Electrolyte composition with improved high-temperature safety and lithium secondary battery containing the same

Abstract

This invention relates to an electrolyte composition for lithium secondary batteries. The above-mentioned electrolyte composition for lithium secondary batteries contains a non-aqueous organic solvent and a fluorine-substituted linear ester solvent and a fluorine-substituted acrylic additive as electrolyte additives, respectively. This allows for the uniform formation of a solid electrolyte film layer (SEI layer) with high lithium ion conductivity and excellent heat resistance on the negative electrode surface when the lithium secondary battery is activated. As a result, the reactivity between the negative electrode active material and the electrolyte composition is significantly reduced, increasing the temperature at which heat generation begins between them (i.e., the heat generation onset temperature), and suppressing heat generation due to deterioration of the negative electrode. Furthermore, a lithium secondary battery containing the above-mentioned electrolyte composition has the advantage of excellent high-temperature safety because it can minimize side reactions of the electrolyte composition that occur on the negative electrode surface when exposed to high temperatures.

Description

[Technical Field]

[0001] This invention relates to an electrolyte composition with improved high-temperature safety and a lithium secondary battery containing the same.

[0002] This application claims priority under Korean Patent Application No. 10-2024-0054519 dated April 24, 2024, and all content disclosed in the documents of said patent application is incorporated herein by reference. [Background technology]

[0003] In recent years, lithium-ion batteries have been widely applied not only to small devices such as portable electronic devices, but also to medium- and large-scale devices such as battery packs for hybrid and electric vehicles, or power storage devices.

[0004] Such lithium secondary batteries are manufactured by coating and drying a composition containing electrode active material onto a current collector to a suitable thickness and length, or by forming the electrode active material itself into a film to create a positive and negative electrode, then winding or laminating them together with an insulating separator film in between to create an electrode assembly, placing it in a can or similar container, and injecting an electrolyte.

[0005] As the demand for lithium-ion batteries increases, research to improve their safety is also progressing actively (see Korean Published Patent Publication No. 10-2022-0105936). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Korean Published Patent No. 10-2022-0105936 [Overview of the project] [Problems that the invention aims to solve]

[0007] The present invention aims to provide an electrolyte composition and a lithium secondary battery containing the same that can more effectively suppress side reactions with the electrolyte that occur on the negative electrode surface when a lithium secondary battery is exposed to high temperatures. [Means for solving the problem]

[0008] To solve the above problem, One embodiment of the present invention is It contains a lithium salt, an electrolyte additive, and a non-aqueous organic solvent. The above non-aqueous organic solvent contains a fluorine-substituted linear ester solvent in an amount of 60% to less than 100% by volume. The present invention provides an electrolyte composition that, when measuring the heat flow rate of a mixture containing a 100% charged negative electrode active material and an electrolyte composition in a 1:0.5 weight ratio, exhibits a heat flow rate of 50.0 W / g or less within the range of 250°C to 400°C.

[0009] For example, the above electrolyte composition may exhibit a heat flow rate in the range of 0.5 W / g to 30 W / g.

[0010] Here, the electrolyte additive may contain one or more compounds represented by the following chemical formula 1:

[0011] [ka]

[0012] In the above chemical formula 1, R1 and R2 are, respectively, fluorogroups or C 1-10 It is a fluorinated alkylene group, p is an integer between 0 and 4. q is an integer between 1 and 10.

[0013] Specifically, the compound represented by the above chemical formula 1 may contain one or more of the acrylic compounds represented by the following structural formulas 1 to 10:

[0014] [ka]

[0015] Furthermore, the above-mentioned electrolyte additive may be included in an amount exceeding 0% by weight and not exceeding 5% by weight, based on the total weight of the electrolyte composition.

[0016] Furthermore, the electrolyte additive may further contain one or more cyclic carbon compounds selected from vinylene carbonate (VC), 1,3-propanesultone (PS), ethylene sulfate (ESa), propylene sulfate (PSa), and butylene sulfate (BSa).

[0017] The above-mentioned cyclic carbon compounds may be included in an amount of 10 parts by weight or more and less than 50 parts by weight, based on 100 parts by weight of the total electrolyte additive.

[0018] Furthermore, the fluorine-substituted linear ester solvent described above may contain one or more compounds represented by the following chemical formula 2:

[0019] [ka]

[0020] In the above chemical formula 2, R3 is hydrogen or C 1~6 It is an alkyl group, R4 and R5 are hydrogen, a fluoro group, or C, respectively. 1-10 It is a fluorinated alkylene group, m is an integer between 1 and 6.

[0021] Specifically, the fluorine-substituted linear ester solvents described above may contain one or more compounds represented by the following structural formulas 11 to 16:

[0022] [ka]

[0023] Further, the non-aqueous organic solvent may comprise one or more carbonate-based solvents selected from the group consisting of ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).

[0024] In this case, the carbonate-based solvent may be contained in a range of more than 0% by volume and 40% by volume or less based on the total weight of the non-aqueous organic solvent.

[0025] On the other hand, the lithium salt has Li as a cation + and includes, as anions, BF4 - , B 10 Cl 10 - , ClO4 - , AlO4 - , AlCl4 - , PF6 - , SbF6 - , AsF6 - , BF2C2O4 - , B(C2O4)2 - , PF4C2O4 - , PF2C4O8 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , (C2O4)2PF2 - , CF3SO3 - , C4F9SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN -, (CF3CF2SO2)2N - , and ((C(CN))2NC(CF3))N - It may include one or more of the following.

[0026] Furthermore, the above negative electrode active material is silicon (Si), silicon carbide (SiC), and silicon oxide (SiO₂). r However, it may be one or more silicon-based negative electrode active materials (0.8 ≤ r ≤ 2.5).

[0027] Furthermore, one embodiment of the present invention is, An electrode assembly including a positive electrode, a negative electrode, and a separation membrane provided between the positive electrode and the negative electrode, The present invention provides a lithium secondary battery comprising the electrolyte composition described above, which is impregnated into the electrode assembly described above.

[0028] Here, the positive electrode may include a positive electrode active layer provided on at least one surface of the positive electrode current collector and containing a positive electrode active material represented by the following chemical formula 3:

[0029] [Chemical formula 3] Li x [Ni y Co z Mn w M 1 v ]O2

[0030] In the above chemical formula 3, M 1 is one or more elements from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo. x, y, z, w, and v are such that 0.9 ≤ x ≤ 1.30, 0.6 ≤ y < 1, and 0 respectively. <z≦0.2、0<w≦0.2、0≦v≦0.1であり、かつ、y+z+w+v=1である。 [Effects of the Invention]

[0031] The electrolyte composition according to the present invention can uniformly form a solid electrolyte film layer (SEI layer) with high lithium ion conductivity and excellent heat resistance on the negative electrode surface when a lithium secondary battery is activated. As a result, the reactivity between the negative electrode active material and the electrolyte composition is significantly reduced, raising the temperature at which heat generation begins between them (i.e., the heat generation onset temperature), thereby suppressing heat generation due to deterioration of the negative electrode. Furthermore, a lithium secondary battery containing the above electrolyte composition has the advantage of excellent high-temperature safety because it can minimize side reactions of the electrolyte composition that occur on the negative electrode surface when exposed to high temperatures.

[0032] The following drawings accompanying this specification illustrate embodiments of the present invention and, together with the detailed description of the invention described later, serve to further illustrate the technical concept of the present invention. Therefore, the present invention should not be construed as being limited solely to the matters described in such drawings. [Brief explanation of the drawing]

[0033] [Figure 1] This graph shows the heat flow rate of an electrolyte composition depending on whether or not the electrolyte additive according to the present invention is used. [Modes for carrying out the invention]

[0034] Since the present invention can be modified in various ways and has a variety of embodiments, specific embodiments will be described in detail.

