Lithium secondary battery having improved safety

Abstract

The present invention relates to an electrolyte composition for a lithium secondary battery. The electrolyte composition for a lithium secondary battery comprises a cyclic ester-based solvent as a main component and a predetermined electrolyte additive, and thus enables the uniform formation of a solid electrolyte interface 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. Consequently, the reactivity between an anode active material and the electrolyte composition is remarkably lowered, resulting in a rise in the temperature at which heat generation begins (that is, an exothermic onset temperature) between the anode active material and the electrolyte composition, thereby suppressing heat generation caused by anode deterioration or the like. Furthermore, a lithium secondary battery comprising the electrolyte composition can minimize side reactions of the electrolyte composition, occurring on the surface of the anode when exposed to high temperatures, thereby exhibiting excellent high-temperature safety.

Description

Lithium secondary batteries with improved safety

[0001] The present invention relates to a lithium secondary battery with improved high-temperature safety.

[0002] This application claims the benefit of priority from Republic of Korea Patent Application No. 10-2024-0037345, dated March 18, 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 provides an electrolyte for a lithium secondary battery and a lithium secondary battery including the same, which can more effectively suppress side reactions between a negative electrode and an electrolyte occurring on the surface of a negative electrode when a lithium secondary battery is exposed to high temperatures.

[0009]

[0010] To solve the above-mentioned problem,

[0011] The present invention,

[0012] Comprising a step of providing a lithium salt, an electrolyte additive and a non-aqueous organic solvent,

[0013] The above electrolyte additive comprises an inorganic compound,

[0014] The above non-aqueous organic solvent contains about 60% by volume or more and less than 100% by volume of a cyclic ester solvent represented by the following chemical formula 1,

[0015] Provided is an electrolyte composition for a lithium secondary battery, which exhibits a heat flux of 30.0 W / g or less within a range of 250°C to 350°C when measuring heat flux for a mixture containing a negative electrode active material and an electrolyte composition of a lithium secondary battery with a 100% state of charge in a weight ratio of 1:0.5:

[0016] [Chemical Formula 1]

[0017]

[0018] In the above chemical formula 1,

[0019] is a single bond or double bond,

[0020] X is hydrogen, fluoro, or vinyl,

[0021] p is an integer from 1 to 5.

[0022]

[0023] In one embodiment, the electrolyte composition can have a heat flux of 5 W / g to 25 W / g.

[0024] The cathode active material applied when measuring heat flow may include at least one of natural graphite, artificial graphite, expanded graphite, non-graphitizable carbon, acetylene black, and Ketjen black.

[0025] In addition, the above-mentioned inorganic compound may include at least one of lithium nitrate (LiNO3), lithium chloride (LiCl), lithium fluoride (LiF), lithium bromide (LiBr), lithium borate (Li3BO3), lithium carbonate (Li2CO3), lithium sulfate (Li2SO4), and lithium phosphate (Li3PO4).

[0026] The above electrolyte additive may be included in an amount of more than 0 wt% and less than 5 wt% based on the total weight of the electrolyte composition.

[0027] The electrolyte composition may further include an electrolyte additive in addition to the inorganic compound. For example, the electrolyte additive may further include one or more cyclic carbon compounds selected from the group consisting of vinylene carbonate (VC), 1,3-propanesultone (PS), ethylene sulfate (ESa), propylene sulfate (PSa), butylene sulfate (BSa), and fluoroethylene carbonate (FEC).

[0028] In this case, the cyclic carbon compound may be included in an amount of 100 to 1000 parts by weight based on 100 parts by weight of the inorganic compound.

[0029] The cyclic ester solvent represented by the above chemical formula 1 may include at least one of dihydrofuranone, vinyldihydrofuranone, fluorodihydrofuranone, furanone, tetrahydropyranone, methyldihydrofuranone, propyltetrahydropyranone, and oxepanone.

[0030] In addition, the non-aqueous organic solvent may further include one or more carbonate solvents selected from ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).

[0031] The above carbonate solvent may be 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.

[0032] The above lithium salt has Li as a cation. + , and contains PF6 as an anion. - , PF4C2O4 - , PF2C4O8 - , (CF3)2PF4 - , (CF3)3PF3 -, (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , (C2O4)2PF2 - , BF2C2O4 - , B(C2O4)2 - , (CF3SO2)2N - , (FSO2)2N - , (CF3CF2SO2)2N - and ((C(CN))2NC(CF3))N - It may include one or more of the following:

[0033]

[0034] Furthermore, the present invention,

[0035] An electrode assembly comprising an anode, a cathode, and a separator provided between the anode and the cathode; and

[0036] A lithium secondary battery is provided, comprising an electrolyte composition according to the present invention described above, which is impregnated into the electrode assembly.

[0037] At this time, the positive electrode is provided on at least one side of the positive electrode collector and may include a positive electrode active layer including a positive electrode active material represented by the following chemical formula 2:

[0038] [Chemical Formula 2]

[0039] Li x [Ni y Co z Mn w M 1 v ]O2

[0040] In the above chemical formula 2,

[0041] M 1 is at least one element selected 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,

[0042] 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.

[0043]

[0044] The electrolyte composition for a lithium secondary battery 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 the negative electrode when the lithium secondary battery is activated. Accordingly, the reactivity between 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 excellent high-temperature safety.

[0045]

[0046] 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.

[0047] Figure 1 is a graph showing the heat flow of an electrolyte composition according to the type of electrolyte additive according to one embodiment of the present invention.

[0048] In some of the accompanying drawings, corresponding components are designated by the same reference numerals. Those skilled in the art will appreciate that the drawings illustrate elements simply and clearly and are not necessarily drawn to scale. For example, to facilitate understanding of various embodiments, the dimensions of some elements depicted in the drawings may be exaggerated relative to other elements. Furthermore, elements of known technology that are useful or essential in commercially feasible embodiments may often not be depicted so as not to obscure the spirit of various embodiments of the present invention.

[0049]

[0050] 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.

[0051] However, this is not intended to limit the present invention to a specific embodiment, but should be understood to include all modifications, equivalents, or substitutes included in the technical scope of the present invention.

[0052] 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.

[0053] 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.

