Non-aqueous electrolyte for lithium secondary batteries and lithium secondary batteries containing the same

Abstract

The present invention provides a non-aqueous electrolyte for a lithium secondary battery and a lithium secondary battery including the same. Specifically, the non-aqueous electrolyte for a lithium secondary battery of the present invention may include a lithium salt, an organic solvent, and a compound represented by Chemical Formula 1 as a first additive. The present invention also provides a lithium secondary battery including the non-aqueous electrolyte for a lithium secondary battery, which has improved high-temperature storage characteristics and high-temperature cycle characteristics.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0111719 filed on September 2, 2022 and Korean Patent Application No. 10-2023-0108612 filed on August 18, 2023, and all contents disclosed in the documents of said Korean patent application are incorporated as a part of the present specification.

[0002] The present invention relates to a non-aqueous electrolyte for lithium secondary batteries and a lithium secondary battery including the same. [Background Art]

[0003] In modern society, as dependence on electric energy is increasingly growing, development of large-capacity power storage devices that can stably supply electric power and increase power output has attracted attention.

[0004] Lithium ion batteries exhibit the highest energy density among commercialized power storage devices, and are used in various applications such as small electronic devices, electric vehicles (EV), and power storage devices.

[0005] In particular, lithium ion batteries applied to electric vehicles are required to maintain cycle characteristics and performance under various environments and have high output characteristics.

[0006] Such a lithium ion battery includes a positive electrode made of a lithium-containing transition metal oxide, a negative electrode capable of storing lithium, a non-aqueous electrolyte containing an organic solvent having a lithium salt, and a separator.

[0007] Meanwhile, lithium hexafluorophosphate (LiPF6), which is mainly used as the lithium salt, is easily decomposed at high temperatures to generate Lewis acid by-products such as HF and PF5, and said by-products react with moisture to generate more Lewis acid by-product (HF).

[0008] These Lewis acid byproducts can erode the electrodes and the passivation film formed on their surfaces, potentially inducing the elution of transition metal ions from the positive electrode. The eluted transition metal ions can accelerate gas generation by promoting the decomposition of the electrolyte solvent, or they can be re-deposited onto the positive electrode, increasing its resistance. They can also migrate to the negative electrode via the electrolyte and be electrodeposited onto it, causing self-discharge of the negative electrode, destruction and regeneration of the SEI (solid electrolyte interphase) film, and resulting in additional lithium ion consumption and increased resistance.

[0009] This series of reactions reduces the amount of available lithium ions in the battery, making it a major cause of battery capacity degradation. Furthermore, if metal ions electrodeposited on the negative electrode grow in a dendritic pattern, it can cause internal short circuits in the battery, leading to a decrease in battery safety.

[0010] Therefore, there is a need for the development of a non-aqueous electrolyte that can remove Lewis acid byproducts (such as HF and PF5) generated by the thermal decomposition of lithium salts, form a stable film on the electrode surface to suppress the elution of transition metals, or suppress the electrodeposition of eluted transition metal ions onto the negative electrode, thereby improving not only safety but also battery performance such as high-rate charge-discharge characteristics. [Overview of the Initiative] [Problems that the invention aims to solve]

[0011] The present invention aims to provide a non-aqueous electrolyte for lithium secondary batteries that forms a stable film on the electrode surface and contains highly reactive Lewis acid byproducts formed as salt decomposition products in the electrolyte, as well as additives with excellent removal effects for acidic materials.

[0012] Furthermore, the present invention aims to provide a lithium secondary battery with improved high-temperature storage characteristics and high-temperature cycling characteristics by including the aforementioned non-aqueous electrolyte for lithium secondary batteries. [Means for solving the problem]

[0013] To achieve the above objective, one embodiment of the present invention is: It comprises a lithium salt, an organic solvent, and a first additive, The first additive provides a non-aqueous electrolyte for lithium secondary batteries, comprising a compound represented by the following chemical formula 1.

[0014] [ka]

[0015] In the above chemical formula 1, Ar is a 5- or 6-membered nitrogen-containing ring. R1 and R2 are each independently alkyl groups having 1 to 8 carbon atoms.

[0016] Another embodiment of the present invention is, The present invention provides a lithium secondary battery comprising a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte for a lithium secondary battery. [Effects of the Invention]

[0017] The non-aqueous electrolyte for lithium secondary batteries of the present invention contains a compound as an additive that includes a 5-membered or 6-membered nitrogen-containing ring group and a phosphoryl group in its structure. This effectively removes Lewis acid byproducts, which are byproducts of the electrolyte salt, forming a strong SEI (synthetic electrolyte inclusion). This suppresses metal elution and reduces gas emissions by suppressing side reactions between the electrolyte and electrodes, thereby improving battery degradation due to electrode deterioration. Therefore, applying such a non-aqueous electrolyte for lithium secondary batteries can realize lithium secondary batteries with improved cycle characteristics and high-temperature storage stability. [Modes for carrying out the invention]

[0018] The present invention will be described in more detail below.

[0019] The terms and words used herein and in the claims are used solely to describe exemplary embodiments and are not intended to limit the invention.

[0020] For example, in this specification, terms such as “includes,” “equip,” or “have” are intended to specify the presence of implemented features, figures, steps, components, or combinations thereof, and other parts may be added unless “only” is used.

