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 lithium secondary batteries, which includes a core containing a foaming agent and a shell surrounding the core, the shell including a polymer having a melting point of 90°C to 120°C, an electrolyte for lithium secondary batteries containing the same, 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, allowing for fast charging. As a result, they have been commercialized for use in laptops, mobile phones, power tools, and electric bicycles, and research and development is actively underway to further improve their energy density.

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

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

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

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

[0007] One embodiment 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 containing a foaming agent and a shell surrounding the core, 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 blowing agent may include a glass blowing agent, a hydrocarbon-based compound, a hydrofluoroolefin (HFO)-based compound, or a combination thereof.

[0014] The glass blowing agent can include silicon dioxide, sodium oxide, and water.

[0015] The glass blowing agent may include 60% to 70% by weight of silicon dioxide, 20% to 30% by weight of sodium oxide, and 5% to 20% by weight of water.

[0016] The polymer may include poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP), polyacrylic acid, polyethylene, poly(methyl methacrylate), polyalkylene oxide, polyalkylene succinate, or a combination thereof.

[0017] The additive may be in the form of a fiber formed using electrospinning.

[0018] 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.

[0019] The additive for lithium secondary batteries may be included in an amount of 0.1 wt % to 10 wt %, 0.1 wt % to 5.0 wt %, or 0.1 wt % to 3.0 wt % based on the total weight of the lithium secondary battery electrolyte.

[0020] 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]

[0021] The additive for lithium secondary batteries has excellent electrolyte impregnation properties, and when applied to an electrolyte, it can maintain battery characteristics without increasing battery resistance.

[0022] In addition, the lithium secondary battery including the additive for lithium secondary batteries according to an embodiment can suppress the occurrence of short circuits due to an increase in resistance above the battery operating temperature, thereby improving the safety of the battery. [Brief explanation of the drawings]

[0023] [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

[0024] 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.

[0025] In the drawings, the thickness of the various layers and regions is exaggerated for clarity.

[0026] 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.

[0027] 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).

[0028] Hereinafter, the term "combination" includes mixtures of two or more, mutual substitutions, and stacked structures of two or more.

[0029] Hereinafter, an additive for a lithium secondary battery according to one embodiment will be described with reference to FIG.

[0030] FIG. 1 is a cross-sectional view of an additive according to one embodiment.

[0031] 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 foaming agent, and the shell 5 includes a polymer having a melting point of 90°C to 120°C.

[0032] The additive 1 can maintain battery characteristics without increasing battery resistance during battery operation. Since the melting point of the shell 5 is within the above range, the shell 5 can be appropriately melted at high temperatures, and the foaming agent in the core 3 can be released in a timely manner, effectively preventing battery short circuits. Furthermore, since the core 3 contains a foaming agent, when the shell 5 of the additive melts at high temperatures, the foaming agent is released to the outside of the core 3 and expands, increasing the battery resistance and causing a voltage drop, thereby preventing battery short circuits.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] The thickness of the core 3 may be, but is not limited to, 0.1 μm to 2.0 μm, for example, 0.1 μm to 1.5 μm, for example, 0.1 μm to 1.2 μm, for example, 0.1 μm to 1.0 μm, for example, 0.3 μm to 2 μm, for example, 0.3 μm to 1.5 μm, for example, 0.3 μm to 1.2 μm, or for example, 0.5 μm to 1.0 μm.

[0038] When the core 3 has a thickness within the above range, the core material is released in a timely manner along with the melting of the shell 5, thereby effectively controlling the occurrence of electrode short circuits, while maintaining battery characteristics without reducing electrolyte impregnation or unnecessarily increasing battery resistance.

[0039] The blowing agent contained in the core 3 may be a commonly used blowing agent, such as a glass blowing agent, a hydrocarbon-based compound, a hydrofluoroolefin (HFO)-based compound, or a combination thereof.

[0040] The glass blowing agent may include silicon dioxide, sodium oxide, and water. The silicon dioxide may be included in an amount of 60 wt% to 70 wt%, for example, 65 wt%, based on 100 wt% of the glass blowing agent, but is not limited thereto. The sodium oxide may be included in an amount of 20 wt% to 30 wt%, for example, 25 wt%, based on 100 wt% of the glass blowing agent, but is not limited thereto. The water is the remaining component in the glass blowing agent excluding silicon dioxide and sodium oxide, and may be included in an amount of, for example, 5 wt% to 20 wt%, for example, 10 wt%, but is not limited thereto.

