Electrolyte for lithium secondary battery and lithium secondary battery comprising same

Abstract

An electrolyte solution for a lithium secondary battery according to an exemplary embodiment may include an additive including a compound having a specific structure, an organic solvent, and a lithium salt. Accordingly, a lithium secondary battery including the electrolyte solution for lithium secondary batteries is suppressed in thickness increase in a high-temperature environment, and may have improved flame retardant characteristics and lifespan characteristics.

Description

Technical Field

[0001] The present disclosure relates to an electrolyte for a lithium secondary battery and a lithium secondary battery containing the same. More specifically, the disclosure relates to an electrolyte for a lithium secondary battery comprising a solvent and an electrolyte salt and a lithium secondary battery containing the same. Background Art

[0002] Secondary batteries are batteries that can be repeatedly charged and discharged and are widely used as power sources for portable electronic devices such as mobile phones and laptops.

[0003] Among secondary batteries, lithium secondary batteries are being actively developed and used because they have high operating voltage and energy density per unit weight, and are advantageous in terms of charging speed and weight reduction.

[0004] A lithium secondary battery may include, for example, an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; and an electrolyte for impregnating the electrode assembly.

[0005] For example, the lithium secondary battery may further include an outer packaging material in the form of a pouch that accommodates the electrode assembly and the electrolyte.

[0006] The positive electrode of a lithium secondary battery can be manufactured, for example, by coating a positive electrode slurry containing a positive electrode active material, a binder, and, if necessary, a conductive material on a positive electrode current collector, followed by drying and rolling.

[0007] The positive electrode active material may be a material in which lithium ions can be reversibly intercalated and deintercalated. For example, the positive electrode active material may be a lithium metal oxide containing metal elements such as nickel (Ni), cobalt (Co), and manganese (Mn).

[0008] Furthermore, as the application range of lithium secondary batteries expands, they are required to have excellent lifespan characteristics, high capacity, and stable operation. Therefore, it is necessary to develop a lithium secondary battery that can provide uniform power and capacity even during repeated charge and discharge. Summary of the Invention

[0009] Technical issues

[0010] A technical problem to be solved by the present disclosure is to provide an electrolyte for a lithium secondary battery with improved thermal stability and chemical stability.

[0011] A technical problem to be solved by the present disclosure is to provide a lithium secondary battery having improved lifespan characteristics and high-temperature storage characteristics.

[0012] The electrolyte disclosed herein can be widely used in electric vehicles, battery charging stations, and other green technology fields such as solar power generation and wind power generation using batteries. In addition, the lithium secondary battery disclosed herein can be used in eco-friendly electric vehicles and hybrid vehicles that prevent climate change by suppressing air pollution and greenhouse gas emissions.

[0013] Technical Solution

[0014] An electrolyte for a lithium secondary battery according to an exemplary embodiment may include: an additive including a compound having a structure represented by the following Chemical Formula 1; an organic solvent; and a lithium salt.

[0015] [Chemical Formula 1]

[0016]

[0017] In Chemical Formula 1, R 1 for ,

[0018] Ar 1 to Ar 6 Each independently is C6 to C 18 Aryl, C7 to C 19 Alkyl aryl or C6 to C 18 halogenated aryl,

[0019] L 1 To L 3 Each independently C1 to C 12 Alkylene, C3 to C 12 Cycloalkylene, C6 to C 12 arylene or C3 to C 12 Heteroarylene,

[0020] When Z is O (oxygen), n is 0, when Z is N (nitrogen), n is 1, and when Z is C (carbon), n is 2.

[0021] In some embodiments, Ar 1 to Ar 6 Can be independently C6 to C 12 Aryl, C7 to C 13 Alkyl aryl or C6 to C 12 The halogenated aryl group, L 1 To L 3 Can be independently C1 to C 12 of alkylene.

[0022] In some embodiments, Ar 1to Ar 6 It can be phenyl, L 1 To L 3 Each may independently be a C1 to C5 alkylene group.

[0023] In some embodiments, the compound having the structure represented by Chemical Formula 1 may include compounds having structures represented by the following Chemical Formulas 2-1 to 2-3.

[0024] [Chemical Formula 2-1]

[0025]

[0026] [Chemical Formula 2-2]

[0027]

[0028] [Chemical formula 2-3]

[0029]

[0030] In some embodiments, the organic solvent may include at least one selected from the group consisting of a carbonate-based organic solvent, an ester-based organic solvent, an ether-based organic solvent, a ketone-based organic solvent, and an aprotic organic solvent.

[0031] In some embodiments, the organic solvent may include a cyclic carbonate-based solvent and a linear carbonate-based solvent.

[0032] In some embodiments, in the organic solvent, a ratio of the volume of the cyclic carbonate-based solvent to the volume of the linear carbonate-based solvent may be 1 / 9 to 1.

[0033] In some embodiments, the additive may be present in an amount of 0.1 wt % to 10 wt % based on the total weight of the electrolyte.

[0034] In some embodiments, the electrolyte may further include at least one auxiliary additive selected from the group consisting of fluorine-containing carbonate-based compounds, lithium phosphate-based compounds, sultone-based compounds, and sulfate-based compounds.

[0035] In some embodiments, the auxiliary additive may be present in an amount of 0.01 wt % to 10 wt % based on the total weight of the electrolyte.

[0036] In some embodiments, in the electrolyte, the weight ratio of the auxiliary additive to the additive may be 0.1 to 5.

[0037] In some embodiments, the fluorine-containing carbonate-based compound may include fluoroethylene carbonate, the lithium phosphate-based compound may include lithium difluorophosphate, the sultone-based compound may include at least one selected from 1,3-propane sultone, 1,4-butane sultone, ethylene sultone, 1,3-propylene sultone, 1,4-butene sultone and 1-methyl-1,3-propylene sultone, and the sulfate-based compound may include at least one selected from vinyl sulfate, trimethylene sulfate and methyltrimethylene sulfate.

