolyte.

[0005] Here, if the potential window of the electrolyte is not wider than the potential difference between the positive and negative electrode active materials, it cannot suppress side reactions of the electrolyte induced at the interface of the electrode active materials.

[0006] However, as the range of applications of secondary batteries expands, there is an increasing demand for batteries with higher energy density and realizing high voltages of 4 V or more. To meet this demand, conventional positive electrodes use high-voltage positive electrode active materials, which results in the potential window of the electrolyte being narrower than the potential window of the electrode active material.

[0007] To solve this problem, a protective film that prevents direct contact between the electrolyte and the electrode active material can be formed to suppress electrolyte decomposition, thereby maintaining capacity during long-term cycling.

[0008] For example, succinonitrile, adiponitrile, glutaronitrile, and the like are used as electrolyte additives for cathode protection. These additives are known to exhibit excellent thermal properties and high-temperature performance, and to reduce voltage drop during the activation process. They also increase ionic conductivity and polarity, and their nitrile groups form strong bonds with transition metals, such as cobalt, on the cathode surface. The metal-ligand bond suppresses various interfacial side reactions, preventing gas generation and micro-short circuiting. However, while these electrolyte additives are effective at protecting the surface of the cathode active material, as described above, they do not form a protective film on the anode active material, and therefore cannot suppress side reactions between the anode active material and the electrolyte. Therefore, adding an electrolyte additive, such as vinylene carbonate, to control reactivity with the anode can improve cell performance.

[0009] On the other hand, electrolyte additives such as vinylene carbonate can reduce the reactivity between the negative electrode and the electrolyte and suppress side reactions of the electrolyte at the negative electrode, but due to their low oxidation resistance, they can generate gas at the positive electrode when driven at high temperature and high voltage for a long period of time.

[0010] Therefore, research is currently required into electrolytes that not only suppress electrolyte side reactions at the negative electrode, but also have a wide oxidation potential window and improve side reactions at the positive electrode. Summary of the Invention [Problem to be solved by the invention]

[0011] An object of the present invention is to provide an electrolyte composition for a lithium secondary battery that not only has a wide oxidation potential window and is improved in side reactions at the positive electrode, but also can be used under high voltage conditions. [Means for solving the problem]

[0012] To solve the above-mentioned problems, In one embodiment, the present invention comprises: The electrolyte additive comprises a non-aqueous organic solvent, a lithium salt, and an electrolyte additive represented by the following chemical formula 1: An electrolyte composition is provided that has an oxidation potential window of 4.5 V or higher.

[0013] [ka]

[0014] In the above chemical formula 1, R1 is [ka] , [ka] or [ka] and R1' and R1'' are each hydrogen or a methyl group; R2 is an oxygen atom, a nitrogen atom, a sulfur atom, an arylene group having 6 to 20 carbon atoms, an aryleneoxy group having 6 to 20 carbon atoms, a heteroarylene group having 5 to 10 carbon atoms and containing one or more heteroatoms selected from N, S, and O, a heteroaryleneoxy group having 5 to 10 carbon atoms and containing one or more heteroatoms selected from N, S, and O, an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, a cycloalkyl group having 5 to 10 carbon atoms, and [ka] Includes one or more of the following: R3 is a fluoro group, an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, or [ka] and the alkyl group, alkoxy group, cycloalkyl group, [ka] and [ka] One or more of the hydrogen atoms contained in may be optionally substituted with a fluorine atom, M includes at least one selected from the group consisting of lithium, sodium, potassium, tetraalkylammonium having 1 to 4 carbon atoms, and tetraalkylphosphonium having 1 to 4 carbon atoms; l is an integer from 1 to 6, m and n are each an integer of 2 to 20.

[0015] In this case, the oxidation potential window of the electrolyte composition may be in the range of 5.0V to 6.0V.

[0016] In addition, in the above chemical formula 1, R2 is an ethylene group, a propylene group, a cyclohexylene group, a phenylene group, an oxymethylene group, a pyrrole group, an oxyphenylene group, an oxynaphthalenyl group, an oxypyrrole group, an oxythiophenylene group, an oxyfuranyl group, or [ka] and R3 is a fluoro group, a methyl group, a fluoromethyl group, a methoxy group, a fluoromethoxy group, or [ka] and the above [ka] One or more of the hydrogen atoms contained in may be optionally substituted with a fluorine atom, M can be lithium.

[0017] As an example, the electrolyte additive represented by Chemical Formula 1 may include one or more compounds selected from the following <Structural Formula 1> to <Structural Formula 17>. [ka] [ka]

[0018] In addition, the electrolyte additive represented by Chemical Formula 1 may be included in an amount of 10 wt % or less based on the total weight of the electrolyte composition.

[0019] The non-aqueous organic solvent may include an ester solvent represented by the following Chemical Formula 2:

[0020] [ka]

[0021] In the above chemical formula 2, [ka] is a single or double bond, X1 and X2 each represent a hydrogen atom, a fluoro group, a methyl group, an ethyl group, a methyl fluoride group, an ethyl fluoride group, or a vinyl group; p is an integer of 1 to 3.

[0022] Specifically, the ester solvent represented by Chemical Formula 2 above may include one or more of dihydrofuranone, vinyldihydrofuranone, fluorodihydrofuranone, furanone, and tetrahydropyranone.

[0023] The non-aqueous organic solvent may further contain one or more auxiliary solvents selected from the group consisting of fluorine-containing ether solvents, fluorine-containing cyclic carbonate solvents, chain carbonate solvents, phosphate solvents, and sulfone solvents.

[0024] In this case, the co-solvent may be contained in an amount of less than 50% by volume based on the total volume of the non-aqueous organic solvent.