[0021] Furthermore, in this specification, "%" means weight percent unless otherwise explicitly indicated.

[0022] In this specification, unless otherwise defined, “substitution” means that at least one hydrogen atom bonded to a carbon atom is replaced by an element other than hydrogen, for example, by an alkyl group having 1 to 5 carbon atoms or by a fluorine element.

[0023] Conventionally, decomposition products formed by the hydrolysis / thermal decomposition of lithium salts, such as hydrogen fluoride (HF), form a film on the electrode surface, causing the transition metals constituting the positive electrode to easily dissolve into the electrolyte. The dissolved transition metal ions are then re-deposited onto the positive electrode, increasing its resistance. Alternatively, transition metals that have moved to the negative electrode via the electrolyte are electrodeposited onto the negative electrode, causing self-discharge of the negative electrode and destroying the SEI (solid electrolyte interphase) film that provides passivation capability to the negative electrode. This promotes additional electrolyte decomposition reactions and increases the interfacial resistance of the negative electrode.

[0024] This series of reactions reduces the amount of available lithium ions in the battery, leading to a decrease in battery capacity. Furthermore, because it involves the decomposition of the electrolyte, it also causes an increase in resistance.

[0025] In the present invention, by including an additive that can effectively remove decomposition products of electrolyte salts which cause such deterioration and poor behavior, a non-aqueous electrolyte solution for a lithium secondary battery that is oxidatively decomposed prior to the organic solvent and can form a strong coating on the surface of a positive electrode, and a lithium secondary battery including the same with improved high-rate charge and discharge performance at high temperatures are provided as an object.

[0026] [Non-aqueous Electrolyte Solution for Lithium Secondary Battery] Specifically, one embodiment of the present invention: comprises a lithium salt, an organic solvent, and a first additive, provided is a non-aqueous electrolyte solution for a lithium secondary battery, comprising, as the first additive, a compound represented by the following Chemical Formula 1.

[0027]

Chemical Formula

[0028] In Chemical Formula 1, Ar is a 5-membered or 6-membered nitrogen-containing ring, R1 and R2 are each independently an alkyl group having 1 to 8 carbon atoms.

[0029] (1) Lithium salt First, in the non-aqueous electrolyte solution for a lithium secondary battery of the present invention, as the lithium salt, those generally used for electrolyte solutions for lithium secondary batteries can be used without limitation, for example, as a cation, Li + is included, and as an anion, F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , B 10 Cl 10 - , AlCl4 - , AlO4 - , PF6 - , CF3SO3 - , CH3CO2- CF3CO2 - AsF6 - SbF6 - CH3SO3 - , (CF3CF2SO2)2N - , (CF3SO2)2N - , (FSO2)2N - BF2C2O4 - BC4O8 - PF4C2O4 - PF2C4O8 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - , C4F9SO3 - CF3CF2SO3 - CF3CF2(CF3)2CO - (CF3SO2) 2CH - CF3(CF2)7SO3 - , and SCN - This includes at least one selected from the group consisting of the following.

[0030] Specifically, the lithium salts are LiCl, LiBr, LiI, LiBF4, LiClO4, and LiB 10 Cl 10It may contain a single substance or a mixture of two or more substances selected from the group consisting of LiAlCl4, LiAlO4, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiN(SO2F)2 (Lithium bis(fluorosulfonyl)imide, LiFSI), LiN(SO2CF2CF3)2 (lithium bis(pentafluoroethanesulfonyl)imide, LiBETI), and LiN(SO2CF3)2 (lithium bis(trifluoromethane sulfonyl)imide, LiTFSI). Preferably, it may contain a single substance or a mixture of two or more substances selected from the group consisting of LiBF4, LiPF6, LiN(SO2F)2 (LiFSI), LiN(SO2CF2CF3)2 (LiBETI), and LiN(SO2CF3)2 (LiTFSI). In addition to these, lithium salts commonly used in the electrolyte of lithium secondary batteries can be used without restriction.

[0031] The lithium salt can be changed as appropriate within the range of normal use, but in order to obtain the optimal effect of forming a corrosion-preventive coating on the electrode surface, it may be included in the electrolyte at a concentration of 0.8 M to 4.0 M, specifically 1.0 M to 3.0 M.

[0032] When the concentration of the lithium salt is within the above range, the viscosity of the non-aqueous electrolyte can be controlled to achieve optimal impregnation, thereby improving the mobility of lithium ions and improving the capacity characteristics and cycle characteristics of the lithium secondary battery.

[0033] (2) Organic solvents Furthermore, the explanation regarding the organic solvent is as follows:

[0034] As the non-aqueous organic solvent, various organic solvents commonly used in non-aqueous electrolytes can be used without restriction. However, the type of organic solvent is not limited as long as it minimizes decomposition due to oxidation reactions during the charging and discharging process of the secondary battery and can exhibit the desired properties together with the additives.

[0035] Specifically, the non-aqueous organic solvent may include a cyclic carbonate organic solvent, a linear carbonate organic solvent, or a mixture thereof.

[0036] The aforementioned cyclic carbonate-based organic solvent is a highly viscous organic solvent that readily dissociates lithium salts in non-aqueous electrolytes due to its high dielectric constant. Specific examples 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, and more particularly, at least one of ethylene carbonate and propylene carbonate.

