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

Abstract

An electrolyte for lithium secondary batteries that improves lifespan, storage performance, and rapid charge / discharge characteristics. [Solution] The electrolyte comprises a non-aqueous organic solvent, a lithium salt, and an additive, and includes a mixture of a first additive represented by chemical formula 1 and a second additive represented by chemical formula 2, with the weight ratio of the first additive to the second additive being 1:10 to 1:150. JPEG2026092706000019.jpg61100 [Chemical formula 2]L 2 -C=(O)-OL 1 -OC=(O)-L 3

Description

Technical Field

[0001] One embodiment of the present invention relates to an electrolyte for a lithium secondary battery and a lithium secondary battery containing 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 promoted.

[0003] A lithium secondary battery is a battery including a positive electrode and a negative electrode containing an active material capable of inserting (intercalation) and desorbing (deintercalation) lithium ions, and an electrolyte, and generates electrical energy by oxidation and reduction reactions when lithium ions are inserted into and desorbed from the positive electrode and the negative electrode.

[0004] The electrolyte of such a lithium secondary battery uses a non-aqueous organic solvent in which a lithium salt is dissolved. In a lithium secondary battery, the characteristics of the battery appear due to 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 parameters for improving the performance of lithium secondary batteries.

Summary of the Invention

Problems to be Solved by the Invention

[0005] One embodiment provides an electrolyte for a lithium secondary battery that improves the life and storage performance and the rapid charge / discharge characteristics in a wide temperature range including low temperature, normal temperature, and high temperature in a lithium secondary battery.

[0006] Another embodiment provides a lithium secondary battery containing this electrolyte.

Means for Solving the Problems

[0007] One embodiment provides an electrolyte for a lithium secondary battery comprising a non-aqueous organic solvent, a lithium salt, and an additive, wherein the additive comprises a mixture of a first additive represented by the following chemical formula 1 and a second additive represented by the following chemical formula 2, and the weight ratio of the first additive to the second additive is 1:10 to 1:150.

[0008] [ka]

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

[0010] [ka]

[0011] In chemical formula 2, L 1 This is a substituted or unsubstituted alkylene group having 1 to 10 carbon atoms. L 2 and L 3 Each of these is independently a substituted or unsubstituted alkyl group having 1 to 3 carbon atoms.

[0012] Another embodiment provides a lithium secondary battery comprising a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and an electrolyte for a lithium secondary battery. [Effects of the Invention]

[0013] An electrolyte according to one embodiment can provide a lithium secondary battery that improves lifespan and storage performance over a wide temperature range including low temperature, room temperature, and high temperature, and improves rapid charge and discharge characteristics. [Brief explanation of the drawing]

[0014] [Figure 1] This is a simplified conceptual diagram showing a lithium secondary battery according to one embodiment of the present invention. [Figure 2] This is a schematic cross-sectional view showing a lithium secondary battery according to one embodiment. [Figure 3] This is a schematic cross-sectional view showing a lithium secondary battery according to one embodiment. [Figure 4] This is a schematic cross-sectional view showing a lithium secondary battery according to one embodiment. [Figure 5] This is a schematic cross-sectional view showing a lithium secondary battery according to one embodiment. [Modes for carrying out the invention]

[0015] To fully understand the structure and effects of the present invention, preferred embodiments will be described with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below and can be carried out in various forms and modified in many ways. The following description is provided to complete the disclosure of the present invention through the description of these embodiments and to fully inform those who are ordinary skill in the art to which the invention pertains.

[0016] 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. Furthermore, in the drawings, the thickness of components is exaggerated for the sake of effective illustration of the technical content. Throughout the specification, the same reference numeral refers to the same component.

[0017] Unless otherwise specified herein, singular nouns may also include plural nouns. Furthermore, unless otherwise specified, “A or B” means “including A, including B, or including A and B.” As used herein, “including” does not exclude the presence or addition of one or more other components.

[0018] In this specification, “these combinations” may mean mixtures, laminates, composites, copolymers, alloys, blends, and reaction products of the constituents.

[0019] In this specification, "substituted" means that, unless otherwise defined, at least one hydrogen atom of a substituent or compound is substituted with deuterium, halogen, hydroxyl group, amino group, C1-C30 amino group, nitro group, C1-C40 silyl group, C1-C30 alkyl group, C1-C10 alkylsilyl group, C6-C30 arylsilyl group, C3-C30 cycloalkyl group, C3-C30 heterocycloalkyl group, C6-C30 aryl group, C2-C30 heteroaryl group, C1-C20 alkoxy group, C1-C10 fluoroalkyl group, cyano group, or a combination thereof.

