Electrolyte additive, electrolyte comprising same for lithium secondary battery, and lithium secondary battery

Abstract

The present invention provides an electrolyte additive, an electrolyte comprising same for a lithium secondary battery, and a lithium secondary battery. Specifically, the present invention can provide an electrolyte for a lithium secondary battery and a lithium secondary battery comprising same, wherein the electrolyte can achieve excellent high-temperature storage characteristics and high-temperature cycle characteristics by comprising an electrolyte additive containing a compound represented by chemical formula 1, which is not easily decomposed at an anode and can effectively inhibit the deterioration of a cathode.

Description

Electrolyte additive, electrolyte for lithium secondary battery and lithium secondary battery containing the same Cross-citation with related application(s) This application claims the benefit of priority to Korean Patent Application No. 10-2023-0118007, filed September 5, 2023, and Korean Patent Application No. 10-2024-0087850, filed July 3, 2024, the entire contents of which are incorporated herein by reference. Technology field The present invention relates to an electrolyte additive, an electrolyte for a lithium secondary battery including the same, and a lithium secondary battery. As modern society becomes increasingly reliant on electrical energy, the development of large-capacity power storage devices capable of stably supplying electricity while simultaneously increasing production is gaining traction. Lithium-ion batteries are the highest energy-density commercially available power storage devices and are used in a variety of applications, including small electronic devices, electric vehicles (EVs), and power storage devices. In particular, for lithium-ion batteries applied to electric vehicles, high output characteristics are required while maintaining cycle characteristics and performance in various environments. A lithium ion battery is composed of a positive electrode made of a transition metal oxide containing lithium, a negative electrode capable of storing lithium, an electrolyte including an organic solvent containing a lithium salt, and a separator. Meanwhile, lithium hexafluorophosphate (LiPF6), which is mainly used as the lithium salt, easily decomposes at high temperatures, generating Lewis acid byproducts such as HF and PF5, which react with moisture to produce more Lewis acid byproducts (HF). These Lewis acid byproducts can erode the passive film formed on the electrode and the electrode surface, causing the elution of transition metal ions from the positive electrode. In addition, the eluted transition metal ions promote the decomposition of the electrolyte solvent, accelerating gas generation, or increasing the resistance of the positive electrode as they are redeposited on the positive electrode. In addition, they move to the negative electrode through the electrolyte and are deposited on the negative electrode, causing self-discharge of the negative electrode, destruction and regeneration of the solid electrolyte interphase (SEI) film, additional lithium ion consumption, and increased resistance. This series of reactions reduces the amount of available lithium ions within the battery, contributing to a major deterioration in battery capacity. Furthermore, when metal ions deposited on the cathode grow in a dendritic fashion, they can cause internal short-circuiting within the battery, compromising the safety of the secondary battery. Therefore, there is a need to develop an electrolyte that can improve battery performance, such as high-rate charge / discharge characteristics as well as safety, by removing Lewis acid byproducts (such as HF and PF5) generated by thermal decomposition of lithium salts and forming a stable film on the electrode surface to suppress transition metal dissolution or suppress the deposition of dissolved transition metal ions on the negative electrode. The present invention is intended to solve the above-mentioned problems, and provides an electrolyte additive capable of suppressing anode deterioration by forming a strong film on the anode surface while remaining in the electrolyte without being easily decomposed on the cathode surface, and an electrolyte for a lithium secondary battery containing the same. In addition, by including the electrolyte for a lithium secondary battery of the present invention, it is intended to provide a lithium secondary battery having improved high-temperature storage characteristics and high-temperature cycle characteristics. [1] The present invention provides an electrolyte additive comprising a compound represented by the following chemical formula 1: [Chemical Formula 1] In the above chemical formula 1, R is an alkyl group having 1 to 10 carbon atoms. [2] The present invention provides an electrolyte additive in the above [1], wherein R is an alkyl group having 1 to 7 carbon atoms. [3] The present invention provides an electrolyte additive in the above [1] or [2], wherein R is an alkyl group having 1 to 5 carbon atoms. [4] The present invention provides an electrolyte additive in which, in at least one of the above [1] to [3], the compound represented by the chemical formula 1 is at least one of the compounds represented by the following chemical formulas 1a to 1c: [Chemical Formula 1a] [Chemical Formula 1b] [Chemical Formula 1c] . [5] The present invention provides an electrolyte for a lithium secondary battery comprising the electrolyte additive of [1]. [6] The present invention provides an electrolyte for a lithium secondary battery, wherein, in the above [5], the electrolyte additive is included in an amount of 0.1 wt% to 5.0 wt% in the electrolyte for a lithium secondary battery. [7] The present invention provides an electrolyte for a lithium secondary battery, wherein the electrolyte for a lithium secondary battery further comprises a lithium salt and a non-aqueous organic solvent, in the above [5] or [6]. [8] The present invention provides an electrolyte for a lithium secondary battery, wherein in at least one of the above [5] to [7], the electrolyte for a lithium secondary battery further comprises at least one other additive selected from the group consisting of a cyclic carbonate compound, a halogen-substituted carbonate compound, a sultone compound, a sulfate compound, a phosphate or phosphite compound, a borate compound, a benzene compound, an amine compound, an imidazole compound, a silane compound, and a lithium salt compound. [9] The present invention provides a lithium secondary battery comprising: a positive electrode; a negative electrode; a separator interposed between the positive electrode and the negative electrode; and an electrolyte for a lithium secondary battery according to [5].

