Electrolyte for rechargeable lithium battery and rechargeable lithium battery including same

Abstract

The invention discloses an electrolyte and a rechargeable lithium battery including the same. The electrolyte comprises a non-aqueous organic solvent, a lithium salt and an additive. The additive includes a compound 1 represented by Chemical Formula 1 and a compound 2 represented by Chemical Formula 2. [Chemical Formula 1] # imgabs0 # [Chemical Formula 2] # imgabs1 #

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to and the benefit of Korean Patent Application No. 10-2023-0155463 filed on November 10, 2023 in the Korean Intellectual Property Office, the entire contents of which are hereby incorporated by reference. Technical Field

[0003] Embodiments of the present disclosure relate to an electrolyte for a rechargeable lithium battery and a rechargeable lithium battery including the same. Background Art

[0004] Recently, with the rapid popularization of electronic devices using batteries (such as mobile phones, laptop computers and electric vehicles), interest in rechargeable lithium batteries with high energy density and high capacity has increased rapidly. Therefore, intensive research has been conducted to improve the performance of rechargeable lithium batteries.

[0005] The rechargeable lithium battery includes a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode and the negative electrode include an active material capable of intercalation and deintercalation, and if lithium ions are intercalated and deintercalated, the rechargeable lithium battery generates electric energy initiated by oxidation and reduction reactions.

[0006] Lithium salts dissolved in non-aqueous organic solvents can be used as electrolytes for rechargeable lithium batteries. The characteristics of rechargeable lithium batteries are exhibited by complex reactions between the positive electrode and the electrolyte and between the negative electrode and the electrolyte. Accordingly, the use of an appropriate or suitable electrolyte is a variable factor for improving rechargeable lithium batteries. Summary of the invention

[0007] Embodiments of the present disclosure provide an electrolyte for a rechargeable lithium battery having improved stability and lifespan characteristics at high temperatures.

[0008] Embodiments of the present disclosure provide a rechargeable lithium battery including an electrolyte.

[0009] According to an embodiment of the present disclosure, an electrolyte for a rechargeable lithium battery may include: a non-aqueous organic solvent; a lithium salt; and an additive. The additive may include a compound 1 represented by Chemical Formula 1 and a compound 2 represented by Chemical Formula 2.

[0010] [Chemical formula 1]

[0011]

[0012] [Chemical formula 2]

[0013]

[0014] In Chemical Formula 1, R1 to R4 may be independently one selected from the group consisting of a hydrogen element, a halogen element, and a substituted or unsubstituted C1 to C5 alkyl group.

[0015] According to an embodiment of the present disclosure, a rechargeable lithium battery may include: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and the electrolyte discussed above. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings, together with the specification, illustrate embodiments of the presently disclosed subject matter, and, together with the description, serve to explain principles of embodiments of the presently disclosed subject matter.

[0017] Figure 1 A simplified conceptual diagram showing a rechargeable lithium battery according to an embodiment of the present disclosure is illustrated.

[0018] Figure 2 is a simplified cross-sectional perspective view of a rechargeable lithium battery according to an embodiment of the present disclosure.

[0019] Figure 3 is a simplified cross-sectional view showing a rechargeable lithium battery according to an embodiment of the present disclosure.

[0020] Figure 4-5 is a simplified perspective view showing a rechargeable lithium battery according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0021] In order to fully understand the layout and effect of the subject matter of the present disclosure, some embodiments of the present disclosure will be described with reference to the attached drawings. However, it should be noted that the present disclosure is not limited to the following example embodiments and can be implemented in various suitable forms. On the contrary, the example embodiments are only provided to illustrate the embodiments of the present disclosure and to make those skilled in the art fully aware of the scope of the present disclosure.

[0022] In this description, it will be understood that if an element is referred to as being on another element, the element may be directly on the other element, or there may be an intervening element between the two. In the accompanying drawings, the size (e.g., thickness) of some components may be exaggerated in order to effectively explain the technical content. Throughout the specification, the same reference numerals refer to the same elements.

[0023] Unless otherwise specifically stated in the description, an expression in a singular form may include an expression in a plural form. In an embodiment, unless otherwise specifically stated, the phrase "A or B" may indicate "A but not B", "B but not A", and "A and B". The terms "comprises / includes" and / or "comprising / including" used in the description do not exclude the existence or addition of one or more other components.

[0024] As used herein, the term "combination thereof" may refer to a mixture, stack, composite, copolymer, alloy, blend, and / or reaction product of the components.

[0025] In the present description, unless separately defined otherwise, the term "substituted" may refer to a substituent or a compound in which at least one hydrogen is replaced by deuterium, halogen, hydroxyl, amino, C1-C30 amine, nitro, C1-C40 silyl, C1-C30 alkyl, C1-C10 alkylsilyl, C6-C30 arylsilyl, C3-C30 cycloalkyl, C3-C30 heterocycloalkyl, C6-C30 aryl, C2-C30 heteroaryl, C1-C20 alkoxy, C1-C10 fluoroalkyl, cyano or a combination thereof.

