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

Abstract

To provide an electrolyte for a lithium secondary battery that ensures safety and has excellent battery performance.SOLUTION: An electrolyte for a lithium secondary battery according to an embodiment includes a lithium salt, a non-aqueous organic solvent, and an additive represented by the following formula (R1 are the same or different, and at least one is an isocyanate group; R2 are the same or different, and at least one is an isocyanate group; R3 are each independently hydrogen or a cyclohexylisocyanate residue; and n is an integer from 1 to 10.)SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] This relates to lithium secondary batteries. [Background technology]

[0002] Recently, with the rapid spread of electronic devices that use batteries, such as mobile phones, laptops, and electric vehicles, the demand for secondary batteries with high energy density and high capacity is rapidly increasing. For this reason, research and development to improve the performance of lithium secondary batteries is being actively conducted.

[0003] A lithium secondary battery is a battery that includes a positive electrode and a negative electrode, each of which includes an active material capable of intercalating and deintercalating lithium ions, and an electrolyte. When lithium ions are intercalated and deintercalated at the positive electrode and the negative electrode, oxidation and reduction reactions occur, producing electrical energy.

[0004] The positive electrode active material of the lithium secondary battery is a lithium-transition metal oxide, the negative electrode active material is a carbon-based material of various types, and the electrolyte is a non-aqueous organic solvent in which a lithium salt is dissolved.

[0005] The characteristics of a lithium secondary battery are determined by the complex reactions between a positive electrode and an electrolyte, a negative electrode and an electrolyte, etc. Therefore, the use of an appropriate electrolyte is one of the important variables for improving the performance of a lithium secondary battery. Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide an electrolyte for a lithium secondary battery that is excellent in battery performance while ensuring safety.

[0007] Another object of the present invention is to provide a lithium secondary battery containing the above-mentioned electrolyte for lithium secondary batteries. [Means for solving the problem]

[0008] The electrolyte for a lithium secondary battery according to one embodiment of the present invention includes a lithium salt, a non-aqueous organic solvent, and an additive represented by the following Chemical Formula 1. [ka] ...chemical formula 1

[0009] In the above formula 1, R1 may be the same or different, each independently being hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, or an isocyanate group, and at least one of the R1 may be an isocyanate group. R2 may be the same or different, each independently being hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, or an isocyanate group, and at least one of the R2 may be an isocyanate group. R3 may be the same or different, each independently being hydrogen or a cyclohexylisocyanate residue. n may be an integer of 1 to 10.

[0010] A lithium secondary battery according to another embodiment of the present invention includes a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, and the electrolyte. Effect of the Invention

[0011] The lithium secondary battery according to one embodiment of the present invention can realize a lithium secondary battery having excellent battery performance while ensuring safety. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram showing a lithium secondary battery according to an embodiment. [Diagram 2] FIG. 1 is a schematic diagram showing a lithium secondary battery according to an embodiment. [Diagram 3] FIG. 1 is a schematic diagram showing a lithium secondary battery according to an embodiment. [Figure 4] FIG. 1 is a schematic diagram showing a lithium secondary battery according to an embodiment. [Diagram 5] FIG. 1 is a schematic diagram showing a lithium secondary battery according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] In order 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 is not limited to the embodiments disclosed below, and may be realized in various forms and may be modified in various ways. However, the description of the present embodiment is provided to complete the disclosure of the present invention and to fully inform those skilled in the art of the present invention of the scope of the invention.

[0014] In this specification, when a component is referred to as being on another component, it means that it may be formed directly on the other component, or a third component may be interposed between them. Also, in the drawings, the thickness of the components is exaggerated for the purpose of effectively explaining the technical content. Throughout the specification, parts designated with the same reference numerals indicate the same components.

[0015] The embodiments described herein are described with reference to cross-sectional views and / or plan views which are ideal exemplary views of the present invention. In the drawings, the thicknesses of films and regions are exaggerated for the effective explanation of the technical contents. Therefore, the regions illustrated in the drawings have schematic attributes, and the patterns of the regions illustrated in the drawings are intended to illustrate a specific form of the region of the element, and are not intended to limit the scope of the invention. In various embodiments of the present specification, terms such as first, second, and third are used to describe various components, but these components should not be limited to such terms. These terms are merely used to distinguish one component from another component. The embodiments described and illustrated herein also include their complementary embodiments.