[0054] 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 cyclic 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 a cyclic ester solvent with respect to the total volume of the non-aqueous organic solvent. In some cases, it may mean that the entire non-aqueous organic solvent is comprised of cyclic ester solvents and contains 100% by volume.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] Hereinafter, the present invention will be described in more detail with reference to the attached drawings.

[0060]

[0061] Electrolyte composition for lithium secondary batteries

[0062] The present invention,

[0063] Contains lithium salt, electrolyte additive and non-aqueous organic solvent,

[0064] The above electrolyte additive comprises an inorganic compound,

[0065] The above non-aqueous organic solvent contains about 60% by volume or more and less than 100% by volume of a cyclic ester solvent represented by the following chemical formula 1,

[0066] Provided is an electrolyte composition for a lithium secondary battery, which exhibits a heat flux of about 30.0 W / g or less within a range of 250°C to 350°C when measuring a heat flux of a mixture containing a negative electrode active material and an electrolyte composition of a lithium secondary battery with a 100% state of charge in a weight ratio of about 1:0.5:

[0067] [Chemical Formula 1]

[0068]

[0069] In the above chemical formula 1,

[0070] is a single bond or double bond,

[0071] X is hydrogen, fluoro, or vinyl,

[0072] p is an integer from 1 to 5.

[0073]

[0074] The electrolyte composition for a lithium secondary battery according to the present invention is a liquid electrolyte, which 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 (e.g., heat 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 excellent high-temperature safety.

[0075] To this end, the electrolyte composition includes a lithium salt, an electrolyte additive, and a non-aqueous organic solvent, and the lithium salt, the electrolyte additive, and the non-aqueous organic solvent may have a predetermined composition.

[0076] In one embodiment, the electrolyte additive may include an inorganic compound, and the inorganic compound may include one or more of lithium nitrate (LiNO3), lithium chloride (LiCl), lithium fluoride (LiF), lithium bromide (LiBr), lithium borate (Li3BO3), lithium carbonate (Li2CO3), lithium sulfate (Li2SO4), and lithium phosphate (Li3PO4).

[0077] As an example, the inorganic compound may include lithium nitrate (LiNO3) and / or lithium sulfate (Li2SO4).

[0078] The above inorganic compound can be included as an electrolyte additive to directly lower the reactivity between lithium ions inserted and / or deintercalated into the negative electrode active material and the electrolyte composition, thereby reducing the amount of heat generated. In addition, the above inorganic compound indirectly participates in the formation of a solid electrolyte membrane layer (SEI layer) during activation of a lithium secondary battery, thereby forming lithium nitride (Li3N), lithium oxide (Li2O), and partially reduced lithium nitrate (LiNO) with high lithium ion transport ability and excellent heat resistance. x , 0 <x<3) 등을 고체 전해질막 층(SEI층)에 제공할 수 있으므로 음극 표면에 내열성이 우수한 고체 전해질막 층(SEI층)이 균일하게 형성되게 할 수 있다.

[0079] As an example, the electrolyte composition including the inorganic compound may have an onset temperature, for example, a temperature at which heat generation of the negative active material begins when exposed to high temperature during differential scanning calorimeter (DSC) analysis, of 250°C or more, 260°C or more, 270°C or more, 250°C to 310°C, 260°C to 310°C, 270°C to 310°C, 265°C to 300°C, more than 270°C and 310°C or less, more than 270°C and 300°C or less, or 275°C to 300°C.

[0080] The above electrolyte additive may further include a cyclic carbon compound together with the above inorganic compound. 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), butylene sulfate (BSa), and fluoroethylene carbonate (FEC).

[0081] As an example, the cyclic carbon compound may include vinylene carbonate (VC), 1,3-propanesultone (PS), ethylene sulfate (ESa) and / or propylene sulfate (PSa).

[0082] The above-mentioned cyclic carbon compound can be included in an electrolyte composition together with an inorganic compound 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.

[0083] The electrolyte composition may include the electrolyte additive described above in a predetermined amount. In one embodiment, the electrolyte additive may be included in an amount of greater than 0 wt% and less than or equal to 5 wt% based on the total weight of the electrolyte composition, for example, greater than 0 wt% and less than or equal to 4 wt%; greater than 0 wt% and less than or equal to 3 wt%; greater than 0 wt% and less than or equal to 2 wt%; greater than 0 wt% and less than or equal to 1 wt%; greater than 0 wt% and less than or equal to 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%.

[0084] The present invention can prevent or suppress a decrease in wettability for a separator by appropriately maintaining the viscosity of the electrolyte composition by controlling the total content of the electrolyte additive within the above-described range, while preventing a decrease in ion conductivity of the electrolyte composition and thus a decrease in battery performance.

[0085] Here, when the electrolyte additive comprises only an inorganic compound, the inorganic compound may be included in the electrolyte composition in an amount equal to the total amount of the electrolyte additive described above.

[0086] In addition, when the electrolyte additive includes both an inorganic compound and a cyclic carbon compound, the total content of the inorganic compound and the cyclic carbon compound can satisfy the entire content range of the electrolyte additive described above. In this case, the content of the inorganic compound and the content of the cyclic carbon compound can form a predetermined ratio.

[0087] For example, when the electrolyte additive includes an inorganic compound and a cyclic carbon compound, the cyclic carbon compound may be included in an amount of about 100 parts by weight to 1,000 parts by weight relative to 100 parts by weight of the inorganic compound. For example, the cyclic carbon compound may be included in an amount of about 100 parts by weight to 900 parts by weight; 100 parts by weight to 800 parts by weight; 100 parts by weight to 700 parts by weight; 300 parts by weight to 900 parts by weight; 450 parts by weight to 900 parts by weight; 400 parts by weight to 800 parts by weight; or 500 parts by weight to 700 parts by weight relative to 100 parts by weight of the inorganic compound.

[0088] If the acidity of the electrolyte composition increases, a concentration polarization phenomenon may occur and the transport speed of lithium ions may decrease. However, the present invention can prevent or suppress the increase in the acidity of the electrolyte composition due to a high proportion of inorganic compounds by controlling the content ratio of the inorganic compound and the cyclic carbon compound as described above. In addition, the present invention can sufficiently improve the heat resistance and thickness uniformity of the solid electrolyte membrane layer (SEI layer) formed on the surface of the negative electrode by controlling the content ratio of the inorganic compound and the cyclic carbon compound as described above.