[0038] A lithium secondary battery according to an exemplary embodiment includes: a positive electrode; a negative electrode opposite to the positive electrode; and the above-described electrolyte for a lithium secondary battery for impregnating the positive electrode and the negative electrode.

[0039] Effects of the Invention

[0040] By using the electrolyte for a lithium secondary battery according to the exemplary embodiment, a bloating phenomenon caused during charge and discharge of the lithium secondary battery can be effectively prevented, and the amount of heat generated by the electrolyte can be reduced.

[0041] The lithium secondary battery according to the exemplary embodiment may include the electrolyte for the lithium secondary battery. Therefore, the lithium secondary battery may have a suppressed thickness increase under a high temperature environment and may have improved flame retardancy and lifespan characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 is a plan view schematically illustrating a lithium secondary battery according to an exemplary embodiment;

[0043] Figure 2 is a cross-sectional view schematically illustrating a lithium secondary battery according to an exemplary embodiment. DETAILED DESCRIPTION

[0044] An electrolyte for a lithium secondary battery according to an exemplary embodiment may include an additive including a compound having a specific structure, an organic solvent, and a lithium salt.

[0045] In addition, the lithium secondary battery according to the exemplary embodiment includes a positive electrode, a negative electrode opposite to the positive electrode, and the electrolyte for the lithium secondary battery for impregnating the positive electrode and the negative electrode.

[0046] Therefore, the flame retardant characteristics and life characteristics of the lithium secondary battery can be improved.

[0047] In the present specification, the "A-based compound" may refer to a compound including a functional group A and a derivative of the compound.

[0048] In this manual, “C a to C b” may refer to “the number of carbon (C) atoms from a to b”.

[0049] In the present specification, "heterocycloalkyl" or "heteroarylene" may refer to a cycloalkyl or arylene group in which at least one carbon is independently substituted by -O-, -S-, or -NH-.

[0050] Hereinafter, the embodiments of the present disclosure will be described in more detail with reference to specific implementation examples and drawings. However, this is merely exemplary, and the present disclosure is not limited to the specific implementation examples described exemplarily.

[0051] <Electrolyte for lithium secondary batteries>

[0052] An electrolyte for a lithium secondary battery (hereinafter, simply referred to as an electrolyte) according to an exemplary embodiment may include an additive including a compound having a structure represented by the following Chemical Formula 1, an organic solvent, and a lithium salt.

[0053] Hereinafter, the constituent elements of the present disclosure will be described in more detail.

[0054] additive

[0055] An electrolyte for a lithium secondary battery according to an exemplary embodiment may include an additive including a compound having a structure represented by the following Chemical Formula 1.

[0056] [Chemical Formula 1]

[0057]

[0058] In Chemical Formula 1, R 1 for ,

[0059] Ar 1 to Ar 6 Each independently is C6 to C 18 Aryl, C7 to C 19 Alkyl aryl or C6 to C 18 halogenated aryl,

[0060] L 1 To L 3 Each independently C1 to C 12 Alkylene, C3 to C 12 Cycloalkylene, C6 to C 12 arylene or C3 to C 12 Heteroarylene;

[0061] When Z is O (oxygen), n may be 0, when Z is N (nitrogen), n may be 1, and when Z is C (carbon), n may be 2.

[0062] For example, Ar 1 to Ar 6 Can be independently C6 to C 12 aryl, C6 to C8 aryl or phenyl.

[0063] For example, Ar 1 to Ar 6 Can be independently C7 to C 13 Alkyl aryl, C7 to C 10 an alkylaryl group of C7 to C8 or an alkylaryl group of C7 to C8.

[0064] For example, Ar 1 to Ar 6 Each of the C6 to C5 alkyl groups may be independently C6 to C5 alkyl groups in which at least one hydrogen atom is substituted by a C1 to C5 alkyl group. 13 The aryl group may be a C6 to C9 aryl group in which at least one hydrogen atom is substituted by a C1 to C4 alkyl group, or a C6 to C7 aryl group in which at least one hydrogen atom is substituted by a C1 to C3 alkyl group.

[0065] For example, Ar 1 to Ar 6 Can be independently C6 to C 12 substituted aryl, C6 to C8 substituted aryl or halogenated phenyl.

[0066] For example, Ar 1 to Ar 6 may be C6 to C 12 The aryl group of C6 to C8 in which at least one hydrogen atom is substituted by a halogen atom, or the phenyl group in which at least one hydrogen atom is substituted by a halogen atom, wherein the halogen atom may be a fluorine atom, a chlorine atom, a bromine atom or an iodine atom.

[0067] For example, L 1 To L 3 Each may independently be a C1 to C8 alkylene group, a C3 to C8 cycloalkylene group, a C6 to C8 arylene group, or a C3 to C8 heteroarylene group.

[0068] For example, in L 1 To L 3 In the aryl, alkylene, cycloalkylene, arylene, or heteroarylene group, hydrogen atoms may be substituted or unsubstituted. For example, they may be substituted by at least one of a halogen group, a C1 to C6 alkyl group, a C2 to C6 alkenyl group, an amino group, a C1 to C6 alkoxy group, a C3 to C7 cycloalkyl group, and a 5-7 atom heterocycloalkyl group. The number of substituents may be one or two or more.

[0069] The halogen group may be a fluoro group (—F), a chloro group (—Cl), a bromo group (—Br), or an iodo group (—I).

[0070] In some embodiments, Ar 1 to Ar 6 Can be independently C6 to C 12 Aryl, C7 to C 13 Alkyl aryl or C6 to C 12 The halogenated aryl group, L 1 To L 3 Can be independently C1 to C 12 In one embodiment, Ar 1 to Ar 6 It can be phenyl, L 1 To L 3 Each may independently be a C1 to C5 alkylene group.