[0025] Furthermore, in one embodiment, the present invention provides an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; There is provided a lithium secondary battery comprising the above-described electrolyte composition according to the present invention.

[0026] In this case, the positive electrode may include at least one positive electrode active material selected from lithium metal oxides represented by the following Formula 3 or 4:

[0027] [Chemical formula 3] Li x [Ni y Co z Mn w M 1 v ]O2

[0028] [Chemical formula 4] LiM 2 p Mn q P r O4

[0029] In the above Chemical Formula 3 and Chemical Formula 4, M 1 is one or more elements selected from the group consisting of 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; x, y, z, w, and v are 1.0≦x≦1.30, 0.5≦y<1, 0 <z≦0.3、0<w≦0.3、0≦v≦0.1であり、かつy+z+w+v=1であり、 M 2 is Ni, Co or Fe, p is 0.05≦p≦1.0, q is 1-p or 2-p; r is 0 or 1.

[0030] Specifically, the positive electrode active material is LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.6 Co 0.2 Mn 0.1 Al 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.15 Al 0.05 O2, LiNi 0.7 Co 0.1 Mn 0.1 Al 0.1 O2 and LiNi 0.5 Mn 1.5 It may contain one or more of O4.

[0031] The negative electrode may include a first negative electrode active material containing a carbon material and a second negative electrode active material containing a silicon material, and the carbon material may include one or more of natural graphite, artificial graphite, expanded graphite, non-graphitizable carbon, carbon black, acetylene black, and ketjen black.

[0032] The silicon material may be silicon (Si), silicon carbide (SiC), or silicon oxide (SiO q , where 0.8≦q≦2.5).

[0033] The second negative electrode active material may be included in an amount of 1 wt % to 20 wt % based on the total weight of the negative electrode active material. [Effects of the Invention]

[0034] The electrolyte composition for a lithium secondary battery according to the present invention includes an electrolyte represented by Chemical Formula 1, and has an oxidation potential window at 4.5 V or higher, thereby improving the oxidation stability of the electrolyte composition and enabling suppression of decomposition of the electrolyte composition at high voltages. DETAILED DESCRIPTION OF THE INVENTION

[0035] Because the present invention is susceptible to various modifications and may have various embodiments, specific embodiments are described in detail in the detailed description.

[0036] However, this is not intended to limit the invention to any particular embodiment, but should be understood to include all modifications, equivalents, or alternatives falling within the spirit and scope of the invention.

[0037] In the present invention, the terms "comprise" and "have" are intended to specify the presence of features, numbers, steps, operations, components, parts or combinations thereof described in the specification, and should be understood as not precluding the presence or possibility of addition of one or more other features, numbers, steps, operations, components, parts or combinations thereof.

[0038] Furthermore, in the present invention, when a layer, film, region, plate, or other portion is described as being "on" another portion, this includes not only the case where it is "directly on" the other portion, but also the case where there is another portion therebetween. Conversely, when a layer, film, region, plate, or other portion is described as being "under" the other portion, this includes not only the case where it is "directly under" the other portion, but also the case where there is another portion therebetween. Furthermore, in this application, being "located on" can include not only the case where it is located at the top, but also the case where it is located at the bottom.

[0039] Furthermore, in the present invention, "comprising as a main component" may mean containing 50 wt% or more (or 50 vol% or more), 60 wt% or more (or 60 vol% or more), 70 wt% or more (or 70 vol% or more), 80 wt% or more (or 80 vol% or more), 90 wt% or more (or 90 vol% or more), or 95 wt% or more (or 95 vol% or more) of a defined component relative to the total weight (or total volume). For example, "comprising graphite as a main component as a negative electrode active material" may mean containing 50 wt% or more, 60 wt% or more, 70 wt% or more, 80 wt% or more, 90 wt% or more, or 95 wt% or more of graphite relative to the total weight of the negative electrode active material. In some cases, it may mean that the entire negative electrode active material is composed of graphite, with the graphite content being 100 wt%.

[0040] The present invention will now be described in more detail.

[0041] <Electrolyte composition for lithium secondary batteries> In one embodiment, the present invention comprises: The electrolyte additive comprises a non-aqueous organic solvent, a lithium salt, and an electrolyte additive represented by the following chemical formula 1: An electrolyte composition is provided that has an oxidation potential window of 4.5 V or higher.

[0042] [ka]

[0043] In the above chemical formula 1, R1 is [ka] , [ka] or [ka] and R1' and R1'' are each hydrogen or a methyl group; R2 is an oxygen atom, a nitrogen atom, a sulfur atom, an arylene group having 6 to 20 carbon atoms, an aryleneoxy group having 6 to 20 carbon atoms, a heteroarylene group having 5 to 10 carbon atoms and containing one or more heteroatoms selected from N, S, and O, a heteroaryleneoxy group having 5 to 10 carbon atoms and containing one or more heteroatoms selected from N, S, and O, an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, a cycloalkyl group having 5 to 10 carbon atoms, and [ka] Includes one or more of the following: R3 is a fluoro group, an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, or [ka] and the alkyl group, alkoxy group, cycloalkyl group, [ka] and [ka] One or more of the hydrogen atoms contained in may be optionally substituted with a fluorine atom, M includes at least one of lithium, sodium, potassium, tetraalkylammonium having 1 to 4 carbon atoms, and tetraalkylphosphonium having 1 to 4 carbon atoms; l is an integer from 1 to 6, m and n are each an integer of 2 to 20.