[0089] In addition, the electrolyte composition includes a non-aqueous organic solvent, and the non-aqueous organic solvent includes a cyclic ester solvent represented by the following chemical formula 1 as a main component:

[0090] [Chemical Formula 1]

[0091]

[0092] In the above chemical formula 1,

[0093] is a single bond or double bond,

[0094] X is hydrogen, fluoro, or vinyl,

[0095] p is an integer from 1 to 5.

[0096]

[0097] According to one embodiment, the cyclic ester solvent represented by the above chemical formula 1 may include one or more of the ester cyclic compounds shown below:

[0098]

[0099]

[0100] Conventionally, fluorine-substituted non-aqueous organic 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 organic solvents have low reduction potentials, leading to problems such as reduced battery capacity or deteriorated cycle characteristics when applied to electrolytes.

[0101] In comparison, the cyclic ester solvent represented by the above chemical formula 1 has a high dielectric constant and thus has excellent electrical performance such as cycle characteristics. In addition, in order for an inorganic compound such as lithium nitrate (LiNO3) to function as an additive, it must be completely dissociated within the electrolyte composition. However, since the inorganic compound exhibits low solubility in a carbonate solvent, if a carbonate solvent is used as a main component as a non-aqueous solvent, the inorganic compound cannot fully function as an electrolyte additive. However, the cyclic ester solvent represented by the above chemical formula 1 exhibits high solubility in the inorganic compound, and thus can induce complete dissociation of the inorganic compound included in the electrolyte composition. In addition, since the cyclic ester solvent represented by the above chemical formula 1 can minimize the transfer of external heat to the negative electrode active material when a lithium secondary battery is exposed to high temperatures, it can have an excellent characteristic of improving the high-temperature safety of a lithium secondary battery.

[0102] The cyclic ester solvent may be included in an amount of about 60% by volume or more based on the total weight of the non-aqueous solvent of the electrolyte composition, for example, about 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.

[0103] The present invention provides a method for controlling the content of a cyclic ester solvent contained in a non-aqueous solvent as described above, thereby allowing sufficient dissociation of an inorganic compound and sufficiently reducing heat transferred to an anode active material when a lithium secondary battery is exposed to high temperatures. In addition, since the cyclic ester solvent has excellent heat resistance, controlling the content within the above range prevents the electrolyte composition from being easily decomposed at high temperatures, and when combined with a predetermined lithium salt according to the present invention, there is an advantage in that the amount of heat transferred to the anode active material can be minimized.

[0104] In addition, the non-aqueous organic solvent may further include a carbonate solvent along with a cyclic ester solvent. The carbonate solvent may assist the cyclic ester solvent, which is the main component of the non-aqueous organic solvent, in controlling the dielectric constant and viscosity of the electrolyte composition. Through this, the carbonate solvent may ensure high ionic conductivity of the electrolyte composition.

[0105] In addition, the carbonate-based solvents can improve the low-temperature performance of the electrolyte composition, and can perform the function of preventing the generation of gas by inducing a side reaction of the electrolyte composition when exposed to high temperatures. Accordingly, from the viewpoint of electrochemical stability against oxidation-reduction and chemical stability against reaction with heat or solutes, the carbonate-based solvent may be used alone by mixing one type with the cyclic ester-based solvent represented by Chemical Formula 1, or two or more types may be mixed with the cyclic ester-based solvent in any combination according to the intended use.

[0106] 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.

[0107] The auxiliary solvent may be mixed with the cyclic ester solvent at a certain volume ratio to control the dielectric constant and viscosity of the electrolyte composition without lowering the solubility of the inorganic compound, which is an electrolyte additive. In one embodiment, the auxiliary solvent may be included in an amount of 40% by volume or less based on the total volume of the non-aqueous organic solvent, for example, about 0% to 40% by volume or less; 0% to 30% by volume or less; 0% to 25% by volume or less; 0% to 20% by volume or less; 0% to 15% by volume or less; 0% to 10% by volume or less; 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 an amount of 10% to 30% by volume.

[0108] The present invention can maintain high compatibility between the ester solvent and the 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, improve the performance of the battery by increasing the charge mobility and / or ion mobility of the battery.

[0109] The electrolyte composition may include a specific lithium salt to reduce the amount of heat transferred to the cathode active material. In one embodiment, the lithium salt may be a cation, Li + , and contains PF6 as an anion. - , PF4C2O4 - , PF2C4O8 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , (C2O4)2PF2 - Lithium phosphate salts containing BF2C2O4; - , B(C2O4)2 - Borate lithium salts including: and (CF3SO2)2N - , (FSO2)2N - , (CF3CF2SO2)2N - , ((C(CN))2NC(CF3))N - It may include at least one type of sulfonylimide lithium salt including the like, or two or more types may be used in combination as needed.

[0110] 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 may be dissolved in a cyclic ester solvent 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. To this end, the lithium salt applied in the present invention may selectively include two or more of the lithium salts described above.

[0111] For example, the lithium salt may be lithium hexafluorophosphate (hereinafter, LiPF6) and lithium bis(trifluoromethanesulfonyl)imide (anion: (CF3SO2)2N). - , Hereinafter, LiFSI) may be included.

[0112] PF6 as a Harry Si anion - LiPF6, which represents LiPF6, is a phosphate-based lithium salt commonly applied to the electrolyte composition of lithium secondary batteries, and has the characteristic of providing high conductivity to carbonate-based electrolytes. However, when LiPF6 is applied alone as a lithium salt, it decomposes into PF5 at about 200°C or higher when exposed to high temperatures. This may cause an unstable state and may reduce the high-temperature durability of the electrode, such as by removing a film derived from organic substances such as solvents and electrode active materials located on the surface of the positive electrode active layer. Therefore, in this embodiment, rather than applying LiPF6 alone as a lithium salt, two or more types are applied as described above.

[0113] In addition, LiFSI, one of the sulfonylimide-based lithium salts, has a high decomposition temperature in carbonate-based solvents, is highly safe at high temperatures, and has high water resistance, so even when in contact with moisture, the amount of hydrogen fluoride (HF) generated is not high. However, the sulfonylimide 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. In addition, for example, 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 are limitations in applying it to the electrolyte composition.