[0020] Specifically, "substitution" can mean that at least one hydrogen atom of a substituent or compound is substituted with deuterium, halogen, C1-C30 alkyl, C1-C10 alkylsilyl, C6-C30 arylsilyl, C3-C30 cycloalkyl, C3-C30 heterocycloalkyl, C6-C30 aryl, C2-C30 heteroaryl, C1-C10 fluoroalkyl, or cyano group. For example, "substitution" can mean that at least one hydrogen atom of a substituent or compound is substituted with deuterium, halogen, C1-C20 alkyl, C6-C30 aryl, C1-C10 fluoroalkyl, or cyano group. Also, "substitution" can mean that at least one hydrogen atom of a substituent or compound is substituted with deuterium, halogen, C1-C5 alkyl, C6-C18 aryl, C1-C5 fluoroalkyl, or cyano group. For example, "substitution" may mean that at least one hydrogen atom of a substituent or compound is substituted with deuterium, a cyano group, a halogen group, a methyl group, an ethyl group, a propyl group, a butyl group, a phenyl group, a biphenyl group, a terphenyl group, a trifluoromethyl group, or a naphthyl group.

[0021] In this specification, unless otherwise defined, "*" means a portion that is bonded to the same or different atoms or substituents. In the chemical formulas described herein, unless otherwise specified, hydrogen can be considered to be bonded in the structure of the chemical formula.

[0022] Figure 1 is a simplified conceptual diagram showing a lithium secondary battery according to an embodiment of the present invention. Referring to Figure 1, the lithium secondary battery may include a positive electrode 10, a negative electrode 20, a separator 30, and an electrolyte ELL.

[0023] The positive electrode 10 and the negative electrode 20 may be separated from each other via a separator 30. The separator 30 may be placed 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 electrolyte ELL. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated in the electrolyte ELL.

[0024] The electrolyte ELL may be a medium for transferring lithium ions between the positive electrode 10 and the negative electrode 20. In the electrolyte ELL, lithium ions may move towards the positive electrode 10 or the negative electrode 20 by passing through the separator 30.

[0025] positive electrode 10 The positive electrode 10 for the 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 includes a positive electrode active material and may further include a binder and / or a conductive material.

[0026] As an example, the positive electrode 10 may further contain an additive that can act as a sacrificial positive electrode.

[0027] The content of the positive electrode active material in the positive electrode active material layer AML1 may be 90% to 99.5% by weight relative to 100% by weight of the positive electrode active material layer AML1. The content of the binder and conductive material may be 0.5% to 5% by weight, respectively, relative to 100% by weight of the positive electrode active material layer AML1.

[0028] The binder plays a role in firmly adhering the positive electrode active material particles to each other and further firmly adhering the positive electrode active material to the current collector COL1. Typical examples of binders include, but are not limited to, polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylate styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, and nylon.

[0029] The conductive material is used to impart conductivity to the electrode, and in the battery being configured, any material that is an electron conductive material without causing a chemical change can be used. 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, metals such as copper, nickel, aluminum, silver, etc., metal-based substances in the form of metal powder or metal fiber, conductive polymers such as polyphenylene derivatives, or mixtures thereof.

[0030] As the current collector COL1, Al may be used, but it is not limited thereto.

[0031] positive electrode active material As the positive electrode active material in the positive electrode active material layer AML1, a compound capable of reversible intercalation and deintercalation of lithium (lithium intercalation compound) may be used. Specifically, at least one of composite oxides of metals selected from cobalt, manganese, nickel, and combinations thereof and lithium may be used.

[0032] 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 compounds, cobalt-free nickel-manganese-based oxides, or combinations thereof.

[0033] As an example, a compound represented by any of the following general formulas may 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), Lia 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 b O2 (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).

[0034] In the above general formula, A is Ni, Co, Mn, or a combination thereof; X is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, 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 This is Mn, Al, or a combination of these.

[0035] For example, the positive electrode active material may be a high-nickel positive electrode active material in which the nickel content relative to 100 mol% of the metal excluding lithium is 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. High-nickel positive electrode active materials can achieve high capacity and can be applied to high-capacity, high-density lithium secondary batteries.

[0036] negative electrode 20 The negative electrode 20 for the lithium secondary battery includes a current collector COL2 and a negative electrode active material layer AML2 located on the current collector COL2. The negative electrode active material layer AML2 includes a negative electrode active material and may further include a binder and / or a conductive material.

[0037] For example, the negative electrode active material layer AML2 may contain 90% to 99% by weight of negative electrode active material, 0.5% to 5% by weight of binder, and 0% to 5% by weight of conductive material.

[0038] The binder plays the role of firmly adhering the negative electrode active material particles to each other and further firmly adhering 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 may be used.

[0039] Examples of non-aqueous binders include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyimide, or combinations thereof.

[0040] 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, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0041] When using an aqueous binder as the negative electrode binder, it may further contain a cellulosic compound that can impart viscosity. As the cellulosic compound, at least one of carboxymethylcellulose, hydroxypropylmethylcellulose, methylcellulose, or alkali metal salts thereof may be used in a mixture. As the alkali metal, Na, K, or Li may be used.