[0071] For example, when Z is C (carbon), n can be 2, where multiple R 1 Can be the same or different.

[0072] In some embodiments, the compound having the structure represented by Chemical Formula 1 may include compounds having structures represented by the following Chemical Formulas 2-1 to 2-3.

[0073] [Chemical Formula 2-1]

[0074]

[0075] [Chemical Formula 2-2]

[0076]

[0077] [Chemical formula 2-3]

[0078]

[0079] In one embodiment, the compound having the structure represented by Chemical Formula 1 may include a compound having a structure represented by any one of Chemical Formulas 2-1 to 2-3.

[0080] For example, when an additive containing a compound having a structure represented by Chemical Formula 1 is included in a lithium secondary battery electrolyte, it stabilizes the electrode interface by stably protecting the electrode surface, thereby suppressing side reactions with the electrolyte. Consequently, the thickness increase of the lithium secondary battery under high temperature conditions is suppressed, and capacity retention, flame retardancy, and lifespan characteristics can be improved.

[0081] In some embodiments, the additive may be present in an amount of 0.1 wt % to 10 wt % based on the total weight of the electrolyte.

[0082] For example, based on the total weight of the electrolyte, the content of the additive may be 0.2 wt % to 9 wt %, 0.3 wt % to 8 wt %, 0.4 wt % to 7 wt %, 0.5 wt % to 6.5 wt %, or 1 wt % to 6 wt %. Within the above range, sufficient passivation and formation of a stable solid electrolyte interface (SEI) film can be achieved, and the migration of lithium ions and the activity of the positive electrode active material can be unimpeded.

[0083] Auxiliary additives

[0084] The electrolyte for a lithium secondary battery according to an exemplary embodiment may further include at least one auxiliary additive selected from a fluorine-containing carbonate-based compound, a lithium phosphate-based compound, a sultone-based compound, and a sulfate-based compound. When the additive and the auxiliary additive are used in combination, a lithium secondary battery having further improved high-temperature storage characteristics can be effectively realized.

[0085] For example, the fluorine-containing carbonate compound may contain a fluorine atom or a substituent bonded with a fluorine atom (eg, a fluorine-substituted alkyl group such as -CF3) on at least one carbon atom of the carbonate compound.

[0086] In some embodiments, the fluorine-containing carbonate-based compound may include a fluorine-containing cyclic carbonate-based compound having a cyclic structure. For example, the fluorine-containing cyclic carbonate-based compound may have a 5-7 membered cyclic structure.

[0087] For example, the fluorine-containing cyclic carbonate-based compound may include fluoroethylene carbonate (FEC).

[0088] In some embodiments, the lithium phosphate-based compound may include a fluorine-containing lithium phosphate-based compound.

[0089] For example, the fluorine-containing lithium phosphate-based compound may include a fluorine atom bonded to a phosphorus atom of the lithium phosphate-based compound or a substituent bonded to a fluorine atom (eg, a fluorine-substituted alkyl group such as CF 3 ).

[0090] In some embodiments, the fluorine-containing lithium phosphate compound may include at least one selected from lithium difluorophosphate (LiPO2F2) and lithium difluoro(bis-oxalato) phosphate. For example, the fluorine-containing lithium phosphate compound may include lithium difluorophosphate (LiPO2F2).

[0091] In some embodiments, the sultone-based compound may include at least one selected from the group consisting of an alkyl sultone-based compound and an alkenyl sultone-based compound.

[0092] In some embodiments, the sultone-based compound may include both an alkyl sultone-based compound and an alkenyl sultone-based compound.

[0093] For example, the alkyl sultone-based compound may include at least one selected from 1,3-propane sultone (PS) and 1,4-butene sultone (PS).

[0094] For example, the alkenyl sultone-based compound may include at least one selected from ethene sultone, 1,3-propene sultone (PRS), 1,4-butene sultone, and 1-methyl-1,3-propene sultone.

[0095] In some embodiments, the sulfate ester compound may include a cyclic sulfate ester compound having a cyclic structure. The cyclic sulfate ester compound may have a 5-7 membered ring structure.

[0096] For example, the cyclic sulfate-based compound may include at least one selected from 1,2-ethylene sulfate (ESA), trimethylene sulfate (TMS), and methyltrimethylene sulfate (MTMS).

[0097] In one embodiment, the auxiliary additive may be present in an amount of 0.01 wt % to 10 wt % based on the total weight of the electrolyte.

[0098] For example, based on the total weight of the electrolyte, the auxiliary additive may be present in an amount of 0.05 to 9 wt %, 0.5 to 8 wt %, 0.8 to 7 wt %, 1.0 to 6 wt %, or 1.5 to 5 wt %. Within these ranges, the durability of the SEI can be increased without hindering the effect of the additive, and the flame retardant properties of the electrolyte can be further improved.

[0099] In some embodiments, in the electrolyte, the ratio of the weight of the auxiliary additive to the weight of the additive may be 0.1 to 5.

[0100] For example, the ratio may be 0.2 to 4.8, 0.3 to 4.5, 0.4 to 4.0, 0.5 to 3.5, or 0.7 to 3. Within the above range, high-temperature storage characteristics and flame retardant characteristics of the lithium secondary battery may be further improved.

[0101] In one embodiment, a fluorine-containing carbonate-based compound, a lithium phosphate-based compound, a sultone-based compound, and a sulfate-based compound may be used together as the auxiliary additive.

[0102] In one embodiment, a fluorine-containing carbonate-based compound and a sultone-based compound may be used together as the auxiliary additive. For example, the electrolyte may contain fluoroethylene carbonate, 1,3-propylene sultone, and 1,3-propane sultone as auxiliary additives.

