Electrolyte for lithium secondary battery and lithium secondary battery comprising same

Abstract

An electrolyte for a secondary battery according to the present disclosure comprises: a lithium salt; an organic solvent comprising a solvent represented by chemical formula 1; and a phosphazene-based additive.

Description

Electrolyte for lithium secondary batteries and lithium secondary batteries including the same

[0001] The present disclosure provides an electrolyte for a lithium secondary battery and a lithium secondary battery comprising the same.

[0002]

[0003] Secondary batteries are batteries that can be repeatedly charged and discharged, and are used as power sources for small electronic devices such as mobile phones and laptop PCs.

[0004] In particular, lithium-ion batteries offer high operating voltage, energy density, and charging speed, as well as advantages in terms of weight reduction. Accordingly, lithium-ion batteries are being applied as a power source for electric vehicles as well as small electronic devices.

[0005] In particular, medium-to-large lithium-ion batteries used in electric vehicles (EVs) and energy storage systems (ESS) must be equipped with superior safety features because the risk of fire and explosion is amplified.

[0006] Meanwhile, a lithium secondary battery may include a negative electrode comprising a negative electrode active material (e.g., graphite); a positive electrode comprising a positive electrode active material (e.g., lithium transition metal oxide particles); and a non-aqueous electrolyte comprising a lithium salt and an organic solvent.

[0007] For example, in a lithium secondary battery, charging and discharging can proceed as the process of lithium ions being inserted and extracted from lithium transition metal oxide particles and graphite is repeated.

[0008] For example, the flame retardant performance of a lithium secondary battery can be improved by varying the composition of the electrolyte. For example, while maintaining the electrochemical performance and lifespan of the lithium secondary battery, the flash point of the lithium secondary battery can be improved and a non-flammable effect can be achieved.

[0009]

[0010] One objective of the present disclosure is to provide an electrolyte for a lithium secondary battery that can improve flame retardant performance and stability.

[0011]

[0012] The electrolyte for a lithium secondary battery according to the present disclosure comprises a lithium salt, an organic solvent comprising a solvent represented by Chemical Formula 1, and a phosphazene-based additive.

[0013] [Chemical Formula 1]

[0014]

[0015] In Chemical Formula 1, R1 and R2 may each be a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms; a substituted or unsubstituted alkenyl group having 2 to 10 carbon atoms; or a substituted or unsubstituted alkoxy group having 1 to 10 carbon atoms.

[0016] In some embodiments, at least one of R1 and R2 in Formula 1 is an alkyl group having 1 to 10 carbon atoms or an alkenyl group having 2 to 10 carbon atoms, and the alkyl group or alkenyl group may be substituted or unsubstituted with an alkoxy group having 1 to 10 carbon atoms.

[0017] In some embodiments, R1 and R2 in Formula 1 are each an alkyl group having 1 to 5 carbon atoms or an alkenyl group having 2 to 4 carbon atoms, and the alkyl group or alkenyl group may be substituted or unsubstituted with an alkoxy group having 1 to 5 carbon atoms.

[0018] In some embodiments, the compound represented by Formula 1 may include a compound represented by any one of Formulas 2-1 to 2-3 below.

[0019] [Chemical Formula 2-1]

[0020]

[0021] [Chemical Formula 2-2]

[0022]

[0023] [Chemical Formula 2-3]

[0024]

[0025] In some embodiments, the solvent represented by Formula 1 may be included in an amount of 5 to 40 volume% relative to the total volume of the organic solvent.

[0026] In some embodiments, the phosphazene-based additive may include at least one selected from the group consisting of methoxy(pentafluoro) cyclotriphosphazene, ethoxy(pentafluoro) cyclotriphosphazene, and propoxy(pentafluoro) cyclotriphosphazene.

[0027] In some embodiments, the phosphazene-based additive may be included in an amount of 1 to 10 weight percent relative to the total weight of the electrolyte.

[0028] In some embodiments, the organic solvent may further include sulfolane.

[0029] In some embodiments, the sulfolane may be included in an amount of 1 to 10 volume% relative to the total volume of the organic solvent.

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

[0031] In some embodiments, the organic solvent may further comprise at least one of propylene carbonate (PC) and diethyl carbonate (DEC).

[0032] In some embodiments, the lithium salt may comprise at least one selected from the group consisting of LiPF6, LIBF4, LiFSI, LiTFSI, LISbF6, LiAsF6, LiN(C2F2SO2)2, CF3SO3Li, and LiC(CF3SO2)3.

[0033] In some embodiments, the lithium salt may be included in the organic solvent at a concentration of 0.1 to 2.0 M.

[0034] In some embodiments, an auxiliary additive may be further included, comprising at least one of a fluorine-containing cyclic carbonate compound, a vinyl group-containing cyclic carbonate compound, a vinylene carbonate compound, a cyclic sulfate compound, a sulfone compound, a fluorine-containing lithium phosphate compound, a lithium borate compound, a lactone compound, and a sulfonyl imide compound.

[0035] In some embodiments, the content of the auxiliary additive may be 0.01 to 10 weight percent of the total weight of the electrolyte.

