Electrolyte additives, non-aqueous electrolytes for lithium secondary batteries containing the same, and lithium secondary batteries

Abstract

The present invention provides an electrolyte additive, a non-aqueous electrolyte for lithium secondary batteries containing the same, and a lithium secondary battery. Specifically, the present invention provides a non-aqueous electrolyte for lithium secondary batteries that can ensure excellent cycle characteristics by applying a non-aqueous electrolyte for lithium secondary batteries that includes an electrolyte additive capable of forming a strong SEI layer on the surface of the negative electrode, and a lithium secondary battery containing the same.

Description

Technical Field

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0136309 filed on October 12, 2023, and all the contents disclosed in the literature of the Korean patent application are incorporated herein by reference as part of this specification.

[0002] The present invention relates to an electrolyte additive, a non-aqueous electrolyte for a lithium secondary battery containing the same, and a lithium secondary battery.

Background Art

[0003] In modern society, as the dependence on electric energy is increasing, the development of a large-capacity power storage device that can stably supply electric power and increase the production amount has attracted attention.

[0004] Among commercially available power storage devices, lithium-ion batteries exhibit the highest energy density and are used in various applications such as small electronic devices, electric vehicles (EVs), and power storage devices.

[0005] In particular, lithium-ion secondary batteries applied to electric vehicles are required to maintain cycle characteristics and performance in various environments and have high output characteristics. Therefore, in order to improve the energy density of lithium secondary batteries, research for developing cathode active materials and anode active materials having a high theoretical capacity has been actively conducted. Specifically, compared with graphite used in currently commercialized batteries, research for applying silicon-based anode active materials such as Si or SiO x (0 < x < 2) has attracted attention.

[0006] However, silicon-based negative electrode active materials have the drawback of undergoing rapid volume changes and expansion due to changes in crystal structure caused by repeated electrochemical charging and discharging, or by the insertion and deinsertion of lithium ions during high-temperature storage. This leads to cracking and degradation of the coating, resulting in severe battery deterioration. In particular, the solid-electrolyte interface layer (SEI layer) formed on the electrode surface due to the decomposition of carbonate-based non-aqueous solvents has poor elasticity, making it difficult to maintain the coating when the silicon-based negative electrode active material expands in volume, thus causing battery degradation.

[0007] Therefore, there is a need to develop an electrolyte that can solve the problem of degradation due to volume expansion of silicon-based anode active materials by forming a stable SEI layer on the surface of the anode that can withstand volume changes of the silicon-based anode active material. [Overview of the project] [Problems that the invention aims to solve]

[0008] The present invention aims to solve the above-mentioned problems and provides an electrolyte additive that can form a strong film on the surface of a silicon-based negative electrode, and a non-aqueous electrolyte for lithium secondary batteries containing the same.

[0009] Furthermore, the present invention aims to provide a lithium secondary battery with improved cycle characteristics by including the non-aqueous electrolyte for lithium secondary batteries. [Means for solving the problem]

[0010] [1] The present invention provides an electrolyte additive comprising a compound represented by the following chemical formula 1.

[0011] [Chemical formula 1] [ka]

[0012] In the above chemical formula 1, R is an alkyl group having 1 to 7 carbon atoms that is substituted with at least one fluorine atom.

[0013] [2] The present invention provides the electrolyte additive described in [1] above, wherein in the chemical formula 1, R is an alkyl group having 1 to 5 carbon atoms substituted with at least one fluorine atom.

[0014] [3] The present invention provides the electrolyte additive according to [1] or [2], wherein in the chemical formula 1, R is a C1-C3 alkyl group substituted with at least one fluorine.

[0015] [4] The present invention provides an electrolyte additive according to any one of [1] to [3] above, wherein the compound represented by chemical formula 1 is at least one of the compounds represented by the following chemical formulas 1A-1 to 1A-3.

[0016] [Chemical formula 1A-1] [ka]

[0017] [Chemical formula 1A-2] [ka]

[0018] [Chemical formula 1A-3] [ka]

[0019] [5] The present invention provides a non-aqueous electrolyte for lithium secondary batteries comprising an electrolyte additive described in any one of [1] to [4] above.

[0020] [6] The present invention provides a non-aqueous electrolyte for lithium secondary batteries according to [5], wherein the electrolyte additive is contained in a non-aqueous electrolyte for lithium secondary batteries in an amount of 0.1% to 10.0% by weight.

[0021] [7] The present invention provides the non-aqueous electrolyte for lithium secondary batteries according to [5] or [6], further comprising a lithium salt and a non-aqueous organic solvent.

[0022] [8] The present invention provides a non-aqueous electrolyte for a lithium secondary battery according to any one of [5] to [7] above, wherein the non-aqueous electrolyte for a lithium secondary battery further comprises at least one other additive selected from the group consisting of cyclic carbonate compounds, halogen-substituted carbonate compounds, sultone compounds, sulfate compounds, phosphate or phosphite compounds, borate compounds, benzene compounds, amine compounds, imidazole compounds, silane compounds, and lithium salt compounds.