[0041] The hydrocarbon-based compound may include hydrocarbons having 1 to 6 carbon atoms, and may include, for example, chlorinated hydrocarbon compounds, non-chlorinated hydrocarbon compounds, or combinations thereof.

[0042] The hydrocarbon-based compound may include, but is not limited to, at least one selected from dichloroethane, propyl chloride, isopropyl chloride, butyl chloride, isobutyl chloride, pentyl chloride, isopentyl chloride, n-butane, isobutane, n-pentane, isopentane, cyclopentane, n-hexane, and combinations thereof.

[0043] The hydrofluoroolefin-based compound may include, for example, a chlorinated hydrofluoroolefin-based compound, a non-chlorinated hydrofluoroolefin-based compound, or all of these.

[0044] The hydrofluoroolefin-based compound may be any known compound in the art, such as trans 1-chloro-3,3,3-trifluoropropene (trans CFCH=CClH), cis 1-chloro-3,3,3-trifluoropropene (cis CFCH=CClH), trans 1-chloro-2,3,3-trifluoropropene (trans CHFCF=CClH), cis 1-chloro-2,3,3-trifluoropropene (cis CHFCF=CClH), trans 1-chloro-1,3,3-trifluoropropene (trans CHFCH=CClF), cis 1-chloro-1,3,3-trifluoropropene (cis CHFCH=CClF), trans 2-chloro-1,3,3-trifluoropropene (trans CHFCCl=CHF), cis 2-chloro-1,3,3-trifluoropropene (cis CHF2CCl=CHF), trans 2-chloro-1,1,3-trifluoropropene (trans CH2FCCl=CF2), cis 2-chloro-1,1,3-trifluoropropene (cis CH2FCCl=CF2), trans 3-chloro-1,2,3-trifluoropropene (trans CHFClCF=CFH), cis 3-chloro-1,2,3-trifluoropropene (cis CHFClCF=CFH), trans 3-chloro-1,1,2-trifluoropropene (trans CH2ClCF=CF2), cis 3-chloro-1,1,2-trifluoropropene (cis CH2ClCF=CF2), trans 3-chloro-2,3,3-trifluoropropene (trans CF2ClCF=CH2), cis 3-chloro-2,3,3-trifluoropropene (cis Monochlorotrifluoropropenes such as CF2ClCF=CH2); trifluoropropenes such as 2,3,3-trifluoropropene (CHF2CF=CH2), 1,1,2-trifluoropropene (CH3CF=CF2), 1,1,3-trifluoropropene (CH2FCH=CF2), and 1,3,3-trifluoropropene (CHF2CH=CHF);Tetrafluoropropenes such as 1,2,3,3-tetrafluoro-1-propene, 2,3,3,3-tetrafluoro-1-propene, 1,3,3,3-tetrafluoro-1-propene, 1,1,2,3-tetrafluoro-1-propene, 1,1,3,3-tetrafluoro-1-propene, 1,2,3,3-tetrafluoro-1-propene; pentafluoropropenes such as 1,2,3,3,3-pentafluoro-1-propene, 1,1,3,3,3-pentafluoro-1-propene, 1,1,2,3,3-pentafluoro-1-propene; 2,3,3,4,4,4-hexafluoro-1-butene, 1,1,1,4 ,4,4-hexafluoro-2-butene, 1,3,3,4,4,4-hexafluoro-1-butene, 1,2,3,4,4,4-hexafluoro-1-butene, 1,2,3,3,4,4-hexafluoro-1-butene, 1,1,2,3,4,4-hexafluoro-2-butene, 1,1,1,2,3,4-hexafluoro-2-butene, 1,1,1,2,3,3-hexafluoro-2-butene, 1,1,1,3,4,4-hexafluoro-2-butene, 1,1,2,3,3,4-hexafluoro-1-butene, and combinations thereof.

[0045] The thickness of the shell 5 may be 0.025 μm to 0.5 μm, for example, 0.025 μm to 0.45 μm, for example, 0.025 μm to 0.4 μm, for example, 0.025 μm to 0.35 μm, for example, 0.025 μm to 0.3 μm, for example, 0.05 μm to 0.5 μm, for example, 0.1 μm to 0.5 μm, for example, 0.15 μm to 0.5 μm, for example, 0.2 μm to 0.5 μm, for example, 0.2 μm to 0.45 μm, or for example, 0.2 μm to 0.4 μm, and is not limited to these.