[0016] The terms used in the present specification are for describing the embodiments and are not intended to limit the present invention. In the present specification, the singular form includes the plural form unless otherwise specified in the text. When used in the specification, "comprises" and / or "comprising" are used, the mentioned components do not exclude the presence or addition of one or more other components.

[0017] As used herein, "combinations thereof" can mean mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0018] In the chemical formulas herein, unless otherwise defined, when a chemical bond is not drawn at a position where a chemical bond should be drawn, this means that a hydrogen atom is bonded to that position.

[0019] In this specification halogen includes F, Cl, Br and I.

[0020] In this specification, transition metals include scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), technetium (Tc), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), cadmium (Cd), and lutetium (L). These include ruthenium (U), hafnium (Hf), tantalum (Ta), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), gold (Au), mercury (Hg), lawrencium (Lr), rutherfordium (Rf), dubnium (Db), seaborgium (Sg), bohrium (Bh), hassium (Hs), meitnerium (Mt), darmstadtium (Ds), roentgenium (Rg), and copernicium (Cn).

[0021] In this specification, unless otherwise specified, normal temperature means 25±10°C.

[0022] In this specification, "deterioration of cell performance" refers, by way of example, to negative effects of lithium secondary batteries such as a decrease in storage capacity and recovery capacity at room temperature and high temperature, a decrease in capacity retention rate at 200 cycles, and an increase in the amount of gas generated during storage at high temperature, but is not limited to these.

[0023] 1 is a schematic diagram showing a lithium secondary battery according to an embodiment of the present invention. Referring to FIG. 1, the lithium secondary battery may include a positive electrode 100, a negative electrode 200, an electrolyte 300, and a separator 400.

[0024] The positive electrode 100 and the negative electrode 200 may be separated from each other by a separator 400. The separator 400 may be disposed between the positive electrode 100 and the negative electrode 200. The positive electrode 100, the negative electrode 200, and the separator 400 may be in contact with an electrolyte solution 300. The positive electrode 100, the negative electrode 200, and the separator 400 may be impregnated in the electrolyte solution 300.

[0025] The electrolyte 300 may be a medium for transmitting lithium ions between the positive electrode 100 and the negative electrode 200. In the electrolyte 300, the lithium ions may pass through the separator 400 and move toward the positive electrode 100 or the negative electrode 200. Hereinafter, the positive electrode 100, the negative electrode 200, the electrolyte 300, and the separator 400 of the lithium secondary battery according to the embodiment of the present invention will be described in more detail.

[0026] Electrolyte for lithium secondary batteries The electrolyte solution 300 for a lithium secondary battery contains a lithium salt, a non-aqueous organic solvent, and an additive.

[0027] A lithium salt is a substance that is dissolved in a non-aqueous organic solvent and acts as a source of lithium ions in a battery to enable basic lithium secondary battery operation and to promote the movement of lithium ions between the positive electrode and the negative electrode.

[0028] As the lithium salt, LiPF6 can be used.

[0029] The concentration of the lithium salt may be 0.1M to 2.0M. In particular, the concentration of the lithium salt may be 0.5M or more, 1.0M or more, or 1.5M or more. The concentration of the lithium salt may be 2.0M or less, 1.7M or less, or 1.5M or less. If the concentration of the lithium salt is less than 0.1M, the conductivity of the electrolyte may decrease, and the performance of the electrolyte may decrease. If the concentration of the lithium salt exceeds 2.0M, the viscosity of the electrolyte may increase, and the mobility of lithium ions may decrease.

[0030] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reactions of the battery can migrate.

[0031] The non-aqueous organic solvent may be a carbonate-based, ester-based, ether-based, ketone-based, or alcohol-based solvent, a non-quantum solvent, or a combination thereof.

[0032] As the carbonate-based solvent, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl pyrrolyl carbonate (MPC), ethyl propyl carbonate (EPC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. may be used. 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. may be used. As the ether-based solvent, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. may be used. Also, as the ketone-based solvent, cyclohexanone, etc. may be used. Examples of the alcohol-based solvent that may be used include ethyl alcohol and isopropyl alcohol. Examples of the non-quantum solvent that may be used include nitriles such as R-CN (R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, which may contain a double bond, an aromatic ring, or an ether group), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane and 1,4-dioxolane, and sulfolanes.

