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

Abstract

To provide an electrolyte for a lithium secondary battery with an improved life characteristics at high temperatures, and a lithium secondary battery including the electrolyte.SOLUTION: There are disclosed an electrolyte for a lithium secondary battery and a lithium secondary battery including the electrolyte. The electrolyte for a lithium secondary battery includes a non-aqueous organic solvent; a lithium salt; and an additive. The additive includes a first compound containing triallyl isocyanurate and a second compound expressed by the following chemical formula.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Embodiments of the present invention relate to an electrolyte for a lithium secondary battery and a lithium secondary battery including the same.

Background Art

[0002] In recent years, with the rapid spread of electronic devices using batteries, such as mobile phones, notebook computers, and electric vehicles, the demand for secondary batteries with high energy density and high capacity has been rapidly increasing. For this reason, research and development for improving the performance of lithium secondary batteries have been actively conducted.

[0003] A lithium secondary battery is a battery including a positive electrode and a negative electrode containing an active material capable of insertion (intercalation) and desorption (deintercalation) of lithium ions, and an electrolyte, and produces electrical energy by oxidation and reduction reactions when lithium ions are inserted / desorbed at the positive electrode and the negative electrode.

[0004] As such an electrolyte of a lithium secondary battery, one in which a lithium salt is dissolved in a non-aqueous organic solvent is used. In a lithium secondary battery, the characteristics of the battery are determined by complex reactions such as between the positive electrode and the electrolyte, and between the negative electrode and the electrolyte. Therefore, the use of an appropriate electrolyte is one of the important factors for improving the performance of a lithium secondary battery.

Summary of the Invention

Problems to be Solved by the Invention

[0005] One embodiment aims to provide an electrolyte for a lithium secondary battery having improved life characteristics at high temperatures.

[0006] Another embodiment aims to provide a lithium secondary battery including the above electrolyte.

Means for Solving the Problems

[0007] One embodiment is an electrolyte for a lithium secondary battery, which includes a non-aqueous solvent, a lithium salt, and an additive. The additive includes a first compound represented by the following Chemical Formula 1 and a second compound represented by the following Chemical Formula 2.

[0008]

Chem.

[0009]

Chem.

[0010] Another embodiment is a lithium secondary battery including the above electrolyte.

Advantages of the Invention

[0011] The electrolyte for a lithium secondary battery according to one embodiment can stabilize the electrodes, suppress the increase in resistance, and improve the life characteristics at high temperatures.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0013] To fully understand the configuration and effects of the present invention, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the present invention can be embodied in various forms and is not limited to the embodiments disclosed below, and various modifications can be made. The following description is provided to make the disclosure of the present invention complete by the description of the present embodiments and to fully inform those of ordinary skill in the technical field to which the present invention pertains of the scope of the invention.

[0014] In this specification, when a component is referred to as being on another component, it means that the component may be directly formed on the other component or a third component may be interposed therebetween. Also, in the drawings, the thickness of the components is exaggerated for an effective explanation of the technical content. Throughout the specification, parts denoted by the same reference numerals indicate the same components.

[0015] Unless otherwise specifically mentioned in this specification, those expressed in the singular may include the plural. Also, unless otherwise specifically mentioned, "A" or "B" may mean "including A, including B, or including both A and B". The expression "including" used in this specification does not exclude the presence or addition of one or more other components in addition to the component mentioned.

[0016] In this specification, "these combinations" may mean a mixture, laminate, composite, copolymer, alloy, blend, reaction product, etc. of components.

[0017] Referring to FIG. 1, the lithium secondary battery may include a positive electrode 10, a negative electrode 20, a separator 30, and an electrolytic solution ELL.

[0018] The positive electrode 10 and the negative electrode 20 may be separated from each other with the separator 30 interposed therebetween. The separator 30 can be disposed between the positive electrode 10 and the negative electrode 20. The positive electrode 10, the negative electrode 20, and the separator 30 may be in contact with the electrolytic solution ELL. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated in the electrolytic solution ELL.

