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

Abstract

The present invention provides an electrolyte for a lithium secondary battery, 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 being contained in a weight ratio of 1:0.4 to 1:4, 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 including the same.

Background Art

[0002] A lithium secondary battery is rechargeable and has an energy density per unit weight that is three times or more higher than that of conventional lead-acid batteries, nickel-cadmium batteries, nickel-metal hydride batteries, nickel-zinc batteries, etc., and can be charged at high speed. Therefore, it has been commercialized for use in notebook computers, mobile phones, power tools, and electric bicycles, and research and development for further improving the energy density is actively underway.

[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 inserting (intercalating) and desorbing (deintercalating) lithium and a negative electrode containing a negative electrode active material capable of inserting and desorbing lithium.

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

[0005] Recently, due to an increase in energy density due to an increase in the capacity of lithium secondary batteries, safety problems have emerged. As one method for improving safety, a method of using a flame retardant as an electrolyte additive is known.

[0006] As the flame retardant, fluorine-based compounds, phosphorus-based compounds, sulfur-based compounds, etc. are mainly used as compounds with less environmental pollution problems and having flame retardancy, but the use of these flame retardants may also cause a decrease in battery performance. Therefore, there is a demand for an electrolyte that improves battery performance while ensuring safety.

Summary of the Invention

Problems to be Solved by the Invention

[0007] An object of one embodiment is to provide a lithium secondary battery with improved normal temperature life characteristics, high temperature life characteristics, and storage characteristics while ensuring battery safety such as thermal safety and penetration stability.

Means for Solving the Problems

[0008] One embodiment of the present invention is a composition containing a non-aqueous organic solvent, a lithium salt, and an additive, wherein the additive contains 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 provided in a weight ratio of 1:0.4 to 1:4 for an electrolytic solution for a lithium secondary battery.

[0009]

Chemical

[0010] In the Chemical Formula 1 and Chemical Formula 2, R 1 and R 2 are each independently a fluoro group or a C1-C4 fluoroalkyl group substituted with at least one fluoro group, X 1 and X 2 are each independently a halogen group or -O-L 1 -R 3 and X 1 and X 2 at least one of them is -O-L 1 -R 3 and L 1 is a single bond or a substituted or unsubstituted C1-C10 alkylene group, R 3are each independently a cyano group (-CN), a difluorophosphate group (-OPF2), a substituted or unsubstituted C1-C10 alkyl group, a substituted or unsubstituted C2-C10 alkenyl group, a substituted or unsubstituted C3-C10 cycloalkyl group, a substituted or unsubstituted C3-C10 cycloalkenyl group, a substituted or unsubstituted C2-C10 alkynyl group, a substituted or unsubstituted C3-C10 cycloalkynyl group, or a substituted or unsubstituted C6-C20 aryl group, X 1 and X 2 are simultaneously -O-L 1 -R 3 in the case of R 3 each independently exists, or two Rs 3 are linked to form a substituted or unsubstituted monocyclic or polycyclic aliphatic heterocycle, or a substituted or unsubstituted monocyclic or polycyclic aromatic heterocycle.

[0011] The first compound and the second compound may be contained in a weight ratio of 1:0.5 to 1:3. The first compound and the second compound may be contained in a weight ratio of 1:0.5 to 1:2. The first compound and the second compound may be contained in a weight ratio of 1:1 to 1:1.5. The chemical formula 1 may be represented by the following chemical formula 1-1 or chemical formula 1-2.

[0012]

Chemical formula

[0013] In chemical formula 2, any one of the X 1 and X 2 is a fluorine group, and the other one is -O-L 2 -R 4 and L 2 is a single bond or a substituted or unsubstituted C1-C10 alkylene group, R 4may be a cyano group (-CN) or a difluorophosphate group (-OPF2). The second compound is represented by the chemical formula 2, and the chemical formula 2 may be represented by the following chemical formula 2-1.

[0014]

Chemical formula

[0015] In the chemical formula 2-1, m is one of the integers from 1 to 5, R 4 is a cyano group (-CN) or a difluorophosphate group (-OPF2). The second compound is represented by the chemical formula 2, In the chemical formula 2, X 1 is -O-L 3 -R 5 That is, X 2 is -O-L 4 -R 6 That is, L 3 and L 4 are each independently a single bond or a substituted or unsubstituted C1-C10 alkylene group, R 5 and R 6 are each independently a substituted or unsubstituted C1-C10 alkyl group, and R 5 and R 6 can be linked to form a substituted or unsubstituted monocyclic or polycyclic aliphatic heterocycle. The second compound may be represented by the following chemical formula 2-2.

[0016]

Chemical formula

[0017] In the chemical formula 2-2, L 5 is a substituted or unsubstituted C2-C5 alkylene group. The second compound may be represented by the following Chemical Formula 2-2a or Chemical Formula 2-2b.

[0018]

Chem.

[0019] In the Chemical Formula 2-2a and Chemical Formula 2-2b, R 7 ~R 16 are each independently hydrogen, a halogen group, or a substituted or unsubstituted C1-C5 alkyl group. The second compound may be any one selected from the compounds listed in the following Group 1.

[0020]

Chem.

[0021] The first compound may be contained in an amount of 0.05% by weight to 2.0% by weight based on the total weight of the electrolyte for a lithium secondary battery. The second compound may be contained in an amount of 0.05% by weight to 5.0% by weight based on the total weight of the electrolyte for a lithium secondary battery. The first compound is contained in an amount of 0.5% by weight to 2.0% by weight based on the total weight of the electrolyte for a lithium secondary battery, and the second compound may be contained in an amount of 0.5% by weight to 5.0% by weight based on the total weight of the electrolyte for a lithium secondary battery. The composition may be contained in an amount of 1.0% by weight to 5.0% by weight based on the total weight of the electrolyte for a lithium secondary battery.

[0022] Another embodiment of the present invention provides a lithium secondary battery including a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and the electrolyte for a lithium secondary battery described above.

Advantages of the Invention

[0023] It is possible to realize a lithium secondary battery in which the safety, room temperature characteristics, and high temperature characteristics of the battery are simultaneously improved.

Brief Description of the Drawings

[0024]

Figure 1

Modes for Carrying Out the Invention

[0025] Hereinafter, a lithium secondary battery according to an embodiment of the present invention will be described in detail with reference to the attached drawings. However, this is presented as an example, and the present invention is not limited thereby. The present invention is defined only by the scope of the claims described later.

