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

Abstract

The electrolyte for a lithium secondary battery according to exemplary embodiments may include an organic solvent, a lithium salt, and an additive comprising a compound represented by a specific chemical formula.

Description

Technology Field

[0001] The present invention relates to an electrolyte for a lithium secondary battery and a lithium secondary battery comprising the same. More specifically, the invention relates to an electrolyte for a lithium secondary battery comprising an organic solvent, a lithium salt, and an additive, and a lithium secondary battery comprising the same. Background Technology

[0002] Rechargeable batteries are batteries capable of repeated charging and discharging, and are widely used as power sources for portable electronic devices such as mobile phones and laptop PCs.

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

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

[0005] A lithium secondary battery may further include, for example, an outer casing 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 by, for example, applying, drying, and rolling a positive electrode slurry comprising a positive electrode active material, a binder, and, if necessary, a conductive material, onto a positive electrode current collector.

[0007] The above-mentioned positive electrode active material may be a material capable of reversible insertion and extraction of lithium ions. For example, the above-mentioned positive electrode active material may be a lithium metal oxide containing metal elements such as nickel (Ni), cobalt (Co), and manganese (Mn).

[0008] Meanwhile, as the application range of lithium-ion batteries expands, there is a growing demand for superior lifespan characteristics, high capacity, and operational stability. Accordingly, there is a need to develop lithium-ion batteries that provide uniform output and capacity even during repeated charging and discharging cycles.

[0009] However, during repeated charging and discharging, for example, the output and capacity may decrease due to surface damage of the nickel-based lithium metal oxide, and side reactions between the nickel-based lithium metal oxide and the electrolyte may occur.

[0010] Korean Published Patent Application No. 10-2019-0119615 discloses a method for improving battery characteristics by adding an additive to an electrolyte for a lithium secondary battery. Prior art literature

[0011] Korean Published Patent Application No. 10-2019-0119615 The problem to be solved

[0012] One objective of the present invention is to provide an electrolyte for a lithium secondary battery that can impart superior chemical stability to the lithium secondary battery.

[0013] One objective of the present invention is to provide a lithium secondary battery having excellent chemical stability. means of solving the problem

[0014] An electrolyte for a lithium secondary battery according to exemplary embodiments may comprise an organic solvent; a lithium salt; and an additive comprising a compound represented by the following chemical formula 1.

[0015] [Chemical Formula 1]

[0016]

[0017] In Formula 1, R1 and R2 are each independently hydrogen, a substituted or unsubstituted C1-C10 alkyl group, a substituted or unsubstituted C2-C10 alkenyl group, a substituted or unsubstituted C2-C10 alkynyl group, a substituted or unsubstituted C5-C12 cycloalkyl group, a substituted or unsubstituted C5-C12 cycloalkenyl group, a substituted or unsubstituted 5-7 member heterocycloalkyl group, a substituted or unsubstituted 5-7 member heterocycloalkenyl group, a substituted or unsubstituted C6-C12 aryl group, or a substituted or unsubstituted 5-7 member heteroaryl group, and R1 and R2 may be connected to each other to form a substituted or unsubstituted 5-7 member heterocycloalkyl group, a substituted or unsubstituted 5-7 member heterocycloalkenyl group, or a substituted or unsubstituted 5-7 member heteroaryl group.

[0018] In one embodiment, R1 and R2 may each independently be a substituted or unsubstituted C1-C10 alkyl group, a substituted or unsubstituted C2-C10 alkenyl group, a substituted or unsubstituted C5-C12 cycloalkyl group, or a substituted or unsubstituted C5-C12 cycloalkenyl group.

[0019] In one embodiment, R1 and R2 may each be independently substituted or unsubstituted C1-C10 alkyl groups.

[0020] In one embodiment, the electrolyte further comprises an auxiliary additive, and the auxiliary additive may include at least one of a fluorine-containing carbonate-based compound, a vinylidene carbonate-based compound, a lithium phosphate-based compound, a sulfone-based compound, a sulfate-based compound, a borate-based compound, a nitrile-based compound, an amine-based compound, a silane-based compound, and a benzene-based compound.

[0021] In one embodiment, the electrolyte further comprises an auxiliary additive, and the auxiliary additive may include a fluorine-containing carbonate-based compound, a vinylidene carbonate-based compound, a lithium phosphate-based compound and a sulfone-based compound.

[0022] In some embodiments, the fluorine-containing carbonate-based compound may have a ring structure.

[0023] In some embodiments, the lithium phosphate-based compound may include a fluorine-containing lithium phosphate-based compound.

[0024] In some embodiments, the sulfonate compound may include an alkyl sulfonate compound and an alkenyl sulfonate compound.

[0025] In one embodiment, the additive may be included in an amount of 0.5 to 2 wt% relative to the total weight of the electrolyte.