[0036] A lithium secondary battery according to exemplary embodiments may include a positive electrode, a negative electrode facing the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte for the lithium secondary battery.

[0037]

[0038] The electrolyte for a lithium secondary battery according to exemplary embodiments may have improved flame retardant performance by including an organic solvent of Formula 1 and a phosphazene-based additive.

[0039] A lithium secondary battery containing an electrolyte according to exemplary embodiments can have improved flame retardant performance and stability.

[0040]

[0041] FIGS. 1 and FIGS. 2 are a planar perspective view and a cross-sectional view, respectively, schematically illustrating a lithium secondary battery according to exemplary embodiments.

[0042] Figures 3 and 4 are graphs showing the flash points and SET values ​​of the examples and comparative examples.

[0043]

[0044] The electrolyte for a lithium secondary battery according to exemplary embodiments may include a lithium salt, an organic solvent having a specific chemical structure, and a phosphazene-based additive.

[0045] In this specification, "X-type compound" may mean a compound containing an X unit in a parent group, a side group, or a substituent.

[0046] As used herein, the term “substituted or unsubstituted” refers to, for example, a deuterium atom, a halogen atom, a cyano group, a nitro group, an amino group, a silyl group, an oxy group, a thio group, a sulfinyl group, a sulfonyl group, a carbonyl group, an ester group, a boron, a phosphine oxide group, a phosphine sulfide group, an alkyl group (for example, C1-C 60 , C1-C 10 alkyl groups), alkenyl groups (e.g., C2-C 60 , C2-C 10 alkenyl group), alkenyl group (e.g., C2-C 60 , C2-C 10 alkynyl group), alkoxy group (e.g., C1-C 60 , C1-C 10 alkoxy groups), hydrocarbon ring groups, aryl groups (e.g., C6-C 60 aryl group), heterocyclic group (e.g., C1-C 60 It may refer to one that is substituted or unsubstituted with one or more substituents selected from the group consisting of heterocyclic groups. For example, "substituted alkyl group" may refer to one in which at least one of the hydrogen atoms of the alkyl group is substituted with the substituent described above, thereby further bonding a substituent to a carbon atom of the alkyl group.

[0047] The above substituent may include a combination selected from the groups described above. For example, at least one of the hydrogen atoms, such as alkyl groups and aryl groups included as substituents, may be substituted with a deuterium atom, a halogen atom, a cyano group, a nitro group, an amino group, a silyl group, an oxy group, a thio group, a sulfinyl group, a sulfonyl group, a carbonyl group, an ester group, a boron, a phosphine oxide group, a phosphine sulfide group, an alkyl group, an alkenyl group, an alkynyl group, a hydrocarbon ring group, an aryl group, or a heterocyclic group.

[0048] Among the above substituents, multivalent substituents such as amino groups, phosphine sulfide groups, phosphine oxide groups, sulfinyl groups, sulfonyl groups, sulfanyl groups, oxy groups, carbonyl groups, and ester groups are C1-C 10 alkyl group of, C1-C 10 alkenyl group of, C1-C 10 It can be substituted with an alkynyl group or an aryl group having 6 to 10 carbon atoms.

[0049] In the term "substituted or unsubstituted Y group having carbon a to b" as used in this specification, carbon a to b refers to the number of carbons in the Y group in an unsubstituted state and does not include the number of carbons in the substituent.

[0050] An alkyl group refers to a monovalent hydrocarbon group from which one hydrogen atom has been removed from a straight-chain or branched-chain hydrocarbon group. For example, the alkyl group may include a methyl group, an ethyl group, a propyl group, a sec-butyl group, a tert-butyl group, an iso-butyl group, a pentyl group, a neopentyl group, a 2-ethylbutyl group, a 3,3-dimethylbutyl group, a hexyl group, a heptyl group, an octyl group, etc.

[0051] An alkenyl group refers to a monovalent unsaturated hydrocarbon group containing a carbon-carbon double bond from which one hydrogen atom has been removed from a straight-chain or branched-chain hydrocarbon group, and for example, the alkenyl group may include an ethenyl group (vinyl group), a propenyl group, a 1-butenyl group, a 2-butenyl group, a pentenyl group, a neopentenyl group, a hexenyl group, a 2-methylpropenyl group, a 3-methylbutenyl group, a 3,3-dimethylpentenyl group, etc.

[0052] The alkoxy group has a structure in which an oxygen atom is bonded to a monovalent hydrocarbon group from which one hydrogen atom has been removed from a straight or branched hydrocarbon group, and for example, the alkoxy group may include a methoxy group (-OCH₃), an ethoxy group (-OCH₂CH₃), a propoxy group (-OCH₂CH₂CH₃), an iso-propoxy group (-OCH(CH3)2), a sec-butoxy group (-OCH(CH₃)CH₂CH₃), a tert-butoxy group (-OC(CH₃)₃), a pentoxy group (-OCH₂(CH₂)₂CH₃), a neopentoxy group (-OCH₂C(CH₃)₃), etc. In addition, the alkoxy group may be bonded to a monovalent unsaturated hydrocarbon group in which an oxygen atom contains a carbon-carbon double bond, and may include, for example, an ethenooxy group (-OCH=CH2), a propenooxy group (-OCH=CHCH3), a 1-butenooxy group (-OCH=CH(CH2)2CH3), a phenyloxy group (-OC6H5), a hexenooxy group (-OCH=CH(CH2)3CH3), etc.

