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

Abstract

The present invention relates to an electrolyte composition for a lithium secondary battery. The electrolyte composition for a lithium secondary battery comprises a fluorine-substituted linear ester-based solvent and a fluorine-substituted acrylic additive as a non-aqueous organic solvent and an electrolyte additive, respectively, and thus can uniformly form a solid electrolyte membrane layer (SEI layer), having high lithium-ion conductivity and excellent heat resistance, on the surface of a negative electrode when the lithium secondary battery is activated. Consequently, the reactivity between a negative electrode active material and the electrolyte composition is remarkably lowered, such that the temperature (that is, the exothermic onset temperature) at which heat generation between the negative electrode active material and the electrolyte composition begins increases, and thus heat generation caused by negative electrode deterioration or the like can be suppressed. Furthermore, a lithium secondary battery comprising the electrolyte composition can minimize side reactions of the electrolyte composition, which occur on the surface of the negative electrode when exposed to high temperatures, and thus has the advantage of exhibiting excellent high-temperature safety.

Description

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

[0001] The present invention relates to an electrolyte composition having improved high-temperature safety and a lithium secondary battery comprising the same.

[0002] This application claims the benefit of priority from Republic of Korea Patent Application No. 10-2024-0054519, dated April 24, 2024, the entire contents of which are incorporated herein by reference.

[0003]

[0004] Recently, lithium secondary batteries are widely used not only in small devices such as portable electronic devices, but also in medium and large devices such as battery packs for hybrid or electric vehicles or power storage devices.

[0005] These lithium secondary batteries are manufactured by applying and drying a composition containing an electrode active material to a current collector in an appropriate thickness and length, or by forming the electrode active material itself into a film shape to produce a positive electrode and a negative electrode, winding or laminating them together with an insulator, a separator, in between to produce an electrode assembly, and then placing the electrode assembly in a can or similar container and injecting an electrolyte.

[0006] As demand for lithium secondary batteries increases, research to improve the safety of secondary batteries is also actively being conducted (see Korean Patent Publication No. 10-2022-0105936).

[0007]

[0008] The present invention aims to provide an electrolyte composition capable of more effectively suppressing side reactions with an electrolyte occurring on the surface of a negative electrode when a lithium secondary battery is exposed to high temperatures, and a lithium secondary battery including the same.

[0009]

[0010] To solve the above-mentioned problem,

[0011] The present invention,

[0012] Contains lithium salt, electrolyte additive and non-aqueous organic solvent,

[0013] The above non-aqueous organic solvent contains a linear ester solvent substituted with fluorine in a range of 60% by volume or more and less than 100% by volume,

[0014] An electrolyte composition is provided which exhibits a heat flux of 50.0 W / g or less within a range of 250°C to 400°C when measuring a heat flux of a mixture containing a negative electrode active material and an electrolyte composition at a weight ratio of 1:0.5 with a 100% state of charge.

[0015]

[0016] For example, the electrolyte composition may exhibit a heat flux in the range of 0.5 W / g to 30 W / g.

[0017] Here, the electrolyte additive may include at least one compound represented by the following chemical formula 1:

[0018] [Chemical Formula 1]

[0019]

[0020] In the above chemical formula 1,

[0021] R1 and R2 are each a fluoro group or C 1-10 is a fluorinated alkylene group,

[0022] p is an integer from 0 to 4,

[0023] q is an integer from 1 to 10.

[0024]

[0025] Specifically, the compound represented by the above chemical formula 1 may include at least one of the acrylic compounds represented by the following <structural formula 1> to <structural formula 10>:

[0026]

[0027]

[0028] Additionally, the electrolyte additive may be included in an amount of more than 0 wt% and less than or equal to 5 wt% based on the total weight of the electrolyte composition.

[0029] In addition, the electrolyte additive may further include 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).

[0030] The above-mentioned cyclic carbon compound 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.

[0031] In addition, the linear ester solvent substituted with fluorine may include at least one compound represented by the following chemical formula 2:

[0032] [Chemical Formula 2]

[0033]

[0034] In the above chemical formula 2,

[0035] R3 is hydrogen or C 1~6 is an alkyl group,

[0036] R4 and R5 are each hydrogen, fluoro or C 1-10 is a fluorinated alkylene group,

[0037] m is an integer from 1 to 6.

[0038]

[0039] Specifically, the linear ester solvent substituted with fluorine may include at least one of the compounds represented by the following structural formulas 11 to 16:

[0040] .

[0041] In addition, the non-aqueous organic solvent may include at least one carbonate solvent 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).

[0042] In this case, the carbonate solvent may be included in a range of more than 0% by volume and less than 40% by volume based on the total weight of the non-aqueous organic solvent.

[0043] Meanwhile, the lithium salt is Li as a cation. + , and contains BF4 as anion. - , 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:

[0044] In addition, the negative electrode active material is silicon (Si), silicon carbide (SiC), and silicon oxide (SiO r , but may be at least one silicon-based negative electrode active material (0.8≤r≤2.5).

[0045]

[0046] Furthermore, the present invention,

[0047] An electrode assembly comprising an anode, a cathode, and a separator provided between the anode and the cathode; and

[0048] A lithium secondary battery is provided, comprising an electrolyte composition according to the present invention described above, which is impregnated into the electrode assembly.

[0049] Here, the positive electrode is provided on at least one surface of the positive electrode current collector and may include a positive electrode active layer including a positive electrode active material represented by the following chemical formula 3:

[0050] [Chemical Formula 3]

[0051] Li x [Ni y Co z Mn w M 1 v ]O2

[0052] In the above chemical formula 3,

[0053] M 1 is at least one element among 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,

[0054] x, y, z, w, and v are 0.9≤x≤1.30, 0.6≤y<1, 0, respectively. <z≤0.2, 0<w≤0.2, 0≤v≤0.1이되, y+z+w+v=1이다.

[0055]

[0056] The electrolyte composition according to the present invention can uniformly form a solid electrolyte membrane layer (SEI layer) having high lithium ion conductivity and excellent heat resistance on the surface of an anode when a lithium secondary battery is activated. Accordingly, the reactivity between the anode active material and the electrolyte composition is significantly reduced, so that the temperature at which heat generation begins between them (i.e., heat generation onset temperature) increases, thereby suppressing heat generation due to anode deterioration, etc. In addition, a lithium secondary battery including the electrolyte composition can minimize side reactions of the electrolyte composition occurring on the surface of the anode when exposed to high temperatures, and thus has the advantage of excellent high-temperature safety.

[0057]

[0058] The following drawings attached to this specification illustrate embodiments of the present invention and, together with the detailed description of the invention described below, serve to further understand the technical idea of ​​the present invention, and therefore, the present invention should not be interpreted as being limited to matters described in such drawings.

[0059] Figure 1 is a graph showing the heat flow of an electrolyte composition depending on whether an electrolyte additive according to the present invention is used.

[0060]

[0061] The present invention can be modified in various ways and has many embodiments, and specific embodiments will be described in detail in the detailed description.

[0062] In the present invention, it should be understood that terms such as “include” or “have” are intended to specify the presence of a feature, number, step, operation, component, part or combination thereof described in the specification, but do not exclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts or combinations thereof.

