Additive for lithium secondary battery, electrolyte for lithium secondary battery including additive, and lithium secondary battery

Abstract

Provided are an additive for a lithium secondary battery, an electrolyte for a lithium secondary battery including the additive, and a lithium secondary battery, in which the additive includes a core and a shell surrounding the core, in which 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 range of 90 DEG C to 120 DEG C.

Description

Technical Field

[0001] The present disclosure relates to an additive for a lithium secondary battery, an electrolyte for a lithium secondary battery including the additive, and a lithium secondary battery. 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. The lithium secondary battery can also be charged at a high rate, and thus is commercially manufactured for laptop computers, cellular phones, power tools, electric bicycles, etc., and research on improving additional energy density has been actively conducted.

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

[0004] In particular, the electrolyte includes an organic solvent in which a lithium salt is dissolved and which critically determines the stability and performance of the lithium secondary battery.

[0005] LiPF, the most commonly used lithium salt as an electrolyte 6 has a problem of reacting with an electrolyte solvent to promote the consumption of the solvent and generating a large amount of gas. When LiPF 6 decomposes, LiF and PF 5 are generated, causing the consumption of the electrolyte in the battery, resulting in deterioration of high-temperature performance and vulnerability of safety.

[0006] Accordingly, there is a need for an electrolyte having improved safety and not deteriorating in performance even under high-temperature conditions. Summary of the Invention

[0007] Technical Problem

[0008] An embodiment provides an additive for a lithium secondary battery having improved thermal stability.

[0009] Another embodiment provides an electrolyte for a lithium secondary battery having improved cycle life characteristics, high-temperature safety, and high-temperature reliability by applying the additive.

[0010] Another embodiment provides a lithium secondary battery including an electrolyte for a lithium secondary battery.

[0011] Technical Solution

[0012] An additive for a lithium secondary battery according to an embodiment 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.

[0013] The ratio of the thickness of the core to the thickness of the shell may be from 1:1 to 4:1.

[0014] 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.

[0015] The flame retardant may include a phosphate compound, a phosphazene compound, or a combination thereof.

[0016] The phosphate compound may include a compound represented by Chemical Formula 1.

[0017] [Chemical Formula 1]

[0018]

[0019] In Chemical Formula 1,

[0020] R 1 ~R 3 are each independently a substituted or unsubstituted C1-C10 alkyl group, and

[0021] a to c are each independently an integer from 0 to 5.

[0022] The phosphazene compound may include a compound represented by Chemical Formula 2.

[0023] [Chemical Formula 2]

[0024]

[0025] In Chemical Formula 2,

[0026] n is 3 or 4,

[0027] R 4 and R 5 are each independently -F, -NR x R y or a substituted or unsubstituted C1-C5 alkoxy group, where R x and R y are each independently a substituted or unsubstituted C1-C30 alkyl group, a substituted or unsubstituted C3-C30 cycloalkyl group, a substituted or unsubstituted C2-C30 alkenyl group, or a C6-C30 substituted or unsubstituted aryl group.

[0028] The phosphazene compound may include a compound represented by Chemical Formula 2-1 or Chemical Formula 2-2.

[0029] [Chemical Formula 2-1]

[0030]

[0031] [Chemical Formula 2-2]

[0032]

[0033] In the above Chemical Formula 2-1 and above Chemical Formula 2-2,

[0034] R 6 ~R 8 Each independently represents hydrogen, a substituted or unsubstituted C1-C10 alkyl group, a C1-C10 fluoroalkyl group, or a combination thereof.

[0035] The polymer may include poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP), polyacrylic acid, polyethylene, poly(methyl methacrylate), polyalkylene oxide, polyalkylene succinate, or a combination thereof.

[0036] The additive may be in the form of fibers formed by electrospinning.

[0037] According to another embodiment, an electrolyte for a lithium secondary battery includes a non-aqueous organic solvent, a lithium salt, and the aforementioned additive for a lithium secondary battery.

[0038] Based on the total weight of the electrolyte for a lithium secondary battery, the amount of the additive for a lithium secondary battery included may be 0.1 wt% to 20 wt%, 0.1 wt% to 15 wt%, or 0.1 wt% to 10 wt%.

[0039] According to another embodiment, a lithium secondary battery includes: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and the aforementioned electrolyte.

[0040] Advantageous Effects

[0041] The additive for a lithium secondary battery according to the embodiment has excellent electrolyte impregnation characteristics and can maintain battery characteristics without increasing battery resistance when applied to the electrolyte.

[0042] In addition, the lithium secondary battery including the additive for a lithium secondary battery according to the embodiment can control the fire of the battery exceeding the battery operating temperature and improve the safety of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 is a cross-sectional view of an additive according to an embodiment.

[0044] Figure 2 is a schematic diagram showing a lithium secondary battery according to an embodiment.

[0045] <Description of Reference Numerals>

[0046] 100: Lithium secondary battery

[0047] 112: Negative electrode

[0048] 113: Diaphragm

[0049] 114: Positive electrode

[0050] 120: Battery housing

[0051] 140: Sealing member Detailed implementation manners

[0052] Hereinafter, the implementation manners will be described in detail so that those of ordinary skill in the art can easily implement them. However, the structure of the actual application can be implemented in several different forms and is not limited to the implementation manners described herein.

[0053] In the drawings, for clarity, the thicknesses of layers, films, panels, regions, etc. are enlarged.

[0054] It will be understood that when an element (such as a layer, film, region, or substrate) is referred to as being "on" another element, it can be directly on the other element or there can also be intervening elements. In contrast, when an element is referred to as being "directly on" another element, there are no intervening elements.