[0042] The dry binder is a fibrous polymeric material, which may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0043] Conductive materials are used to impart conductivity to electrodes, and any electronically conductive material that does not undergo chemical changes can be used in the battery that makes up the battery. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, carbon fiber, carbon nanofiber, and carbon nanotubes; metallic materials in the form of metal powders or metal fibers, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0044] As the current collector COL2, those selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrates coated with conductive metals, and combinations thereof may be used.

[0045] negative electrode active material The negative electrode active material in the negative electrode active material layer AML2 includes substances capable of reversibly intercalating / deintercalating lithium ions, lithium metal, alloys of lithium metal, substances capable of doping and undoping lithium, or transition metal oxides.

[0046] Substances capable of reversibly intercalating / deintercalating lithium ions are carbon-based negative electrode active materials and may include, for example, crystalline carbon, amorphous carbon, or combinations 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, and the like.

[0047] As the alloy of lithium metal, an alloy of lithium and a metal selected from nNa, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn may be used.

[0048] As the substance capable of doping and undoping 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 combinations thereof. The Sn-based negative electrode active material may be Sn, SnO2, a Sn-based alloy, or combinations thereof.

[0049] The silicon-carbon composite may also be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite may have a form in which silicon particles and amorphous carbon are coated on the surface of the silicon particles. For example, it may include secondary particles (core) composed of primary silicon particles and an amorphous carbon coating layer (shell) located on the surface of these secondary particles. Amorphous carbon may also be present between the primary silicon particles; for example, the primary silicon particles may be coated with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0050] The silicon-carbon composite may further contain 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 this core.

[0051] Si-based or Sn-based anode active materials may be used in combination with carbon-based anode active materials.

[0052] 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 multilayer films of two or more layers thereof may be used, and mixed multilayer films such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may be used.

[0053] The separator 30 may include a porous substrate and a coating layer containing organic material, inorganic material, or a combination thereof located on one or both sides of the porous substrate.

[0054] The porous substrate may be a polymer film formed from any polymer selected from polyethylene, polyolefins such as polypropylene, polyesters such as polyethylene terephthalate, polyethylene naphthalate, and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyetherketone, polyaryletherketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, glass fiber, and polytetrafluoroethylene, or from copolymers or mixtures of two or more of these polymers.

[0055] The above organic material may include a polyvinylidene fluoride polymer or a (meth)acrylic polymer.

[0056] The above inorganic materials may include, but are not limited to, Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, bohemite, and inorganic particles selected from combinations thereof.

[0057] The above-mentioned organic and inorganic materials may be mixed within a single coating layer, or they may exist in a form in which a coating layer containing organic materials and a coating layer containing inorganic materials are stacked.

[0058] Electrolyte (ELL) The electrolyte for lithium secondary batteries (ELL) contains a non-aqueous organic solvent and a lithium salt.

[0059] Non-aqueous organic solvents serve as a medium through which ions involved in the electrochemical reaction of batteries can move.

[0060] The non-aqueous organic solvent may be a carbonate, ester, ether, ketone, or alcohol solvent, an aprotic solvent, or a combination thereof.

[0061] Examples of carbonate-based solvents that may be used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).

[0062] Suitable ester solvents include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, and caprolactone.

[0063] As ether-based solvents, dibutyl ether, tetraglyceride, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran may be used. As ketone-based solvents, cyclohexanone may be used. As alcohol-based solvents, ethyl alcohol and isopropyl alcohol may be used. As aprotic solvents, nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and may include a double bond, aromatic ring, or ether group), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane and 1,4-dioxolane, and sulfolanes may be used.

[0064] Non-aqueous organic solvents may be used individually or in combination of two or more.

[0065] Furthermore, when using carbonate-based solvents, cyclic carbonates and linear carbonates may be mixed and used together, and the cyclic carbonates and linear carbonates may be mixed in a volume ratio of 1:1 to 1:9.

[0066] Lithium salts dissolve in organic solvents and act as a source of lithium ions within batteries, enabling the basic operation of lithium secondary batteries and facilitating the movement of lithium ions between the positive and negative electrodes. Typical examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N(lithium bis(fluorosulfonyl)imide (LiFSI), LiC4F9SO3, and LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (where x and y are integers from 1 to 20), may contain one or more selected from lithium trifluoromethanesulfonate, lithium tetrafluoroethersulfonate, lithium difluorobis(oxalate)phosphate (LiDFOB), lithium difluorobis(oxalate)phosphate (LiDFOP), and lithium bis(oxalate)borate (LiBOB).