[0026] In this specification, “substitution” means that, unless otherwise defined, at least one hydrogen in a substituent or a compound is substituted with deuterium, a halogen group, a hydroxyl group, an amino group, a substituted or unsubstituted C1-C30 amine group, a nitro group, a substituted or unsubstituted C1-C40 silyl group, a C1-C30 alkyl group, a C1-C10 alkylsilyl group, a C6-C30 arylsilyl group, a C3-C30 cycloalkyl group, a C3-C30 heterocycloalkyl group, a C6-C30 aryl group, a C2-C30 heteroaryl group, a C1-C20 alkoxy group, a C1-C10 fluoroalkyl group, a cyano group, or a combination thereof. In an example of the present invention, "substituted" means that at least one hydrogen of a substituent or a compound is substituted with deuterium, a halogen group, a C1-C30 alkyl group, a C1-C10 alkylsilyl group, a C6-C30 arylsilyl group, a C3-C30 cycloalkyl group, a C3-C30 heterocycloalkyl group, a C6-C30 aryl group, a C2-C30 heteroaryl group, a C1-C10 fluoroalkyl group, or a cyano group. Also, in a specific example of the present invention, "substituted" means that at least one hydrogen of a substituent or a compound is substituted with deuterium, a halogen group, a C1-C20 alkyl group, a C6-C30 aryl group, a C1-C10 fluoroalkyl group, or a cyano group. Further, in a specific example of the present invention, "substituted" means that at least one hydrogen of a substituent or a compound is substituted with deuterium, a halogen group, a C1-C5 alkyl group, a C6-C18 aryl group, a C1-C5 fluoroalkyl group, or a cyano group. Additionally, in a specific example of the present invention, "substituted" means that at least one hydrogen of a substituent or a 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.

[0027] Lithium secondary batteries can be classified into lithium-ion batteries, lithium-ion polymer batteries, lithium polymer batteries, etc. according to the types of separator membranes and electrolytes used, can be classified into cylindrical, square, coin-shaped, pouch-shaped, etc. according to their forms, and can be classified into bulk type and thin film type according to their sizes. Since the structures and manufacturing methods of these batteries are widely known in the art, detailed descriptions are omitted.

[0028] Here, a cylindrical lithium secondary battery will be taken as an example to explain as an example of a lithium secondary battery. FIG. 1 schematically shows the structure of a lithium secondary battery according to an embodiment. Referring to FIG. 1, a lithium secondary battery 100 according to an embodiment includes a positive electrode 114, a negative electrode 112 positioned opposite to the positive electrode 114, a separator 113 disposed between the positive electrode 114 and the negative electrode 112, and a battery cell including an electrolytic solution (not shown) that impregnates the positive electrode 114, the negative electrode 112, and the separator 113, a battery container 120 that houses the battery cell, and an encapsulating member 140 that seals the battery container 120.

[0029] Hereinafter, a more detailed configuration of the lithium secondary battery 100 according to an embodiment of the present invention will be described. A lithium secondary battery according to an embodiment of the present invention includes an electrolytic solution, a positive electrode, and a negative electrode. The electrolytic solution includes a non-aqueous organic solvent, a lithium salt, and an additive. 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. The first compound and the second compound are included in a weight ratio of 1:0.4 to 1:4.

[0030]

Chemical formula

[0031] In the Chemical Formula 1 and Chemical Formula 2, R 1 and R 2 are each independently a fluoro group or a C1-C4 fluoroalkyl group substituted with at least one fluoro group. X 1 and X 2 are each independently a halogen group or -O-L 1 -R 3 and X 1 and X 2 at least one of them is -O-L 1 -R 3 and L 1is a single bond or a substituted or unsubstituted C1-C10 alkylene group, R 3 each independently is a cyano group (-CN), a difluorophosphate group (-OPF2), a substituted or unsubstituted C1-C10 alkyl group, a substituted or unsubstituted C2-C10 alkenyl group, a substituted or unsubstituted C3-C10 cycloalkyl group, a substituted or unsubstituted C3-C10 cycloalkenyl group, a substituted or unsubstituted C2-C10 alkynyl group, a substituted or unsubstituted C3-C10 cycloalkynyl group, or a substituted or unsubstituted C6-C20 aryl group, X 1 and X 2 are simultaneously -O-L 1 -R 3 in the case of, R 3 each independently exists, or two Rs 3 are linked to form a substituted or unsubstituted monocyclic or polycyclic aliphatic heterocycle, or a substituted or unsubstituted monocyclic or polycyclic aromatic heterocycle.

[0032] The first compound is a compound containing a cesium sulfonylimide salt. The first compound can prevent the positive electrode decomposition phenomenon by being decomposed in the electrolyte to form a film on the surfaces of the positive electrode and the negative electrode and effectively controlling the elution of lithium ions generated from the positive electrode. Specifically, the first compound is reductively decomposed prior to the carbonate-based solvent contained in the non-aqueous organic solvent to form a SEI film (Solid Electrolyte Interface) on the negative electrode, thereby preventing electrolyte decomposition and the decomposition reaction of the electrode due to this, and suppressing the increase in internal resistance due to gas generation. The SEI film formed on the negative electrode is partially decomposed through a reduction reaction during charge and discharge, moves to the positive electrode surface, and also forms a film on the positive electrode surface through an oxidation reaction, thereby preventing the decomposition of the positive electrode surface and the oxidation reaction of the electrolyte, and contributing to the improvement of high-temperature and low-temperature life characteristics.

[0033] That is, the composition can improve the life characteristics and safety of the battery by including the first compound represented by the chemical formula 1.

[0034] In addition, by including both a fluorophosphate compound such as a second compound, not only the flame retardant property but also the gas generation suppression effect inside the battery at high temperature can be further improved by suppressing the high-temperature decomposition effect of the electrolyte through the stabilization of the lithium salt in the electrolyte, and the safety and life characteristics of the battery can be improved simultaneously.

[0035] When the first compound and the second compound are used in combination, a stronger film is formed on the negative electrode surface compared to when each compound is used alone, so the improvement effect of the high-temperature storage characteristics can be further improved.

[0036] As an example, the first compound and the second compound may be included in a weight ratio of 1:0.5 to 1:3. In a specific example, the first compound and the second compound may be included in a weight ratio of 1:0.5 to 1:2, and for example, may be included in a weight ratio of 1:1 to 1:1.5. As an example, R in the chemical formula 1 1 and R 2 may each independently be a fluoro group or a C1-C4 fluoroalkyl group substituted with at least two fluoro groups. As an example, R in the chemical formula 1 1 and R 2 may each independently be a fluoro group or a C1-C4 fluoroalkyl group substituted with at least three fluoro groups.