[0053] An electrolyte for a lithium secondary battery according to exemplary embodiments (hereinafter abbreviated as electrolyte) comprises an organic solvent, and the organic solvent may comprise a solvent represented by the following chemical formula 1.

[0054] [Chemical Formula 1]

[0055]

[0056] In Chemical Formula 1, R1 and R2 may each be a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms; a substituted or unsubstituted alkenyl group having 2 to 10 carbon atoms; or a substituted or unsubstituted alkoxy group having 1 to 10 carbon atoms.

[0057] In some embodiments, at least one of R1 and R2 in Formula 1 is an alkyl group having 1 to 10 carbon atoms or an alkenyl group having 2 to 10 carbon atoms, and the alkyl group or alkenyl group may be substituted or unsubstituted with an alkoxy group having 1 to 10 carbon atoms.

[0058] In some embodiments, R1 and R2 in Formula 1 are each an alkyl group having 1 to 5 carbon atoms or an alkenyl group having 2 to 4 carbon atoms, and the alkyl group or alkenyl group may be substituted or unsubstituted with an alkoxy group having 1 to 5 carbon atoms.

[0059] In some embodiments, the compound represented by Formula 1 may include a compound represented by any one of Formulas 2-1 to 2-3 below.

[0060] [Chemical Formula 2-1]

[0061]

[0062] [Chemical Formula 2-2]

[0063]

[0064] [Chemical Formula 2-3]

[0065]

[0066] In some embodiments, the flash point of the electrolyte for a lithium secondary battery may be raised by an organic solvent containing the solvent represented by Chemical Formula 1. Accordingly, the flame retardant performance and thermal stability of the lithium secondary battery may be improved.

[0067] In some embodiments, the solvent represented by Formula 1 may be included in an amount of 5 to 40 volume% relative to the total volume of the organic solvent. Within this range, the effect of raising the flash point of the electrolyte for a lithium secondary battery may be enhanced, and the flame retardant performance and thermal stability of the lithium secondary battery may be further improved.

[0068] The electrolyte for a lithium secondary battery according to exemplary embodiments may include a phosphazene-based additive.

[0069] In some embodiments, the phosphazene-based additive may include at least one selected from the group consisting of methoxy(pentafluoro) cyclotriphosphazene, ethoxy(pentafluoro) cyclotriphosphazene, and propoxy(pentafluoro) cyclotriphosphazene.

[0070] In some embodiments, when the above-mentioned phosphazene-based additive is included, the flash point of the electrolyte for a lithium secondary battery may be increased and the SET (Self-extinguishing time) characteristics may be improved, and the electrolyte for a lithium secondary battery may have non-flammable performance. Accordingly, the flame-retardant performance and thermal stability of the lithium secondary battery may be improved.

[0071] In some embodiments, when the solvent represented by Chemical Formula 1 and the phosphazene-based additive are used together, the effects of increasing the flash point and improving SET characteristics may be further enhanced.

[0072] In some embodiments, the phosphazene-based additive may be included in an amount of 1 to 10 weight percent relative to the total weight of the electrolyte. Within this range, the effects of increasing the flash point and improving the SET of the electrolyte for a lithium secondary battery may be further enhanced, and the non-flammability performance of the electrolyte for a lithium secondary battery may be further improved.

[0073] In some embodiments, the electrolyte may further include sulfolane. In this case, the effect of increasing the flash point and improving the SET of the electrolyte for a lithium secondary battery may be enhanced, and accordingly, the flame retardant performance and thermal stability of the lithium secondary battery may be improved.

[0074] In some embodiments, the sulfolane may be included in an amount of 1 to 10 volume% relative to the total volume of the organic solvent. Within this range, the effects of increasing the flash point and improving the SET of the electrolyte for a lithium secondary battery may be further enhanced, and the performance of viscosity and conductivity may also be improved.

[0075] In some embodiments, the organic solvent may include at least one selected from the group consisting of carbonate-based organic solvents, ester-based organic solvents, ether-based organic solvents, ketone-based organic solvents, alcohol-based organic solvents, and aprotic organic solvents.

[0076] 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.

[0077] For example, the above linear carbonate-based solvent may include dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, etc.

[0078] For example, the above-mentioned cyclic carbonate-based solvent may include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, etc.

[0079] In some embodiments, the organic solvent may contain more of the linear carbonate-based solvent than the cyclic carbonate-based solvent by volume.

[0080] In some embodiments, the ratio of the volume of the cyclic carbonate-based solvent to the volume of the linear carbonate-based solvent among the organic solvents may be 1 / 9 to 1. For example, the volume ratio may be 1 / 9 to 1, 1 / 9 to 2 / 3, 1 / 6 to 2 / 3, or 1 / 4 to 2 / 3. Within this range, the high-temperature storage performance of the lithium secondary battery may be further improved.

[0081] 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.

[0082] 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.

[0083] For example, the above ketone-based solvent may include cyclohexanone, etc.

