Electrolyte for lithium secondary battery and lithium secondary battery containing the same

Abstract

The present invention provides an electrolyte for lithium secondary batteries, the electrolyte comprising a non-aqueous organic solvent, a lithium salt, and an additive, the additive being a composition comprising a first compound represented by Chemical Formula 1 and a second compound represented by Chemical Formula 2, the first compound and the second compound each being contained in an amount of 0.1 to 10 wt %, and a lithium secondary battery comprising the electrolyte. The details of Chemical Formulas 1 and 2 are as described in the specification.

Description

[Technical Field]

[0001] This description relates to an electrolyte for a lithium secondary battery and a lithium secondary battery containing the same. [Background technology]

[0002] Lithium secondary batteries are rechargeable and have an energy density per unit weight that is more than three times higher than conventional lead-acid batteries, nickel-cadmium batteries, nickel-metal hydride batteries, and nickel-zinc batteries, allowing for fast charging. As a result, they have been commercialized for use in laptops, mobile phones, power tools, and electric bicycles, and research and development is actively underway to further improve their energy density.

[0003] Such a lithium secondary battery is used by injecting an electrolyte into a battery cell including a positive electrode containing a positive electrode active material capable of intercalating and deintercalating lithium, and a negative electrode containing a negative electrode active material capable of intercalating and deintercalating lithium.

[0004] In particular, the electrolyte uses an organic solvent in which a lithium salt is dissolved, and such an electrolyte is important in determining the stability and performance of a lithium secondary battery.

[0005] LiPF6, the most commonly used lithium salt in electrolytes, has the problem of reacting with the organic solvent in the electrolyte, accelerating the depletion of the solvent and generating a large amount of gas. When LiPF6 decomposes, it produces LiF and PF5, which causes electrolyte depletion in the battery, resulting in deterioration of high-temperature performance and safety vulnerabilities.

[0006] Therefore, there is a demand for an electrolyte solution that does not deteriorate in performance even under high temperature conditions and has improved safety. Summary of the Invention [Problem to be solved by the invention]

[0007] One embodiment is directed to providing an electrolyte for a lithium secondary battery with improved thermal stability.

[0008] Another embodiment provides a lithium secondary battery having improved life characteristics, high-temperature safety, and high-temperature reliability by applying the electrolyte, and in particular, having improved high-temperature storage characteristics and internal short circuit safety by reducing the amount of gas generation and the rate of increase in resistance when stored at high temperatures or exposed to internal short circuit conditions. [Means for solving the problem]

[0009] One embodiment of the present invention provides an electrolyte solution for a lithium secondary battery, comprising a non-aqueous organic solvent, a lithium salt, and an additive, the additive comprising a first compound represented by the following Chemical Formula 1 and a second compound represented by the following Chemical Formula 2, the first compound and the second compound each being present in an amount of 0.1 to 10 wt %:

[0010] [ka]

[0011] In the above chemical formula 1 and chemical formula 2, R 1 ~R 3are each independently a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 10 carbon atoms, a substituted or unsubstituted alkynyl group having 2 to 10 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 10 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 10 carbon atoms, a substituted or unsubstituted cycloalkenyl group having 3 to 10 carbon atoms, a substituted or unsubstituted cycloalkynyl group having 3 to 10 carbon atoms, a substituted or unsubstituted aryl group having 6 to 20 carbon atoms, an alkyl group having 1 to 10 carbon atoms substituted with at least one fluoro group, an alkenyl group having 2 to 10 carbon atoms substituted with one fluoro group, an alkynyl group having 2 to 10 carbon atoms substituted with at least one fluoro group, an alkoxy group having 1 to 10 carbon atoms substituted with at least one fluoro group, a cycloalkyl group having 3 to 10 carbon atoms substituted with at least one fluoro group, a cycloalkenyl group having 3 to 10 carbon atoms substituted with at least one fluoro group, a cycloalkynyl group having 3 to 10 carbon atoms substituted with at least one fluoro group, or an aryl group having 6 to 20 carbon atoms substituted with at least one fluoro group; X 1 and X 2 are each independently a halogen group or -OL 1 -R 4 and X 1 and X 2 At least one of them is -OL 1 -R 4 and L 1 is a single bond or a substituted or unsubstituted alkylene group having 1 to 10 carbon atoms, R 4each independently represents a cyano group (-CN), a difluorophosphate group (-OPF2), a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 10 carbon atoms, a substituted or unsubstituted alkynyl group having 2 to 10 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 10 carbon atoms, a substituted or unsubstituted cycloalkenyl group having 3 to 10 carbon atoms, a substituted or unsubstituted cycloalkynyl group having 3 to 10 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 20 carbon atoms; X 1 and X 2 At the same time -OL 1 -R 4 If R 4 exist independently of each other, or The Two R's 4 are linked to form a substituted or unsubstituted monocyclic or polycyclic aliphatic heterocycle, or a substituted or unsubstituted monocyclic or polycyclic aromatic heterocycle.

[0012] The composition may contain the first compound and the second compound in a weight ratio of 0.01:1 to 100:1.

[0013] R of Formula 1 1 ~R 3 may each independently be a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 10 carbon atoms, a substituted or unsubstituted alkynyl group having 2 to 10 carbon atoms, an alkyl group having 1 to 10 carbon atoms substituted with at least one fluoro group, an alkenyl group having 2 to 10 carbon atoms substituted with at least one fluoro group, or an alkynyl group having 2 to 10 carbon atoms substituted with at least one fluoro group.

[0014] R of Formula 1 1 ~R 3may each independently be a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 5 carbon atoms, a substituted or unsubstituted alkynyl group having 2 to 5 carbon atoms, an alkyl group having 1 to 5 carbon atoms substituted with at least one fluoro group, an alkenyl group having 2 to 5 carbon atoms substituted with at least one fluoro group, or an alkynyl group having 2 to 5 carbon atoms substituted with at least one fluoro group.

[0015] The first compound can be selected from the compounds listed in Group 1 below.