[0026] In more detail, the term "substituted" may indicate that at least one hydrogen of a substituent or a compound is replaced by 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. For example, the term "substituted" may indicate that at least one hydrogen of a substituent or a compound is replaced by deuterium, halogen, C1-C20 alkyl, C6-C30 aryl, C1-C10 fluoroalkyl or cyano. In an embodiment, the term "substituted" may indicate that at least one hydrogen of a substituent or a compound is replaced by deuterium, halogen, C1-C5 alkyl, C6-C18 aryl, C1-C5 fluoroalkyl or cyano. For example, the term "substituted" may indicate that at least one hydrogen of the substituent or compound is replaced by deuterium, cyano, halo, methyl, ethyl, propyl, butyl, phenyl, biphenyl, terphenyl, trifluoromethyl, or naphthyl.

[0027] Figure 1 A simplified conceptual diagram showing a rechargeable lithium battery according to an embodiment of the present disclosure is illustrated. Figure 1 , a rechargeable lithium battery may include a positive electrode 10, a negative electrode 20, a separator 30, and an electrolyte ELL.

[0028] The positive electrode 10 and the negative electrode 20 may be spaced apart from each other across the separator 30. The separator 30 may be 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 immersed in the electrolyte ELL.

[0029] The electrolyte ELL may be a medium for lithium ions to be transferred between the positive electrode 10 and the negative electrode 20. In the electrolyte ELL, the lithium ions may move toward one selected from the positive electrode 10 and the negative electrode 20 through the separator 30.

[0030] Positive electrode 10

[0031] The positive electrode 10 for a rechargeable lithium battery may include a positive electrode collector COL1 and a positive electrode active material layer AML1 on the positive electrode collector COL1. The positive electrode active material layer AML1 may include a positive electrode active material and further include a binder and / or a conductive material (eg, an electrically conductive material).

[0032] For example, the positive electrode 10 may further include an additive that may function as a sacrificial positive electrode.

[0033] The amount of the positive electrode active material may range from about 90 wt % to about 99 wt % based on 100 wt % of the positive electrode active material layer AML1. The amount of the binder and the conductive material may each range from about 0.5 wt % to about 5 wt % based on 100 wt % of the positive electrode active material layer AML1.

[0034] The binder can be used to improve the bonding of the positive electrode active material particles to each other and also to improve the bonding of the positive electrode active material to the positive electrode current collector COL 1. The binder may include, for example, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin and / or nylon, but the present disclosure is not limited thereto.

[0035] The conductive material can be used to provide conductivity (e.g., electrical conductivity) to the electrode, and any suitable conductive material that does not cause chemical changes to the rechargeable lithium battery (e.g., does not cause undesirable chemical changes to the rechargeable lithium battery) can be used as the conductive material constituting the rechargeable lithium battery. The conductive material may include, for example, carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber and / or carbon nanotube; metal powder and / or metal fiber containing one or more selected from copper, nickel, aluminum and silver; conductive polymers (e.g., conductive polymers) such as polyphenylene derivatives; or mixtures thereof.

[0036] An Al foil may be used as the positive electrode current collector COL1 , but the present disclosure is not limited thereto.

[0037] Positive electrode active material

[0038] The positive electrode active material in the positive electrode active material layer AML1 may include a compound that can reversibly intercalate and deintercalate lithium (e.g., a lithiated intercalation compound). For example, the positive electrode active material may include at least one type of composite oxide containing lithium and a metal selected from cobalt, manganese, nickel, and a combination thereof.

[0039] The composite oxide may include a lithium transition metal composite oxide, for example, a lithium-nickel oxide (e.g., a lithium-nickel cobalt aluminum (NCA) composite oxide), a lithium-cobalt oxide, a lithium-manganese oxide, a lithium-iron-phosphate compound, a cobalt-free nickel-manganese oxide, or a combination thereof.

[0040] For example, the positive electrode active material may include a compound represented by 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 NeG 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), Lia Mn 1-b G b O2(0.90≤a≤1.8, 0.001≤b≤0.1), Li a Mn 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) and Li a FePO4(0.90≤a≤1.8).

[0041] 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 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, and L 1 It is Mn, Al or a combination thereof.

[0042] For example, based on 100 mol% of the metal excluding lithium in the lithium transition metal composite oxide, the positive electrode active material may be a high nickel-based positive electrode active material having a nickel content of about 80 mol% or more, about 85 mol% or more, about 90 mol% or more, about 91 mol% or more, or about 94 mol% or more and about 99 mol% or less. The high nickel-based positive electrode active material can achieve high capacity and can therefore be applied to high capacity and high density rechargeable lithium batteries.

[0043] Negative electrode 20

[0044] The negative electrode 20 for a rechargeable lithium battery may include a negative electrode current collector COL2 and a negative electrode active material layer AML2 on the negative electrode current collector COL2. The negative electrode active material layer AML2 may include a negative electrode active material and may further include a binder and / or a conductive material (eg, an electrically conductive material).