[0067] Lithium-ion battery Lithium secondary batteries may be classified into cylindrical, rectangular, pouch-shaped, coin-shaped, etc., depending on their form. Figures 2 to 5 are schematic diagrams showing a lithium secondary battery according to one embodiment, with Figure 2 being cylindrical, Figure 3 being rectangular, and Figures 4 and 5 being pouch-shaped. Referring to Figures 2 to 4, the lithium secondary battery 100 may include an electrode assembly 40 with a separator 30 between a positive electrode 10 and a negative electrode 20, and a case 50 in which the electrode assembly 40 is housed. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte (not shown). The lithium secondary battery 100 may include a sealing member 60 that seals the case 50, as shown in Figure 2. Also, in Figure 3, the lithium secondary battery 100 may include a positive electrode lead tab 11 and a positive electrode terminal 12, and a negative electrode lead tab 21 and a negative electrode terminal 22. As shown in Figures 4 and 5, the lithium secondary battery 100 may also include electrode tabs 70, namely a positive electrode tab 71 and a negative electrode tab 72, which function as electrical pathways for inducing current formed in the electrode assembly 40 to the outside.

[0068] The following describes in more detail the electrolyte of a lithium secondary battery according to one embodiment of the present invention.

[0069] An electrolyte for a lithium secondary battery according to one embodiment comprises the aforementioned non-aqueous organic solvent, lithium salt, and additives, wherein the additives include a mixture of a first additive represented by chemical formula 1 (described later) and a second additive represented by chemical formula 2 (described later), with the first additive to the second additive being present in a weight ratio of 1:10 to 1:150.

[0070] The electrolyte can be manufactured by dissolving a lithium salt in a non-aqueous organic solvent, adding the first and second additives in the above weight ratio, and then mixing. The process of mixing the electrolyte is widely known in the field of electrolyte manufacturing and can be used as appropriate by those skilled in the art.

[0071] A non-aqueous organic solvent according to one embodiment of the present invention may contain one or more of the above-mentioned non-aqueous organic solvents.

[0072] In one embodiment, the non-aqueous organic solvent may be a mixture containing ethylene carbonate (EC):ethyl methyl carbonate (EMC):dimethyl carbonate (DMC) in a volume ratio of 10-30:20-50:20-50. Here, the volume ratio is based on a total of 100 volume percent of ethylene carbonate (EC):ethyl methyl carbonate (EMC):dimethyl carbonate (DMC). By satisfying this range, the effects of the additive mixture described later can be easily realized, reducing the reductive decomposition rate of the positive electrode in lithium secondary batteries and further improving the battery life.

[0073] A lithium salt according to one embodiment of the present invention may include one or more selected from the group consisting of LiPF6, LiClO4, LiBF4, lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), LiSO3CF3, LiBOB, LiDFOB, LiDFBOP, LiTFOP, LiPO2F2, LiSbF6, LiAsF6, LiAlO2, LiAlCl4, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N, and LiC4F9SO3. According to one embodiment, LiPF6 can be used as the lithium salt.

[0074] The lithium salt concentration may be between 0.1 M and 3.0 M. Specifically, the lithium salt concentration may be 0.5 M or higher, or 1.0 M or higher. The lithium salt concentration may also be 3.0 M or lower, 2.5 M or lower, or 2.0 M or lower. In this invention, when the lithium salt concentration is between 0.1 M and 2.0 M, the conductivity and viscosity of the electrolyte can be appropriately maintained.

[0075] additives An additive according to one embodiment of the present invention includes a first additive and a second additive.

[0076] Additive #1 A first additive according to one embodiment of the present invention is represented by the following chemical formula 1.

[0077] [ka]

[0078] In chemical formula 1, R1 may be the same or different, and each may independently be hydrogen, a halogen, an alkyl group having 1 to 10 carbon atoms, or an isocyanate group. At least one of R1 may be an isocyanate group.

[0079] R2 may be the same or different, and each may independently be hydrogen, a halogen, an alkyl group having 1 to 10 carbon atoms, or an isocyanate group. At least one of R2 may be an isocyanate group.

[0080] R3 may be the same or different, and each may independently be a hydrogen atom or a cyclohexyl isocyanate residue.

[0081] n can be any integer between 1 and 10.

[0082] An additive according to another embodiment of the present invention can be represented by the following chemical formula 1-1.

[0083] [ka]

[0084] In chemical formula 1-1, R1 may be the same or different, and each may independently be hydrogen, a halogen, an alkyl group having 1 to 10 carbon atoms, or an isocyanate group. At least one of R1 may be an isocyanate group.

[0085] R2 may be the same or different, and each may independently be hydrogen, a halogen, an alkyl group having 1 to 10 carbon atoms, or an isocyanate group. At least one of R2 may be an isocyanate group.

[0086] The first additive according to another embodiment of the present invention can be represented by the following chemical formulas 1-2.

[0087] [ka]

[0088] In chemical formulas 1-2, R1 may be the same or different, and each may independently be hydrogen, a halogen, or an alkyl group having 1 to 10 carbon atoms.

[0089] R2 may be the same or different, and each may independently be hydrogen, a halogen, or an alkyl group having 1 to 10 carbon atoms.

[0090] For example, the first additive may be a compound represented by the following chemical formulas 1-3.

[0091] [ka]

[0092] Another embodiment of the present invention can be represented by the following chemical formulas 1-4.