[0046] By having shell 5 have a thickness within this range, it is possible to effectively prevent electrode short circuits through timely melting of shell 5 and release of core material, while maintaining battery characteristics without unnecessarily increasing battery resistance. In one embodiment, shell 5 may include a polymer having a melting point of 90°C to 120°C, for example, the polymer may be a thermoplastic resin. Such polymers have excellent ionic conductivity and can contribute to battery safety by melting at a specific temperature while maintaining stable conductivity within the battery's operating temperature range. In addition, the polymer included in shell 5 can improve the wettability of the electrolyte.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] The polymer contained in the shell 5 may have a melting point of 90°C to 120°C, and for example, the melting point of the polymer may be 90°C or higher, for example, 95°C or higher, for example, 100°C or higher, or for example, the melting point of the polymer may be 120°C or lower, for example, 115°C or lower, for example, 110°C or lower, but is not limited thereto. When the melting point of the polymer contained in the shell 5 is within this range, the shell 5 is stably maintained within the operating temperature range during battery charge and discharge, preventing an increase in battery resistance, and the shell 5 is appropriately melted at high temperatures of 100°C or higher, and the foaming agent in the core 3 is released in a timely manner, effectively preventing the occurrence of short circuits in the battery.

[0051] 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 is effectively dissolved at high temperatures, rapidly increasing the battery resistance and effectively suppressing the short circuit phenomenon of the battery. 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.

[0052] When preparing the core-shell structured additive 1, the electrospinning process can be carried out by a known process taking into consideration the melting temperatures of the foaming agent and the thermoplastic resin.

[0053] An electrolyte solution for a lithium secondary battery according to another embodiment includes a non-aqueous organic solvent, a lithium salt, and the additives described above.

[0054] The additive 1 may be included in an amount of 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 0.2 wt % or more, e.g., 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 9.0 wt % or less, e.g., 8.0 wt % or less, 7.0 wt % or less, 6.0 wt % or less, 5.0 wt % or less, 4.0 wt % or less, or 3.0 wt % or less, based on the total weight of the electrolyte for lithium secondary batteries, but is not limited thereto.

[0055] 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.

[0056] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0057] The non-aqueous organic solvent may be a carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or aprotic solvent.

[0058] 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.

[0059] 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, which should be widely understood by those skilled in the art.

[0060] In addition, in the case of the carbonate-based solvent, it is preferable to use a mixture of cyclic carbonate and chain carbonate in a volume ratio of 1:1 to 1:9, which can improve the performance of the electrolyte.

[0061] 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.

[0062] The aromatic hydrocarbon solvent may be an aromatic hydrocarbon compound represented by the following Chemical Formula 1:

[0063] [ka] ...chemical formula 1

[0064] In the above chemical formula 1, 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.

[0065] 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.

[0066] The electrolyte may further include vinylene carbonate, vinylethylene carbonate, or an ethylene carbonate-based compound of the following Formula 2 as a life-enhancing additive to improve battery life.

[0067] [ka] ...Chemical formula 2

[0068] In the above chemical formula 2, R 207 and R 208 are the same or different and are selected from hydrogen, a halogen group, a cyano group (CN), a nitro group (NO), or a fluorinated alkyl group having 1 to 5 carbon atoms, 207 and R 208At least one of R is selected from a halogen group, a cyano group (CN), a nitro group (NO), and a fluorinated alkyl group having 1 to 5 carbon atoms, with the proviso that R 207 and R 208 But it's not all hydrogen.

[0069] 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.

[0070] 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.

[0071] 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).

[0072] 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.

[0073] The additive and the electrolyte can be applied to a lithium secondary battery.

[0074] Hereinafter, a lithium secondary battery according to an embodiment will be described with reference to FIG.

[0075] The lithium secondary battery 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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 elements. 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.

[0080] The positive electrode active material may be, for example, one or more lithium composite oxides represented by the following chemical formula 3.

[0081] [Chemical formula 3] Li x M 1 y M 2z M 3 1-y-z O2

[0082] 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 3 may each independently be any one selected from metals such as Ni, Co, Mn, Al, Sr, Mg, or La, and combinations thereof.

[0083] 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).

[0084] 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 Ni-based positive electrode active material.

[0085] For example, the LiNi a Mn b Co c O2 (a+b+c=1) and LiNi a Mn b Co c Al dIn 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).

[0086] For example, the LiNi e Co f Al g In 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).

[0087] 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.

[0088] 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 % respectively based on the total weight of the positive electrode active material layer.

[0089] 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.

[0090] 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.

[0091] The positive electrode current collector may be made of Al, but is not limited thereto.

[0092] 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.

[0093] 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.