[0026] In some embodiments, the auxiliary additive may be included in an amount of 1 to 5 wt% with respect to the total weight of the electrolyte.

[0027] In some embodiments, the ratio of the weight of the auxiliary additive to the weight of the additive in the electrolyte may be 1 to 5.

[0028] A lithium secondary battery according to exemplary embodiments may include a positive electrode; a negative electrode facing the positive electrode; and the electrolyte described above. Effects of the invention

[0029] The electrolyte for a lithium secondary battery according to exemplary embodiments may include a compound represented by the following chemical formula 1 as an additive. In this case, a lithium secondary battery having excellent room temperature capacity retention and improved high-temperature storage characteristics (e.g., low thickness increase rate during high-temperature storage, excellent capacity retention rate and capacity recovery rate, etc.) can be realized.

[0030] The electrolyte for a lithium secondary battery according to exemplary embodiments can form a positive electrolyte interface (CEI) having excellent stability on the surface of the positive electrode. Accordingly, side reactions between the positive electrode active material and the electrolyte can be effectively suppressed. In addition, hydrogen fluoride (HF) in the electrolyte can be easily removed.

[0031] A lithium secondary battery according to exemplary embodiments, including the above-described electrolyte, can exhibit an excellent room temperature capacity retention rate and improved high-temperature storage characteristics (e.g., a low thickness increase rate during high-temperature storage, an excellent capacity retention rate and capacity recovery rate, etc.). Brief explanation of the drawing

[0032] FIG. 1 is a schematic plan view of a lithium secondary battery according to exemplary embodiments. FIG. 2 is a schematic cross-sectional view of a lithium secondary battery according to exemplary embodiments. Specific details for implementing the invention

[0033] In this specification, "~-system compound" may mean a compound that includes the unit of the compound to which "~-system compound" is attached in the parent group, side group, or substituent.

[0034] In this specification, "Ca-Cb" may mean "a to b number of carbon atoms."

[0035] In this specification, "5-7-year-old ~" may mean that the number of atoms forming the ring structure of the corresponding substituent is 5 to 7.

[0036] <Electrolyte for lithium secondary batteries, hereinafter, electrolyte>

[0037] An electrolyte for a lithium secondary battery according to exemplary embodiments may comprise an organic solvent; a lithium salt; and an additive comprising a compound represented by the following chemical formula 1.

[0038] [Chemical Formula 1]

[0039]

[0040] In Chemical Formula 1, R1 and R2 are each independently hydrogen, a substituted or unsubstituted C1-C10 alkyl group, a substituted or unsubstituted C2-C10 alkenyl group, a substituted or unsubstituted C2-C10 alkynyl group, a substituted or unsubstituted C5-C12 cycloalkyl group, a substituted or unsubstituted C5-C12 cycloalkenyl group, a substituted or unsubstituted 5-7 member heterocycloalkyl group, a substituted or unsubstituted 5-7 member heterocycloalkenyl group, a substituted or unsubstituted C6-C12 aryl group, or a substituted or unsubstituted 5-7 member heteroaryl group, and R1 and R2 may be connected to each other to form a substituted or unsubstituted 5-7 member heterocycloalkyl group, a substituted or unsubstituted 5-7 member heterocycloalkenyl group, or a substituted or unsubstituted 5-7 member heteroaryl group.

[0041] The electrolyte according to the exemplary embodiments can realize a lithium secondary battery having an excellent room temperature capacity retention rate and improved high-temperature storage characteristics (e.g., low thickness increase rate during high-temperature storage, excellent capacity retention rate and capacity recovery rate, etc.).

[0042] In addition, the electrolyte according to the exemplary embodiments can form a cathode electrolyte interphase having excellent stability on the surface of the anode. Accordingly, side reactions between the anode active material (e.g., lithium metal oxide) and the electrolyte are effectively suppressed, and hydrogen fluoride (HF) in the electrolyte can be easily removed.

[0043] Hereinafter, each component of the electrolyte for a lithium secondary battery according to exemplary embodiments will be described in more detail.

[0044] additives

[0045] The electrolyte for a lithium secondary battery according to exemplary embodiments may include a compound represented by the following chemical formula 1.

[0046] [Chemical Formula 1]

[0047]

[0048] In Chemical Formula 1, R1 and R2 may each independently be hydrogen, a substituted or unsubstituted C1-C10 alkyl group, a substituted or unsubstituted C2-C10 alkenyl group, a substituted or unsubstituted C2-C10 alkynyl group, a substituted or unsubstituted C5-C12 cycloalkyl group, a substituted or unsubstituted C5-C12 cycloalkenyl group, a substituted or unsubstituted 5-7 member heterocycloalkyl group, a substituted or unsubstituted 5-7 member heterocycloalkenyl group, a substituted or unsubstituted C6-C12 aryl group, or a substituted or unsubstituted 5-7 member heteroaryl group.