[0044] The electrolyte composition for a lithium secondary battery according to the present invention includes a non-aqueous organic solvent, a lithium salt, and an electrolyte additive represented by Chemical Formula 1. The electrolyte additive includes an ionic compound having a mother nucleus, as shown in Chemical Formula 1, in which a vinyl group, a (meth)acrylate group, or an acrylamide group is bonded (i.e., "R1") to one side of a sulfonylimide group at the center via i) a structure containing a saturated hydrocarbon chain or an oxygen atom introduced into the saturated hydrocarbon chain, or ii) a structure extending the conjugation of the sulfonylimide group or having a polyglycol unit (i.e., "R2").

[0045] The electrolyte additive has a vinyl group, (meth)acrylate group, or acrylamide group bonded to one side of a sulfonylimide, and a linker (R2) between them that has either i) a saturated hydrocarbon chain or an oxygen atom introduced into the saturated hydrocarbon chain, or ii) a linker (R2) that extends the conjugation of the sulfonylimide group or has a polyglycol unit. This allows for the formation of a uniform organic and / or inorganic coating on the positive and negative electrode surfaces upon activation of the secondary battery. That is, the electrolyte additive can be directly incorporated in a monomolecular form into the organic and / or inorganic coating formed on the positive and / or negative electrode surfaces upon activation of the secondary battery. The electrolyte additive can also increase the oxidation potential window of the electrolyte, thereby suppressing side reactions between the positive and / or negative electrodes and the electrolyte composition. Therefore, the electrolyte additive can expand the oxidation potential window of the electrolyte composition and simultaneously improve the electrical performance of secondary batteries containing it.

[0046] For this purpose, in the compound represented by the above chemical formula 1, R2 is an ethylene group, a propylene group, a cyclohexylene group, a phenylene group, an oxymethylene group, a pyrrole group, an oxyphenylene group, an oxynaphthalenyl group, an oxypyrrole group, an oxythiophenylene group, an oxyfuranyl group, or [ka] and R3 is a fluoro group, a methyl group, a fluoromethyl group, a methoxy group, a fluoromethoxy group, or [ka] and the above [ka] One or more of the hydrogen atoms contained in may be optionally substituted with a fluorine atom, M is lithium, l is an integer of 1 or 2, and m can be an integer of 2-10.

[0047] As an example, the compound represented by Chemical Formula 1 above may be one or more compounds selected from the following <Structural Formula 1> to <Structural Formula 17>. [ka] [ka]

[0048] The electrolyte additives represented by <Structural Formula 1> to <Structural Formula 17> can uniformly form organic and inorganic coating layers on the surfaces of the positive and negative electrodes during activation of a secondary battery. In addition, the electrolyte additives can easily increase the oxidation potential window of the electrolyte composition, thereby effectively suppressing side reactions between the electrodes and the electrolyte during charge and discharge of the secondary battery.

[0049] As one example, the electrolyte composition according to the present invention may have an oxidation potential window of 4.5 V or more. More specifically, the oxidation potential window of the electrolyte composition may be within a range of 4.5 V to 7.0 V, 5.0 V to 6.5 V, 5.0 V to 6.0 V, 5.3 V to 6.5 V, or 5.5 V to 6.0 V.

[0050] The oxidation potential window refers to a voltage range in which no additional electrochemical reactions occur inside the secondary battery other than the electrochemical oxidation-reduction that occurs between the positive electrode and the negative electrode. The oxidation potential window may be a value measured when a lithium electrode is used as a reference electrode, and thus, the Li / Li + The oxidation potential window of the electrolyte may refer to a relative value relative to the potential window. In the present invention, when the oxidation potential window of the electrolyte is outside the above range, the potential window becomes narrow, and therefore, the nonaqueous electrolyte itself undergoes electrolysis during charge and discharge of the battery, shortening the life of the lithium secondary battery and causing safety issues due to the generated gas. Furthermore, when the electrolyte composition according to the present invention satisfies the above-described oxidation potential window range, stability with respect to the potential applied during charge and discharge of the secondary battery can be improved. As a result, a lithium secondary battery containing the electrolyte composition not only has an improved battery life but also reduces the risk of explosion and the like.

[0051] The electrolyte additive may be included in the electrolyte composition in a specific content. Specifically, the electrolyte additive including the compound represented by Formula 1 may be included in an amount of 10 wt % or less, more specifically, 0.01 wt % to 5 wt %, or more specifically, 0.05 wt % to 3 wt %, or 1.0 wt % to 2.5 wt %, based on the total weight of the electrolyte composition. The present invention prevents an increase in the viscosity of the electrolyte composition, which can result in a decrease in wettability of the electrodes and separator, and also prevents a decrease in the ionic conductivity of the electrolyte composition, which can result in a decrease in battery performance, when an excessive amount of the electrolyte additive is used. Furthermore, the present invention prevents the effects of the electrolyte additive from being insignificantly realized when a small amount of the electrolyte additive is used outside the above range.

[0052] The electrolyte composition according to the present invention is a liquid electrolyte and includes a lithium salt and a non-aqueous organic solvent. The non-aqueous organic solvent may include an ester-based solvent represented by the following Chemical Formula 2 as a main component for synergistic effect with the electrolyte additive:

[0053] [ka]

[0054] In the above chemical formula 2, [ka] is a single or double bond, X1 and X2 each represent a hydrogen atom, a fluoro group, a methyl group, an ethyl group, a methyl fluoride group, an ethyl fluoride group, or a vinyl group; p is an integer of 1 to 3.

[0055] As an example, the ester solvent represented by Chemical Formula 2 above may include one or more of the ester compounds shown below. [ka]

[0056] The ester-based compound by itself provides a lower oxidation potential window for the electrolyte composition compared to a carbonate-based solvent. However, when used in combination with the electrolyte additive represented by Chemical Formula 1, the ester-based compound not only provides a superior oxidation potential window, but also improves the stability of the electrolyte and reduces the amount of gas generation at high temperatures and / or high voltages.