[0094] The material capable of reversibly intercalating / deintercalating lithium ions may be any carbonaceous negative electrode active material commonly used in lithium secondary batteries, and representative examples thereof 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.

[0095] As the alloy of the lithium metal, 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.

[0096] Examples of the substance that can be doped and undoped with lithium include Si, Si-C composite, SiOx (0 < x < 2), 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, 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. Further, at least one of these can be mixed with SiO2 and used.

[0097] As the elements Q and R, 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 can be used.

[0098] Examples of the transition metal oxide include vanadium oxide, lithium vanadium oxide, or lithium titanate.

[0099] 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.

[0100] In the Si-C composite, the Si-based active material may have an average particle size of 50 nm to 200 nm. When the average particle size of the Si-based active material is within this range, volume expansion that occurs during charge and discharge can be suppressed, and conductive path disconnection due to particle crushing during charge and discharge can be prevented.

[0101] The Si-based active material may be included in an amount of 1 to 60 wt % of the total weight of the Si-C composite, for example, 3 to 60 wt %.

[0102] In another specific embodiment, the negative electrode active material may further include crystalline carbon in addition to the Si—C composite.

[0103] 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.

[0104] The crystalline carbon may include, for example, graphite, and more specifically, may include natural graphite, artificial graphite, or a mixture thereof.

[0105] The crystalline carbon may have an average particle size of 5 μm to 30 μm.

[0106] In this specification, the average particle size may be the particle size at 50% by volume (D50) on a cumulative size-distribution curve.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] 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%.

[0111] 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.

[0112] 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.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] 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.

[0117] 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.

[0118] The porous substrate is a substrate containing voids through which lithium ions can move. The porous substrate may be made of, for example, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more of these materials, 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.

[0119] The composite porous substrate may include a porous substrate and a functional layer located 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.

[0120] 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.

[0121] 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.

[0122] 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]

[0123] Additive manufacturing Synthesis Example 1 Polymer solutions containing 1 wt% of a foaming agent (SMG-200B, Hammill) 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 1:1.

[0124] Synthesis Example 2 Polymer solutions containing 2 wt% of a foaming agent (SMG-200B, Hammill) 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 ratio of 2:1.

[0125] Synthesis Example 3 Polymer solutions containing 4 wt% of a foaming agent (SMG-200B, Hammill) 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 ratio of 4:1.

[0126] Synthesis Example 4 A fiber-shaped additive was prepared in the same manner as in Synthesis Example 1, except that electrospinning was performed so that the core and shell thickness ratio was 1:2.

[0127] Synthesis Example 5 A fiber-shaped additive was prepared in the same manner as in Synthesis Example 1, except that electrospinning was performed so that the core and shell thickness ratio was 5:1.

[0128] 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).

[0129] 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).

[0130] Lithium secondary battery manufacturing Example 1 A lithium secondary battery was manufactured using LiCoO2 as the positive electrode, artificial graphite as the negative electrode, and an electrolyte having the following composition:

[0131] (Electrolyte composition) Salt: LiPF61.3M Solvent: ethylene carbonate: propylene carbonate: ethyl propionate: propyl propionate (volume ratio of EC:PC:EP:PP = 15:15:25:45) Additive: 3 parts by weight of fluoroethylene carbonate, 2 parts by weight of the additive prepared by Synthesis Example 1 (wherein, in the electrolyte composition, "parts by weight" refers to the relative weight of the additive relative to 100 parts by weight of the entire electrolyte (lithium salt and non-aqueous organic solvent)).

[0132] Example 2 A lithium secondary battery was manufactured in the same manner as in Example 1, except that 1.5 parts by weight of the additive prepared in Synthesis Example 2 was used instead of the additive prepared in Synthesis Example 1.

[0133] Example 3 A lithium secondary battery was manufactured in the same manner as in Example 1, except that 1.25 parts by weight of the additive prepared in Synthesis Example 3 was used instead of the additive prepared in Synthesis Example 1.

[0134] Comparative Example 1 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the additive prepared in Synthesis Example 1 was not used.

[0135] Comparative Example 2 A lithium secondary battery was manufactured in the same manner as in Example 1, except that 0.1 parts by weight of a foaming agent (SMG-200B, Hammill Co.) was used instead of the additive prepared in Synthesis Example 1.

[0136] Comparative Example 3 A lithium secondary battery was manufactured in the same manner as in Example 1, except that 1 part by weight of a foaming agent (SMG-200B, Hammill Co.) was used instead of the additive prepared in Synthesis Example 1.