[0055] In this specification, "at least one of A, B, or C", "one or a combination of A, B, C", and "one and a combination of A, B, C" mean each individual component and all combinations thereof (e.g., A; B; A and B; A and C; B and C; or A, B, and C).

[0056] Hereinafter, the term "combination" includes mixtures of two or more, intersubstitutions, and stacked structures of two or more.

[0057] In this specification, when no specific limitation is provided, "substituted" means that the hydrogen in the compound is substituted by a substituent selected from the following: deuterium, halogen atom (F, Br, Cl, or I), hydroxyl group, nitro group, cyano group, amino group, azide group, amidino group, hydrazino group, hydrazono group, carbonyl group, carbamoyl group, mercapto group, ester group, carboxyl group or its salt, sulfonic acid group or its salt, phosphoric acid or its salt, C1-C30 alkyl group, C2-C30 alkenyl group, C2-C30 alkynyl group, C6-C30 aryl group, C7-C30 aralkyl group, C1-C30 alkoxy group, C1-C20 heteroalkyl group, C3-C20 heteroarylalkyl group, C3-C30 cycloalkyl group, C3-C15 cycloalkenyl group, C6-C15 cycloalkynyl group, C2-C30 heterocyclic group, and combinations thereof.

[0058] In addition, two adjacent groups among the halogen atoms (F, Br, Cl, or I) for substitution, hydroxyl group, nitro group, cyano group, amino group, azide group, formamidine group, hydrazine group, hyrazone group, carbonyl group, carbamoyl group, mercapto group, ester group, carboxyl group or its salt, sulfonic acid group or its salt, phosphoric acid group or its salt, C1-C30 alkyl group, C2-C30 alkenyl group, C2-C30 alkynyl group, C6-C30 aryl group, C7-C30 aralkyl group, C1-C30 alkoxy group, C1-C20 heteroalkyl group, C3-C20 heteroarylalkyl group, C3-C30 cycloalkyl group, C3-C15 cycloalkenyl group, C6-C15 cycloalkynyl group, C2-C30 heterocyclic group may also be fused to each other to form a ring. For example, a substituted C6-C30 aryl group may be fused with another adjacent substituted C6-C30 aryl group to form a substituted or unsubstituted fluorene ring.

[0059] The following refers to Figure 1 an additive for a lithium secondary battery according to an embodiment is described.

[0060] Figure 1 is a cross-sectional view of an additive according to an embodiment.

[0061] Referring to Figure 1 , an additive 1 according to an 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.

[0062] Since the additive 1 has a structure including the core 3 and the shell 5, the additive 1 can maintain the characteristics of the battery without increasing the resistance of the battery as compared with when a fireproof material (such as a flame retardant) is directly introduced into the battery. In addition, since the core 3 includes materials for enhancing safety (such as a flame retardant, a fire extinguishing agent, or a non-flammable material), when the shell 5 of the additive melts at a high temperature, the materials are released from the core 3 to the outside to control the ignition of the battery, thereby improving the safety of the battery.

[0063] 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, for example, 3:1), but is not limited thereto.

[0064] When the thickness ratio of the core 3 and the shell 5 is within the above range, the time required for the melting of the shell 5 and the release of the core material can be adjusted to an appropriate range, and the occurrence of electrode short circuit at a high temperature can be effectively controlled. In addition, when not in a high temperature state, the shell 5 is not easily damaged, which prevents an unnecessary increase in the battery resistance and deterioration of the battery characteristics.

[0065] When the additive including the core 3 and the shell 5 is in the form of a fiber, the "thickness of the core" refers to the straight-line length of the line segment from the center of the circular surface that is the cross-section of the fiber to a point on the circumference of the core, and the "thickness of the shell" refers to the straight-line length between the point where the line segment intersects the circumference of the core and the point where the line segment intersects the circumference of the shell when connecting the line segment from the center of the circular surface that is the cross-section of the fiber to a point on the circumference of the shell.

[0066] When the additive including the core 3 and the shell 5 is spherical, the "thickness of the core" refers to the length of the line segment from the center of the sphere to a point on the surface of the core, and the "thickness of the shell" refers to the length of the line segment between the point where the line segment intersects the surface of the core and the point where the line segment intersects the surface of the shell when connecting the line segment from the center of the sphere to a point on the surface of the shell.

[0067] The thickness of the core 3 can be from 0.1 μm to 2.0 μm, for example, greater than or equal to 0.1 μm, greater than or equal to 0.15 μm, greater than or equal to 0.20 μm, greater than or equal to 0.25 μm, greater than or equal to 0.30 μm or greater than or equal to 0.35 μm, and less than or equal to 2.0 μm, for example, less than or equal to 1.5 μm, less than or equal to 1.4 μm, less than or equal to 1.3 μm, less than or equal to 1.2 μm, less than or equal to 1.1 μm or less than or equal to 1.0 μm, but not limited thereto.

[0068] Because the core 3 has a thickness within the above range, together with the melting of the shell 5, the material of the core is released in a timely manner, so as to effectively control the occurrence of electrode short circuit while maintaining the battery characteristics, without reducing the electrolyte impregnation characteristics and without unnecessarily increasing the battery resistance.

[0069] The flame retardant included in the core 3 can be a compound having the property of controlling the ignition of the battery by suppressing or slowing down combustion. Specifically, the flame retardant can be a phosphate compound, a phosphazene compound or a combination thereof.