[0057] In addition to the ester-based solvent, the non-aqueous organic solvent may further include one or more co-solvents selected from the group consisting of fluorine-containing ether-based solvents, fluorine-containing cyclic carbonate-based solvents, chain carbonate-based solvents, phosphate-based solvents, and sulfone-based solvents.

[0058] Specifically, the fluorine-containing ether solvent may be 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), and the fluorine-containing cyclic carbonate solvent may be fluoroethylene carbonate (FEC). Furthermore, the chain carbonate solvent may be ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and the phosphate solvent may be trimethyl phosphate (TMP), tris(2-ethylhexyl) phosphate, and the sulfone solvent may be sulfolane, methyl sulfolane, dimethyl sulfoxide, sulfonamide, and the like.

[0059] From the viewpoints of electrochemical stability against oxidation-reduction and chemical stability with respect to reactions with heat and solute, the above auxiliary solvents may be used singly in a mixture with the ester-based solvent, or two or more auxiliary solvents may be used in any combination with the ester-based solvent depending on the application.

[0060] The cosolvent may be mixed with the ester solvent at a certain volume ratio. Specifically, the cosolvent may be contained in an amount of less than 50% by volume based on the total volume of the nonaqueous organic solvent, and more specifically, the cosolvent may be contained in an amount of 40% by volume or less, 30% by volume or less, 20% by volume or less, 1% to 30% by volume, 1% to 20% by volume, 5% to 20% by volume, 10% to 20% by volume, or 20% to 30% by volume based on the total volume of the nonaqueous organic solvent.

[0061] By adjusting the content of the co-solvent in the total non-aqueous organic solvent to the above ratio, the present invention can maintain high compatibility between the ester solvent and the co-solvent, and at the same time, can improve the charge mobility and / or ion mobility of the battery, thereby improving the performance of the battery.

[0062] In addition, the non-aqueous organic solvent may be further mixed with a solvent commonly used in non-aqueous electrolytes in the art, and in this case, the mixed amount may be less than 10 wt % based on the total weight of the non-aqueous organic solvent. Examples of the miscible non-aqueous organic solvent include aprotic organic solvents such as N-methyl-2-pyrrolidinone, ethylene carbonate (EC), propylene carbonate, butylene carbonate, 1,2-dimethoxyethane (DME), tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolane derivatives, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0063] Meanwhile, the lithium salt may be any one used in the art for non-aqueous electrolytes without any particular limitation. Specifically, the lithium salt may be LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 , LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, (CF3SO2)2NLi, (FSO2)2NLi, LiBF2(C2O4)(LiODFB), LiTDI, C4F2LiO8P(LiDFOP), and LiF2NO4S2(LiFSI).

[0064] Although there are no particular limitations on the concentrations of these lithium salts, the lower limit of the preferred concentration range is 0.5 mol / L or more, specifically 0.7 mol / L or more, more specifically 0.9 mol / L or more, and the upper limit of the preferred concentration range is 2.5 mol / L or less, specifically 2.0 mol / L or less, more specifically 1.5 mol / L or less. If the lithium salt concentration is below 0.5 mol / L, the ionic conductivity may decrease, which may result in a decrease in the cycle characteristics and output characteristics of the nonaqueous electrolyte battery. Furthermore, if the lithium salt concentration exceeds 2.5 mol / L, the viscosity of the electrolyte for the nonaqueous electrolyte battery increases, which may also decrease the ionic conductivity, which may result in a decrease in the cycle characteristics and output characteristics of the nonaqueous electrolyte battery.

[0065] Furthermore, when a large amount of lithium salt is dissolved in a non-aqueous organic solvent at once, the liquid temperature may rise due to the heat of dissolution of the lithium salt. If the temperature of the non-aqueous organic solvent rises significantly due to the heat of dissolution of the lithium salt, decomposition of the fluorine-containing lithium salt may be accelerated, resulting in the production of hydrogen fluoride (HF). Hydrogen fluoride (HF) is undesirable because it can cause deterioration of battery performance. Therefore, the temperature at which the lithium salt is dissolved in the non-aqueous organic solvent is not particularly limited, but may be adjusted to −20° C. to 80° C., specifically, 0° C. to 60° C.

[0066] The electrolyte composition may further contain additives in addition to the basic components described above. Additives commonly used in the nonaqueous electrolyte solution of the present invention may be added in any proportion without departing from the spirit and scope of the present invention. Specific examples include cyclohexylbenzene, biphenyl, t-butylbenzene, carbonate, vinylethylene carbonate, difluoroanisole, fluoroethylene carbonate, propane sultone, succinonitrile, and dimethylvinylene carbonate. The additives may have overcharge prevention effects, anode film formation effects, and cathode protection effects. Furthermore, the electrolyte solution for nonaqueous electrolyte batteries may be solidified using a gelling agent or crosslinked polymer, as in the case of nonaqueous electrolyte batteries known as lithium polymer batteries.

[0067] <Lithium secondary battery> Furthermore, in one embodiment, the present invention provides an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; There is provided a lithium secondary battery comprising the above-described electrolyte composition according to the present invention.

[0068] The lithium secondary battery according to the present invention includes an electrode assembly in which a positive electrode, a separator, and a negative electrode are sequentially disposed, and an electrolyte composition in which a lithium salt and an electrolyte additive are dissolved in a non-aqueous organic solvent. The lithium secondary battery includes the electrolyte composition according to the present invention, which has an expanded oxidation potential window, and side reactions such as electrolyte decomposition during operation under high voltage conditions can be reduced, making it useful in fields requiring high voltage operation.

[0069] Each component of the lithium secondary battery will now be described in more detail.

