Additive for lithium secondary battery, electrolyte for lithium secondary battery containing the same, and lithium secondary battery

Abstract

The present invention provides an additive for a lithium secondary battery, which includes a core and a shell surrounding the core, wherein the core includes a flame retardant, a fire extinguishing agent, a non-flammable material, or a combination thereof, and the shell includes a polymer having a melting point of 90°C to 120°C, an electrolyte for a lithium secondary battery including the additive, and a lithium secondary battery.

Description

[Technical Field]

[0001] The present disclosure relates to an additive for a lithium secondary battery, an electrolyte for a lithium secondary battery containing the additive, and a lithium secondary battery. [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, and they can be charged quickly. 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 provides an additive for lithium secondary batteries with improved thermal stability.

[0008] Another embodiment provides an electrolyte for a lithium secondary battery that has improved life characteristics, high-temperature safety, and high-temperature reliability due to the application of the additive.

[0009] Another embodiment provides a lithium secondary battery including the electrolyte solution for lithium secondary batteries. [Means for solving the problem]

[0010] An additive for a lithium secondary battery according to one embodiment includes a core and a shell surrounding the core, the core including a flame retardant, a fire extinguishing agent, a non-flammable material, or a combination thereof, and the shell including a polymer having a melting point of 90°C to 120°C.

[0011] The ratio of the thickness of the core to the thickness of the shell may be 1:1 to 4:1.

[0012] The core may have a thickness of 0.1 μm to 2.0 μm, and the shell may have a thickness of 0.025 μm to 0.5 μm.

[0013] The flame retardant may include a phosphate ester compound, a phosphazene compound, or a combination thereof.

[0014] The phosphate ester compound may include a compound represented by the following Chemical Formula 1:

[0015] [ka] ...chemical formula 1

[0016] In the above chemical formula 1, R 1 ~R 3are each independently a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, a to c are each independently an integer of 0 to 5.

[0017] The phosphazene compound may include a compound represented by the following Formula 2:

[0018] [ka] ...Chemical formula 2

[0019] In the above chemical formula 2, n is 3 or 4, R 4 and R 5 are each independently -F, -NR x R y or a substituted or unsubstituted alkoxy group having 1 to 5 carbon atoms, R x and R y are each independently a substituted or unsubstituted alkyl group having 1 to 30 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 30 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 30 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 30 carbon atoms.

[0020] The phosphazene compound may include a compound represented by the following Formula 2-1 or 2-2.

[0021] [ka] ...Chemical formula 2-1

[0022] [ka] ...Chemical formula 2-2

[0023] In the above chemical formula 2-1 and the above chemical formula 2-2, R6 ~R 8 are each independently hydrogen, a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, a fluoroalkyl group having 1 to 10 carbon atoms, or a combination thereof.

[0024] The polymer may include poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP), polyacrylic acid, polyethylene, poly(methyl methacrylate), polyalkylene oxide, polyalkylene succinate, or a combination thereof.

[0025] The additive may be in the form of a fiber formed using electrospinning.

[0026] According to another embodiment, there is provided an electrolyte solution for a lithium secondary battery, comprising a non-aqueous organic solvent, a lithium salt, and the additive for a lithium secondary battery described above.

[0027] The additive for lithium secondary batteries may be included in an amount of 0.1 wt % to 20 wt %, 0.1 wt % to 15 wt %, or 0.1 wt % to 10 wt % based on the total weight of the electrolyte for lithium secondary batteries.

[0028] According to another embodiment, there is provided a lithium secondary battery comprising: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and the aforementioned electrolyte solution. [Effects of the Invention]

[0029] The additive for a lithium secondary battery according to an embodiment has excellent electrolyte impregnation properties, and when applied to an electrolyte, it can maintain battery characteristics without increasing battery resistance.

[0030] In addition, in a lithium secondary battery including the additive for a lithium secondary battery according to an embodiment, battery ignition is suppressed above the battery operating temperature, thereby improving the safety of the battery. [Brief explanation of the drawings]

[0031] [Figure 1] FIG. 1 is a cross-sectional view of an additive according to one embodiment. [Figure 2] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0032] Although the following detailed description of the embodiments will be given so that those skilled in the art can easily implement the present invention, the actual structure may be realized in various different forms and is not limited to the embodiments described herein.

[0033] In the drawings, the thickness of the various layers and regions is exaggerated for clarity.

[0034] When a layer, film, region, plate, or other part is said to be "on" another part, this includes not only the case where it is "directly on" another part, but also the case where there is another part in between. Conversely, when a part is said to be "directly on" another part, it means that there is no other part in between.