[0019] The electrolyte ELL may be a medium for transmitting lithium ions between the positive electrode 10 and the negative electrode 20. In the electrolyte ELL, lithium ions can move through the separator 30 and move toward the positive electrode 10 or the negative electrode 20.

[0020] Positive electrode 10 The positive electrode 10 for a lithium secondary battery may include a current collector COL1 and a positive electrode active material layer AML1 formed on the current collector COL1. The positive electrode active material layer AML1 contains a positive electrode active material and may further contain a binder and / or a conductive material.

[0021] As an example, the positive electrode 10 may further contain an additive that can function as a sacrificial positive electrode.

[0022] The content of the positive electrode active material in the positive electrode active material layer AML1 may be from 90% by weight to 99.5% by weight based on 100% by weight of the positive electrode active material layer AML1. The contents of the binder and the conductive material may each be from 0.5% by weight to 5% by weight based on 100% by weight of the positive electrode active material layer AML1.

[0023] The binder serves to firmly adhere the positive electrode active material particles to each other and to firmly adhere the positive electrode active material to the current collector COL1. Representative examples of the binder include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylic acid styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, nylon, and the like.

[0024] The conductive material is used to impart conductivity to the electrode, and in the configured battery, any material can be used as long as it is an electron conductive material without causing chemical changes. Examples of the conductive material include carbon-based substances such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, carbon nanotube, metal-based substances containing copper, nickel, aluminum, silver, etc. in the form of metal powder or metal fiber, conductive polymers such as polyphenylene derivatives, or mixtures thereof.

[0025] Al can be used as the current collector COL1, but not limited thereto.

[0026] Positive electrode active material As the positive electrode active material in the positive electrode active material layer AML1, a compound capable of reversible insertion and desorption of lithium (lithiated intercalation compound) can be used. Specifically, one or more of composite oxides of metals selected from cobalt, manganese, nickel, and combinations thereof with lithium can be used.

[0027] The composite oxide may be a lithium transition metal composite oxide. Specific examples include lithium nickel-based oxides, lithium cobalt-based oxides, lithium manganese-based oxides, lithium iron phosphate-based oxides, cobalt-free nickel-manganese-based oxides, or combinations thereof.

[0028] As an example, a compound represented by any one of the following chemical formulas can be used. Li a A 1-b X b O 2-c D c (0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05), Li a Mn 2-b X b O 4-c D c (0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05), Li a Ni1-b-c Co b X c O 2-α D α (0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.5, 0 < α < 2), Li a Ni 1-b-c Mn b X c O 2-α D α (0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.5, 0 < α < 2), Li a Ni b Co c L 1 d G e O 2 (0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.9, 0 ≦ c ≦ 0.5, 0 ≦ d ≦ 0.5, 0 ≦ e ≦ 0.1), Li a NiG b O 2 (0.90 ≦ a ≦ 1.8, 0.001 ≦ b ≦ 0.1), Li a CoG b O 2 (0.90 ≦ a ≦ 1.8, 0.001 ≦ b ≦ 0.1), Li a Mn 1-b G b O 2 (0.90 ≦ a ≦ 1.8, 0.001 ≦ b ≦ 0.1), Li a Mn 2 G b O 4 (0.90 ≦ a ≦ 1.8, 0.001 ≦ b ≦ 0.1), Li a Mn 1-g G g PO 4 (0.90 ≦ a ≦ 1.8, 0 ≦ g ≦ 0.5), Li (3-f) Fe 2 (PO 4 ) 3 (0 ≦ f ≦ 2), Li a FePO 4 (0.90 ≦ a ≦ 1.8).

[0029] In the above chemical formula, A is Ni, Co, Mn, or a combination thereof; X is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is O, F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; L 1 is Mn, Al, or a combination thereof.

[0030] As an example, the positive electrode active material may be a high-nickel-based positive electrode active material having a nickel content of 80 mol% or more, 85 mol% or more, 90 mol% or more, 91 mol% or more, or 94 mol% or more, and 99 mol% or less, based on 100 mol% of the metal obtained by removing lithium from the lithium transition metal composite oxide. Since the high-nickel-based positive electrode active material can achieve a high capacity, it can be applied to high-capacity and high-density lithium secondary batteries.