[0045] For example, the negative electrode active material layer AML2 may include a negative electrode active material in an amount of about 90 wt % to about 99 wt %, a binder in an amount of about 0.5 wt % to about 5 wt %, and a conductive material (eg, an electrically conductive material) in an amount of about 0 wt % to about 5 wt %.

[0046] The binder may be used to improve the binding of the negative electrode active material particles to each other and also to improve the binding of the negative electrode active material to the negative electrode current collector COL 2. The binder may include a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0047] The non-aqueous binder may include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0048] The aqueous binder may include styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluoroelastomer, polyethylene oxide, polyvinyl pyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinyl pyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol or a combination thereof.

[0049] If an aqueous binder is used as a binder in the negative electrode active material layer AML2, a cellulose compound capable of providing or increasing viscosity may be further included. The cellulose compound may include one or more selected from carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose and alkali metal salts thereof. The alkali metal may include Na, K and / or Li.

[0050] The dry binder may include a fibrillated polymer material such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or combinations thereof.

[0051] The conductive material can be used to provide conductivity (e.g., electrical conductivity) to the electrode, and any suitable conductive material that does not cause chemical changes to the rechargeable lithium battery (e.g., does not cause undesirable chemical changes to the rechargeable lithium battery) can be used as the conductive material constituting the rechargeable lithium battery. For example, the conductive material may include a carbon-based material such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber and / or carbon nanotube; a metal powder and / or metal fiber including one or more selected from copper, nickel, aluminum and silver; a conductive polymer (e.g., a conductive polymer) such as a polyphenylene derivative; or a mixture thereof.

[0052] The negative electrode current collector COL2 may include a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, a polymer substrate coated with a conductive metal (eg, an electrically conductive metal), or a combination thereof.

[0053] Negative electrode active material

[0054] The negative electrode active material in the negative electrode active material layer AML2 may include materials that can reversibly intercalate and deintercalate lithium ions, lithium metal, lithium metal alloys, materials that can be doped and undoped with lithium, and / or transition metal oxides.

[0055] Materials that can reversibly intercalate and deintercalate lithium ions may include carbon-based negative electrode active materials such as crystalline carbon, amorphous carbon, or combinations thereof. For example, crystalline carbon may include graphite, such as amorphous, flaky, scaly, spherical, and / or fibrous natural and / or artificial graphite, and amorphous carbon may include soft carbon, hard carbon, mesophase pitch carbon, and / or calcined coke.

[0056] Lithium metal alloys may include alloys of lithium with metals selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn.

[0057] Materials that can be doped and undoped with lithium may include Si-based negative electrode active materials and / or Sn-based negative electrode active materials. Si-based negative electrode active materials may include silicon, silicon-carbon composites, SiO x (0 < x ≤ 2), Si-Q alloys (where Q is an alkali metal, alkaline earth metal, Group 13 element, Group 14 element (excluding Si), Group 15 element, Group 16 element, transition metal, rare earth element, or combinations thereof), or combinations thereof. Sn-based negative electrode active materials may include Sn, SnO2, Sn-based alloys, or combinations thereof.

[0058] The silicon-carbon composite may be a composite of silicon and amorphous carbon. According to an embodiment, the silicon-carbon composite may have a structure in which amorphous carbon is coated on the surface of silicon particles. For example, the silicon-carbon composite may include secondary particles (cores) in which primary silicon particles are aggregated and an amorphous carbon coating (shell) on the surface of the secondary particles. Amorphous carbon may also be between the primary silicon particles. For example, the primary silicon particles may be coated with amorphous carbon. The secondary particles may be dispersed in the amorphous carbon matrix.

[0059] 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 may also include an amorphous carbon coating on the surface of the core.

[0060] Si-based negative electrode active materials and / or Sn-based negative electrode active materials may be used in combination with carbon-based negative electrode active materials.

[0061] Separator 30

[0062] Based on the type (or kind) of the rechargeable lithium battery, the separator 30 may be between the positive electrode 10 and the negative electrode 20. The separator 30 may include one or more selected from a polyethylene separator, a polypropylene separator, and a polyvinylidene fluoride separator, and may be a multilayer separator thereof, such as a polyethylene / polypropylene double-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, and / or a polypropylene / polyethylene / polypropylene three-layer separator.

[0063] The separator 30 may include a porous substrate and a coating on one surface or the opposite surface of the porous substrate, wherein the coating includes an organic material, an inorganic material, or a combination thereof.

[0064] The porous substrate may be a polymer layer comprising one selected from polyolefins (such as polyethylene and polypropylene), polyesters (such as polyethylene terephthalate and polybutylene terephthalate), polyacetals, polyamides, polyimides, polycarbonates, polyether ketones, polyaryletherketones, polyetherimides, polyamideimides, polybenzimidazoles, polyethersulfones, polyphenylene oxides, cyclic olefin copolymers, polyphenylene sulfide, polyethylene naphthalate, glass fibers, and polytetrafluoroethylene (e.g., Teflon), or may comprise copolymers or mixtures of two or more of the above-mentioned materials.