[0084] For example, the above alcohol-based solvent may include at least one of ethyl alcohol and isopropyl alcohol.

[0085] 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.

[0086] In some embodiments, the organic solvent may further include at least one of propylene carbonate (PC) and diethyl carbonate (DEC). As the content of the solvent represented by Formula 1 increases in the electrolyte for a lithium secondary battery, there is an effect of raising the flash point, but disadvantages such as increased viscosity and decreased conductivity appear. In this case, if at least one of propylene carbonate and diethyl carbonate is further included, an effect of improving viscosity and conductivity can be achieved while maintaining the effect of raising the flash point.

[0087] The electrolyte for a lithium secondary battery according to exemplary embodiments may include a lithium salt.

[0088] The above lithium salt is Li + X - It is expressed as, for example, the anion (X) of the above lithium salt - As 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 - Examples of the back can be given.

[0089] In some embodiments, the lithium salt may comprise at least one selected from the group consisting of LiPF6, LIBF4, LiFSI, LiTFSI, LISbF6, LiAsF6, LiN(C2F2SO2)2, CF3SO3Li, and LiC(CF3SO2)3.

[0090] In some embodiments, the lithium salt may comprise at least one selected from the group consisting of LiPF6, LiFSI, and LiTFSI.

[0091] In some embodiments, the lithium salt may be included in the organic solvent at a concentration of 0.1 to 2.0 M.

[0092] The electrolyte for a lithium secondary battery according to exemplary embodiments may further include an auxiliary additive comprising at least one of a fluorine-containing cyclic carbonate compound, a vinyl group-containing cyclic carbonate compound, a vinylene carbonate compound, a cyclic sulfate compound, a sulfone compound, a fluorine-containing lithium phosphate compound, a lithium borate compound, a lactone compound, and a sulfonylimide compound.

[0093] When the above auxiliary additive is further included, a lithium secondary battery with improved flame retardant performance and enhanced stability can be efficiently implemented.

[0094] For example, the above fluorine-containing carbonate compound may include a fluorine atom or a substituent (e.g., a fluorine-substituted alkyl group such as -CF3) bonded to at least one carbon atom of the carbonate compound.

[0095] In some embodiments, the fluorine-containing carbonate compound may include a fluorine-containing cyclic carbonate compound having a cyclic structure. For example, the fluorine-containing cyclic carbonate compound may have a 5- to 7-membered cyclic structure.

[0096] For example, the above fluorine-containing cyclic carbonate compound may include fluoroethylene carbonate (FEC), etc.

[0097] For example, the above lithium phosphate-based compound may include lithium difluoro bis-oxalato phosphate, lithium difluoro phosphate, etc.

[0098] In some embodiments, the sulfonate compound may include at least one selected from the group consisting of alkyl sulfonate compounds and alkenyl sulfonate compounds.

[0099] In some embodiments, the sulfonate compound may include an alkyl sulfonate compound and an alkenyl sulfonate compound together.

[0100] For example, the above alkyl sulfone compounds may include 1,3-propane sultone (PS) and 1,4-butane sultone, etc.

[0101] For example, the above alkenyl sultone compounds may include ethene sultone, 1,3-propene sultone (PRS), 1,4-butene sultone, and 1-methyl-1,3-propene sultone.

[0102] For example, the above borate-based compound may include lithium bis(oxalate) borate, etc.

[0103] In some embodiments, the sulfate compound may include a cyclic sulfate compound having a cyclic structure. The cyclic sulfate compound may have a 5-7-membered cyclic structure.

[0104] For example, the above-mentioned cyclic sulfate compounds may include 1,2-ethylene sulfate (ESA), trimethylene sulfate (TMS), 1,2-propylene sulfate (1,2-propylene sulfate), and methyltrimethylene sulfate (MTMS).

[0105] In some embodiments, the sulfite compound may include a cyclic sulfite compound having a cyclic structure.

[0106] For example, the above-mentioned cyclic sulfite compounds may include ethylene sulfite, butylene sulfite, etc.

[0107] In some embodiments, the content of the auxiliary additive may be 0.01 to 10 weight percent of the total weight of the electrolyte. Within this range, the flame retardant performance and stability of the lithium secondary battery may be further improved.

[0108] A lithium secondary battery according to exemplary embodiments comprises a positive electrode, a negative electrode facing the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte for the lithium secondary battery.

[0109] Hereinafter, a lithium secondary battery according to exemplary embodiments will be described in more detail with reference to the drawings. FIGS. 1 and 2 are a schematic plan perspective view and a cross-sectional view, respectively, showing a lithium secondary battery according to exemplary embodiments.

[0110] 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).

[0111] 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).

[0112] For example, the positive active material layer (110) may include a positive active material. Additionally, the positive active material layer (110) may further include a positive binder and a conductive material.

[0113] For example, the anode (100) can be manufactured by mixing and stirring an anode active material, an anode binder, a conductive material, a dispersion medium, etc. to produce an anode slurry, and then applying, drying, and rolling the anode slurry onto an anode current collector (105).

[0114] For example, the positive current collector (105) may include stainless steel, nickel, aluminum, titanium, copper, or an alloy thereof.

