Electrolyte for rechargeable lithium battery and rechargeable lithium battery including same

Abstract

The present disclosure relates to an electrolyte solution for a rechargeable lithium battery and a rechargeable lithium battery including the electrolyte solution. The invention discloses an electrolyte and a rechargeable lithium battery. The electrolyte solution includes an electrolyte solution for a rechargeable lithium battery, the electrolyte solution for a rechargeable lithium battery including a non-aqueous organic solvent, a lithium salt, and an additive represented by Chemical Formula 1-1 or Chemical Formula 1-2. Chemical formula 1-1 and chemical formula 1-2

Description

[0001] Cross Reference to Related Applications

[0002] This application claims priority to and the benefit of Korean Patent Application No. 10-2024-0105556, filed on August 7, 2024, in the Korean Intellectual Property Office, the entire contents of which are incorporated herein 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 electrolyte. BACKGROUND

[0004] Recently, as electronic devices using batteries, such as mobile phones, laptop computers, and electric vehicles, are rapidly spreading, the demand for rechargeable lithium batteries having high energy density and high capacity is rapidly increasing. Therefore, intensive research has been conducted to improve the performance of rechargeable lithium batteries.

[0005] A rechargeable lithium battery can include a positive electrode, a negative electrode, and an electrolyte, the positive electrode and the negative electrode can include an active material in which lithium ions can be intercalated and deintercalated, and if (for example, when) lithium ions are intercalated and deintercalated, electric energy can be generated by oxidation and reduction reactions.

[0006] A lithium salt dissolved in a non-aqueous organic solvent can be used as an electrolyte for a rechargeable lithium battery. The characteristics of a rechargeable lithium battery are exhibited by complex reactions between the positive electrode and the electrolyte and between the negative electrode and the electrolyte. Accordingly, the use of a suitable or appropriate electrolyte is one variable for improving a rechargeable lithium battery. SUMMARY

[0007] Embodiments of the present disclosure provide an electrolyte for a rechargeable lithium battery, which has improved stability and cycle life characteristics at high temperatures.

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

[0009] According to embodiments of the present disclosure, an electrolyte for a rechargeable lithium battery can include: a non-aqueous organic solvent; a lithium salt; and an additive (hereinafter, can be simply referred to as "additive") represented by Chemical Formula 1-1 or Chemical Formula 1-2.

[0010] Chemical Formula 1-1

[0011]

[0012] Chemical Formula 1-2

[0013]

[0014] In Chemical Formula 1-1,

[0015] L1may be each independently substituted or unsubstituted C1-C10alkylene.

[0016] R1may be each independently hydrogen, substituted or unsubstituted C1-C20alkyl, substituted or unsubstituted C2-C20alkenyl, substituted or unsubstituted C2-C20alkynyl, substituted or unsubstituted C3-C20cycloalkyl, or substituted or unsubstituted C6-C20aryl.

[0017] At least one R1may be substituted or unsubstituted C2-C20alkenyl.

[0018] In Chemical Formula 1-2,

[0019] R2may be each independently hydrogen, substituted or unsubstituted C1-C20alkyl, substituted or unsubstituted C2-C20alkenyl, substituted or unsubstituted C2-C20alkynyl, substituted or unsubstituted C3-C20cycloalkyl, or substituted or unsubstituted C6-C20aryl.

[0020] At least one R2may be substituted or unsubstituted C6-C20aryl.

[0021] According to embodiments of the present disclosure, the rechargeable lithium battery can 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 DRAWINGS

[0022] The accompanying drawings, together with the description, explain the principles of the subject matter of the present disclosure and illustrate embodiments of the subject matter of the present disclosure.

[0023] Figure 1 A simplified conceptual diagram of a rechargeable lithium battery according to embodiments of the present disclosure is shown.

[0024] Figures 2 to 5 A simplified diagram of a rechargeable lithium battery according to embodiments is shown. DETAILED DESCRIPTION

[0025] In order to fully understand the layout and effects of the subject matter of the present disclosure, some embodiments of the present disclosure will be described with reference to the accompanying drawings. However, it should be noted that the present disclosure is not limited to the example embodiments described below, and can be implemented in various suitable forms. Rather, the example embodiments are provided only to disclose the subject matter of the present disclosure, and to fully enable those skilled in the art to understand the scope of the present disclosure.

[0026] In the present disclosure, it will be understood that if (for example, when) an element is referred to as being "on" another element, it can be directly on the other element or intervening elements can be present therebetween. In the drawings, the size of some components (e.g., thickness) can be exaggerated for effective explanation of the technical content of the present disclosure. Throughout the specification, like drawing reference numerals refer to like elements.

[0027] Unless specifically stated otherwise in the description, expressions of the form "A or B" can include A but not B, B but not A, and A and B. The terms "comprises", "comprising", "includes", "including" and / or "comprising" used in the present disclosure are not intended to exclude the presence or addition of one or more other components.