[0070] For example, the phosphate compound can include alkyl phosphate, aryl phosphate, alkyl phosphonate, aryl phosphonate or a combination thereof. For example, the phosphate compound can be trimethyl phosphate, triethyl phosphate, tributyl phosphate, triphenyl phosphate, tricresyl phosphate, tris(xylene) phosphate, tris(2,2,2-trifluoroethyl) phosphate or dimethyl(2-methoxyethoxy)methyl phosphonate, and for example, it is trimethyl phosphate, triethyl phosphate, tributyl phosphate or triphenyl phosphate, but not limited thereto.

[0071] The phosphate compound can be represented by Chemical Formula 1.

[0072] [Chemical Formula 1]

[0073]

[0074] In Chemical Formula 1, R 1 ~R 3 are each independently a substituted or unsubstituted C1-C10 alkyl group, and a-c are each independently an integer from 0 to 5.

[0075] The C1-C10 alkyl group is, for example, methyl, ethyl, propyl, butyl, pentyl, hexyl or heptyl, for example, methyl, ethyl, propyl or butyl, for example, methyl or ethyl, but is not limited thereto.

[0076] a-c are each independently an integer from 0 to 5, an integer from 0 to 3, 0 or 1, but is not limited thereto.

[0077] The phosphazene compound can be represented by Chemical Formula 2.

[0078] [Chemical Formula 2]

[0079]

[0080] In Chemical Formula 2, n is 3 or 4, and R 4 and R 5 are the same or different and are -F, -NRxRy or a substituted or unsubstituted C1-C5 alkoxy group, where R x and R y are the same or different and are a substituted or unsubstituted C1-C30 alkyl group, a substituted or unsubstituted C3-C30 cycloalkyl group, a substituted or unsubstituted C2-C30 alkenyl group or a C6-C30 substituted or unsubstituted aryl group.

[0081] The phosphazene compound can be represented by Chemical Formula 2-1 or Chemical Formula 2-2.

[0082] [Chemical Formula 2-1]

[0083]

[0084] In Chemical Formula 2-1, R 6 and R 7 are each independently hydrogen, a substituted or unsubstituted C1-C10 alkyl group, a C1-C10 fluoroalkyl group or a combination thereof. The C1-C10 alkyl group is, for example, methyl, ethyl, propyl, butyl, pentyl, hexyl or heptyl, for example, methyl, ethyl, propyl or butyl, for example, methyl or ethyl, but is not limited thereto.

[0085] [Chemical Formula 2-2]

[0086]

[0087] In Chemical Formula 2-2,

[0088] R 8Each independently is hydrogen, a substituted or unsubstituted C1-C10 alkyl group, a C1-C10 fluoroalkyl group, or a combination thereof. For example, it is a methyl group, an ethyl group, a propyl group, or a butyl group. For example, it is a methyl group or an ethyl group, but is not limited thereto.

[0089] The fire extinguishing agent included in the core 3 is a material for extinguishing fire and may be a compound having the property of preventing the combustion of the battery. Examples include sodium bicarbonate or carbon tetrachloride, but are not limited thereto.

[0090] The non-flammable material included in the core 3 is a material that is difficult to burn and may use a compound having the property of preventing the spread of fire. Examples include stone, glass, steel, aluminum, etc., but are not limited thereto

[0091] The thickness of the shell 5 may be 0.025 μm to 0.5 μm. For example, it is greater than or equal to 0.025 μm, greater than or equal to 0.05 μm, greater than or equal to 0.075 μm, greater than or equal to 0.10 μm, greater than or equal to 0.125 μm, or greater than or equal to 0.15 μm, and less than or equal to 0.5 μm. For example, it is less than or equal to 0.45 μm, less than or equal to 0.40 μm, less than or equal to 0.35 μm, or less than or equal to 0.30 μm, but is not limited thereto.

[0092] Because the shell 5 has a thickness within the above range, it can be released in a timely manner through the melting of the shell 5 and the materials of the core, effectively controlling the occurrence of electrode short circuit while maintaining the battery characteristics without unnecessarily increasing the battery resistance.

[0093] In an 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 greater than or equal to 90 °C, for example, greater than or equal to 95 °C, for example, greater than or equal to 100 °C, and for example, the melting point of the polymer may be less than or equal to 120 °C, for example, less than or equal to 115 °C, for example, less than or equal to 110 °C. For example, the polymer may be a thermoplastic resin.

[0094] Because the melting point of the polymer included in the shell 5 is within the above range, the shell 5 is stably maintained within the operating temperature range during the charging and discharging of the battery, thus not increasing the resistance of the battery, and the shell 5 can be appropriately melted at a high temperature of 100 °C or higher. In addition, materials for enhancing safety (such as the flame retardant in the core 3) can be released in a timely manner to effectively control the ignition of the battery.

[0095] For 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, and for example, poly(vinylidene fluoride - hexafluoropropylene) (PVDF - HFP), polyalkylene oxide, polyalkylene succinate, or a combination thereof, but is not limited thereto.

[0096] The polyalkylene oxide may be polyethylene oxide, polypropylene oxide, polybutylene oxide, poly(pentylene oxide), poly(hexylene oxide), poly(heptylene oxide), etc., and may be, for example, polyethylene oxide, polypropylene oxide, or polybutylene oxide, and may be, for example, polyethylene oxide, polypropylene oxide, etc., but is not limited thereto.

[0097] The polyalkylene succinate may be polyethylene glycol succinate, polypropylene glycol succinate, polybutylene glycol succinate, polypentylene glycol succinate, polyhexylene glycol succinate, polyheptylene glycol succinate, or polyethylene oxide succinate, and may be, for example, polyethylene glycol succinate, polypropylene glycol succinate, or polybutylene glycol succinate, and may be, for example, polybutylene glycol succinate, but is not limited thereto.