[0063] Additionally, in the present invention, when a part such as a layer, film, region, or plate is described as being "on" another part, this includes not only cases where it is "directly above" the other part, but also cases where there is another part in between. Conversely, when a part such as a layer, film, region, or plate is described as being "under" another part, this includes not only cases where it is "directly below" the other part, but also cases where there is another part in between. Furthermore, in the present application, "on" may include cases where it is placed below as well as above.

[0064] In addition, in the present invention, "comprising as a main component" may mean comprising 50 wt% or more (or 50 vol% or more), 60 wt% or more (or 60 vol% or more), 70 wt% or more (or 70 vol% or more), 80 wt% or more (or 80 vol% or more), 90 wt% or more (or 90 vol% or more), or 95 wt% or more (or 95 vol% or more) of a defined component with respect to the total weight (or total volume). For example, "comprising as a non-aqueous organic solvent a linear ester solvent as a main component" may mean comprising 50 vol% or more, 60 vol% or more, 70 vol% or more, 80 vol% or more, 90 vol% or more, or 95 vol% or more of the linear ester solvent with respect to the total volume of the non-aqueous organic solvent. In some cases, it may also mean that the entire non-aqueous organic solvent is composed of a linear ester solvent and comprises 100 vol%.

[0065]

[0066] Lithium secondary batteries operate at high operating voltages, so aqueous electrolytes, which are highly reactive with lithium, cannot be used. Therefore, organic electrolytes are typically used. These organic electrolytes are prepared by dissolving lithium salts in organic solvents. These organic solvents are stable at high voltages and utilize materials with high ionic conductivity, high dielectric constant, and low viscosity.

[0067] Typically, polar non-aqueous solvents of the carbonate series are used as these organic solvents, and the carbonate series non-aqueous solvents cause an irreversible reaction in which an excessive amount of charge is consumed due to a side reaction between the negative / positive electrode and the electrolyte during the initial charging of a lithium secondary battery. The irreversible reaction forms a passivation layer, such as a solid electrolyte interface layer (SEI layer), on the surface of the negative electrode, and the SEI layer prevents electrolyte decomposition on the surface of the negative electrode during charge and discharge and functions as an ion tunnel. Therefore, the higher the stability and lower the resistance of the SEI layer, the longer the life of the lithium secondary battery.

[0068] Meanwhile, various additives are used in the electrolyte to stabilize the SEI layer, and since the SEI layer formed using conventional general additives is easily deteriorated at high temperatures, the stability of the SEI layer formed by applying conventional general additives is reduced at high temperatures.

[0069] Taking this into consideration, the present invention provides a technology that can further enhance the high-temperature safety of a lithium secondary battery by suppressing side reactions with the electrolyte that occur on the surface of the negative electrode at high temperatures.

[0070] Hereinafter, the present invention will be described in more detail with reference to the attached drawings.

[0071]

[0072] electrolyte composition

[0073] The present invention,

[0074] Contains lithium salt, electrolyte additive and non-aqueous organic solvent,

[0075] The above non-aqueous organic solvent contains a linear ester solvent substituted with fluorine in a range of 60% by volume or more and less than 100% by volume,

[0076] An electrolyte composition is provided which exhibits a heat flux of 50.0 W / g or less within a range of 250°C to 400°C when measuring a heat flux of a mixture containing a negative electrode active material and an electrolyte composition at a weight ratio of 1:0.5 with a 100% state of charge.

[0077]

[0078] The electrolyte composition according to the present invention is a liquid electrolyte, and can uniformly form a solid electrolyte membrane layer (SEI layer) having high lithium ion conductivity and excellent heat resistance on the surface of the negative electrode when a lithium secondary battery is activated. Accordingly, when the lithium secondary battery is charged, the reactivity between the lithium ions inserted into or desorbed from the negative electrode active material and the electrolyte composition is significantly reduced, so that the temperature at which heat generation begins between them (i.e., heat generation onset temperature) increases, thereby suppressing heat generation due to negative electrode deterioration, etc. In addition, a lithium secondary battery including the electrolyte composition can minimize side reactions of the electrolyte composition occurring on the surface of the negative electrode when exposed to high temperatures, and thus has the advantage of excellent high-temperature safety.

[0079] To this end, the electrolyte composition includes a lithium salt, an electrolyte additive, and a non-aqueous organic solvent. The lithium salt, the electrolyte additive, and the non-aqueous organic solvent may have a predetermined composition.

[0080] Specifically, the electrolyte additive may include an organic compound, and the organic compound may be an acrylic compound substituted with fluorine. Specifically, the electrolyte additive may include at least one of the compounds represented by the following chemical formula 1:

[0081] [Chemical Formula 1]

[0082]

[0083] In the above chemical formula 1,

[0084] R1 and R2 are each a fluoro group or C 1-10 is a fluorinated alkylene group,

[0085] p is an integer from 0 to 4, and

[0086] q is an integer from 1 to 10.

[0087]

[0088] Specifically, in the above chemical formula 1,

[0089] R1 and R2 are each a fluoro group or a fluoromethyl group,

[0090] p is an integer from 0 to 2,

[0091] q is an integer between 3 and 6.

[0092]

[0093] The present invention can minimize side reactions of an electrolyte composition when exposed to high temperatures by increasing the heat resistance and uniformity of a film formed on the surface of an anode, i.e., an SEI layer. Specifically, the SEI layer is formed on the surface of the electrode by the irreversible decomposition of an electrolyte before lithium ions are inserted into an anode active material. The SEI layer has the property of allowing lithium ions to pass through, but has the property of blocking the movement of electrons. Therefore, once the SEI layer is formed, electrolyte decomposition due to electron movement between the electrode and the electrolyte is suppressed, and only the selective insertion and desorption of lithium ions are possible. In other words, the SEI layer functions as a protective film that prevents the electrolyte from continuously decomposing, and is therefore a very important element in lithium secondary batteries.

[0094] The above SEI layer is composed of Li2CO3, LiF, and Li2O formed by side reactions of electrolyte components during activation of a secondary battery. In addition, additives included in the electrolyte can participate in the side reactions forming the SEI layer and control the properties and performance of the SEI layer.

[0095] In this regard, fluorine-containing compounds that have been conventionally used as electrolyte additives have a structure that does not produce fluorine-containing side-reactants with high heat resistance during the activation of secondary batteries. Specifically, conventional electrolyte additives have a fluorinated alkyl group (e.g., -CF3, -CF2CF3, - CF2CF2CF3, etc.) in which all hydrogens of the hydrocarbon group are replaced with fluorine atoms. The fluorinated alkyl group includes a CF bond and a C-C bond. The CF bond has a high bond energy compared to a C-H bond and is not easily cleaved by heat. In addition, in the skeleton of the C-C bond, -CF2- also has a higher bond energy than -CH2- and has the characteristic that rotation of the carbon chain is difficult. Therefore, the electrolyte additives have a role of increasing the heat resistance of the components themselves included in the electrolyte because it is difficult to form side-reactants containing fluorine atoms during the activation process of low-energy secondary batteries.

