Non-aqueous electrolyte and lithium secondary battery including the same

Abstract

Embodiments of the present invention provide a non-aqueous electrolyte and a lithium secondary battery comprising the same. The non-aqueous electrolyte comprises a non-aqueous organic solvent comprising a mono-fluoro organic solvent and a di-fluoro organic solvent, a lithium salt, and an additive, wherein the weight ratio of the di-fluoro organic solvent to the weight of the mono-fluoro organic solvent is greater than 3 and less than or equal to 11. This can improve the high-temperature storage characteristics and high-temperature life characteristics of the secondary battery.

Description

Technology Field

[0001] Embodiments of the present invention relate to a non-aqueous electrolyte and a lithium secondary battery comprising the same. More specifically, the invention relates to a non-aqueous electrolyte comprising a non-aqueous solvent and an additive, and a lithium secondary battery comprising the same. Background Technology

[0002] Rechargeable batteries are batteries capable of repeated charging and discharging, and with the advancement of the information and communication and display industries, they are widely applied as power sources for portable electronic communication devices such as camcorders, mobile phones, and laptop PCs. Furthermore, recently, battery packs containing rechargeable batteries are being developed and applied as power sources for eco-friendly vehicles, such as hybrid cars.

[0003] Among the aforementioned secondary batteries, lithium secondary batteries are being actively researched and developed due to their high operating voltage and energy density per unit weight, as well as their advantages in charging speed and weight reduction.

[0004] A lithium secondary battery may include an electrode assembly comprising a positive electrode, a negative electrode, and a separator, and an electrolyte impregnating the electrode assembly. The lithium secondary battery may further include an outer casing, for example, in the form of a pouch, that accommodates the electrode assembly and the electrolyte.

[0005] Lithium metal oxide can be used as an active material for the positive electrode of a lithium secondary battery. Nickel-based lithium metal oxide can be cited as an example of the above lithium metal oxide.

[0006] As the application range of lithium-ion batteries expands, there is a growing demand for longer lifespan, higher capacity, and operational stability. Accordingly, lithium-ion batteries that provide uniform output and capacity even during repeated charge and discharge cycles are desirable.

[0007] However, depending on repeated charging and discharging, for example, the output and capacity may decrease due to surface damage of the nickel-based lithium metal oxide used as the positive electrode active material, and side reactions between the nickel-based lithium metal oxide and the electrolyte may occur.

[0008] For example, as described in Korean Patent Publication No. 10-2019-0119615, a method for improving battery characteristics by modifying a non-aqueous electrolyte for lithium secondary batteries is being studied. Prior art literature

[0009] Korean Patent Publication No. 10-2019-0119615 The problem to be solved

[0010] One objective of the present invention is to provide a non-aqueous electrolyte capable of imparting improved mechanical and chemical stability.

[0011] One objective of the present invention is to provide a lithium secondary battery comprising the above-mentioned non-aqueous electrolyte, with improved operational stability and electrical characteristics. means of solving the problem

[0012] A non-aqueous electrolyte according to exemplary embodiments of the present invention comprises a non-aqueous organic solvent comprising a mono-fluoro organic solvent and a di-fluoro organic solvent, a lithium salt, and an additive, wherein the weight ratio of the di-fluoro organic solvent to the weight of the mono-fluoro organic solvent is greater than 3 and less than or equal to 11.

[0013] In some embodiments, the mono-fluoro organic solvent may be represented by the following chemical formula 1.

[0014] [Chemical Formula 1]

[0015]

[0016] (In Chemical Formula 1, R1 comprises a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted aryl group having 6 to 12 carbon atoms, a substituted or unsubstituted cycloalkyl group having 5 to 12 carbon atoms, a substituted or unsubstituted cycloalkenyl group having 5 to 12 carbon atoms, a substituted or unsubstituted heterocycloalkyl group having 5 to 7 carbon atoms, or a substituted or unsubstituted heterocycloalkenyl group having 5 to 7 carbon atoms).

[0017] In some embodiments, the di-fluoro organic solvent may be represented by the following chemical formula 2.

[0018] [Chemical Formula 2]

[0019]

[0020] (In Chemical Formula 2, R2 is a hydrocarbon comprising a substituted or unsubstituted C1 to C6 alkyl group or a substituted or unsubstituted C6 to C12 1-aryl group, and R3 is a hydrocarbon comprising a substituted or unsubstituted C1 to C6 alkyl group or a substituted or unsubstituted C1 to C6 alkenyl group).

[0021] In some embodiments, the additive may include a boron-based compound.

[0022] In some embodiments, the boron-based compound may include at least one of lithium bis(oxalate) borate (LiBOB), tris(trimethylsilyl) borate (TMSB), and lithium difluoro(oxalato) borate (LiFOB).

[0023] In some embodiments, the content of the additive relative to the total weight of the non-aqueous electrolyte may be 0.1 to 1.0 weight%.

[0024] In some embodiments, auxiliary additives including alkyl sulfone compounds and alkenyl sulfone compounds may be further included.

[0025] In some embodiments, the content of the auxiliary additive relative to the total weight of the non-aqueous electrolyte may be 0.8 to 1.6 weight%.

[0026] In some embodiments, the lithium salt may include at least one of lithium tetrafluoroborate (LiBF4), lithium hexafluorophosphate (LiPF6) and lithium difluorophosphate (LiPO2F2).