[0031] Negative electrode 20 The positive electrode 20 for a lithium secondary battery may include a current collector COL2 and a negative electrode active material layer AML2 formed on the current collector COL2. The negative electrode active material layer AML2 contains a negative electrode active material and may further contain a binder and / or a conductive material.

[0032] For example, the negative electrode active material layer AML2 may contain 90 wt% to 99 wt% of the negative electrode active material, 0.5 wt% to 5 wt% of the binder, and 0 wt% to 5 wt% of the conductive material.

[0033] The binder serves to firmly adhere the negative electrode active material particles to each other and also to firmly adhere the negative electrode active material to the current collector COL2. As the binder, a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof can be used.

[0034] Examples of non-aqueous binders include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene-propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

[0035] Examples of aqueous binders may include styrene-butadiene rubber, (meth)acrylic styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene-propylene-diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyether resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0036] When an aqueous binder is used as the negative electrode binder, it may further contain a cellulose-based compound that can impart viscosity. As this cellulose-based compound, one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or alkali metal salts thereof can be mixed and used. As the alkali metal, Na, K, or Li can be used.

[0037] Dry binders are fiberizable polymer substances, and for example, may be polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, ethylene oxide, or combinations thereof.

[0038] The conductive material is used to impart conductivity to the electrode, and in the configured battery, any material can be used as long as it is an electron conductive material without causing a chemical change. Specific examples include carbon-based substances such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, carbon nanotube, metal-based substances in the form of metal powder or metal fiber including copper, nickel, aluminum, silver, etc., conductive polymers such as polyphenylene derivatives, or a mixture thereof.

[0039] As the current collector COL2, those selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof can be used.

[0040] Negative electrode active material The negative electrode active material in the negative electrode active material layer AML2 includes a material capable of reversibly inserting / desorbing lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping or dedoping with lithium, or a transition metal oxide.

[0041] As the material capable of reversibly inserting / desorbing lithium ions, it may be a carbon-based negative electrode active material, for example, including crystalline carbon, amorphous carbon, or a combination thereof. Examples of crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical or fibrous natural graphite or artificial graphite, and examples of amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, etc.

[0042] As the alloy of lithium metal, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0043] As a substance that can be doped or de-doped with lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used. The Si-based negative electrode active material may be silicon, a silicon-carbon composite, SiOx (0 < x < 2), a Si-Q alloy (Q is selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements (excluding Si), group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof), or a combination thereof. The Sn-based negative electrode active material may be Sn, SnO 2 , a Sn-based alloy, or a combination thereof.

[0044] The silicon-carbon composite may be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite may be in a form in which amorphous carbon is coated on the surface of silicon particles. For example, it may include secondary particles (cores) formed by combining primary silicon particles and an amorphous carbon coating layer (shell) located on the surface of the secondary particles. The amorphous carbon may also be located between the primary silicon particles. For example, the primary silicon particles may be coated with amorphous carbon. The secondary particles may be dispersed and present in an amorphous carbon matrix.

[0045] The silicon-carbon composite may further include crystalline carbon. For example, the silicon-carbon composite may include a core containing crystalline carbon and silicon particles and an amorphous carbon coating layer located on the surface of the core.

[0046] The Si-based negative electrode active material or the Sn-based negative electrode active material may be used by mixing with a carbon-based negative electrode active material.

[0047] Separator 30 Depending on the type of lithium secondary battery, a separator 30 may be present between the positive electrode 10 and the negative electrode 20. As such a separator 30, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof may be used, but a mixed multilayer film such as a two-layer separator of polyethylene / polypropylene, a three-layer separator of polyethylene / polypropylene / polyethylene, or a three-layer separator of polypropylene / polyethylene / polypropylene can also be used.