[0049] In some embodiments, R1 and R2 may be connected to each other to form a ring structure. For example, R1 and R2 may be connected to each other to form a substituted or unsubstituted 5-7 member heterocycloalkyl group, a substituted or unsubstituted 5-7 member heterocycloalkenyl group, or a substituted or unsubstituted 5-7 member heteroaryl group.

[0050] For example, the above alkyl group, alkenyl group and alkynyl group may each independently have a straight chain or branched chain structure.

[0051] For example, the heterocycloalkyl group, heterocycloalkenyl group, and heteroaryl group may each independently include at least one heteroatom among N, O, and S within the ring structure.

[0052] R1 and R2 may each be independently unsubstituted or substituted. For example, "may be substituted" may mean that additional substituents may be attached to R1 and R2.

[0053] For example, substituents that can be further bonded to R1 and R2 may be at least one of a halogen, a C1-C6 alkyl group, a C1-C6 alkoxy group, a C3-C7 cycloalkyl group, a C6-C12 aryl group, a 5-7 heterocycloalkyl group, a 5-7 heteroaryl group, a hydroxyl group (-OH), -NR3R4 (R3 and R4 are each independently hydrogen or a C1-C3 alkyl group), a nitro group (-NO2), a cyano group (-CN), a thiocyanate group (-SCN), and an isothiocyanate group (-NCS).

[0054] In some embodiments, the substituents that can be further bonded to R1 and R2 may be halogens, C1-C6 alkyl groups, or C3-C7 cycloalkyl groups.

[0055] In one embodiment, R1 and R2 may each independently be a substituted or unsubstituted C1-C10 alkyl group, a substituted or unsubstituted C2-C10 alkenyl group, a substituted or unsubstituted C5-C12 cycloalkyl group, or a substituted or unsubstituted C5-C12 cycloalkenyl group.

[0056] In some embodiments, R1 and R2 may each independently be a substituted or unsubstituted C1-C6 alkyl group, a substituted or unsubstituted C2-C6 alkenyl group, a substituted or unsubstituted C5-C7 cycloalkyl group, or a substituted or unsubstituted C5-C7 cycloalkenyl group.

[0057] In one embodiment, R1 and R2 may each be independently a substituted or unsubstituted C1-C10 alkyl group or a substituted or unsubstituted C5-C12 cycloalkyl group.

[0058] In some embodiments, R1 and R2 may each be independently a substituted or unsubstituted C1-C6 alkyl group or a substituted or unsubstituted C5-C7 cycloalkyl group.

[0059] In one embodiment, R1 and R2 may each be independently substituted or unsubstituted C1-C10 alkyl groups. In some embodiments, R1 and R2 may each be independently substituted or unsubstituted C1-C6 alkyl groups. In this case, the lithium secondary battery can achieve a better room temperature capacity retention rate and improved high-temperature storage characteristics.

[0060] In some embodiments, R1 and R2 may be unsubstituted C1-C6 alkyl groups. For example, R1 and R2 may each independently be any one of a methyl group, an ethyl group, an n-propyl group, an iso-propyl group, an n-butyl group, an iso-butyl group, a pentyl group, or a hexyl group.

[0061] In one embodiment, the additive may be included in an amount of 0.5 to 2 wt% relative to the total weight of the electrolyte. In this case, the lithium secondary battery can achieve a better room temperature capacity retention rate and improved high-temperature storage characteristics.

[0062] auxiliary additives

[0063] The electrolyte for a lithium secondary battery according to exemplary embodiments may further include auxiliary additives.

[0064] In one embodiment, the auxiliary additive may include at least one of a fluorine-containing carbonate compound, a vinylidene carbonate compound, a lithium phosphate compound, a sulfone compound, a sulfate compound, a borate compound, a nitrile compound, an amine compound, a silane compound, and a benzene compound.

[0065] For example, the fluorine-containing carbonate compound may have a fluorine atom directly bonded to at least one carbon atom within the structure of the carbonate compound. Alternatively, a substituent (e.g., CF3) to which a fluorine atom is bonded may be bonded to at least one carbon atom within the structure of the carbonate compound. For example, the fluorine-containing carbonate compound may have a fluorine atom or a fluorine-substituted alkyl group bonded to at least one carbon atom within the structure of the carbonate compound.

[0066] In some embodiments, the fluorine-containing carbonate compound may be a cyclic carbonate compound having a ring structure. For example, the fluorine-containing carbonate compound may include fluoroethylene carbonate (FEC).

[0067] For example, the vinylidene carbonate-based compound may include at least one of vinylene carbonate (VC) and vinylethylene carbonate (VEC).