[0093] [ka]

[0094] In chemical formulas 1-4, R1 may be the same or different, and each may independently be hydrogen, a halogen, or an alkyl group having 1 to 10 carbon atoms.

[0095] R2 may be the same or different, and each may independently be hydrogen, a halogen, or an alkyl group having 1 to 10 carbon atoms.

[0096] For example, the first additive can be represented by the following chemical formulas 1-5.

[0097] [ka]

[0098] Second Additive A second additive according to one embodiment of the present invention can be represented by the following chemical formula 2.

[0099] [ka]

[0100] In chemical formula 2, L 1 This is a substituted or unsubstituted alkylene group having 1 to 10 carbon atoms. L 2 and L 3 Each of these is independently a substituted or unsubstituted alkyl group having 1 to 3 carbon atoms.

[0101] For example, L 1 This may be a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms, for example, a substituted or unsubstituted alkylene group having 1 to 3 carbon atoms.

[0102] For example, L 1 -CH2-, -CH2CH2-, or -CH2CH2CH2- may also be used.

[0103] For example, L 2 and L 3 Each of these may independently be a substituted or unsubstituted alkyl group having 1 to 2 carbon atoms.

[0104] For example, the second additive can be represented by the following chemical formula 2-1.

[0105] [ka]

[0106] In chemical formula 2-1, n is an integer between 1 and 5.

[0107] In one embodiment, the second additive may contain one or more compounds represented by the following chemical formulas 2-2 to 2-7.

[0108] [ka]

[0109] For example, the second additive may contain one or more compounds represented by chemical formulas 2-2 to 2-4, for example, one or more compounds represented by chemical formulas 2-2 to 2-3, for example, the compound represented by chemical formula 2-2.

[0110] An additive according to one embodiment of the present invention comprises a mixture of a first additive and a second additive, wherein the weight ratio of the first additive to the second additive is 1:10 to 1:150.

[0111] The inventors of this invention confirmed that the first additive has the effect of forming a protective film at the interface of the negative electrode, but its effect of improving battery life at low temperatures is weak, and it is not possible to achieve a significant capacity retention rate during rapid charging. An electrolyte containing the first and second additives in a weight ratio can improve the battery life not only at room temperature but also over a wide temperature range including low and high temperatures, and can improve the rapid charge and discharge characteristics of the battery. Among diester-based additives, the second additive showed particularly remarkable effects in improving the aforementioned battery life and rapid charge and discharge characteristics.

[0112] If the above weight ratio is lower than 1:10, the amount of the second additive may be insufficient, resulting in a weaker improvement in battery life and rapid charge / discharge characteristics.

[0113] If the above weight ratio is higher than 1:150, the second additive may be present in excessive amounts, resulting in a relative deficiency of the first additive, which may prevent a sufficient protective film from forming on the surface of the negative electrode.

[0114] For example, the above weight ratio may be 1:20 to 1:120. For instance, the above weight ratio may be 1:20 to 1:40, and the effect of the electrolyte becomes more pronounced when it is within this range.

[0115] In one embodiment, when the electrolyte is applied to a battery containing one or more of the following as the positive electrode active material: LFP (Lithium Iron Phosphate), LMFP (Lithium Manganese Iron Phosphate), NCA (Lithium Nickel Cobalt Aluminum Oxide), NCM (Lithium Nickel Cobalt Manganese Oxide), and LCO (Lithium Cobalt Oxide), it may exhibit the aforementioned effects of improving battery life and rapid charge / discharge characteristics. For example, NCA (Lithium Nickel Cobalt Aluminum Oxide) is preferred as the positive electrode active material.

[0116] In one embodiment, the above mixture may be included in the electrolyte additive at an amount of 95% by weight or more, for example, 95-100% by weight or 100% by weight. By satisfying this range, the effects of the mixture described above can be realized, and side reactions of the electrolyte can be suppressed.

[0117] The first additive may be present in an amount of 0.1 to 2% by weight relative to the total volume of the electrolyte. By satisfying this range, the effects of the mixture described above can be achieved. Specifically, the first additive may be present in an amount of 0.2 to 1% by weight or 0.2 to 0.5% by weight relative to the total volume of the electrolyte. When the content of the first additive is within this range, the effects of the mixture described above become significantly higher, and the further effect of not increasing the battery resistance can be demonstrated.

[0118] The second additive may be present in an amount of 5 to 40% by weight relative to the total weight of the electrolyte. By satisfying this range, the effects of the mixture described above can be achieved. Specifically, the second additive may be present in an amount of 5 to 20%, 5 to 15%, or 5 to 10% by weight relative to the total weight of the electrolyte. When the content of the second additive is within this range, the effects of the mixture described above become significantly higher, resulting in improved rapid charging characteristics and the further benefit of no increase in battery resistance.

[0119] As described above, the electrolyte according to the embodiment of the present invention, by including a mixture of the first and second additives in the aforementioned weight ratio with the combination of the non-aqueous organic solvent and lithium salt, increases the capacity retention rate at low and room temperatures, improves the capacity retention rate during high-temperature storage, suppresses the increase in resistance, and simultaneously improves the lifespan characteristics and rapid charge / discharge characteristics of the lithium secondary battery.