[0115] For example, the positive electrode active material may include lithium transition metal oxide particles or lithium iron phosphate compound particles capable of reversible insertion and extraction of lithium ions.

[0116] In one embodiment, the lithium transition metal oxide particles may contain nickel, cobalt, manganese, aluminum, etc.

[0117] In some embodiments, the lithium transition metal oxide particles contain nickel, and the nickel content among the lithium transition metal oxide particles may be 80 mol% or more of the total elements excluding lithium and oxygen.

[0118] In some embodiments, the lithium transition metal oxide particles may be represented by LiNiO2, LiCoO2, LiMnO2, LiMn2O4, or the following chemical formula 2.

[0119] [Chemical Formula 2]

[0120] Li x Ni (1-a-b) Co a M b O y

[0121] In Chemical Formula 2, M is at least one of Al, Zr, Ti, Cr, B, Mg, Mn, Ba, Si, Y, W, and Sr, and 0.9≤x≤1.2, 1.9≤y≤2.1, and 0≤a+b≤0.5.

[0122] In Chemical Formula 2, 0 <a+b≤0.4, 0<a+b≤0.3, 0<a+b≤0.2 또는 0<a+b≤0.1을 만족할 수 있다.

[0123] In some embodiments, the lithium iron phosphate particles may include a compound represented by the following chemical formula 3.

[0124] [Chemical Formula 3]

[0125] Li x Fe 1-y M y (PO 4-z )X z

[0126] In Chemical Formula 3, M may include at least one element selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y. For example, M may include Al, Mg, Co, or Mn.

[0127] In Chemical Formula 3, X may include at least one element selected from the group consisting of F, S, and N. For example, X may include F.

[0128] In Chemical Formula 3, 0.5≤x≤1.5, 0≤y≤0.1, and 0≤z≤0.5. In some embodiments, 0.8≤x≤1.2, 0≤y≤0.05, and 0≤z≤0.1.

[0129] In some embodiments, the lithium iron phosphate may include LiFePO4 with an olivine crystal structure.

[0130] For example, the anode binder may include organic binders such as polyvinylidenefluoride (PVDF), vinylidenefluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyacrylonitrile, and polymethylmethacrylate; and water-based binders such as styrene-butadiene rubber (SBR). Additionally, for example, the anode binder may be used together with a thickener such as carboxymethyl cellulose (CMC).

[0131] For example, the conductive material may include carbon-based conductive materials such as graphite, carbon black, graphene, and carbon nanotubes; and metal-based conductive materials such as perovskite materials such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3.

[0132] The cathode (130) may include a cathode current collector (125) and a cathode active material layer (120) on the cathode current collector (125).

[0133] For example, the negative electrode active material layer (120) may include a negative electrode active material, a negative electrode binder and a conductive material as needed.

[0134] For example, the cathode (130) can be manufactured by mixing and stirring a cathode active material, a cathode binder, a conductive material, a solvent, etc. to produce a cathode slurry, and then applying, drying, and rolling the cathode slurry onto a cathode current collector (125).

[0135] For example, the negative current collector (125) may include gold, stainless steel, nickel, aluminum, titanium, copper, or an alloy thereof, and preferably may include copper or a copper alloy.

[0136] For example, the above-mentioned negative electrode active material may be a material capable of absorbing and extracting lithium ions. For example, the above-mentioned negative electrode active material may include a lithium alloy, a carbon-based active material, a silicon-based active material, etc.

[0137] For example, the lithium alloy may include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, indium, etc.

[0138] For example, the carbon-based active material may include crystalline carbon, amorphous carbon, carbon composites, carbon fibers, etc.

[0139] For example, the amorphous carbon may include hard carbon, coke, mesocarbon microbeads (MCMB) calcined at 1500°C or lower, mesophase pitch-based carbon fiber (MPCF), etc. For example, the crystalline carbon may include natural graphite, artificial graphite, graphitized coke, graphitized MCMB, graphitized MPCF, etc.

[0140] In one embodiment, the negative electrode active material may include a silicon-based active material. For example, the silicon-based active material may be Si, SiO x (0 <x<2), Si / C, SiO / C, Si-Metal 등을 포함할 수 있다.

[0141] The above-described cathode binder and conductive material may be materials substantially identical or similar to the anode binder and conductive material described above. For example, the cathode binder may be a water-based binder such as styrene-butadiene rubber (SBR). Additionally, for example, the cathode binder may be used together with a thickener such as carboxymethyl cellulose (CMC).

[0142] In one embodiment, a separator (140) may be interposed between the anode (100) and the cathode (130).

[0143] In some embodiments, the area of ​​the negative electrode (130) may be larger than the area of ​​the positive electrode (100). In this case, lithium ions generated from the positive electrode (100) can move smoothly to the negative electrode (130) without precipitating in the middle.

[0144] For example, 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. Additionally, for example, the separator (140) may include a nonwoven fabric formed of high-melting-point glass fibers, polyethylene terephthalate fibers, etc.

[0145] For example, an electrode cell may be formed including an anode (100), a cathode (130), and a separator (140).

[0146] For example, a plurality of electrode cells may be stacked to form an electrode assembly (150) (however, for convenience, only one unit cell is shown in FIG. 2).