[0023] [9] The present invention provides a lithium secondary battery comprising a positive electrode, a negative electrode facing the positive electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte for a lithium secondary battery according to at least one of [5] to [8].

[0024]

[10] The present invention provides a lithium secondary battery according to [9], wherein the negative electrode comprises a silicon-based negative electrode active material.

[0025]

[11] The present invention provides a lithium secondary battery according to [9] or

[10] , wherein the negative electrode further comprises a carbon-based negative electrode active material. [Effects of the Invention]

[0026] The non-aqueous electrolyte for lithium secondary batteries according to one embodiment of the present invention includes an electrolyte additive containing vinyl groups and nitrogen (N) atoms capable of forming a strong SEI layer on the electrode surface, thereby enabling the formation of a highly durable amide group and Li3N-containing film on the negative electrode surface. Therefore, using the non-aqueous electrolyte for lithium secondary batteries according to one embodiment of the present invention makes it possible to realize a lithium secondary battery with improved cycle characteristics. The non-aqueous electrolyte according to one embodiment of the present invention is particularly useful in high-power batteries used with high-capacity active materials such as high-nickel positive electrode active materials or silicon negative electrode active materials that undergo large volume changes during charging and discharging. [Modes for carrying out the invention]

[0027] The terms and words used herein and in the claims are for illustrative purposes only and are not intended to limit the invention.

[0028] For example, in this specification, terms such as “includes,” “equip,” or “have” are intended to specify that there are features, figures, steps, components, or combinations thereof that have been implemented, and other parts may be added unless “only” is used.

[0029] Furthermore, in this specification, "%" means "weight %" unless explicitly indicated otherwise.

[0030] 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.

[0031] Conventionally, silicon-based negative electrode active materials for lithium-ion batteries have the advantage of excellent capacity per unit weight. However, repeated charging and discharging can cause serious volume expansion (over 300%) and contraction as lithium ions are inserted and removed, potentially leading to cracking or destruction of the SEI layer formed on the surface of the silicon-based negative electrode active material. Such problems can cause side reactions between the surface of the negative electrode active material and the electrolyte, forming a thick and unstable film at the interface between the silicon-based negative electrode active material and the electrolyte. This leads to increased resistance, increased consumption of the lithium ion source, and further problems such as reduced cycle characteristics and charge / discharge characteristics.

[0032] Therefore, in order to solve the above-mentioned problems, the present inventors aim to provide an electrolyte additive that can form a strong SEI film on a silicon-based negative electrode, and a non-aqueous electrolyte containing the same, and to provide a lithium secondary battery with improved high-rate charge and discharge at high temperatures using the same.

[0033] The present invention will be described in more detail below.

[0034] An electrolyte additive according to one embodiment of the present invention, a non-aqueous electrolyte for a lithium secondary battery containing the same, and a lithium secondary battery include at least one of the configurations disclosed below, and may include any combination of technically possible configurations from the configurations disclosed below.

[0035] [Electrolyte additives] Specifically, embodiments of the present invention provide an electrolyte additive comprising a compound represented by the following chemical formula 1.

[0036] [Chemical formula 1] [ka]

[0037] In the above chemical formula 1, R is an alkyl group having 1 to 7 carbon atoms that is substituted with at least one fluorine atom.

[0038] The compound represented by chemical formula 1, included as the electrolyte additive, contains a vinyl group and a nitrogen element in its structure. During charging and discharging, it is reduced and decomposed before the organic solvent, forming a highly durable amide group and a partially Li3N-containing film on the surface of the silicon-based anode. This suppresses cracking of the SEI film due to contraction / expansion of the silicon-based anode active material. Furthermore, the compound represented by chemical formula 1 contains a fluorine element in its structure, forming a fluorine-containing film with high high-temperature durability and thermal stability on the surface of the anode. This minimizes the decomposition of the SEI layer at high temperatures, thereby reducing side reactions caused by direct contact between silicon and the electrolyte. In particular, because the compound represented by chemical formula 1 of the present invention contains an amide group at the center of its structure, it exhibits superior film stability compared to compounds represented by chemical formula i or chemical formula ii below, which contain a carboxylate group in their structure. This delays the decomposition of the film and the subsequent additional decomposition reaction of the electrolyte. Furthermore, because the amount of hydrocarbon gases such as CO2 and CxHy (x is 1-5, y is 3-12) that decompose when the coating is broken down is small, gas-induced degradation and venting time within the battery can be delayed, further improving the stability of the SEI layer. Therefore, non-aqueous electrolytes for lithium secondary batteries containing such electrolyte additives can be used to manufacture lithium secondary batteries with improved cycle characteristics and capacity characteristics.