[0037] The linear carbonate-based organic solvent is an organic solvent having low viscosity and low dielectric constant, and specific examples may include 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, and specifically may include one of dimethyl carbonate and ethyl methyl carbonate.

[0038] In the present invention, in order to ensure high ionic conductivity, the cyclic carbonate organic solvent and the linear carbonate organic solvent may be mixed and used, in which case the cyclic carbonate organic solvent and the linear carbonate organic solvent may be included in a volume ratio of 10:90 to 50:50, specifically 20:80 to 40:60.

[0039] Furthermore, the organic solvent may further contain at least one of the linear ester organic solvents and cyclic ester organic solvents, which have a lower melting point and higher stability at high temperatures compared to the cyclic carbonate organic solvent and / or linear carbonate organic solvent, in order to produce an electrolyte having high ionic conductivity.

[0040] Typical examples of the linear ester-based organic solvent include at least one organic solvent selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate, and specifically may include at least one of ethyl propionate and propyl propionate.

[0041] The cyclic ester organic solvent may contain at least one selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0042] On the other hand, in the non-aqueous electrolyte of the present invention, the remainder, excluding the lithium salt, the first additive, and the second additive described later, is an organic solvent unless otherwise specified.

[0043] (3) First additive The first additive of the present invention may contain a compound represented by the following chemical formula 1.

[0044] [ka]

[0045] In the above chemical formula 1, Ar is a 5- or 6-membered nitrogen-containing ring. R1 and R2 are each independently alkyl groups having 1 to 8 carbon atoms.

[0046] The five- or six-membered nitrogen-containing ring in the structure of the compound represented by chemical formula 1 is a functional group that acts as a Lewis base. The lone pair of electrons of the nitrogen atom bonds with PF5, suppressing the formation of Lewis acid substances, such as HF, that are generated by the decomposition of PF5. As a result, the degradation behavior of the coating on the surface of the positive or negative electrode due to the chemical reaction caused by Lewis acids can be suppressed, thereby preventing additional electrolyte decomposition of the battery due to coating degradation or destruction. Furthermore, it can mitigate the self-discharge of the secondary battery and improve its high-temperature storage characteristics.

[0047] Furthermore, the compound represented by chemical formula 1 contains a phosphoryl group within its structure that can form an inorganic film on the surface of the negative electrode, thereby suppressing side reactions between the electrolyte and the electrode, and enabling gas reduction and prevention of battery degradation.

[0048] In particular, the compound represented by chemical formula 1 forms a highly passive film on the surfaces of the negative and positive electrodes while the nitrogen-containing ring or functional group such as a phosphoryl group undergoes reductive decomposition. This prevents the self-discharge reaction of the negative electrode caused by additional reductive decomposition reactions of the electrolyte due to the instability of the SEI film, and prevents metal ions from eluting from the positive electrode or electrodepositing of eluted metal ions onto the negative electrode. As a result, it is possible to improve the high-temperature durability of lithium secondary batteries, such as their cycle characteristics and capacity characteristics.

[0049] On the other hand, the compound represented by chemical formula 1 can be the compound represented by chemical formula 1A below.

[0050] [ka]

[0051] In the aforementioned chemical formula 1A, R1 and R2 are each independently alkyl groups having 1 to 8 carbon atoms.

[0052] Furthermore, in the above chemical formula 1A, R1 and R2 may each be an alkyl group having 1 to 5 carbon atoms independently.

[0053] Furthermore, in the above chemical formula 1A, R1 and R2 may each be an alkyl group having 1 to 3 carbon atoms independently.

[0054] Preferably, the compound represented by chemical formula 1A may be one of the compounds represented by chemical formula 1A-1 or chemical formula 1A-2.

[0055] [ka]

[0056] [ka]

[0057] On the other hand, the compound of chemical formula 1 may be included in an amount of 0.5% to 3.0% by weight based on the total weight of the non-aqueous electrolyte.

[0058] When the compound represented by chemical formula 1 is included within the above range, it is possible to manufacture a secondary battery with improved performance by preventing side reactions caused by additives, forming a strong film on the negative and positive electrodes, and effectively preventing deterioration of the negative electrode during rapid charging and discharging. Specifically, when the content of the compound represented by chemical formula 1 is 0.5% by weight or more, the effect of removing thermal decomposition products of lithium salts such as HF or PF5, and the effect of forming a film on the surfaces of the negative and positive electrodes can be maintained more stably during the battery's operating time. Furthermore, when the content of the compound represented by chemical formula 1 is 3.0% 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, and preventing a decrease in the ionic conductivity of the electrolyte, thereby preventing a decrease in rate characteristics and low-temperature life characteristics.

[0059] More specifically, the compound represented by chemical formula 1 may be present in an amount of 0.5% to 2.5% by weight, more preferably 0.5% to 2.0% by weight.

[0060] (4) Second additive Furthermore, the non-aqueous electrolyte for lithium secondary batteries of the present invention may, if necessary, further contain a second additive in the non-aqueous electrolyte to prevent the non-aqueous electrolyte from decomposing in a high-power environment, which can cause the collapse of the negative electrode, or to further improve low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, and the effect of suppressing battery swelling at high temperatures.