[0027] In some embodiments, the weight ratio of the di-fluoro organic solvent to the weight of the mono-fluoro organic solvent may be 4.5 to 9.

[0028] A lithium secondary battery according to exemplary embodiments of the present invention comprises a positive electrode, a negative electrode facing the positive electrode, and the above-described non-aqueous electrolyte. Effects of the invention

[0029] The non-aqueous electrolyte according to exemplary embodiments comprises a non-aqueous organic solvent including a mono-fluoro organic solvent and a di-fluoro organic solvent, wherein the weight ratio of the di-fluoro organic solvent to the weight of the mono-fluoro organic solvent may be greater than 3 and less than or equal to 11. In this case, the fluorine content can be appropriately controlled while sufficiently improving the oxidation resistance and chemical resistance of the secondary battery. Accordingly, the high-temperature storage characteristics and lifespan characteristics of the secondary battery can be improved while preventing a decrease in capacity retention rate.

[0030] In some embodiments, the non-aqueous electrolyte may include a fluorine-based compound within a predetermined content range as an additive. In this case, it is possible to suppress an excessive increase in battery resistance while achieving the effect of improving high-temperature storage characteristics and lifespan characteristics according to the additive. Accordingly, the high-temperature storage characteristics of the secondary battery are improved, and the degradation of capacity and output characteristics can be prevented.

[0031] In some embodiments, the non-aqueous electrolyte may further contain auxiliary additives, including alkyl sulfone compounds and alkenyl sulfone compounds, within a predetermined content range. In this case, side reactions of the additives can be further suppressed while suppressing an excessive increase in battery resistance. Accordingly, capacity reduction can be suppressed while maintaining or improving the high-temperature storage characteristics and lifespan characteristics of the secondary battery according to the mono-fluoro organic solvent and di-fluoro organic solvent described above. Brief explanation of the drawing

[0032] FIGS. 1 and FIGS. 2 are a schematic plan view and a cross-sectional view, respectively, showing a lithium secondary battery according to exemplary embodiments. Specific details for implementing the invention

[0033] Embodiments of the present invention provide a non-aqueous electrolyte comprising an organic solvent, a lithium salt, and an additive. Additionally, embodiments of the present invention provide a lithium secondary battery comprising said non-aqueous electrolyte, with improved low-temperature capacity characteristics and high-temperature life characteristics.

[0034] In exemplary embodiments, the non-aqueous electrolyte may comprise a non-aqueous organic solvent, a lithium salt, and an additive.

[0035] For example, the above-mentioned non-aqueous organic solvent may include an organic compound that provides sufficient solubility for the lithium salt, additive, and auxiliary additive and does not have reactivity with the lithium secondary battery.

[0036] In exemplary embodiments, the non-aqueous organic solvent may include a mono-fluoro organic solvent and a di-fluoro organic solvent.

[0037] As used in this application, the term "mono-fluoro organic solvent" may refer to a compound containing one fluorine (F) atom in one molecule, and the term "di-fluoro organic solvent" may refer to a compound containing two fluorine atoms in one molecule.

[0038] In exemplary embodiments, the mono-fluoro organic solvent may be represented by the following chemical formula 1.

[0039] [Chemical Formula 1]

[0040]

[0041] In Chemical Formula 1, R1 may comprise a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted aryl group having 6 to 12 carbon atoms, a substituted or unsubstituted cycloalkyl group having 5 to 12 carbon atoms, a substituted or unsubstituted cycloalkenyl group having 5 to 12 carbon atoms, a substituted or unsubstituted heterocycloalkyl group having 5 to 7 carbon atoms, or a substituted or unsubstituted heterocycloalkenyl group having 5 to 7 carbon atoms.

[0042] For example, the mono-fluoro organic solvent described above is included in a non-aqueous organic solvent, thereby preventing a decrease in capacity retention rate due to the excessive addition of the di-fluoro organic solvent described later, while sufficiently improving the oxidation resistance of the battery.

[0043] In one embodiment, the mono-fluoro organic solvent may include fluoroethylene carbonate (FEC).

[0044] In exemplary embodiments, the di-fluoro organic solvent may be represented by the following chemical formula 2.

[0045] [Chemical Formula 2]

[0046]

[0047] In Chemical Formula 2, R2 is a hydrocarbon comprising a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms or a substituted or unsubstituted aryl group having 6 to 12 carbon atoms, and R3 may be a hydrocarbon comprising a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms or a substituted or unsubstituted alkenyl group having 1 to 6 carbon atoms.

[0048] For example, the fluorine content in the electrolyte can be increased by using the aforementioned difluoro-based organic solvent together with a monofluoro-based organic solvent. In this case, the oxidation resistance of the secondary battery can be improved. Accordingly, the lifespan characteristics of the secondary battery can be improved, and the amount of gas generated at high temperatures can be reduced.

[0049] For example, if only a mono-fluoro organic solvent is added, a sufficient fluorine content in the electrolyte may not be secured, and thus the aforementioned effect of improving oxidation resistance of the battery may not be realized.

[0050] In one embodiment, the above-described difluoro-based organic solvent may be difluoroethyl acetate (DFA).

[0051] In exemplary embodiments, the weight ratio of the di-fluoro organic solvent to the weight of the mono-fluoro organic solvent may be greater than 3 and less than or equal to 11.