[0035] As used herein, "at least one of A, B, or C," "A, B, C, or one of combinations thereof," and "A, B, C, and one of combinations thereof" refer to each and every component and combination thereof (e.g., A; B; A and B; A and C; B and C; or A, B, and C).

[0036] Hereinafter, the term "combination" includes mixtures of two or more, mutual substitutions, and stacked structures of two or more.

[0037] Unless otherwise defined in this specification, "substituted" means that a hydrogen atom in a compound has been replaced with a deuterium atom, a halogen atom (F, Br, Cl, or I), a hydroxy group, a nitro group, a cyano group, an amino group, an azide group, an amidino group, a hydrazino group, a hydrazono group, a carbonyl group, a carbamoyl group, a thiol group, an ester group, a carboxyl group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, an alkyl group having 1 to 30 carbon atoms, an alkenyl group having 2 to 30 carbon atoms, a 2 to 30 carbon atom group ... It means that the group is substituted with a substituent selected from an alkynyl group having 6 to 30 carbon atoms, an aryl group having 6 to 30 carbon atoms, an arylalkyl group having 7 to 30 carbon atoms, an alkoxy group having 1 to 30 carbon atoms, a heteroalkyl group having 1 to 20 carbon atoms, a heteroarylalkyl group having 3 to 20 carbon atoms, a cycloalkyl group having 3 to 30 carbon atoms, a cycloalkenyl group having 3 to 15 carbon atoms, a cycloalkynyl group having 6 to 15 carbon atoms, a heterocyclic group having 2 to 30 carbon atoms, and combinations thereof.

[0038] Furthermore, two adjacent substituents among the above-mentioned substituted halogen atoms (F, Br, Cl, or I), hydroxy groups, nitro groups, cyano groups, amino groups, azide groups, amidino groups, hydrazino groups, hydrazono groups, carbonyl groups, carbamoyl groups, thiol groups, ester groups, carboxyl groups and salts thereof, sulfonic acid groups and salts thereof, phosphoric acid groups and salts thereof, alkyl groups having 1 to 30 carbon atoms, alkenyl groups having 2 to 30 carbon atoms, alkynyl groups having 2 to 30 carbon atoms, aryl groups having 6 to 30 carbon atoms, arylalkyl groups having 7 to 30 carbon atoms, alkoxy groups having 1 to 30 carbon atoms, heteroalkyl groups having 1 to 20 carbon atoms, heteroarylalkyl groups having 3 to 20 carbon atoms, cycloalkyl groups having 3 to 30 carbon atoms, cycloalkenyl groups having 3 to 15 carbon atoms, cycloalkynyl groups having 6 to 15 carbon atoms, and heterocyclic groups having 2 to 30 carbon atoms may be fused to form a ring. For example, the substituted aryl group having 6 to 30 carbon atoms can be fused with another adjacent substituted aryl group having 6 to 30 carbon atoms to form a substituted or unsubstituted fluorene ring.

[0039] Hereinafter, an additive for a lithium secondary battery according to one embodiment will be described with reference to FIG.

[0040] FIG. 1 is a cross-sectional view of an additive according to one embodiment.

[0041] 1, an additive 1 according to one embodiment includes a core 3 and a shell 5 surrounding the core 3. The core 3 includes a flame retardant, a fire extinguishing agent, a non-flammable material, or a combination thereof, and the shell 5 includes a polymer having a melting point of 90°C to 120°C.

[0042] Since the additive 1 has a structure including a core 3 and a shell 5, it can maintain battery characteristics without increasing battery resistance compared to when a fire-suppressing substance such as a flame retardant is directly introduced into the battery. Also, since the core 3 includes a safety-enhancing substance such as a flame retardant, fire extinguishing agent, or non-flammable material, when the shell 5 of the additive melts at high temperatures, the substance is released from the core 3 to the outside, preventing battery fire and improving battery safety.

[0043] The ratio of the thickness of the core 3 to the thickness of the shell 5 may be 1:1 to 4:1, for example, 3:2, for example, 2:1, for example, 5:2, or for example, 3:1, but is not limited thereto.

[0044] When the thickness ratio of the core 3 to the shell 5 is within the above range, the time required for melting the shell 5 and releasing the core material can be appropriately controlled, thereby effectively preventing the occurrence of electrode short circuits at high temperatures. Furthermore, when the temperature is not high, the shell 5 is less likely to break, preventing an unnecessary increase in battery resistance and a deterioration in battery performance.

[0045] When the additive containing the core 3 and the shell 5 is in the form of a fiber, the "core thickness" refers to the linear length of a line segment extending from the center of the circle that is the cross section of the fiber to a point on the periphery of the core, and the "shell thickness" refers to the linear length between the point where the line segment touches the periphery of the core and the point where the line segment touches the periphery of the shell when the line segment extends from the center of the circle that is the cross section of the fiber to a point on the periphery of the shell.