[0037] As a specific example, R in the chemical formula 1 1 and R 2 may each independently be a fluoro group or a C1-C3 fluoroalkyl group substituted with at least three fluoro groups. As a more specific example, R in the chemical formula 1 1 and R 2may each independently be a fluoro group or a C1-C2 fluoroalkyl group substituted with at least 3 fluoro groups. For example, the compound represented by Chemical Formula 1 above may be represented by the following Chemical Formula 1-1 or Chemical Formula 1-2.

[0038]

Chem.

[0039] As an example, X in Chemical Formula 2 above 1 and X 2 either one of them is a fluoro group, and the other one is -O-L 2 -R 4 and the L 2 is a single bond or a substituted or unsubstituted C1-C10 alkylene group, the R 4 may be a cyano group (-CN) or a difluorophosphate group (-OPF2). Specifically, the second compound is represented by Chemical Formula 2 above, and Chemical Formula 2 may be represented by the following Chemical Formula 2-1.

[0040]

Chem.

[0041] In Chemical Formula 2-1 above, m is one of the integers from 1 to 5, R 4 is a cyano group (-CN) or a difluorophosphate group (-OPF2). As another example, the second compound is represented by Chemical Formula 2 above, in Chemical Formula 2, X 1 is -O-L 3 -R 5 and X 2 is -O-L 4 -R 6 and L 3and L 4 is, independently of one another, a single bond or a substituted or unsubstituted C1-C10 alkylene group, R 5 and R 6 are, independently of one another, a substituted or unsubstituted C1-C10 alkyl group, R 5 and R 6 may be linked to form a substituted or unsubstituted monocyclic or polycyclic aliphatic heterocycle. Specifically, the second compound may be represented by the following Chemical Formula 2-2.

[0042]

Chemical formula

[0043] In the Chemical Formula 2-2, L 5 is a substituted or unsubstituted C2-C5 alkylene group. More specifically, the second compound may be represented by the following Chemical Formula 2-2a or Chemical Formula 2-2b.

[0044]

Chemical formula

[0045] In the Chemical Formula 2-2a and Chemical Formula 2-2b, R 7 ~R 16 are, independently of one another, hydrogen, a halogen group or a substituted or unsubstituted C1-C5 alkyl group. For example, the second compound may be any one selected from the compounds listed in the following Group 1.

[0046]

Chemical formula

[0047] According to one of the most specific embodiments, the additive contained in the electrolyte for a lithium secondary battery according to the present invention can be a composition containing cesium bis(fluorosulfonyl)imide as the first compound and at least one of the compounds listed in the above Group 1 as the second compound.

[0048] According to another one of the most specific embodiments, it can be a composition containing cesium bis(trifluoromethanesulfonyl)imide as the first compound and at least one of the compounds listed in the above Group 1 as the second compound.

[0049] On the other hand, the first compound can be contained in an amount of about 0.05 wt% to about 2.0 wt% based on the total weight of the electrolyte for a lithium secondary battery. As an example, it can be contained in an amount of about 0.1 wt% to about 2.0 wt%, about 0.2 wt% to about 2.0 wt%, about 0.3 wt% to about 2.0 wt%, or about 0.4 wt% to about 2.0 wt%, for example, about 0.5 wt% to about 2.0 wt%.

[0050] Also, the second compound can be contained in an amount of about 0.05 wt% to about 5.0 wt% based on the total weight of the electrolyte for a lithium secondary battery. As an example, it can be contained in an amount of about 0.1 wt% to about 5.0 wt%, about 0.2 wt% to about 5.0 wt%, about 0.3 wt% to about 5.0 wt%, or about 0.4 wt% to about 5.0 wt%, for example, about 0.5 wt% to 5.0 wt%.

[0051] For example, the first compound can be contained in an amount of about 0.5 wt% to about 2.0 wt% based on the total weight of the electrolyte for a lithium secondary battery, and the second compound can be contained in an amount of about 0.5 wt% to about 5.0 wt% based on the total weight of the electrolyte for a lithium secondary battery.

[0052] Specifically, the first compound is contained in an amount of about 0.5 wt% to about 2.0 wt% based on the total weight of the electrolyte for a lithium secondary battery, and the second compound can be contained in an amount of 0.5 wt% to 4.0 wt% based on the total weight of the electrolyte for a lithium secondary battery.

[0053] More specifically, the first compound is contained in an amount of about 0.5% by weight to about 2.0% by weight based on the total weight of the electrolyte for a lithium secondary battery, and the second compound may be contained in an amount of 0.5% by weight to 3.0% by weight based on the total weight of the electrolyte for a lithium secondary battery.

[0054] For example, the first compound is contained in an amount of about 0.5% by weight to about 2.0% by weight based on the total weight of the electrolyte for a lithium secondary battery, and the second compound may be contained in an amount of 0.5% by weight to 1.0% by weight based on the total weight of the electrolyte for a lithium secondary battery.

[0055] The composition containing the first compound and the second compound may be contained in an amount of about 1.0% by weight to about 5.0% by weight based on the total weight of the electrolyte for a lithium secondary battery.

[0056] When the content of the composition and the content of each component in the composition, that is, the first compound and the second compound, are within the above ranges, the safety of the battery such as thermal safety and penetration safety is improved, the gas generation inside the battery is suppressed, and a lithium secondary battery with improved battery characteristics at normal temperature and high temperature can be realized.

[0057] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0058] As the non-aqueous organic solvent, carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or aprotic solvents can be used.

[0059] As the carbonate solvent, 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), butylene carbonate (BC), etc. can be used. As the ester solvent, methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, decanolide, mevalonolactone, caprolactone, etc. can be used. As the ether solvent, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc. can be used. Further, as the ketone solvent, cyclohexanone, etc. can be used. Also, as the alcohol solvent, ethyl alcohol, isopropyl alcohol, etc. can be used, and as the aprotic solvent, R 15 -CN (R 15 is a linear, branched or cyclic hydrocarbon group having 2 to 20 carbon atoms and may contain a double bond aromatic ring or an ether bond), etc. of nitriles, amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolane, etc. can be used.

[0060] The non-aqueous organic solvent can be used alone or in a mixture of one or more. When used in a mixture of one or more, the mixing ratio can be appropriately adjusted according to the target battery performance, which can be widely understood by those skilled in the art.