[0052] For example, if the above weight ratio is 3 or less, the fluorine content in the electrolyte becomes excessively low, which may reduce the oxidation resistance and chemical resistance of the secondary battery. In this case, the occurrence of side reactions between the electrode and the electrolyte of the secondary battery may increase. Consequently, the amount of gas generated increases during high-temperature storage or repeated charging and discharging of the secondary battery, and storage characteristics and / or life characteristics may deteriorate.

[0053] If the above weight ratio exceeds 11, for example, the fluorine content in the electrolyte increases excessively, which may reduce the capacity retention rate during high-temperature storage or repeated charge-discharge cycles. Consequently, the high-temperature storage characteristics and lifespan characteristics of the secondary battery may be degraded.

[0054] For example, when the above weight ratio exceeds 3 and is 11 or less, the oxidation resistance and chemical resistance of the secondary battery are sufficiently improved to improve high-temperature storage characteristics and lifespan characteristics, while the fluorine content is appropriately controlled to prevent a decrease in capacity retention rate.

[0055] In a preferred embodiment, the weight ratio may be 4.5 to 9. In this case, the storage characteristics and lifespan characteristics at high temperatures described above of the secondary battery may be further improved.

[0056] In exemplary embodiments, the non-aqueous organic solvent may further include at least one of a carbonate solvent, an ester solvent, an ether solvent, a ketone solvent, an alcohol solvent, and an aprotic solvent. These may be used alone or in combination of two or more.

[0057] For example, the carbonate-based solvent may include at least one of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate, ethyl propyl carbonate, diethyl carbonate (DEC), dipropyl carbonate, propylene carbonate (PC), ethylene carbonate (EC), and butylene carbonate.

[0058] For example, the ester-based solvent may include at least one of methyl acetate (MA), ethyl acetate (EA), n-propyl acetate (n-PA), 1,1-dimethylethyl acetate (DMEA), methyl propionate (MP), ethyl propionate (EP), gamma-butyrolactone (GBL), decanolide, valerolactone, mevalonolactone, and caprolactone.

[0059] For example, the above ether-based solvent may include at least one of dibutyl ether, tetraethylene glycol dimethyl ether (TEGDME), diethylene glycol dimethyl ether (DEGDME), dimethoxyethane, tetrahydrofuran (THF), and 2-methyltetrahydrofuran.

[0060] For example, the above ketone-based solvent may include cyclohexanone, etc.

[0061] For example, the above alcohol-based solvent may include at least one of ethyl alcohol and isopropyl alcohol.

[0062] For example, the aprotic solvent may include at least one of a nitrile-based solvent, an amide-based solvent (e.g., dimethylformamide), a dioxolane-based solvent (e.g., 1,3-dioxolane), and a sulfolane-based solvent.

[0063] In exemplary embodiments, a lithium salt may be provided as an electrolyte. For example, the lithium salt is Li + X - It can be expressed as.

[0064] For example, the anion (X) of the above lithium salt - ) is F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , SbF6 - , AsF6 -, (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - , (CF3CF2SO2)2N - and PO2F2 - - These may be provided as lithium salt anions, either individually or in combination of two or more types.

[0065] In some embodiments, the lithium salt is lithium tetrafluoroborate (LiBF4) or lithium hexafluorophosphate (LiPF6). 6- It may include at least one of ) and lithium difluorophosphate (LiPO2F2). In this case, a film with excellent thermal stability can be formed on the electrode surface. Accordingly, the non-aqueous electrolyte can achieve excellent ion conductivity and enhanced electrode protection characteristics.

[0066] In one embodiment, the lithium salt may be included in the non-aqueous organic solvent at a concentration of about 0.01 to 5 M, preferably about 0.01 to 2 M. Within this range, the transfer of lithium ions and / or electrons is promoted during the charging and discharging of the lithium secondary battery, thereby ensuring an improved capacity.

[0067] In exemplary embodiments, the additive may include a boron-based compound.

[0068] For example, the boron-based compound may include at least one of lithium bis(oxalate) borate (LiBOB), tris(trimethylsilyl) borate (TMSB), and lithium difluoro(oxalato) borate (LiFOB).

[0069] For example, if the aforementioned boron-based compound is included as an additive, side reactions between the fluorine-based organic solvent and the cathode can be suppressed. Accordingly, it is possible to prevent degradation of storage characteristics and lifespan characteristics at the cathode while using the aforementioned mono-fluoro-based organic solvent and di-fluoro-based organic solvent.

[0070] In some embodiments, the content of the additive relative to the total weight of the non-aqueous electrolyte may be 0.1 to 1.0 weight%. In this case, it is possible to suppress an excessive increase in battery resistance while achieving the effect of improving high-temperature storage characteristics and lifespan characteristics according to the additive. Accordingly, the high-temperature storage characteristics of the secondary battery are improved, and the degradation of capacity and output characteristics can be prevented.

[0071] In exemplary embodiments, the above-described non-aqueous electrolyte may further include auxiliary additives comprising alkyl sulfone compounds and alkenyl sulfone compounds.

[0072] For example, the above alkyl sulfone compound may include at least one of 1,3-propane sulfone (PS) and 1,4-butane sulfone.

[0073] For example, the alkenyl sulfone compound may include at least one of ethensulfone, 1,3-propenesulfone (PRS), 1,4-butenesulfone, and 1-methyl-1,3-propenesulfone.