[0048] The separator 30 may include a porous substrate and a coating layer containing an organic substance, an inorganic substance, or a combination thereof located on one or both surfaces of the porous substrate.

[0049] The porous substrate may be a polymer selected from any one of polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyether ketone, polyaryl ether ketone, polyether imide, polyamide imide, polybenzimidazole, polyether sulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon, and polytetrafluoroethylene, or a polymer film composed of a copolymer or a mixture of two or more of these.

[0050] The above-mentioned organic substance may include a polyvinylidene fluoride polymer or a (meth)acrylic-based polymer.

[0051] The above-mentioned inorganic substance is Al 2 O 3 , SiO 2 , TiO 2 , SnO 2 , CeO 2 , MgO, NiO, CaO, GaO, ZnO, ZrO 2 , Y 2 O 3 , SrTiO 3 , BaTiO 3, Mg(OH) 2 It can include, but is not limited to, inorganic particles selected from boehmite, and combinations thereof.

[0052] The above-mentioned organic and inorganic substances can exist in a form where they are mixed in one coating layer, or in a form where a coating layer containing an organic substance and a coating layer containing an inorganic substance are laminated.

[0053] Electrolyte ELL The electrolyte ELL for a lithium secondary battery contains a non-aqueous organic solvent, a lithium salt, and an additive.

[0054] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0055] The non-aqueous organic solvent may be a carbonate-based, ester-based, ether-based, ketone-based, or alcohol-based solvent, an aprotic solvent, or a combination thereof.

[0056] As the carbonate-based solvent, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl pyrrolyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. can be used.

[0057] As the ester-based solvent, methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, propyl propionate, decanolide, mevalonolactone, valerolactone, caprolactone, etc. can be used.

[0058] As the ether solvent, dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. can be used. Also, as the ketone solvent, cyclohexanone, etc. can be used. As the alcohol solvent, ethyl alcohol, isopropyl alcohol, etc. can be used, and as the aprotic solvent, nitriles such as R-CN (R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may contain a double bond, an aromatic ring, or an ether group), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, 1,4-dioxolane, and sulfolanes, etc. can be used.

[0059] The non-aqueous organic solvent can be used alone or in a mixture of two or more.

[0060] Also, when using a carbonate solvent, a cyclic carbonate and a chain carbonate may be mixed and used, and the cyclic carbonate and the chain carbonate can be mixed at a volume ratio of 1:1 to 1:9.

[0061] The lithium salt is dissolved in an organic solvent, acts as a source of lithium ions in the battery to enable the operation of a basic lithium secondary battery, and plays a role in promoting the movement of lithium ions between the positive electrode and the negative electrode. Representative examples of lithium salts include LiPF 6 、LiBF 4 、LiSbF 6 、LiAsF 6 、LiClO 4 、LiAlO 2 、LiAlCl 4 、LiPO 2 F 2 、LiCl、LiI、LiN(SO 3 C 2 F 5 ) 2 、Li(FSO 2 ) 2 N (lithium bis(fluorosulfonyl)imide (LiFSI), LiC4 F 9 SO 3 、 LiN(C x F 2x+1 SO 2 )(C y F 2y+1 SO 2 )(x and y are positive numbers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluoro(oxalato)borate (LiDFOB), lithium difluorobis(oxalato)phosphate (LiDFBOP), lithium bis(oxalato)borate (LiBOB), and can include one or more selected therefrom.

[0062] As the lithium salt, LiPF 6 can be used.

[0063] The concentration of the lithium salt may be from 0.1 M to 2.0 M.

[0064] The additive may include a second compound represented by the following Chemical Formula 2.

[0065]

Chemical Formula

[0066] The second compound can form a stable film on the surface of the electrode of the lithium secondary battery and improve the cycle characteristics of the lithium battery.