[0033] The aqueous organic solvent may be used alone or in combination of two or more kinds.

[0034] In the latter case, the non-aqueous organic solvent may include carbonate-based solvents and propionate-based solvents.

[0035] The propionate-based solvent may be contained in an amount of 70% by volume or more based on the total amount of the non-aqueous organic solvent, which can improve the high voltage and / or high temperature characteristics of the lithium secondary battery.

[0036] For example, the non-aqueous organic solvent may be a mixed solvent of ethylene carbonate (EC), propylene carbonate (PC), and propyl propionate (PP).

[0037] The additive may be contained in an amount of 0.05 to 10% by weight based on the total amount of the electrolyte. Specifically, the additive may be contained in an amount of 0.1% by weight or more, 0.5% by weight or more, 1% by weight or more, or 5% by weight or more based on the total amount of the electrolyte. The additive may be contained in an amount of 8% by weight or less, 7% by weight or less, or 5% by weight or less based on the total amount of the electrolyte. When the additive is contained in an amount of less than 0.05% by weight based on the total amount of the electrolyte, the effect of solving the problem caused by the transition metal ions eluted from the positive electrode current collector may be insignificant. When the additive is contained in an amount of more than 10% by weight based on the total amount of the electrolyte, the high-temperature life may be deteriorated when performing high-temperature charge-discharge cycles.

[0038] The additive according to one embodiment of the present invention is represented by the following chemical formula 1. [ka] ...chemical formula 1

[0039] In Chemical Formula 1, R1 may be the same or different and each independently represents hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, or an isocyanate group. At least one of R1 may be an isocyanate group.

[0040] In Chemical Formula 1, R2 may be the same or different and each independently represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 10 carbon atoms, or an isocyanate group. At least one of R2 may be an isocyanate group.

[0041] In Chemical Formula 1, R3 may be the same or different, and each R3 is independently hydrogen or a cyclohexylisocyanate residue.

[0042] In Chemical Formula 1, n is an integer from 1 to 10.

[0043] Although the positive electrode active material, which is lithium-transition metal oxide, has a stable structure, transition metal ions are dissolved during charge / discharge processes and high-temperature storage, causing side reactions with moisture, which leads to deterioration of the overall cell performance.

[0044] The electrolyte for lithium secondary batteries using the additive can control moisture and effectively prevent transition metal ions from being dissolved from the positive electrode and precipitated on the surface of the negative electrode, thereby effectively preventing deterioration of cell performance during charge / discharge processes and high-temperature storage.

[0045] The additive according to another embodiment of the present invention may be represented by the following formula 1-1. [ka] ...Chemical formula 1-1

[0046] In Chemical Formula 1-1, R1's are the same or different and each independently represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 10 carbon atoms, or an isocyanate group. At least one of R1's may be an isocyanate group.

[0047] In Chemical Formula 1-1, R2 may be the same or different and each independently represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 10 carbon atoms, or an isocyanate group. At least one of R2 may be an isocyanate group.

[0048] The electrolyte for lithium secondary batteries using the additive can control moisture and effectively prevent transition metal ions from being dissolved from the positive electrode and precipitated on the surface of the negative electrode, thereby effectively preventing deterioration of cell performance during charge / discharge processes and high-temperature storage.

[0049] The additive according to another embodiment of the present invention may be represented by the following formula 1-2. [ka] ...Chemical formula 1-2

[0050] In Chemical Formula 1-2, R1's may be the same or different and each independently represents a hydrogen atom, a halogen atom, or an alkyl group having 1 to 10 carbon atoms.

[0051] In Chemical Formula 1-2, R2's may be the same or different and each independently represents a hydrogen atom, a halogen atom, or an alkyl group having 1 to 10 carbon atoms.

[0052] The electrolyte for lithium secondary batteries using the additive can control moisture and effectively prevent transition metal ions from being dissolved from the positive electrode and precipitated on the surface of the negative electrode, thereby effectively preventing deterioration of cell performance during charge / discharge processes and high-temperature storage.

[0053] The electrolyte contains one transition metal ion or a mixture of two or more transition metal ions.