[0046] When the additive containing the core 3 and the shell 5 is spherical, the "core thickness" refers to the length of a line segment extending from the center of the sphere to a point on the surface of the core, and the "shell thickness" refers to the length between the point where the line segment extends from the center of the sphere to a point on the surface of the shell and the point where the line segment extends from the center of the sphere to a point on the surface of the shell.

[0047] The thickness of the core 3 may be 0.1 μm to 2.0 μm, for example, 0.1 μm or more, 0.15 μm or more, 0.20 μm or more, 0.25 μm or more, 0.30 μm or more, or 0.35 μm or more, and 2.0 μm or less, for example, 1.5 μm or less, 1.4 μm or less, 1.3 μm or less, 1.2 μm or less, 1.1 μm or less, or 1.0 μm or less, but is not limited thereto.

[0048] When the core 3 has a thickness within the above range, the core material is released along with the melting of the shell 5 in a timely manner, which effectively prevents the occurrence of electrode short circuits, while at the same time maintaining battery characteristics by preventing a decrease in electrolyte impregnation and an unnecessary increase in battery resistance.

[0049] The flame retardant contained in the core 3 may be a compound that suppresses or alleviates combustion and has the property of suppressing battery ignition. Specifically, the flame retardant may be a phosphate ester compound, a phosphazene compound, or a combination thereof.

[0050] For example, the phosphate ester compound may be an alkyl phosphate, an aryl phosphate, an alkyl phosphonate, an aryl phosphonate, or a combination thereof. For example, the phosphate ester compound may be trimethyl phosphate, triethyl phosphate, tributyl phosphate, triphenyl phosphate, tricresyl phosphate, trixylenyl phosphate, tris(2,2,2-trifluoroethyl)phosphate, or dimethyl(2-methoxyethoxy)methylphosphonate, such as, but not limited to, trimethyl phosphate, triethyl phosphate, tributyl phosphate, or triphenyl phosphate.

[0051] The phosphate ester compound can be represented by the following Chemical Formula 1.

[0052] JPEG2025534143000006.jpg4272 ...chemical formula 1

[0053] In the above chemical formula 1, R 1 ~R 3 are each independently a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, and a to c are each independently an integer of 0 to 5.

[0054] The alkyl group having 1 to 10 carbon atoms is, for example, a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, or a heptyl group, such as a methyl group, an ethyl group, a propyl group, or a butyl group, such as a methyl group or an ethyl group, but is not limited thereto.

[0055] The a to c are each independently an integer of 0 to 5, an integer of 0 to 3, or 0 or 1, but are not limited to these.

[0056] The phosphazene compound can be represented by the following Chemical Formula 2.

[0057] [ka] ...Chemical formula 2

[0058] In the above chemical formula 2, n is 3 or 4, and R 4 and R 5 are the same or different, -F, -NR x R y or a substituted or unsubstituted alkoxy group having 1 to 5 carbon atoms, R x and R y are the same or different and are a substituted or unsubstituted alkyl group having 1 to 30 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 30 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 30 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 30 carbon atoms.

[0059] The phosphazene compound can be represented by the following formula 2-1 or 2-2.

[0060] [ka] ...Chemical formula 2-1

[0061] In the above chemical formula 2-1, R 6 and R 7are each independently hydrogen, a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, a fluoroalkyl group having 1 to 10 carbon atoms, or a combination thereof. The alkyl group having 1 to 10 carbon atoms is, for example, a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, or a heptyl group, such as a methyl group, an ethyl group, a propyl group, or a butyl group, such as a methyl group or an ethyl group, but is not limited to these.

[0062] [ka] ...Chemical formula 2-2

[0063] In the above chemical formula 2-2, R 8 are each independently a hydrogen atom, a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, a fluoroalkyl group having 1 to 10 carbon atoms, or a combination thereof, such as a methyl group, an ethyl group, a propyl group, or a butyl group, for example, a methyl group or an ethyl group, but are not limited to these.

[0064] The fire extinguishing agent contained in the core 3 may be a compound that is used to extinguish fire and has the property of preventing battery combustion, such as, but not limited to, sodium bicarbonate or carbon tetrachloride.

[0065] The non-combustible material contained in the core 3 is a material that is difficult to burn and can be a compound having the property of preventing the spread of fire, such as, but not limited to, stone, glass, steel, aluminum, etc.

[0066] The thickness of the shell 5 may be 0.025 μm to 0.5 μm, for example, 0.025 μm or more, 0.05 μm or more, 0.075 μm or more, 0.10 μm or more, 0.125 μm or more, or 0.15 μm or more, and 0.5 μm or less, for example, 0.45 μm or less, 0.40 μm or less, 0.35 μm or less, or 0.30 μm or less, but is not limited thereto.