[0028] In the present disclosure, the term "combination thereof" can refer to a mixture, a stack, a composite, a copolymer, an alloy, a blend, and / or a reaction product of ingredients.

[0029] In the present description, unless otherwise specifically defined separately, the term "substituted" can indicate that at least one hydrogen of a substituent or a compound is replaced with deuterium, halo, hydroxyl, amino, C1-C30 amine group, nitro, 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, or a combination thereof

[0030] In more detail, the term "substituted" can indicate that at least one hydrogen of a substituent or a compound is replaced with deuterium, halo, 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-C10 fluoroalkyl group, or cyano. For example, the term "substituted" can indicate that at least one hydrogen of a substituent or a compound is replaced with deuterium, halo, C1-C20 alkyl group, C6-C30 aryl group, C1-C10 fluoroalkyl group, or cyano. In embodiments, the term "substituted" can indicate that at least one hydrogen of a substituent or a compound is replaced with deuterium, halo, C1-C5 alkyl group, C6-C18 aryl group, C1-C5 fluoroalkyl group, or cyano. For example, the term "substituted" can indicate that at least one hydrogen of a substituent or a compound is replaced with deuterium, cyano, halo, methyl, ethyl, propyl, butyl, phenyl, biphenyl, terphenyl, trifluoromethyl, or naphthyl.

[0031] Figure 1A simplified conceptual diagram of a rechargeable lithium battery according to an embodiment of the present disclosure is shown. Referring to Figure 1 The rechargeable lithium battery can include a positive electrode 10, a negative electrode 20, a separator 30, and an electrolyte ELL.

[0032] The positive electrode 10 and the negative electrode 20 can be spaced apart from each other across the separator 30. The separator 30 can be between the positive electrode 10 and the negative electrode 20. The positive electrode 10, the negative electrode 20, and the separator 30 can be in contact with the electrolyte ELL. The positive electrode 10, the negative electrode 20, and the separator 30 can be impregnated with the electrolyte ELL.

[0033] The electrolyte ELL can be a medium through which lithium ions are transported between the positive electrode 10 and the negative electrode 20. In the electrolyte ELL, lithium ions can move toward one of the positive electrode 10 and the negative electrode 20 through the separator 30.

[0034] The positive electrode 10

[0035] The positive electrode 10 for the rechargeable lithium battery can include a positive electrode current collector COL1 and a positive electrode active material layer AML1 on the positive electrode current collector COL1. The positive electrode active material layer AML1 can include a positive electrode active material, and can further include a binder and / or a conductive material (e.g., an electrically conductive material).

[0036] For example, the positive electrode 10 can further include a component that can serve as a sacrificial positive electrode.

[0037] The amount of the positive electrode active material can be about 90 wt% to about 99 wt% with respect to 100 wt% of the positive electrode active material layer AML1. The amount of each of the binder and the conductive material can be about 0.5 wt% to about 5 wt% with respect to 100 wt% of the positive electrode active material layer AML1.

[0038] The binder can serve to improve adhesion between positive electrode active material particles to each other, and also to improve adhesion of the positive electrode active material to the positive electrode current collector COL1. The binder can include, for example, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, an oxirane-containing polymer, polyvinylpyrrolidone, 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.

[0039] Any suitable conductive material that can be used to provide electrode conductivity (e.g., electrical conductivity) or increase electrode electrical conductivity, and does not cause chemical changes in the battery (e.g., does not cause undesirable chemical changes in a rechargeable lithium battery), may be used as a conductive material. Conductive materials may include: for example, carbon-based materials (such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanofibers and / or carbon nanotubes); metal powders and / or metal fibers containing one or more of copper, nickel, aluminum and / or silver; conductive polymers (e.g., electrically conductive polymers) (such as polyphenylene derivatives); or mixtures thereof.

[0040] Aluminum (Al) foil can be used as the positive electrode current collector COL1, but this disclosure is not limited thereto.

[0041] Positive electrode active material

[0042] The positive electrode active material in the positive electrode active material layer AML1 may include compounds that can reversibly insert and deintercalate lithium (e.g., lithiated intercalation compounds). For example, the positive electrode active material may include a composite oxide comprising lithium and at least one of metals selected from cobalt, manganese, nickel and combinations thereof.

[0043] Composite oxides may include lithium transition metal composite oxides, such as lithium nickel oxides (e.g., lithium nickel cobalt aluminum oxides (e.g., LiNi)). 0.91 Co 0.08 Al 0.01 O2), lithium cobalt oxides, lithium manganese oxides, lithium iron phosphate compounds, cobalt-free nickel manganese oxides, or combinations thereof.