[0010] The present invention provides a lithium secondary battery, wherein, in the above [9], the positive electrode includes a positive electrode active material, and the positive electrode active material includes a lithium composite metal oxide including lithium and at least one metal selected from the group consisting of nickel (Ni), cobalt (Co), manganese (Mn), and aluminum (Al). The compound represented by Chemical Formula 1 included as the electrolyte additive of the present invention contains an imidazole functional group in its structure, and thus can form a durable Li3N film on the surface of the positive electrode, thereby effectively supplementing oxygen vacancies that occur when the positive electrode deteriorates, and suppressing additional oxygen desorption. Therefore, by using the electrolyte for a lithium secondary battery of the present invention including the electrolyte additive of the present invention, a lithium secondary battery having excellent high-temperature storage properties and high-temperature cycle characteristics can be realized while minimizing an increase in resistance. The non-aqueous electrolyte of the present invention is particularly useful for a high-power battery used together with a high-capacity active material such as a high-nickel-based positive electrode active material or a silicon-based negative electrode active material. The terms and words used in this specification and claims are for the purpose of describing exemplary embodiments only and are not intended to limit the present invention. For example, in this specification, terms such as "include," "have," or "have" are intended to specify the presence of a feature, number, step, component, or combination thereof, and other parts may be added unless 'only' is used. Additionally, in this specification, “%” means weight percent unless explicitly indicated otherwise. In this specification, unless otherwise defined, “substitution” means that at least one hydrogen bonded to carbon is replaced with an element other than hydrogen, wherein the element other than hydrogen may be an alkyl group having 1 to 5 carbon atoms or a fluorine element, and specifically, may be an alkyl group having 1 to 5 carbon atoms. Conventionally, when the film formed on the electrode surface by Lewis acid by-products and / or decomposition products, such as hydrogen fluoride (HF), formed by hydrolysis / thermal decomposition of lithium salts is deteriorated, transition metal ions are easily eluted from the positive electrode, and the eluted transition metal ions are redeposited on the positive electrode, which causes an increase in the positive electrode resistance. In addition, the eluted transition metal ions move to the negative electrode through the electrolyte and are then eluted on the negative electrode, causing self-discharge of the negative electrode and destroying the solid electrolyte interphase (SEI) film that provides passivation to the negative electrode, thereby promoting additional electrolyte decomposition reactions and causing an increase in the interfacial resistance of the negative electrode. This series of side reactions not only reduces the amount of available lithium ions in the battery, resulting in a deterioration in the battery capacity, but also causes a decomposition reaction that causes loss of electrolyte, leading to an increase in battery resistance and poor behavior. Accordingly, the present invention provides an electrolyte additive that effectively removes byproducts / decomposition products of electrolyte salts that cause deterioration and poor behavior of such batteries, and at the same time, is not easily decomposed and remains in the electrolyte, thereby continuously reducing deterioration of the anode film, and an electrolyte for a lithium secondary battery including the same, thereby providing a lithium secondary battery with improved high-temperature storage characteristics and high-temperature cycle characteristics. Hereinafter, the present invention will be described in detail. The electrolyte additive according to the present invention, the electrolyte for a lithium secondary battery including the same, and the lithium secondary battery include at least one of the following disclosed configurations, and may include any combination between technically possible configurations among the following configurations. electrolyte additives Specifically, in an embodiment of the present invention, an electrolyte additive comprising a compound represented by the following chemical formula 1 is provided. [Chemical Formula 1] In the above chemical formula 1, R is an alkyl group having 1 to 10 carbon atoms. Most electrolyte additives first form a film by undergoing reduction and decomposition on the cathode surface. This makes it difficult to maintain a stable film formation effect on the anode surface during operation. This can lead to continued deterioration of the anode surface during high-temperature storage or high-temperature cycling, potentially leading to secondary battery degradation. To solve these problems, it is very important to control the additive's remaining presence in the electrolyte by suppressing the reactivity between the additive and the cathode so that the reactivity between the additive and the cathode can be improved. Specifically, the compound represented by chemical formula 1, which is an electrolyte additive of the present invention, has Li included in its structure. +As the ion is dissociated by the solvent, an anionic functional group, a carboxylate group (-COO), is attached to the α-position of the two nitrogen atoms contained in the imidazole functional group. - ) are substituted. These anionic compounds remain in the electrolyte because the reduction reaction on the negative electrode surface, which has a relative potential of (-), is suppressed during operation, and the reactivity with the positive electrode surface is enhanced, thereby forming a durable inorganic film (Li3N) on the positive electrode surface, thereby suppressing deterioration of the positive electrode surface. In particular, this film has high acid resistance, so that film deterioration by Lewis acid (HF) can be alleviated, and thus not only can the elution of transition metals from the positive electrode be suppressed, but also the oxygen vacancy that occurs when a high-concentration nickel-based positive electrode active material is deteriorated can be effectively supplemented, thereby suppressing additional oxygen desorption. In the case of most imidazole compounds, there is a disadvantage of being rapidly decomposed on the cathode surface because they are neutral, but the compound of the present invention has a carboxylate group (-COO) in the imidazole functional group. - ) is substituted, the reactivity with the cathode is suppressed while the reactivity with the anode is improved, thereby enhancing the film-enhancing effect on the surface of the cathode. Therefore, by using an electrolyte for a lithium secondary battery including the electrolyte additive of the present invention, a lithium secondary battery can be realized that has excellent high-temperature storage properties and high-temperature