[0074] The aforementioned auxiliary additives may further include, for example, anhydrous compounds such as succinic anhydride and maleic anhydride, and nitrile compounds such as glutarnitrile, succinic acid nitrile, and adiponitrile. These may be added in addition to the aforementioned sulfone compounds, either individually or in combination of two or more.

[0075] In one embodiment, the auxiliary additive may further include at least one of polyethylene sulfide (PES), vinylene carbonate (VC), and vinylethylene carbonate (VEC).

[0076] In some embodiments, the content of the auxiliary additive relative to the total weight of the non-aqueous electrolyte may be 0.8 to 1.6 weight%. In this case, the side reactions of the aforementioned additive can be further suppressed while suppressing an excessive increase in battery resistance. Accordingly, the reduction in capacity can be suppressed while maintaining or improving the effect of improving the lifespan characteristics of the secondary battery according to the aforementioned mono-fluoro organic solvent and di-fluoro organic solvent.

[0077] A lithium secondary battery according to exemplary embodiments of the present invention may include a positive electrode, a negative electrode facing the positive electrode, and the above-described non-aqueous electrolyte.

[0078] FIGS. 1 and FIGS. 2 are a schematic plan view and a cross-sectional view, respectively, illustrating a lithium secondary battery according to exemplary embodiments. For example, FIG. 2 is a cross-sectional view taken along line II' of FIG. 1.

[0079] Referring to FIGS. 1 and 2, a lithium secondary battery may include a positive electrode (100) and a negative electrode (130) facing the positive electrode (100).

[0080] The positive electrode (100) may include a positive electrode current collector (105) and a positive electrode active material layer (110) on the positive electrode current collector (105).

[0081] The positive active material layer (110) may include a positive active material, a positive binder and a conductive material as needed.

[0082] The positive electrode (100) can be manufactured by, for example, mixing and stirring a positive electrode active material, a positive electrode binder, a conductive material, a dispersion medium, etc. to produce a positive electrode slurry, and then applying, drying, and rolling the slurry onto a positive electrode current collector (105).

[0083] The positive current collector (105) may include, for example, stainless steel, nickel, aluminum, titanium, copper, or an alloy thereof, and more preferably, aluminum or an aluminum alloy.

[0084] The above-mentioned positive electrode active material may be a material capable of reversible insertion and extraction of lithium ions. The above-mentioned positive electrode active material may be, for example, a lithium metal oxide containing metal elements such as nickel, cobalt, manganese, and aluminum.

[0085] For example, the lithium metal oxide can be represented by the following chemical formula 5.

[0086] [Chemical Formula 5]

[0087] Li a Ni x M 1-x O 2+y

[0088] In Chemical Formula 1, a is 0.9≤a≤1.2, x is 0.5≤x≤0.99, y is -0.1≤y≤0.1, and M can represent one or more elements selected from Na, Mg, Ca, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Ba, or Zr.

[0089] When the Ni content in the cathode active material or lithium-transition metal oxide increases, relative chemical stability, such as the high-temperature storage stability of the secondary battery, may deteriorate. Furthermore, due to surface damage to the cathode active material or adverse reactions with the non-aqueous electrolyte caused by repeated charge / discharge cycles, sufficient high power / high capacity characteristics corresponding to the high Ni content may not be realized.

[0090] However, as described above, an additive having a specific chemical structure can capture / remove active oxygen around the cathode active material or in the non-aqueous electrolyte. Accordingly, high power / high capacity characteristics through a high Ni content (e.g., Ni 80 mol% or more) can be maintained substantially uniformly for a long time even in a high-temperature environment.

[0091] A slurry can be prepared by mixing and stirring the above positive active material with a binder, a conductive material and / or a dispersant, etc., in a solvent. A positive electrode (100) can be prepared by coating the slurry onto a positive electrode current collector (105), and then compressing and drying it.

[0092] The positive current collector (105) may include, for example, stainless steel, nickel, aluminum, titanium, copper, or an alloy thereof, and preferably may include aluminum or an aluminum alloy.

[0093] The above binder may include, for example, organic binders such as vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidenefluoride (PVDF), polyacrylonitrile, and polymethylmethacrylate, or water-based binders such as styrene-butadiene rubber (SBR), and may be used together with a thickener such as carboxymethyl cellulose (CMC).

[0094] For example, a PVDF-based binder can be used as the anode binder. In this case, the amount of binder required to form the anode active material layer can be reduced, and the amount of the anode active material can be relatively increased, thereby improving the output and capacity of the secondary battery.

[0095] The above conductive material may be included to promote electron transfer between active material particles. For example, the conductive material may include carbon-based conductive materials such as graphite, carbon black, graphene, carbon nanotubes, etc., and / or metal-based conductive materials such as perovskite materials such as tin, tin oxide, titanium oxide, LaSrCoO3, LaSrMnO3, etc.

[0096] The negative electrode (130) may include a negative electrode current collector (125) and a negative electrode active material layer (120) formed by coating a negative electrode active material onto the negative electrode current collector (125).

[0097] The above-mentioned negative electrode active material may be any material known in the art capable of absorbing and extracting lithium ions, without any particular limitation. For example, carbon-based materials such as crystalline carbon, amorphous carbon, carbon composites, and carbon fibers; lithium alloys; silicon (Si)-based compounds; or tin may be used. Examples of the above-mentioned amorphous carbon include hard carbon, coke, mesocarbon microbeads (MCMB), and mesophase pitch-based carbon fibers (MPCF).