[0035] In the present invention, terms such as "includes" and "have" are intended to specify the presence of features, numbers, steps, operations, components, parts, or combinations thereof as described in the specification, without prejudice to the presence or possibility of adding one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0036] Furthermore, in this invention, when a part such as a layer, film, region, or plate is described as being "on top" of another part, this includes not only the case where it is "directly above" the other part, but also the case where there is another part in between. Conversely, when a part such as a layer, film, region, or plate is described as being "below" another part, this includes not only the case where it is "directly below" the other part, but also the case where there is another part in between. Also, in this application, "positioned on top" may include not only the upper part, but also the case where it is positioned below.

[0037] Furthermore, in the present invention, "contains as a main component" may mean that the defined component is contained in an amount of 50% or more by weight (or 50% by volume), 60% or more by weight (or 60% by volume), 70% or more by weight (or 70% by volume), 80% or more by weight (or 80% by volume), 90% or more by weight (or 90% by volume), or 95% or more by weight (or 95% by volume) of the total weight (or total volume). For example, "contains a linear ester solvent as a main component as a non-aqueous organic solvent" may mean that the linear ester solvent is contained in an amount of 50% or more by volume, 60% or more by volume, 70% or more by volume, 80% or more by volume, 90% or more by volume, or 95% or more by volume of the total volume of the non-aqueous organic solvent. In some cases, it may also mean that the entire non-aqueous organic solvent consists of a linear ester solvent and is contained in an amount of 100% by volume.

[0038] Because lithium secondary batteries operate at high drive voltages, aqueous electrolytes, which are highly reactive with lithium, are not used; instead, organic electrolytes are generally employed. These organic electrolytes are manufactured by dissolving lithium salts in an organic solvent. The organic solvents used are stable under high voltages and utilize materials with high ionic conductivity, dielectric constant, and low viscosity.

[0039] Generally, carbonate-based polar non-aqueous solvents are used as such organic solvents. These carbonate-based non-aqueous solvents cause an irreversible reaction during the initial charging of lithium secondary batteries, where an excess charge is used due to a side reaction between the negative / positive electrode and the electrolyte. This irreversible reaction causes a passivation layer, such as a solid electrolyte interface layer (SEI layer), to form on the negative electrode surface. The SEI layer prevents the decomposition of the electrolyte on the negative electrode surface during charging and discharging and acts as an ion tunnel. Therefore, the higher the stability and lower the resistance of the SEI layer, the longer the lifespan of the lithium secondary battery.

[0040] On the other hand, various additives are added to the electrolyte to stabilize the SEI layer, but since the SEI layer formed using conventional common additives deteriorates easily at high temperatures, the stability of the SEI layer formed using conventional common additives decreased at high temperatures.

[0041] In view of these points, the present invention provides a technology that can further enhance the high-temperature safety of lithium secondary batteries by suppressing side reactions with the electrolyte that occur on the negative electrode surface at high temperatures.

[0042] The present invention will be described in more detail below with reference to the attached drawings.

[0043] <Electrolyte composition> The present invention It contains a lithium salt, an electrolyte additive, and a non-aqueous organic solvent. The above non-aqueous organic solvent contains a fluorine-substituted linear ester solvent in an amount of 60% to less than 100% by volume. The present invention provides an electrolyte composition that, when measuring the heat flow rate of a mixture containing a 100% charged negative electrode active material and an electrolyte composition in a 1:0.5 weight ratio, exhibits a heat flow rate of 50.0 W / g or less within the range of 250°C to 400°C.

[0044] The electrolyte composition according to the present invention is a liquid electrolyte that can uniformly form a solid electrolyte film layer (SEI layer) on the negative electrode surface during activation of a lithium secondary battery, exhibiting high lithium ion conductivity and excellent heat resistance. As a result, the reactivity between lithium ions inserted into or detached from the negative electrode active material and the electrolyte composition during charging of the lithium secondary battery is significantly reduced, thereby raising the temperature at which heat generation begins between them (i.e., the heat generation onset temperature), and suppressing heat generation due to deterioration of the negative electrode. Furthermore, a lithium secondary battery containing the above electrolyte composition has the advantage of excellent high-temperature safety because it can minimize side reactions of the electrolyte composition that occur on the negative electrode surface when exposed to high temperatures.

[0045] For this purpose, the electrolyte composition comprises a lithium salt, an electrolyte additive, and a non-aqueous organic solvent. The lithium salt, electrolyte additive, and non-aqueous organic solvent may have a predetermined composition.

[0046] Specifically, the electrolyte additive may contain an organic compound, and the organic compound may be a fluorine-substituted acrylic compound. Specifically, the electrolyte additive may contain one or more compounds represented by the following chemical formula 1:

[0047] [ka]

[0048] In the above chemical formula 1, R1 and R2 are, respectively, fluorogroups or C 1-10 It is a fluorinated alkylene group, p is an integer between 0 and 4. q is an integer between 1 and 10.

[0049] Specifically, in the above chemical formula 1, R1 and R2 are a fluoro group or a methyl fluoride group, respectively. p is an integer between 0 and 2. q is an integer between 3 and 6.

[0050] The present invention can minimize side reactions of the electrolyte composition during high-temperature exposure by improving the heat resistance and uniformity of the coating formed on the negative electrode surface, i.e., the SEI layer. Specifically, the SEI layer is formed on the electrode surface by irreversible decomposition of the electrolyte before lithium ions are inserted into the negative electrode active material. The SEI layer has the property of allowing lithium ions to pass through while blocking electron movement. Therefore, once the SEI layer is formed, the decomposition of the electrolyte due to electron movement between the electrode and the electrolyte is suppressed, and only selective insertion and removal of lithium ions becomes possible. In other words, the SEI layer plays a role as a protective film that prevents the electrolyte from continuing to decompose, and is therefore a very important element in lithium secondary batteries.

[0051] The SEI layer described above is composed of Li2CO3, LiF, and Li2O, which are formed by side reactions of electrolyte components during the activation of the secondary battery. Furthermore, additives contained in the electrolyte participate in the side reactions that form the SEI layer, thereby adjusting the properties and performance of the SEI layer.

[0052] In this regard, conventional fluorine-containing compounds used as electrolyte additives have a structure that prevents the formation of highly heat-resistant fluorine-containing by-reactants during the activation of secondary batteries. Specifically, conventional electrolyte additives have alkyl fluorides in which all hydrogen atoms of the hydrocarbon group are replaced by fluorine (e.g., -CF3, -CF2CF3, -CF2CF2CF3, etc.). These alkyl fluorides contain CF bonds and CC bonds. The CF bond has a higher bond energy compared to the CH bond and is not easily broken by heat. Similarly, in the CC bond skeleton, -CF2- also has a higher bond energy than -CH2- and is characterized by difficulty in rotating the carbon chain. Therefore, these electrolyte additives have played a role in increasing the heat resistance of the components contained in the electrolyte itself, as it is difficult for them to form fluorine-containing by-reactants during the activation process of secondary batteries.

[0053] However, the compound represented by chemical formula 1 according to the present invention includes an acrylate group having an unsaturated hydrocarbon group and an alkyl group bonded to the oxygen atom of the acrylate group. In this case, the alkyl group has a chemical structure in which the terminal carbon atom is partially substituted with a fluorine element. Therefore, the CH bond partially contained can be easily cleaved during the activation of the secondary battery, and thus it can have higher reactivity compared to conventional electrolyte additives. That is, the terminal carbon atom of the alkyl group can be relatively easily defluorinated as a CF bond, which is relatively less reactive. The defluorinated reaction product thus produced (e.g., fluorine ions, the activated compound before defluorination, etc.) reacts with lithium ions to form LiF, and at the same time, by being directly inserted into the SEI layer and participating in its development, it can achieve high ionic conductivity and excellent heat resistance of the SEI layer.