[0039] [Chemical formula i] [ka]

[0040] [Chemical formula ii] [ka]

[0041] On the other hand, in the above chemical formula 1, R may be an alkyl group having 1 to 5 carbon atoms substituted with at least one fluorine atom. More specifically, R may be an alkyl group having 1 to 3 carbon atoms substituted with at least one fluorine atom.

[0042] More specifically, the compound represented by chemical formula 1 may be at least one of the compounds represented by chemical formulas 1A-1 to 1A-3 below. Preferably, the compound represented by chemical formula 1 may be the compound represented by chemical formula 1A-3 below, in which R, which is substituted with a relatively large amount of highly durable fluorine, has a perfluoro structure.

[0043] [Chemical formula 1A-1] [ka]

[0044] [Chemical formula 1A-2] [ka]

[0045] [Chemical formula 1A-3] [ka]

[0046] [Non-aqueous electrolyte for lithium secondary batteries] Furthermore, one embodiment of the present invention provides a non-aqueous electrolyte for lithium secondary batteries, which includes an electrolyte additive according to one embodiment of the present invention.

[0047] The non-aqueous electrolyte for lithium secondary batteries may further comprise a lithium salt, an organic solvent, and optionally other additives.

[0048] (1) Electrolyte additives A non-aqueous electrolyte for a lithium secondary battery according to one embodiment of the present invention may contain an electrolyte additive comprising the compound represented by the chemical formula 1, but in this case, the description of the compound will be omitted as it would be redundant with the above description.

[0049] On the one hand, considering the effect of forming a stable film on the surface of the electrode and the effect of removing the thermal decomposition products of the lithium salt, the content of the electrolyte additive may be 10.0% by weight or less, specifically 0.1% to 10.0% by weight based on the total weight of the non-aqueous electrolyte.

[0050] When the electrolyte additive is contained within the above content range, drawbacks such as side reactions, capacity reduction, and resistance increase caused by the additive can be suppressed as much as possible, and by forming a strong film on the surface of the positive electrode, the transition metal elution of the positive electrode active material at high temperature can be effectively suppressed, the thermal decomposition products of the lithium salt can be effectively removed, and excellent high-temperature durability can be realized.

[0051] That is, when the content of the electrolyte additive is 0.1% by weight or more, the effect of removing the thermal decomposition products of the lithium salt can be maintained even if the driving time increases, and by forming a stable film on the surface of the electrode, the suppression effect of transition metal elution and the like can be further improved. Further, when the content of the electrolyte additive is 10.0% by weight or less, side reactions caused by the slightly excessive additive can be prevented.

[0052] Specifically, the electrolyte additive may be contained at 0.1% to 8.0% by weight, or may be contained at 0.5% to 8.0% by weight, specifically may be contained at 0.5% to 5.0% by weight, and more specifically may be contained at 0.5% to 3.0% by weight based on the total weight of the non-aqueous electrolyte for the lithium secondary battery.

[0053] (2) Lithium salt As the lithium salt, those commonly used in non-aqueous electrolytes for lithium secondary batteries can be used without limitation. For example, as the cation, it contains Li + and as the anion, F - 、Cl - 、Br - 、I - 、NO3 - 、N(CN)2 <000000⑧>、BF4 - 、ClO4 - 、B 10 Cl10 - 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 - , and CF3(CF2)7SO3 - At least one of the following groups can be selected.

[0054] Specifically, the lithium salts are LiCl, LiBr, LiI, LiBF4, LiClO4, and LiB 10 Cl 10The electrolyte may include 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). In addition to these, lithium salts commonly used as electrolytes in lithium secondary batteries can be used without limitation.

[0055] The lithium salt may 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.

[0056] 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.

[0057] (3) Non-aqueous organic solvents Furthermore, the explanation regarding non-aqueous organic solvents is as follows:

[0058] As the non-aqueous organic solvent, various organic solvents commonly used in non-aqueous electrolytes can be used without limitation. The type of organic solvent is not limited as long as it can minimize decomposition due to oxidation reactions during the charging and discharging process of the secondary battery and exhibit the desired properties together with the additives.

[0059] Specifically, the non-aqueous organic solvent may include (i) a cyclic carbonate organic solvent, (ii) a linear carbonate organic solvent, or (iii) a mixture thereof.

[0060] The (i) 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.

[0061] The (ii) 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.

[0062] In order to ensure a higher ionic conductivity, the non-aqueous electrolyte for a lithium secondary battery according to one embodiment of the present invention may use (i) a cyclic carbonate-based organic solvent and (ii) a linear carbonate-based organic solvent in combination. In this case, the cyclic carbonate-based organic solvent and the linear carbonate-based organic solvent may be mixed in a volume ratio of 10:90 to 50:50, specifically 20:80 to 40:60.

[0063] Furthermore, the non-aqueous electrolyte for lithium secondary batteries according to one embodiment of the present invention may further include, as the non-aqueous organic solvent, at least one ester-based organic solvent, which has a lower melting point and higher stability at high temperatures compared to the cyclic carbonate-based organic solvent and / or linear carbonate-based organic solvent, (iv) a linear ester-based organic solvent and (v) a cyclic ester-based organic solvent.