[0098] Examples of the above-mentioned crystalline carbon include graphite-based carbons such as natural graphite, artificial graphite, graphitized coke, graphitized MCMB, and graphitized MPCF. Examples of elements included in the above-mentioned lithium alloy include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium.

[0099] The above silicon-based compound may include, for example, silicon-carbon composite compounds such as silicon oxide or silicon carbide (SiC).

[0100] For example, the above-described binder, conductive material, thickener, etc. can be mixed and stirred together in the above-described cathode active material and solvent to form a slurry. The cathode (130) can be manufactured by coating the slurry onto at least one surface of the cathode current collector (125), and then compressing and drying it.

[0101] A separator (140) may be interposed between the anode (100) and the cathode (130). The separator (140) may include a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, an ethylene / methacrylate copolymer, etc. The separator (140) may also include a nonwoven fabric formed of high-melting-point glass fibers, polyethylene terephthalate fibers, etc.

[0102] In some embodiments, the area (e.g., the contact area with the separator (140)) and / or volume of the negative electrode (130) may be larger than that of the positive electrode (100). Accordingly, lithium ions generated from the positive electrode (100) can be smoothly transferred to the negative electrode (130) without precipitating, for example, in the middle.

[0103] According to exemplary embodiments, an electrode cell is defined by an anode (100), a cathode (130), and a separator (140), and a plurality of electrode cells may be stacked to form, for example, an electrode assembly (150) in the form of a jelly roll. For example, the electrode assembly (150) may be formed by winding, laminating, folding, etc., of the separator (140).

[0104] A lithium secondary battery can be defined by housing an electrode assembly (150) in a case (160) together with a non-aqueous electrolyte according to the exemplary embodiments described above. According to the exemplary embodiments, a non-aqueous electrolyte comprising the additive and auxiliary additive described above can be used as the electrolyte.

[0105] As illustrated in FIG. 1, electrode tabs (positive tabs and negative tabs) may protrude from the positive current collector (105) and negative current collector (125) belonging to each electrode cell, respectively, and extend to one side of the case (160). The electrode tabs may be fused together with the one side of the case (160) to form electrode leads (positive lead (107) and negative lead (127)) that extend or are exposed to the outside of the case (160).

[0106] The above lithium secondary battery can be manufactured in, for example, a cylindrical, prismatic, pouch, or coin type using a can.

[0107] Hereinafter, preferred embodiments are presented to aid in understanding the present invention; however, these embodiments are merely illustrative of the invention and are not intended to limit the appended claims. It is obvious to those skilled in the art that various changes and modifications to the embodiments are possible within the scope and spirit of the invention, and that such variations and modifications fall within the scope of the appended claims.

[0108] Example 1

[0109] (1) Preparation of non-aqueous electrolyte

[0110] A solution was prepared by dissolving 1.0 M LiPF6 in a mixed non-aqueous organic solvent of PC / FEC / EMC / DFA (21:5:29:45; weight ratio). Subsequently, lithium bisoxalate borate (LiBOB) was added to and mixed into the solution as an additive to an amount of 0.8 wt% relative to the total weight of the non-aqueous electrolyte.

[0111] In addition, as auxiliary additives, 0.3 wt% of 1,3-propane sulfone (PS), 0.7 wt% of 1,3-propene sulfone (PRS), and 0.5 wt% of polyethylene sulfide (PES) (total 1.5 wt%) were added and mixed to the total weight of the non-aqueous electrolyte to prepare a non-aqueous electrolyte.

[0112] (2) Manufacturing of lithium secondary batteries

[0113] Li[Ni as a positive electrode active material 0.8 Co 0.1 Mn 0.1 ]O 2, A slurry was prepared by mixing carbon black as a conductive material and polyvinylidene fluoride (PVdF) as a binder in a weight ratio of 92:5:3. The slurry was uniformly coated onto an aluminum foil 15 μm thick and vacuum dried at 130°C to produce a positive electrode for a lithium secondary battery.

[0114] A cathode slurry was prepared comprising 95 wt% natural graphite as a cathode active material, 1 wt% Super-P as a conductive material, 2 wt% styrene-butadiene rubber (SBR) as a binder, and 2 wt% carboxymethyl cellulose (CMC) as a thickener. The cathode was manufactured by uniformly coating the cathode slurry onto a copper foil 15 μm thick, drying, and pressing.

[0115] As described above, the positive and negative electrodes manufactured were each cut to a predetermined size and stacked, and a separator (polyethylene, thickness 20 μm) was interposed between the positive and negative electrodes to form an electrode cell, after which the tab portions of the positive and negative electrodes were welded. The welded combination of positive / separator / negative electrode was placed into a pouch, and three sides excluding the surface for injecting the electrolyte were sealed. At this time, the portion containing the electrode tabs was included in the sealing portion. The non-aqueous electrolyte manufactured in (1) above was injected through the remaining surface excluding the sealing portion, and after sealing the remaining surface, the lithium secondary battery was manufactured by impregnating for 12 hours.

[0116] Example 2

[0117] A non-aqueous electrolyte and a lithium secondary battery were prepared in the same manner as in Example 1, except that a mixed solvent of PC / FEC / EMC / DFA (21:6:28:45; weight ratio) was used as the non-aqueous organic solvent when preparing the non-aqueous electrolyte.