[0065] The organic material may include a polyvinylidene fluoride-based copolymer and / or a (meth)acrylic acid-based copolymer.

[0066] The inorganic material may include 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, but the present disclosure is not limited thereto.

[0067] The organic material and the inorganic material may be present mixed together in one coating layer, or may be present as a stack of a coating layer including an organic material and a coating layer including an inorganic material.

[0068] Electrolyte ELL

[0069] The electrolyte ELL for a rechargeable lithium battery may include a non-aqueous organic solvent and a lithium salt.

[0070] The non-aqueous organic solvent may be used as a medium for transferring ions participating in the electrochemical reaction of the rechargeable lithium battery.

[0071] The non-aqueous organic solvent may include a carbonate solvent, an ester solvent, an ether solvent, a ketone solvent, an alcohol solvent, an aprotic solvent, or a combination thereof.

[0072] The carbonate-based solvent may include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC) and / or butylene carbonate (BC).

[0073] The ester solvent may include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, propyl propionate, decanoic acid lactone, mevalonolactone, valerolactone and / or caprolactone.

[0074] Ether solvents may include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran and / or tetrahydrofuran. Ketone solvents may include cyclohexanone. Aprotic solvents may include nitrile, such as R-CN (wherein R is a hydrocarbon group having a C2 to C20 linear, branched or cyclic structure, and may include a double bond, an aromatic ring and / or an ether group); amide, such as dimethylformamide; dioxolane, such as 1,3-dioxolane and / or 1,4-dioxolane; and / or sulfolane.

[0075] The nonaqueous organic solvent may be used alone or as a mixture of two or more species.

[0076] In an embodiment, if a carbonate-based solvent is used, a cyclic carbonate and a chain carbonate may be mixed together and used, and the cyclic carbonate and the chain carbonate may be mixed together in a volume ratio of about 1:1 to about 1:9.

[0077] The lithium salt may be a material dissolved in a non-aqueous organic solvent to serve as a supply source of lithium ions in a rechargeable lithium battery, and plays a role in achieving the basic operation of the rechargeable lithium battery and promoting the movement of lithium ions between the positive electrode and the negative electrode. The lithium salt may include, for example, selected from LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N, lithium bis(fluorosulfonyl)imide (LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (wherein x and y are integers of 1 to 20), at least one of lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluoro(oxalato)borate (LiDFOB), lithium difluorobis(oxalato)phosphate (LiDFBOP) and lithium bis(oxalato)borate (LiBOB).

[0078] The lithium salt may include LiPF6.

[0079] The lithium salt may have a concentration of about 0.1M to about 2.0M.

[0080] The additive may include a vinylene carbonate compound. The vinylene carbonate compound may be added to the electrolyte to form a solid electrolyte interface (SEI) layer (hereinafter, also referred to as a "protective film"). The vinylene carbonate compound may be vinylene carbonate, vinyl ethylene carbonate, or a combination thereof.

[0081] The amount of vinylene carbonate compounds present may be about 0.01wt% to about 5wt% relative to the total weight of the electrolyte. For example, the amount of vinylene carbonate compounds present may be equal to or greater than about 0.05wt%, equal to or greater than about 0.1wt%, or equal to or greater than about 0.5wt% relative to the total weight of the electrolyte. The amount of vinylene carbonate compounds present may be equal to or less than about 3wt%, equal to or greater than about 2wt%, or equal to or greater than about 1.5wt% relative to the total weight of the electrolyte. If the vinylene carbonate compounds have the aforementioned concentration in the electrolyte, a solid electrolyte interface (SEI) layer having an appropriate or suitable impedance (e.g., resistance) may be formed on the electrode surface to improve the cycle characteristics of the rechargeable lithium battery.

[0082] The additive may include Compound 1 represented by Chemical Formula 1 below.

[0083] [Chemical formula 1]

[0084]

[0085] In Chemical Formula 1, R1 to R4 may independently be a hydrogen element, a halogen element, or a substituted or unsubstituted C1 to C5 alkyl group. In an embodiment of Chemical Formula 1, R1 to R4 may be a hydrogen element.

[0086] Compound 1 may include a sultone group. Compound 1 may form a stable film on the surface of the positive electrode and may inhibit or reduce the decomposition of the electrolyte at high temperature. Therefore, it may be possible to inhibit or reduce the generation of gas in a rechargeable lithium battery and to improve the high temperature life and high temperature storage performance of the rechargeable lithium battery.