[0103] In some embodiments, the auxiliary additive may further include at least one of a borate-based compound, a nitrile-based compound, an amine-based compound, a silane-based compound, and a benzene-based compound.

[0104] For example, the borate-based compound may include at least one selected from lithium tetraphenylborate and lithium difluoro(oxalato)borate (LiODFB).

[0105] For example, the nitrile compound may include at least one selected from succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, octanonitrile, heptonitrile, cyclopentanenitrile, cyclohexanenitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile and 4-fluorophenylacetonitrile.

[0106] For example, the amine compound may include at least one selected from triethanolamine and ethylenediaminefluorophenylacetonitrile.

[0107] For example, the silane-based compound may include tetraethylenesilane, etc.

[0108] For example, the phenyl compound may include at least one selected from monofluorobenzene, difluorobenzene, trifluorobenzene, and tetrafluorobenzene.

[0109] Organic solvents and lithium salts

[0110] For example, the organic solvent may include an organic compound that has sufficient solubility for the lithium salt, the additive, and the auxiliary additive and is unreactive in a lithium secondary battery.

[0111] In some embodiments, the organic solvent may include at least one selected from the group consisting of a carbonate-based solvent, an ester-based solvent, an ether-based solvent, a ketone-based solvent, an alcohol-based solvent, and an aprotic solvent.

[0112] In some embodiments, the organic solvent may include a carbonate-based solvent, and the carbonate-based solvent may include a linear carbonate-based solvent and a cyclic carbonate-based solvent.

[0113] For example, the linear carbonate-based solvent may include dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, and the like.

[0114] For example, the cyclic carbonate-based solvent may include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, and the like.

[0115] In some embodiments, the organic solvent may include more of the linear carbonate-based solvent than the cyclic carbonate-based solvent on a volume basis.

[0116] In some embodiments, in the organic solvent, the volume ratio of the cyclic carbonate-based solvent to the volume ratio of the linear carbonate-based solvent may be 1 / 9 to 1. For example, the ratio may be 1 / 9 to 1, 1 / 9 to 2 / 3, 1 / 6 to 2 / 3, or 1 / 4 to 2 / 3. Within the above range, the high temperature storage characteristics of the lithium secondary battery can be further improved.

[0117] For example, the ester-based solvent may include at least one of methyl acetate (MA), ethylacetate (EA), n-propyl acetate (n-PA), 1,1-dimethylethyl acetate (DMEA), methyl propionate (MP), ethyl propionate (EP), γ-butyrolactone (GBL), decanolide, valerolactone, mevalonolactone, and caprolactone.

[0118] For example, the 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.

[0119] For example, the ketone-based solvent may include cyclohexanone and the like.

[0120] For example, the alcohol-based solvent may include at least one of ethyl alcohol and isopropyl alcohol.

[0121] For example, the aprotic solvent may include at least one of a nitrile-based solvent, an amide-based solvent (eg, dimethylformamide), a dioxolane-based solvent (eg, 1,3-dioxolane), and a sulfolane-based solvent.

[0122] In some embodiments, the electrolyte may include a lithium salt.

[0123] For example, the lithium salt may be Li + X - express.

[0124] For example, the anion (X - ) may be selected from F - 、Cl - Br- , I - 、NO3 - 、N(CN)2 - 、BF4 - 、ClO4 - PF6 - 、(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 - and (CF3CF2SO2)2N - At least one of .

[0125] In some embodiments, the lithium salt may include at least one selected from LiBF4 and LiPF6.

[0126] In some embodiments, the concentration of the lithium salt relative to the organic solvent may be 0.01 M to 5 M, 0.01 M to 4 M, 0.5 M to 3 M, or 0.5 M to 2 M. Within the above concentration range, lithium ions and / or electrons can migrate smoothly during charge and discharge of the lithium secondary battery.

[0127] <Lithium Secondary Battery>

[0128] Figure 1 and Figure 2 1 and 2 are schematic plan views and cross-sectional views respectively illustrating a lithium secondary battery according to an exemplary embodiment. Figure 2 It is along Figure 1 A cross-sectional view taken along line II'.

[0129] Reference Figure 1 and Figure 2The lithium secondary battery may include an electrode assembly 150 including a positive electrode 100, a negative electrode 130, and a separator 140 interposed therebetween. The electrode assembly 150 may be housed in a case 160 together with the electrolyte according to the exemplary embodiment described above and impregnated in the electrolyte.

[0130] 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 .

[0131] For example, the positive active material layer 110 may include a positive active material and a binder, and further include a conductive material.

[0132] For example, the positive electrode 100 may be manufactured by mixing a positive active material, a positive binder, a conductive material, a dispersant, and the like in a solvent to prepare a positive electrode slurry, coating the slurry on the positive electrode collector 105 , and performing drying and rolling.

[0133] For example, the positive electrode current collector 105 may include stainless steel, nickel, aluminum, titanium, copper, or alloys thereof, preferably aluminum or aluminum alloys. The thickness of the positive electrode current collector may be, for example, 10 μm to 50 μm, but is not limited thereto.

[0134] For example, the positive electrode active material may include a material in which lithium ions can be reversibly intercalated and deintercalated.

[0135] For example, the positive electrode active material may include lithium metal oxide containing metal elements such as nickel, cobalt, manganese, and aluminum.

[0136] For example, the lithium metal oxide may be represented by the following Chemical Formula 3.

[0137] [Chemical Formula 3]

[0138] Li x Ni a Co b M c O y

[0139] In Chemical Formula 3, M may be at least one of Al, Zr, Ti, Cr, B, Mg, Mn, Ba, Si, Y, W, and Sr, and may be 0.9≤x≤1.2, 1.9≤y≤2.1, 0.5≤a≤1, and 0≤c / (a+b)≤0.13.

[0140] For example, in the chemical formula 3, c may be 0≤c≤0.11.