[0067] When the shell 5 has a thickness within the above range, the occurrence of electrode short circuits can be effectively controlled by timely melting of the shell 5 and release of the core material, and at the same time, the battery resistance is not unnecessarily increased, thereby maintaining the battery characteristics.

[0068] In one embodiment, the shell 5 may include a polymer having a melting point of 90° C. to 120° C. For example, the melting point of the polymer may be 90° C. or higher, such as 95° C. or higher, or 100° C. or higher, or may be 120° C. or lower, such as 115° C. or lower, or 110° C. or lower. For example, the polymer may be a thermoplastic resin.

[0069] Since the melting point of the polymer contained in the shell 5 is within the above range, the shell 5 can be stably maintained within the operating temperature range during charging and discharging of the battery, preventing an increase in the resistance of the battery, and the shell 5 can be appropriately melted at high temperatures of 100° C. or higher. In addition, safety-enhancing substances such as flame retardants in the core 3 can be released in a timely manner, effectively preventing battery ignition.

[0070] By way of example, the thermoplastic resin may be poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP), polyacrylic acid, polyethylene, poly(methyl methacrylate), polyalkylene oxide, polyalkylene succinate, or a combination thereof, such as, but not limited to, poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP), polyalkylene oxide, polyalkylene succinate, or a combination thereof.

[0071] The polyalkylene oxide may be polyethylene oxide, polypropylene oxide, polybutylene oxide, polypentylene oxide, polyhexylene oxide, polyheptylene oxide, etc., such as polyethylene oxide, polypropylene oxide, or polybutylene oxide, such as polyethylene oxide, polypropylene oxide, etc., but is not limited thereto.

[0072] The polyalkylene succinate may be polyethylene succinate, polypropylene succinate, polybutylene succinate, polypentylene succinate, polyhexylene succinate, polyheptylene succinate, or polyoxyethylene succinate, for example, polyethylene succinate, polypropylene succinate, or polybutylene succinate, for example, polybutylene succinate, but is not limited thereto.

[0073] The additive 1 may be in the form of a fiber formed by electrospinning. When the additive is in the form of a fiber, the core material can be effectively dissolved at high temperatures, thereby effectively preventing battery fires. In addition to the fiber form, the additive 1 may be in the form of an amorphous, plate-like, spherical, or other shape, but is not limited thereto, as long as it has a structure including a core 3 and a shell 5 surrounding the core 3.

[0074] When preparing the core-shell structured additive 1, the electrospinning process can be carried out by a known process taking into consideration the safety enhancing substances such as flame retardants and the melting temperature of the thermoplastic resin.

[0075] The additive 1 may be included in an amount of 0.1 wt % to 20 wt %, 0.1 wt % to 15 wt %, or 0.1 wt % to 10 wt % based on the total weight of the electrolyte for lithium secondary batteries. For example, the additive may be included in an amount of 0.1 wt % or more, e.g., 0.2 wt % or more, 0.3 wt % or more, 0.4 wt % or more, 0.5 wt % or more, 0.6 wt % or more, 0.7 wt % or more, 0.8 wt % or more, 0.9 wt % or more, or 1 wt % or more, and 15.0 wt % or less, e.g., 14.0 wt % or less, 13.0 wt % or less, 12.0 wt % or less, 11.0 wt % or less, 10.0 wt % or less, or 9.0 wt % or less based on the total weight of the electrolyte for lithium secondary batteries, but is not limited thereto.

[0076] When the content of Additive 1 is within the above range, the battery characteristics can be maintained without increasing the battery resistance at the battery operating temperature, and the battery resistance can be increased above the battery operating temperature, thereby realizing a lithium secondary battery with improved safety.

[0077] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0078] The non-aqueous organic solvent may be a carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or aprotic solvent.

[0079] Examples of the carbonate solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), 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. The ketone solvent may be cyclohexanone, etc. The alcohol solvent may be ethyl alcohol, isopropyl alcohol, etc. The aprotic solvent may be nitriles such as R-CN (R is a hydrocarbon group having 2 to 20 carbon atoms and having a linear, branched, or cyclic structure, and may contain a double-bonded aromatic ring or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolanes, etc.

[0080] The non-aqueous organic solvents may be used alone or in combination of two or more thereof. When two or more thereof are used in combination, the mixing ratio may be appropriately adjusted depending on the desired battery performance, as would be readily understood by those skilled in the art.

[0081] 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 can be excellent.

[0082] 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.

[0083] The aromatic hydrocarbon solvent may be an aromatic hydrocarbon compound represented by the following formula 4:

[0084] [ka] ...chemical formula 4

[0085] In the above chemical formula 4, R 201 ~R 206 are the same or different and may be hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, a haloalkyl group, or a combination thereof.