[0068] In some embodiments, the lithium phosphate-based compound may be a fluorine-containing lithium phosphate-based compound.

[0069] For example, the above fluorine-containing lithium phosphate compound may have fluorine directly bonded to a phosphorus (P) atom of the lithium phosphate compound, or may have a substituent (e.g., CF3, etc.) bonded to a fluorine atom. For example, the above fluorine-containing lithium phosphate compound may have a fluorine atom or a fluorine-substituted alkyl group bonded to a phosphorus atom of the lithium phosphate compound.

[0070] In some embodiments, the fluorine-containing lithium phosphate-based compound may include at least one of lithium difluorophosphate (LiPO2F2) and lithium difluoro(bisoxalato)phosphate.

[0071] In some embodiments, the sulfonate compound may include at least one of an alkyl sulfonate compound and an alkenyl sulfonate compound.

[0072] In some embodiments, The above sulfonate compound may include alkyl sulfonate compounds and alkenyl sulfonate compounds together.

[0073] For example, the above alkyl sulfone compound may include at least one of 1,3-propane sulfone (PS) and 1,4-butane sulfone.

[0074] For example, the alkenyl sulfone compound may include at least one of ethensulfone, 1,3-propenesulfone (PRS), 1,4-butenesulfone, and 1-methyl-1,3-propenesulfone.

[0075] For example, the sulfate-based compound may include at least one of ethylene sulfate (ESA), trimethylene sulfate (TMS), and methyltrimethylene sulfate (MTMS).

[0076] For example, the borate-based compound may include at least one of lithium tetraphenyl borate and lithium difluoro(oxalato) borate (LiODFB).

[0077] For example, the nitrile-based compound may include at least one of succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanitrile, cyclopentane carbonitrile, cyclohexane carbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

[0078] For example, the above amine-based compound may include at least one of triethanolamine and ethylenediamine.

[0079] For example, the above silane-based compound may include tetravinyl silane, etc.

[0080] For example, the above benzene-based compound may include at least one of monofluorobenzene, difluorobenzene, trifluorobenzene, and tetrafluorobenzene.

[0081] In one embodiment, the auxiliary additive may include a fluorine-containing carbonate-based compound, a vinylidene carbonate-based compound, a lithium phosphate-based compound, and a sulfone-based compound. In this case, by combining with an additive containing the compound of Formula 1 described above, a lithium secondary battery having a superior room temperature capacity retention rate and improved high-temperature storage characteristics can be realized.

[0082] In some embodiments, the auxiliary additive may be included in an amount of 1 to 5 wt% relative to the total weight of the electrolyte. In this case, a lithium secondary battery having a better room temperature capacity retention rate and improved high-temperature storage characteristics can be realized.

[0083] In some embodiments, the ratio of the weight of the auxiliary additive to the weight of the additive in the electrolyte may be 1 to 5, preferably 1.25 to 4.75, more preferably 1.5 to 4.5, and even more preferably 1.75 to 3.5. In this case, the room temperature capacity retention rate and high temperature storage characteristics of the lithium secondary battery may be further improved.

[0084] Organic solvents and lithium salts

[0085] The above organic solvent may include, for example, an organic compound that has sufficient solubility for the lithium salt, the additive, and the auxiliary additive and does not have reactivity in the battery.

[0086] For example, the organic solvent may include at least one 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.

[0087] For example, the carbonate-based solvent may include at least one of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate.

[0088] 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.

[0089] 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.

[0090] For example, the above ketone-based solvent may include cyclohexanone, etc.

[0091] For example, the above alcohol-based solvent may include at least one of ethyl alcohol and isopropyl alcohol.

[0092] 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.

[0093] In some embodiments, the organic solvent may include the carbonate-based solvent, and the carbonate-based solvent may include at least one of ethylene carbonate (EC), ethylmethyl carbonate (EMC), dimethyl carbonate (DMC) and diethyl carbonate (DEC).

[0094] The above electrolyte includes a lithium salt, and the lithium salt is Li + X - It can be expressed as.

[0095] For example, the anion (X) of the above lithium salt - ) is 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 - It can be any one selected from the back.

[0096] In some embodiments, the lithium salt may include at least one of LiBF4 and LiPF6.

[0097] In one embodiment, the lithium salt may be included in the organic solvent at a concentration of 0.01 to 5 M, more preferably 0.01 to 2 M. Within the concentration range, lithium ions and / or electrons can be smoothly moved during charging and discharging of the battery.

[0098] Lithium secondary battery

[0099] A lithium secondary battery according to exemplary embodiments may include a positive electrode; a negative electrode facing the positive electrode; and an electrolyte for the lithium secondary battery described above.