[0070] The electrode assembly includes a positive electrode, a separator, and a negative electrode. The positive electrode includes a positive electrode mixture layer prepared by applying a slurry containing a positive electrode active material onto a positive electrode current collector, drying, and pressing the slurry, and may optionally further include a conductive material, a binder, and other additives, as needed.

[0071] The positive electrode active material is a material that can undergo an electrochemical reaction on a positive electrode current collector and may include one or more lithium metal oxides represented by the following Chemical Formula 3 and Chemical Formula 4 that are capable of reversibly intercalating and deintercalating lithium ions.

[0072] [Chemical formula 3] Li x [Ni y Co z Mn w M 1 v ]O2

[0073] [Chemical formula 4] LiM 2p Mn q P r O4

[0074] In the above Chemical Formula 3 and Chemical Formula 4, M 1 is one or more elements selected from the group consisting of 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; x, y, z, w, and v are 1.0≦x≦1.30, 0.5≦y<1, 0 <z≦0.3、0<w≦0.3、0≦v≦0.1であり、かつy+z+w+v=1であり、 M 2 is Ni, Co or Fe, p is 0.05≦p≦1.0, q is 1-p or 2-p; r is 0 or 1.

[0075] The lithium metal oxides represented by Chemical Formula 3 and Chemical Formula 4 above are materials containing high amounts of nickel (Ni) and manganese (Mn), respectively, and when used as a positive electrode active material, have the advantage of being able to stably supply high-capacity and / or high-voltage electricity.

[0076] In this case, the lithium metal oxide represented by the above chemical formula 3 is LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.6 Co 0.2 Mn 0.1 Al 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.15 Al 0.05 O2, LiNi 0.7 Co 0.1 Mn 0.1 Al0.1 O2, etc., and the lithium metal oxide represented by the above chemical formula 4 is LiNi 0.7 Mn 1.3 O4, LiNi 0.5 Mn 1.5 O4, LiNi 0.3 Mn 1.7 O4, LiFePO4, LiFe 0.9 Mn 0.1 PO4, LiFe 0.7 Mn 0.3 PO4, LiFe 0.5 Mn 0.5 PO4, etc., which may be used alone or in combination.

[0077] Positive electrode active materials such as lithium iron phosphate (LiFePO4) have difficulty achieving the voltage conditions necessary for the formation of an organic-inorganic film on the surface of the positive electrode composite layer during the battery activation process, making it difficult to stably form the organic-inorganic film. However, when used as positive electrode active materials, lithium metal oxides represented by Chemical Formulas 3 and 4 can easily achieve the voltage conditions necessary for the formation of an organic-inorganic film during the battery activation process, thereby forming a stable and uniform organic-inorganic film on the positive electrode surface. Furthermore, the organic-inorganic film thus formed can suppress oxidation of the electrolyte composition induced on the positive electrode surface.

[0078] The positive electrode active material may be included in an amount of 85 parts by weight or more, specifically 90 parts by weight or more, 93 parts by weight or more, or 95 parts by weight or more, based on the weight of the positive electrode composite layer.

[0079] The positive electrode mixture layer may further contain a conductive material, a binder, other additives, and the like, in addition to the positive electrode active material.

[0080] The conductive material is used to improve the electrical performance of the positive electrode and may be one commonly used in the art. Specifically, the conductive material may include at least one selected from natural graphite, artificial graphite, carbon black, acetylene black, denka black, ketjen black, Super P, channel black, furnace black, lamp black, thermal black, graphene, and carbon nanotubes.

[0081] The conductive material may be included in an amount of 0.1 to 5 parts by weight based on the weight of each positive electrode composite layer, specifically 0.1 to 4 parts by weight, 2 to 4 parts by weight, 1.5 to 5 parts by weight, 1 to 3 parts by weight, 0.1 to 2 parts by weight, or 0.1 to 1 part by weight.

[0082] The binder functions to bind the positive electrode active material, the positive electrode additive, and the conductive material together, and any material having this function may be used without particular limitation. Specifically, the binder may include one or more resins selected from polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethylmethacrylate, and copolymers thereof. As one example, the binder may include polyvinylidene fluoride.

[0083] The binder may be contained in an amount of 1 to 10 parts by weight, specifically 2 to 8 parts by weight, or 1 to 5 parts by weight, based on the weight of each positive electrode mixture layer.

[0084] The total thickness of the positive electrode composite layer is not particularly limited, but may specifically be 50 μm to 300 μm, more specifically 100 μm to 200 μm, 80 μm to 150 μm, 120 μm to 170 μm, 150 μm to 300 μm, 200 μm to 300 μm, or 150 μm to 190 μm.

[0085] The positive electrode may use a positive electrode current collector that has high conductivity without inducing chemical changes in the battery. For example, the positive electrode current collector may be stainless steel, aluminum, nickel, titanium, calcined carbon, or the like. When the positive electrode current collector is made of aluminum or stainless steel, it may also be surface-treated with carbon, nickel, titanium, silver, or the like. The average thickness of the current collector may be preferably 3 μm to 500 μm, taking into account the conductivity and total thickness of the positive electrode to be manufactured.

[0086] Furthermore, the negative electrode, like the positive electrode, includes a negative electrode mixture layer produced by applying a negative electrode active material onto a negative electrode current collector, drying it, and pressing it, and may further selectively contain a conductive material, a binder, other additives, and the like, as necessary.

[0087] The negative electrode active material may include a carbon material, specifically, a material containing carbon as a main component, such as one or more selected from natural graphite, artificial graphite, expanded graphite, non-graphitizable carbon, carbon black, acetylene black, and ketjen black.