[0147] For example, an electrode assembly (150) can be formed by winding, lamination, zigzag-folding, etc. of a separator (140).

[0148] A lithium secondary battery according to exemplary embodiments may include a positive electrode lead (107) connected to a positive electrode (100) and protruding outside of a case (160); and a negative electrode lead (127) connected to a negative electrode (130) and protruding outside of a case (160).

[0149] For example, the positive electrode (100) and the positive electrode lead (107) may be electrically connected. Likewise, the negative electrode (130) and the negative electrode lead (127) may be electrically connected.

[0150] For example, the positive lead (107) can be electrically connected to the positive current collector (105). Additionally, the negative lead (130) can be electrically connected to the negative current collector (125).

[0151] For example, the positive current collector (105) may include a protrusion (positive tab, 106) on one side. A positive active material layer (110) may not be formed on the positive tab (106). The positive tab (106) may be integral with the positive current collector (105) or connected by welding or the like. The positive current collector (105) and the positive lead (107) may be electrically connected through the positive tab (106).

[0152] Likewise, the negative current collector (125) may include a protrusion (negative tab, 126) on one side. A negative active material layer (120) may not be formed on the negative tab. The negative tab (126) may be integral with the negative current collector (125) or connected by welding or the like. The negative current collector (125) and the negative lead (127) may be electrically connected through the negative tab (126).

[0153] In one embodiment, the electrode assembly (150) may include a plurality of positive electrodes and a plurality of negative electrodes. For example, the plurality of positive electrodes and the plurality of negative electrodes may be arranged alternately with respect to each other, and a separator may be interposed between the positive electrodes and the negative electrodes. Accordingly, a lithium secondary battery according to one embodiment of the present invention may include a plurality of positive electrode tabs and a plurality of negative electrode tabs protruding from each of the plurality of positive electrodes and the plurality of negative electrodes.

[0154] In one embodiment, the positive tabs (or negative tabs) may be laminated, pressed, and welded to form a positive tab laminate (or negative tab laminate). The positive tab laminate may be electrically connected to a positive lead (107). Additionally, the negative tab laminate may be electrically connected to a negative lead (127).

[0155] For example, the electrode assembly (150) and the above-described electrolyte can be housed together in a case (160) to form a lithium secondary battery.

[0156] The above lithium secondary battery can be manufactured in, for example, cylindrical, prismatic, pouch, or coin types.

[0157] In the following, embodiments of the present invention are further described with reference to specific experimental examples. The embodiments and comparative examples included in the experimental examples are merely illustrative of the present 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 present invention, and that such variations and modifications fall within the scope of the appended claims.

[0158]

[0159] Example 1

[0160] (1) Electrolyte preparation

[0161] 0.2M LiFSI and 0.8M LiPF6 solutions were prepared by dissolving LiFSI and LiPF6 in a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), sulfolane (SFL), and Bis(2-methoxyethyl) carbonate (BMEC) mixed in a ratio of 25:63:2:10 (v / v).

[0162] To the above solution, 7 wt% of Ethoxy(pentafluoro)cyclotriphosphazene (PFPN) was added as an additive, and 0.5 wt% of vinylene carbonate (VC) and 1 wt% of fluoroethylene carbonate (FEC) were added as auxiliary additives to prepare an electrolyte for a lithium secondary battery.

[0163] (2) Lithium secondary battery manufacturing

[0164] An anode slurry was prepared by dispersing Li(Ni0.8Co0.1Mn0.1)O2, polyvinylidene fluoride (PVdF), and carbon black in N-methyl-2-pyrrolidone (NMP) in a weight ratio of 92:4:4.

[0165] The above anode slurry was applied onto an aluminum foil (thickness: 20 μm) having a protrusion on one side (hereinafter, anode tab) (excluding the protrusion portion), and an anode was manufactured by drying and rolling.

[0166] A cathode slurry was prepared by dispersing crystalline artificial graphite, acetylene black, and PVDF in NMP in a weight ratio of 92:1:7.

[0167] The above cathode slurry was applied onto a copper foil (thickness: 15 μm) having a protrusion on one side (hereinafter, cathode tab) (excluding the protrusion portion), and the cathode was manufactured by drying and rolling.

[0168] A cell was formed by interposing a polyethylene separator (thickness: 20 μm) between the anode and the cathode. An anode lead and a cathode lead were welded and connected to the anode tab and the cathode tab, respectively.

[0169] The cell was housed inside a pouch such that a portion of the positive lead and the negative lead were exposed to the outside. The electrolyte described above was injected into the pouch, and the pouch was sealed to manufacture a lithium secondary battery.

[0170] (3) Mars charging and discharging

[0171] The lithium secondary batteries of the examples and comparative examples were subjected to a phosphating charge / discharge (charge / discharge conditions: charged in 0.2C CC / CV mode (4.2V, 0.05C cut-off) and then discharged in 0.2C CC mode (2.5V cut-off), and a standard charge / discharge (charge / discharge conditions: charged in 0.5C CC / CV mode (4.2V, 0.05C cut-off), then discharged in 0.5C CC mode (2.5V cut-off), and then charged in 0.5C CC / CV mode (4.2V, 0.05C cut-off). After that, 1C CC / CV charging (4.2V CUT-OFF) was performed.