[0061] Such a second additive may include, as a typical example, at least one second additive selected from the group consisting of cyclic carbonate compounds, halogen-substituted carbonate compounds, sultone compounds, sulfate compounds, phosphate compounds, borate compounds, nitrile compounds, benzene compounds, amine compounds, silane compounds, and lithium salt compounds.

[0062] Examples of the aforementioned cyclic carbonate compounds include vinylene carbonate (VC) or vinylethylene carbonate.

[0063] Examples of halogen-substituted carbonate compounds include fluoroethylene carbonate (FEC).

[0064] Examples of the sultone compound include 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.

[0065] Examples of the sulfate compounds include ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS).

[0066] Examples of the phosphate compound include one or more compounds selected from the group consisting of lithium difluoro(bisoxalato) phosphate, lithium difluorophosphate, tris(trimethylsilyl) phosphate, tris(2,2,2-trifluoroethyl) phosphate, and tris(trifluoroethyl) phosphate.

[0067] Examples of the borate-based compounds include tetraphenylborate and lithium oxalyldifluoroborate.

[0068] The nitrile compounds include 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.

[0069] Examples of the benzene-based compound include fluorobenzene, and examples of the amine-based compound include triethanolamine or ethylenediamine.

[0070] Examples of the silane compounds include tetravinylsilane.

[0071] The lithium salt-based compound mentioned above is one or more compounds selected from the group consisting of LiPO2F2, LiODFB, LiBOB (lithium bisoxalate borate (LiB(C2O4)2), and LiBF4), which are different from the lithium salt contained in the non-aqueous electrolyte.

[0072] If the second additive includes at least one of vinylene carbonate, vinylethylene carbonate, and succinonitrile, an even stronger SEI film can be formed on the surface of the negative electrode during the initial activation process of the secondary battery.

[0073] On the other hand, the second additive can be used in a mixture of two or more types, and may be present in an amount of 50% by weight or less, specifically 0.01% to 10% by weight, based on the total weight of the non-aqueous electrolyte, preferably 0.05% to 5.0% by weight. If the content of the second additive is less than 0.01% by weight, the effect of improving the low-temperature output of the battery, as well as the high-temperature storage characteristics and high-temperature life characteristics, will be minimal. If the content of the second additive exceeds 50% by weight, excessive side reactions may occur in the electrolyte during battery charging and discharging. In particular, if an excessive amount of the SEI film-forming additive is added, it may not decompose sufficiently at high temperatures and may remain unreacted or precipitated in the electrolyte at room temperature. Therefore, there is a risk of side reactions occurring that reduce the life or resistance characteristics of the secondary battery.

[0074] [Lithium-ion secondary battery] Another embodiment of the present invention provides a lithium secondary battery containing a non-aqueous electrolyte for lithium secondary batteries of the present invention.

[0075] The lithium secondary battery of the present invention can be manufactured by conventional methods known in the art, specifically by forming an electrode assembly in which a positive electrode, a negative electrode, and a separator between the positive and negative electrodes are sequentially stacked, housing it in a battery case, and then adding the non-aqueous electrolyte for lithium secondary batteries of the present invention.

[0076] Next, each component of the lithium secondary battery of the present invention will be described in more detail.

[0077] (1) Positive electrode The positive electrode according to the present invention includes a positive electrode active material layer containing a positive electrode active material, and if necessary, the positive electrode active material layer may further contain a conductive material and / or a binder.

[0078] The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and specifically, it may include a lithium composite metal oxide represented by the following Chemical Formula 2, which contains lithium and at least one metal selected from the group consisting of nickel (Ni), cobalt (Co), manganese (Mn), iron (Fe), and aluminum (Al).

[0079] [Chemical Formula 2] Li 1+a Ni x Co y M 1 z M 2 w O2

[0080] In Chemical Formula 2, M 1 is Mn, Al, or a combination thereof, M 2 is at least one selected from the group consisting of Al, Zr, W, Ti, Mg, Ca, and Sr, and 0≦a≦0.5, 0.55<x<1.0, 0<y≦0.4, 0<z≦0.4, and 0≦w≦0.1.

[0081] Said 1+a represents the atomic fraction of lithium in the lithium transition metal oxide, and may satisfy 0≦a≦0.5, preferably 0≦a≦0.2, more preferably 0≦a≦0.1.

[0082] Said x represents the atomic fraction of nickel among all transition metal elements in the lithium transition metal oxide, and may satisfy 0.55<x<1.0, specifically 0.6≦x≦0.98, more specifically 0.6≦x≦0.95.

[0083] Said y represents the atomic fraction of cobalt among all transition metal elements in the lithium transition metal oxide, and may satisfy 0<y≦0.4, specifically 0<y≦0.3, more specifically 0.05≦y≦0.3.

[0084] Said z represents the atomic fraction of M 1 element among all transition metal elements in the lithium transition metal oxide, and may satisfy 0<z≦0.4, preferably 0<z≦0.3, more preferably 0.01≦z≦0.3.

[0085] Said w represents the atomic fraction of M 2 element among all transition metal elements in the lithium transition metal oxide, and satisfies 0<w≦0.1, preferably 0<w≦0.05, more preferably 0<w≦0.02.