[0100] FIGS. 1 and FIGS. 2 are a schematic plan view and a cross-sectional view, respectively, showing a lithium secondary battery according to exemplary embodiments. FIGS. 2 is a cross-sectional view cut along line II' of FIGS. 1.

[0101] 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).

[0102] 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).

[0103] The positive active material layer (110) may include a positive active material, a positive binder and a conductive material as needed.

[0104] The positive electrode (100) can be manufactured by, for example, mixing and stirring a positive electrode active material, a positive electrode binder, a conductive material, a dispersion medium, etc. to produce a positive electrode slurry, and then applying, drying, and rolling the slurry onto a positive electrode current collector (105).

[0105] The positive current collector (105) may include, for example, stainless steel, nickel, aluminum, titanium, copper, or an alloy thereof, and more preferably, aluminum or an aluminum alloy.

[0106] The above-mentioned positive electrode active material may be a material capable of reversible insertion and extraction of lithium ions. The above-mentioned positive electrode active material may be, for example, a lithium metal oxide containing metal elements such as nickel, cobalt, manganese, and aluminum.

[0107] For example, the lithium metal oxide can be represented by the following chemical formula 2.

[0108] [Chemical Formula 2]

[0109] Li x Ni a Co b M c O y

[0110] In Chemical Formula 2, M is at least one of Al, Zr, Ti, Cr, B, Mg, Mn, Ba, Si, Y, W, and Sr, and may be 0.9≤x≤1.1, 1.9≤y≤2.1, 0.5≤a≤1, 0≤c / (a+b)≤0.13, and 0≤c≤0.11.

[0111] In some embodiments, the lithium metal oxide may have a nickel content of 60 mol% or more, 70 mol% or more, 80 mol% or more, 83 mol% or more, or 85 mol% or more among all elements excluding lithium and oxygen.

[0112] For example, in Chemical Formula 2, 0.6≤a≤1, or more preferably 0.8≤a≤1.

[0113] In some embodiments, 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, alloys thereof, or oxides thereof. These may be used alone or in combination of two or more.

[0114] When the nickel content in the above lithium metal oxide increases, the relative chemical stability, for example, room temperature capacity retention rate and high temperature storage characteristics may be inferior. However, in the case of a lithium secondary battery according to exemplary embodiments, by including the above-described electrolyte, even if a high-nickel lithium metal oxide (nickel 80 mol% or more) is included as a positive electrode active material, excellent room temperature capacity retention rate and improved high temperature storage characteristics can be achieved.

[0115] 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, the anode binder may be used together with a thickener such as carboxymethyl cellulose (CMC).

[0116] 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.

[0117] The cathode (130) may include a cathode current collector (125) and a cathode active material layer (120) on the cathode current collector (125).

[0118] The negative electrode active material layer (120) may include a negative electrode active material, a negative electrode binder and a conductive material as needed.

[0119] 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 it onto a cathode current collector (125).

[0120] For example, the negative current collector (125) may include gold, stainless steel, nickel, aluminum, titanium, copper, or an alloy thereof, and more preferably, may include copper or a copper alloy.

[0121] The above-mentioned negative electrode active material may be a material capable of absorbing and extracting lithium ions. The above-mentioned negative electrode active material may include, for example, carbon-based materials such as crystalline carbon, amorphous carbon, carbon composites, carbon fibers; silicon-based materials; lithium alloys; etc.

[0122] For example, the amorphous carbon may be hard carbon, coke, mesocarbon microbeads (MCMB) calcined at 1500°C or lower, mesophase pitch-based carbon fiber (MPCF), etc. The crystalline carbon may be, for example, natural graphite, graphitized coke, graphitized MCMB, graphitized MPCF, etc.

[0123] For example, the above silicon-based material is Si, SiO x (0 <x<2), Si / C, SiO / C, Si-Metal 등을 포함할 수 있다.

[0124] For example, the lithium alloy may include metallic elements such as aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, and indium.

[0125] The above-described cathode binder and conductive material may be substantially the same or similar materials as the above-described anode binder and conductive material. The above-described cathode binder may be, for example, a water-based binder such as styrene-butadiene rubber (SBR) for compatibility with carbon-based active material, and may be used together with a thickener such as carboxymethyl cellulose (CMC).

[0126] A separator (140) may be interposed between the positive electrode (100) and the negative electrode (130). In some embodiments, the area of ​​the negative electrode (130) (e.g., the contact area with the separator (140)) may be larger than the area of ​​the positive electrode (100). Accordingly, lithium ions generated from the positive electrode (100) can be smoothly moved to the negative electrode (130) without precipitating in the middle.

[0127] 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.

[0128] The separator (140) may include a nonwoven fabric formed of high-melting-point glass fibers, polyethylene terephthalate fibers, etc.