[0088] The negative electrode active material may further include a silicon material together with the carbon material. The silicon material refers to a material containing silicon atoms as a main component. Such silicon materials may include silicon (Si), silicon carbide (SiC), silicon monoxide (SiO), or silicon dioxide (SiO2) alone or in combination. When silicon monoxide (SiO) and silicon dioxide (SiO2) are uniformly mixed or composited as silicon (Si)-containing materials and contained in the negative electrode composite layer, they are referred to as silicon oxide (SiO q, where 0.8≦q≦2.5).

[0089] The silicon material may be included in an amount of 1 wt% to 20 wt% of the total weight of the negative electrode active material, specifically 3 wt% to 10 wt%, 8 wt% to 15 wt%, 13 wt% to 18 wt%, or 2 wt% to 8 wt%. By adjusting the content of the silicon material within the above range, the present invention can maximize the energy density of the battery.

[0090] The negative electrode current collector is not particularly limited as long as it has high conductivity and does not induce chemical changes in the battery. For example, the negative electrode current collector may be made of copper, stainless steel, nickel, titanium, calcined carbon, etc. When the negative electrode current collector is made of copper or stainless steel, it may also be surface-treated with carbon, nickel, titanium, silver, etc. The average thickness of the negative electrode current collector may be preferably 1 μm to 500 μm, taking into account the conductivity and total thickness of the negative electrode to be manufactured.

[0091] Meanwhile, the separator interposed between the positive and negative electrodes of each unit cell refers to an insulating thin film with high ion permeability and mechanical strength. The separator may be any commonly used material in the art, but specifically, may contain one or more polymers selected from the group consisting of polypropylene, polyethylene, and polyethylene-propylene copolymers, which are chemically resistant and hydrophobic. The separator may be in the form of a porous polymer substrate, such as a sheet or nonwoven fabric containing the above-mentioned polymers. In some cases, the separator may be in the form of a composite separator, in which organic or inorganic particles are coated on the porous polymer substrate with an organic binder. The separator may have an average pore diameter of 0.01 μm to 10 μm and an average thickness of 5 μm to 300 μm.

[0092] Meanwhile, the lithium secondary battery according to the present invention is not particularly limited, and may be variously applied to a cylindrical shape, a prismatic shape, a pouch shape, a coin shape, etc. depending on the application. The lithium secondary battery according to an embodiment of the present invention may be a pouch-type secondary battery.

[0093] The present invention will be described in more detail below with reference to examples and experimental examples.

[0094] However, the following examples and experimental examples are merely illustrative of the present invention, and the content of the present invention is not limited to the following examples and experimental examples.

[0095] <Examples 1 to 25 and Comparative Examples 1 to 4. Preparation of electrolyte compositions for lithium secondary batteries> A non-aqueous electrolyte composition for a lithium secondary battery was prepared by weighing the electrolyte additive based on the weight of the entire electrolyte composition and mixing it with a non-aqueous solvent in which LiPF6 was dissolved at 1 M. The type of lithium salt, the composition of the non-aqueous solvent, and the type and content of the electrolyte additive are as shown in Table 1 below.

[0096] [Table 1A] [Table 1B]

[0097] Comparative Example 5: Preparation of Electrolyte Composition for Lithium Secondary Battery A nonaqueous electrolyte composition for a lithium secondary battery was prepared in the same manner as in Example 1, except that an oligomer (weight average molecular weight: 2,500 to 5,000) obtained by polymerizing the compound represented by Structural Formula 1 was used as the electrolyte additive instead of the compound represented by Structural Formula 1.

[0098] <Examples 26 to 50 and Comparative Examples 6 to 10. Production of Lithium Secondary Batteries> The positive electrode active material is LiNi with a particle size of 5 μm. 0.7 Co 0.1Mn 0.1 Al 0.1 O2 was prepared and mixed with polyvinylidene fluoride as a carbon-based conductive material and binder in N-methylpyrrolidone (NMP) in a weight ratio of 94:3:3 to form a slurry, which was then cast onto an aluminum sheet, dried in a vacuum oven at 120°C, and rolled to produce a positive electrode.

[0099] Separately, a negative electrode active material was prepared by mixing natural graphite and artificial graphite in a 1:1 weight ratio. 97 parts by weight of the negative electrode active material and 3 parts by weight of styrene butadiene rubber (SBR) were mixed with water to form a slurry, which was then cast onto a copper sheet, dried in a vacuum oven at 130°C, and rolled to produce a negative electrode.

[0100] The obtained positive and negative electrodes were inserted into a case with a separator made of 18 μm polypropylene, and then the electrolyte compositions prepared in the above Examples and Comparative Examples as shown in Table 2 below were injected to assemble a lithium secondary battery.

[0101] Each assembled lithium secondary battery was initially charged. Specifically, the lithium secondary battery was initially charged at 55±2°C under the conditions shown in Table 2 below to a cut-off voltage of 4.2 V to produce an activated lithium secondary battery.

[0102] [Table 2]

[0103] <Experimental Example 1.> In order to evaluate the performance of the electrolyte composition according to the present invention, the following experiments were carried out on the electrolyte compositions used in the Preparation Examples and Comparative Examples.

[0104] a) Cyclic voltammetry (CV) evaluation of three-electrode battery First, to confirm that a coating layer was formed on the positive electrode surface, three-electrode batteries were fabricated by injecting the electrolyte compositions used in Examples 1 to 25 and Comparative Examples 1 to 5 into batteries containing a platinum electrode, a platinum electrode, and a lithium metal electrode as three electrodes, and cyclic voltammetry (CV) analysis was performed on each of the fabricated batteries. The cyclic voltammetry (CV) was performed at 60°C, in the observation range of 3.0 V to 6.0 V (based on lithium), and at a measurement rate of 10 mV / s. The lithium (Li / Li + The potential at which the electrolyte composition was oxidatively decomposed relative to the electrolyte composition was calculated, and the results are shown in Table 3 below.