[0118] Example 3

[0119] A non-aqueous electrolyte and a lithium secondary battery were prepared in the same manner as in Example 1, except that a mixed solvent of PC / FEC / EMC / DFA (21:8:26:45; weight ratio) was used as the non-aqueous organic solvent when preparing the non-aqueous electrolyte.

[0120] Example 4

[0121] A non-aqueous electrolyte and a lithium secondary battery were prepared in the same manner as in Example 1, except that a mixed solvent of PC / FEC / EMC / DFA (21:10:24:45; weight ratio) was used as the non-aqueous organic solvent when preparing the non-aqueous electrolyte.

[0122] Example 5

[0123] A non-aqueous electrolyte and a lithium secondary battery were prepared in the same manner as in Example 1, except that a mixed solvent of PC / FEC / EMC / DFA (21:13:21:45; weight ratio) was used as the non-aqueous organic solvent when preparing the non-aqueous electrolyte.

[0124] Example 6

[0125] A non-aqueous electrolyte and a lithium secondary battery were prepared in the same manner as in Example 1, except that LiBOB was added as an additive at 0.08 wt% relative to the total weight of the non-aqueous electrolyte when preparing the non-aqueous electrolyte.

[0126] Example 7

[0127] A non-aqueous electrolyte and a lithium secondary battery were prepared in the same manner as in Example 1, except that LiBOB was added as an additive at 1.1% by weight relative to the total weight of the non-aqueous electrolyte when preparing the non-aqueous electrolyte.

[0128] Example 8

[0129] A non-aqueous electrolyte and a lithium secondary battery were prepared in the same manner as in Example 1, except that 0.2 wt% of PS and 0.5 wt% of PRS (total 0.7 wt%) were added as auxiliary additives relative to the total weight of the non-aqueous electrolyte when preparing the non-aqueous electrolyte.

[0130] Example 9

[0131] A non-aqueous electrolyte and a lithium secondary battery were prepared in the same manner as in Example 1, except that PS 0.2 wt%, PRS 0.5 wt%, and PES 0.2 wt% (total 0.9 wt%) were added as auxiliary additives relative to the total weight of the non-aqueous electrolyte when preparing the non-aqueous electrolyte.

[0132] Example 10

[0133] A non-aqueous electrolyte and a lithium secondary battery were prepared in the same manner as in Example 1, except that PS 0.5 wt%, PRS 0.7 wt%, and PES 0.5 wt% (total 1.7 wt%) were added as auxiliary additives relative to the total weight of the non-aqueous electrolyte when preparing the non-aqueous electrolyte.

[0134] Comparative Example 1

[0135] A non-aqueous electrolyte and a lithium secondary battery were prepared in the same manner as in Example 1, except that a mixed solvent of EC / EMC (25:75; weight ratio) was used as the non-aqueous organic solvent when preparing the non-aqueous electrolyte.

[0136] Comparative Example 2

[0137] A non-aqueous electrolyte and a lithium secondary battery were prepared in the same manner as in Example 1, except that a mixed solvent of PC / EMC / DFA (21:58:21; weight ratio) was used as the non-aqueous organic solvent when preparing the non-aqueous electrolyte.

[0138] Comparative Example 3

[0139] A non-aqueous electrolyte and a lithium secondary battery were prepared in the same manner as in Example 1, except that a mixed solvent of PC / EMC / FEC (21:58:21; weight ratio) was used as the non-aqueous organic solvent when preparing the non-aqueous electrolyte.

[0140] Comparative Example 4

[0141] A non-aqueous electrolyte and a lithium secondary battery were prepared in the same manner as in Example 1, except that a mixed solvent of PC / FEC / EMC / DFA (21:4:30:45; weight ratio) was used as the non-aqueous organic solvent when preparing the non-aqueous electrolyte.

[0142] Comparative Example 5

[0143] A non-aqueous electrolyte and a lithium secondary battery were prepared in the same manner as in Example 1, except that a mixed solvent of PC / FEC / EMC / DFA (21:15:19:45; weight ratio) was used as the non-aqueous organic solvent when preparing the non-aqueous electrolyte.

[0144] The types and contents of the additives and auxiliary additives used in the above-described examples and comparative examples are shown in Table 1 below.

[0145] division weight ratio of di-fluoro organic solvent to mono-fluoro organic solvent Additive content (weight%) Auxiliary Additive Content (Weight%) Example 1 9 0.8 1.5 Example 2 7.5 0.8 1.5 Example 3 5.625 0.8 1.5 Example 4 4.5 0.8 1.5 Example 5 3.46 0.8 1.5 Example 6 5.625 0.08 1.5 Example 7 5.625 1.1 1.5 Example 8 5.625 0.8 0.7 Example 9 5.625 0.8 0.9 Example 10 5.625 0.8 1.7 Comparative Example 1 - 0.8 1.5 Comparative Example 2 - 0.8 1.5 Comparative Example 3 - 0.8 1.5 Comparative Example 4 11.25 0.8 1.5 Comparative Example 5 3 0.8 1.5

[0146] Experimental example

[0147] (1) Initial performance evaluation

[0148] 1) Initial dose evaluation

[0149] For the lithium secondary batteries according to the above-described embodiments and comparative examples, charging (CC / CV 1 / 3C 4.2V 0.05C CUT-OFF) and discharging (CC 1 / 3C 2.5V CUT-OFF) were performed, and the initial discharge capacity was measured.