[0061] In the case of the carbonate solvent, it is preferable to use a mixture of cyclic carbonate and chain carbonate. In this case, the cyclic carbonate and the chain carbonate may be used by mixing them at a volume ratio of 1:9 to 9:1, so that the performance of the electrolytic solution may be excellent.

[0062] In particular, in one embodiment of the present invention, the non-aqueous organic solvent may contain the cyclic carbonate and the chain carbonate at a volume ratio of 2:8 to 5:5. As a specific example, the cyclic carbonate and the chain carbonate may be contained at a volume ratio of 2:8 to 4:6.

[0063] As a more specific example, the cyclic carbonate and the chain carbonate may be contained at a volume ratio of 2:8 to 3:7. The non-aqueous organic solvent may further contain an aromatic hydrocarbon organic solvent in the carbonate solvent. At this time, the carbonate solvent and the aromatic hydrocarbon solvent may be mixed at a volume ratio of 1:1 to 30:1.

[0064] As the aromatic hydrocarbon solvent, an aromatic hydrocarbon compound represented by the following Chemical Formula 4 can be used.

[0065] [Chemical Formula]

[0066] In Chemical Formula 4, R 17 ~R 22 are the same as or different from each other and are selected from the group consisting of hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, a haloalkyl group, and combinations thereof.

[0067] 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, fluorotoluene, 2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,3,4-trifluorotoluene, 2,3,5-trifluorotoluene, chlorotoluene, 2,3-dichlorotoluene, 2,4-dichlorotoluene, 2,5-dichlorotoluene, 2,3,4-trichlorotoluene, 2,3,5-trichlorotoluene, iodotoluene, 2,3-diiodotoluene, 2,4-diiodotoluene, 2,5-diiodotoluene, 2,3,4-triiodotoluene, 2,3,5-triiodotoluene, xylene, and those selected from the group consisting of combinations thereof.

[0068] The lithium salt is dissolved in a non-aqueous organic solvent, acts as a source of lithium ions in the battery to enable the operation of a basic lithium secondary battery, and plays a role in promoting the movement of lithium ions between the positive electrode and the negative electrode. Representative examples of such lithium salts include LiPF6, LiBF4, lithium difluoro(oxalate)borate (LiDFOB), LiPO2F2, LiSbF6, LiAsF6, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide: LiFSI), LiC4F9SO3, LiClO4, LiAlO2, LiAlCl4, LiN(C x F 2x+1 SO2)(Cy F 2y+1 SO2) (where x and y are natural numbers, for example, integers from 1 to 20), one or more selected from the group consisting of LiCl, LiI, and LiB(C2O4)2 (lithium bis(oxalato) borate: LiBOB). The concentration of the lithium salt is preferably used in the range of 0.1 M to 2.0 M. If the concentration of the lithium salt is within the above range, since the electrolyte has appropriate conductivity and viscosity, it can exhibit excellent electrolyte performance, and lithium ions can move effectively.

[0069] The positive electrode includes a positive electrode current collector and a positive electrode active material layer located thereon, and the positive electrode active material layer contains a positive electrode active material. As the positive electrode active material, a compound (lithiated insertion compound) capable of reversible insertion and desorption of lithium can be used. Specifically, at least one of composite oxides of metals selected from cobalt, manganese, nickel, and combinations thereof with lithium can be used.

[0070] Of course, those having a coating layer on the surface of the composite oxide can also be used, or the composite oxide and the composite oxide having a coating layer can be mixed and used. This coating layer can contain at least one coating element compound selected from the group consisting of oxides of coating elements, hydroxides of coating elements, oxyhydroxides of coating elements, oxycarbonates of coating elements, and hydroxycarbonates of coating elements. The compounds forming these coating layers can be amorphous or crystalline. As the coating elements contained in the coating layer, Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof can be used. The coating layer forming step can use any coating method as long as such elements are used in the compound and do not adversely affect the physical properties of the positive electrode active material (for example, spray coating, dipping method, etc.). Since this is a content well understood by those skilled in the art, detailed description is omitted.

[0071] The positive electrode active material can be, for example, one or more of the lithium composite oxides represented by the following Chemical Formula 3. [Chemical Formula 3] Li x M 1 y M 2 z M 3 1-y-z O2 In the Chemical Formula 3, 0.5 ≦ x ≦ 1.8, 0 < y ≦ 1, 0 ≦ z ≦ 1, 0 ≦ y + z ≦ 1, M 1 , M 2 and M 3 can each independently be any one selected from metals such as Ni, Co, Mn, Al, Sr, Mg, or La and combinations thereof.

[0072] In one embodiment, the M 1 and M 2 can each independently be Ni or Co, and the M3 can be a metal such as Co, Mn, Al, Sr, Mg or La. In a specific embodiment, the M 1 and M 2 can each independently be Ni or Co, and the M 3 can be Mn or Al, but is not limited thereto.

[0073] In a more specific embodiment, the positive electrode active material can be a lithium composite oxide represented by the following Chemical Formula 3-1 or Chemical Formula 3-2. [Chemical Formula 3-1] Li x1 Ni y1 Co z1 Al 1-y1-z1 O2 In the Chemical Formula 3-1, 1 ≦ x1 ≦ 1.2, 0 < y1 < 1, and 0 < z1 < 1, [Chemical Formula 3-2] Li x2 Ni y2 Co z2 Mn 1-y2-z2 O2 In the Chemical Formula 3-2, 1 ≦ x2 ≦ 1.2, 0 < y2 < 1, and 0 < z2 < 1.

[0074] As an example, in the Chemical Formula 3-1, 1 ≦ x1 ≦ 1.2, 0.5 ≦ y1 < 1, and 0 < z1 ≦ 0.5 may be possible. As a specific example, in the Chemical Formula 3-1, 1 ≦ x1 ≦ 1.2, 0.6 ≦ y1 < 1, and 0 < z1 ≦ 0.5 may be possible. As a more specific example, in the Chemical Formula 3-1, 1 ≦ x1 ≦ 1.2, 0.7 ≦ y1 < 1, and 0 < z1 ≦ 0.5 may be possible.

[0075] For example, in the Chemical Formula 3-1, 1 ≦ x1 ≦ 1.2, 0.8 ≦ y1 < 1, and 0 < z1 ≦ 0.5 may be possible. As an example, in the Chemical Formula 3-2, 1 ≦ x2 ≦ 1.2, 0.3 ≦ y2 < 1, and 0.3 ≦ z2 < 1 may be possible. As a specific example, in Chemical Formula 3-2, 1 ≦ x2 ≦ 1.2, 0.6 ≦ y2 < 1, and 0.3 ≦ z2 < 1 may be satisfied.