[0120] According to another embodiment of the present invention, a lithium secondary battery can be provided comprising a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and an electrolyte, wherein the electrolyte comprises a non-aqueous organic solvent, a lithium salt, and an additive, and the additive comprises a mixture of a first additive and a second additive, with the first additive and the second additive present in a weight ratio of 1:10 to 1:150.

[0121] Lithium-ion batteries can be applied to automobiles, mobile phones, and / or various forms of electronic devices, and the present invention is not limited to these.

[0122] The positive electrode active material may include, for example, a lithium nickel oxide represented by the following chemical formula 3, a lithium cobalt oxide represented by the following chemical formula 4, a lithium iron phosphate compound represented by the following chemical formula 5, a cobalt-free lithium nickel-manganese oxide represented by the following chemical formula 6, or a combination thereof.

[0123] [Chemical formula 3] Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1

[0124] In chemical formula 3, 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 2Each of the elements is independently 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.

[0125] In chemical formula 3, either 0.6 ≤ x1 ≤ 1, 0 ≤ y1 ≤ 0.4, and 0 ≤ z1 ≤ 0.4, or 0.70 ≤ x1 ≤ 1, 0 ≤ y1 ≤ 0.25, and 0 ≤ z1 ≤ 0.05.

[0126] [Chemical formula 4] Li a2 Co x2 M 3 y2 O 2-b2 X b2

[0127] In chemical formula 4, 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 X 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.

[0128] [Chemical formula 5] Li a3 Fe x3 M 4 y3 PO 4-b3 X b3

[0129] In chemical formula 5, 0.9 ≤ a³ ≤ 1.8, 0.6 ≤ x³ ≤ 1, 0 ≤ y³ ≤ 0.4, and 0 ≤ b³ ≤ 0.1, and M 4X 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.

[0130] [Chemical formula 6] Li a4 Ni x4 Mn y4 M 5 z4 O 2-b4 X b4

[0131] In chemical formula 6, 0.9 ≤ a² ≤ 1.8, 0.8 ≤ x₄ < 1, 0 <y4≦0.2、0≦z4≦0.2、0.9≦x4+y4+z4≦1.1、および0≦b4≦0.1であり、M 5 X 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.

[0132] In particular, the electrolyte of the aforementioned embodiment can significantly improve the degradation of cell performance in batteries using the lithium nickel oxide represented by chemical formula 3.

[0133] In one specific embodiment, the negative electrode active material may include at least one of graphite and a Si composite.

[0134] When the negative electrode active material contains both a Si composite and graphite, the Si composite and graphite may be present in the form of a mixture, in which case they may be present in a weight ratio of 1:99 to 50:50. More specifically, the Si composite and graphite may be present in a weight ratio of 3:97 to 20:80 or 5:95 to 20:80.

[0135] The Si composite includes a core containing Si-based particles and an amorphous carbon coating layer. For example, the Si-based particles may include one or more of Si-C composites, SiO x (0 < x ≤ 2), and Si alloys. For example, the Si-C composite may include a core containing Si particles and crystalline carbon, and an amorphous carbon coating layer located on the surface of the core.

[0136] The crystalline carbon may include, for example, graphite, and more specifically, may include natural graphite, artificial graphite, or a mixture thereof.

[0137] When the positive electrode contains a nickel-based positive electrode active material and the negative electrode contains a silicon-carbon composite, the effect of improving the high-temperature stability of the lithium secondary battery is particularly large. The lithium secondary battery of this combination can also operate at a high voltage of 4.2 V or more.

Examples

[0138] Hereinafter, examples and comparative examples of the present invention will be described. However, the following examples are merely one example of the present invention, and the present invention is not limited to the following examples.

[0139] (1) Preparation of electrolyte 1.5 M of LiPF6 was dissolved in a non-aqueous organic solvent in which ethylene carbonate (EC): ethyl methyl carbonate (EMC): dimethyl carbonate (DMC), which are carbonate solvents, were mixed at a volume ratio of 20:40:40 (total 100 basis). After adding the first additive and the second additive at the contents (unit: wt%) shown in Table 1 below, respectively, the obtained mixtures were mixed to prepare an electrolyte.

[0140] The molar concentration (M) of the lithium salt means the amount (number of moles) of the lithium salt dissolved in 1 L of the electrolyte. The volume ratio of the non-aqueous organic solvent means the volume ratio of EC: EMC: DMC. The wt% of the additive means the relative weight of the additive with respect to 100 wt% of the whole electrolyte (lithium salt + non-aqueous organic solvent) excluding the additive.

[0141] As the first additive, a compound represented by the following chemical formulas 1-3 was used.

[0142] As the second additive, the compound represented by the following chemical formula 2-2 was used.