[0150] 2) Discharge DCIR Evaluation

[0151] According to the above-described embodiments and comparative examples, the State of Charge (SOC) of the lithium secondary battery was set to 60%, and the C-rate was sequentially increased or decreased to 0.2C, 0.5C, 1.0C, 1.5C, 2.0C, 2.5C, and 3.0C. When the charging and discharging of the corresponding C-rate was carried out for 10 seconds, the terminal point of the voltage was constructed using a linear equation, and the slope was adopted as DCIR (DC internal resistance).

[0152] (2) Evaluation of high-temperature storage characteristics - 60 ℃

[0153] After leaving the lithium secondary batteries according to the above-described embodiments and comparative examples in a 60°C chamber for 8 weeks, the following evaluation was performed.

[0154] 1) Evaluation of capacity retention rate - 60 ℃

[0155] The discharge capacity was measured by discharging the lithium secondary battery (CC 1 / 3C 2.5V CUT-OFF). The discharge capacity was divided by the initial capacity measured in Experimental Example (1)1) to calculate the percentage.

[0156] The method for measuring discharge capacity was performed in the same way as in Experimental Example (1)1).

[0157] 2) Measurement of gas generation amount

[0158] A lithium secondary battery that had been left in the above 60°C chamber for 8 weeks was left for an additional 4 weeks under the same conditions, then left at room temperature for 30 minutes, and placed in a chamber for measuring the amount of gas generated. After creating a vacuum in the chamber, nitrogen gas was filled to create atmospheric pressure. At this time, the nitrogen volume (V0) and the internal chamber pressure (P0) were measured. After creating a vacuum inside the chamber again, a hole was made in the battery and the internal chamber pressure (P1) was measured, and the amount of gas generated was calculated according to the following formula.

[0159] Gas generation amount (mL) = (V0 / P0)*P1

[0160] (3) Evaluation of high-temperature life characteristics - 45 ℃

[0161] The lithium secondary batteries according to the above-described embodiments and comparative examples were charged (CC / CV 1 / 3C 4.2V 0.05C CUT-OFF) and discharged (CC 1 / 3C 2.5V CUT-OFF) 1,000 times in a 45°C chamber.

[0162] 1) Evaluation of volume retention rate - 45 ℃

[0163] The capacity retention rate of the lithium secondary battery was calculated as a percentage by dividing the discharge capacity measured at the 1,000th discharge by the initial capacity measured in the above experimental example (1)1).

[0164] Capacity Retention Rate = (1,000th Discharge Capacity / Initial Capacity) × 100 (%)

[0165] 2) Measurement of gas generation amount

[0166] For a lithium secondary battery that has undergone 1,000 cycles of charging and discharging in a 45 ℃ chamber, the amount of gas generated was measured in the same manner as in the above experimental example (2)3).

[0167] (4) Measurement of charge / discharge cycles when room temperature capacity retention rate reaches 90% - 25 ℃

[0168] For the lithium secondary batteries according to the above-described embodiments and comparative examples, charging (CC / CV 1 / 3C 4.2V 0.05C CUT-OFF) and discharging (CC 1 / 3C 2.5V CUT-OFF) at room temperature (25 ℃) were repeated as many times as the capacity retention rate reached 90%, and the number of times was measured.

[0169] The evaluation results according to the above-described experimental examples are shown in Tables 2 and 3 below.

[0170] division Initial performance evaluation Evaluation of high-temperature storage characteristics (60 ℃) Initial capacity (mAh) DCIR(mΩ) Capacity retention rate (%) Gas generation amount (mL) Example 1 1,870 40.01 85 22.67 Example 2 1,865 41.11 87 23.28 Example 3 1,852 41.72 90 24.75 Example 4 1,858 42.30 92 25.82 Example 5 1,855 42.74 93 26.90 Example 6 1,860 39.91 85 28.11 Example 7 1,821 45.90 89 22.54 Example 8 1,866 40.22 84 30.24 Example 9 1,851 42.23 88 26.71 Example 10 1,815 46.19 90 23.17 Comparative Example 1 1,864 42.10 65 54.98 Comparative Example 2 1,870 40.93 70 46.20 Comparative Example 3 1,855 39.52 74 45.92 Comparative Example 4 1,849 40.05 75 17.50 Comparative Example 5 1,860 40.98 91 42.78

[0171] division High-temperature life characteristics evaluation (45 ℃) Number of charge / discharge cycles when the capacity retention rate reaches 90% at room temperature (25 ℃) Capacity retention rate (%, 1000 cycle) Gas generation amount (mL) Example 1 80 14.88 340 Example 2 81 15.26 342 Example 3 83 16.10 376 Example 4 84 17.98 430 Example 5 86 19.22 452 Example 6 78 23.64 315 Example 7 83 17.52 371 Example 8 76 24.11 310 Example 9 80 19.10 332 Example 10 82 18.05 380 Comparative Example 1 63 168.3 117 Comparative Example 2 65 107.1 172 Comparative Example 3 68 98.51 166 Comparative Example 4 70 22.30 264 Comparative Example 5 85 53.28 480

[0172] Referring to Tables 2 and 3, the embodiments of the present invention, in which the weight ratio of di-fluoro organic solvent to mono-fluoro organic solvent is greater than 3 and less than or equal to 11, were evaluated to have superior high-temperature storage characteristics, high-temperature life characteristics, and room-temperature capacity retention rate compared to comparative examples.