[0076] As a more specific example, in Chemical Formula 3-2, 1 ≦ x2 ≦ 1.2, 0.7 ≦ y2 < 1, and 0.3 ≦ z2 < 1 may be satisfied. For example, as a specific example, in Chemical Formula 3-2, 1 ≦ x2 ≦ 1.2, 0.8 ≦ y2 < 1, and 0.3 ≦ z2 < 1 may be satisfied.

[0077] The content of the positive electrode active material may be 90% to 98% by weight based on the total weight of the positive electrode active material layer.

[0078] In one embodiment of the present invention, the positive electrode active material layer may selectively contain a conductive material and a binder. At this time, the content of the binder may be 1% to 5% by weight based on the total weight of the positive electrode active material layer. The contents of the conductive material and the binder may each be 1% to 5% by weight based on the total weight of the positive electrode active material layer.

[0079] The conductive material is used to impart conductivity to the positive electrode, and in the configured battery, any electron conductive material that does not cause a chemical change can be used. Examples thereof include carbon-based substances such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, and carbon fiber; metal-based substances such as metal powders or metal fibers of copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or a conductive material containing a mixture thereof can be used.

[0080] The binder serves to make the positive electrode active material particles adhere well to each other and also make the positive electrode active material adhere well to the current collector. Typical examples thereof include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc., but are not limited thereto.

[0081] As the positive electrode current collector, Al can be used, but is not limited thereto.

[0082] The negative electrode includes a negative electrode current collector and a negative electrode active material layer including a negative electrode active material formed on the negative electrode current collector. The negative electrode active material includes a material capable of reversibly inserting / desorbing lithium ions, lithium metal, an alloy of lithium metal, a material dopable and dedopable with lithium, or a transition metal oxide.

[0083] As the material capable of reversibly inserting / desorbing lithium ions, a carbon material can be used, and any carbon-based negative electrode active material generally used in a lithium secondary battery can be used. Typical examples thereof include crystalline carbon, amorphous carbon, or both of them can be used. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical or fibrous natural graphite or artificial graphite. Examples of the amorphous carbon include soft carbon, hard carbon, mesophase pitch carbide, calcined coke, etc.

[0084] 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.

[0085] As the substance capable of doping and undoping lithium, Si, Si-C composite, SiOx(0 < x < 2), Si-Q alloy (where Q is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, transition metals, rare earth elements and combinations thereof, and is not Si), Sn, SnO2, Sn-R 22 (where R 22 is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, transition metals, rare earth elements and combinations thereof, and is not Sn), etc. can be mentioned, and at least one of these can also be used by mixing with SiO2.

[0086] 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.

[0087] Examples of the transition metal oxide include vanadium oxide, lithium vanadium oxide or lithium titanium oxide.

[0088] In a specific embodiment, the negative electrode active material can be a Si-C composite including a Si-based active material and a carbon-based active material. In the Si-C composite, the average particle size of the Si-based active material can be 50 nm to 200 nm.

[0089] When the average particle size of the Si-based active material is within the above range, volume expansion occurring during charge and discharge can be suppressed, and interruption of the conductive path due to particle crushing during charge and discharge can be prevented. The Si-based active material may be contained in an amount of 1 to 60% by weight, for example, 3 to 60% by weight, based on the total weight of the Si-C composite.

[0090] In another specific example, the negative electrode active material may further contain crystalline carbon together with the above-described Si-C composite. When the negative electrode active material contains both the Si-C composite and crystalline carbon, the Si-C composite and the crystalline carbon may be contained in the form of a mixture. In this case, the Si-C composite and the crystalline carbon may be contained in a weight ratio of 1:99 to 50:50. More specifically, the Si-C composite and the crystalline carbon may be contained in a weight ratio of 5:95 to 20:80.

[0091] The crystalline carbon may include, for example, graphite, and more specifically, may include natural graphite, artificial graphite, or a mixture thereof. The average particle size of the crystalline carbon may be 5 μm to 30 μm.

[0092] In this specification, the average particle size may be the particle size (D50) at 50% by volume in the cumulative size-distribution curve.

[0093] The Si-C composite may further include a shell surrounding the surface of the Si-C composite, and the shell may include amorphous carbon. The amorphous carbon may include soft carbon, hard carbon, mesophase pitch carbide, calcined coke, or a mixture thereof. 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, based on 100 parts by weight of the carbon-based active material.

[0094] In the negative electrode active material layer, the content of the negative electrode active material can be 95% to 99% by weight based on the total weight of the negative electrode active material layer.

[0095] In one embodiment of the present invention, the negative electrode active material layer contains a binder and may further selectively contain a conductive material. In the negative electrode active material layer, the content of the binder can be 1% to 5% by weight based on the total weight of the negative electrode active material layer. When further containing a conductive material, 90% to 98% by weight of the negative electrode active material, 1% to 5% by weight of the binder, and 1% to 5% by weight of the conductive material can be used.

[0096] The binder serves to make the negative electrode active material particles adhere well to each other and also make the negative electrode active material adhere well to the current collector. As the binder, a water-insoluble binder, a water-soluble binder, or a combination thereof can be used.

[0097] Examples of the water-insoluble binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0098] Examples of the water-soluble binder include rubber-based binders or polymer resin binders. 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.

[0099] When a water-soluble binder is used as the negative electrode binder, a cellulose-based compound capable of imparting viscosity can be further included as a thickener. Examples of this cellulose-based compound include carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or alkali metal salts thereof, and one or more of these can be mixed and used. As the alkali metal, Na, K, or Li can be used. The content of such a thickener used can be 0.1 to 3 parts by weight based on 100 parts by weight of the negative electrode active material. The conductive material is used to impart conductivity to the electrode, and in the battery being constructed, any electron conductive material that does not cause a chemical change can be used. Examples thereof 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 powders or metal fibers of copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or conductive materials containing mixtures thereof can be used.

[0100] As the negative electrode current collector, those 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 can be used.

[0101] Depending on the type of lithium secondary battery, a separator may be present between the positive electrode and the negative electrode. Such a separator can be a porous substrate or a composite porous substrate.

[0102] The porous substrate, as a substrate containing voids, allows lithium ions to move through the voids. As the porous substrate, for example, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof can be used, and it goes without saying that mixed multilayer films such as a two-layer separator of polyethylene / polypropylene, a three-layer separator of polyethylene / polypropylene / polyethylene, and a three-layer separator of polypropylene / polyethylene / polypropylene can be used.