[0086] 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, and combinations thereof.

[0087] The electrolyte may further include vinylene carbonate, vinylethylene carbonate, or an ethylene carbonate-based compound of the following Formula 5 as a life-enhancing additive to improve battery life.

[0088] [ka] ...chemical formula 5

[0089] In the above chemical formula 5, R 207 and R 208 are the same or different and can be selected from hydrogen, a halogen group, a cyano group (CN), a nitro group (NO2), or a fluorinated alkyl group having 1 to 5 carbon atoms.

[0090] 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.

[0091] The lithium salt is dissolved in a non-aqueous organic solvent and serves as a source of lithium ions in the battery, enabling basic operation of a lithium secondary battery, and promoting the movement of lithium ions between the positive electrode and the negative electrode.

[0092] Representative examples of the lithium salt include LiPF6, LiBF4, LiDFOP, 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)(C y F 2y+1 SO2) (where x and y are natural numbers, for example, integers of 1 to 20), LiCl, LiI, or LiB(C2O4)2 (lithium bis(oxalato)borate: LiBOB).

[0093] The lithium salt concentration is preferably within the 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.

[0094] The additive and the electrolyte can be applied to a lithium secondary battery.

[0095] Hereinafter, a lithium secondary battery according to an embodiment will be described with reference to FIG.

[0096] The lithium secondary battery 100 according to one embodiment includes a positive electrode 114 including a positive electrode active material; a negative electrode 112 including a negative electrode active material; and the aforementioned electrolyte solution.

[0097] 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, into cylindrical, prismatic, coin, and pouch types depending on the shape, and into bulk and thin film types depending on the size. The structures and manufacturing methods of these batteries are widely known in the art, so detailed description will be omitted.

[0098] Here, a cylindrical lithium secondary battery will be described as an example of a lithium secondary battery. FIG. 2 is a schematic diagram illustrating the structure of a lithium secondary battery according to an embodiment. Referring to FIG. 2, 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. The positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, and the positive electrode active material layer includes a positive electrode active material.

[0099] The positive electrode active material may be a compound capable of reversibly intercalating and deintercalating lithium (lithiated intercalation compound). Specifically, at least one of composite oxides of lithium and metals including cobalt, manganese, nickel, or a combination thereof may be used.

[0100] The composite oxide may be a composite oxide in which a portion of the metal is replaced with a metal other than the metal. The composite oxide may be a phosphate compound, such as at least one selected from LiFePO4, LiCoPO4, and LiMnPO4. The composite oxide may also have a coating layer on its surface. Alternatively, the composite oxide may be mixed with a composite oxide having a coating layer. The coating layer may contain at least one coating element compound selected from the group consisting of oxides, hydroxides, oxyhydroxides, oxycarbonates, and hydroxycarbonates of the coating element. The compound forming the coating layer may be amorphous or crystalline. The coating element contained in the coating layer may be Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof. The coating layer forming 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, and detailed description thereof will be omitted as it is well understood by those skilled in the art.

[0101] The positive electrode active material may be, for example, one or more lithium composite oxides represented by the following chemical formula 3.

[0102] [Chemical formula 3] Li x M 1 y M 2 z M 3 1-y-z O2 In the above chemical formula 3, 0.5≦x≦1.8, 0 <y≦1、0≦z≦1、0≦y+z≦1、M 1 , M 2 , and M 3may each independently be any one selected from metals such as Ni, Co, Mn, Al, Sr, Mg, or La, and combinations thereof.

[0103] In one embodiment, the positive electrode active material is LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi a Mn b Co c O2(a+b+c=1), LiNi a Mn b Co c Al d O2(a+b+c+d=1) or LiNi e Co f Al g O2(e+f+g=1).

[0104] For example, the LiNi a Mn b Co c O2(a+b+c=1), LiNi a Mn b Co c Al d O2(a+b+c+d=1), and LiNi e Co f Al g The positive electrode active material selected from O2 (e+f+g=1) may be a high nickel (high Ni) based positive electrode active material.

[0105] For example, the LiNi a Mn b Co c O2 (a+b+c=1) and LiNi a Mn b Co c Al d In the case of O2 (a+b+c+d=1), the nickel content may be 60% or more (a≧0.6), more specifically 80% or more (a≧0.8).

[0106] For example, the LiNi e Co f Al gIn the case of O2 (e+f+g=1), the nickel content may be 60% or more (e≧0.6), more specifically 80% or more (e≧0.8).

[0107] 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.

[0108] 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 1.0 wt % to 5.0 wt % based on the total weight of the positive electrode active material layer.

[0109] 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 electron-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 thereof.