cycle characteristics while minimizing the increase in resistance by preventing side reactions between the cathode and the electrolyte. Meanwhile, the compound represented by chemical formula 1 included as an electrolyte additive in the present invention has a carboxylate group (-COO) at the α-position of two nitrogen atoms. -) is substituted, and a methyl group, which is an electron donating group (EDG), is directly bonded to the nitrogen atom, so that the reactivity with the positive electrode is improved compared to the compound represented by the following chemical formula 3 in which a carboxylate is directly substituted on the nitrogen atom, so that a more solid inorganic film (Li3N) can be formed on the positive electrode surface. In other words, in order to increase the reactivity between the electron-deficient positive electrode and the additive, it is desirable that the electrons are localized as much as possible toward the nitrogen atom. However, in the case of the compound represented by the following chemical formula 3 in which a carboxylate, which is an electron withdrawing group (EWG), is bonded to the nitrogen atom, it is difficult to localize the electrons by pulling them from the nitrogen atom, so that the reactivity between the positive electrode and the additive is relatively reduced, and the film-forming effect may be reduced. [Chemical Formula 3] In addition, the compound represented by Chemical Formula 1 included as the electrolyte additive of the present invention has an alkyl group, which is an electron donating functional group, directly bonded to the nitrogen atom, compared to compounds such as compounds represented by Chemical Formula 4 below, in which hydrogen is bonded to the nitrogen atom, so that electrons are enriched in the nitrogen atom portion, and thus the reduction and decomposition reaction at the cathode is suppressed, and the reactivity with the anode is improved, thereby enhancing the film-improving effect on the anode surface. [Chemical Formula 4] In addition, the compound represented by the chemical formula 1 included as the electrolyte additive of the present invention has improved reactivity with the anode compared to a compound that does not include an anionic functional group, such as the compound represented by the chemical formula 5 below, and thus can obtain a continuous film regeneration effect on the surface of the anode, thereby effectively suppressing anode deterioration. [Chemical Formula 5] Therefore, by using an electrolyte for a lithium secondary battery containing such an electrolyte additive, it is possible to improve high-temperature durability, such as cycle characteristics and storage characteristics, of a lithium secondary battery. Meanwhile, in the compound represented by the above chemical formula 1, R may be an alkyl group having 1 to 7 carbon atoms, and further, R may be an alkyl group having 1 to 5 carbon atoms. Additionally, the alkyl group may be substituted or unsubstituted. Specifically, the alkyl group may be substituted with an alkyl group having 1 to 5 carbon atoms. Specifically, the compound represented by the above chemical formula 1 may include at least one of the compounds represented by the following chemical formulas 1a to 1c. [Chemical Formula 1a] [Chemical Formula 1b] [Chemical Formula 1c] . Electrolyte for lithium secondary batteries In addition, in one embodiment of the present invention, an electrolyte for a lithium secondary battery is provided including the electrolyte additive of the present invention. The electrolyte for the above lithium secondary battery may further include a lithium salt, an organic solvent, and optionally other additives. (1) Electrolyte additive The electrolyte for a lithium secondary battery of the present invention may include an electrolyte additive including a compound represented by the chemical formula 1. In this case, the description of the compound overlaps with the above-described content, so its description is omitted. Meanwhile, the content of the electrolyte additive may be included in an amount of 0.1 wt% to 5.0 wt% based on the total weight of the non-aqueous electrolyte, taking into account the effect of forming a stable film on the electrode surface and the effect of removing thermal decomposition products of lithium salt. When the above electrolyte additive is included in the above content range, it is possible to form a solid film on the surface of the positive electrode while suppressing as much as possible the side effects such as side reactions caused by the additive, capacity reduction, and increased resistance, and effectively suppress the elution of transition metals from the positive electrode active material at high temperatures, and effectively remove thermal decomposition products of lithium salts, thereby realizing excellent high-temperature durability. That is, when the content of the electrolyte additive is 0.1 wt% or more, the effect of removing thermal decomposition products of lithium salts can be maintained even when the operating time increases, and a stable film can be formed on the electrode surface to further improve the effect of inhibiting transition metal dissolution, etc. In addition, when the content of the electrolyte additive is 5.0 wt% or less, side reactions caused by additives included in a relatively large amount can be prevented. Specifically, the electrolyte additive may be included in an amount of 0.1 wt% to 5.0 wt%, specifically 0.3 wt% to 4.0 wt%, and more specifically 0.4 wt% to 4.0 wt%, based on the total weight of the electrolyte for a lithium secondary battery. (2) Lithium salt The above lithium salt can be used without limitation as an electrolyte for lithium secondary batteries, for example, Li as a cation. + , and the anion is 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 - At least one selected from the group consisting of Specifically, the lithium salt is LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10 , 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). In addition to these, lithium salts commonly used in electrolytes of lithium secondary batteries can be used without limitation. The above lithium salt can be appropriately changed within a commonly usable range, but in order to obtain an optimal effect of forming a film for preventing corrosion on the electrode surface, it can be included in the electrolyte at a concentration of 0.8 M to 4.0 M, specifically, at a concentration of 1.0 M to 3.0 M. 