[0103] The composite porous substrate can be in a form including a porous substrate and a functional layer located on the porous substrate. From the viewpoint of enabling additional functions to be added, the functional layer can be, for example, at least one of a heat-resistant layer and an adhesive layer. For example, the heat-resistant layer can contain a heat-resistant resin and optionally a filler. Also, the adhesive layer can contain an adhesive resin and optionally a filler. The filler can be an organic filler or an inorganic filler.

[0104] [Examples] Hereinafter, examples and comparative examples of the present invention will be described. Such the following examples are merely one example of the present invention, and the present invention is not limited to the following examples.

[0105] Fabrication of Lithium Secondary Battery Example 1 As the positive electrode active material, LiNi0.91 Co 0.07 Al 0.02 O₂, polyvinylidene fluoride as a binder, and Ketjen black as a conductive material were mixed at a weight ratio of 97:2:1 respectively, and dispersed in N-methylpyrrolidone to produce a positive electrode active material slurry. The positive electrode active material slurry was coated on an aluminum foil with a thickness of 14 μm, dried at 110 °C, and then rolled (press) to produce a positive electrode. A mixture in which artificial graphite and a Si-C composite were mixed at a weight ratio of 93:7 was used as the negative electrode active material. The negative electrode active material, styrene-butadiene rubber binder as a binder, and carboxymethyl cellulose as a thickener were mixed at a weight ratio of 97:1:2 respectively, and dispersed in distilled water to produce a negative electrode active material slurry.

[0106] As the Si-C composite, one in which a core containing artificial graphite and silicon particles and a coal-based pitch was coated on the surface of the core was used. The negative electrode active material slurry was coated on a copper foil with a thickness of 10 μm, dried at 100 °C, and then rolled (press) to produce a negative electrode. The manufactured positive electrode and negative electrode were assembled with a separator made of a 25-μm-thick polyethylene material to produce an electrode assembly, and an electrolyte was injected to fabricate a lithium secondary battery.

[0107] The composition of the electrolyte is as follows. (Composition of the electrolyte) Salt: LiPF₆ 1.5 M Solvent: ethylene carbonate: ethyl methyl carbonate: dimethyl carbonate (EC: EMC: DMC = 20:10:70 by volume ratio) Additive: a composition containing 0.5 wt% of cesium bis(trifluoromethanesulfonyl)imide represented by the following Chemical Formula 1-2 and 0.5 wt% of a compound represented by the following Chemical Formula z-1 (However, in the composition of the electrolyte, "wt%" is based on the content of the entire electrolyte (lithium salt + non-aqueous organic solvent + additive).)

[0108] [Chemistry]

[0109] Example 2 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the additive composition was produced using the compound represented by the following chemical formula z-2 instead of the compound represented by the chemical formula z-1.

[0110] [Chemistry]

[0111] Example 3 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the additive composition was produced using the compound represented by the following chemical formula z-3 instead of the compound represented by the chemical formula z-1.

[0112] [Chemistry]

[0113] Example 4 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the additive composition was produced using 0.75% by weight of the compound represented by the following chemical formula z-4 instead of the compound represented by the chemical formula z-1.

[0114] [Chemistry]

[0115] Examples 5 to 8 A lithium secondary battery was fabricated in the same manner as in Examples 1 to 4, except that cesium bis(fluorosulfonyl)imide represented by the following chemical formula 1-1 was used instead of cesium bis(trifluoromethanesulfonyl)imide represented by the chemical formula 1-2.

[0116] [Chem.]

[0117] Example 9 A lithium secondary battery was fabricated in the same manner as in Example 1, except that 1.0% by weight of the compound represented by the chemical formula z-1 was used to produce the additive composition.

[0118] Example 10 A lithium secondary battery was fabricated in the same manner as in Example 2, except that 1.0% by weight of the compound represented by the chemical formula z-2 was used to produce the additive composition.

[0119] Example 11 A lithium secondary battery was fabricated in the same manner as in Example 3, except that 1.0% by weight of the compound represented by the chemical formula z-3 was used to produce the additive composition.

[0120] Example 12 A lithium secondary battery was fabricated in the same manner as in Example 4, except that 1.0% by weight of the compound represented by the chemical formula z-4 was used to produce the additive composition.

[0121] Examples 13 to 16 A lithium secondary battery was fabricated in the same manner as in Examples 9 to 12, respectively, except that cesium bis(fluorosulfonyl)imide represented by the chemical formula 1-1 was used instead of cesium bis(trifluoromethanesulfonyl)imide represented by the chemical formula 1-2.

[0122] Comparative Example 1 A lithium secondary battery was fabricated in the same manner as in Example 1, except that an electrolyte solution not containing an additive was used.

[0123] Comparative Example 2 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the electrolyte was produced using an additive that does not contain the compound represented by Chemical Formula z-1.

[0124] Comparative Example 3 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the electrolyte was produced using 0.5% by weight of the compound represented by Chemical Formula 1-1 alone.

[0125] Comparative Example 4 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the electrolyte was produced using an additive that does not contain the compound represented by Chemical Formula 1-2.

[0126] Comparative Example 5 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the electrolyte was produced using an additive containing 0.5% by weight of Li(CF3SO2)2N instead of the compound represented by Chemical Formula 1-2.

[0127] Comparative Example 6 A lithium secondary battery was fabricated in the same manner as in Comparative Example 4, except that the electrolyte was produced using an additive containing the compound represented by Chemical Formula z-2 instead of the compound represented by Chemical Formula z-1.

[0128] Comparative Example 7 A lithium secondary battery was fabricated in the same manner as in Comparative Example 5, except that the electrolyte was produced using an additive composition containing the compound represented by Chemical Formula z-2 instead of the compound represented by Chemical Formula z-1.

[0129] Comparative Example 8 A lithium secondary battery was fabricated in the same manner as in Comparative Example 4, except that the electrolyte was produced using an additive containing the compound represented by Chemical Formula z-3 instead of the compound represented by Chemical Formula z-1.

[0130] Comparative Example 9 A lithium secondary battery was fabricated in the same manner as in Comparative Example 5, except that an electrolyte solution was produced using an additive composition in which a compound represented by Chemical Formula z-3 was used instead of the compound represented by Chemical Formula z-1 in the composition.