[0172]

[0173] Examples and Comparative Examples

[0174] Except for adjusting the electrolyte composition as shown in Table 1 below, an electrolyte for a lithium secondary battery and a lithium secondary battery were prepared in the same manner as in Example 1.

[0175]

[0176] Lithium salt (mol / L) Organic solvent (v / v) PFPN Additive (wg%) Auxiliary additive (wg%) LiFSILiPF6VCFEC Example 1 0.20.8EC / EMC / SFL / BMEC(25 / 63 / 2 / 10)70.51.0 Example 20.20.8EC / EMC / SFL / BMEC(25 / 58 / 2 / 15)70.51.0 Example 3 0.20.8EC / EMC / SFL / BMEC(25 / 53 / 2 / 20)70.51.0 Example 4 0.20.8EC / EMC / SFL / BMEC(25 / 43 / 2 / 30)70.51.0 Example 5 0.20.8EC / EMC / DEC / SFL / BMEC(25 / 53 / 10 / 2 / 10)70.51.0 Example 60.20.8EC / EMC / PC / SFL / BMEC(25 / 53 / 10 / 2 / 10)70.51.0 Example 70.20.8EC / EMC / SFL / BMEC(25 / 63 / 2 / 10)40.51.0 Example 80.20.8EC / EMC / BMEC(25 / 65 / 10)70.51.0 Comparative Example 1-1.0EC / EMC / BMEC(25 / 65 / 10)-0.51.0 Comparative Example 20.20.8EC / EMC / SFL(25 / 73 / 2)70.51.0 Comparative Example 30.20.8EC / EMC / SFL / BMEC(25 / 63 / 2 / 10)-0.51.0 Comparative Example 40.20.8EC / EMC / BMEC(25 / 65 / 10)-0.51.0 Comparative Example 50.20.8EC / EMC / SFL / BMEC(25 / 60 / 5 / 10)-0.51.0 Comparative Example 60.20.8EC / EMC / SFL / BMEC(25 / 58 / 7 / 10)-0.51.0

[0177] The components listed in Table 1 are as follows.

[0178] LiFSI: Lithium bis(fluorosulfonyl)imide)

[0179] LiPF6: Lithium hexafluorophosphate

[0180] EC: Ethylene Carbonate

[0181] EMC: Ethyl Methyl Carbonate

[0182] SFL: Sulfolane

[0183] BMEC: Bis(2-methoxyethyl) carbonate

[0184] DEC: Diethyl Carbonate

[0185] PC: Propylene Carbonate

[0186] PFPN: Ethoxy(pentafluoro)cyclotriphosphazene

[0187] VC: vinylene carbonate

[0188] FEC: Fluoroethylene Carbonate

[0189]

[0190] Experimental Example

[0191] The physical properties of the electrolytes and batteries of the examples and comparative examples were evaluated by the following method, and the results are shown in Table 2, Figure 3, and Figure 4.

[0192]

[0193] (1) Flash point measurement

[0194] For the electrolytes of the examples and comparative examples, the flash point was measured using the automatic flash point meter (ATG-8AFC) of Tanaka Scientific by applying the tag-closed flash point measurement method of KS M 2010.

[0195] (2) SET measurement

[0196] SET represents the time from when the electrolyte ignites until it is extinguished, and a value that takes into account the weight of the electrolyte is used. After adding 0.5g of electrolyte to the measuring container, the time from ignition until extinguishing was recorded, and the self-extinguishing time (self-extinguishing time (second, s), SET) was measured as the average value obtained from 5 measurements.

[0197] (3) Viscosity measurement

[0198] The viscosity of the electrolytes of the examples and comparative examples was measured at 25°C using a BROOLFIELD DV2T.

[0199] (4) Measurement of electrical conductivity

[0200] The electrical conductivity of the electrolytes of the examples and comparative examples was measured at 25°C using a Mettler-Toledo SD30.

[0201]

[0202] Flash Point (°C) SET (sec / g) Viscosity (cP) Electrical Conductivity (mS / cm) Non-flammability Example 1 40.0 -4.0 56.68 Non-flammable Example 2 47.0 -4.3 36.35 Non-flammable Example 35 3.0 -5.7 85.22 Non-flammable Example 4 65.0 -5.8 85.17 Non-flammable Example 5 42.0 -4.1 16.27 Non-flammable Example 6 50.0 -4.4 86.58 Non-flammable Example 7 38.5 -4.0 56.68 Non-flammable Example 8 38.5 -4.0 36.72 Non-flammable Comparative Example 1 26.5 13.23 3.4 0 6.09 - Comparative Example 2 33.5 -3.4 0 7.45 Non-flammable Comparative Example 327.0983.129.10-Comparative Example 427.01253.427.24-Comparative Example 527.51153.857.98-Comparative Example 628.01123.987.54-

[0203] Referring to Tables 1 and 2, and Figures 3 and 4 above, Examples 1 to 7, which contain all of SFL, BMEC, and PFPN, showed an increase in the flash point of the electrolyte and an improvement in SET characteristics compared to Comparative Example 3, which contains only SFL and BMEC. When comparing Comparative Example 4, which contains only BMEC, with Comparative Examples 3, 5, and 6, which contain BMEC and SFL, it can be seen that there is almost no effect of increasing the flash point and improving SET characteristics with increasing SFL content. On the other hand, it can be seen that when PFPN is included, as in Example 1, an effect of increasing the flash point and improving SET characteristics appears.