[0098] Additive 1 may be in the form of fibers (i.e., fibers formed by electrospinning). When Additive 1 is in the form of fibers, the material of the core can be effectively released at high temperatures, effectively controlling battery fires. In addition to the fibrous form, Additive 1 may have a structure including a core 3 and a shell 5 surrounding the core 3, and may be in irregular, plate - like, spherical, etc. forms, but is not limited thereto.

[0099] When preparing Additive 1 with a core - shell structure, considering the melting points of materials for enhancing safety (such as flame retardants and thermoplastic resins), the electrospinning process can be carried out by known processes.

[0100] Based on the total weight of the electrolyte for a lithium secondary battery, the amount of Additive 1 included may be 0.1 wt% - 20 wt%, 0.1 wt% - 15 wt%, or 0.1 wt% - 10 wt%. For example, based on the total weight of the electrolyte for a lithium secondary battery, the amount of the additive included may be greater than or equal to 0.1 wt%, for example, greater than or equal to 0.2 wt%, greater than or equal to 0.3 wt%, greater than or equal to 0.4 wt%, greater than or equal to 0.5 wt%, greater than or equal to 0.6 wt%, greater than or equal to 0.7 wt%, greater than or equal to 0.8 wt%, greater than or equal to 0.9 wt%, or greater than or equal to 1 wt% and less than or equal to 15.0 wt%, for example, less than or equal to 14.0 wt%, less than or equal to 13.0 wt%, less than or equal to 12.0 wt%, less than or equal to 11.0 wt%, less than or equal to 10.0 wt%, or less than or equal to 9.0 wt%, but is not limited thereto.

[0101] When the content of Additive 1 is within the above range, the battery characteristics are maintained at the battery operating temperature without increasing the battery resistance, and above the battery operating temperature, the battery resistance increases, thereby realizing a lithium secondary battery with improved safety.

[0102] The non-aqueous organic solvent serves as a medium for transporting ions participating in the electrochemical reaction of the battery.

[0103] The non-aqueous organic solvent can be carbonates, esters, ethers, ketones, alcohols or aprotic solvents.

[0104] Carbonate solvents may 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), butylene carbonate (BC), etc. Ester solvents may include methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, decanolide, mevalonolactone, caprolactone, etc. Ether solvents may include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, 2-methyltetrahydrofuran, tetrahydrofuran, etc. In addition, ketone solvents may include cyclohexanone, etc. Alcohol solvents may include ethanol, isopropanol, etc., and aprotic solvents may include nitriles (such as R-CN, where R is a hydrocarbon group having a C2-C20 straight-chain, branched-chain or cyclic structure and may include double bonds, aromatic rings or ether bonds, etc.), dioxolanes (such as 1,3-dioxolane, etc.), sulfolane, etc.

[0105] The non-aqueous organic solvent can be used alone or in combination of one or more, and when used in combination of one or more, the mixing ratio can be appropriately adjusted according to the desired battery performance, which is widely understood by those skilled in the relevant art.

[0106] The carbonate solvent is prepared by mixing a cyclic carbonate and a chain carbonate. When the cyclic carbonate and the chain carbonate are mixed together at a volume ratio of 1:1 to 9:1, the electrolyte performance can be improved.

[0107] In addition to the carbonate solvent, the non-aqueous organic solvent may further include an aromatic hydrocarbon organic solvent. Herein, the carbonate solvent and the aromatic hydrocarbon organic solvent can be mixed at a volume ratio of 1:1 to 30:1.

[0108] The aromatic hydrocarbon organic solvent can be an aromatic hydrocarbon compound of Chemical Formula 4.

[0109] [Chemical Formula 4]

[0110]

[0111] In Chemical Formula 4, R 201 ~R206 are the same or different and are selected from hydrogen, halogen, C1-C10 alkyl, haloalkyl or a combination thereof.

[0112] Specific examples of the aromatic hydrocarbon organic solvent may be selected from 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 a combination thereof.

[0113] The electrolyte may further include vinylene carbonate, ethylene vinyl carbonate or the ethylene carbonate compound of Chemical Formula 5 as a cycle life enhancing additive to improve the battery cycle life.

[0114] [Chemical Formula 5]

[0115]

[0116] In Chemical Formula 5, R 207 and R 208 are the same or different and may be selected from hydrogen, halo group, cyano group (CN), nitro group (NO 2 ) or a fluorinated alkyl group having 1-5 carbon atoms.

[0117] Examples of the ethylene carbonate compounds may include difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate or fluoroethylene carbonate. The amount of the cycle life enhancing additive may be used within an appropriate range.

[0118] The lithium salt dissolved in the non-aqueous organic solvent supplies lithium ions in the battery, ensures the basic operation of the lithium secondary battery, and improves the transport of lithium ions between the positive electrode and the negative electrode.

[0119] Examples of the lithium salt include those selected from LiPF 6 , LiBF 4 , LiDFOP, LiDFOB, LiPO 2 F2 , LiSbF 6 , LiAsF 6 , LiN(SO 2 C 2 F 5 ) 2 , Li(CF 3 SO 2 ) 2 N, LiN(SO 3 C 2 F 5 ) 2 , Li(FSO 2 ) 2 N (Lithium bis(fluorosulfonyl)imide: LiFSI), LiC 4 F 9 SO 3 , LiClO 4 , LiAlO 2 , LiAlCl 4 , LiN(C x F 2x+1 SO 2 )(C y F 2y+1 SO 2 )(where x and y are natural numbers, for example, integers from 1 to 20), LiCl, LiI or LiB(C 2 O 4 ) 2 (Lithium bis(oxalato)borate: LiBOB)) or at least one of them.