[0141] In some embodiments, the content of nickel in the elements other than lithium and oxygen in the lithium metal oxide may be 60 mol % or more, 70 mol % or more, 80 mol % or more, 83 mol % or more, or 85 mol % or more.

[0142] For example, in the chemical formula 3, 0.6≤a≤1 or 0.8≤a≤1 may be sufficient.

[0143] In one embodiment, the lithium metal oxide may further include a coating element or a doping element. For example, the coating element or doping element may include Al, Ti, Ba, Zr, Si, B, Mg, P, Sr, W, La, or alloys thereof or oxides thereof. These may be used alone or in combination of two or more. The lithium metal oxide is passivated by the coating element or doping element, thereby further improving the stability and life of the lithium metal oxide against penetration by external objects.

[0144] For example, when the nickel content in the lithium metal oxide increases, chemical stability (e.g., high-temperature storage characteristics) may be relatively deteriorated. However, in the case of the lithium secondary battery according to the exemplary embodiment, since the electrolyte is included, even if a high-nickel lithium metal oxide (nickel is 80 mol % or more) is included, improved high-temperature storage characteristics can be provided.

[0145] For example, the positive electrode binder may include an organic binder such as polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyacrylonitrile, or polymethyl methacrylate; or an aqueous binder such as styrene-butadiene rubber (SBR). Furthermore, the positive electrode binder may be used together with a thickener such as carboxymethyl cellulose (CMC).

[0146] For example, the conductive material may include carbon-based conductive materials such as graphite, carbon black, graphene, and carbon nanotubes; or metal-based conductive materials such as tin, tin oxide, titanium oxide, LaSrCoO 3 , and LaSrMnO 3 , etc., which may be perovskite materials.

[0147] The negative electrode 130 may include a negative electrode current collector 125 and a negative electrode active material layer 120 on the negative electrode current collector 125 .

[0148] For example, the negative active material layer 120 may include a negative active material and a negative binder, and further include a conductive material.

[0149] For example, the negative electrode 130 can be manufactured by mixing and stirring the negative electrode active material, the negative electrode binder, and the conductive material in a solvent to prepare a negative electrode slurry, and then coating the negative electrode slurry on the negative electrode current collector 125 and drying and calendering it.

[0150] For example, the negative electrode current collector 125 can include gold, stainless steel, nickel, aluminum, titanium, copper, or their alloys. Preferably, it can include copper or a copper alloy. The thickness of the negative electrode current collector can be, for example, 10 μm to 50 μm, but is not limited thereto.

[0151] For example, the negative electrode active material can be a material capable of intercalating and deintercalating lithium ions. For example, the negative electrode active material can include carbon-based materials such as crystalline carbon, amorphous carbon, carbon composites, carbon fibers, etc.; silicon-based materials; lithium alloys, etc.

[0152] For example, the amorphous carbon can include hard carbon, coke, mesocarbon microbeads (MCMB) fired at a temperature below 1500 °C, mesophase pitch-based carbon fiber (MPCF), etc. For example, the crystalline carbon can include natural graphite, artificial graphite, graphitized coke, graphitized MCMB, graphitized MPCF, etc.

[0153] For example, the silicon-based material can include Si, SiO x (0 < x < 2), Si / C, SiO / C, Si-metal, etc.

[0154] For example, the lithium alloy can include elements such as aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, indium, etc.

[0155] The negative electrode binder and the conductive material can be substances substantially the same or similar to the above-mentioned positive electrode binder and conductive material. For example, for the compatibility with the carbon-based active material, the negative electrode binder can be an aqueous binder such as styrene-butadiene rubber (SBR), and can be used together with a thickener such as carboxymethyl cellulose (CMC).

[0156] In one embodiment, the separator 140 can be interposed between the positive electrode 100 and the negative electrode 130. In some embodiments, the area of the negative electrode 130 (for example, the contact area with the separator 140) can be larger than the area of the positive electrode 100. Therefore, lithium ions generated from the positive electrode 100 can smoothly move to the negative electrode 130 without precipitating in the middle. According to an embodiment, the thickness of the separator can be 10 μm to 20 μm, but the present disclosure is not limited thereto.

[0157] For example, the separator 140 may include a porous polymer film made of polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer.

[0158] For example, the separator 140 may include non-woven fabric formed of high-melting-point glass fiber, polyethylene terephthalate fiber, or the like.

[0159] For example, an electrode cell including a positive electrode 100, a negative electrode 130, and a separator 140 may be formed. In addition, a plurality of electrode cells may be stacked to form an electrode assembly 150. For example, the electrode assembly 150 may be formed by winding, laminating, z-folding, or stack-folding the separator 140.

[0160] The electrode assembly 150 may be housed in a case 160 together with the above-described electrolyte for a lithium secondary battery to form a lithium secondary battery.

[0161] like Figure 1 As shown, the tabs (positive tabs or negative tabs) may protrude from the positive current collector 105 and the negative current collector 125 belonging to each electrode cell and extend to one side of the casing 160. The electrode tabs may be fused together and connected to the electrode lead (positive lead 107 or negative lead 127) extending to the outside of the casing 160.

[0162] For example, the lithium secondary battery may be manufactured in a cylindrical shape, a prismatic shape, a pouch shape, a coin shape, or the like using a can.

[0163] The following is a further description of the embodiments of the present invention with reference to specific experimental examples. The examples and comparative examples included in the experimental examples are intended only to illustrate the present invention and are not intended to limit the scope of the appended claims. Various changes and modifications may be made to the embodiments within the scope and technical concept of the present invention, which will be apparent to those skilled in the art, and such variations and modifications also fall within the scope of the appended claims.