[0054] The compound represented by chemical formula 1, which can impart excellent ionic conductivity and heat resistance to the SEI layer upon activation, may contain one or more of the acrylic compounds represented by the following structural formulas:

[0055] [ka]

[0056] The compounds shown in <Structural Formula 1> to <Structural Formula 10> above have the characteristic of encapsulating a vinyl group within the acrylate group, which decomposes during the activation of the secondary battery and easily participates in the formation of the SEI layer. Furthermore, because the above compounds have a structure in which the terminal carbon of the alkyl group bonded to the oxygen atom of the acrylate group is partially substituted with a fluorine element, they can uniformly form an SEI layer with excellent ionic conductivity and heat resistance during the activation of the secondary battery.

[0057] As an example, an electrolyte composition containing the compound represented by the above chemical formula 1 may have an onset temperature of 250°C or higher, which is the temperature at which the negative electrode active material begins to exothermically when exposed to high temperatures during differential scanning calorimeter analysis. Specifically, the onset temperature may be in the range of 260°C or higher, 270°C or higher, 250°C to 400°C, 260°C to 380°C, 270°C to 360°C, 285°C to 340°C, over 280°C and 360°C or lower, over 290°C and 350°C or lower, or 300°C to 340°C.

[0058] Furthermore, the compound represented by the above chemical formula 1 may be included in the electrolyte composition in predetermined amounts. Specifically, the compound represented by the above chemical formula 1 may be included in a range of more than 0% by weight and up to 5% by weight relative to the total weight of the electrolyte composition, and more specifically, it may be included in a range of more than 0% by weight and up to 4% by weight, more than 0% by weight and up to 3% by weight, more than 0% by weight and up to 2% by weight, more than 0% by weight and up to 1% by weight, more than 0% by weight and up to 0.9% by weight, 0.1% to 5% by weight, 0.1% to 4% by weight, 0.1% to 3% by weight, 0.1% to 2% by weight, 0.1% to 1% by weight, 0.5% to 4% by weight, 1% to 5% by weight, 2% to 4.5% by weight, 2.5% to 5% by weight, 3% to 5% by weight, 2% to 4% by weight, or 3% to 4.5% by weight relative to the total weight of the electrolyte composition.

[0059] The present invention can prevent the use of excessive amounts outside the above range, which would increase the viscosity of the electrolyte composition and reduce its wettability to the electrodes and separation membrane, by adjusting the total content of the compound represented by Chemical Formula 1 to the above range. Furthermore, the present invention can suppress the reduction of the ionic conductivity of the electrolyte composition and the resulting decrease in battery performance. Moreover, the present invention can prevent the use of trace amounts of electrolyte additives outside the above range, which would result in only a slight effect from the additives being realized.

[0060] The electrolyte additive described above may further contain a cyclic carbon compound along with the compound represented by chemical formula 1. For example, the cyclic carbon compound may include one or more of vinylene carbonate (VC), 1,3-propanesultone (PS), ethylene sulfate (ESa), propylene sulfate (PSa), and butylene sulfate (BSa).

[0061] For example, the above cyclic carbon compounds may include vinylene carbonate (VC), 1,3-propanesultone (PS), ethylene sulfate (ESa), and / or propylene sulfate (PSa).

[0062] The above-mentioned cyclic carbon compound, when included in the electrolyte composition together with the compound represented by chemical formula 1, can not only increase the initial charge-discharge capacity of the lithium secondary battery, but also suppress the decomposition of the non-aqueous organic solvent, which makes up the majority of the electrolyte composition, under high-temperature conditions. Therefore, it is possible to improve the cycle characteristics of the lithium secondary battery while suppressing gas generation.

[0063] On the other hand, the electrolyte additive may be in the range of more than 0% by weight and up to 10% by weight based on the total weight of the electrolyte composition, and specifically, it may be in the range of more than 0% by weight and up to 7.5% by weight, 1% to 7.5% by weight, 3% to 6.5% by weight, or 4.5% to 6.5% by weight.

[0064] Furthermore, if the electrolyte additive contains both a compound represented by chemical formula 1 and a cyclic carbon compound, the cyclic carbon compound may be included in a predetermined proportion relative to the total electrolyte additive. Specifically, the cyclic carbon compound may be included in an amount of 10 parts by weight or more and less than 50 parts by weight per 100 parts by weight of the total electrolyte additive. For example, the cyclic carbon compound may be included in an amount of 10 to 49 parts by weight, 15 to 49 parts by weight, 20 to 47 parts by weight, 30 to 49 parts by weight, 20 to 40 parts by weight, 10 to 30 parts by weight, or 40 to 47 parts by weight per 100 parts by weight of the total electrolyte additive.

[0065] Generally, when the acidity of an electrolyte composition increases, concentration polarization occurs, which can reduce the transport rate of lithium ions. However, the present invention can prevent the acidity of the electrolyte composition after the activation process from increasing due to a high proportion of the compound represented by chemical formula 1, by adjusting the content ratio of inorganic compounds and cyclic carbon compounds as described above. Furthermore, the present invention can prevent the problem that the heat resistance and thickness uniformity of the SEI layer formed on the negative electrode surface cannot be sufficiently improved due to a lower proportion of the compound represented by chemical formula 1 than the range described above.

[0066] Furthermore, the electrolyte composition contains a non-aqueous organic solvent, the non-aqueous organic solvent mainly comprising a fluorine-substituted linear ester solvent. Specifically, the fluorine-substituted linear ester solvent may contain one or more compounds represented by the following chemical formula 2:

[0067] [ka]

[0068] In the above chemical formula 2, R3 is hydrogen or C 1~6 It is an alkyl group, R4 and R5 are hydrogen, a fluoro group, or C, respectively. 1-10 It is a fluorinated alkylene group, m is an integer between 1 and 6.

[0069] Specifically, in chemical formula 2 above, R3 is a methyl group, an ethyl group, or a propyl group. R4 and R5 are hydrogen or fluoro groups, respectively. m is an integer between 2 and 5.

[0070] Specifically, the fluorine-substituted linear ester solvents described above may contain one or more compounds represented by the following structural formulas 11 to 16:

[0071] [ka]

[0072] Conventionally, fluorine-substituted non-aqueous carbonate solvents, such as fluoroethylene carbonate (FEC), have been used as electrolytes for lithium secondary batteries to suppress the decomposition of the electrolyte composition on the positive and / or negative electrode surfaces and to improve high-temperature safety. However, such fluorine-based carbonate solvents have a low reduction potential, which can lead to problems such as a decrease in battery capacity or a deterioration in cycle characteristics when applied to the electrolyte.

[0073] In contrast, the fluorine-substituted linear ester solvent exhibits high ionic conductivity at low temperatures, low viscosity, and excellent wettability to electrode assemblies. Furthermore, the fluorine-substituted linear ester solvent has a high oxidation reaction potential in the range of 4.5V or higher, specifically in the range of 5.0V or higher, and does not easily decompose even when overcharging occurs, thus possessing high safety characteristics. In addition, the linear ester solvent represented by chemical formula 2 can minimize the transfer of external heat to the negative electrode active material when lithium secondary batteries are exposed to high temperatures, thus possessing excellent properties for improving the high-temperature safety of lithium secondary batteries.