[0120] The lithium salt can be used in the concentration range of 0.1 M to 2.0 M. If the lithium salt is included in the above concentration range, due to the optimal electrolyte conductivity and viscosity, the electrolyte can have excellent performance and lithium ion mobility.

[0121] The additive and the electrolyte can be applied to a lithium secondary battery.

[0122] Hereinafter, a lithium secondary battery according to an embodiment is described with reference to Figure 2 the description.

[0123] A lithium secondary battery 100 according to an 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.

[0124] Depending on the types of the separator and the electrolyte, lithium secondary batteries can be classified into lithium ion batteries, lithium ion polymer batteries, and lithium polymer batteries. Depending on the shape, lithium secondary batteries can also be classified into cylindrical, prismatic, coin-type, pouch-type, etc. Additionally, depending on the size, lithium secondary batteries can be block-type and thin film-type. The structures and manufacturing methods of these batteries related to the art are well-known in the art.

[0125] Here, a cylindrical lithium secondary battery is exemplarily described as an example of a lithium secondary battery. Figure 2 FIG. is a schematic diagram showing a lithium secondary battery according to an embodiment. Refer to Figure 2 , the lithium secondary battery 100 includes a battery cell, an electrolyte (not shown) for the lithium secondary battery, a battery case 120 that houses the battery cell, and a sealing member 140 that seals the battery case 120. The battery cell includes a positive electrode 114, a negative electrode 112 opposite to the positive electrode 114, and a separator 113 between the positive electrode 114 and the negative electrode 112. The electrolyte impregnates the positive electrode 114, the negative electrode 112, and the separator 113. The positive electrode includes a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector, where the positive electrode active material layer includes a positive electrode active material.

[0126] The positive electrode active material may include a compound capable of intercalating and deintercalating lithium (lithiated intercalation compound). Specifically, at least one composite oxide of lithium and a metal including cobalt, manganese, nickel, or a combination thereof can be used.

[0127] A part of the metal of the composite oxide can be replaced with a metal other than another metal, and the composite oxide can be at least one selected from phosphate compounds. For example, LiFePO 4 , LiCoPO 4 or LiMnPO 4 , and a composite oxide having a coating on its surface can also be used, or a composite oxide and a composite oxide having a coating can be mixed and used. The coating may include at least one coating element compound selected from oxides of coating elements, hydroxides of coating elements, hydroxyoxides of coating elements, oxycarbonates of coating elements, and hydroxycarbonates of coating elements. The compound for the coating can be amorphous or crystalline. The coating elements included in the coating may include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof. By using these elements in the compound, the coating can be provided in a method that has no adverse effect on the characteristics of the positive electrode active material. For example, the method may include any coating method (e.g., spraying, dip coating, etc.), but since it is well-known to those skilled in the art, it is not explained in more detail.

[0128] The positive electrode active material may be at least one of, for example, lithium composite oxides represented by Chemical Formula 3.

[0129] [Chemical Formula 3]

[0130] Li x M 1 y M 2 z M 3 1-y-z O 2

[0131] In Chemical Formula 3,

[0132] 0.5 ≤ x ≤ 1.8, 0 < y ≤ 1, 0 ≤ z ≤ 1, 0 ≤ y + z ≤ 1, and M 1 、M 2 and M 3 may each independently be a metal selected from Ni, Co, Mn, Al, Sr, Mg, or La, etc., and combinations thereof.

[0133] In an embodiment, the positive electrode active material may be selected from LiCoO 2 、LiNiO 2 、LiMnO 2 、LiMn 2 O 4 、LiNi a Mn b Co c O 2 (a + b + c = 1), LiNi a Mn b Co c Al d O 2 (a + b + c + d = 1) and LiNi e Co f Al g O 2 (e + f + g = 1) and at least one of them.

[0134] For example, selected from LiNi a Mn b Co c O 2 (a + b + c = 1), LiNi a Mn b Co c Al d O 2 (a + b + c + d = 1) and LiNi e Co f Al g O 2(e + f + g = 1), the positive electrode active material can be a high-nickel (high Ni) type positive electrode active material.

[0135] For example, in LiNi a Mn b Co c O 2 (a + b + c = 1) and LiNi a Mn b Co c Al d O 2 (a + b + c + d = 1), the nickel content can be 60% or more (a ≥ 0.6), and more specifically, 80% or more (a ≥ 0.8).

[0136] For example, in LiNi e Co f Al g O 2 (e + f + g = 1), the nickel content can be 60% or more (e ≥ 0.6), and more specifically, 80% or more (e ≥ 0.8).

[0137] Based on the total weight of the positive electrode active material layer, the amount of the positive electrode active material included can be 90 wt% to 98 wt%.

[0138] The positive electrode active material layer may optionally include a conductive material and a binder. At this time, based on the total weight of the positive electrode active material layer, the contents of the conductive material and the binder can be 1.0 wt% to 5.0 wt% respectively.

[0139] The conductive material is used to provide positive electrode conductivity, and any conductive material can be used as the conductive material unless it causes a chemical change. Examples of the conductive material can include: carbon-based materials (such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.); metal-based materials including metal powders or metal fibers such as copper, nickel, aluminum, silver, etc.; conductive polymers (such as polyphenylene derivatives); or mixtures thereof.

[0140] The binder improves the bonding characteristics between the positive electrode active material particles and the bonding characteristics between the positive electrode active material particles and the current collector. Examples of the binder can be 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, nylon, etc., but are not limited thereto.

[0141] Al can be used as the positive electrode current collector, but is not limited thereto.

[0142] The negative electrode includes a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector and including a negative electrode active material.