[0096] 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 an oxygen atom of the acrylate group. At this time, the alkyl group has a chemical structure in which a carbon atom located at the terminal is partially substituted with a fluorine element. Therefore, when a secondary battery is activated, some of the included C-H bonds can be easily broken, so that it can have higher reactivity compared to conventional electrolyte additives. That is, the carbon atom located at the terminal of the alkyl group can relatively easily undergo defluorination of the C-F bond, which has relatively low reactivity. The defluorination reactants thus generated (e.g., fluorine ions, activated compounds prior to defluorination, etc.) react with lithium ions to form LiF, and can also be directly inserted into and participate in the SEI layer, thereby realizing high ionic conductivity and excellent heat resistance of the SEI layer.

[0097] The compound represented by chemical formula 1, which can provide excellent ion conductivity and heat resistance to the SEI layer upon activation, may include at least one of the acrylic compounds represented by the following <structural formula 1> to <structural formula 10>:

[0098]

[0099]

[0100] The compounds of the above <Structural Formula 1> to <Structural Formula 10> have a characteristic that they contain a vinyl group within the acrylate group, and thus are easily decomposed upon activation of the secondary battery, thereby participating in the formation of the SEI layer. In addition, the 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, and thus can uniformly form an SEI layer with excellent ion conductivity and heat resistance upon activation of the secondary battery.

[0101] For example, the electrolyte composition including the compound represented by the above chemical formula 1 may have an onset temperature of 250°C or higher, i.e., a temperature at which heat generation of the negative active material begins when exposed to high temperature during differential scanning calorimetry analysis. Specifically, the onset temperature may be 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, more than 280°C and less than or equal to 360°C, more than 290°C and less than or equal to 350°C, or 300°C to 340°C.

[0102] In addition, the compound represented by the above chemical formula 1 may be included in the electrolyte composition in a predetermined content. Specifically, the compound represented by the above chemical formula 1 may be included in a range of more than 0 wt% and less than 5 wt% based on the total weight of the electrolyte composition, and more specifically, more than 0 wt% and less than 4 wt%; more than 0 wt% and less than 3 wt%; more than 0 wt% and less than 2 wt%; more than 0 wt% and less than 1 wt%; more than 0 wt% and less than 0.9 wt%; 0.1 wt% to 5 wt%; 0.1 wt% to 4 wt%; 0.1 wt% to 3 wt%; 0.1 wt% to 2 wt%; 0.1 wt% to 1 wt%; 0.5 wt% to 4 wt%; 1 wt% to 5 wt%; 2 wt% to 4.5 wt%; 2.5 wt% to 5 wt%; 3 wt% to 5 wt%; 2 wt% to 4 wt%; or 3 wt% to 4.5 wt%.

[0103] The present invention can prevent the use of an excess amount outside the above range, which increases the viscosity of the electrolyte composition and reduces wettability for electrodes and separators, by controlling the total content of the compound represented by Chemical Formula 1 within the above-described range. In addition, the present invention can prevent the use of a trace amount of the electrolyte additive outside the above-described range, which causes the additive's effect to be minimal.

[0104] The above electrolyte additive may further include a cyclic carbon compound together with the compound represented by the above 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).

[0105] For example, the cyclic carbon compound may include vinylene carbonate (VC), 1,3-propanesultone (PS), ethylene sulfate (ESa) and / or propylene sulfate (PSa).

[0106] The above-mentioned cyclic carbon compound can be included in an electrolyte composition together with a compound represented by Chemical Formula 1 to not only increase the initial charge / discharge capacity of a lithium secondary battery, but also suppress the decomposition of a non-aqueous organic solvent that makes up most of the electrolyte composition under high-temperature conditions, thereby suppressing gas generation and improving the cycle characteristics of a lithium secondary battery at the same time.

[0107] Meanwhile, the electrolyte additive may be present in a range of more than 0 wt% and less than 10 wt% based on the total weight of the electrolyte composition, and specifically, may be present in a range of more than 0 wt% and less than 7.5 wt%, 1 wt% to 7.5 wt%, 3 wt% to 6.5 wt%, or 4.5 wt% to 6.5 wt%.

[0108] In addition, when the electrolyte additive includes both the compound represented by Chemical Formula 1 and the cyclic carbon-based compound, the cyclic carbon-based compound may be included in a predetermined content ratio with respect to the entire electrolyte additive. Specifically, the cyclic carbon-based compound may be included in an amount of 10 parts by weight or more and less than 50 parts by weight with respect to 100 parts by weight of the entire electrolyte additive. For example, the cyclic carbon-based compound may be included in an amount of 10 parts by weight to 49 parts by weight; 15 parts by weight to 49 parts by weight; 20 parts by weight to 47 parts by weight; 30 parts by weight to 49 parts by weight; 20 parts by weight to 40 parts by weight; 10 parts by weight to 30 parts by weight; or 40 parts by weight to 47 parts by weight with respect to 100 parts by weight of the entire electrolyte additive.

[0109] In general, when the acidity of an electrolyte composition increases, a concentration polarization phenomenon may occur and the transport speed of lithium ions may decrease. However, the present invention can prevent the acidity of the electrolyte composition from increasing after the activation process due to a high proportion of the compound represented by Chemical Formula 1 by controlling the content ratio of the inorganic compound and the cyclic carbon compound as described above. In addition, the present invention can prevent the problem of insufficient improvement in the heat resistance and thickness uniformity of the SEI layer formed on the surface of the negative electrode due to a lower proportion of the compound represented by Chemical Formula 1 than the above-described range.

[0110] In addition, the electrolyte composition includes a non-aqueous organic solvent, and the non-aqueous organic solvent includes a linear ester solvent substituted with fluorine as a main component. Specifically, the linear ester solvent substituted with fluorine may include one or more of the compounds represented by the following chemical formula 2:

[0111] [Chemical Formula 2]

[0112]

[0113] In the above chemical formula 2,

[0114] R3 is hydrogen or C 1~6 is an alkyl group,

[0115] R4 and R5 are each hydrogen, fluoro or C 1-10 is a fluorinated alkylene group,

[0116] m is an integer from 1 to 6.

[0117]

[0118] Specifically, in the above chemical formula 2,

[0119] R3 is a methyl group, ethyl group or propyl group,

[0120] R4 and R5 are each hydrogen or fluoro group,

[0121] m is an integer between 2 and 5.

[0122]

[0123] Specifically, the linear ester solvent substituted with fluorine may include at least one of the compounds represented by the following structural formulas 11 to 16:

[0124]

[0125]

[0126] Conventionally, fluorine-substituted non-aqueous carbonate solvents, such as fluoroethylene carbonate (FEC), have been used in lithium secondary battery electrolytes to suppress electrolyte decomposition on the surfaces of the positive and / or negative electrodes and enhance high-temperature safety. However, these fluorine-substituted carbonate solvents have low reduction potentials, leading to problems such as reduced battery capacity or deteriorated cycle characteristics when applied to electrolytes.

[0127] In comparison, the linear ester solvent substituted with fluorine exhibits high ionic conductivity at low temperatures and has low viscosity, resulting in excellent wettability in the electrode assembly. In addition, the linear ester solvent substituted with fluorine has a high oxidation reaction potential of 4.5 V or higher, specifically, 5.0 V or higher, and thus is not easily decomposed even when overcharging occurs, thereby exhibiting high safety. In addition, the linear ester solvent represented by the chemical formula 2 can minimize the transfer of external heat to the negative electrode active material when the lithium secondary battery is exposed to high temperatures, and thus can have an excellent effect of improving the high-temperature safety of the lithium secondary battery.