[0143] In Comparative Example 5, the compound represented by the following chemical formula 7 was used.

[0144] [ka]

[0145] (2) Manufacturing of lithium secondary batteries LiNi 0.75 Co 0.23 Al 0.02 A mixture of 7% by weight of O2, 0.5% by weight of synthetic graphite powder, 0.8% by weight of carbon black (Ketjenblack), 0.2% by weight of acrylonitrile rubber, and 1.5% by weight of polyvinylidene fluoride (PVdF) was prepared. These were added to N-methyl-2-pyrrolidone (NMP), and the resulting mixture was stirred for 30 minutes using a mechanical stirrer to prepare a cathode active material slurry. The slurry was applied to a 20 μm thick aluminum current collector to a thickness of approximately 60 μm using a doctor blade, dried in a hot air dryer at 100°C for 0.5 hours, then further dried under vacuum and at 120°C for 4 hours, and rolled to produce a cathode.

[0146] A negative electrode active material slurry was prepared by mixing 98% by weight of a negative electrode active material consisting of graphite and Si composite in a weight ratio of 95.8:4.2, 1% by weight of styrene-butadiene rubber (SBR), and 1% by weight of carboxymethylcellulose (CMC). These were then added to distilled water, and the resulting mixture was stirred for 60 minutes using a mechanical stirrer. The slurry was then coated onto a 10 μm thick copper current collector to a thickness of approximately 60 μm using a doctor blade, dried in a hot air dryer at 100°C for 0.5 hours, further dried under vacuum and at 120°C for 4 hours, and then rolled to produce the negative electrode.

[0147] A positive electrode, a negative electrode, and a 16 μm thick polyethylene separator were assembled to form an electrode assembly, and an electrolyte was injected into the electrode assembly to fabricate a circular lithium secondary battery.

[0148] (3) Examples of evaluation Lithium-ion batteries were evaluated using the following method.

[0149] Evaluation 1: Low-temperature charge / discharge cycle evaluation (low-temperature lifespan) The room-temperature charge-discharge characteristics of lithium secondary batteries in the examples and comparative examples were evaluated. Specifically, 400 charge-discharge cycles were performed on the lithium secondary batteries under the conditions of -10°C, 0.33C charging (CC / CV, 4.2V, 0.025C Cut-off) / 0.5C discharging (CC, 2.5V Cut-off). The capacity retention rate was calculated according to the following formula. Capacity retention rate (%) = (Discharge capacity after 400 cycles / Discharge capacity after 1 cycle) × 100

[0150] Evaluation 2: Room temperature charge / discharge cycle evaluation (room temperature lifespan) The room-temperature charge-discharge characteristics of lithium secondary batteries in the examples and comparative examples were evaluated. Specifically, 1000 charge-discharge cycles were performed on the lithium secondary batteries under the conditions of 25°C, 0.5C charging (CC / CV, 4.2V, 0.025C Cut-off) / 0.5C discharging (CC, 2.5V Cut-off). The capacity retention rate was calculated according to the following formula. Capacity retention rate (%) = (Discharge capacity after 1000 cycles / Discharge capacity after 1 cycle) × 100

[0151] Evaluation 3: Volume retention rate after high-temperature storage (High-temperature storage 1) The lithium secondary batteries of the examples and comparative examples were subjected to three repeated cycles of 0.33C CC / CV charging (4.2V, 0.025C CUT-OFF) and 0.33C CC discharge (2.5V CUT-OFF) at 25°C, and the discharge capacity C1 was measured on the third cycle. After the charged lithium secondary batteries were stored at 60°C for 60 days, they were left at room temperature for an additional 30 minutes, and then discharged at 0.33C CC (2.5V CUT-OFF), and the discharge capacity C2 was measured. The capacity retention rate was calculated as follows and is shown in Table 1 below. Capacity retention rate (%)=C2 / C1×100(%)

[0152] Evaluation 4: DCIR increase rate after high-temperature storage (High-temperature storage 2) Initial DC resistance (DCIR) (ΔV / ΔI (voltage change / current change)) was measured for lithium secondary batteries in the examples and comparative examples. Afterward, the maximum energy state inside the battery was set to a fully charged state (SOC 100%), and the batteries were stored at 60°C for 60 days. After discharging at 0.33C to SOC 50%, the DC resistance was measured again, and the DCIR increase rate (%) was calculated according to the following formula. The results are shown in Table 1 below. DCIR increase rate (%) = (DCIR after 60 days / initial DCIR) × 100

[0153] Rating 5: Evaluation of rapid charge / discharge characteristics For the lithium secondary batteries of the examples and comparative examples, charging was performed at 25°C and 2.5~4.2V for 5 cycles each at C-rates of 0.1C, 0.2C, 0.5C, 1C, 2C, and 5C, and discharging at 0.5C C-rate. The capacity retention rate was calculated using Evaluation 3 as a reference while performing 5, 10, 15, 20, 25, and 30 charge-discharge cycles. Table 1 below shows the capacity retention rate after 30 cycles.