[0064] The (iv) linear ester organic solvent mentioned above includes, as a typical 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 specifically may include at least one of ethyl propionate and propyl propionate.

[0065] The (v) 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.

[0066] On the other hand, in the non-aqueous electrolyte for lithium secondary batteries according to one embodiment of the present invention, the remainder, excluding the lithium salt, electrolyte additives, and other additives described later, is a non-aqueous organic solvent unless otherwise specified.

[0067] (4) Other additives Furthermore, the non-aqueous electrolyte for lithium secondary batteries according to one embodiment of the present invention may further contain other additives as needed to prevent the electrolyte from decomposing in a high-power environment, which can cause the anode to collapse, 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. On the other hand, when other additives are included, the compound represented by chemical formula 1 may be named the first additive, and the other additive may be named the second additive.

[0068] Such other additives may include, as typical examples, at least one other 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.

[0069] Examples of the aforementioned cyclic carbonate compounds include vinylene carbonate (VC) or vinylethylene carbonate.

[0070] Examples of halogen-substituted carbonate compounds include fluoroethylene carbonate (FEC).

[0071] Examples of the sultone compounds 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.

[0072] Examples of the sulfate compounds include ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS).

[0073] 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.

[0074] Examples of the borate-based compounds include tetraphenylborate and lithium oxalyldifluoroborate.

[0075] The nitrile compounds mentioned above 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.

[0076] Examples of the benzene-based compound include fluorobenzene, and examples of the amine-based compound include triethanolamine or ethylenediamine.

[0077] Examples of the silane compounds include tetravinylsilane.

[0078] The lithium salt-based compound is a compound different from the lithium salt contained in the electrolyte, and includes one or more compounds selected from the group consisting of LiPO2F2, LiODFB, LiBOB (lithium bisoxalate borate (LiB(C2O4)2), and LiBF4).

[0079] If the other additives include at least one of vinylene carbonate, vinylethylene carbonate, succinonitrile, or 1,3-propanesultone, an even stronger SEI film can be formed on the surface of the negative electrode during the initial activation process of the secondary battery.

[0080] On the other hand, two or more of the aforementioned other additives may be used in mixture form, and may be present in an amount of 50% by weight or less, specifically 0.01 to 10% by weight, and preferably 0.05 to 5.0% by weight, based on the total weight of the electrolyte. If the content of the aforementioned other additives is less than 0.01% by weight, the improvement in the low-temperature output of the battery, as well as the improvement in high-temperature storage characteristics and high-temperature life characteristics, will be minimal. If the content of the aforementioned other additives exceeds 50% by weight, excessive side reactions may occur in the electrolyte during charging and discharging of the battery. 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.

[0081] [Lithium-ion rechargeable battery] Furthermore, yet another embodiment of the present invention provides a lithium secondary battery comprising a non-aqueous electrolyte for a lithium secondary battery according to one embodiment of the present invention.

[0082] The lithium secondary battery can be manufactured by housing an electrode assembly, which includes the positive electrode, a negative electrode facing the positive electrode, and a separator interposed between the positive electrode and the negative electrode, in a battery case, and then injecting the aforementioned non-aqueous electrolyte.

[0083] As explained above, the negative electrode, positive electrode, and separator will be explained below.

[0084] (1) Positive electrode The positive electrode may contain a positive electrode active material.

[0085] The positive electrode active material is a compound capable of reversible intercalation and deintercalation, and is not particularly limited as long as it is a positive electrode active material used in the art. Specifically, it may include a lithium metal composite oxide. More specifically, the lithium metal composite oxide may include a lithium composite metal oxide represented by the following Chemical Formula 2, which contains at least one metal selected from the group consisting of nickel (Ni), cobalt (Co), manganese (Mn), iron (Fe), and aluminum (Al), and lithium.

[0086] [Chemical Formula 2] Li 1+a Ni x Co y M 1 z M 2 w O2

[0087] In the 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.

[0088] The 1 + a represents the molar ratio of lithium in the lithium composite metal oxide, and 0 ≦ a ≦ 0.5, preferably 0 ≦ a ≦ 0.2, more preferably 0 ≦ a ≦ 0.1.

[0089] The x represents the molar ratio of nickel among all the transition metals excluding lithium in the lithium composite metal oxide, and 0.55 < x < 1.0, more specifically 0.6 ≦ x ≦ 0.98, and still more specifically 0.6 ≦ x ≦ 0.95.

[0090] The y represents the molar ratio of cobalt among all the transition metals excluding lithium in the lithium composite metal oxide, and 0 < y ≦ 0.4, specifically 0 < y ≦ 0.3, more specifically 0.05 ≦ y ≦ 0.3.