[0067] The second compound may be contained in an amount of 0.01% by weight to 10% by weight of the total weight of the electrolyte. Specifically, the second compound may be contained in an amount of 0.05% by weight or more, 0.1% by weight or more, 0.5% by weight or more, or 1% by weight or more of the total weight of the electrolyte. The second compound may be contained in an amount of 7% by weight or less, 5% by weight or less, or 2% by weight or less of the total weight of the electrolyte. By having the above-described concentration, the second compound can appropriately reduce the resistance on the surface of the electrode of the lithium secondary battery and improve the output performance of the battery.

[0068] The additive may further contain a first compound represented by the following chemical formula 1.

[0069] [Chemical formula]

[0070] The first compound acts as a crosslinking agent in a film formed on the surface of the electrode of the lithium secondary battery in combination with the second compound, and a film with improved density can be formed on the electrode.

[0071] The first compound may be contained in an amount of 0.01% by weight to 1% by weight of the total weight of the electrolyte. Specifically, the first compound may be contained in an amount of 0.05% by weight or more, 0.1% by weight or more, or 0.2% by weight or more of the total weight of the electrolyte. The first compound may be contained in an amount of 0.75% by weight or less, or 0.5% by weight or less of the total weight of the electrolyte. By containing the first compound within the above range, it can sufficiently serve as a crosslinking agent to strengthen the film, appropriately reduce the resistance on the surface of the electrode of the lithium secondary battery, and improve the output performance of the battery.

[0072] The content of the first compound may be lower than the content of the second compound.

[0073] For 1 part by weight of the first compound, the second compound may be contained in an amount of 1 to 10 parts by weight. Specifically, for 1 part by weight of the first compound, the second compound may be contained in an amount of 1 to 5 parts by weight, 1 to 2.5 parts by weight, or 1 to 2 parts by weight. By containing the second compound within the above range, it can sufficiently serve as a crosslinking agent to strengthen the film, appropriately reduce the resistance on the surface of the electrode of the lithium secondary battery, and improve the output performance of the battery.

[0074] The additive may be contained in an amount of 0.1% by weight to 2% by weight of the total weight of the electrolyte solution. Specifically, the additive may be contained in an amount of 0.1% by weight to 1.5% by weight, 0.1% by weight to 1.5% by weight, 0.6% by weight to 1.5% by weight, or 0.7% by weight to 1.5% by weight of the total weight of the electrolyte solution. When the additive is contained in an amount exceeding the above range, the viscosity of the electrolyte solution containing the additive may increase excessively, and the wettability with respect to the positive electrode and the negative electrode may decrease. On the other hand, when the content of the additive is less than the above range, the above-described effects may not be fully exhibited.

[0075] Lithium secondary battery The lithium secondary battery can be classified into a cylindrical type, a prismatic type, a pouch type, a coin type, etc. according to its form. FIGS. 2 to 5 are schematic views showing a lithium secondary battery according to an embodiment, and it can be said that FIG. 2 shows a cylindrical shape, FIG. 3 shows a prismatic shape, and FIGS. 4 and 5 show a pouch type battery form. Referring to FIGS. 2 to 4, the lithium secondary battery 100 may include an electrode assembly 40 having a separator 30 interposed between a positive electrode 10 and a negative electrode 20, and a housing 50 in which the electrode assembly 40 is embedded. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte solution (not shown). The lithium secondary battery 100 may include a sealing member 60 for sealing the housing 50 as shown in FIG. 2. Further, as shown in FIG. 3, the lithium secondary battery 100 may include a positive electrode lead tab 11, a positive electrode terminal 12, a negative electrode lead tab 21, and a negative electrode terminal 22. As shown in FIGS. 4 and 5, the lithium secondary battery 100 may include electrode tabs 70, that is, a positive electrode tab 71 and a negative electrode tab 72, which serve as electrical paths for guiding the current formed by the positive electrode assembly 40 to the outside.

[0076] The lithium secondary battery according to an embodiment of the present invention can be applied to automobiles, mobile phones, and / or various forms of electrical devices, etc., but the present invention is not limited thereto.

Examples

[0077] Hereinafter, examples and comparative examples of the present invention will be described. However, the following examples are merely examples of the present invention, and the present invention is not limited to the following examples.