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, and the mobility of lithium ions can be improved, thereby improving the capacity characteristics and cycle characteristics of the lithium secondary battery. (3) Non-aqueous organic solvent Additionally, the description of non-aqueous organic solvents is as follows. As the above non-aqueous organic solvent, various organic solvents commonly used in non-aqueous electrolytes can be used without limitation. There is no limitation on the type of the solvent as long as it can minimize decomposition due to oxidation reactions, etc. during the charge / discharge process of a secondary battery and can exhibit the desired characteristics together with additives. Specifically, the non-aqueous organic solvent may include (i) a cyclic carbonate-based organic solvent, (ii) a linear carbonate-based organic solvent, or (iii) a mixed organic solvent thereof. The above (i) cyclic carbonate-based organic solvent is a high-viscosity organic solvent that has a high dielectric constant and thus facilitates the dissociation of lithium salts in a non-aqueous electrolyte. As a specific example, the organic solvent may include at least one organic solvent selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, and vinylene carbonate, and among these, at least one of ethylene carbonate and propylene carbonate may be included. The above (ii) linear carbonate-based organic solvent is an organic solvent having low viscosity and low dielectric constant, and specific examples thereof may include at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), methylpropyl carbonate, and ethylpropyl carbonate, and specifically may include one of dimethyl carbonate and ethylmethyl carbonate. In order to secure higher ion conductivity, the electrolyte for a lithium secondary battery of the present invention can be used in combination with the (iii) cyclic carbonate-based organic solvent and the linear carbonate-based organic solvent. In this case, the cyclic carbonate-based organic solvent and the linear carbonate-based organic solvent can be mixed and used in a volume ratio of 10:90 to 50:50, specifically 20:80 to 40:60. In addition, the electrolyte for a lithium secondary battery of the present invention may additionally include at least one organic solvent among (iv) linear ester organic solvent and (v) cyclic ester organic solvent, which has a lower melting point and higher stability at high temperatures than the cyclic carbonate organic solvent and / or linear carbonate organic solvent, as the non-aqueous organic solvent. The above (iv) linear ester organic solvent may include, as a representative example, 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 may specifically include at least one of ethyl propionate and propyl propionate. The above (v) cyclic ester organic solvent may include at least one selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone. Meanwhile, the remainder of the electrolyte for a lithium secondary battery of the present invention, excluding the lithium salt, electrolyte additive, and other additives described below, may be an organic solvent unless otherwise specified. (4) Other additives In addition, the electrolyte for a lithium secondary battery of the present invention may additionally include other additives in the electrolyte as needed to prevent the electrolyte from decomposing in a high-power environment and causing cathode collapse, or to further improve low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, and high-temperature battery expansion suppression effects. These other additives may include at least one other additive selected from the group consisting of, for example, 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. The above cyclic carbonate compound may include vinylene carbonate (VC) or vinylethylene carbonate. The above halogen-substituted carbonate compound may include fluoroethylene carbonate (FEC). The above sultone compound may include at least one compound selected from the group consisting of 1,3-propane sultone (PS), 1,4-butane sultone, ethene sultone, 1,3-propene sultone (PRS), 1,4-butene sultone, and 1-methyl-1,3-propene sultone. The above sulfate compounds may include ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS). The above phosphate compound may include at least one compound 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. The above borate compounds include tetraphenylborate and lithium oxalyldifluoroborate. The above nitrile compound may include at least one compound selected from the group consisting of succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentane carbonitrile, cyclohexane carbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile. The above benzene compound may include fluorobenzene, and the above amine compound may include triethanolamine or ethylenediamine. Tetravinylsilane can be cited as the above silane compound. The above lithium salt compound is a compound different from the lithium salt included in the electrolyte, and may include at least one compound selected from the group consisting of LiPO2F2, LiODFB, LiBOB (lithium bisoxalatoborate (LiB(C2O4)2) and LiBF4. Among these other additives, when vinylene carbonate, vinylethylene carbonate or succinonitrile is included, a more robust SEI film can be formed on the negative electrode surface during the initial activation process of the secondary battery. Meanwhile, two or more of the above-described other additives may be mixed and used, and may be included in an amount of 30 wt% or less, specifically 0.01 to 10 wt%, and preferably 0.05 to 5.0 wt%, based on the total weight of the electrolyte. If the content of the above-described other additives is less than 0.01 wt%, the effects of improving the low-temperature output of the battery and the high-temperature storage characteristics and high-temperature lifespan characteristics are minimal, and if the content of the above-described other additives exceeds 30 wt%, there is a possibility that excessive side reactions may occur in the electrolyte during charge and discharge of the battery. In particular, when the above-described SEI film forming additives are added in excessive amounts, they may not be sufficiently decomposed at high temperatures and may remain unreacted or precipitated in the electrolyte at room temperature. Accordingly, side reactions that reduce the lifespan or resistance characteristics of the secondary battery may occur. lithium secondary battery In addition, in another embodiment of the present invention, a lithium secondary battery including the electrolyte for a lithium secondary battery of the present invention is provided. Meanwhile, the lithium secondary battery of the present invention can be manufactured by forming an electrode assembly in which a positive electrode, a negative electrode, and a separator are sequentially laminated between the positive electrode and the negative electrode, storing the electrode assembly in a battery case, and then injecting the electrolyte of the present invention. The method for manufacturing the lithium secondary battery of the present invention can be manufactured and applied according to a conventional method known in the art, and is specifically described below. (1) Bipolar The positive electrode according to the present invention may include a positive electrode active material layer including a positive electrode active material, and, if necessary, the positive electrode active material layer may further include a conductive material and / or a binder. The above positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and specifically may include a lithium composite metal oxide containing lithium and at least one metal selected from the group consisting of nickel (Ni), cobalt (Co), manganese (Mn), iron (Fe), and aluminum (Al). Specifically, the lithium composite metal oxide may include a compound represented by the following chemical formula 2. [Chemical Formula 2] Li 1+a Ni x Co y M 1 z M 2 w O2 In the above 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, 0≤w≤0.1 이다. The above 1+a represents the molar ratio of lithium in the lithium composite metal oxide, and may be 0≤a≤0.5, preferably 0≤a≤0.2, and more preferably 0≤a≤0.1. The above x represents the molar ratio of nickel among all transition metals excluding lithium in the lithium composite metal oxide, and is 0.55. <x<1.0, 더욱 구체적으로는 0.6≤x≤0.98, 보다 더 구체적으로는 0.6≤x≤0.95일 수 있다. The above y represents the molar ratio of cobalt among all transition metals excluding lithium in the lithium composite metal oxide, and is 0. <y≤0.4, 구체적으로 0<y≤0.3, 더욱 구체적으로는 0.05≤y≤0.3일 수 있다. The above z is M among all transition metals excluding lithium in the lithium composite metal oxide. 