[0164] <Synthesis example>

[0165] (1) Preparation of Additive I (oxybis(ethane-2,1-diyl)tetraphenyl bis(phosphate))

[0166] 100 mL of toluene, 17.83 g (66.37 mmol) of diphenyl chlorophosphate, and 7.36 g (72.69 mmol) of triethylamine were weighed and added to a round-bottom flask. The reactor was then cooled to 0°C, and 3.35 g (31.61 mmol) of diethylene glycol was slowly added to the mixture over 10 minutes. The mixture was then stirred at room temperature for 21 hours.

[0167] After the reaction was completed, the organic layer was washed with water three times, and toluene was removed by drying under reduced pressure. The concentrated solution was column purified with hexane and ethyl acetate to obtain 13.09 g of additive I having a structure represented by the following chemical formula 2-1 (yield: 72.6%).

[0168] 1H-NMR chemical shift (600 MHz, Chloroform-d) analysis of Additive I, δ: 7.33-7.38 (m, 8H), 7.18–7.28 (m, 12H), 4.32–4.36 (t, 4H), 3.67-3.69 (t, 4H)

[0169] [Chemical Formula 2-1]

[0170]

[0171] (oxybis(ethane-2,1-diyl)tetraphenyl bis(phosphate))

[0172] (2) Preparation of Additive II (Nitrilotris(ethane-2,1-diyl)hexaphenyltris(phosphate))

[0173] Tetrahydrofuran (120 mL), triethanolamine (2.0 g, 13.4 mmol), triethylamine (5.4 g, 56.6 mmol) and 4-dimethylaminopyridine (0.2 g, 2.0 mmol) were added sequentially to a round-bottom flask and then cooled to 0° C. Diphenyl chlorophosphate (12.6 g, 46.9 mmol) was slowly added to the mixture solution over 0.5 hours, then the temperature was raised to 60° C. and further stirred for 2 hours.

[0174] After the reaction, 100 mL of water was slowly added dropwise to the stirred liquid, the organic layer was separated, and the mixture was further washed three times with 50 mL of distilled water. The solvent was then dried and purified by silica gel column to obtain 3.0 g of additive II having a structure represented by the following chemical formula 2-2 (yield: 26%).

[0175] 1H-NMR (CDCl3, 600 MHz) analysis of Additive II: 7.35-7.29 (t, 12H), 7.22-7.21 (m, 18H), 4.22-4.18 (q, 6H), 2.90-2.87 (t, 6H)

[0176] [Chemical Formula 2-2]

[0177]

[0178] (Nitrilotris(ethane-2,1-diyl)hexaphenyltris(phosphate))

[0179] (3) Additive III ((2,2-bis(((diphenyloxyphosphino)oxy)methyl)propane-1,3-diyltetraphenylbis Preparation of (phosphate)))

[0180] Tetrahydrofuran (800 mL), pentaerythritol (8.0 g, 58.8 mmol), triethylamine (29.7 g, 246.8 mmol), and 4-dimethylaminopyridine (1.4 g, 11.8 mmol) were sequentially added to a round-bottom flask, and then cooled to 0° C. Diphenyl chlorophosphate (66.3 g, 246.8 mmol) was slowly added to the mixture solution over 0.5 hours, then the temperature was raised to 60° C. and further stirred for 7 hours.

[0181] After the reaction, 500 mL of water was slowly added dropwise to the stirred liquid, the organic layer was separated, and the mixture was further washed three times with 200 mL of water. The solvent was then dried and purified by silica gel column to obtain 27.0 g of additive III having a structure represented by the following chemical formula 2-3 (yield: 43%).

[0182] 1H-NMR (CDCl3, 600 MHz) analysis of Additive III: 7.30-7.29 (d, 16H), 6.99-6.96 (t, 16H), 6.80-6.77 (t, 8H), 4.23-4.22 (d, 8H)

[0183] [Chemical formula 2-3]

[0184]

[0185] (2,2-bis(((diphenoxyphosphino)oxy)methyl)propane-1,3-diyltetraphenyl bis(phosphate))

[0186] <Examples and Comparative Examples>

[0187] Example 1

[0188] (1) Preparation of electrolyte

[0189] Prepare a 1 M LiPF6 solution (EC / EMC mixed solvent with a volume ratio of 25:75).

[0190] Based on the total weight of the electrolyte (100 wt %), 1 wt % of fluoroethylene carbonate (FEC), 0.5 wt % of 1,3-propylene sultone (PRS) and 0.5 wt % of 1,3-propane sultone (PS) were added to the LiPF6 solution, and 5 wt % of the additive I (oxybis(ethane-2,1-diyl)tetraphenylbis(phosphate)) according to the synthesis example was added to prepare an electrolyte.

[0191] (2) Preparation of lithium secondary battery samples

[0192] The positive electrode slurry was prepared by mixing a positive electrode active material, a carbon black conductive material, and a polyvinylidene fluoride (PVdF) binder in a weight ratio of 92:5:3 in NMP for dispersion. 0.6 Co 0.2 Mn 0.2 ]O2 and Li[Ni 0.8 Co 0.1 Mn 0.1 ]O2 is mixed in a weight ratio of 6:4.

[0193] The positive electrode slurry was manufactured by uniformly coating the positive electrode slurry on an aluminum foil (15 μm thick) having a protrusion (positive electrode tab) on one side, excluding the protrusion, drying the aluminum foil, and then rolling the aluminum foil.

[0194] The negative electrode slurry was prepared by mixing a negative electrode active material, a styrene-butadiene rubber (SBR) binder, and a carboxymethyl cellulose (CMC) thickener in distilled water at a weight ratio of 97:1:2, wherein the negative electrode active material was obtained by mixing artificial graphite and natural graphite at a weight ratio of 7:3.

[0195] The negative electrode slurry was uniformly coated on a copper foil (15 μm thick) having a protrusion (negative electrode tab) on one side, excluding the protrusion, and then rolled after drying to manufacture a negative electrode.