[0087] The amount of compound 1 present may be about 0.01 wt% to about 10 wt% relative to the total weight of the electrolyte. For example, the amount of compound 1 present may be equal to or greater than about 0.05 wt%, equal to or greater than 0.1 wt%, equal to or greater than 0.5 wt%, or equal to or greater than 1 wt% relative to the total weight of the electrolyte. The amount of compound 1 present may be equal to or less than about 7 wt%, equal to or less than about 5 wt%, or equal to or less than about 2 wt% relative to the total weight of the electrolyte. If compound 1 is present in the aforementioned concentration range, a protective film having an appropriate or suitable film impedance (e.g., resistance) may be formed on the electrode surface of a rechargeable lithium battery to improve the cycle characteristics of the rechargeable lithium battery, and gas generation in the rechargeable lithium battery may be suppressed or reduced to improve the high temperature life and high temperature storage performance of the rechargeable lithium battery.

[0088] The additive may include Compound 2 represented by Chemical Formula 2 below.

[0089] [Chemical formula 2]

[0090]

[0091] Compound 2 can reduce the impedance (e.g., resistance) of the electrode surface to improve battery output performance. Relative to the total weight of the electrolyte, the amount of compound 2 present may be about 0.01wt% to about 10wt%. For example, relative to the total weight of the electrolyte, the amount of compound 2 present may be equal to or greater than about 0.05wt%, equal to or greater than about 0.1wt%, equal to or greater than about 0.5wt%, or equal to or greater than about 1wt%. Relative to the total weight of the electrolyte, the amount of compound 2 present may be equal to or less than about 7wt%, equal to or less than about 5wt%, or equal to or less than about 2wt%. If compound 2 is present in the aforementioned concentration range, the impedance (e.g., resistance) of the electrode surface of the rechargeable lithium battery can be moderately reduced to improve battery output performance.

[0092] The additive may include Compound 1 and Compound 2. Based on the combination of Compound 1 and Compound 2, the additive may not only improve high temperature performance of the rechargeable lithium battery but also improve impedance (eg, resistance) increase rate, thereby improving battery output performance.

[0093] In the additive, the amount of compound 2 present may be about 0.1 parts by weight to about 10 parts by weight relative to about 1 part by weight of compound 1. For example, in the additive, the amount of compound 2 present may be about 0.2 parts by weight to about 5 parts by weight or about 0.5 parts by weight to about 2 parts by weight relative to about 1 part by weight of compound 1. If compound 1 and compound 2 are present in the aforementioned ratio range, the rechargeable lithium battery can improve high temperature performance and impedance (e.g., resistance) increase rate, which can lead to improvement in battery output performance.

[0094] The additive may be present in an amount of about 0.1 wt% to about 10 wt% relative to the total weight of the electrolyte. For example, the additive may be present in an amount of about 0.5 wt% to about 7 wt%, about 1 wt% to about 4 wt%, about 2.1 wt% to about 4 wt%, or about 2.5 wt% to about 3.5 wt% relative to the total weight of the electrolyte. If an additive exceeding the above range is included, the viscosity of the electrolyte including the additive will be excessively increased and the wettability to the positive electrode and the negative electrode will be reduced. If an additive less than the amount of the above range is included, the above-mentioned effect will not be significant.

[0095] Rechargeable lithium battery

[0096] The rechargeable lithium batteries may be classified into cylindrical, prismatic, pouch-type, and / or coin-type (or types of rechargeable lithium batteries) based on their shapes. Figure 2 to Figure 5 is a simplified diagram showing a rechargeable lithium battery according to an embodiment. Figure 2 A cylindrical rechargeable lithium battery is shown, Figure 3 A prismatic rechargeable lithium battery is shown, and Figure 4-5 A pouch-type rechargeable lithium battery is shown. Figure 2 to Figure 4 , the rechargeable lithium battery 100 may include an electrode assembly 40, wherein the separator 30 is between the positive electrode 10 and the negative electrode 20, and may further include a case 50 in which the electrode assembly 40 is accommodated. The positive electrode 10, the negative electrode 20, and the separator 30 may be immersed in an electrolyte. The rechargeable lithium battery 100 may include a sealing member 60 that seals the case 50, such as Figure 2 In the implementation mode, as explained in Figure 3 As explained in , the rechargeable lithium battery 100 may include a positive electrode lead tab 11, a positive electrode terminal 12, a negative electrode lead tab 21, and a negative electrode terminal 22. Figure 4-5 As shown in FIG. 1 , the rechargeable lithium battery 100 may include an electrode tab 70 ( Figure 5 ) or the positive electrode terminal tab 71 and the negative electrode terminal tab 72 ( Figure 4 ).

[0097] The rechargeable lithium battery according to an embodiment of the present disclosure may be applied to a car, a mobile phone, and / or any other suitable electric device, but the present disclosure is not limited thereto.

[0098] Examples and comparative examples of the present disclosure will be described below. The following examples are merely embodiments of the present disclosure, and the present disclosure is not limited to the following examples.

[0099] Examples and Comparative Examples

[0100] Example 1

[0101] (1) Preparation of electrolyte

[0102] About 1.0 M of LiPF 6 was dissolved in a non-aqueous organic solvent in which ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed together in a volume ratio of about 20:20:60, and additives were added to prepare an electrolyte.