[0091] where z represents the molar ratio of element M among all transition metals excluding lithium in the lithium composite metal oxide, and 0 < z ≤ 0.4, preferably 0 < z ≤ 0.3, more preferably 0.01 ≤ z ≤ 0.3. 1 where w represents the molar ratio of element M among all transition metals excluding lithium in the lithium composite metal oxide, and 0 < w ≤ 0.1, preferably 0 < w ≤ 0.05, more preferably 0 < w ≤ 0.02.

[0092] where w represents the molar ratio of element M among all transition metals excluding lithium in the lithium composite metal oxide, and 0 < w ≤ 0.1, preferably 0 < w ≤ 0.05, more preferably 0 < w ≤ 0.02. 2 where w represents the molar ratio of element M among all transition metals excluding lithium in the lithium composite metal oxide, and 0 < w ≤ 0.1, preferably 0 < w ≤ 0.05, more preferably 0 < w ≤ 0.02.

[0093] Specifically, in order to realize a high-capacity battery, the cathode active material contains a lithium composite transition metal oxide such as Li(Ni 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, or Li(Ni 0.90 Mn 0.05 Co 0.05 )O2, etc. Specifically, Li(Ni 0.8 Mn 0.1 Co​​​​​​​​​​​​​​​​​​​​​)It may contain a high-nickel (High-Ni) based lithium composite transition metal oxide such as O2.

[0094] Although the positive electrode active material containing such a high-nickel based lithium composite transition metal oxide has a drawback of being vulnerable to side reactions with the electrolyte, by using the electrolyte according to an embodiment of the present invention together, a stable passive film is formed on the surface of the positive electrode, and the side reactions with the electrolyte can be suppressed and reduced.

[0095] In addition, the positive electrode active material according to an embodiment of the present invention may, if necessary, together with the lithium composite metal oxide represented by Chemical Formula 2, a lithium-manganese based oxide (for example, LiMnO2, LiMn2O4, etc.), a lithium-cobalt based oxide (for example, LiCoO2, etc.), a lithium-nickel based oxide (for example, LiNiO2, etc.), a lithium-nickel-manganese based oxide (for example, LiNi 1-Y Mn Y O2 (0 < Y < 1), LiMn 2-Z Ni Z O4 (0 < Z < 2), a lithium-nickel-cobalt based oxide (for example, LiNi 1-Y1 Co Y1 O2 (0 < Y1 < 1), a lithium-manganese-cobalt based oxide (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), etc. may be used in combination.

[0096] The positive electrode active material may be in the form of particles. Specifically, the average particle diameter (D 50 ) of the positive electrode active material may be 1 μm to 30 μm.

[0097] The positive electrode may include a positive electrode current collector and a positive electrode mixture layer disposed on at least one side of the positive electrode current collector. At this time, the positive electrode mixture layer may contain the aforementioned positive electrode active material.

[0098] The thickness of the positive electrode current collector is typically 3 to 500 μm.

[0099] The positive electrode current collector may have its surface textured to enhance the bonding force of the positive electrode active material. For example, the positive electrode current collector can be used in various forms such as film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0100] The positive electrode mixture layer is disposed on at least one side of the positive electrode current collector. Specifically, the positive electrode mixture layer may be disposed on one or both sides of the positive electrode current collector.

[0101] The positive electrode active material may be included in the positive electrode mixture layer in an amount of 70% to 99% by weight, specifically 80% to 98% by weight, taking into consideration the sufficient capacity exertion of the positive electrode active material.

[0102] The positive electrode mixture layer may further contain a binder and / or conductive material along with the positive electrode active material.

[0103] 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. 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 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. One of these may be used alone or in mixtures of two or more.

[0104] 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 mixture layer.

[0105] 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.

[0106] 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 mixture layer.

[0107] A positive electrode according to such an embodiment 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 coating a positive electrode slurry containing a positive electrode active material and selectively a binder, conductive material, and solvent for forming the positive electrode slurry onto a positive electrode current collector, followed by drying and rolling. Alternatively, a positive electrode can be manufactured by mixing a positive electrode active material and selectively a binder, conductive material, etc., to produce a film, and then laminating it onto a positive electrode current collector.

[0108] The solvent for forming the positive electrode slurry may include, for example, at least one selected from the group consisting of distilled water, N-methylpyrrolidone, ethanol, methanol, and isopropyl alcohol, preferably N-methylpyrrolidone, in order to facilitate the dispersion of the positive electrode active material, binder, and / or conductive material.

[0109] (2) Negative electrode Next, I will explain the negative electrode.

[0110] A negative electrode according to one embodiment of the present invention includes a negative electrode mixture layer containing a negative electrode active material, the negative electrode mixture layer may further include a conductive material and / or a binder as needed.

[0111] As the aforementioned negative electrode active material, a silicon-based negative electrode active material may be used alone.

[0112] The silicon-based negative electrode active material is, for example, metallic silicon (Si) or silicon oxide (SiO x, where 0 < x < 2), silicon carbide (SiC), and Si-Y alloy (where 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 include one or more selected from the group consisting of. The element Y may be 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.