[0086] Specifically, to achieve a high-capacity battery, the positive electrode active material may be Li(Ni 0.6 Mn 0.2 Co 0.2 )O₂ having a Ni content of 0.55 atm% or more, Li(Ni 0.7 Mn 0.15 Co 0.15 )O₂, Li(Ni 0.7 Mn 0.2 Co 0.1 )O₂, Li(Ni 0.8 Mn 0.1 Co 0.1 )O₂, Li(Ni 0.8 Co 0.15 Al 0.05 )O₂, Li(Ni 0.86 Mn 0.07 Co 0.05 Al 0.02 )O₂, or Li(Ni 0.90 Mn 0.05 Co 0.05 )O₂, and may include lithium composite transition metal oxides such as the above.

[0087] Furthermore, the positive electrode active material of the present invention, together with the lithium composite metal oxide represented by the aforementioned Chemical Formula 2, may be used in combination with lithium-manganese based oxides (for example, LiMnO2, LiMn2O4, etc.), lithium-cobalt based oxides (for example, LiCoO2, etc.), lithium-nickel based oxides (for example, LiNiO2, etc.), lithium-nickel-manganese based oxides (for example, LiNi 1-Y Mn Y O2 (0<Y<1), LiMn 2-Z Ni Z O4 (0<Z<2), lithium-nickel-cobalt based oxides (for example, LiNi 1-Y1 Co Y1 O2 (0<Y1<1), lithium-manganese-cobalt based oxides (for example, LiCo 1-Y2 Mn Y2 O2 (0<Y2<1), LiMn 2-Z1 Co Z1 O4 (0<Z1<2), or Li(Ni p1 Co q1 Mn r2 )O4 (0<p1<2, 0<q1<2, 0<r2<2, p1+q1+r2=2) and the like.

[0088] Based on the total weight of the positive electrode active material layer, the positive electrode active material may be included in a content of 80 wt% to 98 wt%, more specifically 85 wt% to 98 wt%. When the positive electrode active material is included within the above range, excellent capacity characteristics can be exhibited.

[0089] Next, the conductive material is used to impart conductivity to the electrodes and can be used in the battery without any particular limitations as long as it does not cause a chemical change and has electronic conductivity. Specific examples include carbon black such as carbon black, acetylene black (or Denka black), Ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powder such as natural graphite, artificial graphite, or graphite with a highly developed crystalline structure; conductive fibers such as carbon fibers or metal fibers; conductive powders such as carbon fluoride powder, aluminum powder, or nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and polyphenylene derivatives. One of these may be used alone, or a mixture of two or more may be used.

[0090] The conductive material may be included in an amount of 0.1% to 10% by weight, preferably 0.1% to 5% by weight, based on the total weight of the positive electrode active material layer.

[0091] Next, the binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the current collector.

[0092] Examples of such binders include fluoropolymer binders containing polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); rubber binders containing styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, and styrene-isoprene rubber; cellulose binders containing carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, and regenerated cellulose; polyalcohol binders containing polyvinyl alcohol; polyolefin binders containing polyethylene and polypropylene; polyimide binders; polyester binders; and silane binders. One of these may be used alone or in mixtures of two or more.

[0093] The binder may be present in an amount of 0.1% to 15% by weight, preferably 0.1% to 10% by weight, based on the total weight of the positive electrode active material layer.

[0094] Such a positive electrode of the present invention can be manufactured by a positive electrode manufacturing method known in the art. For example, the positive electrode can be manufactured by a method in which a positive electrode slurry, prepared by dissolving or dispersing a positive electrode active material, a binder, and / or a conductive material in a solvent, is applied to a positive electrode current collector, and then dried and rolled to form a positive electrode active material layer, or by a method in which the positive electrode active material layer is cast onto another support, the support is peeled off, and the resulting film is laminated onto the positive electrode current collector.

[0095] On the other hand, the positive electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector usually has a thickness of 3 μm to 500 μm, and the adhesion strength of the positive electrode material may be increased by forming fine irregularities on the surface of the current collector. For example, it can be used in various forms such as film, sheet, foil, mesh, porous material, foam, and nonwoven fabric.

[0096] The solvent may be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. One of these may be used alone, or a mixture of two or more. The amount of solvent used is not particularly limited, and should be adjusted to ensure that the cathode composite material has an appropriate viscosity, taking into consideration the coating thickness of the cathode composite material, the manufacturing yield, and the workability of the workability.

[0097] (2) Negative electrode Next, I will explain the negative electrode.

[0098] The negative electrode according to the present invention comprises a negative electrode active material layer containing a negative electrode active material, the negative electrode active material layer may further contain a conductive material and / or a binder as needed.

[0099] As the anode active material, various anode active materials used in this industry, such as carbon-based anode active materials, silicon-based anode active materials, or mixtures thereof, may be used.

[0100] According to one embodiment, the anode active material may include a carbon-based anode active material, and the carbon-based anode active material can be any of the various carbon-based anode active materials used in the industry, such as graphite-based materials such as natural graphite, artificial graphite, and Kish graphite; high-temperature calcined carbon such as pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and petroleum or coal tar pitch-derived cokes, as well as soft carbon and hard carbon. The shape of the carbon-based anode active material is not particularly limited, and materials of various shapes such as amorphous, plate-like, flaky, spherical, or fibrous can be used.

[0101] Preferably, at least one carbon-based negative electrode active material, such as natural graphite and artificial graphite, can be used as the negative electrode active material. In order to increase adhesion to the current collector and suppress detachment of the active material, both natural graphite and artificial graphite may be used.