1It represents the molar ratio of elements, 0 <z≤0.4, 바람직하게는 0<z≤0.3, 더 바람직하게는 0.01≤z≤0.3일 수 있다. The above w is M among all transition metals excluding lithium in the lithium composite metal oxide. 2 It represents the molar ratio of elements, 0 <w≤0.1, 바람직하게는 0<w≤0.05, 더 바람직하게는 0<w≤0.02이다. Specifically, the positive electrode active material is Li(Ni) having a Ni content of 0.55 atm% or more in order to realize a high-capacity battery. 0.6 Mn 0.2 Co 0.2 )O2, 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, Li(Ni 0.90 Mn 0.05 Co 0.05 )O2 or Li(Ni 0.9 Mn 0.03 Co 0.06 Al 0.01 ) may include lithium composite transition metal oxides such as O2. In addition, the cathode active material of the present invention may be a lithium composite metal oxide represented by the above chemical formula 2, depending on the use of the secondary battery, together with a lithium-manganese oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt oxide (e.g., LiCoO2, etc.), a lithium-nickel oxide (e.g., LiNiO2, etc.), a lithium-nickel-manganese oxide (e.g., LiNi 1-Y Mn Y O2(0 <Y<1), LiMn2-z Ni z O4(0<Z<2), lithium-nickel-cobalt oxide (e.g., LiNi 1-Y1 Co Y1 O2(0 <Y1<1), 리튬-망간-코발트계 산화물(예를 들면, 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) can also be used in combination. The above positive electrode active material may be included in an amount of 80 to 98 wt%, more specifically 85 to 98 wt%, based on the total weight of the positive electrode active material layer. When the positive electrode active material is included in the above range, excellent capacity characteristics can be exhibited. Next, the conductive material is used to provide conductivity to the electrode, and in the battery to be formed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any particular limitation. 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 crystal structure; conductive fibers such as carbon fibers or metal fibers; conductive powders such as fluorocarbon powder, aluminum powder, or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and polyphenylene derivatives, and the like. One of these may be used alone or a mixture of two or more may be used. The above-mentioned conductive material may be included in an amount of 0.1 to 10 wt%, preferably 0.1 to 5 wt%, based on the total weight of the positive electrode active material layer. Next, the binder serves to improve the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Examples of such binders include a fluororesin binder including polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); a rubber binder including styrene butadiene rubber (SBR), acrylonitrile-butadiene rubber, and styrene-isoprene rubber; a cellulose binder including carboxyl methyl cellulose (CMC), starch, hydroxy propyl cellulose, and regenerated cellulose; a polyalcohol binder including polyvinyl alcohol; a polyolefin binder including polyethylene and polypropylene; a polyimide binder; a polyester binder; and a silane binder, of which one alone or a mixture of two or more may be used. The above binder may be included in an amount of 0.1 to 15 wt%, preferably 0.1 to 10 wt%, based on the total weight of the positive electrode active material layer. The positive electrode of the present invention can be manufactured according to 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 onto a positive electrode current collector, followed by drying and rolling to form an active material layer, or by a method in which the positive electrode active material layer is cast onto a separate support, and then the support is peeled off to obtain a film, which is then laminated onto a positive electrode current collector. The positive electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the positive electrode current collector may typically have a thickness of 3 to 500 μm, and fine unevenness may be formed on the surface of the positive electrode current collector to increase the adhesive strength of the positive electrode material. For example, the positive electrode current collector may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric. The solvent may be a solvent generally used in the relevant technical field, and may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one of these may be used alone or as a mixture of two or more. The amount of the solvent used may be adjusted to an extent that the positive electrode composite has an appropriate viscosity, taking into consideration the coating thickness of the positive electrode composite, manufacturing yield, workability, etc., and is not particularly limited. (2) Cathode Next, let's explain the cathode. The negative electrode according to the present invention includes a negative electrode active material layer including a negative electrode active material, and the negative electrode active material layer may further include a conductive material and / or a binder, if necessary. As the above negative electrode active material, various negative electrode active materials used in the art can be used, for example, carbon-based negative electrode active materials, silicon-based negative electrode active materials, or mixtures thereof. According to one embodiment, the negative electrode active material may include a carbon-based negative electrode active material, and as the carbon-based negative electrode active material, various carbon-based negative electrode active materials used in the art, for example, 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, soft carbon, hard carbon, etc. may be used. The shape of the carbon-based negative electrode active material is not particularly limited, and materials of various shapes such as amorphous, plate-like, flaky, spherical, or fibrous may be used. Preferably, the negative electrode active material may use at least one carbon-based negative electrode active material among natural graphite and artificial graphite, and natural graphite and artificial graphite may be used together to increase adhesion to the current collector and suppress desorption of the active material. According to another embodiment, the negative electrode active material may be used together with a silicon-based negative electrode active material together with the carbon-based negative electrode active material. The above silicon-based negative electrode active material is, for example, metallic silicon (Si), silicon oxide (SiO x, here 0 <x<2) 실리콘 탄화물(SiC) 및 Si-Y 합금(상기 Y는 알칼리 금속, 알칼리 토금속, 13족 원소, 14족 원소, 전이금속, 희토류 원소 및 이들의 조합으로 이루어진 군에서 선택되는 원소이며, Si은 아님)로 이루어진 군으로부터 선택된 1종 이상을 포함할 수 있다. 