[0105] [Table 3]

[0106] As shown in Table 3, it was confirmed that the electrolyte composition according to the present invention, which contains an electrolyte additive represented by Chemical Formula 1, widens the oxidation potential window. Specifically, the electrolyte compositions of the examples, which contain an electrolyte additive, showed an increase in current at about 5.15±0.05 V or more. In contrast, the comparative electrolyte compositions, which do not contain an electrolyte additive or contain an electrolyte additive different from the present invention, showed an increase in current at 4.90±0.05 V or less.

[0107] This increase in current indicates that oxidative decomposition of the electrolyte occurs, forming an organic-inorganic coating layer on the surface of the positive electrode. This means that the oxidation potential window of the electrolyte composition of the Example is expanded by about 0.25 V or more compared to the electrolyte composition of the Comparative Example, due to the inclusion of the electrolyte additive represented by Chemical Formula 1. These results demonstrate that the electrolyte composition of the present invention has improved oxidation stability.

[0108] b) Differential capacity curve analysis of half-cell To confirm the effect of the electrolyte composition according to the present invention on the surface of the negative electrode, half-cells were fabricated using lithium metal and graphite (a mixture of artificial graphite and natural graphite in a weight ratio of 9:1), and the electrolyte compositions prepared in Examples 1 to 25 and Comparative Examples 1 to 5 were injected into the half-cells. The half-cells were then charged at 25°C from 3.5±0.5 V to 0.05 V at a rate of 0.005 C, and the potential (V) and capacity (mAh) were measured. The potential was then differentiated from the capacity (dQ / dV) to calculate the reduction potential.

[0109] As a result, it was confirmed that the electrolyte compositions of the examples containing the electrolyte additive represented by Chemical Formula 1 according to the present invention showed a downward peak at a voltage of around 1.32 V relative to lithium, unlike the electrolyte compositions of the comparative examples which did not contain an electrolyte additive. This downward peak indicates that a reduction reaction occurred on the surface of the graphite electrode, which is the negative electrode, and that the electrolyte additive represented by Chemical Formula 1 contained in the electrolyte composition was converted into a coating material through a reduction reaction on the surface of the negative electrode at around 1.32 V relative to lithium.

[0110] These results show that in the lithium secondary battery according to the present invention, a reduction reaction is induced on the surface of the negative electrode during the activation process, resulting in the formation of an organic / inorganic coating layer.

[0111] <Experimental Example 2.> In order to evaluate the oxidation stability of the electrolyte composition according to the present invention under high temperature and high voltage conditions, the high rate discharge capacity and gas generation amount were measured for the lithium secondary batteries manufactured in Examples 26 to 50 and Comparative Examples 6 to 10.

[0112] Specifically, the lithium secondary batteries of Examples 26 to 50 and Comparative Examples 6 to 10 were each activated by charging at 25°C at a rate of 0.33 C to 4.2 V under CC-CV conditions, and then discharging at a rate of 0.33 C to 2.5 V under CC conditions. Thereafter, each activated lithium secondary battery was charged at a rate of 0.33 C to 4.5 V under CC-CV conditions, and then discharged at a rate of 0.33 C to 2.5 V under CC conditions. Three cycles of charge and discharge were performed, with the above charge and discharge counting as one cycle.

[0113] The volume of the secondary battery was then measured using Archimedes' principle. The battery was then fully charged at 60°C under CC-CV conditions at a rate of 0.33C to 4.5V, and then discharged at a rate of 2.5C to 2.5V under CC conditions to measure the high-temperature high-rate discharge capacity. After the high-rate discharge capacity measurement was completed, the volume of the secondary battery was measured in the same manner as the previous volume measurement, and the volume change was calculated. The volume change was considered to represent the amount of gas generated during high-temperature / high-rate charge / discharge. The results are shown in Table 4 below.

[0114] [Table 4]

[0115] The lithium secondary battery according to the present invention contains the electrolyte composition of the present invention with an expanded oxidation potential window and has excellent oxidation stability, and therefore exhibits excellent battery performance under high temperature and high voltage conditions.

[0116] Specifically, it was confirmed that the lithium secondary batteries manufactured in the examples contained an electrolyte composition containing the electrolyte additive represented by Chemical Formula 1, and exhibited a high discharge capacity of 665 mAh or more under high temperature and high voltage conditions. In particular, when the electrolyte composition of the lithium secondary batteries in the examples contained an ester-based organic solvent, the amount of gas generated by decomposition of the electrolyte composition during charge and discharge was low, at less than 1900 μL.

[0117] These results show that the lithium secondary battery according to the present invention contains an electrolyte represented by Chemical Formula 1, contains an electrolyte composition having an oxidation potential window of 4.5 V or more, and exhibits excellent electrical performance even under high temperature and / or high voltage conditions.

[0118] Although the present invention has been described above with reference to preferred embodiments, it will be understood that those skilled in the art or those with ordinary knowledge in the art can make various modifications and changes to the present invention without departing from the spirit and technical scope of the present invention as set forth in the claims below.

[0119] Therefore, the technical scope of the present invention should not be limited to the content described in the Summary of the Invention of the specification, but should be defined by the claims.