[0128] The linear ester solvent substituted with fluorine may be included in an amount of 60% by volume or more based on the total weight of the non-aqueous organic solvent of the electrolyte composition, and more specifically, may be included in an amount 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% to 99% by volume, 70% to 99% by volume, 80% to 99% by volume, 90% to 99% by volume, 95% to 99% by volume, 60% to 80% by volume, or 70% to 90% by volume.

[0129] The present invention prevents the problem of heat transferred to the negative electrode active material not being sufficiently reduced when the content of the fluorine-substituted linear ester solvent contained in the non-aqueous organic solvent is controlled as described above to be less than 60% by volume when the lithium secondary battery is exposed to high temperatures. In addition, since the fluorine-substituted linear ester solvent has excellent heat resistance, when the content is controlled within the above range, the electrolyte composition is not easily decomposed at high temperatures, and when combined with a predetermined electrolyte additive according to the present invention, there is an advantage of being able to minimize the amount of heat transferred to the negative electrode active material.

[0130] In addition, the non-aqueous organic solvent may further include a carbonate solvent together with a fluorine-substituted linear ester solvent. The carbonate solvent may assist the fluorine-substituted linear ester solvent, which is the main component of the non-aqueous organic solvent, thereby controlling the dielectric constant of the electrolyte composition. This may ensure high ionic conductivity of the electrolyte composition.

[0131] In addition, the carbonate-based solvents can perform a function of preventing gas generation due to side reactions of the electrolyte composition when exposed to high temperatures. Accordingly, from the viewpoints of electrochemical stability against oxidation-reduction and chemical stability against reactions with heat or solutes, one type of the carbonate-based solvent may be mixed with the fluorine-substituted linear ester-based solvent, or two or more types may be mixed with the fluorine-substituted linear ester-based solvent in any combination according to the intended use.

[0132] These carbonate 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 alone or in combination of two or more.

[0133] In addition, the auxiliary solvent may be mixed at a certain volume ratio with a linear ester solvent substituted with fluorine to control the dielectric constant of the electrolyte composition without lowering 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, more than 0% by volume but less than 40% by volume; more than 0% by volume but less than 30% by volume; more than 0% by volume but less than 25% by volume; more than 0% by volume but less than 20% by volume; more than 0% by volume but less than 15% by volume; more than 0% by volume but less than 10% by volume; 1% to 40% by volume; 1% to 30% by volume; 1% to 20% by volume; 1% to 10% by volume; 1% to 5% by volume; 20% to 40% by volume based on the total volume of the non-aqueous organic solvent. Or it may be included in the range of 10% to 30% by volume.

[0134] The present invention can maintain high compatibility between a linear ester solvent substituted with fluorine and an auxiliary solvent by controlling the content of the auxiliary solvent in the entire non-aqueous organic solvent to the above ratio, and at the same time, can improve the performance of the battery by increasing the charge mobility and / or ion mobility of the battery.

[0135] In addition, the electrolyte composition may include a specific lithium salt to reduce the amount of heat transferred to the positive electrode active material. Specifically, the lithium salt may be Li as a cation. + , and contains BF4 as anion. - , 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:

[0136] The lithium salt basically imparts conductivity to the organic solvent constituting the electrolyte, while also inducing passivation of the negative electrode through SEI formation. In the present invention, the lithium salt is dissolved in a linear ester solvent and can perform the function of delaying 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.

[0137] Meanwhile, the lithium salt applied in the present invention may selectively include two or more types of the lithium salts described above.

[0138] For example, the lithium salt may be lithium hexafluorophosphate (hereinafter, LiPF6) and lithium bis(trifluoromethanesulfonyl)imide (anion: (CF3SO2)2N). - , Hereinafter, LiFSI) may be included.

[0139] PF6 as a Harry Si anion - LiPF6, which represents lithium phosphate, is a phosphate-based lithium salt commonly used in the electrolyte composition of lithium secondary batteries, and has the characteristic of providing high conductivity to carbonate-based electrolytes. However, when LiPF6 is used alone as a lithium salt, it decomposes into PF5 at temperatures above about 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, which reduces the high-temperature durability of the electrode.

[0140] In addition, LiFSI, one of the sulfonimide-based lithium salts, has a high decomposition temperature in carbonate-based solvents, is highly safe at high temperatures, and has high water resistance, so that even when in contact with moisture, the amount of hydrogen fluoride (HF) generated is not high. However, the sulfonyl imide group of LiFSI itself has a significantly high reactivity with aluminum, which causes corrosion of the positive electrode current collector when applied to the electrolyte composition, and especially, when the inorganic additive of the present invention is excluded, the heat flow that transfers heat to the negative electrode active material is high, so there is a limitation that it is difficult to apply to the electrolyte composition.

[0141] When applied together, LiPF6 and LiFSI not only have the effect of significantly improving the low-temperature safety of LiPF6, but also can significantly reduce the heat flow through which the electrolyte composition transfers heat to the negative electrode active material.

[0142] At this time, when the phosphate-based lithium salt among the lithium salts 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 the molal concentration (M), and specifically, 1:0.4 to 0.9 or 1:0.6 to 0.8. The present invention can maximize the effect of lowering the heat flow of the electrolyte composition while minimizing the disadvantages of each lithium salt by controlling the ratio of the first lithium salt and the second lithium salt as described above.

[0143] The concentration of these lithium salts may satisfy a predetermined concentration in order to maintain the inherent function of the lithium salt while enhancing the high-temperature safety effect. For example, the preferable concentration of the lithium salt may have a lower limit of 0.5 mol / L or more, specifically 0.7 mol / L or more, more specifically 0.9 mol / L or more; and an upper limit of 2.5 mol / L or less, specifically 2.0 mol / L or less, more specifically 1.5 mol / L or less. If the concentration of the lithium salt is less than 0.5 mol / L, the ionic conductivity may decrease, which may deteriorate the cycle characteristics and output characteristics of the non-aqueous electrolyte battery. In addition, if the concentration of the lithium salt exceeds 2.5 mol / L, the viscosity of the electrolyte for the non-aqueous electrolyte battery may increase, which may also deteriorate the ionic conductivity, and there is a concern that the cycle characteristics and output characteristics of the non-aqueous electrolyte battery may also deteriorate.

[0144] In addition, when a large amount of lithium salt is dissolved in a non-aqueous organic solvent at once, the liquid temperature may rise due to the heat of dissolution of the lithium salt. If the temperature of the non-aqueous organic solvent rises significantly due to the heat of dissolution of the lithium salt in this way, in the case of a lithium salt containing fluorine, there is a concern that decomposition may be accelerated and hydrogen fluoride (HF) may be generated. Hydrogen fluoride (HF) is not desirable because it causes deterioration of battery performance. Therefore, the temperature when dissolving the lithium salt in the non-aqueous organic solvent is not particularly limited, but can be controlled to -20°C to 80°C, and specifically, can be controlled to 0°C to 60°C.