[0204] When comparing Examples 1 to 4, which contain all of SFL, BMEC, and PFPN, with Comparative Example 2, which contains only SFL and PFPN, it can be confirmed that an increase in flash point occurs as the BMEC content increases.

[0205] At this time, when DEC or PC is additionally included in the organic solvent as in Examples 5 and 6, it can be confirmed that viscosity and electrical conductivity are improved while the effect of raising the flash point is maintained.

[0206] The above description is merely an example of applying the principles of the present disclosure, and other configurations may be included without departing from the scope of the present invention.

[0207]

[0208] [Explanation of the symbol]

[0209] 100: Anode

[0210] 105: Positive current collector

[0211] 106: Positive tab

[0212] 107: Positive lead

[0213] 110: Positive active material layer

[0214] 120: Cathode active material layer

[0215] 125: Cathode current collector

[0216] 126: Cathode tab

[0217] 127: Cathode lead

[0218] 130: Cathode

[0219] 140: Separator

[0220] 150: Electrode assembly

[0221] 160: Case

Claims

Lithium salt; An organic solvent comprising a solvent represented by the following chemical formula 1; and Electrolyte for lithium secondary batteries containing phosphazene-based additives: [Chemical Formula 1] (In Chemical Formula 1, R1 and R2 are each a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms; a substituted or unsubstituted alkenyl group having 2 to 10 carbon atoms; or a substituted or unsubstituted alkoxy group having 1 to 10 carbon atoms). An electrolyte for a lithium secondary battery according to claim 1, wherein at least one of R1 and R2 in Formula 1 is an alkyl group having 1 to 10 carbon atoms or an alkenyl group having 2 to 10 carbon atoms, and said alkyl group or alkenyl group is substituted or unsubstituted with an alkoxy group having 1 to 10 carbon atoms. An electrolyte for a lithium secondary battery according to claim 1, wherein R1 and R2 in Formula 1 are each an alkyl group having 1 to 5 carbon atoms or an alkenyl group having 2 to 4 carbon atoms, and said alkyl group or alkenyl group is substituted or unsubstituted with an alkoxy group having 1 to 5 carbon atoms. An electrolyte for a lithium secondary battery according to claim 1, wherein the first additive represented by Formula 1 comprises a compound represented by any one of Formulas 2-1 to 2-3 below: [Chemical Formula 2-1] [Chemical Formula 2-2] [Chemical Formula 2-3] An electrolyte for a lithium secondary battery according to claim 1, comprising 5 to 40 volume% of a solvent represented by Formula 1 relative to the total volume of the organic solvent. An electrolyte for a lithium secondary battery according to claim 1, wherein the phosphazene-based additive comprises at least one selected from the group consisting of methoxy(pentafluoro) cyclotriphosphazene, ethoxy(pentafluoro) cyclotriphosphazene, and propoxy(pentafluoro) cyclotriphosphazene. An electrolyte for a lithium secondary battery according to claim 1, comprising the phosphazene-based additive in an amount of 1 to 10 weight% relative to the total weight of the electrolyte. An electrolyte for a lithium secondary battery according to claim 1, further comprising sulfolane. An electrolyte for a lithium secondary battery according to claim 8, comprising 1 to 10 volume% of the sulfolane relative to the total volume of the organic solvent. An electrolyte for a lithium secondary battery according to claim 1, wherein the organic solvent comprises 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, an alcohol-based organic solvent, and an aprotic organic solvent. An electrolyte for a lithium secondary battery according to claim 10, wherein the organic solvent comprises at least one of propylene carbonate (PC) and diethyl carbonate (DEC). The electrolyte for a lithium secondary battery according to claim 1, wherein the lithium salt comprises at least one selected from the group consisting of LiPF6, LIBF4, LiFSI, LiTFSI, LISbF6, LiAsF6, LiN(C2F2SO2)2, CF3SO3Li, and LiC(CF3SO2)3. An electrolyte for a lithium secondary battery according to claim 12, wherein the lithium salt is contained in the organic solvent at a concentration of 0.1 to 2.0 M. An electrolyte for a lithium secondary battery according to claim 1, further comprising an auxiliary additive comprising at least one of a fluorine-containing cyclic carbonate-based compound, a vinyl group-containing cyclic carbonate-based compound, a vinylene carbonate-based compound, a cyclic sulfate-based compound, a sulfone-based compound, a fluorine-containing lithium phosphate-based compound, a lithium borate-based compound, a lactone-based compound, and a sulfonyl imide-based compound. An electrolyte for a lithium secondary battery according to claim 14, wherein the content of the auxiliary additive is 0.01 to 10 weight% of the total weight of the electrolyte. anode; A negative electrode facing the above positive electrode; A separator interposed between the anode and the cathode; and A lithium secondary battery comprising an electrolyte for a lithium secondary battery according to claim 1.

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