[0103] As additives, vinylene carbonate was added in an amount of 1 wt % relative to the total amount of the electrolyte, compound 1 represented by the following chemical formula 1-1 was added in an amount of 0.1 wt % relative to the total amount of the electrolyte, and compound 2 represented by the following chemical formula 2 was added in an amount of 1 wt % relative to the total amount of the electrolyte.

[0104] [Chemical formula 1-1]

[0105]

[0106] [Chemical formula 2]

[0107]

[0108] The additive according to Chemical Formula 1-1 may be prepared by the following synthesis example.

[0109] Synthesis example

[0110] 0.1 mmol of 2-hydroxybenzyl alcohol and 0.125 mmol of sodium bisulfite were added dropwise to a Schlenk flask (wherein 100 ml of H2O was present), and the mixture was allowed to flow and stirred for 24 hours. Thereafter, an excess of phosphorus oxychloride was added to the compound obtained by filtering the resulting precipitate, and the resulting mixture was reacted neat at 125° C. for 1 hour without a solvent. Thereafter, purification was performed using a Soxhlet extractor to obtain a compound represented by Chemical Formula 1-1.

[0111] (2) Manufacturing of rechargeable lithium batteries

[0112] LiNi as the positive electrode active material 0.84 Co 0.12 Al 0.04 O2, polyvinylidene fluoride as a binder, and acetylene black as a conductive material were mixed together in a weight ratio of 96:3:1, and the mixture was dispersed in N-methylpyrrolidone to prepare a positive electrode active material slurry.

[0113] The positive electrode active material slurry was coated on an Al foil having a thickness of 15 μm, dried at a temperature of 100° C., and then pressed to produce a positive electrode.

[0114] Artificial graphite, a styrene-butadiene rubber binder, and carboxymethyl cellulose were mixed together in a weight ratio of 98:1:1, and dispersed in distilled water to prepare a negative electrode active material slurry.

[0115] The negative electrode active material slurry was coated on a copper (Cu) foil having a thickness of 10 μm, dried at 100° C., and then pressed to manufacture a negative electrode.

[0116] The positive electrode, the negative electrode, and a 10 μm-thick polyethylene separator were assembled to manufacture an electrode assembly, and an electrolyte was introduced to manufacture a rechargeable lithium battery.

[0117] Example 2

[0118] A rechargeable lithium battery was manufactured in substantially the same manner as in Example 1, except that, as additives, vinylene carbonate was added in an amount of 1 wt % relative to the total amount of the electrolyte, compound 1 represented by Chemical Formula 1-1 was added in an amount of 0.5 wt % relative to the total amount of the electrolyte, and compound 2 represented by Chemical Formula 2 was added in an amount of 1 wt % relative to the total amount of the electrolyte.

[0119] Example 3

[0120] A rechargeable lithium battery was manufactured in substantially the same manner as in Example 1, except that, as additives, vinylene carbonate was added in an amount of 1 wt % relative to the total amount of the electrolyte, compound 1 represented by Chemical Formula 1-1 was added in an amount of 1 wt % relative to the total amount of the electrolyte, and compound 2 represented by Chemical Formula 2 was added in an amount of 1 wt % relative to the total amount of the electrolyte.

[0121] Example 4

[0122] A rechargeable lithium battery was manufactured in substantially the same manner as in Example 1, except that, as additives, vinylene carbonate was added in an amount of 1 wt % relative to the total amount of the electrolyte, compound 1 represented by Chemical Formula 1-1 was added in an amount of 2 wt % relative to the total amount of the electrolyte, and compound 2 represented by Chemical Formula 2 was added in an amount of 1 wt % relative to the total amount of the electrolyte.

[0123] Example 5

[0124] A rechargeable lithium battery was manufactured in substantially the same manner as in Example 1, except that, as additives, vinylene carbonate was added in an amount of 1 wt % relative to the total amount of the electrolyte, compound 1 represented by Chemical Formula 1-1 was added in an amount of 5 wt % relative to the total amount of the electrolyte, and compound 2 represented by Chemical Formula 2 was added in an amount of 1 wt % relative to the total amount of the electrolyte.

[0125] Example 6

[0126] A rechargeable lithium battery was manufactured in substantially the same manner as in Example 1, except that, as additives, vinylene carbonate was added in an amount of 1 wt % relative to the total amount of the electrolyte, compound 1-1 represented by Chemical Formula 1 was added in an amount of 1 wt % relative to the total amount of the electrolyte, and compound 2 represented by Chemical Formula 2 was added in an amount of 5 wt % relative to the total amount of the electrolyte.

[0127] Comparative Example 1

[0128] A rechargeable lithium battery was manufactured in substantially the same method as that of Example 1, except that vinylene carbonate was added as an additive in an amount of 1 wt % relative to the total amount of the electrolyte, and neither Compound 1 nor Compound 2 was added.