[0145] The electrolyte composition according to the present invention has the composition described above, so that a solid electrolyte membrane layer (SEI layer) can be uniformly formed on the surface of the negative electrode when a lithium secondary battery is activated, thereby minimizing side reactions between lithium ions generated on the surface of the negative electrode and the electrolyte composition, thereby improving the high-temperature safety of the lithium secondary battery.

[0146] For example, the electrolyte composition may exhibit a heat flux of 30.0 W / g or less within a range of 250°C to 400°C when measuring the heat flux of a mixture containing a negative active material and an electrolyte composition at a weight ratio of 1:0.5 with a 100% state of charge. For example, the electrolyte composition may exhibit a heat flux 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 within a range of 250°C to 400°C when measuring the heat flux.

[0147] Here, the negative electrode active material may be a silicon-based negative electrode active material commonly used as a negative electrode active material of a lithium secondary battery. Specifically, the silicon-based negative electrode active material may be silicon (Si), silicon carbide (SiC), and silicon oxide (SiO). r , but may include one or more of the following (0.8≤r≤2.5).

[0148] 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 an atomic ratio of 1:1. In some cases, a carbon layer may be formed on the surface of pure silicon (pure Si); or it may be a composite formed by mixing pure silicon (pure Si) and graphite in a molar ratio of 1:1. The silicon carbide (SiC) may include carbon atoms and may be formed as pure silicon (pure Si) or silicon oxide (SiO). r ) Compared to lithium-ion batteries, secondary batteries have a relatively low volume expansion rate and high conductivity during charging and discharging, which provides excellent performance in terms of lifespan and output.

[0149] The above "heat flow rate" refers to the amount of heat flowing per unit weight, and can particularly indicate the degree of heat generation of a secondary battery. As a result of analyzing the electrolyte composition of the present invention using a thermal analysis method, the electrolyte composition exhibited a lower heat flow rate compared to a conventional electrolyte composition. Here, the thermal analysis method simulates a degradation phenomenon in which the performance of a secondary battery deteriorates when the secondary battery is exposed to high temperature or spontaneously generates heat due to an external mechanical factor, and the measured heat flow rate at this time represents the degree of heat (e.g., heat amount) generated by a high-temperature reaction between the electrolyte composition and the charged negative electrode active material when simulating the high-temperature degradation phenomenon of the secondary battery. The heat flow rate may increase or decrease depending on the type or content ratio of each component constituting the electrolyte composition, and may also increase or decrease depending on whether an SEI layer including lithium ions is formed on the surface of the negative electrode active layer. A decrease in the heat flow rate means that the amount of heat generated between the negative electrode active material and the electrolyte composition is reduced. This means that the degree to which lithium ions intercalated into the negative electrode active material react with the electrolyte composition is reduced, thereby reducing the heat generated. These results indicate that the electrolyte composition has a lower reactivity with lithium ions within the negative electrode active material under high-temperature conditions, thereby improving the thermal safety of lithium secondary batteries.

[0150]

[0151] lithium secondary battery

[0152] Furthermore, the present invention,

[0153] An electrode assembly comprising an anode, a cathode, and a separator provided between the anode and the cathode; and

[0154] A lithium secondary battery is provided, comprising an electrolyte composition according to the present invention described above, which is impregnated into the electrode assembly.

[0155]

[0156] A lithium secondary battery according to the present invention includes an electrode assembly having a structure in which a separator is arranged between a plurality of positive electrodes and a plurality of negative electrodes alternately stacked, and an electrolyte composition in which the electrode assembly is impregnated.

[0157] The above electrolyte composition can uniformly form a solid electrolyte membrane layer (SEI layer) having high lithium ion conductivity and excellent heat resistance on the surface of a negative electrode when a lithium secondary battery is activated.

[0158] Accordingly, the lithium secondary battery including this has a significantly lower reactivity between the negative electrode active material (specifically, lithium ions inserted into the negative electrode active material) and the electrolyte composition, so that the temperature at which heat generation begins between them (i.e., heat generation onset temperature) increases, thereby suppressing heat generation due to negative electrode deterioration, etc. In addition, since side reactions of the electrolyte composition occurring on the negative electrode surface when the lithium secondary battery including the electrolyte composition is exposed to high temperatures can be minimized, there is an advantage of excellent high-temperature safety.

[0159] The above lithium secondary battery includes an electrode assembly and an electrolyte composition in which the electrode assembly is impregnated. Here, the electrolyte composition has the same composition as described above, so a detailed description thereof is omitted.

[0160] Below, each component of the electrode assembly is described in detail.

[0161] The electrode assembly includes an anode, a cathode, and a separator interposed between the anode and the cathode.

[0162] Here, the positive electrode includes a positive electrode active layer provided on at least one surface of the positive electrode current collector. The positive electrode active layer is a material capable of electrochemically reacting on the positive electrode current collector to realize electrical activity, and includes a lithium metal oxide represented by the chemical formula 3 as a main component, which is capable of reversibly intercalating and deintercalating lithium ions:

[0163] [Chemical Formula 3]

[0164] Li x [Ni y Co z Mn w M 1 v ]O2

[0165] In the above chemical formula 3,

[0166] M 1 is at least one element among 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,

[0167] x, y, z, w, and v are 0.9≤x≤1.30, 0.6≤y<1, 0, respectively. <z≤0.2, 0<w≤0.2, 0≤v≤0.1이되, y+z+w+v=1이다.

[0168]

[0169] The lithium metal oxide represented by the above chemical formula 3 is an oxide mixed with lithium (Li) and transition metals nickel (Ni), cobalt (Co), and manganese (Mn), and is characterized in that the content of nickel (Ni) is 60% or more (i.e., 60 mol%) of the total mole fraction of transition metals.

[0170] The ternary NCM cathode active material, which is mainly composed of nickel (Ni), cobalt (Co), and manganese (Mn), has the advantages of high capacity of LiNiO2 (LNO), excellent electrochemical performance of LiCoO2 (LCO), and stability of LiMn2O4 (LMO).

[0171] LiNi is one of these cathode active materials. 0.95 Co 0.03 Mn 0.02 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.9 Co 0.6 Mn 0.4 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi0.85 Co 0.1 Mn 0.05 O2, LiNi 0.85 Co 0.05 Mn 0.1 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.75 Co 0.2 Mn 0.15 O2, LiNi 0.7 Co 0.2 Mn 0.1 O2, LiNi 0.7 Co 0.15 Mn 0.15 O2, LiNi 0.7 Co 0.1 Mn 0.2 O2, LiNi 0.7 Co 0.2 Mn 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.6 Co 0.2 Mn 0.1 Al 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.15 Al 0.05 O2, and LiNi 0.7 Co 0.1 Mn 0.1 Al 0.1 One or more types of O2 can be mentioned.

[0172] In addition, the 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 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.

[0173] In addition, the positive electrode active layer may further include a conductive agent, a binder, other additives, etc., along with the positive electrode active material, as needed.

[0174] At this time, the conductive material is used to improve the electrical performance of the anode, and can be applied as a material commonly used in the art. Specifically, it can include at least one of graphite materials such as natural graphite and artificial graphite; carbon black such as acetylene black, Denka black, Ketjen black, Super-P, channel black, furnace black, lamp black, and summer black; graphene; and carbon nanotubes.