[0173] However, Example 6, in which the additive content was less than 0.5% by weight relative to the total weight of the non-aqueous electrolyte, failed to sufficiently suppress side reactions between the electrode and the fluorine-based organic solvent, resulting in reduced storage characteristics and lifespan characteristics at relatively high temperatures compared to other examples.

[0174] In addition, Example 7, in which the additive content exceeded 1.0 wt% relative to the total weight of the non-aqueous electrolyte, had an excessive amount of additive added, which increased the battery resistance and consequently lowered the initial capacity relatively compared to other examples.

[0175] Example 8, in which the auxiliary additive content was less than 0.8% by weight relative to the total weight of the non-aqueous electrolyte, had an excessively low auxiliary additive content, resulting in a relatively reduced effect of improving lifespan and storage characteristics compared to other examples.

[0176] In addition, Example 10, in which the content of the auxiliary additive exceeds 1.6% by weight relative to the total weight of the non-aqueous electrolyte, had an increased battery resistance due to the excessive addition of the auxiliary additive, and consequently, the initial capacity was relatively lower compared to other examples.

[0177] Comparative Example 1, which did not use a fluorine-based organic solvent, showed significantly reduced storage characteristics and lifespan characteristics at high temperatures and capacity retention rate at room temperature compared to the examples.

[0178] Comparative Example 2, which used only a mono-fluoro organic solvent, and Comparative Example 3, which used only a di-fluoro organic solvent, showed significantly reduced storage characteristics and lifespan characteristics at high temperatures and capacity retention rate at room temperature compared to the examples.

[0179] In addition, Comparative Example 4, in which the weight ratio of di-fluoro organic solvent to mono-fluoro organic solvent exceeds 11, showed a reduced capacity retention rate during high-temperature storage and repeated charge-discharge compared to the Examples.

[0180] Comparative Example 5, in which the weight ratio of di-fluoro organic solvent to mono-fluoro organic solvent is 3 or less, showed reduced oxidation resistance and chemical resistance of the secondary battery compared to the examples, resulting in reduced storage characteristics and lifespan characteristics at high temperatures. Explanation of the symbols

[0181] 100: Anode 105: Anode current collector 107: Anode Lead 110: Anode Active Material Layer 120: Cathode active material layer 125: Cathode current collector 127: Cathode Lead 130: Cathode 140: Separator 150: Electrode assembly 160: Case

Claims

Claim 1 A non-aqueous electrolyte comprising a non-aqueous organic solvent including a mono-fluoro organic solvent and a di-fluoro organic solvent; a lithium salt; and an additive including a boron compound, wherein the weight ratio of the di-fluoro organic solvent to the weight of the mono-fluoro organic solvent is greater than 3 and less than or equal to 11. Claim 2 Claim 1, wherein the mono-fluoro organic solvent is a non-aqueous electrolyte represented by the following chemical formula 1: [Chemical Formula 1] (In Chemical Formula 1, R1 comprises a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted aryl group having 6 to 12 carbon atoms, a substituted or unsubstituted cycloalkyl group having 5 to 12 carbon atoms, a substituted or unsubstituted cycloalkenyl group having 5 to 12 carbon atoms, a substituted or unsubstituted heterocycloalkyl group having 5 to 7 carbon atoms, or a substituted or unsubstituted heterocycloalkenyl group having 5 to 7 carbon atoms). Claim 3 Claim 1, wherein the di-fluoro organic solvent is a non-aqueous electrolyte represented by the following chemical formula 2: [Chemical Formula 2] (In Chemical Formula 2, R2 is a hydrocarbon comprising a substituted or unsubstituted C1 to C6 alkyl group or a substituted or unsubstituted C6 to C12 aryl group, and R3 is a hydrocarbon comprising a substituted or unsubstituted C1 to C6 alkyl group or a substituted or unsubstituted C1 to C6 alkenyl group). Claim 4 delete Claim 5 A non-aqueous electrolyte according to claim 1, wherein the boron-based compound comprises at least one of lithium bis(oxalate) borate (LiBOB), tris(trimethylsilyl) borate (TMSB), and lithium difluoro(oxalato) borate (LiFOB). Claim 6 A non-aqueous electrolyte according to claim 1, wherein the content of the additive relative to the total weight of the non-aqueous electrolyte is 0.1 to 1.0 weight%. Claim 7 A non-aqueous electrolyte according to claim 1, further comprising an auxiliary additive including an alkyl sulfone compound and an alkenyl sulfone compound. Claim 8 A non-aqueous electrolyte according to claim 7, wherein the content of the auxiliary additive relative to the total weight of the non-aqueous electrolyte is 0.8 to 1.6 weight%. Claim 9 A non-aqueous electrolyte according to claim 1, wherein the lithium salt comprises at least one of lithium tetrafluoroborate (LiBF4), lithium hexafluorophosphate (LiPF6), and lithium difluorophosphate (LiPO2F2). Claim 10 A non-aqueous electrolyte according to claim 1, wherein the weight ratio of the di-fluoro organic solvent to the weight of the mono-fluoro organic solvent is 4.5 to 9. Claim 11 A lithium secondary battery comprising: a positive electrode; a negative electrode facing the positive electrode; and a non-aqueous electrolyte of claim 1.

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