[0016] [ka]

[0017] X in the above Chemical Formula 2 1 and X 2 one of which is a fluoro group and the other is -OL 1 -R 4 and L 1 is a single bond or a substituted or unsubstituted alkylene group having 1 to 10 carbon atoms, and R 4 may be a cyano group (-CN) or a difluorophosphate group (-OPF2).

[0018] The second compound is represented by Chemical Formula 2, which can be represented by Chemical Formula 2-1 below.

[0019] [ka]

[0020] In the above chemical formula 2-1, m is an integer from 1 to 5; R 5 is a cyano group (-CN) or a difluorophosphate group (-OPF2).

[0021] The second compound is represented by Chemical Formula 2, In the above Chemical Formula 2, X 1 Ha-OL 2 -R 6 and X 2 Ha-OL 3 -R 7 and L 2 and L 3 each independently represents a single bond or a substituted or unsubstituted alkylene group having 1 to 10 carbon atoms, R 6 and R 7 are each independently a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, and R 6 and R 7 can be linked to form a substituted or unsubstituted monocyclic aliphatic heterocycle or a polycyclic aliphatic heterocycle.

[0022] The second compound can be represented by the following formula 2-2.

[0023] [ka]

[0024] In the above chemical formula 2-2, L 4 is a substituted or unsubstituted alkylene group having 2 to 5 carbon atoms.

[0025] The second compound is represented by Chemical Formula 2-2, which can be represented by Chemical Formula 2-2a or 2-2b below.

[0026] [ka]

[0027] In the above chemical formula 2-2a and chemical formula 2-2b, R 8 ~R 17 are each independently a hydrogen atom, a halogen group, or a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms.

[0028] The second compound may be any one selected from the compounds listed in Group 2 below.

[0029] [ka]

[0030] The first compound may be contained in an amount of 0.1 to 5.0 wt % based on the total weight of the electrolyte solution for a lithium secondary battery.

[0031] The second compound may be contained in an amount of 0.1 to 5.0 wt % based on the total weight of the electrolyte solution for a lithium secondary battery.

[0032] The composition may be included in an amount of 0.2 to 20 wt % based on the total weight of the electrolyte solution for lithium secondary batteries.

[0033] Another embodiment of the present invention provides a lithium secondary battery including a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, and the aforementioned electrolyte for a lithium secondary battery. [Effects of the Invention]

[0034] By applying an additive with improved thermal safety, it is possible to suppress the increase in internal resistance and gas generation of the battery after being left at high temperatures, and to suppress the voltage drop, thereby realizing a lithium secondary battery with improved high-temperature characteristics and internal short circuit safety. [Brief explanation of the drawings]

[0035] [Figure 1] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment of the present invention. [Figure 2] 1 is a graph showing temperature and voltage changes due to heat exposure at 140° C. for lithium secondary batteries according to Examples 1 to 6 and Comparative Examples 1 to 6. [Figure 3] 1 is a graph showing temperature and voltage changes due to heat exposure at 142° C. for lithium secondary batteries according to Examples 1 to 6 and Comparative Examples 1 to 6. [Figure 4] 1 is a graph showing the measurement of the time point at which a CID (Current Interrupt Device) is activated when the lithium secondary batteries according to Examples 1 to 6 and Comparative Examples 1 to 6 are left at a high temperature of 90° C.; [Figure 5] 1 is a graph showing the room-temperature charge-discharge cycle characteristics of the lithium secondary batteries according to Examples 1 to 6 and Comparative Examples 1 to 6. DETAILED DESCRIPTION OF THE INVENTION

[0036] Hereinafter, a lithium secondary battery according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings, which are given by way of example only and are not intended to limit the present invention, which is defined only by the scope of the claims that follow.

[0037] Unless otherwise defined, the term "substituted" as used herein means that at least one hydrogen atom in a substituent or compound is replaced with deuterium, a halogen group, a hydroxyl group, an amino group, a substituted or unsubstituted amine group having 1 to 30 carbon atoms, a nitro group, a substituted or unsubstituted silyl group having 1 to 40 carbon atoms, an alkyl group having 1 to 30 carbon atoms, an alkylsilyl group having 1 to 10 carbon atoms, an arylsilyl group having 6 to 30 carbon atoms, a cycloalkyl group having 3 to 30 carbon atoms, a heterocycloalkyl group having 3 to 30 carbon atoms, an aryl group having 6 to 30 carbon atoms, a heteroaryl group having 2 to 30 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a fluoroalkyl group having 1 to 10 carbon atoms, a cyano group, or a combination thereof.

[0038] In one embodiment of the present invention, "substituted" means that at least one hydrogen atom in a substituent or compound is substituted with deuterium, a halogen group, an alkyl group having 1 to 30 carbon atoms, an alkylsilyl group having 1 to 10 carbon atoms, an arylsilyl group having 6 to 30 carbon atoms, a cycloalkyl group having 3 to 30 carbon atoms, a heterocycloalkyl group having 3 to 30 carbon atoms, an aryl group having 6 to 30 carbon atoms, a heteroaryl group having 2 to 30 carbon atoms, a fluoroalkyl group having 1 to 10 carbon atoms, or a cyano group. In another specific embodiment of the present invention, "substituted" means that at least one hydrogen atom in a substituent or compound is substituted with deuterium, a halogen group, an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 30 carbon atoms, a fluoroalkyl group having 1 to 10 carbon atoms, or a cyano group. In another specific embodiment of the present invention, "substituted" means that at least one hydrogen atom in a substituent or compound is substituted with deuterium, a halogen group, an alkyl group having 1 to 5 carbon atoms, an aryl group having 6 to 18 carbon atoms, a fluoroalkyl group having 1 to 5 carbon atoms, or a cyano group. In addition, in a specific example of the present invention, "substituted" means that at least one hydrogen atom in a substituent or compound is substituted with deuterium, a cyano group, a halogen group, a methyl group, an ethyl group, a propyl group, a butyl group, a phenyl group, a biphenyl group, a terphenyl group, a trifluoromethyl group, or a naphthyl group.