[0114] 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.

[0115] 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. For example, the mixing ratio of the first lithium salt and the second lithium salt may be about 1:0.1 to 1.0 based on the molal concentration (M), and may be, for example, about 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.

[0116] The concentration of these lithium salts may satisfy a predetermined concentration in order to increase the high-temperature safety effect while maintaining the inherent function of the lithium salt. For example, the lower limit of the concentration of the lithium salt may be about 0.5 mol / L or more, for example, about 0.7 mol / L or more, or about 0.9 mol / L or more; and the upper limit may be about 2.5 mol / L or less, or about 2.0 mol / L or less, or about 1.5 mol / L or less. By maintaining the concentration of the lithium salt within the above range, the ionic conductivity can be appropriately maintained, and the cycle characteristics and output characteristics of the non-aqueous electrolyte battery can be improved. In addition, by maintaining the concentration of the lithium salt within the above range, the viscosity of the electrolyte for the non-aqueous electrolyte battery can be maintained at an appropriate value, and the ionic conductivity can be appropriately maintained without deteriorating, and the cycle characteristics and output characteristics of the non-aqueous electrolyte battery can be improved.

[0117] 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. When 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, decomposition may be accelerated, and hydrogen fluoride (HF), which causes deterioration of battery performance, may be generated. Therefore, the temperature when dissolving the lithium salt in the non-aqueous organic solvent is not particularly limited, but may be controlled to about -20°C to ~80°C, and for example, may be controlled to about 0°C to ~60°C.

[0118] 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 with the electrolyte composition occurring on the surface of the negative electrode, thereby improving the high-temperature safety of the lithium secondary battery.

[0119] For example, the electrolyte composition may exhibit a heat flux of about 30.0 W / g or less within a range of 250°C to 350°C when measuring the heat flux of a mixture including a negative active material of a lithium secondary battery with a 100% state of charge and an electrolyte composition in a weight ratio of about 1:0.5. For example, the electrolyte composition may exhibit a heat flux of about 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 350°C when measuring the heat flux.

[0120] The above-mentioned negative electrode active material may be a carbon-based negative electrode active material commonly used as a negative electrode active material for lithium secondary batteries. For example, the above-mentioned negative electrode active material may include one or more of natural graphite, artificial graphite, expanded graphite, non-graphitizable carbon, acetylene black, and Ketjen black.

[0121] The above "heat flow rate" refers to the amount of heat flowing per unit weight, and can indicate, for example, the degree of heat generation of a secondary battery. As a result of performing a thermal analysis method that simulates the deterioration phenomenon of a secondary battery, in which the secondary battery is exposed to high temperature or spontaneously generates heat due to an external mechanical factor, on the electrolyte composition according to the present invention, the electrolyte composition exhibited a relatively low heat flow rate compared to a conventional electrolyte composition. Here, the heat flow measured according to the thermal analysis result indicates the degree of heat (e.g., heat quantity) generated or transferred between the electrolyte composition and the negative electrode active material of a charged lithium secondary battery when simulating the high-temperature deterioration 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, or measurement conditions, and may also increase or decrease depending on whether an inorganic negative electrode film 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 or transferred between the negative electrode active material and the electrolyte composition is reduced. For example, 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 reduced reactivity with lithium ions within the negative electrode active material under high-temperature conditions, thereby improving the thermal safety of lithium secondary batteries.

[0122]

[0123] lithium secondary battery

[0124] A lithium secondary battery according to one embodiment of the present invention,

[0125] An electrode assembly comprising an anode, a cathode, and a separator provided between the anode and the cathode; and

[0126] A lithium secondary battery comprising the electrolyte composition according to the present invention described above, which is impregnated into the electrode assembly, is provided. The lithium secondary battery according to one embodiment of the present invention may additionally include a case, and may be manufactured in a prismatic type, pouch type, coin type, or cylindrical type, depending on the manufacturing form.

[0127]

[0128] 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.

[0129] 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.

[0130] Accordingly, the lithium secondary battery including this has a significantly lower reactivity between the negative electrode active material (e.g., lithium ions inserted into the negative electrode active material) and the electrolyte composition, so that the temperature at which heat generation begins between them (e.g., heat generation onset temperature) increases, thereby suppressing heat generation due to negative electrode deterioration, etc. In addition, since the side reaction 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.

[0131] 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.

[0132] Below, each component of the electrode assembly is described in detail.

[0133] The electrode assembly includes an anode, a cathode, and a separator interposed between the anode and the cathode.

[0134] 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 2 as a main component, which is capable of reversibly intercalating and deintercalating lithium ions:

[0135] [Chemical Formula 2]

[0136] Li x [Ni y Co z Mn w M 1 v ]O2

[0137] In the above chemical formula 2,

[0138] M 1 is at least one element selected 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,

[0139] 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.

[0140]

[0141] The lithium metal oxide represented by the above chemical formula 2 is an oxide mixed with lithium (Li) and transition metals nickel (Ni), cobalt (Co), and manganese (Mn), and the nickel (Ni) content is about 60% or more (e.g., 60 mol%) of the total mole fraction of transition metals.

[0142] 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).

[0143] 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 0.06 Mn 0.04 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.85 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 0.1 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 0.05 Mn 0.25 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 Mn0.1 Al 0.1 One or more types of O2 can be mentioned.

[0144] In addition, the positive electrode active material may be included in an amount of about 85 parts by weight or more based on the total weight of the positive electrode active layer, for example, about 90 parts by weight or more, 93 parts by weight or more, or 95 parts by weight or more.

[0145] The above-mentioned positive electrode active layer may further include a conductive agent, a binder, other additives, etc., along with the positive electrode active material, as needed.

[0146] The above-mentioned 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 selected from graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, channel black, furnace black, lamp black, and summer black; graphene; and carbon nanotubes.

[0147] In addition, the conductive material may be included in an amount of about 0.1 to 5 parts by weight based on the total weight of the positive electrode active layer, for example, about 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.

[0148] 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. For example, the binder may include one or more resins 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).