[0129] An electrode cell may be formed including an anode (100), a cathode (130), and a separator (140). Additionally, 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, lamination, zigzag-folding, etc., of the separator (140).

[0130] 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).

[0131] 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.

[0132] 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).

[0133] For example, the positive current collector (105) may include a protrusion (positive tab, not shown) on one side. A positive active material layer (110) may not be formed on the positive tab. The positive tab 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.

[0134] Likewise, the negative current collector (125) may include a protrusion (negative tab, not shown) on one side. A negative active material layer (120) may not be formed on the negative tab. The negative tab 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.

[0135] 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 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.

[0136] 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).

[0137] The electrode assembly (150) and the electrolyte for the lithium secondary battery described above can be housed together in a case (160) to form a lithium secondary battery.

[0138] The above lithium secondary battery can be manufactured in, for example, a cylindrical, prismatic, pouch, or coin type using a can.

[0139] Preferred embodiments and comparative examples of the present invention are described below. However, the following examples are merely preferred embodiments of the present invention, and the present invention is not limited to the following examples.

[0140] [Example 1]

[0141] (1) Preparation of electrolyte

[0142] A 1 M LiPF6 solution (EC / EMC mixed solvent with a volume ratio of 25:75) was prepared.

[0143] 1 wt% of a compound represented by the following chemical formula 3 was added and mixed as an additive to the above LiPF6 solution based on the total weight of the electrolyte.

[0144] [Chemical Formula 3]

[0145]

[0146] Additionally, as auxiliary additives, 1 wt% of fluoroethylene carbonate (FEC), 0.3 wt% of vinylethylene carbonate, 0.7 wt% of LiPO2F2, 0.5 wt% of 1,3-propane sulfone (PS), and 1 wt% of 1,3-propene sulfone (PRS) were added and mixed to prepare the electrolyte of Example 1.

[0147] (2) Preparation of lithium secondary battery samples

[0148] Li(Ni) 0.8 Co 0.1 Mn 0.1 An anode slurry was prepared by mixing and dispersing O2, carbon black, and polyvinylidene fluoride (PVdF) in NMP in a weight ratio of 92:5:3.

[0149] The above anode slurry was uniformly applied to an area excluding the protrusion of an aluminum foil (15 μm thickness) having a protrusion (anode tab) on one side, dried, and then rolled to manufacture an anode.

[0150] A cathode slurry was prepared by mixing and dispersing a cathode active material, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) in distilled water in a weight ratio of 97:1:2, with artificial graphite and natural graphite mixed in a weight ratio of 7:3.

[0151] The above cathode slurry was uniformly applied to an area excluding the protrusion of a copper foil (15 μm thickness) having a protrusion (cathode tab) on one side, dried, and then rolled to manufacture a cathode.

[0152] An electrode assembly was formed by interposing a polyethylene separator (thickness 20 μm) between the anode and the cathode. Next, an anode lead and a cathode lead were welded and connected to the anode tab and the cathode tab, respectively.

[0153] The electrode assembly is housed inside a pouch (case) so that a portion of the positive lead and the negative lead are exposed to the outside, and three sides excluding the surface of the electrolyte injection part are sealed.

[0154] A lithium secondary battery sample was prepared by injecting the electrolyte prepared in (1) above, sealing the surface of the electrolyte injection part, and then impregnating it for 12 hours.

[0155] [Example 2]

[0156] The procedure was carried out in the same manner as Example 1, except that no auxiliary additives were added during the preparation of the electrolyte.

[0157] [Example 3]

[0158] The procedure was carried out in the same manner as Example 1, except that 0.5 wt% fluoroethylene carbonate, 0.15 wt% vinylethylene carbonate, 0.35 wt% LiPO2F2, 0.25 wt% 1,3-propane sulfone, and 0.5 wt% 1,3-propene sulfone were added as auxiliary additives when preparing the electrolyte.

[0159] [Example 4]

[0160] The procedure was carried out in the same manner as Example 1, except that 1.25 wt% of fluoroethylene carbonate, 0.5 wt% of vinylethylene carbonate, 21 wt% of LiPO2F, 0.75 wt% of 1,3-propane sulfone, and 1.25 wt% of 1,3-propene sulfone were added as auxiliary additives when preparing the electrolyte.

[0161] [Example 5]

[0162] The procedure was carried out in the same manner as Example 1, except that 1.25 wt% of fluoroethylene carbonate, 0.75 wt% of vinylethylene carbonate, 21 wt% of LiPO2F, 1 wt% of 1,3-propane sulfone, and 1.25 wt% of 1,3-propene sulfone were added as auxiliary additives when preparing the electrolyte.

[0163] [Comparative Example 1]

[0164] The procedure was carried out in the same manner as Example 1, except that the compound represented by Chemical Formula 3 above was not added when preparing the electrolyte.