[0039] Lithium secondary batteries can be classified into lithium ion batteries, lithium ion polymer batteries, and lithium polymer batteries depending on the type of separator and electrolyte used, and into cylindrical, prismatic, coin, and pouch types depending on the shape, and into bulk and thin film types depending on the size. The structure and manufacturing methods of these batteries are widely known in the art, so detailed description will be omitted.

[0040] Here, a cylindrical lithium secondary battery will be described as an example of a lithium secondary battery. Figure 1 illustrates a schematic structure of a lithium secondary battery according to an embodiment. Referring to Figure 1, a lithium secondary battery 100 according to an embodiment includes a battery cell including a positive electrode 114, a negative electrode 112 facing the positive electrode 114, a separator 113 disposed between the positive electrode 114 and the negative electrode 112, and an electrolyte (not shown) impregnating the positive electrode 114, the negative electrode 112, and the separator 113; a battery container 120 containing the battery cell; and an encapsulation member 140 sealing the battery container 120.

[0041] The configuration of the lithium secondary battery 100 according to one embodiment of the present invention will be described in more detail below.

[0042] A lithium secondary battery according to one embodiment of the present invention includes an electrolyte, a positive electrode, and a negative electrode.

[0043] The electrolyte solution includes a non-aqueous organic solvent, a lithium salt, and an additive, and the additive is a composition including a first compound represented by the following chemical formula 1 and a second compound represented by the following chemical formula 2, and the first compound and the second compound are each included in an amount of 0.1 to 10 wt %.

[0044] [ka]

[0045] In the above chemical formula 1 and chemical formula 2, R 1 ~R 3are each independently a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 10 carbon atoms, a substituted or unsubstituted alkynyl group having 2 to 10 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 10 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 10 carbon atoms, a substituted or unsubstituted cycloalkenyl group having 3 to 10 carbon atoms, a substituted or unsubstituted cycloalkynyl group having 3 to 10 carbon atoms, a substituted or unsubstituted aryl group having 6 to 20 carbon atoms, an alkyl group having 1 to 10 carbon atoms substituted with at least one fluoro group, an alkenyl group having 2 to 10 carbon atoms substituted with one fluoro group, an alkynyl group having 2 to 10 carbon atoms substituted with at least one fluoro group, an alkoxy group having 1 to 10 carbon atoms substituted with at least one fluoro group, a cycloalkyl group having 3 to 10 carbon atoms substituted with at least one fluoro group, a cycloalkenyl group having 3 to 10 carbon atoms substituted with at least one fluoro group, a cycloalkynyl group having 3 to 10 carbon atoms substituted with at least one fluoro group, or an aryl group having 6 to 20 carbon atoms substituted with at least one fluoro group; X 1 and X 2 are each independently a halogen group or -OL 1 -R 4 and X 1 and X 2 At least one of them is -OL 1 -R 4 and L 1 is a single bond or a substituted or unsubstituted alkylene group having 1 to 10 carbon atoms, R 4each independently represents a cyano group (-CN), a difluorophosphate group (-OPF2), a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 10 carbon atoms, a substituted or unsubstituted alkynyl group having 2 to 10 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 10 carbon atoms, a substituted or unsubstituted cycloalkenyl group having 3 to 10 carbon atoms, a substituted or unsubstituted cycloalkynyl group having 3 to 10 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 20 carbon atoms; X 1 and X 2 At the same time -OL 1 -R 4 If R 4 exist independently of each other, or The Two R's 4 are linked to form a substituted or unsubstituted monocyclic or polycyclic aliphatic heterocycle, or a substituted or unsubstituted monocyclic or polycyclic aromatic heterocycle.

[0046] The first compound is a phosphate-based compound that forms a solid-phase char film with insulating properties when the battery is exposed to high temperatures, thereby suppressing the combustion reaction between the electrolyte and gas components on the electrode surface, and can capture radical products generated during the combustion reaction of the electrolyte or gas components inside the battery, thereby terminating the radical chain reaction.

[0047] In addition, by including a fluorophosphate-based compound represented by the second compound, the flame retardant properties are improved and adverse effects of lithium salt decomposition products in the electrolyte solution that are generated during high-temperature decomposition are controlled.

[0048] Generally, the decomposition of lithium salt anions, such as hexafluorophosphate anions, produces by-products such as lithium fluoride (LiF) and phosphorus pentafluoride (PF5), a strong Lewis acid. LiF increases the resistance at the electrode surface, while PF5 etches and destroys the stable electrode coating components that have already formed.

[0049] However, the second compound binds to and stabilizes phosphorus pentafluoride, thereby suppressing the strong acidity of phosphorus pentafluoride and capturing oxygen gas generated by the collapse of the positive electrode structure, thereby suppressing the electrolyte combustion reaction at high temperatures.

[0050] That is, the composition contains both the first compound represented by Formula 1 and the second compound represented by Formula 2, thereby improving both the high temperature safety and flame retardancy of the battery.

[0051] For example, the composition may contain the first compound and the second compound in a weight ratio of 0.01:1 to 100:1.

[0052] As a specific example, the composition may contain the first compound and the second compound in a weight ratio of 0.02:1 to 100:1, 0.03:1 to 100:1, 0.04:1 to 100:1, or 0.05:1 to 100:1.

[0053] As another specific example, the composition may contain the first compound and the second compound in a weight ratio of 0.01:1 to 80:1, 0.01:1 to 60:1, 0.01:1 to 40:1, or 0.01:1 to 20:1.

[0054] In one embodiment, the composition can include the first compound and the second compound in a weight ratio of 0.01:1, 0.05:1, 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 10:1, 20:1, 30:1, 40:1, 50:1, or 100:1.

[0055] When the mixing ratio of the first compound and the second compound is as described above, the degree of improvement in effect can be maximized.

[0056] For example, R in Formula 1 1 ~R 3may each independently be a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 10 carbon atoms, a substituted or unsubstituted alkynyl group having 2 to 10 carbon atoms, an alkyl group having 1 to 10 carbon atoms substituted with at least one fluoro group, an alkenyl group having 2 to 10 carbon atoms substituted with at least one fluoro group, or an alkynyl group having 2 to 10 carbon atoms substituted with at least one fluoro group.