[0149] In addition, the binder may be included in an amount of about 0.1 to 5 parts by weight based on the total weight of the positive electrode active layer, for example, about 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 about 0.1 to 1 part by weight.

[0150] The total thickness of the above-described positive electrode active layer is not particularly limited, but may be, for example, about 50 μm to 300 μm, or about 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.

[0151] The positive electrode can be 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. 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 from about 3㎛ to 500㎛, taking into account the conductivity and total thickness of the positive electrode being manufactured.

[0152] The above 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.

[0153] The above-mentioned negative electrode active layer includes a carbon-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.

[0154] The above carbon-based negative electrode active material refers to a material whose main component is carbon atoms, and such carbon-based negative electrode active material may include graphite. The graphite may include at least one of natural graphite and artificial graphite.

[0155] For example, the carbon-based negative electrode active material may include mixed graphite that is a mixture of natural graphite and artificial graphite. In this case, the mixed graphite may be a mixture of natural graphite and artificial graphite in a weight ratio of about 10 to 50:50 to 90, or about 10 to 30:70 to 90. By controlling the content ratio of natural graphite and artificial graphite as described above, the mixed graphite can prevent or suppress a decrease in the adhesive strength between the negative electrode current collector and the negative electrode active layer due to less than about 10 parts by weight of natural graphite with respect to the total weight, and can prevent or suppress a decrease in the charge / discharge capacity of the negative electrode due to more than 50 parts by weight of natural graphite.

[0156] The above carbon-based negative electrode active material is not particularly limited in its shape, but may have the shape of a spherical graphite assembly formed by an assembly of a plurality of flake-shaped graphite. Examples of the flake graphite include, in addition to natural graphite and artificial graphite, mesophase calcined carbon (bulk mesophase) made from tar and pitch, and graphitized coke (raw coke, green coke, pitch coke, needle coke, petroleum coke, etc.). For example, the above carbon-based negative electrode active material may be an assembly using a plurality of highly crystalline natural graphites. In addition, one graphite assembly may be formed by an assembly of about 2 to 100 flake-shaped graphite, for example, about 3 to 20 flakes.

[0157] In addition, the negative electrode active material may be included in an amount of about 85 parts by weight or more based on the total weight of the negative electrode active layer, for example, about 90 parts by weight or more, 93 parts by weight or more, or 95 parts by weight or more.

[0158] The negative electrode active layer according to the present invention may optionally further include a conductive agent, a binder, other additives, etc., as needed, in addition to the carbon-based negative electrode active material as the main component.

[0159] 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.

[0160] For example, the cathode active layer may contain carbon black, carbon nanotubes, carbon fibers, etc. alone or in combination as a conductive material.

[0161] The content of the conductive material may be about 0.1 parts by weight to 10 parts by weight based on 100 parts by weight of the entire negative electrode active layer, for example, about 0.1 parts by weight to 8 parts by weight, 0.1 parts by weight to 5 parts by weight, 0.1 parts by weight to 3 parts by weight, 2 parts by weight to 6 parts by weight, or about 0.5 parts by weight 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 reducing 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 reducing the charging capacity, or the problem of the rapid charging characteristics from deteriorating due to an increase in the loading amount of the negative electrode active layer.

[0162] In addition, the binder may be appropriately applied as a component that assists in the bonding of the negative electrode active material and the conductive material and the bonding to the current collector, and may be applied 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.

[0163] The content of the binder may be about 0.1 to 10 parts by weight based on 100 parts by weight of the entire negative electrode active layer, for example, about 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 or suppress a decrease in the adhesive strength of the active layer due to a low content of binder or a decrease in the electrical properties of the electrode due to an excessive amount of binder.

[0164] The average thickness of the above-described negative electrode active layer may be about 100 ㎛ to 300 ㎛, for example, about 100 ㎛ to 250 ㎛; 100 ㎛ to 250 ㎛; or about 130 ㎛ to 190 ㎛. The present invention can uniformly align the crystal planes of the carbon-based negative electrode active material contained in each region by controlling the average thickness of the negative electrode active layer within the above range, thereby improving the high-rate charge / discharge performance and energy density of a battery including the negative electrode.

[0165]

[0166] 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 about 1 ㎛ to 500 ㎛ in consideration of the conductivity and total thickness of the negative electrode to be manufactured.

[0167] Meanwhile, the separator 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 art, but for example, one containing at least one polymer selected from the group consisting of 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 about 0.01 μm to 10 μm, and an average thickness of about 5 μm to 300 μm.

[0168] 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.

[0169]

[0170] Method for producing electrolyte composition

[0171] Furthermore, the present invention provides a method for preparing the electrolyte composition described above.

[0172] Specifically, the method for preparing the electrolyte composition includes the steps of providing a lithium salt, an electrolyte additive, and a non-aqueous organic solvent,

[0173] The above electrolyte additive comprises an inorganic compound,

[0174] The above non-aqueous organic solvent contains about 60% by volume or more and less than 100% by volume of a cyclic ester solvent represented by the following chemical formula 1,

[0175] When measuring the heat flow rate of a mixture containing the negative active material of a lithium secondary battery with a 100% state of charge and the manufactured electrolyte composition in a weight ratio of 1:0.5, the mixture exhibits a heat flow rate of 30.0 W / g or less within the range of 250°C to 350°C:

[0176] [Chemical Formula 1]

[0177]

[0178] In the above chemical formula 1,

[0179] is a single bond or double bond,

[0180] X is hydrogen, fluoro, or vinyl,

[0181] p is an integer from 1 to 5.

[0182]

[0183] The electrolyte composition manufactured according to the method for manufacturing 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 the negative electrode when the lithium secondary battery is activated. Accordingly, the reactivity between 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, the lithium secondary battery including the above 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 excellent high-temperature safety.

[0184] In the method for manufacturing the above electrolyte composition, the components and content constituting the electrolyte additive, the type of the cyclic ester solvent represented by chemical formula 1 included in the non-aqueous organic solvent, etc. are the same as those described above in the 'electrolyte composition', so a detailed description is omitted.

[0185]

[0186] Hereinafter, the present invention will be described in more detail through examples and experimental examples.

[0187] 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.