[0074] The fluorine-substituted linear ester solvent described above may be included in an amount of 60% by volume or more relative to the total weight of the non-aqueous organic solvent in the electrolyte composition, more specifically in the ranges of 60% by volume or more but less than 100% by volume, 70% by volume or more but less than 100% by volume, 75% by volume or more but less than 100% by volume, 80% by volume or more but less than 100% by volume, 85% by volume or more but less than 100% by volume, 90% by volume or more but less than 100% by volume, 60% by volume to 99% by volume, 70% by volume to 99% by volume, 80% by volume to 99% by volume, 90% by volume to 99% by volume, 95% by volume to 99% by volume, 60% by volume to 80% by volume, or 70% by volume to 90% by volume.

[0075] The present invention can prevent the problem that when the content of a fluorine-substituted linear ester solvent contained in a non-aqueous organic solvent is adjusted as described above to be in the range of less than 60% by volume, the heat transferred to the negative electrode active material during high-temperature exposure of a lithium secondary battery is not sufficiently reduced. Furthermore, since the fluorine-substituted linear ester solvent has excellent heat resistance, when the content is adjusted to the above range, the electrolyte composition does not easily decompose at high temperatures, and when combined with a predetermined electrolyte additive according to the present invention, the amount of heat transferred to the negative electrode active material can be minimized.

[0076] Furthermore, the non-aqueous organic solvent may further contain a carbonate-based solvent along with a fluorine-substituted linear ester solvent. The carbonate-based solvent plays a supporting role to the fluorine-substituted linear ester solvent, which is the main component of the non-aqueous organic solvent, and can control the dielectric constant of the electrolyte composition. This ensures high ionic conductivity of the electrolyte composition.

[0077] Furthermore, the carbonate-based solvent can function to prevent the induction of side reactions in the electrolyte composition and the generation of gases when exposed to high temperatures. For this reason, from the viewpoint of electrochemical stability against oxidation-reduction and chemical stability with respect to heat and reactions with solutes, one type of carbonate-based solvent may be mixed with the fluorine-substituted linear ester solvent, or two or more types may be mixed with the fluorine-substituted linear ester solvent in any combination according to the application.

[0078] Such carbonate-based solvents may include ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc., and these may be used individually or in combination of two or more.

[0079] Furthermore, the auxiliary solvent may be mixed with a fluorine-substituted linear ester solvent to satisfy a certain volume ratio when mixed with the fluorine-substituted linear ester solvent in order to control the dielectric constant of the electrolyte composition without reducing the solubility of the compound represented by chemical formula 1, which is an electrolyte additive. Specifically, the auxiliary solvent may be included in a range of 40% by volume or less based on the total volume of the non-aqueous organic solvent, and more specifically, in a range of more than 0% by volume and 40% by volume or less, more than 0% by volume and 30% by volume or less, more than 0% by volume and 25% by volume or less, more than 0% by volume and 20% by volume or less, more than 0% by volume and 15% by volume or less, more than 0% by volume and 10% by volume or less, 1% by volume to 40% by volume, 1% by volume to 30% by volume, 1% by volume to 20% by volume, 1% by volume to 10% by volume, 1% by volume to 5% by volume, 20% by volume to 40% by volume, or 10% by volume to 30% by volume, based on the total volume of the non-aqueous organic solvent.

[0080] The present invention can maintain high compatibility between the fluorine-substituted linear ester solvent and the auxiliary solvent by adjusting the content of the auxiliary solvent in the total non-aqueous organic solvent to the above ratio, and at the same time improve the performance of the battery by increasing the charge mobility and / or ion mobility of the battery.

[0081] Furthermore, the electrolyte composition may contain a specific lithium salt to reduce the amount of heat transferred to the positive electrode active material. Specifically, the lithium salt may contain Li as a cation. + Includes anions, as BF4 - , B 10 Cl 10 - ClO4 - AlO4 - AlCl4 - PF6 - SbF6 - AsF6 - BF2C2O4 - B(C2O4)2 - PF4C2O4 - PF2C4O8 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P- (C2O4)2PF2 - CF3SO3 - , C4F9SO3 - CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2) 2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - , (CF3CF2SO2)2N - and ((C(CN))2NC(CF3))N - It may include one or more of the following.

[0082] The lithium salt described above essentially imparts conductivity to the organic solvent constituting the electrolyte, while also playing a role in inducing passivation of the negative electrode through SEI formation. In the present invention, the lithium salt dissolves in a linear ester solvent and can function to delay the side reaction between lithium ions desorbed from the negative electrode and the electrolyte composition when the lithium secondary battery is exposed to high temperatures.

[0083] On the other hand, the lithium salt used in the present invention may selectively contain two or more of the above-mentioned lithium salts.

[0084] For example, the above lithium salts are lithium hexafluorophosphate (LiPF6) and lithium bis(trifluoromethanesulfonyl)imide (anion: (CF3SO2)2N - This may include LiFSI (and so on).

[0085] PF6 as an anion upon dissociation -LiPF6, as shown above, is a phosphate-based lithium salt commonly used in electrolyte compositions for lithium secondary batteries, and is characterized by its ability to impart high conductivity to carbonate-based electrolytes. However, when LiPF6 is used as a lithium salt alone, it decomposes into PF5 at temperatures above approximately 200°C when exposed to high temperatures. This is highly unstable and removes the CEI (Cathode Electrolyte Interphase) layer located on the surface of the positive electrode active layer, thus reducing the high-temperature durability of the electrode.

[0086] Furthermore, LiFSI, a sulfonimide lithium salt, has a high decomposition temperature in carbonate solvents, high high-temperature safety, high water resistance, and does not generate a large amount of hydrogen fluoride (HF) even when in contact with moisture. However, the sulfonylimide group of LiFSI itself is highly reactive with aluminum, which causes corrosion of the positive electrode current collector when applied to electrolyte compositions. In particular, when the inorganic additive of the present invention is excluded, the heat transfer rate to the negative electrode active material is high, which presents limitations in its application to electrolyte compositions.

[0087] When LiPF6 and LiFSI are applied together in this manner, it not only significantly improves the low high-temperature safety of LiPF6, but also significantly reduces the heat flow rate through which the electrolyte composition transfers heat to the negative electrode active material.

[0088] In this case, when the phosphate-based lithium salt in the lithium salt used in combination is referred to as the first lithium salt and the sulfonylimide-based lithium salt is referred to as the second lithium salt, the first lithium salt and the second lithium salt may have a predetermined mixing ratio. Specifically, the mixing ratio of the first lithium salt and the second lithium salt may be 1:0.1 to 1.0 based on molar concentration (M), and more specifically, it may be 1:0.4 to 0.9 or 1:0.6 to 0.8. By adjusting the ratio of the first lithium salt and the second lithium salt as described above, the present invention can maximize the effect of reducing the heat flow rate of the electrolyte composition while minimizing the disadvantages of each lithium salt.

[0089] The concentrations of these lithium salts can meet predetermined levels to enhance high-temperature safety while maintaining the inherent functions of the lithium salts. For example, the preferred concentrations of the lithium salts may have a lower limit of 0.5 mol / L or higher, specifically 0.7 mol / L or higher, more specifically 0.9 mol / L or higher, and an upper limit of 2.5 mol / L or lower, specifically 2.0 mol / L or lower, more specifically 1.5 mol / L or lower. If the lithium salt concentration falls below 0.5 mol / L, the ionic conductivity decreases, which may reduce the cycle characteristics and power characteristics of the non-aqueous electrolyte battery. Furthermore, if the lithium salt concentration exceeds 2.5 mol / L, the viscosity of the electrolyte for the non-aqueous electrolyte battery increases, which may also reduce the ionic conductivity and potentially reduce the cycle characteristics and power characteristics of the non-aqueous electrolyte battery.