[0057] As a specific example, R 1 ~R 3 may each independently be a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 5 carbon atoms, a substituted or unsubstituted alkynyl group having 2 to 5 carbon atoms, an alkyl group having 1 to 5 carbon atoms substituted with at least one fluoro group, an alkenyl group having 2 to 5 carbon atoms substituted with at least one fluoro group, or an alkynyl group having 2 to 5 carbon atoms substituted with at least one fluoro group.

[0058] For example, the first compound can be selected from the compounds listed in Group 1 below.

[0059] [ka]

[0060] For example, X in Formula 2 1 and X 2 one of which is a fluoro group and the other is -OL 1 -R 4 and L 1 is a single bond or a substituted or unsubstituted alkylene group having 1 to 10 carbon atoms, R 4 may be a cyano group (-CN) or a difluorophosphate group (-OPF2).

[0061] As a specific example, the second compound is represented by Chemical Formula 2, which can be represented by the following Chemical Formula 2-1.

[0062] [ka]

[0063] In the above chemical formula 2-1, m is an integer from 1 to 5; R 5 is a cyano group (-CN) or a difluorophosphate group (-OPF2).

[0064] For example, the second compound is represented by Formula 2, wherein X 1 Ha-OL 2 -R 6 and X 2 Ha-OL 3 -R 7 and L 2 and L 3 are each independently a single bond or a substituted or unsubstituted alkylene group having 1 to 10 carbon atoms, and R 6 and R 7 are each independently a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, and R 6 and R 7 can be linked to form a substituted or unsubstituted monocyclic aliphatic heterocycle or a polycyclic aliphatic heterocycle.

[0065] As a specific example, the second compound can be represented by the following Chemical Formula 2-2.

[0066] [ka]

[0067] In the above chemical formula 2-2, L 4 is a substituted or unsubstituted alkylene group having 2 to 5 carbon atoms.

[0068] As a more specific example, the second compound is represented by Chemical Formula 2-2, which can be represented by Chemical Formula 2-2a or 2-2b below.

[0069] [ka]

[0070] In the above chemical formula 2-2a and chemical formula 2-2b, R 8 ~R 17 are each independently a hydrogen atom, a halogen group, or a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms.

[0071] For example, the second compound may be any one selected from the compounds listed in Group 2 below.

[0072] [ka]

[0073] According to a most specific embodiment, the additive contained in the electrolyte for a lithium secondary battery according to the present invention may be a composition including at least one of the compounds listed in Group 1 as a first compound and at least one of the compounds listed in Group 2 as a second compound.

[0074] For example, the additive contained in the electrolyte for a lithium secondary battery according to the present invention may be a composition including, as a first compound, any one of Compound 1-a, Compound 1-b, and Compound 1-c of Group 1, and, as a second compound, Compound 2-a or Compound 2-d of Group 2.

[0075] In one embodiment, the first compound and the second compound may each be contained in an amount of 0.1 to 5.0 wt %.

[0076] The composition may be included in an amount of 0.2 to 20 wt % based on the total weight of the electrolyte solution for lithium secondary batteries.

[0077] For example, the composition may be included in an amount of 0.2 to 10 wt % based on the total weight of the electrolyte for a lithium secondary battery.

[0078] When the content of the composition and the content of each component in the composition, i.e., the first compound and the second compound, are within the above ranges, the safety of the battery, such as thermal safety and internal short circuit safety, is improved, and gas generation inside the battery is suppressed, thereby realizing a lithium secondary battery with improved battery characteristics at room temperature and high temperature.

[0079] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0080] The non-aqueous organic solvent may be a carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or aprotic solvent.

[0081] Examples of the carbonate solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). Examples of the ester solvent include methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, decanolide, mevalonolactone, and caprolactone. Examples of the ether solvent include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, and tetrahydrofuran. In addition, cyclohexanone or the like can be used as the ketone solvent, ethyl alcohol, isopropyl alcohol or the like can be used as the alcohol solvent, and R 18 -CN(R 18 (wherein R is a hydrocarbon group having 2 to 20 carbon atoms and having a linear, branched, or cyclic structure, and may contain a double bond, aromatic ring, or ether bond), nitriles such as dimethylformamide, amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolanes, etc. can be used.

[0082] The non-aqueous organic solvents may be used alone or in combination of two or more. When two or more non-aqueous organic solvents are used in combination, the mixing ratio may be appropriately adjusted depending on the desired battery performance, which should be widely understood by those skilled in the art.

[0083] In addition, in the case of the carbonate-based solvent, it is preferable to use a mixture of cyclic carbonate and chain carbonate, and in this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of 1:1 to 1:9, the performance of the electrolyte is shown to be excellent.

[0084] In particular, in one embodiment of the present invention, the non-aqueous organic solvent may contain the cyclic carbonate and the chain carbonate in a volume ratio of 2:8 to 5:5, and as a specific example, the cyclic carbonate and the chain carbonate may be contained in a volume ratio of 2:8 to 4:6.

[0085] As a more specific example, the cyclic carbonate and the chain carbonate may be contained in a volume ratio of 2:8 to 3:7.

[0086] The non-aqueous organic solvent may further include an aromatic hydrocarbon-based organic solvent in addition to the carbonate-based solvent, and the carbonate-based solvent and the aromatic hydrocarbon-based solvent may be mixed in a volume ratio of 1:1 to 30:1.

[0087] The aromatic hydrocarbon solvent may be an aromatic hydrocarbon compound represented by the following formula 3:

[0088] [ka]

[0089] In the above chemical formula 3, R 19 ~R 24 are the same or different and are selected from the group consisting of hydrogen, halogen, alkyl groups having 1 to 10 carbon atoms, haloalkyl groups, and combinations thereof.

[0090] Specific examples of the aromatic hydrocarbon solvent include benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene, 1,2,4-triiodobenzene, toluene, fluorobenzene, fluoroisopropyl ether ... and combinations thereof.