[0165] Experimental Example 1: Initial Performance Evaluation (Room Temperature, 25℃)

[0166] (1) Initial dose evaluation

[0167] After charging the secondary batteries of the examples and comparative examples at a 0.5C-rate CC / CV (4.2V, 0.05C cut-off), 0.5C-rate CC discharge (2.7V cut-off) was performed three times.

[0168] The third discharge capacity value was used as the initial capacity of the battery, and the resulting values ​​were listed in Table 1 below.

[0169] (2) Evaluation of the initial thickness of the battery

[0170] After charging the secondary batteries of the examples and comparative examples at room temperature with a 0.5C-rate CC / CV (4.2V 0.05C cut-off), the thickness of the batteries was measured using a flat plate thickness measuring device (Mitutoyo, 543-490B).

[0171] The measured thickness of the battery is listed in Table 1 below.

[0172] (3) Evaluation of internal resistance (C_DCIR and D_DCIR)

[0173] 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 the voltage termination point was constructed using a linear equation when charging and discharging at the corresponding C-rate was performed for 10 seconds, and the slope was adopted as DCIR.

[0174] The measured D_DCIR values ​​are listed in Table 1.

[0175] Experimental Example 2: Evaluation of Room Temperature Capacity Retention Rate (Ret.) (25℃)

[0176] For the secondary batteries of the examples and comparative examples, CC / CV charging (0.5C 4.3V 0.05C CUT-OFF) and CC discharging (1.0C 3.0V CUT-OFF) were repeated 1,000 times at room temperature (25℃).

[0177] The room temperature capacity retention rate was calculated as the percentage of the value obtained by dividing the discharge capacity measured at the 1000th cycle by the initial capacity measured in (1) of Experimental Example 1 above.

[0178] Room temperature capacity retention rate = (1000th discharge cycle capacity / Initial capacity) × 100 (%)

[0179] The calculated room temperature capacity retention rate is listed in Table 1.

[0180] Experimental Example 3: Evaluation of High-Temperature Storage Characteristics

[0181] For the batteries of the examples and comparative examples, the following evaluation was performed after "high-temperature storage" by leaving them for 14 weeks under atmospheric exposure conditions of 60°C using a constant temperature device and then leaving them for an additional 30 minutes at room temperature.

[0182] (1) Evaluation of battery thickness after high-temperature storage

[0183] After storing the charged batteries of the examples and comparative examples at high temperature, the thickness of the batteries was measured using a flat plate thickness measuring device (Mitutoyo, 543-490B).

[0184] The measured battery thickness is listed in Table 1.

[0185] When the initial thickness of the battery measured in (1) of Experimental Example 1 above is denoted as A and the thickness of the battery after high-temperature storage is denoted as B, the increase rate of the battery thickness after high-temperature storage is calculated using the following mathematical formula 1 and is listed in Table 1.

[0186] [Mathematical Formula 1]

[0187] Thickness increase rate (%) = (BA) / A × 100

[0188] (2) Evaluation of capacity retention rate (Ret) after high-temperature storage

[0189] After storing the charged batteries of the example and comparative example at a high temperature, the discharge capacity was measured by performing a 0.5C-rate CC discharge (2.7V cut-off).

[0190] The capacity retention rate was calculated as a percentage by dividing the discharge capacity after high-temperature storage by the initial capacity measured in (1) of Experimental Example 1 above.

[0191] Capacity retention rate (%) = (Discharge capacity after high-temperature storage / Initial capacity) × 100

[0192] The calculated capacity retention rate values ​​are listed in Table 1 below.

[0193] (3) Evaluation of capacity recovery rate (Rec) after high-temperature storage

[0194] After measuring the capacity retention rate according to (2) above for the batteries of the example and comparative example, the discharge capacity was measured by charging at a 0.5C-rate CC / CV (4.2V, 0.05C cut-off) and discharging at a 0.5C-rate CC (2.7V cut-off).

[0195] The capacity recovery rate was calculated as a percentage by dividing the discharge capacity after measuring the capacity retention rate by the initial capacity measured in (1) of Experimental Example 1 above.

[0196] Capacity Recovery Rate (%) = (Discharge Capacity after Capacity Retention Rate Measurement / Initial Capacity) × 100

[0197] The calculated dose recovery rate values ​​are listed in Table 1 below.