[0113] Since the silicon-based negative electrode active material exhibits higher capacity characteristics than the carbon-based negative electrode active material, more excellent capacity characteristics can be obtained. However, the negative electrode containing the silicon-based negative electrode active material contains more oxygen (O)-rich components in the SEI film than the graphite negative electrode, and the SEI film containing the O-rich component tends to be further decomposed when a Lewis acid such as HF or PF5 is present in the electrolyte. Therefore, in order for the negative electrode containing the silicon-based negative electrode active material 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 remove (or scavenge) the generated Lewis acids. The non-aqueous electrolyte according to an embodiment of the present invention contains an electrolyte additive capable of forming a stable film on the surface of the silicon-based negative electrode, so that when using a negative electrode containing a silicon-based active material, the decomposition of the SEI film can be effectively suppressed.

[0114] On the other hand, the negative electrode may further include a normal negative electrode active material capable of reversibly intercalating / deintercalating lithium ions, specifically, a carbon-based negative electrode active material, in addition to the silicon-based negative electrode active material, if necessary, in the lithium battery.

[0115] As the carbon-based anode active material, various carbon-based anode active materials used in this industry can be used, such as graphite-based materials like natural graphite, artificial graphite, and Kish graphite; pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as 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.

[0116] Specifically, the carbon-based negative electrode active material can be at least one of natural graphite and artificial graphite, and both natural graphite and artificial graphite may be used to enhance adhesion to the current collector and suppress detachment of the active material.

[0117] On the other hand, when both the silicon-based anode active material and the carbon-based anode active material are used as the anode active material according to one embodiment of the present invention, their mixing ratio may be 3:97 to 99:1 by weight, preferably 5:95 to 15:85. When the mixing ratio of the silicon-based anode active material and the carbon-based anode active material satisfies the above range, the capacity characteristics are improved, the volume expansion of the silicon-based anode active material is suppressed, and excellent cycle performance can be ensured.

[0118] The negative electrode may include a negative electrode current collector and a negative electrode mixture layer disposed on at least one side of the negative electrode current collector. In this case, the negative electrode active material may be included in the negative electrode mixture layer.

[0119] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. Specifically, the negative electrode current collector may be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloy.

[0120] The negative electrode current collector typically has a thickness of 3 to 500 μm.

[0121] The negative electrode current collector may have its surface textured to enhance the bonding force of the negative electrode active material. For example, the negative electrode current collector can be used in various forms such as film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0122] The negative electrode mixture layer is disposed on at least one side of the negative electrode current collector. Specifically, the negative electrode mixture layer may be disposed on one or both sides of the negative electrode current collector.

[0123] The negative electrode active material may be included in the negative electrode mixture layer in an amount of 60% to 99% by weight, in order to minimize the effect of volume expansion / contraction on the battery and to achieve sufficient capacity in a secondary battery. When the content of the negative electrode active material satisfies the above range, excellent capacity characteristics and electrochemical properties can be obtained.

[0124] The negative electrode mixture layer may further contain a conductive material and / or a binder together with the silicon-based active material.

[0125] 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 mixture layer. Such a 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.

[0126] 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 mixture 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.

[0127] 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 mixture layer.

[0128] 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 coating the negative electrode current collector with a negative electrode slurry containing a negative electrode active material and selectively a binder, conductive material, and solvent for forming the negative electrode slurry, followed by drying and rolling. Alternatively, the negative electrode can be manufactured by manufacturing a film by mixing the negative electrode active material and selectively a binder, conductive material, etc., and then laminating it onto the negative electrode current collector.

[0129] The solvent for forming the negative electrode slurry may include, for example, at least one selected from the group consisting of distilled water, N-methylpyrrolidone, ethanol, methanol, and isopropyl alcohol, preferably distilled water, in order to facilitate the dispersion of the negative electrode active material, binder, and / or conductive material.

[0130] (3) Separator A lithium secondary battery according to one embodiment of the present invention includes a separator between the positive electrode and the negative electrode.

[0131] The separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separator commonly used in lithium secondary batteries is acceptable and not particularly limited. In particular, a separator that has low resistance to the movement of lithium salt ions and excellent electrolyte moisture retention capacity is preferred.

[0132] 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.

[0133] The lithium secondary battery according to the above embodiment of the present invention 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).

[0134] 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.

[0135] A lithium secondary battery according to one embodiment of 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.

[0136] The present invention will be described in detail below with reference to examples. However, the examples of the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the examples detailed below. The examples of the present invention are provided to give a more complete explanation of the present invention to a person of average skill in the art.

[0137] [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, which was a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 30:70, to a concentration of 1.0 M. Then, 0.1% by weight of the compound represented by chemical formula 1A-1, 0.5% by weight of vinylene carbonate (VC), and 0.5% by weight of 1,3-propanesultone (PS) were added (see Table 1 below).