[0091] The electrolyte may further include vinylene carbonate, vinylethylene carbonate, or an ethylene carbonate-based compound of the following Formula 4 as a life-promoting additive to improve battery life.

[0092] [ka]

[0093] In the above chemical formula 4, R 25 and R 26 are the same or different and are selected from the group consisting of hydrogen, a halogen group, a cyano group (CN), a nitro group (NO), and a fluorinated alkyl group having 1 to 5 carbon atoms; 25 and R 26At least one of R is selected from the group consisting of a halogen group, a cyano group (CN), a nitro group (NO2), and a fluorinated alkyl group having 1 to 5 carbon atoms, with the proviso that R 25 and R 26 But it's not all hydrogen.

[0094] Representative examples of the ethylene carbonate compound include difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, fluoroethylene carbonate, etc. When such a life-improving additive is further used, the amount used can be appropriately adjusted.

[0095] The lithium salt is dissolved in a non-aqueous organic solvent and acts as a lithium ion source in the battery, enabling basic lithium secondary battery operation and promoting the movement of lithium ions between the positive electrode and the negative electrode. Representative examples of such lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide (LiFSI)), LiC4F9SO3, LiClO4, LiAlO2, LiAlCl4, LiPO2F 2、 LiN(C x F 2x+1 SO2)(C y F 2y+1The lithium salt may be one or more selected from the group consisting of Li(SO2) (where x and y are natural numbers, e.g., integers of 1 to 20), LiCl, LiI, LiB(C2O4)2 (lithium bis(oxalato)borate: LiBOB), LiDFOB (lithium difluoro(oxalato)borate), and Li[PF2(C2O4)2] (lithium difluoro(bisoxalato)phosphate). The lithium salt concentration is preferably within a range of 0.1 M to 2.0 M. When the lithium salt concentration is within this range, the electrolyte has appropriate conductivity and viscosity, thereby exhibiting excellent electrolyte performance and allowing lithium ions to migrate effectively.

[0096] The positive electrode includes a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector, and the positive electrode active material layer includes a positive electrode active material.

[0097] As the positive electrode active material, a compound capable of reversible intercalation and deintercalation of lithium (lithiated intercalation compound) can be used.

[0098] Specifically, at least one of composite oxides of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof can be used.

[0099] Of course, the composite oxide may have a coating layer on its surface, or a mixture of the composite oxide and a composite oxide having a coating layer may be used. The coating layer may include at least one coating element compound selected from the group consisting of oxides of the coating elements, hydroxides of the coating elements, oxyhydroxides of the coating elements, oxycarbonates of the coating elements, and hydroxycarbonates of the coating elements. The compounds forming the coating layer may be amorphous or crystalline. The coating elements contained in the coating layer may be Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof. The coating layer formation process may be performed using any coating method (e.g., spray coating, dipping, etc.) that does not adversely affect the physical properties of the positive electrode active material using such elements in the compound. Since this method is well understood by those skilled in the art, detailed explanations will be omitted.

[0100] The positive electrode active material may be, for example, one or more lithium composite oxides represented by the following chemical formula 5. [Chemical formula 5] Li x M 1 1-y-z M 2 y M 3 z O2 In the above chemical formula 5, 0.5≦x≦1.8, 0≦y<1, 0≦z<1, 0≦y+z<1, M 1 , M 2 and M 3 may each independently be any one selected from metals such as Ni, Co, Mn, Al, Sr, Mg, or La, and combinations thereof.

[0101] In one embodiment, the M 1 may be a metal such as Co, Mn, Al, Sr, Mg or La,2 and M 3 may each independently be Ni or Co.

[0102] In a specific embodiment, the M 1 may be Mn or Al, and said M 2 and M 3 may each independently be Ni or Co, but is not limited to this.

[0103] In a more specific embodiment, the positive electrode active material may be a lithium composite oxide represented by the following Formula 5-1 or 5-2. [Chemical formula 5-1] Li x1 Ni y1 Co z1 Al 1-y1-z1 O2 In the above chemical formula 5-1, 1≦x1≦1.2, 0 <y1<1、そして0<z1<1である。 [Chemical formula 5-2] Li x2 Ni y2 Co z2 Mn 1-y2-z2 O2 In the above chemical formula 5-2, 1≦x2≦1.2, 0 <y2<1、そして0<z2<1である。

[0104] For example, in the above formula 5-1, 1≦x1≦1.2, 0.5≦y1<1, and 0 <z1≦0.5であってもよい。

[0105] As a specific example, in the above Chemical Formula 5-1, 1≦x1≦1.2, 0.6≦y1<1, and 0 <z1≦0.5であってもよい。

[0106] As a more specific example, in the above Chemical Formula 5-1, 1≦x1≦1.2, 0.7≦y1<1, and 0 <z1≦0.5であってもよい。

[0107] For example, in the above formula 5-1, 1≦x1≦1.2, 0.8≦y1<1, and 0 <z1≦0.5であってもよい。

[0108] For example, in Formula 5-2, 1≦x2≦1.2, 0.3≦y2<1, and 0.3≦z2<1.

[0109] As a specific example, in the above Chemical Formula 5-2, 1≦x2≦1.2, 0.6≦y2<1, and 0.3≦z2<1 may be satisfied.

[0110] As a more specific example, in the above Chemical Formula 5-2, 1≦x2≦1.2, 0.7≦y2<1, and 0.3≦z2<1 may be satisfied.

[0111] For example, in the above chemical formula 5-2, 1≦x2≦1.2, 0.8≦y2<1, and 0.3≦z2<1.

[0112] The content of the positive electrode active material may be 90 wt % to 98 wt % based on the total weight of the positive electrode active material layer.

[0113] In one embodiment of the present invention, the positive electrode active material layer may optionally include a conductive material and a binder, and the content of the conductive material and the binder may be 1 wt % to 5 wt % respectively based on the total weight of the positive electrode active material layer.

[0114] The conductive material is used to impart conductivity to the positive electrode, and any material can be used as long as it does not cause a chemical change in the constructed battery and is electronically conductive. Examples of such a conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, and carbon fiber; metal-based materials such as metal powder or metal fiber of copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; and conductive materials containing mixtures of these.