[0090] Furthermore, dissolving a large amount of lithium salt in a non-aqueous organic solvent at once may cause the liquid temperature to rise due to the heat of dissolution of the lithium salt. When the temperature of the non-aqueous organic solvent rises significantly due to the heat of dissolution of the lithium salt, in the case of lithium salts containing fluorine, decomposition may be accelerated, and hydrogen fluoride (HF) may be generated. Hydrogen fluoride (HF) is undesirable because it causes deterioration of battery performance. Therefore, the temperature at which the above lithium salt is dissolved in a non-aqueous organic solvent is not particularly limited, but can be adjusted to -20°C to 80°C, and specifically to 0°C to 60°C.

[0091] The electrolyte composition according to the present invention, having the above-described composition, can uniformly form a solid electrolyte film layer (SEI layer) on the negative electrode surface when a lithium secondary battery is activated. This minimizes side reactions between lithium ions generated on the negative electrode surface and the electrolyte composition, thereby improving the high-temperature safety of the lithium secondary battery.

[0092] As an example, when measuring the heat flow of a mixture containing the negative electrode active material in a 100% filled state and the electrolyte composition at a weight ratio of 1:0.5, the electrolyte composition may exhibit a heat flow within the range of 250°C to 400°C of 30.0 W / g or less. For example, when measuring the heat flow as described above, the electrolyte composition may exhibit a heat flow within the range of 250°C to 400°C of 5 W / g to 25 W / g, 5 W / g to 20 W / g, 10 W / g to 25 W / g, 15 W / g to 25 W / g, 17 W / g to 23 W / g, or 19 W / g to 22 W / g.

[0093] Here, the negative electrode active material described above may be a silicon-based negative electrode active material that is commonly used as a negative electrode active material for lithium secondary batteries. Specifically, the silicon-based negative electrode active material described above includes silicon (Si), silicon carbide (SiC), and silicon oxide (SiO r , provided that 0.8≦r≦2.5) may include one or more of the above.

[0094] For example, the silicon-based negative electrode active material described above may include silicon carbide (SiC). The above-mentioned silicon carbide may refer to silicon carbide in which carbon atoms and silicon atoms are chemically bonded at an atomic ratio of 1:1. In some cases, it may be a composite obtained by forming a carbon layer on the surface of pure silicon, or mixing pure silicon and graphite at a molar ratio of 1:1 to form a composite. The above-mentioned silicon carbide (SiC) contains carbon atoms, compared with pure silicon and silicon oxide (SiO r ), it has the advantages of relatively lower volume expansion rate, higher conductivity, and excellent performance in terms of service life and output during charge and discharge of secondary batteries.

[0095] The term "heat flow rate" above refers to the amount of heat flowing per unit weight, and can particularly indicate the degree of heat generation in a secondary battery. Analysis of the electrolyte composition of the present invention using a thermal analysis method revealed that the electrolyte composition exhibited a lower heat flow rate compared to conventional electrolyte compositions. Here, the thermal analysis method simulates the degradation phenomenon in which the performance of a secondary battery deteriorates when it is exposed to high temperatures or when it spontaneously generates heat due to external mechanical factors. The heat flow rate measured at this time indicates the degree of heat (e.g., heat quantity) generated by the high-temperature reaction between the electrolyte composition and the charged negative electrode active material when simulating the high-temperature degradation phenomenon of a secondary battery. The heat flow rate can increase or decrease depending on the type and content ratio of each component constituting the electrolyte composition, and can also increase or decrease depending on whether or not a lithium ion-containing SEI layer is formed on the surface of the negative electrode active layer. A reduction in such heat flow rate means that the amount of heat generated between the negative electrode active material and the electrolyte composition decreases. In other words, the degree to which lithium ions intercalated in the negative electrode active material react with the electrolyte composition is reduced, and the heat generated therefrom decreases. These results indicate that the reactivity of the electrolyte composition with lithium ions in the negative electrode active material decreased under high-temperature conditions, which means that the thermal safety of lithium secondary batteries is improved.

[0096] <Lithium-ion secondary battery> Furthermore, the present invention is An electrode assembly including a positive electrode, a negative electrode, and a separator membrane provided between the positive electrode and the negative electrode, The present invention provides a lithium secondary battery comprising the electrolyte composition described above, which is impregnated into the electrode assembly described above.

[0097] The lithium secondary battery according to the present invention comprises an electrode assembly having a structure in which a separation membrane is arranged between a plurality of positive electrodes and a plurality of negative electrodes that are alternately stacked, and an electrolyte composition in which the electrode assembly is impregnated.

[0098] The above electrolyte composition can uniformly form a solid electrolyte film layer (SEI layer) on the negative electrode surface of a lithium secondary battery, exhibiting high lithium ion conductivity and excellent heat resistance during activation.

[0099] Therefore, the above lithium secondary battery including the same has significantly reduced reactivity between the negative electrode active material (specifically, lithium ions inserted into the negative electrode active material) and the electrolyte composition, so the temperature at which heat generation starts between them (i.e., the heat generation onset temperature) increases, and heat generation caused by degradation of the negative electrode or the like can be suppressed. In addition, since side reactions of the electrolyte composition that occur on the surface of the negative electrode when the lithium secondary battery including the above electrolyte composition is exposed to high temperatures can be minimized, there is an advantage that the lithium secondary battery is excellent in high-temperature safety.

[0100] The above lithium secondary battery includes an electrode assembly and an electrolyte composition with which the electrode assembly is impregnated. Here, since the above electrolyte composition has the same configuration as described above, a detailed description is omitted.

[0101] Hereinafter, each configuration of the above electrode assembly will be described in detail.

[0102] The above electrode assembly includes a positive electrode, a negative electrode, and a separation membrane interposed between the positive electrode and the negative electrode.

[0103] Here, the above positive electrode includes a positive electrode active layer provided on at least one surface of a positive electrode current collector. The above positive electrode active layer is a substance that can electrochemically react on the positive electrode current collector to realize electrical activity, and contains, as a main component, the lithium metal oxide represented by Chemical Formula 3 above, which enables reversible intercalation and deintercalation of lithium ions:

[0104] [Chemical Formula 3] Li x [Ni y Co z Mn w M 1 v O₂

[0105] In Chemical Formula 3 above, M 1is one or more elements from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo. x, y, z, w, and v are such that 0.9 ≤ x ≤ 1.30, 0.6 ≤ y < 1, and 0 respectively. <z≦0.2、0<w≦0.2、0≦v≦0.1であり、かつ、y+z+w+v=1である。

[0106] The lithium metal oxide represented by the above chemical formula 3 is an oxide obtained by mixing lithium (Li) with the transition metals nickel (Ni), cobalt (Co), and manganese (Mn), characterized in that the nickel (Ni) content is 60% or more of the total mole fraction of the transition metals (i.e., 60 mol% or more).

[0107] The three-component NCM-based cathode active material, primarily composed of nickel (Ni), cobalt (Co), and manganese (Mn), combines the advantages of LiNiO2 (LNO), LiCoO2 (LCO), and LiMn2O4 (LMO).