[0110] 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.

[0111] The positive electrode current collector may be made of Al, but is not limited thereto.

[0112] 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.

[0113] 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.

[0114] The material capable of reversibly intercalating / deintercalating lithium ions may be any carbonaceous negative electrode active material commonly used in lithium secondary batteries, representative examples of which include crystalline carbon, amorphous carbon, or a combination of these. Examples of crystalline carbon include graphite, such as amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite. Examples of amorphous carbon include soft or hard carbon, mesophase pitch carbide, and calcined coke.

[0115] As the lithium metal alloy, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0116] Examples of substances that can be doped and undoped with lithium include Si, Si-C composites, SiOx (0 < x < 2), Si-Q alloys (where Q is an element selected from 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 (where R is an element selected from 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. Also, at least one of these can be mixed with SiO2 and used.

[0117] Examples of the elements Q and R include those selected from 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.

[0118] Examples of the transition metal oxides include vanadium oxides, lithium vanadium oxides, or lithium titanium oxides.

[0119] In a specific embodiment, the negative electrode active material may be a Si-C composite containing a Si-based active material and a carbon-based active material.

[0120] In the Si-C composite, the average particle size of the Si-based active material may be 50 nm to 200 nm. When the average particle size of the Si-based active material is within this range, volume expansion generated during charge and discharge can be suppressed, and the interruption of the conductive path due to particle crushing during charge and discharge can be prevented.

[0121] 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.

[0122] In another specific embodiment, the negative electrode active material may further include crystalline carbon in addition to the Si—C composite.

[0123] 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.

[0124] The crystalline carbon may include, for example, graphite, and more specifically, may include natural graphite, artificial graphite, or a mixture thereof.

[0125] The crystalline carbon may have an average particle size of 5 μm to 30 μm.

[0126] In this specification, the average particle size may be the particle size at 50% by volume (D50) on a cumulative size-distribution curve.

[0127] 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.

[0128] 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.

[0129] 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.

[0130] In one embodiment, 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 negative electrode active material layer further includes a conductive material, the negative electrode active material may be 90 wt% to 98 wt%, the binder may be 1 wt% to 5 wt%, and the conductive material may be 1 wt% to 5 wt%.

[0131] The binder serves to firmly adhere the negative active material particles to each other and to the current collector. The binder may be a water-insoluble binder, a water-soluble binder, or a combination thereof.

[0132] The water-insoluble binder may be polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0133] 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.

[0134] 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 Na, K, or Li. 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.

[0135] The conductive material is used to impart conductivity to the electrode, and any material that is electron-conductive and does not cause a chemical change in the constructed battery can be used. Examples of conductive materials that can be used 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 thereof.

[0136] 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.

[0137] Depending on the type of lithium secondary battery, a separator may be present between the positive electrode and the negative electrode. The separator may be a porous substrate or a composite porous substrate.

[0138] 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 layers thereof, such as 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.

[0139] 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, allowing for additional functionality. For example, the heat-resistant layer may include a heat-resistant resin and, optionally, a filler. The adhesive layer may include an adhesive resin and, optionally, a filler. The filler may be an organic filler or an inorganic filler.

[0140] The additive for a lithium secondary battery according to an embodiment may be included in the electrolyte solution as described above, and may also be applied to a current collector, an electrode tap, a separator, etc. of a lithium secondary battery.

[0141] When the additive is applied to a current collector or an electrode tab, the additive may be dispersed in a suitable solvent and coated as a coating solution on the uncoated portion of the current collector or the electrode tab. When the additive is applied to a separator, the additive may be incorporated into a separator component, or a coating solution in which the additive is dispersed in a suitable solvent may be coated on at least one surface of the separator.

[0142] The above-described embodiments of the present invention will be described in more detail with reference to the following examples, which are for illustrative purposes only and are not intended to limit the scope of the present invention. [Example]

[0143] Additive manufacturing Synthesis Example 1 Polymer solutions containing 5 wt% of flame retardant (triphenyl phosphate) and 10 wt% of poly(vinylidene fluoride hexafluoropropylene) (PVDF-HFP) were prepared, and electrospun to produce a fiber-shaped additive with a core-to-shell thickness of 1:1.

[0144] Synthesis Example 2 Polymer solutions containing 10 wt% of a flame retardant (triphenyl phosphate) and 10 wt% of poly(vinylidene fluoride hexafluoropropylene) (PVDF-HFP) were prepared, and then electrospun to produce a fiber-shaped additive with a core-to-shell thickness ratio of 2:1.

[0145] Synthesis Example 3 Polymer solutions containing 10 wt% of a flame retardant (triphenyl phosphate) and 10 wt% of poly(vinylidene fluoride hexafluoropropylene) (PVDF-HFP) were prepared, and then electrospun to produce a fiber-shaped additive with a core-to-shell thickness ratio of 4:1.