[0078] 1. Examples and Comparative Examples 1-1. Example 1 (1) Preparation of Electrolyte 1.0 M LiPF was dissolved in a non-aqueous organic solvent in which ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed at a volume ratio of 20:20:60, and additives were further added to prepare an electrolyte. 6

[0079] As the additives, a first compound and a second compound represented by Chemical Formula 1 and Chemical Formula 2 below were used. The first compound and the second compound were added in amounts of 0.2 wt% and 1 wt%, respectively, based on the total amount of the electrolyte.

[0080] [Chemical Formula]

[0081] [Chemical Formula]

[0082] (2) Fabrication of Lithium Secondary Battery As the positive electrode active material, NCA (LiNiCoAlO 2 ), polyvinylidene fluoride as a binder, and acetylene black as a conductive material were mixed at a weight ratio of 96:3:1, respectively, and dispersed in N-methylpyrrolidone to prepare a positive electrode active material slurry.

[0083] The positive electrode active material slurry was coated on an Al foil with a thickness of 15 μm, heated at 100 °C, and then rolled to fabricate a positive electrode.

[0084] A silicon negative electrode active material, a styrene-butadiene rubber binder, and carboxymethyl cellulose were mixed at a weight ratio of 98:1:1, respectively, and dispersed in distilled water to prepare a negative electrode active material slurry.

[0085] ​The negative electrode active material slurry was coated on a Cu foil with a thickness of 10 μm, heated at 100 °C, and then rolled to fabricate a negative electrode.

[0086] The positive electrode, negative electrode, and a separator made of a polyethylene material with a thickness of 10 μm were assembled to fabricate an electrode assembly, and an electrolytic solution was injected into the electrode assembly to fabricate a lithium secondary battery.

[0087] 1-2. Example 2 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the first compound was added as an additive at a content of 0.5% by weight based on the total amount of the electrolytic solution, and the second compound was added at a content of 1% by weight based on the total amount of the electrolytic solution.

[0088] 1-3. Example 3 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the first compound was added as an additive at a content of 0.2% by weight based on the total amount of the electrolytic solution, and the second compound was added at a content of 0.5% by weight based on the total amount of the electrolytic solution.

[0089] 1-4. Example 4 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the first compound was added as an additive at a content of 0.1% by weight based on the total amount of the electrolytic solution, and the second compound was added at a content of 0.5% by weight based on the total amount of the electrolytic solution.

[0090] 1-5. Comparative Example 1 A lithium secondary battery was fabricated in the same manner as in Example 1, except that no additive was added.

[0091] 1-6. Comparative Example 2 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the fourth compound represented by the following Chemical Formula 4 was added as an additive at a content of 0.2% by weight based on the total amount of the electrolytic solution, and the second compound was added at a content of 1% by weight based on the total amount of the electrolytic solution.

[0092]

Chemical formula

[0093] 1-7. Comparative Example 3 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the fourth compound was added as an additive at a content of 0.5% by weight based on the total amount of the electrolytic solution, and the second compound was added at a content of 1% by weight based on the total amount of the electrolytic solution.

[0094] 1-8. Comparative Example 4 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the fifth compound represented by the following Chemical Formula 5 was added as an additive at a content of 0.2% by weight based on the total amount of the electrolytic solution, and the second compound was added at a content of 1% by weight based on the total amount of the electrolytic solution.

[0095] [Chemical Formula]

[0096] 1-9. Comparative Example 5 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the fifth compound was added as an additive at a content of 0.5% by weight based on the total amount of the electrolytic solution, and the second compound was added at a content of 1% by weight based on the total amount of the electrolytic solution.

[0097] 1-10. Comparative Examples 6 to 8 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the first compound was added as an additive at contents of 0.2% by weight, 0.5% by weight, and 1% by weight based on the total amount of the electrolytic solution, and the second compound was not added.

[0098] 1-11. Comparative Examples 9 to 11 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the first compound was not added, and the second compound was added as an additive at contents of 0.2% by weight, 0.5% by weight, and 1% by weight based on the total amount of the electrolytic solution.