[0108] Such positive electrode active materials include LiNi 0.95 Co 0.03 Mn 0.02 O2, LiLiLi 0.9 Co 0.05 Mn 0.05 O2, LiLiLi 0.9 Co 0.6 Mn 0.4 O2, LiLiLi 0.9 Co 0.05 Mn 0.05 O2, Lithium 0.85 Co 0.1 Mn 0.05 O2, LiLiLi 0.85 Co 0.05 Mn 0.1 O2, LiLiLi 0.8 Co 0.1 Mn 0.1 O2, LiLiLi 0.75 Co 0.2 Mn 0.15 O2, LiLiLi 0.7 Co 0.2 Mn0.1 O2, LiLiLi 0.7 Co 0.15 Mn 0.15 O2, LiLiLi 0.7 Co 0.1 Mn 0.2 O2, LiLiLi 0.7 Co 0.2 Mn 0.1 O2, LiLiLi 0.6 Co 0.2 Mn 0.2 O2, LiLiLi 0.6 Co 0.2 Mn 0.1 Al 0.1 O2, LiLiLi 0.6 Co 0.2 Mn 0.15 Al 0.05 O2 and LiNi 0.7 Co 0.1 Mn 0.1 Al 0.1 One or more types of O2 are listed.

[0109] Furthermore, the above-mentioned positive electrode active material may be included in an amount of 85 parts by weight or more based on 100 parts by weight of the entire positive electrode active layer. Specifically, the above-mentioned positive electrode active material may be included in an amount of 90 parts by weight or more, 93 parts by weight or more, or 95 parts by weight or more based on 100 parts by weight of the entire positive electrode active layer.

[0110] Furthermore, the positive electrode active layer may, if necessary, further contain conductive materials, binders, and other additives along with the positive electrode active material.

[0111] In this case, the conductive material is used to improve the electrical performance of the positive electrode, and may be one of those commonly used in the industry. Specifically, it may include graphite substances such as natural graphite and artificial graphite; carbon blacks such as acetylene black, Denka black, Ketjen black, Super P, channel black, furnace black, lamp black, and thermal black; graphene; and carbon nanotubes.

[0112] Furthermore, the conductive material may be included in amounts of 0.1 to 5 parts by weight based on 100 parts by weight of the entire positive electrode active layer. Specifically, the conductive material may be included in amounts of 0.1 to 4 parts by weight, 2 to 4 parts by weight, 1.5 to 5 parts by weight, 0.5 to 3.5 parts by weight, 1 to 3 parts by weight, 0.1 to 2.5 parts by weight, 0.1 to 2 parts by weight, or 0.1 to 1 part by weight based on 100 parts by weight of the entire positive electrode active layer.

[0113] Furthermore, the binder plays a role in binding the positive electrode active material, positive electrode additive, and conductive material together, and any binder having this function can be used without particular limitation. Specifically, the binder may include one or more resins selected from polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, and copolymers thereof. For example, the binder may include polyvinylidene fluoride (PVDF).

[0114] Furthermore, the above binder may be included in amounts of 0.1 to 5 parts by weight based on 100 parts by weight of the entire positive electrode active layer. Specifically, the above binder may be included in amounts of 0.1 to 4 parts by weight, 2 to 4 parts by weight, 1.5 to 5 parts by weight, 0.5 to 3.5 parts by weight, 1 to 3 parts by weight, 0.1 to 2.5 parts by weight, 0.1 to 2 parts by weight, or 0.1 to 1 part by weight based on 100 parts by weight of the entire positive electrode active layer.

[0115] The total thickness of the positive electrode active layer described above is not particularly limited, but specifically it may be 50 μm to 300 μm. More specifically, the total thickness of the positive electrode active layer may be 100 μm to 200 μm, 80 μm to 150 μm, 120 μm to 170 μm, 150 μm to 300 μm, 200 μm to 300 μm, or 150 μm to 190 μm.

[0116] Furthermore, the positive electrode can be made of a material that has high conductivity without inducing chemical changes in the battery, as the positive electrode current collector. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, etc., can be used, and in the case of aluminum or stainless steel, materials that have been surface-treated with carbon, nickel, titanium, silver, etc., may be used. The average thickness of the current collector can be appropriately set between 3 μm and 500 μm, taking into consideration the conductivity and total thickness of the manufactured positive electrode.

[0117] Furthermore, the negative electrode, like the positive electrode, includes a negative electrode active layer containing a negative electrode active material on at least one surface of the negative electrode current collector.

[0118] The above-mentioned negative electrode active layer contains a silicon-based negative electrode active material as a negative electrode active material in order to achieve electrical activity through a reversible oxidation-reduction reaction during the charging and discharging of the battery.

[0119] The silicon-based negative electrode active material mentioned above refers to a material whose main component is silicon atoms. This silicon-based negative electrode active material can reversibly adsorb and release a large amount of lithium during the charging and discharging of a secondary battery, and has a high theoretical maximum capacity of approximately 4020 mAh / g (9800 mAh / cc, specific gravity 2.23). Therefore, it has the advantage of being able to achieve high energy density and / or high capacity of the negative electrode.

[0120] Examples of silicon-based negative electrode active materials include silicon (Si), silicon carbide (SiC), and silicon oxide (SiO₂). r However, this may include one or more of the following (0.8 ≤ r ≤ 2.5).

[0121] For example, the silicon-based negative electrode active material may include silicon carbide (SiC). The silicon carbide may refer to silicon carbide in which carbon atoms and silicon atoms are chemically bonded in a 1:1 atomic ratio. In some cases, it may be a carbon layer formed on the surface of pure silicon (pure Si), or a composite of pure silicon (pure Si) and graphite mixed in a 1:1 molar ratio. The silicon carbide (SiC) may contain carbon atoms and may also include pure silicon (pure Si) or silicon oxide (SiO₂).r Compared to other batteries, secondary batteries have the advantage of a relatively low volume expansion rate and high conductivity during charging and discharging, resulting in superior performance in terms of lifespan and output.

[0122] Furthermore, the silicon-based anode active material may be included in an amount of 85 parts by weight or more based on 100 parts by weight of the entire anode active layer, specifically in an amount of 90 parts by weight or more, 93 parts by weight or more, or 95 parts by weight or more.

[0123] On the other hand, the negative electrode active layer according to the present invention may selectively further contain conductive materials, binders, and other additives as needed, along with the silicon-based negative electrode active material, which is the main component.

[0124] The above conductive material may contain, but is not limited to, one or more types of carbon black such as acetylene black or Ketjen black; carbon nanotubes; or carbon fibers.

[0125] For example, the negative electrode active layer may contain carbon black, carbon nanotubes, carbon fibers, etc., individually or in combination as conductive materials.

[0126] The content of the conductive material can be 0.1 to 10 parts by weight per 100 parts by weight of the entire negative electrode active layer, and specifically, it can be 0.1 to 8 parts by weight, 0.1 to 5 parts by weight, 0.1 to 3 parts by weight, 2 to 6 parts by weight, or 0.5 to 2 parts by weight. By controlling the content of the conductive material within the above range, the present invention can prevent an increase in the resistance of the negative electrode and a decrease in charging capacity due to a low content of conductive material, and can suppress problems such as a decrease in the content of the negative electrode active material and a decrease in charging capacity due to an excessive amount of conductive material, or a decrease in rapid charging characteristics due to an increase in the loading amount of the negative electrode active layer.

[0127] Furthermore, the above-mentioned binder is a component that assists in the bonding of silicon-based negative electrode active material to conductive materials and to the current collector, and can be appropriately applied within a range that does not degrade the electrical properties of the electrode. Specifically, the above-mentioned binder may include one or more selected from vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber (SBR), and fluororubber.

[0128] The binder content may be 0.1 to 10 parts by weight per 100 parts by weight of the entire negative electrode active layer, specifically 0.1 to 8 parts by weight, 0.1 to 5 parts by weight, 0.1 to 3 parts by weight, or 2 to 6 parts by weight. By controlling the binder content in the negative electrode active layer within the above range, the present invention can prevent a decrease in the adhesive strength of the active layer due to a low binder content or a decrease in the electrical properties of the electrode due to an excessive amount of binder.