[0054] The electrolyte may contain one or a mixture of two or more ions selected from the group consisting of iron ions, phosphate ions, cobalt ions, manganese ions, nickel ions, aluminum ions, and halogen ions.

[0055] The electrolyte may include iron ions.

[0056] Positive electrodes for lithium secondary batteries The lithium secondary battery positive electrode 100 includes a first current collector COL1 and a positive electrode active material layer AML1 formed on the first current collector COL1. The positive electrode active material layer AML1 includes a positive electrode active material, and may further include a binder and / or a conductive material.

[0057] As an example, the positive electrode may further include an additive that may act as a sacrificial positive electrode.

[0058] The content of the positive electrode active material may be 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 be 0.5% by weight to 5% by weight, based on 100% by weight of the positive electrode active material layer AML1.

[0059] The binder can serve to effectively adhere the positive electrode active material particles to each other and to effectively adhere the positive electrode active material to the first 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, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylic styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, and nylon.

[0060] The conductive material is used to give electrical conductivity to the electrode, and any conductive material can be used as long as it does not cause chemical changes in the battery that is constructed. Examples of the conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0061] The first current collector COL1 can be made of Al, but is not limited to this.

[0062] positive electrode active material The positive electrode active material is a compound capable of reversibly inserting and extracting lithium (lithiated intercalation compound). More specifically, one or more of composite oxides of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof can be used.

[0063] The composite oxide may be a lithium transition metal composite oxide, and 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.

[0064] As an example, the positive electrode active material may be a compound represented by any one of the following chemical formulas: 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 Ni 1-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 O2(0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0≦d≦0.5, 0≦e≦0.1);Li a NiG bO2(0.90≦a≦1.8, 0.001≦b≦0.1);Li a CoG b O2(0.90≦a≦1.8, 0.001≦b≦0.1);Li a Mn 1-b G b O2(0.90≦a≦1.8, 0.001≦b≦0.1);Li a Mn2G b O4(0.90≦a≦1.8, 0.001≦b≦0.1);Li a Mn 1-g G g PO4(0.90≦a≦1.8, 0≦g≦0.5);Li (3-f) Fe2(PO4)3(0≦f≦2);Li a FePO4(0.90≦a≦1.8).

[0065] 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.

[0066] As an example, the positive electrode active material may be a high-nickel 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 relative to 100 mol% of metals excluding lithium from the lithium transition metal composite oxide. The high-nickel positive electrode active material can achieve high capacity and can therefore be applied to high-capacity, high-density lithium secondary batteries.

[0067] The positive electrode active material may include, for example, a lithium nickel-based oxide represented by the following chemical formula 2, a lithium cobalt-based oxide represented by the following chemical formula 3, a lithium iron phosphate-based oxide represented by the following chemical formula 4, a cobalt-free lithium nickel-manganese oxide represented by the following chemical formula 5, or a combination thereof.

[0068] Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1 ...Chemical formula 2 In Chemical Formula 2, 0.9≦a1≦1.8, 0.3≦x1≦1, 0≦y1≦0.7, 0≦z1≦0.7, 0.9≦x1+y1+z1≦1.1, and 0≦b1≦0.1; M 1 and M 2 are each independently one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

[0069] In Chemical Formula 2, 0.6≦x1≦1, 0≦y1≦0.4, and 0≦z1≦0.4, or 0.8≦x1≦1, 0≦y1≦0.2, and 0≦z1≦0.2 may be satisfied.

[0070] Li a2 Co x2 M 3 y2 O 2-b2 X b2 ...chemical formula 3 In Chemical Formula 3, 0.9≦a2≦1.8, 0.7≦x2≦1, 0≦y2≦0.3, 0.9≦x2+y2≦1.1, and 0≦b2≦0.1; M 3 is one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Se, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

[0071] Li a3 Fe x3 M 4 y3 PO 4-b3 X b3 ...chemical formula 4 In Chemical Formula 4, 0.9 ≦ a3 ≦ 1.8, 0.6 ≦ x3 ≦ 1, 0 ≦ y3 ≦ 0.4, and 0 ≦ b3 ≦ 0.1, and M 4 is one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Co, Cr, Cu, Mg, Mn, Mo, Ni, Se, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