[0129] Comparative Example 2

[0130] A rechargeable lithium battery was manufactured in substantially the same manner as in Example 1, except that, as an additive, vinylene carbonate was added in an amount of 1 wt % relative to the total amount of the electrolyte, compound 1-1 represented by Chemical Formula 1 was added in an amount of 2 wt % relative to the total amount of the electrolyte, and compound 2 was not added.

[0131] Comparative Example 3

[0132] A rechargeable lithium battery was manufactured in substantially the same manner as in Example 1, except that vinylene carbonate was added as an additive in an amount of 1 wt % relative to the total amount of the electrolyte, Compound 1 was not added, and Compound 2 represented by Chemical Formula 2 was added in an amount of 1 wt % relative to the total amount of the electrolyte.

[0133] Comparative Example 4

[0134] A rechargeable lithium battery was manufactured in substantially the same manner as in Example 1, except that, as additives, vinylene carbonate was added in an amount of 1 wt % relative to the total amount of the electrolyte, compound 1 represented by Chemical Formula 1-1 was added in an amount of 10 wt % relative to the total amount of the electrolyte, and compound 2 represented by Chemical Formula 2 was added in an amount of 1 wt % relative to the total amount of the electrolyte.

[0135] Evaluation Example

[0136] The rechargeable lithium battery was evaluated by the following method.

[0137] Evaluation 1: Storage characteristics at high temperature (60°C)

[0138] After the rechargeable lithium batteries according to the embodiments and comparative examples were allowed to measure their ΔV / ΔI (voltage change / current change) as the initial direct current internal resistance (DCIR), the maximum energy state inside the rechargeable lithium battery was changed to a fully charged state (SOC 100%), and the rechargeable lithium battery was stored at a high temperature (60°C) for 30 days in this state, and then the direct current internal resistance was measured to calculate the DCIR increase rate (%) after high temperature storage according to the following equation 1, and Table 1 lists the following results.

[0139] Equation 1

[0140] DCIR increase rate after high temperature storage (%) = (DCIR after 30 days of high temperature storage / initial DCIR) × 100 Table 1

[0141]

[0142] Evaluation 2: Storage characteristics at high temperature (45°C)

[0143] After measuring ΔV / ΔI (voltage change / current change) as the initial direct current internal resistance (DCIR) of the rechargeable lithium batteries according to the embodiments and comparative examples, the maximum energy state inside the rechargeable lithium battery is changed to a fully charged state (SOC 100%), and the rechargeable lithium battery is stored at a high temperature (45°C) for 30 days in this state, and then the direct current internal resistance is measured to calculate the DCIR increase rate (%) after high temperature storage according to the following equation 1, and Table 2 lists the following results.

[0144] Equation 1

[0145] DCIR increase rate after high temperature storage (%) = (DCIR after 30 days of high temperature storage / initial DCIR) × 100 Table 2

[0146]

[0147]

[0148] Evaluation 3: Charge / discharge characteristics at high temperature (45°C)

[0149] The rechargeable lithium batteries according to the examples and comparative examples were evaluated for charge / discharge characteristics at 45° C. The rechargeable lithium batteries according to the examples and comparative examples were charged and discharged for 120 cycles at 45° C. under the conditions of 0.5C charge (CC / CV, 4.3V, 0.05C cutoff) and 0.5C discharge (CC, 2.8V cutoff) as 1 cycle.

[0150] The capacity retention rate was calculated according to the following equation 2 and the results are listed in Table 3.

[0151] Equation 2

[0152] Capacity retention rate (%) = (discharge capacity after 120 cycles / discharge capacity after 1 cycle) × 100

[0153] Table 3

[0154] category Capacity retention at 45°C (%) Example 1 95.1 Example 2 95.5 Example 3 95.7 Example 4 95.3 Example 5 93.8 Example 6 94.8 Comparative Example 1 75.2 Comparative Example 2 93.7 Comparative Example 3 94.5 Comparative Example 4 93.1

[0155] Evaluation 4: Gas generation characteristics at high temperature (60°C)

[0156] The rechargeable lithium batteries according to the embodiments and comparative examples were evaluated for high temperature gas generation characteristics. The rechargeable lithium batteries were allowed to change their internal maximum energy state to a fully charged state (SOC 100%) and stored at a high temperature (60°C) for 30 days in the changed state, and then the gas generation amount was evaluated, and the results are listed in Table 4.

[0157] The volume change before and after high-temperature storage was measured, and the volume change was calculated as a mass change using Archimedes' method.

[0158] Table 4

[0159]

[0160]

[0161] Comprehensive Assessment

[0162] Referring to Tables 1 and 2, in Comparative Example 1 using an additive that does not include either Compound 1 or Compound 2, DCIR increases dramatically after storage at high temperatures (60°C or 45°C). In addition, in Comparative Example 3 using an additive that does not include Compound 1, DCIR also increases dramatically after storage at high temperatures (60°C or 45°C). In contrast, in Examples 1 to 6, Comparative Example 2, and Comparative Example 4, DCIR does not increase dramatically even after storage at high temperatures (60°C or 45°C). This can show that the additive including Compound 1 improves high temperature characteristics.