[0099] 1-12. Comparative Examples 12 to 15 In Comparative Examples 12 to 15, a lithium secondary battery was fabricated in the same manner as in Example 1, except that the first compound and the second compound were added such that the weight ratio was substantially 1:1. At this time, the first compound and the second compound were added at contents of 0.2 wt%, 0.5 wt%, 1 wt%, and 2 wt% respectively based on the total amount of the electrolytic solution.

[0100] 1-13. Comparative Examples 16 to 18 In Comparative Examples 16 to 18, a lithium secondary battery was fabricated in the same manner as in Example 1, except that the first compound and the second compound were added such that the weight of the first compound was greater than the weight of the second compound. At this time, the first compound was added at contents of 2 wt%, 1 wt%, and 1 wt% respectively based on the total amount of the electrolytic solution, and the second compound was added at contents of 1 wt%, 0.5 wt%, and 0.2 wt% respectively based on the total amount of the electrolytic solution.

[0101] 1-14. Comparative Example 19 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the first compound was added as an additive at a content of 1 wt% based on the total amount of the electrolytic solution, and the second compound was added at a content of 2 wt% based on the total amount of the electrolytic solution.

[0102] The contents of the compounds contained in the additives of the electrolytic solutions according to each Example and Comparative Example are shown in Table 1 below.

[0103]

Table 1

[0104] 2. Evaluation The lithium secondary battery was evaluated by the method described below.

[0105] 2-1. Evaluation 1: Evaluation of characteristics during storage at high temperature (60 °C) For the lithium secondary batteries according to the examples and comparative examples, after measuring the initial residual capacity (0.33C discharge), recovery capacity (discharge at 0.33C after CC-CV charging at 0.33C), and DC resistance (DCIR) as the ΔV / ΔI (change in voltage / change in current) value, the maximum energy state inside the battery was set to the fully charged state (SOC 100%), stored for 80 days, and then the DC resistance was measured to measure the increase rate (%) of DCIR. Then, after storing the lithium secondary battery in a chamber at 60°C for 80 days, the residual capacity, recovery capacity, and DC resistance were measured respectively, and the residual capacity, recovery capacity, and DCIR increase rate were calculated according to the following formula 1. The results are shown in Table 2.

[0106] Formula 1 Residual capacity (%) = (Discharge capacity after 80 days / Initial discharge capacity) * 100 Recovery capacity (%) = (Recovery capacity after 80 days / Initial recovery capacity) * 100 DCIR increase rate (%) = { (DCIR after 80 days / Initial DCIR) - 1} * 100

[0107]

Table 2

[0108] 2-2. Evaluation 2: Life evaluation at high temperature (45°C) For the lithium secondary batteries according to the examples and comparative examples, in a chamber at 45°C, under the conditions of 0.5C to 1.0C charging (CC / CV, 4.25V, 0.025C Cut-off) / 1.0C discharging (CC, 2.75V, Cut-off), after performing 300 charge-discharge cycles, the residual capacity and DCIR were calculated according to the following formula 2. The results are shown in Table 3. Formula 2 Residual capacity (%) = (Discharge capacity after 300 cycles / Initial discharge capacity) * 100 DCIR increase rate (%) = { (DCIR after 300 cycles / Initial DCIR) - 1} * 100

[0109]

Table 3

[0110] 2-3. Evaluation 3: Characteristic Evaluation during Fast Charging For the lithium secondary batteries according to the examples and comparative examples, under the conditions of charging at 0.33C to 2.7C (CC / CV, 4.25V, 0.025C Cut-off) / discharging at 0.33C (CC, 2.75V, Cut-off), the charge and discharge cycles of the lithium secondary batteries were performed 300 times at 35°C, and then the remaining capacity and DCIR were calculated according to Formula 2. The results are shown in Table 4.