[0102] According to other embodiments, the negative electrode active material may include a silicon-based negative electrode active material together with the carbon-based negative electrode active material.

[0103] The silicon-based negative electrode active material is, for example, metallic silicon (Si) or silicon oxide (SiO x, here, 0<x<2), silicon carbide (SiC), and Si-Y alloy (wherein Y is an element selected from the group consisting of alkali metals, alkaline earth metals, group 13 elements, group 14 elements, transition metals, rare earth elements, and combinations thereof, and is not Si) may comprise one or more selected from the group consisting of the foregoing. Said element Y may be one selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db (dubnium), Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

[0104] Since the silicon-based negative electrode active material exhibits higher capacity characteristics than carbon-based negative electrode active materials, when the silicon-based negative electrode active material is further included, more excellent capacity characteristics can be obtained. However, a negative electrode containing a silicon-based negative electrode active material contains more oxygen-rich (O-rich) components in the SEI film than a graphite negative electrode, and an SEI film containing oxygen-rich components tends to be more easily decomposed when a Lewis acid such as HF or PF5 is present in the electrolyte. Therefore, in order to maintain a stable SEI film for a negative electrode containing a silicon-based negative electrode active material, it is necessary to suppress the generation of Lewis acids such as HF and PF5 in the electrolyte, or to remove (or scavenge) the generated Lewis acids. The non-aqueous electrolyte according to the present invention forms stable coatings on the positive electrode and the negative electrode, and contains an electrolyte additive excellent in Lewis acid scavenging effect, so that the decomposition of the SEI coating can be effectively suppressed when using a negative electrode containing a silicon-based active material.

[0105] On the other hand, the mixing ratio of the silicon-based negative electrode active material to the carbon-based negative electrode active material may be 3:97 to 99:1 by weight, preferably 5:95 to 15:85. When the mixing ratio of the silicon-based negative electrode active material to the carbon-based negative electrode active material satisfies the above range, capacity characteristics are improved, volume expansion of the silicon-based negative electrode active material is suppressed, and excellent cycle performance can be ensured.

[0106] The negative electrode active material may be present in an amount of 80% to 99% by weight, based on the total weight of the negative electrode active material layer. When the content of the negative electrode active material meets the above range, excellent capacitance characteristics and electrochemical properties can be obtained.

[0107] Next, the conductive material is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 10% by weight or less, preferably 5% by weight or less, based on the total weight of the negative electrode active material layer. Such conductive material is not particularly limited as long as it does not cause a chemical change in the battery and is conductive, and may be used, for example, carbon black such as carbon black, acetylene black (or Denka black), Ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powder such as natural graphite, artificial graphite, or graphite with a well-developed crystalline structure; conductive fibers such as carbon fibers or metal fibers; conductive powders such as fluorinated carbon powder, aluminum powder, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and polyphenylene derivatives.

[0108] The binder is a component that assists in bonding between the conductive material, active material, and current collector, and is usually added at a concentration of 0.1% to 10% by weight based on the total weight of the negative electrode active material layer. Examples of binders include fluoropolymer binders containing polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); rubber binders containing styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, and styrene-isoprene rubber; cellulose binders containing carboxyl methyl cellulose (CMC), starch, hydroxypropyl cellulose, and regenerated cellulose; polyalcohol binders containing polyvinyl alcohol; polyolefin binders containing polyethylene and polypropylene; polyimide binders; polyester binders; and silane binders.

[0109] The binder may be present in an amount of 0.1% to 15% by weight, preferably 0.1% to 10% by weight, based on the total weight of the negative electrode active material layer.

[0110] The negative electrode can be manufactured by a negative electrode manufacturing method known in the art. For example, the negative electrode can be manufactured by a method in which a negative electrode slurry, prepared by selectively dissolving or dispersing a negative electrode active material, a binder, and a conductive material in a solvent, is applied to a negative electrode current collector, and then rolled and dried to form an active material layer, or by a method in which the negative electrode active material layer is cast onto another support, and then the support is peeled off to obtain a film which is then laminated onto the negative electrode current collector.

[0111] 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. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. The negative electrode current collector usually has a thickness of 3 μm to 500 μm, and, similar to the positive electrode current collector, the bonding force of the negative electrode active material may be strengthened by forming fine irregularities on the surface of the current collector. For example, it can be used in various forms such as film, sheet, foil, mesh, porous material, foam, and nonwoven fabric.

[0112] The solvent may be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. One of these may be used alone, or a mixture of two or more. The amount of solvent used is not particularly limited, as long as it can be adjusted so that the negative electrode slurry has an appropriate viscosity, taking into consideration the coating thickness of the negative electrode mixture, the production yield, and the workability.

[0113] (3) Separator The lithium secondary battery according to the present invention includes a separator between the positive electrode and the negative electrode.

[0114] The separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. It can be used without particular limitations as long as it is one that is commonly used as a separator in lithium secondary batteries. In particular, it is preferable that it has low resistance to the movement of lithium salt ions and has excellent electrolyte moisture absorption capacity.