[0137] Comparative Example 4 A lithium secondary battery was manufactured in the same manner as in Example 1, except that 2 parts by weight of the additive prepared in Comparative Synthesis Example 1 was used instead of the additive prepared in Synthesis Example 1.

[0138] Comparative Example 5 A lithium secondary battery was manufactured in the same manner as in Example 1, except that 2 parts by weight of the additive prepared in Comparative Synthesis Example 2 was used instead of the additive prepared in Synthesis Example 1.

[0139] Evaluation 1: Capacity retention rate evaluation The lithium secondary batteries according to Examples 1 to 3 and Comparative Examples 1 to 5 were charged at 0.5C / 4.4V with a 0.05C cut-off charge, and then stored at 60°C for 4 weeks, after which the delta OCV (ΔOCV) was measured, and the results are shown in Table 1. A small ΔOCV value means an excellent capacity retention rate.

[0140] [Table 1]

[0141] Referring to Table 1 above, the lithium secondary batteries according to Examples 1 to 3 exhibit smaller ΔOCV values ​​during high temperature storage evaluation than the lithium secondary batteries according to Comparative Examples 3 and 4. This shows that the lithium secondary batteries according to Examples 1 to 3 have better cell capacity retention rates at high temperatures than the lithium secondary batteries according to Comparative Examples.

[0142] Evaluation 2: Heat exposure evaluation The lithium secondary batteries according to Examples 1 to 3 and Comparative Examples 1 to 5 were placed in a chamber, and the temperature was increased from room temperature (25°C) at a rate of 5±2°C per minute. The temperature was maintained at this temperature for about 1 hour, and the changes in the lithium secondary batteries were observed. This process was repeated twice, and the results are shown in Table 2 below.

[0143] [Table 2]

[0144] In Table 2, "NG" means that thermal runaway was observed at the exposure temperature, "OK" means that thermal runaway was not observed at the exposure temperature, and (-) means that thermal exposure evaluation was not performed.

[0145] In Examples 1 to 3, when exposed to high temperatures, the shell of the additive according to one embodiment melts, releasing the foaming agent contained in the core, increasing the volume of the foaming agent and causing a sudden rise in battery resistance, so thermal runaway did not occur even when evaluated for high-temperature heat exposure up to 136°C. In contrast, in Comparative Examples 1, 2, and 5, thermal runaway was observed when exposed to a temperature of 130°C. This is interpreted as the thermal runaway occurring when the additive according to the present invention is not included or a small amount of foaming agent is added, due to the lack of a device to control short circuits between electrodes at high temperatures.

[0146] Therefore, it can be seen that the lithium secondary batteries according to the examples maintain their battery characteristics within the battery operating temperature range and are superior in safety at high temperatures compared to the lithium secondary batteries according to the comparative examples.

[0147] 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]

[0148] 100: Lithium secondary battery 112: Negative electrode 113: Separator 114: Positive electrode 120:Battery container 140: Enclosure material

Claims

1. a core containing a blowing agent, and a shell surrounding the core; The additive for lithium secondary batteries, wherein the shell 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. 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 foaming agent comprises a glass foaming agent, a hydrocarbon-based compound, a hydrofluoroolefin (HFO)-based compound, or a combination thereof.

5. 5. The additive for lithium secondary batteries according to claim 4, wherein the glass foaming agent comprises silicon dioxide, sodium oxide, and water.

6. 5. The additive for lithium secondary batteries according to claim 4, wherein the glass foaming agent comprises 60% to 70% by weight of silicon dioxide, 20% to 30% by weight of sodium oxide, and 5% to 20% by weight of water.

7. 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.

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

9. non-aqueous organic solvents, lithium salts, and An additive for lithium secondary batteries according to any one of claims 1 to 8, An electrolyte for a lithium secondary battery comprising:

10. 10. The electrolyte solution for a lithium secondary battery according to claim 9, wherein the additive for a lithium secondary battery is included in an amount of 0.1 wt % to 10 wt % based on the total weight of the electrolyte solution for a lithium secondary battery.

11. 10. The electrolyte solution for a lithium secondary battery according to claim 9, wherein the additive for a lithium secondary battery is included in an amount of 0.1 wt % to 5.0 wt % based on the total weight of the electrolyte solution for a lithium secondary battery.

12. 10. The electrolyte solution for a lithium secondary battery according to claim 9, wherein the additive for a lithium secondary battery is included in an amount of 0.1 wt % to 3.0 wt % based on the total weight of the electrolyte solution for a lithium secondary battery.

13. a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and The electrolyte of claim 9 ; A lithium secondary battery comprising:

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