[0111]

Table 4

[0112] 3. Results In Comparative Examples 2 to 5, as a result of applying the 4th compound and the 5th compound, which are partially structurally similar to the 1st compound but have different main skeletons, instead of the 1st compound, the DCIR increase rate was high, and the high-temperature storage characteristics, lifespan, and characteristics during fast charging deteriorated.

[0113] Also, in Comparative Examples 6 to 11, as a result of adding only one of the 1st compound or the 2nd compound, it was confirmed that not only in the examples but also the DCIR increase rate was higher than that in Comparative Examples 2 to 5, and the high-temperature storage characteristics, lifespan, and characteristics during fast charging decreased.

[0114] Also, as a result of comparing Comparative Examples 12 to 19 with the examples, it was confirmed that the content ratio and total content of the 1st compound and the 2nd compound affect the DCIR increase rate.

[0115] Although the preferred embodiments of the present invention have been described so far, the present invention is not limited thereto, and can be variously modified and implemented within the scope of the claims, the mode for carrying out the invention, and the scope of the attached drawings, and it is natural that this also belongs to the scope of the present invention.

Explanation of Reference Numerals

[0116] 100: Lithium secondary battery, 10: Positive electrode, 11: Positive electrode lead tab, 12: Positive electrode terminal, 20: Negative electrode, 21: Negative electrode lead tab, 22: Negative electrode terminal, 30: Separator, 40: Electrode assembly, 50: Housing, 60: Sealing member, 70: Electrode tab, 71: Positive electrode tab, 72: Negative electrode tab

Claims

1. A non-aqueous organic solvent; A lithium salt; and an additive, The additive comprises a first compound represented by the following Chemical Formula 1 and a second compound represented by the following Chemical Formula 2: 【Chemistry 1】 【Chemistry 2】

2. The electrolyte for a lithium secondary battery according to claim 1 , wherein the first compound is contained in an amount of 0.01% by weight to 1% by weight based on the total weight of the electrolyte.

3. 2. The electrolyte for a lithium secondary battery according to claim 1, wherein the additive is contained in an amount of 0.1% by weight to 2% by weight based on the total weight of the electrolyte.

4. The electrolyte for a lithium secondary battery according to claim 1 , wherein the content of the first compound is lower than the content of the second compound.

5. The electrolyte for a lithium secondary battery according to claim 4 , comprising 1 to 10 parts by weight of the second compound based on 1 part by weight of the first compound.

6. 2. The electrolyte solution for a lithium secondary battery according to claim 1, wherein the non-aqueous organic solvent comprises at least one selected from the group consisting of ethylene carbonate, propylene carbonate, propyl propionate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl ethyl carbonate, and butylene carbonate.

7. 7. The electrolyte for a lithium secondary battery according to claim 6, wherein the non-aqueous organic solvent contains ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate.

8. The lithium salt is LiPF ６ , LiBF ４ , LiSbF ６ , LiAsF ６ , LiClO ４ , LiAlO ２ , LiAlCl ４ , LiPO ２ F ２ , LiCl, LiI, LiN(SO ３ C ２ F ５ ) ２ , Li(FSO ２ ) ２ N(lithium bis(fluorosulfonyl)imide (LiFSI), and LiC ４ F ９ SO ３ 2. The electrolyte for a lithium secondary battery according to claim 1, wherein the electrolyte is one or more selected from the group consisting of:

9. 2. The electrolyte for a lithium secondary battery according to claim 1, wherein the concentration of the lithium salt is 0.1M to 2.0M.

10. a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; The electrolyte solution according to any one of claims 1 to 9. Lithium secondary battery.

11. The positive electrode active material includes a lithium metal oxide represented by the following formula 3: [Chemical formula 3] Li ａ Ni １－ｂ－ｃ Co ｂ X ｃ O ２－α D α X is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is O, F, S, P, or a combination thereof; The lithium secondary battery according to claim 10, wherein 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.5, and 0<α<2.

12. The lithium secondary battery of claim 10 , wherein the negative electrode active material comprises a carbon-based negative electrode active material, a Si-based negative electrode active material, a Sn-based negative electrode active material, or a combination thereof.

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