[0143] The negative electrode active material may include a material that reversibly intercalates / deintercalates lithium ions, lithium metal, a lithium metal alloy, a material capable of doping / dedoping lithium, or a transition metal oxide.

[0144] The material that reversibly intercalates / deintercalates lithium ions may include a carbon material. The carbon material may be any carbon-based negative electrode active material commonly used in lithium secondary batteries, and examples of the carbon material may be crystalline carbon, amorphous carbon, or a mixture thereof. The crystalline carbon may be amorphous or natural graphite or artificial graphite in the form of flakes, sheets, spheres, or fibers. The amorphous carbon may be soft carbon, hard carbon, a mesophase pitch carbonization product, calcined coke, etc.

[0145] The lithium metal alloy includes 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.

[0146] The material capable of doping / dedoping lithium may be Si, a Si—C composite, SiO x (0 < x < 2), a Si—Q alloy (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, SnO 2 , a Sn—R alloy (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. At least one of these materials may be mixed with SiO 2 .

[0147] The element Q and the element R may be 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.

[0148] The transition metal oxide may be a vanadium oxide, a lithium vanadium oxide, or a lithium titanium oxide.

[0149] In a specific embodiment, the negative electrode active material may be a Si—C composite including a Si-based active material and a carbon-based active material.

[0150] The average particle size of the Si-based active material in the Si-C composite can be 50 nm to 200 nm. When the average particle size of the Si-based active material is within the above range, volume expansion occurring during charging and discharging can be suppressed, and interruption of the conduction path due to particle breakage during charging and discharging can be prevented.

[0151] Based on the total weight of the Si-C composite, the amount of the Si-based active material included can be 1 wt% to 60 wt%, for example, 3 wt% to 60 wt%.

[0152] In another specific embodiment, the negative electrode active material may further include crystalline carbon and the aforementioned Si-C composite.

[0153] When the negative electrode active material includes both the Si-C composite and crystalline carbon at the same time, the included Si-C composite and crystalline carbon may be in the form of a mixture, and the weight ratio of the included Si-C composite and crystalline carbon can be 1:99 to 50:50. More specifically, the weight ratio of the included Si-C composite and crystalline carbon can be 5:95 to 20:80.

[0154] The crystalline carbon may include, for example, graphite, and more specifically, may include natural graphite, artificial graphite, or a mixture thereof.

[0155] The average particle size of the crystalline carbon can be 5 μm to 30 μm.

[0156] In this specification, the average particle size can be the particle size (D50) at 50% by volume in the cumulative size distribution curve.

[0157] 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 carbonization products, calcined coke, or a mixture thereof.

[0158] Based on 100 parts by weight of the carbon-based active material, the amount of the amorphous carbon included can be 1 part by weight to 50 parts by weight, for example, 5 parts by weight to 50 parts by weight or 10 parts by weight to 50 parts by weight.

[0159] In the negative electrode active material layer, based on the total weight of the negative electrode active material layer, the amount of the negative electrode active material included can be 95 wt% to 99 wt%.

[0160] In an embodiment, the negative electrode active material layer includes a binder and optionally includes a conductive material. In the negative electrode active material layer, based on the total weight of the negative electrode active material layer, the content of the binder may be 1 wt% to 5 wt%. When the negative electrode active material layer further includes a conductive material, the negative electrode active material layer includes 90 wt% to 98 wt% of the negative electrode active material, 1 wt% to 5 wt% of the binder, and 1 wt% to 5 wt% of the conductive material.

[0161] The binder improves the binding characteristics between the negative electrode active material particles and the binding characteristics between the negative electrode active material particles and the current collector. The binder includes a water-insoluble binder, a water-soluble binder, or a combination thereof.

[0162] The water-insoluble binder may be selected from polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0163] 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 a combination thereof. The polymer resin binder may be selected from polytetrafluoroethylene, ethylene propylene copolymer, poly(ethylene oxide), polyvinylpyrrolidone, epichlorohydrin polymer, polyphosphazene, polyacrylonitrile, polystyrene, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and a combination thereof.

[0164] When the water-soluble binder is used as the negative electrode binder, a cellulose-based compound may be further used as a thickener to provide viscosity. The cellulose-based compound includes one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or an alkali metal salt thereof. The alkali metal may be Na, K, or Li. Based on 100 parts by weight of the negative electrode active material, the amount of such thickener included may be 0.1 part by weight to 3 parts by weight.

[0165] A conductive material is included to provide electrode conductivity, and any electronically conductive material may be used as the conductive material unless it causes a chemical change in the battery. Examples of the conductive material include: carbon-based materials (such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.); metal-based materials including metal powders or metal fibers such as copper, nickel, aluminum, silver, etc.; conductive polymers (such as polyphenylene derivatives); or mixtures thereof.

[0166] The negative electrode current collector may include one selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and a combination thereof.

[0167] Depending on the type of battery, the lithium secondary battery may further include a separator between the negative electrode and the positive electrode. The separator may be a porous substrate or a composite porous substrate.

[0168] The porous substrate is a substrate including pores through which lithium ions can move. The porous substrate may include, for example, polyethylene, polypropylene, polyvinylidene fluoride, and multilayers thereof (such as polyethylene / polypropylene bilayer separators, polyethylene / polypropylene / polyethylene trilayer separators, and polypropylene / polyethylene / polypropylene trilayer separators).

[0169] The composite porous substrate may have a form including a porous substrate and a functional layer on the porous substrate. From the perspective of ensuring additional functions, the functional layer may be, for example, at least one of a heat-resistant layer and an adhesive layer. For example, the heat-resistant layer may include a heat-resistant resin and optionally include a filler. Additionally, the adhesive layer may include an adhesive resin and optionally include a filler. The filler may be an organic filler or an inorganic filler.