[0175] In addition, the conductive material may be included in an amount 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 an amount 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.

[0176] In addition, the binder serves to bind the positive electrode active material, the positive electrode additive, and the conductive material to each other, and any binder having this function may be used without particular limitation. Specifically, the binder may include at least one resin selected from polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-co-HFP), polyvinylidene fluoride (PVdF), polyacrylonitrile, polymethylmethacrylate, and copolymers thereof. For example, the binder may include polyvinylidene fluoride (PVdF).

[0177] In addition, the binder may be included in an amount of 0.1 to 5 parts by weight based on 100 parts by weight of the entire positive electrode active layer. Specifically, the binder may be included in an amount 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.

[0178] The total thickness of the positive electrode active layer is not particularly limited, but may be specifically 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.

[0179] In addition, the positive electrode can be used as a positive electrode current collector that has high conductivity without causing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, etc. can be used, and in the case of aluminum or stainless steel, a material surface-treated with carbon, nickel, titanium, silver, etc. can also be used. In addition, the average thickness of the current collector can be appropriately applied in the range of 3 µm to 500 µm, taking into account the conductivity and total thickness of the positive electrode to be manufactured.

[0180] Furthermore, the negative electrode, like the positive electrode, has a negative electrode active layer including a negative electrode active material on at least one surface of the negative electrode current collector.

[0181] The above negative electrode active layer includes a silicon-based negative electrode active material as a negative electrode active material to implement electrical activity through a reversible redox reaction during charging and discharging of the battery.

[0182] The above silicon-based negative electrode active material refers to a material whose main component is silicon atoms. The silicon-based negative electrode active material can reversibly adsorb and release a large amount of lithium during charging and discharging of a secondary battery, and thus has a large 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.

[0183] These silicon-based negative electrode materials include silicon (Si), silicon carbide (SiC), and silicon oxide (SiO). r , but may include one or more of the following (0.8≤r≤2.5).

[0184] 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 an atomic ratio of 1:1. In some cases, a carbon layer may be formed on the surface of pure silicon (pure Si); or it may be a composite formed by mixing pure silicon (pure Si) and graphite in a molar ratio of 1:1. The silicon carbide (SiC) may include carbon atoms and may be formed as pure silicon (pure Si) or silicon oxide (SiO). r ) Compared to lithium-ion batteries, secondary batteries have a relatively low volume expansion rate and high conductivity during charging and discharging, which provides excellent performance in terms of lifespan and output.

[0185] In addition, the silicon-based negative 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 negative electrode active layer, and specifically, 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.

[0186] Meanwhile, the negative electrode active layer according to the present invention may optionally further include a conductive agent, a binder, other additives, etc., as needed, along with the silicon-based negative electrode active material as the main component.

[0187] The above-mentioned challenge material may include, but is not limited to, one or more types of carbon black such as acetylene black and Ketjen black; carbon nanotubes; and carbon fibers.

[0188] For example, the cathode active layer may contain carbon black, carbon nanotubes, carbon fibers, etc. alone or in combination as a conductive material.

[0189] At this time, the content of the conductive material may be 0.1 to 10 parts by weight based on 100 parts by weight of the entire negative electrode active layer, and specifically, may 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 the resistance of the negative electrode from increasing due to a low content of the conductive material, thereby lowering the charging capacity, and can prevent the problem of the content of the negative electrode active material decreasing due to an excessive amount of the conductive material, thereby lowering the charging capacity, or the problem of the rapid charging characteristics deteriorating due to an increase in the loading amount of the negative electrode active layer.

[0190] In addition, the above binder can be appropriately applied as a component that assists in the bonding of the silicon-based negative electrode active material and the conductive material and the bonding to the current collector, within a range that does not deteriorate the electrical properties of the electrode. Specifically, the binder may include at least one selected from vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVdF), polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene butadiene rubber (SBR), and fluoroelastomer.

[0191] The content of the binder may be 0.1 to 10 parts by weight based on 100 parts by weight of the entire negative electrode active layer, and specifically, may be 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 content of the binder contained in the negative electrode active layer within the above range, the present invention can prevent the adhesive strength of the active layer from being lowered due to a low content of binder or the electrical properties of the electrode from being lowered due to an excessive amount of binder.

[0192] Furthermore, the average thickness of the cathode active layer may 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 controlling the average thickness of the cathode active layer within the above range.

[0193]

[0194] In addition, the negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, nickel, titanium, calcined carbon, etc. can be used. In the case of copper or stainless steel, a material surface-treated with carbon, nickel, titanium, silver, etc. can also be used. In addition, the average thickness of the negative electrode current collector can be appropriately applied from 1 ㎛ to 500 ㎛ in consideration of the conductivity and total thickness of the negative electrode to be manufactured.

[0195] Meanwhile, the separator interposed between the anode and cathode 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 art, but specifically, one containing at least one polymer among polypropylene, polyethylene, and polyethylene-propylene copolymers having chemical resistance and hydrophobicity can be used. The separator may have a porous polymer substrate form such as a sheet or non-woven fabric containing the above-described polymer, and in some cases, may have a composite separator form in which organic or inorganic particles are coated on the porous polymer substrate using an organic binder. In addition, the separator may have an average pore diameter of 0.01 μm to 10 μm, and an average thickness of 5 μm to 300 μm.

[0196] Furthermore, the lithium secondary battery according to the present invention is not particularly limited, but can be applied in various forms such as cylindrical type, prismatic type, pouch type, or coin type depending on the performance purpose. The lithium secondary battery according to one embodiment of the present invention may be a pouch type secondary battery.

[0197]

[0198] Hereinafter, the present invention will be described in more detail through examples and experimental examples.

[0199] However, the following examples and experimental examples are only illustrative of the present invention, and the content of the present invention is not limited to the following examples and experimental examples.

[0200]

[0201] Examples 1 to 7 and Comparative Examples 1 to 7. Preparation of electrolyte composition for lithium secondary batteries

[0202] As non-aqueous organic solvents, linear ester solvents represented by <Structural Formula 11> and <Structural Formula 13> and ethylene carbonate (EC), ethyl methyl carbonate (EMC), and fluoroethylene carbonate (FEC) were prepared, respectively, and LiPF6 was prepared as a lithium salt.

[0203] In addition, as a compound represented by chemical formula 1, which is an electrolyte additive, compounds represented by <structural formula 6> and <structural formula 10> were prepared, and as a comparative group of the compounds, compounds represented by <structural formula 17> and <structural formula 18> were prepared separately.

[0204] Additionally, LiBOB, LiODFB, LiDFOP, vinylene carbonate (VC), 1,3-propanesultone (PS), ethylene sulfate (ESa), and fluoroethylene carbonate (FEC) were prepared as additional electrolyte additives.

[0205] The prepared LiPF6 was added to a non-aqueous organic solvent at 30°C to 40°C to satisfy 1 molal concentration (M), and an electrolyte additive was added to prepare an electrolyte composition.