상기 원소 Y로는 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, 및 이들의 조합으로 이루어진 군에서 선택될 수 있다. Since the silicon-based negative electrode active material exhibits higher capacity characteristics than the carbon-based negative electrode active material, when the silicon-based negative electrode active material is additionally included, even better capacity characteristics can be obtained. However, in the case of the negative electrode containing the silicon-based negative electrode active material, compared to the graphite negative electrode, the SEI film contains more oxygen (O)-rich components, and the SEI film containing O-rich components tends to be more easily decomposed when a Lewis acid such as HF or PF5 is present in the electrolyte. Therefore, in the case of the negative electrode containing the silicon-based negative electrode active material, in order to maintain a stable SEI film, 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 acid. Since the electrolyte according to the present invention forms a stable film on the positive and negative electrodes and includes an electrolyte additive having an excellent Lewis acid removal effect, it can effectively suppress the decomposition of the SEI film when using the negative electrode containing the silicon-based active material. Meanwhile, the mixing ratio of the silicon-based negative electrode active material and 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 and the carbon-based negative electrode active material satisfies the above range, the capacity characteristics can be improved while the volume expansion of the silicon-based negative electrode active material is suppressed, thereby ensuring excellent cycle performance. The above negative active material may be included in an amount of 80 wt% to 99 wt% based on the total weight of the negative active material layer. When the content of the negative active material satisfies the above range, excellent capacity characteristics and electrochemical characteristics can be obtained. Next, the conductive agent is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 10 wt% or less, preferably 5 wt% or less, based on the total weight of the negative electrode active material layer. The conductive agent is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and examples thereof 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 crystal structure; conductive fibers such as carbon fibers or metal fibers; conductive powders such as fluorocarbon powder, aluminum powder, or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and polyphenylene derivatives. The binder is a component that assists in bonding between the conductive material, the active material, and the current collector, and is typically added in an amount of 0.1 wt% to 10 wt% based on the total weight of the negative electrode active material layer. Examples of the binder include a fluororesin binder including polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); a rubber binder including styrene butadiene rubber (SBR), acrylonitrile-butadiene rubber, and styrene-isoprene rubber; a cellulose binder including carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, and regenerated cellulose; a polyalcohol binder including polyvinyl alcohol; a polyolefin binder including polyethylene and polypropylene; and a polyimide binder. Polyester binders; and silane binders, etc. The above binder may be included in an amount of 0.1 to 15 wt%, preferably 0.1 to 10 wt%, based on the total weight of the negative electrode active material layer. The above negative electrode can be manufactured according to a negative electrode manufacturing method known in the art. For example, the negative electrode can be manufactured by applying a negative electrode slurry prepared by dissolving or dispersing a negative electrode active material and optionally a binder and a conductive material in a solvent on a negative electrode current collector, rolling, and drying to form an active material layer, or by casting the negative electrode active material layer on a separate support, then peeling off the support, and laminating the resulting film on a negative electrode current collector. The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector can typically have a thickness of 3 ㎛ to 500 ㎛, and like the positive electrode current collector, fine unevenness can be formed on the surface of the current collector to strengthen the bonding strength of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc. The solvent may be a solvent generally used in the relevant technical field, and may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one of these may be used alone or a mixture of two or more thereof. The amount of the solvent used may be adjusted to an extent that the negative electrode slurry has an appropriate viscosity, taking into consideration the coating thickness of the negative electrode composite, manufacturing yield, workability, etc., and is not particularly limited. (3) Separator A lithium secondary battery according to the present invention includes a separator between the positive electrode and the negative electrode. The above separator separates the negative electrode and the positive electrode and provides a passage for the movement of lithium ions. If it is a separator commonly used in lithium secondary batteries, it can be used without any special restrictions. In particular, it is preferable that it has low resistance to the movement of lithium salt ions and excellent electrolyte absorption capacity. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, may be used as the separator. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure. The lithium secondary battery according to the present invention as described above can be usefully used in portable devices such as mobile phones, laptop computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs). There is no particular limitation on the external shape of the lithium secondary battery of the present invention, but it may be a cylindrical shape using a can, a square shape, a pouch shape, or a coin shape. The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for a small device, but can also be preferably used as a unit battery in a medium- to large-sized battery module including a plurality of battery cells. Example Example 1. (Manufacturing of non-aqueous electrolyte for lithium secondary batteries) LiPF6 was dissolved to 1.0 M in an organic solvent containing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 30:70, and then 0.5 wt% of a compound represented by the chemical formula 1a and 0.5 wt% of vinylene carbonate (VC) were added to prepare a non-aqueous electrolyte for a lithium secondary battery (see Table 1 below). (Secondary battery manufacturing) The cathode active material (Li(Ni)) was added to the solvent N-methyl-2-pyrrolidone (NMP). 