[0188]

[0189] Examples 1 to 11 and Comparative Examples 1 to 9. Preparation of electrolyte composition for lithium secondary batteries.

[0190] As non-aqueous solvents, dihydrofuranone (DHF), fluorodihydrofuranone (FDHF), ethylene carbonate (EC), ethylmethyl carbonate (EMC), and fluoroethylene carbonate (FEC) were prepared, and as lithium salts, LiPF6, LiBF4, and LiFSI were prepared.

[0191] In addition, as electrolyte additives, inorganic compounds such as lithium nitrate (LiNO3) and lithium sulfate (Li2SO4) were prepared, and as additional electrolyte additives, LIBOB, LiODFB, LiDFOP, vinylene carbonate (VC), 1,3-propanesultone (PS), ethylene sulfate (ESa), and fluoroethylene carbonate (FEC) were prepared.

[0192] Each prepared lithium salt was added to a non-aqueous organic solvent at 30°C to 40°C to satisfy the molal concentration (M) shown in Table 1, and an electrolyte additive was added to prepare an electrolyte composition.

[0193] At this time, the types of non-aqueous organic solvent, lithium salt, and electrolyte additive used in the electrolyte composition were as shown in Table 1 below. In addition, the content of each component was adjusted as shown in Table 1 below, and the content ratio of each component of the non-aqueous organic solvent was adjusted based on the total volume of the non-aqueous organic solvent, and the electrolyte additive was adjusted based on the total weight of the electrolyte composition.

[0194] Non-aqueous organic solvent [unit: vol.%] Lithium salt [unit: M] Electrolyte additive [unit: wt.%] Example 1 DHF:EC=95:5 LiPF6:LiFSI=0.7:0.5 VC:PS:ESa:FEC:LiNO3=1:0.5:1:0.5:0.5 Example 2 DHF:EC=85:15 LiPF6:LiFSI=0.7:0.5 VC:PS:ESa:FEC:LiNO3=1:0.5:1:0.5:0.5 Example 3 DHF:EC=50:50 LiPF6:LiFSI=0.7:0.5 VC:PS:ESa:FEC:LiNO3=1:0.5:1:0.5:0.5 Example 4FDHF:EC=85:15LiPF6:LiFSI=0.7:0.5VC:PS:ESa:FEC:LiNO3=1:0.5:1:0.5:0.5Example 5DHF:EC=85:15LiPF6VC:PS:ESa:FEC:LiNO3=1:0.5:1:0.5:0.5Example 6DHF:EC=85:15LiBF4VC:PS:ESa:FEC:LiNO3=1:0.5:1:0.5:0.5Example 7DHF:EC=85:15LiFSIVC:PS:ESa:FEC:LiNO3=1:0.5:1:0.5:0.5Example 8DHF:EC=85:15LiPF6:LiFSI=0.7:0.5VC:PS:ESa:FEC:LiNO3=1:0.5:1:0.5:0.1Example 9DHF:EC=85:15LiPF6:LiFSI=0.7:0.5VC:PS:ESa:FEC:LiNO3=1:0.5:1:0.5:1Example 10DHF:EC=85:15LiPF6:LiFSI=0.7:0.5VC:PS:ESa:FEC:LiNO3=1:0.5:1:0.5:2Example 11DHF:EC=85:15LiPF6:LiFSI=0.7:0.5VC:PS:ESa:FEC:Li2SO4=1:0.5:1:0.5:0.5Comparative Example 1EC=100LiPF6:LiFSI=0.7:0.5VC:PS:ESa:FEC:LiNO3=1:0.5:1:0.5:0.5Comparative example 2EC:EMC=70:30LiPF6:LiFSI=0.7:0.5VC:PS:ESa:FEC:LiNO3=1:0.5:1:0.5:0.5Comparative example 3FEC:EC=85:15LiPF6:LiFSI=0.7:0.5VC:PS:ESa:FEC:LiNO3=1:0.5:1:0.5:0.5Comparative Example 4DHF=100LiPF6:LiFSI=0.7:0.5VC:PS:ESa:FEC:LiNO3=1:0.5:1:0.5:0.5Comparative Example 5DHF:EC=85:15LiPF6:LiFSI=0.7:0.5VC:PS:ESa:FEC=1:0.5:1:0.5Comparative Example 6DHF:EC=85:15LiPF6:LiFSI=0.7:0.5VC:PS:ESa:FEC:LiODFB=1:0.5:1:0.5:0.5Comparative Example 7DHF:EC=85:15LiPF6:LiFSI=0.7:0.5VC:PS:ESa:FEC:LiBOB=1:0.5:1:0.5:0.5Comparative Example 8DHF:EC=85:15LiPF6:LiFSI=0.7:0.5VC:PS:ESa:FEC:LiDFOP=1:0.5:1:0.5:0.5Comparative example 9DHF:EC=85:15LiPF6:LiFSI=0.7:0.5VC:PS:ESa:FEC:LiTDI=1:0.5:1:0.5:0.5EC: ethylene carbonate, EMC: ethyl methyl carbonate, FEC: fluoro ethylene carbonate, DHF: dihydrofuranone, FDHF: fluorodihydrofuranone, LiPF6: Lithium hexafluorophosphate, LiBF4: Lithium tetrafluoroborate, LiFSI: Lithium bis(trifluoromethanesulfonyl)imide, LiN(FSO2)2, LiBOB: Lithium bis(oxalate)borate, LiB(C2O4)2, LiODFB: Lithium difluoro(oxalato)borate, LiBF2(CO2)2)LiDFOP: Lithium difluorobis-(oxalato)phosphate, LiPF2(C2O4)2)LiTDI: Lithium 2-trifluoromethyl-4,5-dicyanoimidazole.

[0195]

[0196] Examples 12 to 22 and Comparative Examples 10 to 18. Manufacturing of lithium secondary batteries.

[0197] LiNi with a particle size of 5㎛ as a cathode active material 0.86 Co 0.05 Mn 0.07 Al 0.02O2 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 on an aluminum foil, dried in a vacuum oven at 120°C, and then rolled to prepare a positive electrode having a positive electrode active layer with a thickness of 160 μm.