[0115] The binder serves to firmly adhere the positive electrode active material particles to each other and to firmly adhere the positive electrode active material to the current collector. Representative examples of the binder include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, and nylon.

[0116] The positive electrode current collector may be made of Al, but is not limited thereto.

[0117] The negative electrode includes a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector and containing a negative electrode active material.

[0118] The negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, a lithium metal alloy, a material capable of being doped with and dedoped from lithium, or a transition metal oxide.

[0119] The material capable of reversibly intercalating / deintercalating lithium ions is a carbon material, and any carbon-based negative electrode active material commonly used in lithium secondary batteries can be used, representative examples of which include crystalline carbon, amorphous carbon, or a combination of these. Examples of crystalline carbon include amorphous, plate-like, flake-like, spherical, or fibrous graphite, such as natural graphite or artificial graphite. Examples of amorphous carbon include soft carbon, hard carbon, mesophase pitch carbide, and calcined coke.

[0120] As the alloy of the lithium metal, an alloy of lithium and a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0121] As the substance capable of doping and undoping lithium, Si, Si-C composite, SiO x (0 < x < 2), Si-Q alloy (where Q is an element selected from the group consisting of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a Group 15 element, a Group 16 element, a transition metal, a rare earth element, and combinations thereof, and is not Si), Sn, SnO2, Sn-R 22 (where R 22 is an element selected from the group consisting of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a Group 15 element, a Group 16 element, a transition metal, a rare earth element, and combinations thereof, and is not Sn), etc. can be mentioned, and at least one of these can also be mixed with SiO2 and used.

[0122] The elements Q and R 22 can be those selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

[0123] Examples of the transition metal oxide include vanadium oxide, lithium vanadium oxide, or lithium titanate.

[0124] In a specific embodiment, the negative electrode active material may be a Si-C composite including a Si-based active material and a carbon-based active material.

[0125] In the Si-C composite, the average particle size of the Si-based active material may be 50 nm to 200 nm.

[0126] When the average particle size of the Si-based active material is within the above range, volume expansion that occurs during charge and discharge can be suppressed, and conductive path disconnection due to particle crushing during charge and discharge can be prevented.

[0127] The Si-based active material may be included in an amount of 1 to 60 wt % of the total weight of the Si-C composite, for example, 3 to 60 wt %.

[0128] In another specific embodiment, the negative electrode active material may further include crystalline carbon in addition to the Si—C composite.

[0129] When the negative electrode active material includes both a Si-C composite and crystalline carbon, the Si-C composite and crystalline carbon may be included in the form of a mixture, and in this case, the Si-C composite and crystalline carbon may be included in a weight ratio of 1:99 to 50:50. More specifically, the Si-C composite and crystalline carbon may be included in a weight ratio of 5:95 to 20:80.

[0130] The crystalline carbon may include, for example, graphite, and more specifically, may include natural graphite, artificial graphite, or a mixture thereof.

[0131] The crystalline carbon may have an average particle size of 5 μm to 30 μm.

[0132] In this specification, the average particle size may be the particle size at 50% volume ratio (D50) on a cumulative size-distribution curve.

[0133] The Si—C composite may further include a shell surrounding the surface of the Si—C composite, and the shell may include amorphous carbon.

[0134] The amorphous carbon may include soft carbon, hard carbon, mesophase pitch charcoal, calcined coke, or a mixture thereof.

[0135] The amorphous carbon may be contained in an amount of 1 to 50 parts by weight, for example, 5 to 50 parts by weight, or 10 to 50 parts by weight, relative to 100 parts by weight of the carbon-based active material.

[0136] The content of the negative electrode active material in the negative electrode active material layer may be 95 wt % to 99 wt % based on the total weight of the negative electrode active material layer.

[0137] In one embodiment of the present invention, the negative electrode active material layer includes a binder and may optionally further include a conductive material. The content of the binder in the negative electrode active material layer may be 1 wt% to 5 wt% based on the total weight of the negative electrode active material layer. When the conductive material is further included, the negative electrode active material may be used in an amount of 90 wt% to 98 wt%, the binder in an amount of 1 wt% to 5 wt%, and the conductive material in an amount of 1 wt% to 5 wt%.

[0138] The binder serves to firmly adhere the negative active material particles to each other and to the current collector, and may be a water-insoluble binder, a water-soluble binder, or a combination thereof.

[0139] The non-water-soluble binder may be polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0140] The water-soluble binder may be a rubber-based binder or a polymer resin binder. The rubber-based binder may be selected from styrene butadiene rubber, acrylated styrene butadiene rubber (SBR), acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, and combinations thereof. The polymer resin binder may be selected from polytetrafluoroethylene, ethylene propylene copolymer, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0141] When a water-soluble binder is used as the negative electrode binder, a cellulose-based compound capable of imparting viscosity may be further included as a thickener. The cellulose-based compound may be a mixture of one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or alkali metal salts thereof. The alkali metal may be sodium, potassium, or lithium. The amount of the thickener used may be 0.1 to 3 parts by weight per 100 parts by weight of the negative electrode active material.

[0142] The conductive material is used to impart conductivity to the electrodes, and any material can be used as long as it does not cause a chemical change in the constructed battery and is electronically conductive. Examples of such a conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, and carbon fiber; metal-based materials such as metal powder or metal fiber of copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; and conductive materials containing mixtures of these.

[0143] The negative electrode current collector may be selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0144] Depending on the type of lithium secondary battery, a separator may be present between the positive electrode and the negative electrode. Such a separator may be a porous substrate or a composite porous substrate.

[0145] The porous substrate is a substrate containing voids through which lithium ions can move. The porous substrate may be made of, for example, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more of these materials. Of course, a mixed multilayer film such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may also be used.

[0146] The composite porous substrate may include a porous substrate and a functional layer disposed on the porous substrate. The functional layer may be, for example, at least one of a heat-resistant layer and an adhesive layer, from the viewpoint of enabling additional functions to be added. For example, the heat-resistant layer may include a heat-resistant resin and, optionally, a filler.