[0206] At this time, the type and content of the non-aqueous organic solvent used in the electrolyte composition are adjusted as shown in Table 1, and the type and content of the electrolyte additive are as shown in Table 2. Here, the content of each component of the non-aqueous organic solvent was adjusted as a volume percentage (i.e., volume%) based on the total volume of the non-aqueous organic solvent. In addition, the compound represented by Chemical Formula 1 included in the electrolyte additive and the additional electrolyte additive were adjusted as a weight percentage (weight%) based on the total weight of the electrolyte composition.

[0207] Electrolyte additive Added electrolyte additive type content [based on electrolyte composition weight] Type content [based on electrolyte composition weight] Example 1 <Structural formula 10> 1 wt% VC:PS:Esa 1:0.5:1 wt% Example 23 wt% VC:PS:Esa 1:0.5:1 wt% Example 35 wt% VC:PS:Esa 1:0.5:1 wt% Example 4 <Structural Formula 6> 3 wt% VC:PS:Esa1:0.5:1 wt% Example 5 <Structural formula 10> 3 wt%--Example 63 wt%VC:PS:Esa1:0.5:1 wt%Example 73 wt%VC:PS:Esa1:0.5:1 wt%Comparative Example 13 wt%VC:PS:Esa1:0.5:1 wt%Comparative Example 23 wt%VC:PS:Esa1:0.5:1 wt%Comparative Example 33 wt%VC:PS:Esa1:0.5:1 wt%Comparative Example 4--VC:PS:Esa1:0.5:1 wt%Comparative Example 5--VC:PS:Esa1:0.5:1 wt%Comparative Example 6<Structural Formula 17> -VC:PS:Esa1:0.5:1 wt% Comparative Example 7 <Structural Formula 18> -VC:PS:Esa1:0.5:1 wt%

[0208] Non-aqueous organic solvent Linear ester solvent content Carbonate solvent content Example 1 <Structural formula 11> 90 vol% FEC10 vol% Example 290 vol% FEC10 vol% Example 390 vol% FEC10 vol% Example 490 vol% FEC10 vol% Example 590 vol% FEC10 vol% Example 660 vol% FEC40 vol% Example 7 <Structural Formula 13> 90% by volume FEC10% by volume Comparative Example 1 <Structural Formula 11> 40 vol% FEC60 vol% Comparative Example 2--EC:EMC70:30 vol% Comparative Example 3--EC:FEC30:70 vol% Comparative Example 4--EC:EMC70:30 vol% Comparative Example 5 <Structural Formula 11> 90% by volume FEC10% by volume Comparison example 690% by volume FEC10% by volume Comparison example 790% by volume FEC10% by volume

[0209]

[0210] Examples 8 to 14 and Comparative Examples 8 to 14. Manufacturing of lithium secondary batteries

[0211] LiNi with a particle size of 5㎛ as a cathode active material 0.86 Co 0.05 Mn 0.07 Al 0.02 O2 was prepared, and polyvinylidene fluoride as a carbon-based conductive agent and binder was mixed with N-methyl pyrrolidone (NMP) in a weight ratio of 94:3:3 to prepare a positive electrode slurry having a solid content of 45%. The prepared positive electrode slurry was cast onto an aluminum foil. After drying in a vacuum oven at 120°C, the slurry was rolled to produce a positive electrode having a positive electrode active layer with a thickness of 160 μm.

[0212] Separately, silicon carbide (SiC, average particle size: approximately 3±0.5㎛) 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 prepare a negative electrode slurry having a solid content of 40%. The negative electrode slurry was cast on a copper foil, dried in a vacuum oven at 130℃, and then rolled to prepare a negative electrode having a 180㎛ thick negative electrode active layer.

[0213] A separator made of 18 μm polypropylene was interposed between the positive and negative electrodes obtained above, inserted into a case, and then the electrolyte compositions manufactured in Examples 1 to 7 and Comparative Examples 1 to 7 were injected as shown in Table 3 below to assemble a lithium secondary battery.

[0214] Each assembled lithium secondary battery was initially charged. Specifically, the lithium secondary battery was initially charged to a charge end voltage of 4.2 V at 55±2°C to manufacture an activated lithium secondary battery.

[0215] Types of manufactured lithium secondary batteries Types of electrolyte compositions used Example 8 Electrolyte composition of Example 1 Example 9 Electrolyte composition of Example 2 Example 10 Electrolyte composition of Example 3 Example 11 Electrolyte composition of Example 4 Example 12 Electrolyte composition of Example 5 Example 13 Electrolyte composition of Example 6 Example 14 Electrolyte composition of Example 7 Comparative Example 8 Electrolyte composition of Comparative Example 1 Comparative Example 9 Electrolyte composition of Comparative Example 2 Comparative Example 10 Electrolyte composition of Comparative Example 3 Comparative Example 11 Electrolyte composition of Comparative Example 4 Comparative Example 12 Electrolyte composition of Comparative Example 5 Comparative Example 13 Electrolyte composition of Comparative Example 6 Comparative Example 14 Electrolyte composition of Comparative Example 7

[0216]

[0217] Experimental example.

[0218] In order to evaluate the high-temperature safety of the electrolyte composition for a lithium secondary battery according to the present invention and the lithium secondary battery including the same, the following experiments were conducted.

[0219]

[0220] 1) Measurement of heat onset temperature and heat flow between the negative electrode active material and electrolyte composition

[0221] Each of the lithium secondary batteries manufactured in Examples 8 to 14 and Comparative Examples 8 to 14 was fully charged (SOC 100%) at 25°C at a rate of 0.5C under CC-CV conditions to 4.25 V, and the fully charged lithium secondary batteries were disassembled. In the disassembled lithium secondary batteries, silicon carbide (SiC), which is an anode active material, and an electrolyte composition were weighed and mixed at a weight ratio of 1:0.5.

[0222] The prepared mixture was injected into the sample can of a differential scanning calorimeter (DSC) to prepare a sample, and the exothermic onset temperature and heat flow rate of the prepared sample were measured. At this time, the temperature of the sample was increased at a heating rate of 10±0.1℃ / min, and the temperature change and heat flow rate were measured in the range of 100℃ to 500℃.

[0223] From the measured results, the heat flow between the negative active material and electrolyte composition included in each lithium secondary battery was evaluated. Among the measured results, if there were two or more valid heat flow peaks within the temperature range of 100℃ to 500℃, the value of the peak showing the largest heat flow was determined as the corresponding heat flow. The results are shown in Table 4 and Fig. 1 below.

[0224]

[0225] 2) Thermal runaway test evaluation

[0226] The lithium secondary batteries manufactured in Examples 8 to 14 and Comparative Examples 8 to 14 were charged under constant current (CC) conditions maintained at 1.25 A until reaching 4.2 V at 25°C, and maintained at 4.2 V. Upon completion of charging, they were activated by discharging under constant current (CC) conditions maintained at 1.25 A until 2.85 V. Afterwards, each activated lithium secondary battery was allowed to rest for 6 hours at 25°C.