[0146] Comparative synthesis example 1 A fiber-shaped additive was prepared in the same manner as in Synthesis Example 1, except that a polymer solution containing polyethylene glycol (PEG) was used instead of poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP).

[0147] Comparative synthesis example 2 A fiber-shaped additive was prepared in the same manner as in Synthesis Example 1, except that a polymer solution containing polypropylene (PP) was used instead of poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP).

[0148] Lithium secondary battery manufacturing Example 1 LiNi as the positive electrode active material 0.88 Co 0.07 Al0.05 O2, polyvinylidene fluoride as a binder, and acetylene black as a conductive material were mixed in a weight ratio of 96:2:2, and dispersed in N-methylpyrrolidone to prepare a positive electrode active material slurry.

[0149] 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.

[0150] 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.

[0151] 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.

[0152] 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.

[0153] 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. The electrolyte composition is as follows:

[0154] (Electrolyte composition) Salt: LiPF61.3M Solvent: ethylene carbonate (EC): propylene carbonate (PC): ethyl propionate (EP): propyl propionate (PP) = 15:15:25:45 (volume ratio) Additives: 3 parts by weight of fluoroethylene carbonate, 3 parts by weight of SN, 15 parts by weight of the additive produced in Synthesis Example 1 (However, in the electrolyte composition, "parts by weight" refers to the relative weight of the additive with respect to 100 parts by weight of the entire electrolyte (lithium salt + non-aqueous organic solvent).)

[0155] Example 2 A lithium secondary battery was manufactured in the same manner as in Example 1, except that 20 parts by weight of the additive prepared in Synthesis Example 2 was used instead of the additive prepared in Synthesis Example 1.

[0156] Example 3 A lithium secondary battery was manufactured in the same manner as in Example 1, except that 10.25 parts by weight of the additive prepared in Synthesis Example 3 was used instead of the additive prepared in Synthesis Example 1.

[0157] Comparative Example 1 A lithium secondary battery was manufactured in the same manner as in Example 1, except that the additive prepared in Synthesis Example 1 was not used.

[0158] Comparative Example 2 A lithium secondary battery was manufactured in the same manner as in Example 1, except that 2 parts by weight of a flame retardant (triphenyl phosphate; Sigma-Aldrich) was used instead of the additive prepared in Synthesis Example 1.

[0159] Comparative Example 3 A lithium secondary battery was manufactured in the same manner as in Example 1, except that 10 parts by weight of a flame retardant (triphenyl phosphate) was used instead of the additive prepared in Synthesis Example 1.

[0160] Comparative Example 4 A lithium secondary battery was manufactured in the same manner as in Example 1, except that the additive prepared in Comparative Synthesis Example 1 was used instead of the additive prepared in Synthesis Example 1.

[0161] Comparative Example 5 A lithium secondary battery was manufactured in the same manner as in Example 1, except that the additive prepared in Comparative Synthesis Example 2 was used instead of the additive prepared in Synthesis Example 1.

[0162] Evaluation 1: High temperature life evaluation For the lithium secondary batteries according to Examples 1 to 3 and Comparative Examples 1 to 5, the lithium secondary batteries were charged at a constant current of 0.5 C at 45°C until the voltage reached 4.4 V, and then cut off at a current of 0.05 C in constant voltage mode while maintaining 4.4 V. The batteries were then discharged at a constant current of 0.5 C until the voltage reached 3.0 V during discharge. This process was repeated 100 times. The capacity retention rates after 100 cycles, calculated using the following formula 1, are shown in Table 1.

[0163] [Formula 1] Capacity retention rate at 100 cycles [%] = [50 cycle discharge capacity / 1 cycle discharge capacity] x 100

[0164] [Table 1]

[0165] Referring to Table 1 above, it can be seen that the lithium secondary batteries according to Examples 1 to 3 are superior to the lithium secondary batteries according to Comparative Examples 3 to 5 in high-temperature life.

[0166] Evaluation 2: Penetration safety evaluation For the lithium secondary batteries according to Examples 1 to 3 and Comparative Examples 1 to 5, the lithium secondary batteries were charged at 0.5C / 4.4V with a 0.05C cut-off charge, and then allowed to rest for 10 minutes. Then, a pin having a diameter of 5 mm was used to completely penetrate the center of the battery at speeds of 50 mm / sec, 100 mm / sec, 150 mm / sec, and 200 mm / sec to evaluate the penetration stability, and the results are shown in Table 2.