[0115] Specifically, as separators, porous polymer films, such as those made from polyolefin polymers like ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof, can be used. Alternatively, ordinary porous nonwoven fabrics, such as those made from high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, coated separators containing ceramic components or polymeric substances may be used to ensure heat resistance or mechanical strength, and may be selectively used as single-layer or multi-layer structures.

[0116] 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).

[0117] The external shape of the lithium secondary battery of the present invention is not particularly limited, but may be cylindrical, rectangular, pouch-shaped, or coin-shaped, using a can.

[0118] 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.

[0119] [Examples] Example 1. (Manufacturing of non-aqueous electrolytes for lithium secondary batteries) A non-aqueous electrolyte for lithium secondary batteries was prepared by dissolving LiPF6 in a non-aqueous organic solvent prepared by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 30:70 to a concentration of 1.0 M. Then, a compound represented by chemical formula 1A-1 was added at a concentration of 0.5% by weight, and vinylene carbonate (VC) was added at a concentration of 0.5% by weight (see Table 1 below).

[0120] (Manufacturing of Secondary Battery) To N-methyl-2-pyrrolidone (NMP) as a solvent, a positive electrode active material (Li(Ni 0.9 Mn 0.03 Co 0.06 Al 0.01 )O₂), a conductive material (carbon black), and a binder (polyvinylidene fluoride) were added at a weight ratio of 97.6:0.8:1.6 to prepare positive electrode slurry (with a solid content of 60.0% by weight). The positive electrode slurry was applied onto a positive electrode current collector (Al thin film) having a thickness of 13.5 µm, dried, and then roll-pressed to manufacture a positive electrode.

[0121] A negative electrode active material (graphite:SiO = 94:6 by weight ratio), a binder (SBR-CMC), and a conductive material (carbon black) were added at a weight ratio of 97.6:0.8:1.6 to water as a solvent to prepare negative electrode slurry (with a solid content of 60% by weight). The negative electrode slurry was applied onto a copper (Cu) thin film, which serves as a negative electrode current collector having a thickness of 6 µm, dried, and then roll-pressed to manufacture a negative electrode.

[0122] After an electrode assembly was manufactured by interposing polypropylene as a porous separator between the positive electrode and the negative electrode manufactured as above, the electrode assembly was housed in a battery case, and the prepared non-aqueous electrolyte for a lithium secondary battery was injected into the battery case, thereby manufacturing a lithium secondary battery.

[0123] Example 2. (Manufacturing of Non-aqueous Electrolyte for Lithium Secondary Battery) After LiPF₆ was dissolved in a non-aqueous organic solvent to a concentration of 1.0 M, a compound represented by Chemical Formula 1A-1 was added to a content of 1.0% by weight, and vinylene carbonate (VC) was added to a content of 0.5% by weight, thereby manufacturing a non-aqueous electrolyte for a lithium secondary battery.

[0124] (Manufacturing of Secondary Battery) A lithium secondary battery was manufactured in the same manner as in Example 1, except that the non-aqueous electrolyte for lithium secondary batteries manufactured above was injected instead of the non-aqueous electrolyte used in Example 1 (see Table 1 below).

[0125] Comparative Example 1. (Manufacturing of non-aqueous electrolytes for lithium secondary batteries) A non-aqueous electrolyte was prepared by dissolving LiPF6 in a non-aqueous organic solvent to a concentration of 1.0 M, and then adding vinylene carbonate (VC) as an additive to a concentration of 0.5% by weight.

[0126] (Manufacturing of secondary batteries) A lithium secondary battery was manufactured in the same manner as in Example 1, except that the non-aqueous electrolyte for lithium secondary batteries manufactured above was injected instead of the non-aqueous electrolyte used in Example 1 (see Table 1 below).

[0127] Comparative Example 2. (Manufacturing of non-aqueous electrolytes for lithium secondary batteries) After dissolving LiPF6 in a non-aqueous organic solvent to a concentration of 1.0 M, a non-aqueous electrolyte was prepared by adding, as an additive, the compound represented by the following chemical formula 3 in an amount of 0.5% by weight, instead of the compound represented by chemical formula 1A-1, and vinylene carbonate (VC) in an amount of 0.5% by weight.

[0128] [ka]

[0129] (Manufacturing of secondary batteries) A lithium secondary battery was manufactured in the same manner as in Example 1, except that the non-aqueous electrolyte for lithium secondary batteries manufactured above was injected instead of the non-aqueous electrolyte used in Example 1 (see Table 1 below).

[0130] Comparative Example 3. (Manufacturing of non-aqueous electrolytes for lithium secondary batteries) After dissolving LiPF6 in a non-aqueous organic solvent to a concentration of 1.0 M, a non-aqueous electrolyte was prepared by adding, as an additive, the compound represented by the following chemical formula 4 in an amount of 0.5% by weight, instead of the compound represented by chemical formula 1A-1, and vinylene carbonate (VC) in an amount of 0.5% by weight.

[0131] [ka]

[0132] (Manufacturing of secondary batteries) A lithium secondary battery was manufactured in the same manner as in Example 1, except that the non-aqueous electrolyte for lithium secondary batteries manufactured above was injected instead of the non-aqueous electrolyte used in Example 1 (see Table 1 below).