[0163] Referring to Table 3, in Comparative Example 1 using an additive including neither Compound 1 nor Compound 2, the capacity retention rate depending on the charge / discharge cycle at a high temperature (60° C. or 45° C.) was lowered, thereby reducing the charge / discharge cycle life.

[0164] In contrast, in Examples 1 to 6 and Comparative Examples 2 to 4 (each of which uses an additive including one or both of Compound 1 and Compound 2), it has been determined that the capacity retention rate depending on the charge / discharge cycle at high temperature (60° C. or 45° C.) is maintained at an appropriate or suitable level or higher than an appropriate or suitable level. In particular, compared to other Examples and Comparative Examples, it was determined that even when a relatively small amount of additive was used in Examples 1 to 4 (each of which uses an additive including both Compound 1 and Compound 2), the capacity retention rate depending on the charge / discharge cycle at high temperature (60° C. or 45° C.) was maintained at an appropriate or suitable level or higher than an appropriate or suitable level.

[0165] Referring to Table 4, in Comparative Example 1 using an additive that includes neither Compound 1 nor Compound 2, a large amount of gas generation was evaluated when stored at a high temperature (60°C). In the comparative example using an additive that does not include Compound 1, a relatively large amount of gas generation was evaluated compared to other embodiments and comparative examples. In contrast, in Examples 1 to 6, Comparative Example 2 and Comparative Example 4 (each of which uses an additive including Compound 1), it was determined that gas generation was effectively suppressed when stored at a high temperature (60°C). In particular, compared to other embodiments and comparative examples, it was determined that in the case of Examples 1 to 4 (each of which uses an additive including Compound 1 and Compound 2), even with a relatively small amount of additive, gas generation was effectively suppressed when stored at a high temperature (60°C).

[0166] The electrolyte according to the embodiment for a rechargeable lithium battery may achieve stability of an electrode and suppression or reduction of an impedance (eg, resistance) increase, and thus, may have the effect of improving stability at high temperatures and lifespan characteristics.

[0167] Although the subject matter of the present invention has been described in conjunction with what are presently considered to be practical example embodiments, it should be understood that the disclosure is not limited to the disclosed embodiments, but is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims and their equivalents. Therefore, the foregoing embodiments should be understood as examples and not to limit the present disclosure in any way.

Claims

1. An electrolyte for a rechargeable lithium battery, the electrolyte comprising: Non-aqueous organic solvents; Lithium salts; and additive, wherein the additive comprises a compound 1 represented by chemical formula 1 and a compound 2 represented by chemical formula 2, [Chemical formula 1] [Chemical formula 2] In Chemical Formula 1, R1 to R4 are independently one selected from hydrogen, halogen, and substituted or unsubstituted C1 to C5 alkyl.

2. The electrolyte according to claim 1, wherein the additive is present in an amount of 0.1 wt% to 10 wt% relative to the total weight of the electrolyte.

3. The electrolyte according to claim 1, wherein: The compound 1 is present in an amount of 0.01 wt% to 10 wt% relative to the total weight of the electrolyte, and The compound 2 is present in an amount of 0.01 wt % to 10 wt % relative to the total weight of the electrolyte. The electrolyte according to claim 1 , wherein R1 to R4 are hydrogen elements.

5. The electrolyte according to claim 4, wherein the amount of the compound 1 present is 0.5 wt% to 2 wt% relative to the total weight of the electrolyte.

6. The electrolyte of claim 1, wherein the nonaqueous organic solvent comprises at least one selected from the group consisting of ethylene carbonate, propylene carbonate, propyl propionate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate and butylene carbonate.

7. The electrolyte of claim 6, wherein the nonaqueous organic solvent comprises ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate.

8. The electrolyte of claim 1, wherein the lithium salt comprises a salt selected from the group consisting of LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N, lithium bis(fluorosulfonyl)imide, LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2), at least one of lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluoro(oxalate)borate, lithium difluorobis(oxalate)phosphate and lithium bis(oxalate)borate, wherein x and y are integers of 1 to 20.

9. The electrolyte according to claim 1, wherein the concentration of the lithium salt is in the range of 0.1M to 2.0M.

10. A rechargeable lithium battery comprising: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and The electrolyte according to any one of claims 1 to 9.

11. The rechargeable lithium battery of claim 10, wherein the positive electrode active material comprises a lithium metal oxide represented by Chemical Formula 3, [Chemical formula 3] Li a Ni 1-b-c Co b X c O 2-α D α Wherein in chemical formula 3, X is Al, Mn, Cr, Fe, Mg, Sr, V, a rare earth element or a combination thereof, D is F, S, P or a combination thereof, 0.90≤a≤1.8， 0≤b≤0.5， 0≤c≤0.5, and 0<α<2。 12 . The rechargeable lithium battery of claim 10 , wherein the negative electrode active material comprises a carbon-based negative electrode active material, a silicon-based negative electrode active material, a tin-based negative electrode active material, or a combination thereof.

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