[0167] [Table 2]

[0168] In Table 2, "NG" means that thermal runaway was observed at the exposure temperature, "OK" means that a sudden voltage drop was observed without thermal runaway at the exposure temperature, and (-) means that thermal exposure evaluation was not performed.

[0169] The lithium secondary batteries according to Comparative Examples 1 and 2 exhibited thermal runaway at penetration speeds of 150 mm / s and 200 mm / s, and were inferior in battery stability.

[0170] The lithium secondary battery according to Comparative Example 5 was observed to experience thermal runaway at 200 mm / s. This is interpreted as meaning that the additive contained in the lithium secondary battery according to Comparative Example 5 was unable to protect the core material due to the thin shell thickness, and the core and shell materials mixed at the operating temperature of the cell, failing to improve performance and safety.

[0171] In contrast, no thermal runaway phenomenon was observed in the lithium secondary batteries according to Examples 1 to 3, even at a low penetration speed of 50 mm / s. This indicates that the lithium secondary batteries according to Examples 1 to 3 have superior battery stability compared to the lithium secondary battery according to the comparative example.

[0172] Although the preferred embodiments of the present invention have been described in detail above, the scope of the invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concept of the invention defined in the claims below also fall within the scope of the invention. [Explanation of symbols]

[0173] 100: Lithium secondary battery 112: Negative electrode 113: Separator 114: Positive electrode 120:Battery container 140: Enclosure material

Claims

1. a core and a shell surrounding the core, the core comprises a fire retardant, a fire extinguishing agent, a non-combustible material, or a combination thereof; The shell is an additive for a lithium secondary battery, which comprises a polymer having a melting point of 90°C to 120°C.

2. 2. The additive for lithium secondary batteries according to claim 1, wherein the ratio of the thickness of the core to the thickness of the shell is 1:1 to 4:

1.

3. 2. The additive for lithium secondary batteries according to claim 1, wherein the core has a thickness of 0.1 μm to 2.0 μm, and the shell has a thickness of 0.025 μm to 0.5 μm.

4. The additive for lithium secondary batteries according to claim 1 , wherein the flame retardant is a phosphate ester compound, a phosphazene compound, or a combination thereof.

5. The additive for a lithium secondary battery according to claim 1 , wherein the phosphate ester compound is represented by the following Chemical Formula 1: 【Chemical 1】 ...Chemical formula 1 In the above chemical formula 1, R １ ~R ３ are each independently a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, a to c are each independently an integer of 0 to 5.

6. The additive for a lithium secondary battery according to claim 1 , wherein the phosphazene compound is represented by the following Chemical Formula 2: 【Chemistry 2】 ...Chemical formula 2 In the above chemical formula 2, n is 3 or 4; R ４ and R ５ are the same or different, -F, -NR ｘ R ｙ or a substituted or unsubstituted alkoxy group having 1 to 5 carbon atoms, R ｘ and R ｙ are the same or different and are a substituted or unsubstituted alkyl group having 1 to 30 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 30 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 30 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 30 carbon atoms.

7. The additive for a lithium secondary battery according to claim 1, wherein the phosphazene compound is represented by the following chemical formula 2-1 or 2-2: 【Chemistry 3】 ...Chemical formula 2-1 【Chemistry 4】 ...Chemical formula 2-2 In the above chemical formula 2-1 and the above chemical formula 2-2, R ６ ~R ８ are each independently hydrogen, a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, a fluoroalkyl group having 1 to 10 carbon atoms, or a combination thereof.

8. 2. The additive for lithium secondary batteries according to claim 1, wherein the polymer comprises poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP), polyacrylic acid, polyethylene, poly(methyl methacrylate), polyalkylene oxide, polyalkylene succinate, or a combination thereof.

9. The additive for a lithium secondary battery according to claim 1 , wherein the additive is in the form of a fiber formed by electrospinning.

10. non-aqueous organic solvents, lithium salts, and The additive for lithium secondary batteries according to any one of claims 1 to 9.

1. An electrolyte for a lithium secondary battery comprising:

11. 11. The electrolyte solution for a lithium secondary battery according to claim 10, wherein the additive for a lithium secondary battery is contained in an amount of 0.1 wt % to 20 wt % based on the total weight of the electrolyte solution for a lithium secondary battery.

12. 11. The electrolyte solution for a lithium secondary battery according to claim 10, wherein the additive for a lithium secondary battery is contained in an amount of 0.1 wt % to 15 wt % based on the total weight of the electrolyte solution for a lithium secondary battery.

13. 11. The electrolyte solution for a lithium secondary battery according to claim 10, wherein the additive for a lithium secondary battery is contained in an amount of 0.1 wt % to 10 wt % based on the total weight of the electrolyte solution for a lithium secondary battery.

14. a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and The electrolyte of claim 10; A lithium secondary battery comprising:

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