[0133] [Table 1]

[0134] On the other hand, in Table 1 above, the abbreviations for the compounds have the following meanings: EC: Ethylene carbonate EMC: Ethyl methyl carbonate VC: Vinylen carbonate

[0135] [Experimental Example] Experimental Example 1. Evaluation of the rate of increase in resistance after high-temperature storage. The lithium secondary batteries produced in the examples and comparative examples underwent an activation process by charging at a rate of 0.1C for 3 hours. They were then charged at 25°C at a rate of 0.33C to 4.2V under constant current / constant voltage conditions (0.05C cut-off), fully charged to 100% SOC, and stored at high temperature (60°C) for 16 weeks. Afterward, they were transferred to a charger / discharger at room temperature (25°C), their resistance was measured, and the resistance increase rate was calculated using Equation 1 below. The results are shown in Table 2 below.

[0136] [Formula 1] Resistance increase rate (%) = {(Resistance after high-temperature storage - Initial resistance) / Initial resistance} × 100

[0137] Experimental Example 2. Evaluation of gas generation after high-temperature storage. The lithium secondary batteries produced in the examples and comparative examples underwent an activation process by charging at a rate of 0.1C for 3 hours. Then, they were fully charged to 100% SOC at 25°C under constant current / constant voltage conditions (0.05C cut-off) at a rate of 0.33C up to 4.2V. After storing the fully charged batteries at a high temperature (60°C) for 16 weeks, the amount of gas generated was measured at room temperature (25°C) by GC analysis. The relative gas generation amount for each battery was calculated as a percentage, with the gas generation amount measured in Comparative Example 1 set to 100%, and is shown in Table 2 below.

[0138] Experimental Example 3. Evaluation of Capacity Retention Rate After High-Temperature Cycle The lithium secondary batteries manufactured in the examples and comparative examples underwent an activation process by charging at a rate of 0.1C for 3 hours. Then, they were fully charged to 100% of State of Charge (SOC) at 25°C under constant current / constant voltage conditions (0.05C cut-off) at a rate of 0.33C up to 4.2V. The fully charged batteries were then charged at 45°C under constant current / constant voltage conditions at a rate of 0.33C up to 4.2V, and discharged under constant current conditions at a rate of 0.33C up to 2.8V. This constituted one cycle, and after 300 cycles, the capacity retention rate after 300 cycles was calculated using Equation 2 below, and the results are shown in Table 2.

[0139] [Formula 2] Capacity retention rate (%) = (Capacity after 300 cycles / Capacity after 1 cycle) × 100

[0140] [Table 2]

[0141] Referring to Table 2 above, it can be seen that the secondary batteries of Examples 1 and 2 of the present invention showed a decrease in resistance increase rate (%) and gas generation rate (%), and an improvement in capacity retention rate (%) compared to the lithium secondary batteries of Comparative Examples 1 to 3.

Claims

1. The solution comprises a lithium salt, an organic solvent, and a first additive. The first additive comprises a compound represented by the following chemical formula 1, The compound represented by the chemical formula 1 is included in a non-aqueous electrolyte for lithium secondary batteries in an amount of 0.5% to 3.0% by weight, based on the total weight of the non-aqueous electrolyte for lithium secondary batteries. 【Chemistry 1】 (In the above chemical formula 1, Ar is a 5-membered or 6-membered nitrogen-containing ring. R １ and R ２ These are, independently, alkyl groups having 1 to 8 carbon atoms.

2. The non-aqueous electrolyte for lithium secondary batteries according to claim 1, wherein the compound represented by chemical formula 1 is the compound represented by the following chemical formula 1A. 【Chemistry 2】 (In the above chemical formula 1A, R １ and R ２ These are, independently, alkyl groups having 1 to 8 carbon atoms.

3. The aforementioned R １ and R ２ The non-aqueous electrolyte for lithium secondary batteries according to claim 2, wherein each of them is an alkyl group having 1 to 5 carbon atoms, independently.

4. The aforementioned R １ and R ２ The non-aqueous electrolyte for lithium secondary batteries according to claim 2, wherein each of them is an alkyl group having 1 to 3 carbon atoms, independently.

5. The non-aqueous electrolyte for lithium secondary batteries according to claim 2, wherein the compound represented by chemical formula 1A is the compound represented by chemical formula 1A-1 or the compound represented by chemical formula 1A-2. 【Transformation 3】 【Chemistry 4】

6. The non-aqueous electrolyte for lithium secondary batteries according to claim 1, wherein the compound represented by chemical formula 1 is contained in an amount of 0.5% to 2.5% by weight based on the total weight of the non-aqueous electrolyte for lithium secondary batteries.

7. The non-aqueous electrolyte for a lithium secondary battery according to claim 1, further comprising at least one second additive selected from the group consisting of cyclic carbonate compounds, halogen-substituted carbonate compounds, sultone compounds, sulfate compounds, phosphate compounds, borate compounds, nitrile compounds, benzene compounds, amine compounds, silane compounds, and lithium salt compounds.

8. A positive electrode containing a positive electrode active material, A negative electrode containing a negative electrode active material, A separator interposed between the positive electrode and the negative electrode, A lithium secondary battery comprising a non-aqueous electrolyte for lithium secondary batteries according to any one of claims 1 to 7.

9. The lithium secondary battery according to claim 8, wherein the positive electrode active material comprises at least one metal selected from the group consisting of nickel (Ni), cobalt (Co), manganese (Mn), iron (Fe), and aluminum (Al), and lithium.

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