[0072] Li a4 Ni x4 Mn y4 M 5 z4 O 2-b4 X b4 ···Chemical Formula 5 In Chemical Formula 5, 0.9 ≦ a4 ≦ 1.8, 0.8 ≦ x4 < 1, 0 < y4 ≦ 0.2, 0 ≦ z4 ≦ 0.2, 0.9 ≦ x4 + y4 + z4 ≦ 1.1, and 0 ≦ b4 ≦ 0.1, and M 5 is one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

[0073] In particular, the electrolyte of the above-described embodiment can significantly improve the performance degradation of the cells of a battery to which the lithium iron phosphate-based oxide represented by the above Chemical Formula 4 is applied.

[0074] Negative electrodes for lithium secondary batteries The negative electrode 200 for a lithium secondary battery includes a second current collector COL2 and a negative electrode active material layer AML2 formed on the second 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.

[0075] For example, the negative electrode active material layer AML2 may contain 90% to 99% by weight of a negative electrode active material, 0.5% to 5% by weight of a binder, and 0% to 5% by weight of a conductive material.

[0076] The binder may serve to firmly adhere the negative active material particles to each other and to firmly adhere the negative active material to the second current collector COL2. The binder may be a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0077] Non-aqueous binders include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymers, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

[0078] The aqueous binder may be selected from styrene-butadiene rubber, (meth)acrylate 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.

[0079] When an aqueous binder is used as the negative electrode binder, it may further contain a cellulose-based compound that can impart viscosity. As the cellulose-based compound, one or more of carboxymethylcellulose, hydroxypropylmethylcellulose, methylcellulose, or alkali metal salts thereof may be mixed and used. As the alkali metal, Na, K, or Li may be used.

[0080] The dry binder may be a fiberizable polymeric material, such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, ethylene oxide, or combinations thereof.

[0081] The conductive material is used to give electrical conductivity to the electrode, and any conductive material can be used as long as it does not cause a chemical change in the battery that is constructed. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0082] The second current collector COL2 of the negative electrode can be 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.

[0083] negative electrode active material The negative electrode active material may include a material capable of reversibly inserting / extracting lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping or dedoping lithium, or a transition metal oxide.

[0084] The material capable of reversibly inserting / extracting lithium ions may be a carbon-based negative electrode active material, and may include, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of crystalline carbon include graphite such as amorphous, plate-like, flake-like, spherical, or fibrous natural graphite and artificial graphite. Examples of amorphous carbon include soft or hard carbon, mesophase pitch carbide, calcined coke, etc.

[0085] As an 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 may be used.

[0086] 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 may 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, SnO2, a Sn-based alloy, or a combination thereof.

[0087] 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, and for example, the primary silicon particles may be coated with amorphous carbon. The secondary particles may be present dispersed in an amorphous carbon matrix.

[0088] 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.

[0089] The Si-based negative electrode active material or the Sn-based negative electrode active material can be used by mixing with a carbon-based negative electrode active material.

[0090] Separator Depending on the type of lithium secondary battery, a separator 400 may be present between the positive electrode and the negative electrode. As such a separator, 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 polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may also be used.

[0091] The separator may include a porous substrate and a coating layer comprising an organic, an inorganic, or a combination thereof located on one or both sides of the porous substrate.

[0092] The porous substrate may be a polymer membrane made of any one polymer selected from polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyether ketone, polyaryl ether ketone, polyetherimide, polyamide imide, polybenzimidazole, polyether sulfone, polyphenylene oxide, cyclic olefin copolymers, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon, and polytetrafluoroethylene, or a copolymer or mixture of two or more of these polymers.

[0093] The organic material may include a polyvinylidene fluoride polymer or a (meth)acrylic polymer.

[0094] The inorganics may include, but are not limited to, inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof.

[0095] The organic material and the inorganic material may be mixed in one coating layer, or a coating layer containing an organic material and a coating layer containing an inorganic material may be laminated.