0.9 Mn 0.03 Co 0.06 Al 0.01 )O2), a conductive agent (carbon black), and a binder (polyvinylidene fluoride) were added in a weight ratio of 97.6:0.8:1.6 to prepare a positive electrode slurry (solid content 60.0 wt%). The positive electrode slurry was applied to a 13.5 μm thick positive electrode current collector (Al thin film) and dried, and then roll pressed to prepare a positive electrode. A negative electrode slurry (solid content: 60 wt%) was prepared by adding a negative electrode active material (graphite:SiO = 94:6 weight ratio), a binder (SBR-CMC), and a conductive agent (carbon black) to water as a solvent in a weight ratio of 97.6:0.8:1.6. The negative electrode slurry was applied to a 6 μm thick copper (Cu) thin film as a negative electrode current collector, dried, and then roll pressed to prepare a negative electrode. An electrode assembly was manufactured by interposing a porous separator polypropylene between the positive and negative electrodes manufactured above, and then the assembly was placed in a battery case, and the electrolyte for a lithium secondary battery manufactured above was injected to manufacture a lithium secondary battery. Example 2. A lithium secondary battery was manufactured in the same manner as in Example 1, except that a non-aqueous electrolyte for a lithium secondary battery was manufactured by dissolving LiPF6 in a non-aqueous organic solvent to a concentration of 1.0 M and then adding 0.5 wt% of a compound represented by the chemical formula 1b and 0.5 wt% of vinylene carbonate (VC) (see Table 1 below). Example 3. A lithium secondary battery was manufactured in the same manner as in Example 1, except that a non-aqueous electrolyte for a lithium secondary battery was manufactured by dissolving LiPF6 in a non-aqueous organic solvent to a concentration of 1.0 M and then adding 0.5 wt% of a compound represented by the chemical formula 1c and 0.5 wt% of vinylene carbonate (VC) (see Table 1 below). Comparative Example 1. A lithium secondary battery was manufactured in the same manner as in Example 1, except that a non-aqueous electrolyte for a lithium secondary battery was manufactured 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 wt% (see Table 1 below). Comparative Example 2. A lithium secondary battery was manufactured in the same manner as in Example 1, except that LiPF6 was dissolved in a non-aqueous organic solvent to a concentration of 1.0 M, and then 0.5 wt% of a compound represented by the following chemical formula 3 and 0.5 wt% of vinylene carbonate (VC) were added as additives instead of the compound represented by the chemical formula 1a to manufacture a non-aqueous electrolyte for a lithium secondary battery (see Table 1 below). [Chemical Formula 3] Comparative Example 3. A lithium secondary battery was manufactured in the same manner as in Example 1, except that LiPF6 was dissolved in a non-aqueous organic solvent to a concentration of 1.0 M, and then 0.5 wt% of a compound represented by the following chemical formula 4 and 0.5 wt% of vinylene carbonate (VC) were added as additives instead of the compound represented by the chemical formula 1a to manufacture a non-aqueous electrolyte for a lithium secondary battery (see Table 1 below). [Chemical Formula 4] Comparative Example 4. A lithium secondary battery was manufactured in the same manner as in Example 1, except that LiPF6 was dissolved in a non-aqueous organic solvent to a concentration of 1.0 M, and then 0.5 wt% of a compound represented by the following chemical formula 5 and 0.5 wt% of vinylene carbonate (VC) were added as additives instead of the compound represented by the chemical formula 1a to manufacture a non-aqueous electrolyte for a lithium secondary battery (see Table 1 below). [Chemical Formula 5] Non-aqueous organic solvent lithium salt additive other additive (wt%) type content (wt%) Example 1 EC:EMC = 30:70 volume ratio 1.0M LiPF6 chemical formula 1a 0.5 VC (0.5) Example 2 chemical formula 1b 0.5 Example 3 chemical formula 1c 0.5 Comparative example 1--Comparative example 2 chemical formula 30.5 Comparative example 3 chemical formula 40.5 Comparative example 4 chemical formula 50.5 Meanwhile, the abbreviations of the compounds in Table 1 above mean the following. EC: Ethylene carbonate EMC: Ethyl methyl carbonate VC: Vinylene Carbonate Experimental example Experimental Example 1. Evaluation of High-Temperature Storage Characteristics For the lithium secondary batteries manufactured in each of the examples and comparative examples, the activation (formation) process was performed by charging at a 0.1C rate for 3 hours, and then the batteries were charged under constant current / constant voltage conditions (0.05C cut-off) at a 0.33C rate at 25℃ to 4.2V, fully charged to 100% SOC, and stored at a high temperature (60℃) for 16 weeks. Afterwards, the batteries were transferred to a charger / discharger at room temperature (25℃), and the resistance was measured, and the resistance increase rate was calculated using the following equation 1, and the results are shown in Table 2 below. [Formula 1] Resistance increase rate (%) = {(Resistance after high temperature storage - initial resistance) / initial resistance} × 100 Resistance Increase Rate (%) Example 120.94 Example 218.35 Example 319.22 Comparative Example 152.44 Comparative Example 248.39 Comparative Example 353.14 Comparative Example 448.21 Looking at Table 2 above, it can be seen that the resistance increase rate (%) after high-temperature storage is improved in the case of the secondary batteries of Examples 1 to 3 of the present invention compared to the lithium secondary batteries of Comparative Examples 1 to 4. Experimental Example 2. Evaluation of High-Temperature Cycle Characteristics For the lithium secondary batteries manufactured in each of the examples and comparative examples, the activation (formation) process was performed by charging at a 0.1C rate for 3 hours, and then charging under constant current / constant voltage conditions (0.05C cut-off) at a 0.33C rate at 25℃ was performed to 4.2 V to reach a full charge to 100% SOC. The fully charged batteries were charged under constant current / constant voltage conditions at a 0.33C rate at 45℃ to 4.2 V, and discharged under constant current conditions at a 0.33C rate to 2.8 V as one cycle, and 300 cycles were performed. Then, the capacity retention rate after 300 cycles was calculated using Equation 2 below, and the results are shown in Table 3 below. [Formula 2] Capacity retention rate (%) = (Capacity after 300 cycles / Capacity after 1 cycle) × 100 Capacity retention rate (%) Example 187.52 Example 288.35 Example 388.11 Comparative example 181.89 Comparative example 284.38 Comparative example 382.05 Comparative example 484.54 Looking at Table 3 above, it can be seen that the secondary batteries of Examples 1 to 3 of the present invention have improved capacity retention rates (%) after high-temperature cycling compared to the lithium secondary batteries of Comparative Example 1 that applied an electrolyte that did not include the additive of the present invention, or the lithium secondary batteries of Comparative Examples 2 to 4 that applied an electrolyte that included compounds of Chemical Formulas 3 to 5 in the same amount instead of the additive of the present invention.