[0227] Then, the battery was fully charged (SOC100%) under constant current (CC) conditions maintained at 1.25 A until it reached 4.2 V at 25℃, and a thermal runaway test was performed using an accelerating rate calorimetry (ARC). At this time, the accelerating rate calorimeter (ARC) was a product of THT (Thermal Hazard Technology), and the thermal runaway test was performed using the heat-wait-search (HWS) method. The heat-wait-search (HWS) method heated the temperature of the insulated oven chamber equipped with each lithium secondary battery from 50℃ to 190℃ by increasing the temperature by 5℃ at a rate of 10℃ / min and waiting for 10 minutes. Here, when each heated lithium secondary battery showed a temperature change of 0.02℃ / min or more during a 10-minute standby, it was recognized that self-heating corresponding to thermal runaway (TR) was in progress, and from that point on, no separate thermal energy was applied so that the temperature would change due to self-heating of each secondary battery. After the self-heating of the secondary battery, the self-heating profile of the secondary battery 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.

[0228] Type of electrolyte composition DSC analysis of lithium secondary battery During thermal runaway test, highest temperature Exothermic onset temperature Heat flow Example 1 305~330℃ Approximately 7.1±0.5 W / g 355.1℃ Example 2 305~330℃ Approximately 6.2±0.5 W / g 340.3℃ Example 3 305~330℃ Approximately 6.8±0.5 W / g 351.3℃ Example 4 290~315℃ Approximately 7.4±0.5 W / g 348.5℃ Example 5 275~295℃ Approximately 7.9±0.5 W / g 317.9℃ Example 6 255~275℃ Approximately 10.3±0.5 W / g 399.5℃ Example 7 295~310℃ Approximately 7.2±0.5 W / g350.2℃Comparative example 1220~240℃Approximately 22.6±0.5 W / g420.1℃Comparative example 2190~205℃Approximately 117.4±0.5 W / g663.5℃Comparative example 3195~210℃Approximately 90±0.5 W / g510.5℃Comparative example 4170~180℃Approximately 138±0.5 W / g891.7℃Comparative example 5250~270℃Approximately 87±0.5 W / g521.0℃Comparative example 6215~235℃Approximately 38±0.5 W / g442.5℃Comparative example 7225~245℃Approximately 30±0.5 W / g451.3℃

[0229]

[0230] It can be seen that the electrolyte composition for a lithium secondary battery according to the present invention and the lithium secondary battery including the same have excellent high-temperature safety.

[0231] Specifically, the electrolyte compositions of the examples exhibited a high temperature (exothermic onset temperature) of 255°C or higher, more specifically, 275°C or higher, at which heat generation begins due to a reaction between the negative active material and the electrolyte composition when exposed to high temperatures. In addition, the electrolyte compositions of the examples exhibited a low heat flux of about 15 W / g or lower, and a lithium secondary battery including the electrolyte composition exhibited a low maximum temperature of 400°C or lower during a thermal runaway test.

[0232] This means that the electrolyte composition manufactured in the example effectively suppresses the reaction between the negative electrode active material and the electrolyte composition when exposed to high temperatures, thereby improving heat generation due to the reaction between the negative electrode active material and the electrolyte composition.

[0233] From these results, it can be seen that the electrolyte composition for a lithium secondary battery according to the present invention not only has excellent electrical performance, but also has an excellent effect of improving safety issues caused by the negative electrode active material at high temperatures by controlling the heat flow between the negative electrode active material and the electrolyte composition to a low level within a predetermined range.

[0234]

[0235] Although the present invention has been described above with reference to preferred embodiments thereof, it will be understood by those skilled in the art or having ordinary knowledge in the art that the present invention can be variously modified and changed within the scope of the claims set forth below.

[0236] Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be defined by the patent claims.

Claims

1. Contains lithium salt, electrolyte additive and non-aqueous organic solvent, The above non-aqueous organic solvent contains 60% by volume or more and less than 100% by volume of a linear ester solvent substituted with fluorine, An electrolyte composition for a lithium secondary battery, which exhibits a heat flux of 50.0 W / g or less within a range of 250 to 400°C when measuring heat flux for a mixture containing a negative electrode active material and an electrolyte composition at a weight ratio of 1:0.5 with a 100% state of charge.

2. In paragraph 1, An electrolyte composition for a lithium secondary battery having a heat flux in the range of 0.5 W / g to 30 W / g.

3. In paragraph 1, The electrolyte additive is an electrolyte composition for a lithium secondary battery comprising at least one compound represented by the following chemical formula 1: [Chemical Formula 1] In the above chemical formula 1, R1 and R2 are each a fluoro group or C 1-10 is a fluorinated alkylene group, p is an integer from 0 to 4, q is an integer from 1 to 10.

4. In paragraph 3, The compound represented by the above chemical formula 1 is an electrolyte composition for a lithium secondary battery comprising at least one of the acrylic compounds represented by the following <structural formula 1> to <structural formula 10>: .

5. In paragraph 1, An electrolyte composition for a lithium secondary battery, wherein the electrolyte additive is included in an amount of more than 0 wt% and less than 5 wt% based on the total weight of the electrolyte composition.

6. In paragraph 1, An electrolyte composition for a lithium secondary battery, wherein the electrolyte additive further comprises at least one cyclic carbon compound selected from the group consisting of vinylene carbonate (VC), 1,3-propanesultone (PS), ethylene sulfate (ESa), propylene sulfate (PSa), and butylene sulfate (BSa).

7. In paragraph 6, An electrolyte composition for a lithium secondary battery, wherein the above-mentioned cyclic carbon compound is 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.

8. In paragraph 1, The above fluorine-substituted linear ester solvent is an electrolyte composition for a lithium secondary battery comprising at least one compound represented by the following chemical formula 2: [Chemical Formula 2] In the above chemical formula 2, R3 is hydrogen or C 1~6 is an alkyl group, R4 and R5 are each hydrogen, fluoro or C 1-10 is a fluorinated alkylene group, m is an integer from 1 to 6.

9. In paragraph 1, The above fluorine-substituted linear ester solvent is an electrolyte composition for a lithium secondary battery comprising at least one compound represented by the following <structural formula 11> to <structural formula 16>: .

10. In paragraph 1, An electrolyte composition for a lithium secondary battery, wherein the non-aqueous organic solvent comprises at least one carbonate solvent 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).

11. In paragraph 10, An electrolyte composition for a lithium secondary battery, wherein the carbonate solvent is included in an amount of more than 0% by volume and less than or equal to 40% by volume based on the total weight of the non-aqueous organic solvent.

12. In paragraph 1, The above lithium salt is, Li as a cation + Including, BF4 as anion - , 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 - A lithium secondary battery containing at least one of the following:

13. In paragraph 1, The above negative active materials are silicon (Si), silicon carbide (SiC), and silicon oxide (SiO). r , but, 0.8≤r≤2.5) is characterized by at least one silicon-based negative electrode active material.

14. An electrode assembly including an anode, a cathode, and a separator provided between the anode and the cathode; and A lithium secondary battery comprising an electrolyte composition according to claim 1, which is impregnated into the electrode assembly.

15. In paragraph 14, A lithium secondary battery comprising a positive electrode active layer provided on at least one side of a positive electrode current collector and including a positive electrode active material represented by the following chemical formula 3: [Chemical Formula 3] Li x [Ni y Co z Mr w M 1 v ]O2 In the above chemical formula 3, M 1 is at least one element among 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 0.9≤x≤1.30, 0.6≤y<1, 0, respectively. <z≤0.2, 0<w≤0.2, 0≤v≤0.1이되, y+z+w+v=1이다.

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