[0154] The results for ratings 1 through 5 are shown in Table 1 below. [Table 1]

[0155] (4) Discussion Referring to Table 1, the electrolytes of the examples showed improved lifespan and storage performance in lithium secondary batteries over a wide temperature range, including low, room, and high temperatures, as well as improved rapid charge and discharge characteristics.

[0156] However, as shown in Table 1, Comparative Examples 1 and 2, which do not contain one or more of the first and second additives of the present invention, Comparative Examples 3 and 4, which deviate from the weight ratio of the present invention, and Comparative Example 5, which satisfies the weight ratio of the present invention but does not contain the second additive of the present invention, were insufficiently effective in simultaneously improving lifespan, storage performance, and rapid charge / discharge characteristics over a wide temperature range including low, room, and high temperatures, compared to the examples.

[0157] Although preferred embodiments of the present invention have been described above, the present invention is not limited thereto and can be implemented in various ways within the scope of the claims, the detailed description of the invention, and the accompanying drawings, and these also naturally fall within the scope of the present invention.

Claims

1. Non-aqueous organic solvents, Lithium salts, and Contains additives, The aforementioned additive comprises a mixture of a first additive represented by the following chemical formula 1 and a second additive represented by the following chemical formula 2. The weight ratio of the first additive to the second additive is 1:10 to 1:

150. 【Chemistry 1】 In the aforementioned chemical formula 1, R １ These may be the same or different, and each is independently hydrogen, a halogen, an alkyl group having 1 to 10 carbon atoms, or an isocyanate group. R １ At least one of them is an isocyanate group, R ２ These may be the same or different, and each may independently be hydrogen, a halogen, an alkyl group having 1 to 10 carbon atoms, or an isocyanate group. The aforementioned R ２ At least one of them is an isocyanate group, R ３ These may be the same or different, and each is independently a hydrogen or cyclohexyl isocyanate residue. n is an integer between 1 and 10. 【Chemistry 2】 In the aforementioned chemical formula 2, L １ This is a substituted or unsubstituted alkylene group having 1 to 10 carbon atoms. L ２ and L ３ The electrolyte for lithium secondary batteries is an electrolyte in which each of the following is independently a substituted or unsubstituted alkyl group having 1 to 3 carbon atoms.

2. The electrolyte for a lithium secondary battery according to claim 1, wherein the weight ratio is 1:20 to 1:

120.

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

4. The electrolyte for a lithium secondary battery according to claim 1, wherein the second additive is contained in the electrolyte in an amount of 5% to 40% by weight.

5. The first additive is represented by the following chemical formula 1-2, 【Transformation 3】 In the aforementioned chemical formula 1-2, R １ may be the same or different and each independently is hydrogen, halogen, or an alkyl group having 1 to 10 carbon atoms, R ２ The electrolyte for a lithium secondary battery according to claim 1, wherein each of the elements may be the same or different, and each is independently hydrogen, a halogen, or an alkyl group having 1 to 10 carbon atoms.

6. The electrolyte for a lithium secondary battery according to claim 1, wherein the first additive is a compound represented by the following chemical formulas 1-3. 【Chemistry 4】

7. The second additive is represented by the following chemical formula 2-1, 【Transformation 5】 The electrolyte for a lithium secondary battery according to claim 1, wherein in the chemical formula 2-1, n is an integer from 1 to 5.

8. The electrolyte for a lithium secondary battery according to claim 1, wherein the mixture is contained in the additive of the electrolyte for a lithium secondary battery in an amount of 95% by weight or more.

9. The electrolyte for a lithium secondary battery according to claim 1, wherein the non-aqueous organic solvent is a mixture containing ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate in a volume ratio of 10 to 30: 20 to 50: 20 to 50.

10. The lithium salt is LiPF ６ LiClO ４ LiBF ４ , (Lithium bis(fluorosulfonyl)imide, LiTFSI, LiSO ３ CF ３ , LiBOB, LiDFOB, LiDFBOP, LiTFOP, LiPO ２ F ２ LiSbF ６ LiAsF ６ LiAlO ２ LiAlCl ４ , LiCl, LiI, LiN(SO ３ C ２ F ５ ) ２ Li(FSO) ２ ) ２ N, and LiC ４ F ９ SO ３ The electrolyte for a lithium secondary battery according to claim 1, which is one or more selected from the group consisting of the following.

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

12. Positive electrode containing positive electrode active material, A negative electrode containing a negative electrode active material, and A lithium secondary battery comprising the electrolyte according to any one of claims 1 to 11.

13. The lithium secondary battery according to claim 12, wherein the positive electrode active material comprises lithium nickel cobalt aluminum oxide.

14. The lithium secondary battery according to claim 12, wherein the negative electrode active material comprises at least one of graphite and a Si composite.

15. The lithium secondary battery according to claim 12, wherein the lithium secondary battery is cylindrical, prismatic, pouch-type, or coin-type.

Images