[0131] Comparative Example 10 A lithium secondary battery was fabricated in the same manner as in Comparative Example 4, except that an electrolyte solution was produced using an additive in which 0.75% by weight of a compound represented by Chemical Formula z-4 was used instead of the compound represented by Chemical Formula z-1 in the composition.

[0132] Comparative Example 11 A lithium secondary battery was fabricated in the same manner as in Comparative Example 5, except that an electrolyte solution was produced using an additive composition in which 0.75% by weight of a compound represented by Chemical Formula z-4 was used instead of the compound represented by Chemical Formula z-1 in the composition.

[0133] Comparative Example 12 A lithium secondary battery was fabricated in the same manner as in Example 1, except that an electrolyte solution was produced using an additive composition in which 0.5% by weight of LiDFOB was used instead of the compound represented by Chemical Formula z-1.

[0134] Comparative Example 13 A lithium secondary battery was fabricated in the same manner as in Example 1, except that an additive composition was produced by changing the content of cesium bis(trifluoromethanesulfonyl)imide represented by Chemical Formula 1-2 to 2.0% by weight.

[0135] Comparative Example 14 A lithium secondary battery was fabricated in the same manner as in Example 1, except that an additive composition was produced by changing the content of the compound represented by Chemical Formula z-1 to 5.0% by weight.

[0136] Comparative Example 15 A lithium secondary battery was fabricated in the same manner as in Example 2, except that the content of cesium bis(trifluoromethanesulfonyl)imide represented by Chemical Formula 1-2 was changed to 2.0% by weight to produce an additive composition.

[0137] Comparative Example 16 A lithium secondary battery was fabricated in the same manner as in Example 2, except that the content of the compound represented by Chemical Formula z-2 was changed to 5.0% by weight to produce an additive composition.

[0138] Comparative Example 17 A lithium secondary battery was fabricated in the same manner as in Example 3, except that the content of cesium bis(trifluoromethanesulfonyl)imide represented by Chemical Formula 1-2 was changed to 2.0% by weight to produce an additive composition.

[0139] Comparative Example 18 A lithium secondary battery was fabricated in the same manner as in Example 3, except that the content of the compound represented by Chemical Formula z-3 was changed to 5.0% by weight to produce an additive composition.

[0140] Comparative Example 19 A lithium secondary battery was fabricated in the same manner as in Example 4, except that the content of cesium bis(trifluoromethanesulfonyl)imide represented by Chemical Formula 1-2 was changed to 2.0% by weight to produce an additive composition.

[0141] Comparative Example 20 A lithium secondary battery was fabricated in the same manner as in Example 4, except that the content of the compound represented by Chemical Formula z-4 was changed to 5.0% by weight to produce an additive composition. The compositions of the additives for the lithium secondary batteries according to Examples 1 to 8 and Comparative Examples 1 to 20 are as described in Table 1 below.

[0142]

Table 1A

Table 1B

[0143] Evaluation 1: Evaluation of Initial Resistance Characteristics The cells produced according to Examples 1 to 16 and Comparative Examples 1 to 20 were charged at 4 A and 4.2 V at room temperature (25°C), cut off at 100 mA, and allowed to rest for 30 minutes. Then, after discharging at 10 A for 10 seconds, 1 A for 10 seconds, and 10 A for 4 seconds, the current and voltage at the 18-second point and the 23-second point were measured respectively, and the initial resistance (the difference between the resistance at the 18-second point and the resistance at the 23-second point) was calculated by the formula ΔR = ΔV / ΔI and shown in Table 2 below.

[0144] Evaluation 2: Evaluation of Room Temperature Life Characteristics The lithium secondary batteries produced according to Examples 1 to 16 and Comparative Examples 1 to 20 were charged at a constant current-constant voltage of 1.0 C and 4.2 V and a cut-off condition of 0.33 C at room temperature (25°C) and discharged at a constant current of 1.0 C and 3.0 V. After 200 charge-discharge cycles, the discharge capacity was measured, and the capacity ratio (capacity retention rate) at 200 cycles with respect to the discharge capacity per cycle was calculated, and the results are shown in Table 2.

[0145] Evaluation 3: Evaluation of High Temperature Storage Characteristics The lithium secondary batteries of Examples 1 to 16 and Comparative Examples 1 to 20 were charged at a 0.5 C charge-discharge rate in a 4.2 V CC / CV mode for 3 hours, then left in a 90°C chamber for 20 hours, and the time point when the CID (Current Interrupt Device) operates was measured and the results are shown in Table 2 below. The CID (Current Interrupt Device) is an element that senses a change in pressure, that is, a pressure increase, inside a sealed element and cuts off the current by itself when the pressure exceeds a certain level. Since this is self-evident in the art, the description thereof is omitted. By measuring the time point when the CID operates, the high temperature storage characteristics of the lithium secondary battery can be evaluated.

[0146] Evaluation 4: Evaluation of Thermal Exposure After charging the lithium secondary batteries according to Examples 1 to 16 and Comparative Examples 1 to 20 at a charging rate of 0.5C under the 4.2V / 3hr cut-off condition in a 3.0V discharged state, the evaluation of thermal exposure was carried out. After placing the lithium secondary batteries according to Examples 1 to 16 and Comparative Examples 1 to 20 in a chamber, the temperature was increased from room temperature to 140°C at a rate of 5°C per minute, and the changes in the lithium secondary batteries were observed while maintaining at the said temperature for about 1 hour, and the results are shown in Table 2 below.

[0147] Evaluation 5: Evaluation of Through-Safety The through characteristics of the lithium secondary batteries according to Examples 1 to 16 and Comparative Examples 1 to 20 were evaluated by the following method, and the results of the two evaluations are shown in Table 2 below. For the through-limit evaluation, after charging to SOC (state of charge) 50 (capacity corresponding to half of the total capacity of 100), the cell was penetrated at a speed of 150 mm / s using a 3.0π nail to evaluate the safety of the battery. The evaluation criteria are as follows.

[0148] (Evaluation Criteria) L0: No reaction L1: Reversible damage occurs to the battery performance L2: Irreversible damage occurs to the battery performance L3: The weight of the battery electrolyte decreases by less than 50% L4: The weight of the battery electrolyte decreases by 50% or more L5: Ignition or flame occurs (no rupture or explosion) L6: Battery rupture (no explosion) L7: Battery explosion

[0149] [Table 2]

[0150] Referring to Table 2, it can be seen that among the additive compositions, the lithium secondary batteries according to Comparative Examples 1, 4, 6, 8, and 10 that do not contain the first compound, and Comparative Examples 5, 7, 9, and 11 that contain other additives instead of the first compound, have all deteriorated in capacity retention characteristics, high-temperature storage characteristics, thermal exposure characteristics, and penetration characteristics compared to the lithium secondary batteries according to Examples 1 to 16.