Claims

1. The electrolyte includes a non-aqueous organic solvent, a lithium salt, and an electrolyte additive represented by the following chemical formula 1: The oxidation potential window is 4.5 V or more, 【Chemistry 1】 In the above Chemical Formula 1, R １ teeth 【Chemistry 2】 、 【Transformation 3】 or 【Chemistry 4】 and R １ ' and R １ '' are hydrogen or a methyl group, R ２ represents an arylene group having 6 to 20 carbon atoms, an aryleneoxy group having 6 to 20 carbon atoms, a heteroarylene group having 5 to 10 carbon atoms and containing one or more heteroatoms selected from N, S, and O, a heteroaryleneoxy group having 5 to 10 carbon atoms and containing one or more heteroatoms selected from N, S, and O, an alkylene group having 1 to 10 carbon atoms, a cycloalkylene group having 5 to 10 carbon atoms, and 【Transformation 5】 Contains one or more of the following: R3 is a fluoro group, an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, or 【Transformation 6】 and the alkyl group, alkoxy group, cycloalkyl group, 【Transformation 7】 and 【Transformation 8】 One or more hydrogen atoms contained in M includes one or more of lithium, sodium, potassium, tetraalkylammonium having 1 to 4 carbon atoms, and tetraalkylphosphonium having 1 to 4 carbon atoms; l is an integer from 1 to 6, An electrolyte composition wherein m and n are each an integer of 2 to 20.

2. 2. The electrolyte composition according to claim 1, wherein the oxidation potential window is within a range of 5.0V to 6.0V.

3. R2 is an ethylene group, a propylene group, a cyclohexylene group, a phenylene group, an oxymethylene group, a pyrrole group, an oxyphenylene group, an oxynaphthalenyl group, an oxypyrrole group, an oxythiophenylene group, an oxyfuranyl group, or 【Chemistry 9】 and R3 is a fluoro group, a methyl group, a fluoromethyl group, a methoxy group, a fluoromethoxy group, or 【Chemistry 10】 and 【Chemistry 11】 One or more hydrogen atoms contained in 10. The electrolyte composition of claim 1, wherein M is lithium.

4. 2. The electrolyte composition according to claim 1, wherein the electrolyte additive represented by Chemical Formula 1 includes one or more compounds selected from the following <Structural Formula 1> to <Structural Formula 3> and <Structural Formula 5> to <Structural Formula 17>. 【Chemistry 12】 【Chemistry 13】

5. The electrolyte composition of claim 1 , wherein the electrolyte additive represented by Chemical Formula 1 is contained in an amount of 10 wt % or less based on the total weight of the electrolyte composition.

6. The non-aqueous organic solvent includes an ester solvent represented by the following Chemical Formula 2: 【Chemistry 14】 In the above Chemical Formula 2, 【Chemistry 15】 is a single or double bond, X1 and X2 each represent a hydrogen atom, a fluoro group, a methyl group, an ethyl group, a methyl fluoride group, an ethyl fluoride group, or a vinyl group; 2. The electrolyte composition according to claim 1, wherein p is an integer of 1 to 3.

7. The electrolyte composition according to claim 6, wherein the ester-based solvent represented by Chemical Formula 2 includes at least one of dihydrofuranone, vinyldihydrofuranone, fluorodihydrofuranone, furanone, and tetrahydropyranone.

8. 8. The electrolyte composition according to claim 1, wherein the non-aqueous organic solvent further comprises one or more co-solvents selected from the group consisting of fluorine-containing ether-based solvents, fluorine-containing cyclic carbonate-based solvents, chain carbonate-based solvents, phosphate-based solvents, and sulfone-based solvents.

9. The electrolyte composition according to claim 8 , wherein the co-solvent is contained in an amount of less than 50% by volume based on the total volume of the non-aqueous organic solvent.

10. an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; A lithium secondary battery comprising the electrolyte composition of claim 1.

11. The positive electrode includes at least one positive electrode active material selected from lithium metal oxides represented by the following Chemical Formula 3 or Chemical Formula 4: [Chemical formula 3] Li ｘ [Ni ｙ Co ｚ Mn ｗ M １ ｖ ]O ２ [Chemical formula 4] LiM ２ ｐ Mn ｑ P ｒ O ４ In the chemical formula 3 and the chemical formula 4, M １ is one or more elements 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; x, y, z, w, and v are each in the ranges 1.0≦x≦1.30, 0.5≦y<1, 0<z≦0.3, 0<w≦0.3, and 0≦v≦0.1, and y+z+w+v=1; M ２ is Ni, Co or Fe, p is 0.05≦p≦1.0, q is 1-p or 2-p; 11. The lithium secondary battery according to claim 10, wherein r is 0 or 1.

12. The positive electrode active material is LiNi ０．８ Co ０．１ Mn ０．１ O ２ , LiNi ０．６ Co ０．２ Mn ０．２ O ２ , LiNi ０．９ Co ０．０５ Mn ０．０５ O ２ , LiNi ０．６ Co ０．２ Mn ０．１ Al ０．１ O ２ , LiNi ０．６ Co ０．２ Mn ０．１５ Al ０．０５ O ２ , LiNi ０．７ Co ０．１ Mn ０．１ Al ０．１ O ２ and LiNi ０．５ Mn １．５ O ４ The lithium secondary battery according to claim 11, comprising one or more of:

13. the negative electrode includes a first negative electrode active material containing a carbon material and a second negative electrode active material containing a silicon material; The lithium secondary battery according to claim 10, wherein the carbon material comprises at least one of natural graphite, artificial graphite, expanded graphite, non-graphitizable carbon, carbon black, acetylene black, and ketjen black.

14. The silicon materials include silicon (Si), silicon carbide (SiC), and silicon oxide (SiO ｑ 14. The lithium secondary battery according to claim 13, wherein q is one or more of:

15. The lithium secondary battery of claim 13, wherein the second negative electrode active material is included in an amount of 1 wt % to 20 wt % based on the total weight of the negative electrode active material.

16. A liquid electrolyte comprising a non-aqueous organic solvent, a lithium salt, and an electrolyte additive, The electrolyte additive includes a compound represented by the following structural formula 4: An electrolyte composition having an oxidation potential window of 4.5 V or higher. 【Chemistry 16】

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