[0170] The additive for a lithium secondary battery according to an embodiment may be included in the electrolyte as described above, and may also be applied to a current collector, an electrode tab, a separator, etc. of the lithium secondary battery.

[0171] When the additive is applied to the current collector or the electrode tab, the additive may be coated on an uncoated area of the current collector or the electrode tab using a coating solution dispersed in an appropriate solvent. When the additive is applied to the separator, the additive may be included in the separator assembly, or a coating solution in which the additive is dispersed in an appropriate solvent may be coated on at least one surface of the separator.

[0172] Mode of Invention

[0173] Hereinafter, the present disclosure will be explained in more detail with reference to examples. However, these examples are exemplary, and the present disclosure is not limited thereto.

[0174] Preparation of Additive

[0175] Synthesis Example 1

[0176] An additive was prepared as follows: A polymer solution including 5 wt% of a flame retardant (triphenyl phosphate) and 10 wt% of poly(vinylidene fluoride hexafluoropropylene) (PVDF-HFP) was prepared, and then electrospun to have a thickness ratio of 1:1 between the core and the shell.

[0177] Synthesis Example 2

[0178] The additive is prepared as follows: A polymer solution is prepared which respectively includes 10 wt% of a flame retardant (triphenyl phosphate) and 10 wt% of poly(vinylidene fluoride - hexafluoropropylene) (PVDF - HFP), and then electrospinning is carried out on it so that the thickness ratio between the core and the shell is 2:1.

[0179] Synthesis Example 3

[0180] The additive is prepared as follows: A polymer solution is prepared which respectively includes 10 wt% of a flame retardant (triphenyl phosphate) and 10 wt% of poly(vinylidene fluoride - hexafluoropropylene) (PVDF - HFP), and then electrospinning is carried out on it so that the thickness ratio between the core and the shell is 4:1.

[0181] Comparative Synthesis Example 1

[0182] A fibrous additive is manufactured in the same manner as in Synthesis Example 1, except that a polymer solution including polyethylene glycol (PEG) instead of poly(vinylidene fluoride - hexafluoropropylene) (PVDF - HFP) is used.

[0183] Comparative Synthesis Example 2

[0184] A fibrous additive is manufactured in the same manner as in Synthesis Example 1, except that a polymer solution including polypropylene (PP) instead of poly(vinylidene fluoride - hexafluoropropylene) (PVDF - HFP) is used.

[0185] Manufacture of Lithium Secondary Battery Monomer

[0186] Example 1

[0187] By using LiNi with a weight ratio of 96:2:2 as the positive electrode active material 0.88 Co 0.07 Al 0.05 O 2 as well as polyvinylidene fluoride as the binder and Ketjen black as the conductive material, and dispersing the mixture in N - methylpyrrolidone, a positive electrode active material slurry is prepared.

[0188] The positive electrode active material slurry is coated on a 14 - μm - thick Al foil, dried at 110 °C, and pressed to manufacture a positive electrode.

[0189] The negative electrode active material is prepared by mixing artificial graphite and Si - C composite with a weight ratio of 93:7, and then the negative electrode active material, styrene - butadiene rubber binder as the binder and carboxymethyl cellulose as the tackifier with a mixing weight ratio of 97:1:2, and then dispersed in distilled water to prepare a negative electrode active material slurry.

[0190] The Si-C composite is in the form of a core including artificial graphite and silicon particles, and coal tar pitch coated on the surface of the core.

[0191] The negative electrode active material paste was coated on a 10-μm thick Cu foil, dried at 100°C, and pressed to fabricate a negative electrode.

[0192] An electrode assembly was fabricated by assembling the fabricated positive electrode and negative electrode and a separator made of polyethylene with a thickness of 25 μm, and an electrolytic solution was injected to fabricate a lithium secondary battery cell, and the composition of the electrolytic solution is as follows.

[0193] (Composition of the electrolytic solution)

[0194] Salt: 1.3 M LiPF 6

[0195] Solvent: ethylene carbonate (EC): propylene carbonate (PC): ethyl propionate (EP): propyl propionate (PP) = 15:15:25:45 (volume ratio)

[0196] Additive: 3 parts by weight of fluoroethylene carbonate, 3 parts by weight of SN, and 15 parts by weight of the additive prepared in Synthesis Example 1

[0197] (In the composition of the electrolytic solution, "parts by weight" means the relative weight of the additive based on 100 parts by weight of the total electrolytic solution (lithium salt + non-aqueous organic solvent).)

[0198] Example 2

[0199] A lithium secondary battery cell was fabricated in the same manner as in Example 1, except that 20 parts by weight of the additive according to Synthesis Example 2 was used instead of the additive according to Synthesis Example 1.

[0200] Example 3

[0201] A lithium secondary battery cell was fabricated in the same manner as in Example 1, except that 10.25 parts by weight of the additive according to Synthesis Example 3 was used instead of the additive according to Synthesis Example 1.

[0202] Comparative Example 1

[0203] A lithium secondary battery cell was fabricated in the same manner as in Example 1, except that the additive according to Synthesis Example 1 was not used.

[0204] Comparative Example 2

[0205] A lithium secondary battery cell was fabricated in the same manner as in Example 1, except that 2 parts by weight of a flame retardant (triphenyl phosphate; Sigma-Aldrich Co., Ltd.) was used instead of the additive according to Synthesis Example 1.