[0129] Furthermore, the average thickness of the negative electrode active layer can be 100 μm to 300 μm, specifically 100 μm to 250 μm, 100 μm to 250 μm, or 130 μm to 190 μm. The present invention can improve energy density by adjusting the average thickness of the negative electrode active layer to the above range.

[0130] Furthermore, the negative electrode current collector is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery. For example, copper, stainless steel, nickel, titanium, and calcined carbon can be used, and in the case of copper or stainless steel, those with surface treatment with carbon, nickel, titanium, silver, etc., may be used. The average thickness of the negative electrode current collector can be appropriately applied from 1 μm to 500 μm, taking into consideration the conductivity and total thickness of the negative electrode to be manufactured.

[0131] On the other hand, the separation membrane interposed between the positive and negative electrodes of each unit cell is an insulating thin film having high ion permeability and mechanical strength, and is not particularly limited as long as it is commonly used in the industry, but specifically, it can contain one or more polymers from among chemically resistant and hydrophobic polypropylene, polyethylene, or polyethylene-propylene copolymer. The above separation membrane may take the form of a porous polymer substrate such as a sheet or nonwoven fabric containing the above polymer, and in some cases, it may take the form of a composite separation membrane in which organic or inorganic particles are coated on the above porous polymer substrate with an organic binder. Furthermore, the above separation membrane may have an average pore diameter of 0.01 μm to 10 μm and an average thickness of 5 μm to 300 μm.

[0132] Furthermore, the lithium secondary battery according to the present invention is not particularly limited, but can be applied in various forms such as cylindrical, prismatic, pouch, or coin-type depending on the application. A lithium secondary battery according to one embodiment of the present invention may be a pouch-type secondary battery.

[0133] The present invention will be described in more detail below with reference to examples and experimental examples.

[0134] However, the following examples and experimental cases are illustrative of the present invention, and the content of the present invention is not limited to the following examples and experimental cases.

[0135] <Examples 1-7 and Comparative Examples 1-7: Production of Electrolyte Compositions for Lithium Secondary Batteries> As non-aqueous organic solvents, linear ester solvents represented by <Structural Formula 11> and <Structural Formula 13>, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and fluoroethylene carbonate (FEC) were prepared, and LiPF6 was prepared as the lithium salt.

[0136] Furthermore, compounds represented by chemical formula 1, which are electrolyte additives, were prepared, specifically those represented by structural formulas 6 and 10, respectively. Compounds represented by structural formulas 17 and 18 were also prepared separately as a comparative group of the above compounds.

[0137] Furthermore, LiBOB, LiODFB, LiDFOP, vinylene carbonate (VC), 1,3-propanesultone (PS), ethylene sulfate (ESa), and fluoroethylene carbonate (FEC) were prepared as additional electrolyte additives.

[0138] The prepared LiPF6 was added to a non-aqueous organic solvent at 30°C to 40°C to achieve a molar concentration (M), and an electrolyte additive was added to produce an electrolyte composition.

[0139] At this time, the types and contents of non-aqueous organic solvents used in the electrolyte composition were adjusted as shown in Table 1, and the types and contents of electrolyte additives are as shown in Table 2. Here, the contents of each component of the non-aqueous organic solvent were adjusted by volume percentage (i.e., volume %) based on the total volume of the non-aqueous organic solvent. In addition, the compounds represented by chemical formula 1 contained in the electrolyte additives and the additional electrolyte additives were adjusted by weight percentage (weight %) based on the total weight of the electrolyte composition.

[0140] [Table 1]

[0141] [Table 2]

[0142] <Examples 8-14 and Comparative Examples 8-14: Manufacturing of Lithium Secondary Batteries> LiNi with a particle size of 5 μm is used as the positive electrode active material. 0.86 Co 0.05 Mn 0.07 Al 0.02 O2 was prepared and mixed with polyvinylidene fluoride and N-methylpyrrolidone (NMP) in a weight ratio of 94:3:3 as a carbon-based conductive material and binder to produce a cathode slurry with a solid content of 45%. The produced cathode slurry was cast onto an aluminum sheet. After drying in a vacuum oven at 120°C, it was rolled to produce a cathode with a cathode active layer with a thickness of 160 μm.

[0143] Separately, silicon carbide (SiC, average particle size: approximately 3 ± 0.5 μm) was prepared as a silicon-based negative electrode active material. 97 parts by weight of the prepared silicon-based negative electrode active material and 3 parts by weight of styrene-butadiene rubber (SBR) were mixed with water to produce a negative electrode slurry with a solid content of 40%. The negative electrode slurry was cast onto a copper sheet, dried in a vacuum oven at 130°C, and then rolled to produce a negative electrode with a negative electrode active layer with a thickness of 180 μm.

[0144] A separation membrane made of 18 μm polypropylene was interposed between the positive and negative electrodes obtained above, and after inserting them into a case, the electrolyte compositions previously prepared in Examples 1-7 and Comparative Examples 1-7 were injected to assemble the lithium secondary battery, as shown in Table 3 below.

[0145] Initial charging was performed on each assembled lithium secondary battery. Specifically, the lithium secondary batteries were initially charged to a charging termination voltage of 4.2V at 55±2℃ to produce activated lithium secondary batteries.

[0146] [Table 3]

[0147] <Example of experiment> To evaluate the high-temperature safety of the electrolyte composition for lithium secondary batteries according to the present invention and the lithium secondary battery containing it, the following experiments were conducted.

[0148] 1) Measurement of exothermic onset temperature and heat flow rate between the negative electrode active material and the electrolyte composition. Each lithium secondary battery produced in Examples 8-14 and Comparative Examples 8-14 was fully charged to 4.25V (SOC 100%) under CC-CV conditions at a rate of 0.5C at 25°C, and the fully charged lithium secondary batteries were disassembled. In the disassembled lithium secondary batteries, silicon carbide (SiC), which is the negative electrode active material, and the electrolyte composition were weighed and mixed in a 1:0.5 weight ratio.

[0149] The prepared mixture was poured into the sample container of a differential scanning calorimeter (DSC) to prepare the sample, and the exothermic onset temperature and heat flow rate of the prepared sample were measured. During this process, the temperature change and heat flow rate of the sample were measured in the range of 100°C to 500°C while increasing the temperature at a heating rate of 10 ± 0.1°C / min.

[0150] Based on the measured results, the heat flow rate between the negative electrode active material and the electrolyte composition in each lithium secondary battery was evaluated. If there were two or more effective heat flow rate peaks within the temperature range of 100°C to 500°C in the measured results, the value of the peak showing the largest heat flow rate was determined to be the heat flow rate. The results are shown in Table 4 and Figure 1 below.

[0151] 2) Evaluation of thermal runaway tests The lithium secondary batteries produced in Examples 8-14 and Comparative Examples 8-14 were each charged at 25°C under constant current (CC) conditions, maintaining a current of 1.25A until they reached 4.2V, and the voltage was maintained at 4.2V. After charging was complete, they were activated by discharging under constant current (CC) conditions, maintaining a current of 1.25A until they reached 2.85V. Subsequently, each activated lithium secondary battery was left to rest at 25°C for 6 hours.

[0152] Subsequently, the batteries were fully charged (SOC 100%) under constant current (CC) conditions, maintaining 1.25A until they reached 4.2V at 25°C. A thermal runaway test was then performed using an accelerated rate calorimetry (ARC). The ARC used was a product of Thermal Hazard Technology (THT), and the thermal runaway test was conducted using the heat-wait-search (HWS) method. In the HWS method, the temperature of the insulated oven chamber in which each lithium secondary battery was installed was increased from 50°C to 190°C at a rate of 10°C / min, followed by a 10-minute wait. If a lithium secondary battery showed a temperature change of 0.02°C / min or more during the 10-minute wait period, it was recognized that self-heating corresponding to thermal runaway (TR) was progressing, and no additional thermal energy was applied thereafter, allowing the temperature to change due to the self-heating of each secondary battery. After the secondary battery self-heated, its self-heating profile was measured, and the maximum temperature of the secondary battery was calculated from the measured self-heating profile. The results are shown in Table 4 below.