[0147] The adhesive layer may also include an adhesive resin and, optionally, a filler.

[0148] The filler may be an organic filler or an inorganic filler.

[0149] Examples and comparative examples of the present invention will be described below. However, the following examples are merely one embodiment of the present invention, and the present invention is not limited to the following examples. [Example]

[0150] Fabrication of lithium secondary batteries Comparative Example 1 LiNi as the positive electrode active material 0.88 Co 0.07 Al 0.05 O2, polyvinylidene fluoride as a binder, and Ketjen black as a conductive material were mixed in a weight ratio of 97:2:1 and dispersed in N-methylpyrrolidone to prepare a positive electrode active material slurry.

[0151] The positive electrode active material slurry was coated on an aluminum foil having a thickness of 14 μm, dried at 110° C., and then pressed to prepare a positive electrode.

[0152] A mixture of artificial graphite and Si-C composite in a weight ratio of 93:7 was used as the negative electrode active material. The negative electrode active material and binder, styrene-butadiene rubber binder, and carboxymethyl cellulose thickener were mixed in a weight ratio of 97:1:2 and dispersed in distilled water to prepare a negative electrode active material slurry.

[0153] The Si-C composite has a core containing artificial graphite and silicon particles, and the surface of the core is coated with coal-based pitch.

[0154] The negative electrode active material slurry was coated on a copper foil having a thickness of 10 μm, dried at 100° C., and then pressed to prepare a negative electrode.

[0155] The prepared positive and negative electrodes were assembled with a 25 μm thick polyethylene separator to prepare an electrode assembly, and an electrolyte was injected to prepare a lithium secondary battery.

[0156] The electrolyte composition is as follows: (Electrolyte composition) Salt: LiPF61.5M Solvent: ethylene carbonate: ethyl methyl carbonate: dimethyl carbonate (EC:EMC:DMC = 20:10:70 volume ratio)

[0157] Comparative Example 2 A lithium secondary battery was fabricated in the same manner as in Comparative Example 1, except that 2.0 wt % of the compound of the following Formula 1-a was added to the electrolyte. (However, in the electrolyte composition, "wt %" is based on the total electrolyte content (lithium salt + non-aqueous organic solvent + additives).)

[0158] [ka]

[0159] Comparative Example 3 A lithium secondary battery was fabricated in the same manner as in Comparative Example 1, except that 2.0 wt % of the compound of the following Formula 1-b was added to the electrolyte.

[0160] [ka]

[0161] Comparative Example 4 A lithium secondary battery was fabricated in the same manner as in Comparative Example 1, except that 2.0 wt % of a compound represented by the following Formula 1-c was added to the electrolyte.

[0162] [ka]

[0163] Comparative Example 5 A lithium secondary battery was fabricated in the same manner as in Comparative Example 1, except that 2.0 wt % of the compound of the following Formula 2-a was added to the electrolyte.

[0164] [ka]

[0165] Comparative Example 6 A lithium secondary battery was fabricated in the same manner as in Comparative Example 1, except that 2.0 wt % of a compound represented by the following Formula 2-d was added to the electrolyte.

[0166] [ka]

[0167] Examples 1 to 42 and Comparative Examples 7 to 18 A lithium secondary battery was fabricated in the same manner as in Comparative Example 1, except that the composition was changed as shown in Table 1 below.

[0168] [Table 1A] [Table 1B]

[0169] Evaluation 1: Heat exposure evaluation The lithium secondary batteries according to Examples 1 to 42 and Comparative Examples 1 to 18 were charged in a 3.0 V discharge state at a 0.5 C charge rate under a 4.2 V / 3 hr cutoff condition, and then subjected to a heat exposure evaluation.

[0170] The lithium secondary batteries according to Examples 1 to 42 and Comparative Examples 1 to 18 were placed in a chamber, and the temperature was increased from room temperature to 140°C and 142°C at a rate of 5°C per minute. These temperatures were maintained for about one hour, and the changes in the lithium secondary batteries were observed. The results are shown in Table 2, Figure 2, and Figure 3. The dotted line indicates the change in voltage over time, and the solid line indicates the change in temperature over time.

[0171] In Table 2, if the temperature is maintained and no thermal runaway occurs, it is indicated as OK, and if sudden thermal runaway occurs when exposed to high temperatures, it is indicated as NG.

[0172] [Table 2A] [Table 2B]

[0173] Referring to Table 2, it can be seen that the lithium secondary batteries according to Examples 1 to 42 maintained their temperature and did not experience thermal runaway when exposed to high temperatures. In contrast, sudden thermal runaway was observed in the lithium secondary batteries according to Comparative Examples 1 to 18. In particular, the lithium secondary batteries according to Comparative Examples 2 to 6 did not experience thermal runaway when exposed to heat at 140°C, but eventually did experience thermal runaway when exposed to heat at 142°C.

[0174] In particular, FIG. 2 and FIG. 3 show temperature and voltage change profiles for some of the examples and comparative examples.

[0175] FIG. 2 is a graph showing the temperature and voltage changes caused by heat exposure at 140° C. for the lithium secondary batteries according to Examples 1 to 6 and Comparative Examples 1 to 6.

[0176] FIG. 3 is a graph showing the temperature and voltage changes caused by heat exposure at 142° C. for the lithium secondary batteries according to Examples 1 to 6 and Comparative Examples 1 to 6.

[0177] 2 and 3, a sudden voltage drop was observed in the lithium secondary batteries according to Examples 1 to 6 and Comparative Examples 1 to 6. When a cylindrical battery is suddenly exposed to high temperatures, gas is generated, increasing the internal pressure, which activates the battery protection circuit (CID), causing a sudden voltage drop. The occurrence of a sudden voltage drop indicates that the lithium secondary batteries according to Examples 1 to 6 and Comparative Examples 1 to 6 activated their protection circuits due to gas generation caused by exposure to high temperatures.