[0138] (Manufacturing of secondary batteries) Lithium nickel-manganese-cobalt-aluminum oxide (Li(Ni)) is used as the positive electrode active material particle. 0.86 Mn 0.07 Co 0.05 Al 0.02 A positive electrode slurry (solid content 75.50% by weight) was prepared by adding carbon black as a conductive material and polyvinylidene fluoride as a binder in a weight ratio of 97.74:0.7:1.56 to N-methyl-2-pyrrolidone (NMP) as a solvent. The positive electrode slurry was applied to a 15 μm thick positive electrode current collector (a thin Al film), dried, and roll-pressed to produce a positive electrode.

[0139] A negative electrode slurry (solid content: 26% by weight) was prepared by adding a negative electrode active material (graphite and SiO=95:5 by weight ratio), a conductive material (carbon black), and a binder (SBR-CMC) in a weight ratio of 97.8:0.2:2.0 to water, which was used as a solvent. The negative electrode slurry was then applied to a 15 μm thick copper (Cu) thin film, which served as a negative electrode current collector, and dried. Finally, the negative electrode was manufactured by roll pressing.

[0140] After manufacturing an electrode assembly by interposing polypropylene as a porous separator between the positive electrode and negative electrode manufactured as described above, the assembly was placed in a battery case, and the manufactured non-aqueous electrolyte for lithium secondary batteries was poured in to produce a lithium secondary battery.

[0141] <Example 2> (Manufacturing of non-aqueous electrolytes for lithium secondary batteries) A non-aqueous electrolyte for lithium secondary batteries was prepared 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% by weight of the compound represented by chemical formula 1A-1, 0.5% by weight of vinylene carbonate (VC), and 0.5% by weight of 1,3-propanesultone (PS) was added (see Table 1 below).

[0142] (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 as described above was injected.

[0143] <Example 3> (Manufacturing of non-aqueous electrolytes for lithium secondary batteries) A non-aqueous electrolyte for lithium secondary batteries was prepared 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 1.0% by weight of the compound represented by chemical formula 1A-1, 0.5% by weight of vinylene carbonate (VC), and 0.5% by weight of 1,3-propanesultone (PS) were added (see Table 1 below).

[0144] (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 as described above was injected.

[0145] <Example 4> (Manufacturing of non-aqueous electrolytes for lithium secondary batteries) A non-aqueous electrolyte for lithium secondary batteries was prepared 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 3.0% by weight of the compound represented by chemical formula 1A-1, 0.5% by weight of vinylene carbonate (VC), and 0.5% by weight of 1,3-propanesultone (PS) were added (see Table 1 below).

[0146] (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 as described above was injected.

[0147] <Example 5> (Manufacturing of non-aqueous electrolytes for lithium secondary batteries) A non-aqueous electrolyte for lithium secondary batteries was prepared 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 5.0% by weight of the compound represented by chemical formula 1A-1, 0.5% by weight of vinylene carbonate (VC), and 0.5% by weight of 1,3-propanesultone (PS) were added (see Table 1 below).

[0148] (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 as described above was injected.

[0149] <Example 6> (Manufacturing of non-aqueous electrolytes for lithium secondary batteries) A non-aqueous electrolyte for lithium secondary batteries was produced in the same manner as in Example 3, except that the compound represented by chemical formula 1A-2 was added instead of the compound represented by chemical formula 1A-1 to produce the non-aqueous electrolyte (see Table 1 below).

[0150] (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 as described above was injected.

[0151] <Example 7> (Manufacturing of non-aqueous electrolytes for lithium secondary batteries) A non-aqueous electrolyte for lithium secondary batteries was produced in the same manner as in Example 3, except that the compound represented by chemical formula 1A-3 was added instead of the compound represented by chemical formula 1A-1 to produce the non-aqueous electrolyte (see Table 1 below).

[0152] (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 as described above was injected.

[0153] <Example 8> (Manufacturing of non-aqueous electrolytes for lithium secondary batteries) A non-aqueous electrolyte for lithium secondary batteries was prepared 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 a compound represented by chemical formula 1A-1 was added in an amount of 7.0% by weight, vinylene carbonate (VC) in an amount of 0.5% by weight, and 1,3-propanesultone (PS) in an amount of 0.5% by weight (see Table 1 below).

[0154] (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 as described above was injected.

[0155] <Example 9> (Manufacturing of non-aqueous electrolytes for lithium secondary batteries) A non-aqueous electrolyte for lithium secondary batteries was prepared 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 10.0% by weight of the compound represented by chemical formula 1A-1, 0.5% by weight of vinylene carbonate (VC), and 0.5% by weight of 1,3-propanesultone (PS) were added (see Table 1 below).

[0156] (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 as described above was injected.