[0096] Lithium secondary battery The lithium secondary battery according to the embodiment of the present invention may be classified into a cylindrical type, a square type, a pouch type, a coin type, and the like according to the shape. FIGS. 2 to 5 are schematic diagrams showing a lithium secondary battery according to an embodiment, in which FIG. 2 shows a circular type, FIG. 3 shows a square type, and FIGS. 4 and 5 show a pouch type battery shape. Referring to FIGS. 2 to 5, the lithium secondary battery 1 includes an electrode assembly 500 having a separator 400 interposed between a positive electrode 100 and a negative electrode 200, and a case 600 in which the electrode assembly 500 is embedded. The positive electrode 100, the negative electrode 200, and the separator 400 may be impregnated with an electrolyte 300. The lithium secondary battery 1 may include a sealing member 700 that seals the case 600 as shown in FIG. 2. In addition, in FIG. 3, the lithium secondary battery 1 may include a positive electrode lead tab 110, a positive electrode terminal 120, a negative electrode lead tab 210, and a negative electrode terminal 220. As shown in FIGS. 3 and 4, the lithium secondary battery 1 may include electrode tabs 800, i.e., a positive electrode tab 810 and a negative electrode tab 820, which serve as electrical paths for conducting the current generated in the positive electrode assembly 500 to the outside.

[0097] The lithium secondary battery according to an embodiment of the present invention may be applied to automobiles, mobile phones, and / or various types of electric devices, but the present invention is not limited thereto.

[0098] Examples and comparative examples of the present invention are described below, but the following examples are merely one embodiment of the present invention and the present invention is not limited to the following examples.

[0099] Examples and Comparative Examples An electrolyte and a lithium secondary battery were manufactured as follows.

[0100] Example 1 (1) Electrolyte production An electrolyte was prepared by dissolving 1.15 M LiPF6 in a non-aqueous organic solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 20:40:40, and adding 0.5 wt% of an additive.

[0101] The additive used was the one represented by the following chemical formula 1-1-1. [ka] ···Chemical formula 1-1-1

[0102] (2) Manufacture of lithium secondary batteries LiFePO4 as a positive electrode active material, polyvinylidene fluoride as a binder, and acetylene black as a conductive material were mixed in a weight ratio of 96:3:1, and dispersed in N-methylpyrrolidone to prepare a positive electrode active material slurry.

[0103] The positive electrode active material slurry was coated onto an Al foil having a thickness of 15 μm to form a layer, which was then dried at 100° C. and pressed to prepare a positive electrode.

[0104] Artificial graphite was used as the negative electrode active material, and the negative electrode active material was mixed with a styrene-butadiene rubber binder and carboxymethyl cellulose in a weight ratio of 98:1:1, respectively, and dispersed in distilled water to prepare a negative electrode active material slurry.

[0105] The negative electrode active material slurry was coated onto a Cu foil with a thickness of 10 μm to form a layer, which was then dried at 100° C. and rolled to prepare a negative electrode.

[0106] The produced positive and negative electrodes were assembled with a 10 μm thick separator made of polyethylene to produce an electrode assembly, and the above electrolyte was injected into the electrode assembly to produce a lithium secondary battery.

[0107] Example 2 An electrolyte and a lithium secondary battery were prepared in the same manner as in Example 1, except that LiCoO2 was used as the positive electrode active material.

[0108] Example 3 An electrolyte and a lithium secondary battery were prepared in the same manner as in Example 1, except that Li(NiCoAl)O2 was used as the positive electrode active material.

[0109] Example 4 An electrolyte and a lithium secondary battery were prepared in the same manner as in Example 1, except that Li(NiCoMn)O2 was used as the positive electrode active material.

[0110] Comparative Example 1 An electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 1, except that no additives were added when preparing the electrolyte solution.

[0111] Comparative Example 2 An electrolyte and a lithium secondary battery were prepared in the same manner as in Example 1, except that no additives were added when preparing the electrolyte and LiCoO2 was used as the positive electrode active material.

[0112] Comparative Example 3 An electrolyte and a lithium secondary battery were prepared in the same manner as in Example 1, except that no additives were added when preparing the electrolyte and Li(NiCoAl)O2 was used as the positive electrode active material.

[0113] Comparative Example 4 An electrolyte and a lithium secondary battery were prepared in the same manner as in Example 1, except that no additives were added when preparing the electrolyte and Li(NiCoMn)O2 was used as the positive electrode active material.