[0198] Separately, a carbon-based negative electrode active material was prepared by mixing natural graphite and artificial graphite in a weight ratio of 3:7. 97 parts by weight of the prepared 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 onto a copper foil, dried in a vacuum oven at 130°C, and then rolled to prepare a negative electrode having a 180 μm thick negative electrode active layer.

[0199] 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 prepared in Examples 1 to 11 and Comparative Examples 1 to 9 were injected as shown in Table 2 below to assemble a lithium secondary battery.

[0200] Each assembled lithium secondary battery was initially charged. Specifically, the lithium secondary batteries were initially charged to a charge end voltage of 4.2 V at 55±2°C under the conditions shown in Table 2 below, thereby manufacturing activated lithium secondary batteries.

[0201] Types of manufactured lithium secondary batteries Types of electrolyte compositions Example 12 Electrolyte composition of Example 1 Example 13 Electrolyte composition of Example 2 Example 14 Electrolyte composition of Example 3 Example 15 Electrolyte composition of Example 4 Example 16 Electrolyte composition of Example 5 Example 17 Electrolyte composition of Example 6 Example 18 Electrolyte composition of Example 7 Example 19 Electrolyte composition of Example 8 Example 20 Electrolyte composition of Example 9 Example 21 Electrolyte composition of Example 10 Example 22 Electrolyte composition of Example 11 Comparative Example 10 Electrolyte composition of Comparative Example 1 Comparative Example 11 Electrolyte composition of Comparative Example 2 Comparative Example 12 Electrolyte composition of Comparative Example 3 Comparative Example 13 Electrolyte composition of Comparative Example 4 Comparative Example 14 Electrolyte composition of Comparative Example 5 Comparative Example 15 Electrolyte composition of Comparative Example 6 Comparative Example 16 Electrolyte composition of Comparative Example 7 Comparative Example 17 Electrolyte composition of Comparative Example 8 Comparative Example 18 Electrolyte composition of Comparative Example 9

[0202]

[0203] Experimental example.

[0204] 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.

[0205]

[0206] 1) Evaluation of the solubility of electrolyte additives

[0207] The degree of dissolution of inorganic additives contained in the electrolyte compositions prepared in Examples 1-11 and Comparative Examples 1-9 was evaluated. Specifically, each electrolyte composition was subjected to reduced pressure filtration using filter paper. The presence of inorganic additives remaining in the filter paper was then confirmed.

[0208] As a result, it was found that the electrolyte composition containing dihydrofuran (DHF) as a non-aqueous organic solvent did not leave any inorganic additives on the filter paper. However, in the case of the electrolyte composition not containing dihydrofuran (DHF), it was confirmed that the inorganic additives did not dissolve in the non-aqueous organic solvent and remained largely intact.

[0209] This means that inorganic additives such as lithium nitrate and lithium sulfate have high solubility in the cyclic ester solvent represented by chemical formula 1, but low solubility in the carbonate organic solvent commonly used in electrolyte compositions.

[0210]

[0211] 2) Measurement of heat onset temperature and heat flow between the negative electrode active material and electrolyte composition

[0212] Each of the lithium secondary batteries manufactured in Examples 12 to 22 and Comparative Examples 10 to 18 was fully charged to 4.25 V at a rate of 0.5 C at 25°C under CC-CV conditions, and the fully charged lithium secondary batteries were disassembled. In the disassembled lithium secondary batteries, the mixed graphite as a negative electrode active material and the electrolyte composition were weighed and mixed at a weight ratio of 1:0.5.

[0213] 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℃, and the temperature change and heat flow rate were measured in the range of 100℃ to 400℃.

[0214] 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 400℃, the value of the peak showing the largest heat flow was determined as the corresponding heat flow. The results are shown in Table 3 and Fig. 1 below.

[0215]

[0216] 3) Thermal runaway test evaluation

[0217] The lithium secondary batteries manufactured in Examples 12 to 22 and Comparative Examples 10 to 18 were charged under constant current (CC) conditions maintained at 1.25 A until they reached 4.2 V at 25°C, and then 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 they reached 2.85 V. Afterwards, each activated lithium secondary battery was allowed to rest for 6 hours at 25°C.

[0218] Then, the batteries were fully charged under constant current (CC) conditions maintained at 1.25 A until they reached 4.2 V at 25°C, and a thermal runaway test was performed using an accelerating rate calorimetry (ARC). The ARC was manufactured by Thermal Hazard Technology (THT), and the thermal runaway test was performed 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 mounted was increased from 50°C to 190°C at a rate of 10°C / min by 5°C and then waited 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 3 below.

[0219] Type of electrolyte composition DSC analysis of lithium secondary battery Maximum temperature during thermal runaway test [℃] Exothermic onset temperature [℃] Heat flow Example 1 280~300 Approximately 24±0.5 W / g 249.6 Example 2 280~300 Approximately 22±0.5 W / g 245.0 Example 3 265~275 Approximately 26±0.5 W / g 262.3 Example 4 280~300 Approximately 24±0.5 W / g 250.7 Example 5 265~275 Approximately 28±0.5 W / g 277.4 Example 6 265~275 Approximately 30±0.5 W / g 282.5 Example 7 265~275 Approximately 27±0.5 W / g 274.9 Example 8280~290Approximately 26±0.5 W / g266.8Example 9280~300Approximately 24±0.5 W / g251.9Example 10280~300Approximately 25±0.5 W / g256.3Example 11280~300Approximately 23±0.5 W / g252.4Comparative Example 1170~180Approximately 60±0.5 W / g519.8Comparative Example 2170~180Approximately 60±0.5 W / g520.1Comparative Example 3170~180Approximately 60±0.5 W / g519.5Comparative Example 4225~230Approximately 34±0.5 W / g310.7Comparative Example 5225~230Approximately 59±0.5 W / g521.0Comparative example 6265~275Approximately 38±0.5 W / g442.5Comparative example 7250~265Approximately 30±0.5 W / g451.3Comparative example 8250~265Approximately 37±0.5 W / g439.7Comparative example 9240~250Approximately 37±0.5 W / g476.2

[0220]

[0221] 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.