[0196] An electrode assembly was formed by inserting a polyethylene separator (thickness of 20 μm) between the positive electrode and the negative electrode. Then, a positive electrode lead and a negative electrode lead were welded to the positive electrode tab and the negative electrode tab, respectively.

[0197] The electrode assembly is housed in a pouch (casing) such that portions of the positive electrode lead and the negative electrode lead are exposed to the outside, and then three surfaces excluding the electrolyte injection portion are sealed.

[0198] The electrolyte prepared in (1) was injected, the electrolyte injection portion was sealed, and then immersed for 12 hours to prepare a lithium secondary battery sample.

[0199] Example 2

[0200] An electrolyte and a lithium secondary battery sample were prepared by the same method as in Example 1, except that 5 wt % of Additive II (nitrilotris(ethane-2,1-diyl)hexaphenyltris(phosphate)) according to the Synthesis Example was used instead of Additive I.

[0201] Example 3

[0202] An electrolyte and a lithium secondary battery sample were prepared by the same method as in Example 1, except that 5 wt % of Additive III (2,2-bis(((diphenoxyphosphino)oxy)methyl)propane-1,3-diyltetraphenylbis(phosphate)) according to the synthesis example was used instead of Additive I.

[0203] Example 4

[0204] An electrolyte solution and a lithium secondary battery sample were prepared by the same method as in Example 1, except that the content of the additive I was changed from 5 wt % to 1 wt %.

[0205] Example 5

[0206] An electrolyte solution and a lithium secondary battery sample were prepared by the same method as in Example 1, except that the content of the additive I was changed from 5 wt % to 10 wt %.

[0207] Example 6

[0208] An electrolyte solution and a lithium secondary battery sample were prepared by the same method as in Example 2, except that the content of Additive II was changed from 5 wt % to 1 wt %.

[0209] Example 7

[0210] An electrolyte solution and a lithium secondary battery sample were prepared by the same method as in Example 2, except that the content of Additive II was changed from 5 wt % to 10 wt %.

[0211] Example 8

[0212] An electrolyte solution and a lithium secondary battery sample were prepared by the same method as in Example 3, except that the content of Additive III was changed from 5 wt % to 1 wt %.

[0213] Example 9

[0214] An electrolyte solution and a lithium secondary battery sample were prepared by the same method as in Example 3, except that the content of Additive III was changed from 5 wt % to 10 wt %.

[0215] Comparative Example 1

[0216] An electrolyte solution and a lithium secondary battery sample were prepared by the same method as in Example 1, except that Additive I was not used.

[0217] The electrolyte compositions of Examples and Comparative Examples are shown in Table 1 below.

[0218] [Table 1]

[0219]

[0220] <Experimental Example>

[0221] (1) Thermal exposure measurement (hot box test)

[0222] The lithium secondary batteries of Examples 1 to 3 and Comparative Example 1 were placed in an oven, heated to 150° C. at 5° C. / min, and then the time (delay time) required for the battery cells to explode during the 3-hour oven period was measured.

[0223] (2) Evaluation of initial characteristics

[0224] 2-1) Evaluation of initial capacity

[0225] The lithium secondary batteries of Examples and Comparative Examples were subjected to three times of 0.5C rate CC / CV charge (4.2V, 0.05C cut-off) and 0.5C rate CC discharge (2.7V cut-off) at 25°C, and then the discharge capacity was measured. The discharge capacity was designated as C1.

[0226] 2-2) Evaluation of internal resistance (DCIR)

[0227] For the lithium secondary batteries of the embodiments and comparative examples, at the SOC 60% point, the C-rate was increased or decreased to 0.2C, 0.5C, 1.0C, 1.5C, 2.0C, 2.5C and 3.0C, and a straight line equation was constructed from the voltage endpoints when charging for 10 seconds and discharging for 10 seconds at each C-rate, and the slope of the straight line equation was used as DCIR, and the DCIR was used as R1.

[0228] (3) Evaluation of life performance (45°C)

[0229] 3-1) Evaluation of capacity retention

[0230] The lithium secondary batteries of Examples and Comparative Examples were charged to 4.2 V at 1 C and discharged to 2.75 V at 1 C at 45° C., and the charge and discharge were repeated 600 times, and the discharge capacity C2 at the 600th time was measured.

[0231] The capacity retention rate was calculated according to the following formula.

[0232] Capacity retention rate (%) = (C2 / C1) × 100

[0233] 3-2) Evaluation of resistance increase rate

[0234] The secondary batteries of Examples and Comparative Examples were charged to 4.2 V at 0.5 C and placed in a chamber at 45° C. for 4 hours. DCIR was then measured using the same method as in 2-2). The measured DCIR was defined as R2.

[0235] The DCIR increase rate was calculated according to the following formula.

[0236] DCIR increase rate (%) = {(R2-R1) / R1+1}×100 (%)

[0237] (4) Evaluation of high temperature storage characteristics (60°C)

[0238] 4-1) Evaluation of capacity retention after high-temperature storage

[0239] The lithium secondary batteries of Examples and Comparative Examples were charged to 4.2 V at 0.5 C at 25° C. and stored at high temperature (60° C.) for 13 weeks. After storage at high temperature, the lithium secondary batteries were CC discharged at 0.5 C (2.7 V cutoff) to measure the discharge capacity C3.

[0240] The capacity retention rate after high temperature storage was calculated according to the following formula.

[0241] Capacity retention rate (%) = (C3 / C1) × 100

[0242] 4-2) Evaluation of resistance increase rate after high-temperature storage

[0243] The secondary batteries of Examples and Comparative Examples were charged to 4.2 V at 0.5 C at 25° C. and then stored at 60° C. for 13 weeks. The DCIR of the lithium secondary batteries after storage at high temperature was measured using the same method as in 2-2). The measured DCIR was used as R3.

[0244] The DCIR increase rate after high-temperature storage was calculated according to the following formula.