[0114] Comparative Example 5 An electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 1, except that an additive represented by the following Chemical Formula 1-1-2 was used in preparing the electrolyte solution. [ka] ...Chemical formula 1-1-2

[0115] Comparative Example 6 An electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 1, except that an additive represented by the following Chemical Formula 1-1-3 was used in preparing the electrolyte solution. [ka] ...Chemical formula 1-1-3

[0116] Evaluation example The lithium secondary batteries were evaluated as follows.

[0117] Evaluation 1: Evaluation of high temperature (60℃) storage characteristics - DCIR increase rate For the lithium secondary batteries according to each of the Examples and Comparative Examples, the initial DC resistance (DCIR) was measured using a ΔV / ΔI (change in voltage / change in current) value, and the maximum energy state inside the battery was set to a fully charged state (SOC 100%). In this state, the batteries were stored at high temperature (60° C.) for 30 days, after which the DC resistance was measured and the DCIR increase rate (%) was calculated according to the following Equation 1. The results are shown in Table 1 below. [Formula 1] DCIR increase rate (%) = (DCIR after 30 days / initial DCIR) * 100 [Table 1]

[0118] Evaluation 2: Evaluation of room temperature charge / discharge cycle characteristics The lithium secondary batteries according to each of the Examples and Comparative Examples were evaluated for their room temperature charge-discharge characteristics. Specifically, the lithium secondary batteries were subjected to 200 charge-discharge cycles under the conditions of 25° C., 0.33 C charge (CC / CV, 4.45 V, 0.025 C cut-off) / 1.0 C discharge (CC, 2.5 V cut-off).

[0119] The capacity retention rate was calculated according to the following formula 2. The results are shown in Table 2 below. [Formula 2] Capacity retention rate (%) = (discharge capacity after 200 cycles / discharge capacity after 1 cycle) * 100 [Table 2]

[0120] Evaluation 3: Evaluation of high temperature (45℃) charge / discharge cycle characteristics The lithium secondary batteries according to the examples and comparative examples were evaluated for high-temperature charge-discharge characteristics. Specifically, the lithium secondary batteries were subjected to 200 charge-discharge cycles under the conditions of 45° C., 0.33 C charge (CC / CV, 4.45 V, 0.025 C cut-off) / 1.0 C discharge (CC, 2.5 V cut-off).

[0121] The capacity retention rate was calculated according to the following formula 2. The results are shown in Table 3 below. [Formula 2] Capacity retention rate (%) = (discharge capacity after 200 cycles / discharge capacity after 1 cycle) * 100 [Table 3]

[0122] Evaluation 4: Evaluation of high temperature (60℃) gas generation characteristics The lithium secondary batteries according to each Example and Comparative Example were evaluated for high-temperature gas generation characteristics. Specifically, the maximum energy state inside the battery was set to full charge (SOC 100%), and the battery was stored in this state at high temperature (60°C) for 10 or 30 days, after which the amount of gas generated was evaluated, and the results are shown in Table 4 below. The amount of gas generated was determined by measuring the volume change before and after high-temperature storage, and converting it into mass change using the Archimedes method. [Table 4]

[0123] General Referring to Table 1 above, when an electrolyte solution containing no additives was used (Comparative Examples 1 to 4), and when additives represented by chemical formula 1-1-2 (Comparative Example 5) and chemical formula 1-1-3 (Comparative Example 6) were used, the DCIR increased rapidly after storage at high temperature (60°C). Therefore, the comparative examples can be evaluated as having poor high-temperature storage properties.

[0124] However, when an electrolyte containing an additive according to the concept of the present invention was used (Examples 1 to 4), it was confirmed that the DCIR increase rate was improved when left at high temperature (60° C.).

[0125] Referring to Tables 2 and 3, when an electrolyte solution containing no additives was used (Comparative Examples 1 to 4) and when additives represented by chemical formulas 1-1-2 (Comparative Example 5) and 1-1-3 (Comparative Example 6) were used, the capacity retention rate at room temperature and high temperature (45°C) was reduced, and the life span at room temperature and high temperature (45°C) was deteriorated. However, when an electrolyte solution containing an additive according to the concept of the present invention was used (Examples 1 to 4), it was confirmed that the capacity retention rate at room temperature and high temperature (45°C) was improved.