[0222] Referring to Table 3, in the case of the Examples, the exothermic onset temperature, which is the temperature at which heat generation begins due to the reaction between the negative active material and the electrolyte composition when exposed to high temperatures, showed a value in the range of approximately 265℃ to 300℃, while in the case of the Comparative Examples, the value was significantly lower, approximately 170℃ to 275℃. In addition, the heat flux value was in the range of approximately 22 W / g to 30 W / g in the case of the Examples, while in the case of the Comparative Examples, the value was larger, approximately 30 W / g to 60 W / g. In addition, in the thermal runaway test, the maximum temperature was in the range of 245℃ to 282.5℃ in the Examples, while in the case of the Comparative Examples, the value was in the range of 310.7℃ to 521℃, which was much higher.

[0223] Referring to Fig. 1, the electrolyte compositions of Example 2, indicated by a dotted line, exhibited a low heat flux of around 20 W / g, and Comparative Example 9, indicated by a solid line, exhibited a heat flux value of around 60 W / g.

[0224] 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.

[0225] 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.

[0226]

[0227] 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 a scope that does not depart from the technical scope of the present invention as set forth in the claims to be described below.

[0228] 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 electrolyte additive comprises an inorganic compound, The above non-aqueous organic solvent contains about 60% by volume or more and less than 100% by volume of a cyclic ester solvent represented by the following chemical formula 1, An electrolyte composition for a lithium secondary battery, which exhibits a heat flux of 30.0 W / g or less within a range of 250°C to 350°C when measuring a heat flux of a mixture containing a negative electrode active material and an electrolyte composition of a lithium secondary battery with a 100% state of charge in a weight ratio of 1:0.5: [Chemical Formula 1] In the above chemical formula 1, is a single bond or double bond, X is hydrogen, fluoro, or vinyl, p is an integer from 1 to 5.

2. In paragraph 1, An electrolyte composition for a lithium secondary battery having a heat flux of 5 W / g to 25 W / g.

3. In paragraph 1, The above inorganic compound is an electrolyte composition for a lithium secondary battery, which comprises at least one of lithium nitrate (LiNO3), lithium chloride (LiCl), lithium fluoride (LiF), lithium bromide (LiBr), lithium borate (Li3BO3), lithium carbonate (Li2CO3), lithium sulfate (Li2SO4), and lithium phosphate (Li3PO4).

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

5. 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), butylene sulfate (BSa), and fluoroethylene carbonate (FEC).

6. In paragraph 5, An electrolyte composition for a lithium secondary battery, wherein the above-mentioned cyclic carbon compound is included in an amount of 100 to 1000 parts by weight based on 100 parts by weight of the inorganic compound.

7. In paragraph 1, A lithium secondary battery electrolyte composition comprising at least one of dihydrofuranone, vinyldihydrofuranone, fluorodihydrofuranone, furanone, tetrahydropyranone, methyldihydrofuranone, propyltetrahydropyranone, and oxepanone, wherein the cyclic ester solvent represented by the above chemical formula 1 is selected from the group consisting of dihydrofuranone, vinyldihydrofuranone, fluorodihydrofuranone, furanone, tetrahydropyranone, methyldihydrofuranone, propyltetrahydropyranone, and oxepanone.

8. 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).

9. In paragraph 8, An electrolyte composition for a lithium secondary battery, wherein the carbonate solvent is included in an amount of more than about 0% by volume and less than or equal to 40% by volume based on the total weight of the non-aqueous organic solvent.

10. In paragraph 1, The above lithium salt is, Li as a cation + Including, PF6 as anion - , PF4C2O4 - , PF2C4O8 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , (C2O4)2PF2 - , BF2C2O4 - , B(C2O4)2 - , (CF3SO2)2N - , (FSO2)2N - , (CF3CF2SO2)2N - and ((C(CN))2NC(CF3))N - An electrolyte composition for a lithium secondary battery comprising at least one of the following.

11. In paragraph 1, An electrolyte composition for a lithium secondary battery, wherein the negative electrode active material comprises at least one of natural graphite, artificial graphite, expanded graphite, non-graphitizable carbon, acetylene black, and Ketjen black.

12. 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.

13. In paragraph 12, 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 2: [Chemical Formula 2] Li x [Ni y Co z Mr w M 1 v ]O2 In the above chemical formula 2, M 1 is at least one element selected 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 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.

14. A step of providing a lithium salt, an electrolyte additive and a non-aqueous organic solvent, The above electrolyte additive comprises an inorganic compound, The above non-aqueous organic solvent contains about 60% by volume or more and less than 100% by volume of a cyclic ester solvent represented by the following chemical formula 1, A method for manufacturing an electrolyte composition for a lithium secondary battery, which exhibits a heat flux of 30.0 W / g or less within a range of 250°C to 350°C when measuring heat flux for a mixture containing a negative electrode active material and an electrolyte composition of a lithium secondary battery with a 100% state of charge in a weight ratio of 1:0.5: [Chemical Formula 1] In the above chemical formula 1, is a single bond or double bond, X is hydrogen, fluoro, or vinyl, p is an integer from 1 to 5.

15. In paragraph 14, A method for producing an electrolyte composition for a lithium secondary battery having a heat flux of 5 W / g to 25 W / g.

16. In paragraph 14, A method for producing an electrolyte composition for a lithium secondary battery, wherein the above inorganic compound comprises at least one of lithium nitrate (LiNO3), lithium chloride (LiCl), lithium fluoride (LiF), lithium bromide (LiBr), lithium borate (Li3BO3), lithium carbonate (Li2CO3), lithium sulfate (Li2SO4), and lithium phosphate (Li3PO4).

17. In paragraph 14, A method for producing 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.

18. In paragraph 14, A method for producing 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), butylene sulfate (BSa), and fluoroethylene carbonate (FEC).

19. In paragraph 18, A method for producing an electrolyte composition for a lithium secondary battery, wherein the above-mentioned cyclic carbon compound is included in an amount of 100 to 1000 parts by weight based on 100 parts by weight of the inorganic compound.

20. In paragraph 14, A method for producing an electrolyte composition for a lithium secondary battery, wherein the cyclic ester solvent represented by the above chemical formula 1 comprises at least one of dihydrofuranone, vinyldihydrofuranone, fluorodihydrofuranone, furanone, tetrahydropyranone, methyldihydrofuranone, propyltetrahydropyranone, and oxepanone.

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