[0157] <Comparative Example 1> (Manufacturing of non-aqueous electrolytes for lithium secondary batteries) A non-aqueous electrolyte for lithium secondary batteries was prepared in the same manner as in Example 1, except that LiPF6 was dissolved in a non-aqueous organic solvent to a concentration of 1.5 M, and then 0.5% by weight of vinylene carbonate (VC) and 0.5% by weight of 1,3-propanesultone (PS) were added as additives to produce the non-aqueous electrolyte (see Table 1 below).

[0158] (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 as described above was injected.

[0159] <Comparative Example 2> (Manufacturing of non-aqueous electrolytes for lithium secondary batteries) A non-aqueous electrolyte for lithium secondary batteries was produced in the same manner as in Example 3, except that 1.0% by weight of the compound represented by Chemical Formula 3 below was added as an additive instead of the compound represented by Chemical Formula 1A-1 (see Table 1 below).

[0160] [Chemical formula 3] [ka]

[0161] (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 as described above was injected.

[0162] [Table 1]

[0163] 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 PS: 1,3-propanethultone

[0164] [Example of experiment] <Experimental Example 1: Evaluation of High-Temperature Cycle Characteristics> High-temperature cycle characteristics were evaluated for each of the secondary batteries manufactured in Examples 1 to 9, as well as the secondary batteries manufactured in Comparative Examples 1 and 2.

[0165] Specifically, the secondary batteries manufactured in Examples 1 to 9, as well as the secondary batteries manufactured in Comparative Examples 1 and 2, were each charged to 4.2V with a constant current of 1C at 45°C, and discharged to 2.5V with a constant current of 1.0C. One cycle was defined as this, and after 200 charge-discharge cycles, the capacity retention rate relative to the initial capacity after one cycle was measured. The results are shown in Table 2 below.

[0166] [Table 2]

[0167] Referring to Table 2, it can be seen that the secondary batteries of Examples 1 to 9, which are equipped with an electrolyte for lithium secondary batteries containing the additive of the present invention, have a relatively improved capacity retention rate after 200 cycles at high temperatures compared to the secondary batteries of Comparative Examples 1 and 2.

[0168] <Experimental Example 2. Evaluation of High-Temperature Storage Characteristics> High-temperature storage characteristics were evaluated for each of the secondary batteries manufactured in Examples 1 to 9, as well as the secondary batteries manufactured in Comparative Examples 1 and 2.

[0169] Specifically, the secondary batteries manufactured in Examples 1 to 9, as well as the secondary batteries manufactured in Comparative Examples 1 and 2, were fully charged to 4.3V and then stored at 60°C for 8 weeks.

[0170] Before saving, the capacity of the fully charged rechargeable battery was measured and set as the initial capacity of the rechargeable battery.

[0171] After 8 weeks, the capacity of the stored secondary batteries was measured, and the decrease in capacity during the 8-week storage period was calculated. The percentage of the decreased capacity relative to the initial capacity of the secondary batteries was calculated to derive the capacity retention rate after 8 weeks. The results are shown in Table 3 below.

[0172] [Table 3]

[0173] Referring to Table 3, it can be seen that the secondary batteries of Examples 1 to 9, which are equipped with an electrolyte for lithium secondary batteries containing the additive of the present invention, have improved capacity retention rates after high-temperature storage compared to the secondary batteries of Comparative Examples 1 and 2.

Claims

1. An electrolyte additive containing the compound represented by the following chemical formula 1. [Chemical formula 1] 【Chemistry 1】 (In the above chemical formula 1, R is an alkyl group having 1 to 7 carbon atoms, substituted with at least one fluorine atom.

2. The electrolyte additive according to claim 1, wherein R in the chemical formula 1 is an alkyl group having 1 to 5 carbon atoms substituted with at least one fluorine atom.

3. The electrolyte additive according to claim 1, wherein R in the chemical formula 1 is an alkyl group having 1 to 3 carbon atoms substituted with at least one fluorine atom.

4. The electrolyte additive according to claim 1, wherein the compound represented by chemical formula 1 is at least one of the compounds represented by the following chemical formulas 1A-1 to 1A-3. [Chemical formula 1A-1] 【Chemistry 2】 [Chemical formula 1A-2] 【Transformation 3】 [Chemical formula 1A-3] 【Chemistry 4】

5. A non-aqueous electrolyte for a lithium secondary battery, comprising the electrolyte additive described in claim 1.

6. The non-aqueous electrolyte for lithium secondary batteries according to claim 5, wherein the electrolyte additive is contained in the non-aqueous electrolyte for lithium secondary batteries in an amount of 0.1% to 10.0% by weight.

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

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

9. Positive electrode and, A negative electrode opposite the positive electrode, A separator interposed between the positive electrode and the negative electrode, A lithium secondary battery comprising a non-aqueous electrolyte for a lithium secondary battery as described in claim 5.

10. The lithium secondary battery according to claim 9, wherein the negative electrode contains a silicon-based negative electrode active material.

11. The lithium secondary battery according to claim 10, wherein the negative electrode further comprises a carbon-based negative electrode active material.

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