[0206] Comparative Example 3

[0207] A lithium secondary battery cell was fabricated in the same manner as in Example 1, except that 10 parts by weight of a flame retardant was used instead of the additive according to Synthesis Example 1.

[0208] Comparative Example 4

[0209] A lithium secondary battery cell was fabricated in the same manner as in Example 1, except that the additive according to Comparative Synthesis Example 1 was used instead of the additive according to Synthesis Example 1.

[0210] Comparative Example 5

[0211] A lithium secondary battery cell was fabricated in the same manner as in Example 1, except that the additive according to Comparative Synthesis Example 2 was used instead of the additive according to Synthesis Example 1.

[0212] Evaluation 1: High-temperature cycle life evaluation

[0213] At 45 °C, the lithium secondary battery cells according to Examples 1 to 3 and Comparative Examples 1 to 5 were charged at a constant current rate of 0.5C to a voltage of 4.4V, and then, cut off at a current rate of 0.05C in the constant voltage mode of 4.4V. Subsequently, the battery cells were discharged at a constant current rate of 0.5C to a voltage of 3.0V. This process was repeated 100 times. The charging and discharging experimental results were used to calculate the capacity retention rate at the 100th cycle according to Calculation Equation 1, which is shown in Table 1.

[0214] [Calculation Equation 1]

[0215] Capacity retention rate at the 100th cycle [%] = [Discharge capacity at the 50th cycle / Discharge capacity at the 1st cycle] × 100

[0216] [Table 1]

[0217]

[0218] Referring to Table 1, the lithium secondary battery cells according to Examples 1 to 3 exhibited excellent high-temperature cycle life compared to the lithium secondary battery cells according to Comparative Examples 3 to 5.

[0219] Evaluation 2: Penetration Safety Evaluation

[0220] The lithium secondary battery cells according to Examples 1 to 3 and Comparative Examples 1 to 5 were charged under the conditions of 0.5C / 4.4V and cut off at 0.05C, and then paused for 10 minutes. The penetration stability was evaluated by completely penetrating the centers of the lithium secondary battery cells with a needle having a diameter of 5 mm at speeds of 50 mm / second, 100 mm / second, 150 mm / second, and 200 mm / second, respectively, and the results are shown in Table 1.

[0221] [Table 2]

[0222]

[0223] In Table 2, "NG" means that thermal runaway was observed at the exposure temperature, and "OK" means that a sharp voltage drop was observed without thermal runaway at the exposure temperature. (-) means that the thermal exposure evaluation was not performed.

[0224] The lithium secondary battery cells according to Comparative Examples 1 and 2 exhibited thermal runaway at penetration speeds of 150 mm / s and 200 mm / s, indicating deteriorated battery stability.

[0225] The lithium secondary battery cell of Comparative Example 5 exhibited thermal runaway at 200 mm / s. This is explained as the additive included in the lithium secondary battery cell according to Comparative Example 5 having a too thin shell to protect the core material, so that the core and shell materials were mixed at the operating temperature of the battery cell, and thus the performance and safety could not be improved.

[0226] On the other hand, it was confirmed that the lithium secondary battery cells of Examples 1 to 3 did not exhibit thermal runaway at a low penetration speed of 50 mm / s. Accordingly, the lithium secondary battery cells of Examples 1 to 3 exhibited excellent battery stability compared with the lithium secondary battery cells according to the comparative examples.

[0227] Although the present invention has been described in conjunction with exemplary embodiments that are presently considered to be practical, it should be understood that the present invention is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the claims.

Claims

1. An additive for a lithium secondary battery, comprising: a core, and a shell surrounding the core, wherein the core comprises a flame retardant, a fire extinguishing agent, a non-flammable material, or a combination thereof, and the shell comprises a polymer having a melting point of 90 °C to 120 °C.

2. The additive for a lithium secondary battery 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. The additive for a lithium secondary battery 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 a lithium secondary battery according to claim 1, wherein the flame retardant comprises 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 Chemical Formula 1: [Chemical Formula 1] wherein, in Chemical Formula 1, R 1 ~R 3 Each independently is a substituted or unsubstituted C1-C10 alkyl group, and each of a to c independently is an integer from 0 to 5.

6. The additive for a lithium secondary battery according to claim 1, wherein the phosphazene compound is represented by Chemical Formula 2: [Chemical Formula 2] wherein, in Chemical Formula 2, n is 3 or 4, and R 4 and R 5 are the same or different and are -F, -NR x R y or a substituted or unsubstituted C1-C5 alkoxy group, wherein R x and R y are the same or different and are a substituted or unsubstituted C1-C30 alkyl group, a substituted or unsubstituted C3-C30 cycloalkyl group, a substituted or unsubstituted C2-C30 alkenyl group or a C6-C30 substituted or unsubstituted aryl group.

7. The additive for a lithium secondary battery according to claim 1, wherein the phosphazene compound is represented by Chemical Formula 2-1 or Chemical Formula 2-2: [Chemical Formula 2-1] [Chemical Formula 2-2] wherein, in the above Chemical Formula 2-1 and the above Chemical Formula 2-2, R 6 ~R 8 Each independently is hydrogen, a substituted or unsubstituted C1-C10 alkyl group, a C1-C10 fluoroalkyl group or a combination thereof.

8. The additive for a lithium secondary battery 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 fibers formed by electrospinning.

10. An electrolyte for a lithium secondary battery, comprising: a non-aqueous organic solvent, a lithium salt, and the additive for a lithium secondary battery according to any one of claims 1 to 9.

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

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

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

14. A lithium secondary battery, comprising: a positive electrode comprising a positive electrode active material; a negative electrode comprising a negative electrode active material; and the electrolyte according to claim 10.

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