[0126] Referring to Table 4 above, it was evaluated that the amount of gas generated was large when stored at high temperature (60°C) when an electrolyte solution containing no additives was used (Comparative Examples 1 to 4) and when additives represented by Chemical Formula 1-1-2 (Comparative Example 5) and Chemical Formula 1-1-3 (Comparative Example 6) were used. However, it was confirmed that gas generation was effectively suppressed when stored at high temperature (60°C) when an electrolyte solution containing an additive according to the concept of the present invention was used (Examples 1 to 4).

[0127] From the above evaluation results, it was confirmed that the additive according to the concept of the present invention has an excellent effect in preventing the deterioration of cell performance.

[0128] In particular, the additive according to the concept of the present invention has a high reduction potential and a low oxidation potential even though it contains an isocyanate group, and therefore, unlike Comparative Examples 5 and 6, which have poor chemical stability, it has been confirmed that the additive has an excellent effect of stably controlling moisture and preventing deterioration of cell performance.

[0129] Although the present invention has been described above with reference to a preferred embodiment, the present invention is not limited thereto, and can be embodied in various modified forms within the scope of the claims, the embodiments of the invention, and the accompanying drawings, which of course also fall within the scope of the present invention. [Explanation of symbols]

[0130] 1: lithium secondary battery, 100: positive electrode, 110: positive electrode lead tab, 120: positive electrode terminal, 200: negative electrode, 210: negative electrode lead tab, 220: negative electrode terminal, 300: electrolyte, 400: separator, 500: electrode assembly, 600: housing, 700: sealing member, 800: electrode tab, 810: positive electrode tab, 820: Negative electrode tab

Claims

1. A lithium salt; A non-aqueous organic solvent; and an additive represented by the following chemical formula 1: Electrolyte for lithium secondary batteries. 【Chemistry 1】 ...Chemical formula 1 (In the above Chemical Formula 1, R １ are the same or different, and each independently represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 10 carbon atoms, or an isocyanate group; １ At least one of the groups is an isocyanate group, R ２ are the same or different, and each independently represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 10 carbon atoms, or an isocyanate group; ２ At least one of the groups is an isocyanate group, R ３ are the same or different and each independently represents hydrogen or a cyclohexyl isocyanate residue, n is an integer from 1 to 10.

2. The electrolyte for a lithium secondary battery according to claim 1, wherein the additive is represented by the following chemical formula 1-1: 【Chemistry 2】 ...Chemical formula 1-1 (In the above Chemical Formula 1-1, R １ are the same or different, and each independently represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 10 carbon atoms, or an isocyanate group; １ At least one of the groups is an isocyanate group, R ２ are the same or different, and each independently represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 10 carbon atoms, or an isocyanate group; ２ At least one of the groups is an isocyanate group.

3. The electrolyte for a lithium secondary battery according to claim 1, wherein the additive is represented by the following formula 1-2: 【Chemistry 3】 ...Chemical formula 1-2 (In the above Chemical Formula 1-2, R １ are the same or different and each independently represents a hydrogen atom, a halogen atom, or an alkyl group having 1 to 10 carbon atoms; R ２ are the same or different and each independently represents hydrogen, halogen, or an alkyl group having 1 to 10 carbon atoms.

4. 2. The electrolyte for a lithium secondary battery according to claim 1, wherein the additive is contained in an amount of 0.05% by weight to 10% by weight based on the total amount of the electrolyte.

5. The electrolyte for a lithium secondary battery according to claim 1 , wherein the non-aqueous organic solvent comprises a carbonate-based solvent.

6. 6. The electrolyte for a lithium secondary battery according to claim 5, wherein the carbonate-based solvent contains ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC).

7. The electrolyte for lithium secondary batteries according to claim 6, wherein the ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) are contained in a volume ratio of 1:1 to 3:1 to 3.

8. The lithium salt is LiPF ６ The electrolyte for a lithium secondary battery according to claim 1,

9. 2. The electrolyte for lithium secondary batteries 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 lithium secondary battery according to claim 10 , wherein the positive electrode active material comprises a lithium iron phosphate compound.

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.

13. The lithium secondary battery according to claim 10, wherein the additive is contained in an amount of 0.05% by weight to 10% by weight based on the total amount of the electrolyte.

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