[0198] Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example 1 Initial performance evaluation Capacity (mAh) 1733 1706 1734 1729 1710 1739 Thickness (mm) 5.22 5.25 5.17 5.28 5.40 5.41 D_DCIR(mΩ) 39.3 39.9 39.6 39 41.6 39.4 High-temperature storage evaluation (14 weeks) Thickness (mm) 6.53 7.47 6.83 6.4 6.31 8.12 Thickness increase rate (%) 25 42 32 21 17 50 Ret.(%) 86.4 74.7 86.7 85.7 84.8 76.0 Rec.(%) 87.5 75.9 87.7 86.6 85.8 77.8 Room temperature lifespan evaluation (1,000 times) Ret.(%) 82.8 79.2 83.9 82.1 80.8 78.6

[0199] Referring to Table 1 above, it can be seen that the secondary batteries of the examples have superior room temperature capacity retention rate and high temperature storage characteristics (thickness increase rate, capacity retention rate, capacity recovery rate, etc.) compared to the secondary batteries of the comparative examples.

[0200] In addition, referring to Examples 1, 3, 4, and 5, it can be seen that when the content of the auxiliary additive relative to the content of the additive in the electrolyte is within a specific weight ratio range, it exhibits superior room temperature capacity retention rate and high temperature storage characteristics. Explanation of the symbols

[0201] 100: Anode 105: Anode current collector 107: Anode Lead 110: Anode Active Material Layer 120: Cathode active material layer 125: Cathode current collector 127: Cathode Lead 130: Cathode 140: Separator 150: Electrode assembly 160: Case

Claims

Claim 1 Electrolyte for a lithium secondary battery comprising: an organic solvent; a lithium salt; and an additive comprising a compound represented by the following chemical formula 1: [Chemical Formula 1] In Formula 1, R1 and R2 are each independently hydrogen, a substituted or unsubstituted C1-C10 alkyl group, a substituted or unsubstituted C2-C10 alkenyl group, a substituted or unsubstituted C2-C10 alkynyl group, a substituted or unsubstituted C5-C12 cycloalkyl group, a substituted or unsubstituted C5-C12 cycloalkenyl group, a substituted or unsubstituted 5-7 member heterocycloalkyl group, a substituted or unsubstituted 5-7 member heterocycloalkenyl group, a substituted or unsubstituted C6-C12 aryl group, or a substituted or unsubstituted 5-7 member heteroaryl group, and R1 and R2 may be connected to each other to form a substituted or unsubstituted 5-7 member heterocycloalkyl group, a substituted or unsubstituted 5-7 member heterocycloalkenyl group, or a substituted or unsubstituted 5-7 member heteroaryl group. Claim 2 An electrolyte for a lithium secondary battery according to claim 1, wherein R1 and R2 are each independently a substituted or unsubstituted C1-C10 alkyl group, a substituted or unsubstituted C2-C10 alkenyl group, a substituted or unsubstituted C5-C12 cycloalkyl group, or a substituted or unsubstituted C5-C12 cycloalkenyl group. Claim 3 An electrolyte for a lithium secondary battery according to claim 1, wherein R1 and R2 are each independently substituted or unsubstituted C1-C10 alkyl groups. Claim 4 An electrolyte for a lithium secondary battery according to claim 1, wherein the electrolyte further comprises an auxiliary additive, and the auxiliary additive comprises at least one of a fluorine-containing carbonate-based compound, a vinylidene carbonate-based compound, a lithium phosphate-based compound, a sulfone-based compound, a sulfate-based compound, a borate-based compound, a nitrile-based compound, an amine-based compound, a silane-based compound, and a benzene-based compound. Claim 5 An electrolyte for a lithium secondary battery according to claim 1, wherein the electrolyte further comprises an auxiliary additive, and the auxiliary additive comprises a fluorine-containing carbonate-based compound, a vinylidene carbonate-based compound, a lithium phosphate-based compound and a sulfone-based compound. Claim 6 In claim 5, the fluorine-containing carbonate-based compound has a ring structure, an electrolyte for a lithium secondary battery. Claim 7 An electrolyte for a lithium secondary battery according to claim 5, wherein the lithium phosphate-based compound comprises a fluorine-containing lithium phosphate-based compound. Claim 8 An electrolyte for a lithium secondary battery according to claim 5, wherein the sulfonate compound comprises an alkyl sulfonate compound and an alkenyl sulfonate compound. Claim 9 An electrolyte for a lithium secondary battery according to claim 1, wherein the additive is included in an amount of 0.5 to 2 wt% with respect to the total weight of the electrolyte. Claim 10 An electrolyte for a lithium secondary battery according to claim 5, wherein the auxiliary additive is included in an amount of 1 to 5 wt% with respect to the total weight of the electrolyte. Claim 11 An electrolyte for a lithium secondary battery according to claim 5, wherein the ratio of the weight of the auxiliary additive to the weight of the additive in the electrolyte is 1 to 5. Claim 12 A lithium secondary battery comprising: a positive electrode; a negative electrode facing the positive electrode; and an electrolyte for a lithium secondary battery according to claim 1.

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