Claims

1. An electrolyte additive comprising a compound represented by the following chemical formula 1: [Chemical Formula 1] In the above chemical formula 1, R is an alkyl group having 1 to 10 carbon atoms.

2. In claim 1, An electrolyte additive wherein the above R is an alkyl group having 1 to 7 carbon atoms.

3. In claim 1, An electrolyte additive wherein the above R is an alkyl group having 1 to 5 carbon atoms.

4. In claim 1, An electrolyte additive wherein the compound represented by the above chemical formula 1 is at least one of the compounds represented by the following chemical formulas 1a to 1c: [Chemical Formula 1a] [Chemical Formula 1b] [Chemical Formula 1c] .

5. An electrolyte for a lithium secondary battery comprising the electrolyte additive of claim 1.

6. In claim 5, An electrolyte for a lithium secondary battery, wherein the electrolyte additive is included in an amount of 0.1 wt% to 5.0 wt% in the electrolyte for a lithium secondary battery.

7. In claim 5, The electrolyte for a lithium secondary battery further comprises a lithium salt and a non-aqueous organic solvent.

8. In claim 5, The electrolyte for a lithium secondary battery further comprises at least one other additive selected from the group consisting of a cyclic carbonate compound, a halogen-substituted carbonate compound, a sultone compound, a sulfate compound, a phosphate or phosphite compound, a borate compound, a benzene compound, an amine compound, an imidazole compound, a silane compound, and a lithium salt compound.

9. Anode; cathode; a separator interposed between the anode and cathode; and A lithium secondary battery comprising the electrolyte for a lithium secondary battery according to claim 5.

10. In claim 9, The above positive electrode includes a positive electrode active material, A lithium secondary battery comprising a lithium composite metal oxide containing lithium and at least one metal selected from the group consisting of nickel (Ni), cobalt (Co), manganese (Mn), and aluminum (Al), wherein the positive electrode active material is a lithium composite metal oxide containing lithium.

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