[0178] However, even when exposed to a temperature of 140°C, the lithium secondary batteries according to Examples 1 to 6 maintained the temperature at 140°C and did not experience thermal runaway, whereas the lithium secondary battery according to Comparative Example 1 maintained the temperature at 140°C when exposed to a temperature of 140°C, but it was confirmed that a sudden thermal runaway occurred at 240°C or higher (at 78 minutes).

[0179] When the temperature was raised a little further to 142°C, it was confirmed that the lithium secondary batteries according to Comparative Examples 2 to 6 as well as Comparative Example 1 also experienced thermal runaway at temperatures above 200°C. This indicates that the lithium secondary batteries according to Comparative Examples 1 to 6 did not simply generate gas, but also experienced thermal runaway, causing the batteries to explode.

[0180] Therefore, it is understood that the lithium secondary batteries according to Examples 1 to 42 have higher thermal stability than the lithium secondary batteries according to Comparative Examples 1 to 18.

[0181] Evaluation 2: High temperature storage characteristics evaluation The lithium secondary batteries of Examples 1 to 6 and Comparative Examples 1 to 6 were charged at a 0.5C charge / discharge rate to 4.35V in a CC / CV mode for 3 hours, and then left in a 90°C chamber for 110 hours, and the activation time of the CID (Current Interrupt Device) was measured.

[0182] The CID (Current Interrupt Device) is a device that detects a change in pressure within a sealed device, i.e., a pressure increase, and cuts off current when the pressure exceeds a certain level. This is obvious to those skilled in the art, so a detailed description of this will be omitted.

[0183] The high-temperature storage characteristics of the lithium secondary battery were evaluated by measuring the time when the CID was activated, and the measurement results are shown in FIG. 4.

[0184] FIG. 4 is a graph showing the measurement of the activation time of the CID (Current Interrupt Device) of the lithium secondary batteries according to Examples 1 to 6 and Comparative Examples 1 to 6.

[0185] The high-temperature storage characteristics of a lithium secondary battery can be evaluated by measuring the CID activation time.

[0186] 4, Comparative Examples 1 to 6 exhibited a rapid voltage drop before about 100 hours when stored at a high temperature of 90°C, whereas Examples 1 to 6 containing an additive according to an embodiment of the present invention exhibited no voltage drop until at least 110 hours, demonstrating the effect of delaying electrolyte decomposition, thereby reducing resistance increase and delaying OCV drop. In other words, the lithium secondary battery according to the present invention exhibits excellent suppression of gas generation during high-temperature storage.

[0187] Evaluation 3: Room temperature life characteristics evaluation The lithium secondary batteries manufactured in Examples 1 to 6 and Comparative Examples 1 to 6 were charged and discharged for 250 cycles at room temperature (25°C) between 2.5 V and 4.2 V at a 0.5 C C-rate, and the change in discharge capacity was measured. The capacity ratio at 250 cycles to the single discharge capacity (capacity retention rate) was calculated, and the results are shown in FIG. 5.

[0188] FIG. 5 is a graph showing the room-temperature charge-discharge cycle characteristics of the lithium secondary batteries according to Examples 1 to 6 and Comparative Examples 1 to 6.

[0189] Referring to FIG. 5, it can be seen that in Examples 1 to 6, the lifespan is not significantly reduced compared to Comparative Examples 1 to 6.

[0190] Therefore, in the case of a lithium secondary battery using the specific mixed composition according to the present embodiment as an additive, excellent thermal stability can be significantly improved without reducing the lifespan.

[0191] Although the preferred embodiment of the present invention has been described above, the present invention is not limited thereto, and various modifications can be made within the scope of the claims, the detailed description of the invention, and the accompanying drawings, and it is to be understood that these modifications also fall within the scope of the present invention. [Explanation of symbols]

[0192] 100: Lithium secondary battery 112: Negative electrode 113: Separator 114: Positive electrode 120:Battery container 140: Enclosure material

Claims

1. non-aqueous organic solvents, lithium salts, and Contains additives, The additive is a composition including a first compound represented by the following chemical formula 1 and a second compound, an electrolyte solution for a lithium secondary battery, the electrolyte solution containing the first compound and the second compound each in an amount of 0.1 to 10% by weight; 【Chemistry 7】 In the above chemical formula 1, R １ ~R ３ each independently represents a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 5 carbon atoms, a substituted or unsubstituted alkynyl group having 2 to 5 carbon atoms, an alkyl group having 1 to 5 carbon atoms substituted with at least one fluoro group, an alkenyl group having 2 to 5 carbon atoms substituted with at least one fluoro group, or an alkynyl group having 2 to 5 carbon atoms substituted with at least one fluoro group, The second compound is any one of a compound of the following formula 2-1 and a compound 2-d: 【Chemistry 8】 (In the above chemical formula 2-1, m is an integer from 1 to 5; R ５ is a difluorophosphate group (-OPF ２ ) is) 【Chemistry 10】 。

2. 2. The electrolyte solution for a lithium secondary battery according to claim 1, wherein the composition contains the first compound and the second compound in a weight ratio of 0.01:1 to 100:

1.

3. 2. The electrolyte solution for a lithium secondary battery according to claim 1, wherein the first compound is any one selected from the compounds listed in Group 1 below: 【Chemistry 2】 。

4. The electrolyte solution for a lithium secondary battery according to claim 1, wherein the second compound is any one of the following compounds 2-a and 2-d: 【Chemistry 6】 。

5. 2. The electrolyte for a lithium secondary battery according to claim 1, wherein the first compound is contained in an amount of 0.1 to 5.0 wt % based on the total weight of the electrolyte for a lithium secondary battery.

6. 2. The electrolyte for a lithium secondary battery according to claim 1, wherein the second compound is contained in an amount of 0.1 to 5.0 wt % based on the total weight of the electrolyte for a lithium secondary battery.

7. 10. The electrolyte for a lithium secondary battery according to claim 1, wherein the composition is contained in an amount of 0.2 to 20 wt % based on the total weight of the electrolyte for a lithium secondary battery.

8. a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and A lithium secondary battery comprising the electrolyte solution for lithium secondary batteries according to any one of claims 1 to 7.

Images