[0153] [Table 4]

[0154] The electrolyte composition for lithium secondary batteries and the lithium secondary battery containing the same according to the present invention exhibit excellent high-temperature safety.

[0155] Specifically, the electrolyte compositions of the examples showed a high onset temperature (heat generation onset temperature) of 255°C or higher, more specifically 275°C or higher, when exposed to high temperatures, due to the reaction between the negative electrode active material and the electrolyte composition. Furthermore, the electrolyte compositions of the examples showed a low heat flow rate in the range of approximately 15 W / g or less, and the lithium secondary battery containing the above electrolyte composition showed a low maximum temperature in the range of 400°C or lower during thermal runaway testing.

[0156] This means that the electrolyte composition produced in the examples effectively suppresses the reaction between the negative electrode active material and the electrolyte composition when exposed to high temperatures, and improves the heat generated by the reaction between the negative electrode active material and the electrolyte composition.

[0157] These results show that the electrolyte composition for lithium secondary batteries according to the present invention not only has excellent electrical performance, but also has an excellent effect in adjusting the heat flow rate between the negative electrode active material and the electrolyte composition to a low range, thereby improving safety issues related to the negative electrode active material at high temperatures.

[0158] While preferred embodiments of the present invention have been described above with reference to those skilled in the art or those with ordinary knowledge in the art, it will be understood that the present invention can be modified and altered in various ways without departing from the claims set forth below.

[0159] Therefore, the technical scope of the present invention is not limited to what is described in the summary of the invention in the specification, but may be defined by the claims.

Claims

1. It contains a lithium salt, an electrolyte additive, and a non-aqueous organic solvent. The aforementioned non-aqueous organic solvent contains 60% or more by volume and less than 100% by volume of a fluorine-substituted linear ester solvent. An electrolyte composition for lithium secondary batteries that, when measuring the heat flow rate of a mixture containing a 100% charged negative electrode active material and an electrolyte composition in a weight ratio of 1:0.5, exhibits a heat flow rate of 50.0 W / g or less within the range of 250°C to 400°C.

2. The electrolyte composition for lithium secondary batteries according to claim 1, wherein the heat flow rate is in the range of 0.5 W / g to 30 W / g.

3. The electrolyte additive contains one or more compounds represented by the following chemical formula 1: 【Chemistry 1】 In the aforementioned chemical formula 1, R １ and R ２ These are, respectively, a fluoro group or C １－１０ It is a fluorinated alkylene group, p is an integer between 0 and 4. The electrolyte composition for lithium secondary batteries according to claim 1, wherein q is an integer from 1 to 10.

4. The electrolyte composition for lithium secondary batteries according to claim 3, wherein the compound represented by chemical formula 1 comprises one or more acrylic compounds represented by the following structural formulas 1 to 10. 【Chemistry 2】 。

5. The electrolyte composition for lithium secondary batteries according to any one of claims 1 to 3, wherein the electrolyte additive is included in an amount exceeding 0% by weight and not exceeding 5% by weight, based on the total weight of the electrolyte composition.

6. The electrolyte composition for lithium secondary batteries according to any one of claims 1 to 3, wherein the electrolyte additive further comprises one or more cyclic carbon compounds selected from vinylene carbonate (VC), 1,3-propanesultone (PS), ethylene sulfate (ESa), propylene sulfate (PSa), and butylene sulfate (BSa).

7. The electrolyte composition for lithium secondary batteries according to claim 6, wherein the cyclic carbon compound is contained in an amount of 10 parts by weight or more and less than 50 parts by weight per 100 parts by weight of the total electrolyte additive.

8. The fluorine-substituted linear ester solvent contains one or more compounds represented by the following chemical formula 2: 【Transformation 3】 In the aforementioned chemical formula 2, R ３ is hydrogen or C １～６ It is an alkyl group, R ４ and R ５ These are hydrogen, a fluoro group, or C, respectively. １－１０ It is a fluorinated alkylene group, The electrolyte composition for lithium secondary batteries according to any one of claims 1 to 3, wherein m is an integer from 1 to 6.

9. The electrolyte composition for lithium secondary batteries according to any one of claims 1 to 3, wherein the fluorine-substituted linear ester solvent comprises one or more compounds represented by the following structural formulas 11 to 16. 【Chemistry 4】

10. The electrolyte composition for lithium secondary batteries according to any one of claims 1 to 3, wherein the non-aqueous organic solvent further comprises one or more carbonate-based solvents selected from ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).

11. The electrolyte composition for lithium secondary batteries according to claim 10, wherein the carbonate-based solvent is contained in an amount of more than 0% and 40% or less by weight relative to the total weight of the non-aqueous organic solvent.

12. The aforementioned lithium salt is Li as a cation ＋ comprising アニオンとして、BF ４ － B １０ Cl １０ － Clo ４ － Hello ４ － Alcl ４ － PF ６ － 、SbF ６ － 、AsF ６ － BF ２ C ２ O ４ － B (C ２ O ４ ) ２ － PF ４ C ２ O ４ － PF ２ C ４ O ８ － 、(CF ３ ) ２ Pf ４ － 、(CF ３ ) ３ Pf ３ － 、(CF ３ ) ４ Pf ２ － 、(CF ３ ) ５ Pf － 、(CF ３ ) ６ P － 、(C ２ O ４ ) ２ Pf ２ － CF ３ So ３ － C ４ F ９ So ３ － CF ３ CF ２ So ３ － , (CF ３ SO ２ ) ２ N － , (FSO ２ ) ２ N － , CF ３ CF ２ (CF ３ ) ２ CO － , (CF ３ SO ２ ) ２ CH － , (SF ５ ) ３ C － , (CF ３ SO ２ ) ３ C － , CF ３ (CF ２ ) ７ SO ３ － , CF ３ CO ２ － , CH ３ CO ２ － , SCN － , (CF ３ CF ２ SO ２ ) ２ N － , and ((C(CN)) ２ NC(CF ３ ))N － The electrolyte composition for a lithium secondary battery according to any one of claims 1 to 3, comprising one or more selected from the above.

13. The negative electrode active material is silicon (Si), silicon carbide (SiC), and silicon oxide (SiO2). ｒ The electrolyte composition for lithium secondary batteries according to any one of claims 1 to 3, wherein the silicon-based negative electrode active material is one or more of the following (provided that 0.8 ≤ r ≤ 2.5).

14. An electrode assembly including a positive electrode, a negative electrode, and a separation membrane provided between the positive electrode and the negative electrode, A lithium secondary battery comprising an electrolyte composition according to any one of claims 1 to 3, which is impregnated into the electrode assembly.

15. The positive electrode is provided on at least one surface of the positive electrode current collector and includes a positive electrode active layer containing a positive electrode active material represented by the following chemical formula 3. [Chemical formula 3] Li ｘ [Ni ｙ Co ｚ Mn ｗ M １ ｖ ]O ２ In the aforementioned chemical formula 3, M １ is one or more elements from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo. The lithium secondary battery according to claim 14, wherein x, y, z, w, and v are 0.9 ≤ x ≤ 1.30, 0.6 ≤ y < 1, 0 < z ≤ 0.2, 0 < w ≤ 0.2, 0 ≤ v ≤ 0.1, and y + z + w + v = 1, respectively.

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