[0151] In addition, among the additive compositions, the lithium secondary batteries according to Comparative Examples 1 to 3 that do not contain the second compound, and the lithium secondary battery according to Comparative Example 12 that contains other additives instead of the second compound, have deteriorated in capacity retention characteristics and high-temperature storage characteristics compared to the lithium secondary batteries according to Examples 1 to 16.

[0152] Moreover, the lithium secondary batteries according to Comparative Examples 13, 15, 17, and 19 in which the ratio of the first compound and the second compound is less than 1:0.4 have solubility problems and it is impossible to measure the battery characteristics. It can be seen that the lithium secondary batteries according to Comparative Examples 14, 16, 18, and 20 in which the ratio of the first compound and the second compound exceeds 1:4 have deteriorated in capacity retention characteristics and high-temperature storage characteristics compared to the lithium secondary batteries according to Examples 1 to 16.

[0153] Therefore, it can be seen that the lithium secondary batteries according to the examples have improved capacity retention characteristics, high-temperature storage characteristics, and / or thermal exposure characteristics and penetration characteristics compared to the lithium secondary batteries according to the comparative examples that do not satisfy such conditions by containing a specific combination of additives in a specific ratio.

[0154] Although the preferred embodiments of the present invention have been described above, the present invention is not limited thereto, and it can be variously modified and implemented within the scope of the claims, the detailed description of the invention, and the appended drawings, and it is natural that this also belongs to the scope of the present invention.

Explanation of Reference Numerals

[0155] 100: Lithium secondary battery 112: Negative electrode 113: Separator 114: Positive electrode 120: Battery container 140: Encapsulation member

Claims

1. A non-aqueous organic solvent, a lithium salt, and an additive, wherein the additive is a composition containing 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 are contained in a weight ratio of 1:1 to 1:2, the first compound is contained in an amount of 0.5% by weight to 2.0% by weight based on the total weight of the electrolyte for a lithium secondary battery, and the second compound is contained in an amount of 0.5% by weight to 5.0% by weight based on the total weight of the electrolyte for a lithium secondary battery. An electrolyte for a lithium secondary battery. 【Chemical 1】 (In the above Chemical Formula 1 and Chemical Formula 2, R １ and R ２ are each independently a fluoro group or a C1-C4 fluoroalkyl group substituted with at least one fluoro group, X １ and X ２ are each independently a halogen group, or -O-L １ -R ３ wherein X １ and X ２ at least one of which is -O-L １ -R ３ wherein L １ is a single bond or a substituted or unsubstituted C1-C10 alkylene group, R ３ is, independently of each other, a cyano group (-CN), a difluorophosphate group (-OPF ２） , a substituted or unsubstituted C1-C10 alkyl group, a substituted or unsubstituted C2-C10 alkenyl group, a substituted or unsubstituted C3-C10 cycloalkyl group, a substituted or unsubstituted C3-C10 cycloalkenyl group, a substituted or unsubstituted C2-C10 alkynyl group, a substituted or unsubstituted C3-C10 cycloalkynyl group, or a substituted or unsubstituted C6-C20 aryl group, X １ and X ２ are simultaneously -O-L １ -R ３ in the case of R ３ each exist independently or Two Rs ３ are linked to form a substituted or unsubstituted monocyclic or polycyclic aliphatic heterocycle, or a substituted or unsubstituted monocyclic or polycyclic aromatic heterocycle.)

2. The electrolyte for a lithium secondary battery according to Claim 1, wherein the first compound and the second compound are contained in a weight ratio of 1:1 to 1:1.

5.

3. The electrolyte for a lithium secondary battery according to Claim 1, wherein the Chemical Formula 1 is represented by the following Chemical Formula 1-1 or Chemical Formula 1-2. 【Chemical Formula 2】

4. X of the chemical formula 2 １ and X ２ Any one of them is a fluoro group, and the other one is -O-L ２ -R ４ where L ２ is a single bond or a substituted or unsubstituted C1-C10 alkylene group, R ４ is a cyano group (—CN) or a difluorophosphate group (—OPF ２ ), the electrolyte for a lithium secondary battery according to claim 1.

5. The second compound is represented by the Chemical Formula 2, The electrolyte for a lithium secondary battery according to Claim 3, wherein the Chemical Formula 2 is represented by the following Chemical Formula 2-1. [Chemical Formula 3] (In the above Chemical Formula 2-1, m is one of the integers from 1 to 5, R ４ is a cyano group (—CN) or a difluorophosphate group (—OPF ２ ).)

6. The second compound is represented by the Chemical Formula 2, In the Chemical Formula 2, X １ is -O-L ３ -R ５ and X ２ is -O-L ４ -R ６ and L ３ and L ４ each independently represents a single bond or a substituted or unsubstituted C1-C10 alkylene group, R ５ and R ６ are each independently a substituted or unsubstituted C1-C10 alkyl group, and R ５ and R ６ are linked to form a substituted or unsubstituted monocyclic or polycyclic aliphatic heterocycle. The electrolyte for a lithium secondary battery according to claim 1.

7. The electrolyte for a lithium secondary battery according to Claim 6, wherein the second compound is represented by the following Chemical Formula 2-2. 【Chemical 4】 (In the above Chemical Formula 2-2, L ５ is a substituted or unsubstituted C2-C5 alkylene group.)

8. The electrolyte for a lithium secondary battery according to Claim 7, wherein the second compound is represented by the following Chemical Formula 2-2a or Chemical Formula 2-2b. [Chemical Formula 5] (In the above Chemical Formula 2-2a and Chemical Formula 2-2b, R ７ ~R １６ are each independently hydrogen, a halogen group, or a substituted or unsubstituted C1-C5 alkyl group.)

9. The electrolyte for a lithium secondary battery according to Claim 1, wherein the second compound is any one selected from the compounds listed in the following Group 1. 【Chemical Formula 6】

10. The electrolyte for a lithium secondary battery according to Claim 1, wherein the composition is contained in an amount of 1.0% by weight to 5.0% by weight based on the total weight of the electrolyte for a lithium secondary battery.

11. A positive electrode containing a positive electrode active material; A negative electrode containing a negative electrode active material; and A lithium secondary battery containing the electrolyte for a lithium secondary battery according to any one of Claims 1 to 10.

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