[0245] DCIR increase rate (%) = {(R3-R1) / R1+1}×100 (%)

[0246] 4-3) Evaluation of thickness increase rate after high-temperature storage

[0247] The secondary batteries of Examples and Comparative Examples were charged to 4.2 V at 0.5 C at 25° C., and the initial thickness T1 of the batteries was measured using a thickness measuring device (Mitutoyo Corporation, 543-490B).

[0248] After that, the secondary batteries of Examples and Comparative Examples were left at high temperature (60° C.) for 13 weeks, and then the thickness T2 of the batteries was measured using a thickness measuring device (Mitutoyo Corporation, 543-490B).

[0249] The thickness increase rate of the battery after high-temperature storage was calculated according to the following formula.

[0250] Battery thickness increase rate (%) = {(T2-T1) / T1+1}×100(%)

[0251] [Table 2]

[0252]

[0253] 1) 45℃ performance: 600 times

[0254] 2) Storage at 60°C: 60°C, SOC 100%, 13 weeks

[0255] [Table 3]

[0256]

[0257] 1) 45℃ performance: 600 times

[0258] 2) Storage at 60°C: 60°C, SOC 100%, 13 weeks

[0259] Referring to Tables 2 and 3, the flame retardant properties, 45°C performance, and high temperature (60°C) storage properties (effect of suppressing thickness increase, effect of suppressing resistance increase, and increase in capacity retention) of the lithium secondary battery of the embodiment are improved compared with the secondary battery of Comparative Example 1.

[0260] On the other hand, the lithium secondary battery of Comparative Example 1, which did not use an additive containing a compound having a specific structure, had a high initial capacity and a low initial resistance. However, after performance measurement at 45°C and storage at high temperature (60°C), the capacity retention rate deteriorated and the resistance further increased. In addition, the thickness of the lithium secondary battery of Comparative Example 1 further increased after storage at high temperature (60°C).

[0261] The above-described contents are merely examples of the application of the principles of the present disclosure, and other configurations may be further included without departing from the scope of the present disclosure.

Claims

1. An electrolyte for a lithium secondary battery, comprising: An additive comprising a compound having a structure represented by the following Chemical Formula 1; organic solvents; and lithium salts, [Chemical Formula 1] In Chemical Formula 1, R 1 for , Ar 1 to Ar 6 Each independently is C6 to C 18 Aryl, C7 to C 19 Alkyl aryl or C6 to C 18 halogenated aryl, L 1 To L 3 Each independently C1 to C 12 Alkylene, C3 to C 12 Cycloalkylene, C6 to C 12 arylene or C3 to C 12 Heteroarylene, When Z is oxygen, n is 0, when Z is nitrogen, n is 1, and when Z is carbon, n is 2.

2. The electrolyte for lithium secondary batteries according to claim 1, wherein Ar 1 to Ar 6 Each independently is C6 to C 12 Aryl, C7 to C 13 Alkyl aryl or C6 to C 12 The halogenated aryl group, L 1 To L 3 Each independently C1 to C 12 of alkylene.

3. The electrolyte for lithium secondary batteries according to claim 1, wherein Ar 1 to Ar 6 Phenyl, L 1 To L 3 Each is independently a C1 to C5 alkylene group.

4. The electrolyte for lithium secondary batteries according to claim 1, wherein The compound having the structure represented by the Chemical Formula 1 includes compounds having structures represented by the following Chemical Formulas 2-1 to 2-3, [Chemical Formula 2-1] [Chemical Formula 2-2] [Chemical formula 2-3] 。 5. The electrolyte for lithium secondary batteries according to claim 1, wherein The organic solvent includes at least one selected from the group consisting of a carbonate-based organic solvent, an ester-based organic solvent, an ether-based organic solvent, a ketone-based organic solvent, and an aprotic organic solvent.

6. The electrolyte for lithium secondary batteries according to claim 1, wherein The organic solvent includes a cyclic carbonate-based solvent and a linear carbonate-based solvent.

7. The electrolyte for lithium secondary batteries according to claim 6, wherein In the organic solvent, a ratio of the volume of the cyclic carbonate-based solvent to the volume of the linear carbonate-based solvent is 1 / 9 to 1.

8. The electrolyte for lithium secondary batteries according to claim 1, wherein The content of the additive is 0.1 wt % to 10 wt % based on the total weight of the electrolyte for lithium secondary batteries.

9. The electrolyte for lithium secondary batteries according to claim 1, wherein The electrolyte for lithium secondary batteries further comprises at least one auxiliary additive selected from the group consisting of fluorine-containing carbonate-based compounds, lithium phosphate-based compounds, sultone-based compounds, and sulfate-based compounds.

10. The electrolyte for lithium secondary batteries according to claim 9, wherein The auxiliary additive may be present in an amount of 0.01 wt % to 10 wt % based on the total weight of the electrolyte for a lithium secondary battery.

11. The electrolyte for lithium secondary batteries according to claim 9, wherein In the electrolyte for lithium secondary batteries, the weight ratio of the auxiliary additive to the additive is 0.1 to 5.

12. The electrolyte for lithium secondary batteries according to claim 9, wherein The fluorine-containing carbonate compound includes fluoroethylene carbonate, The lithium phosphate-based compound includes lithium difluorophosphate, The sultone-based compound includes at least one selected from 1,3-propane sultone, 1,4-butane sultone, ethylene sultone, 1,3-propene sultone, 1,4-butene sultone and 1-methyl-1,3-propene sultone, The sulfate-based compound includes at least one selected from vinyl sulfate, trimethylene sulfate, and methyltrimethylene sulfate.

13. A lithium secondary battery comprising: positive electrode; a negative electrode opposite to the positive electrode; as well as The electrolyte solution for a lithium secondary battery according to claim 1 is used for impregnating the positive electrode and the negative electrode.

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