[0044] 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 (where 0.90≤a≤1.8, 0≤b≤0.5, and 0≤c≤0.05); Li a Mn 2-b X b O 4-c D c (where 0.90≤a≤1.8, 0≤b≤0.5, and 0≤c≤0.05); Li a Ni 1-b-c Co b X c O 2-α D α (where 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, and 0<α<2); Li aNi 1-b-c Mn b X c O 2-α D α (where 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, and 0<α<2); Li a Ni b Co c L 1 d G e O2 (where 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, and 0 ≤ e ≤ 0.1); Li a NiG b O2 (where 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); Li a CoG b O2 (where 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); Li a Mn 1-b G b O2 (where 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); Li a Mn2G b O4 (where 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); Li a Mn 1-g G g PO4 (where 0.90 ≤ a ≤ 1.8 and 0 ≤ g ≤ 0.5); Li (3-f) Fe2(PO4)3 (where 0 ≤ f ≤ 2); and Li a FePO4 (where 0.90≤a≤1.8).

[0045] In the above chemical formulas, 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; and L... 1 It is Mn, Al, or a combination thereof.

[0046] For example, the positive electrode active material can be a high-nickel positive electrode active material, wherein the nickel content of the high-nickel positive electrode active material is equal to or greater than about 80 mol%, equal to or greater than about 85 mol%, equal to or greater than about 90 mol%, equal to or greater than about 91 mol%, equal to or greater than about 94 mol%, and equal to or less than about 99 mol% relative to 100 mol% of lithium transition metal composite oxide (high-nickel positive electrode active material). High-nickel positive electrode active materials can achieve high capacity and therefore can be used in high-capacity and high-density rechargeable lithium batteries.

[0047] negative electrode 20

[0048] 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 (e.g., an electrically conductive material).

[0049] For example, the negative electrode active material layer AML2 may include about 90 wt% to about 99.5 wt% of negative electrode active material, about 0.5 wt% to about 5 wt% of binder, and about 0 wt% to about 5 wt% of conductive material (e.g., electrically conductive material).

[0050] The binder can be used to improve the adhesion between the particles of the negative electrode active material and to improve the adhesion between the negative electrode active material and the negative electrode current collector COL2. The binder may include non-aqueous binders, aqueous binders, dry binders, or combinations thereof.

[0051] Non-aqueous adhesives may include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene-propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyimide, or combinations thereof.

[0052] Waterborne adhesives may include styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluoroelastomers, polyethylene oxide, polyvinylpyrrolidone, polyepoxychloropropane, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, or combinations thereof.

[0053] If (for example, when) an aqueous binder is used as a binder in the negative electrode active material layer AML2, it may further include a cellulose compound capable of providing or increasing viscosity. The cellulose compound may include one or more selected from carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, and their alkali metal salts. The alkali metal may include Na, K, and / or Li.

[0054] Dry adhesives may include fibrous polymeric materials, such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or combinations thereof.

[0055] Any suitable conductive material that can be used to provide electrode conductivity (e.g., electrical conductivity) or increase electrode electrical conductivity, and does not cause chemical changes in the battery (e.g., does not cause undesirable chemical changes in a rechargeable lithium battery), can be used as a conductive material. For example, conductive materials may include: carbon-based materials (such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanofibers, and / or carbon nanotubes); metal powders and / or metal fibers including one or more of copper, nickel, aluminum, and / or silver; conductive polymers (e.g., electrically conductive polymers) (such as polyphenylene derivatives); or mixtures thereof.

[0056] The negative electrode current collector COL2 may include copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or a combination thereof.

[0057] Negative electrode active material

[0058] The negative electrode active material in the negative electrode active material layer AML2 may include materials that can reversibly insert and deintercalate lithium ions, lithium metal, lithium metal alloys, materials that can be doped and dedoped with lithium, and / or transition metal oxides.

[0059] Materials capable of reversibly inserting and deintercalating 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, flake, sheet, spherical, and / or fibrous natural graphite and / or artificial graphite, and amorphous carbon may include soft carbon, hard carbon, mesophase pitch carbonization products, and / or calcined coke.

[0060] 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.

[0061] Materials that can be doped and dedoped with lithium can include Si-based negative electrode active materials and / or Sn-based negative electrode active materials. Si-based negative electrode active materials can include silicon, silicon-carbon composites, and SiO₂.x (where 0 < x ≤ 2), Si-Q alloy (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 a combination thereof), or a combination thereof. The Sn-based negative electrode active material may include Sn, SnO k (0 < K ≤ 2, for example, SnO2), Sn-based alloy, or a combination thereof.

[0062] 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. The amorphous carbon may also be between the primary silicon particles, and for example, the primary silicon particles may be coated with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0063] 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.

[0064] The Si-based negative electrode active material and / or the Sn-based negative electrode active material may be used in combination with a carbon-based negative electrode active material.

[0065] Separator 30

[0066] Depending 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 polyethylene, polypropylene, and polyvinylidene fluoride, and may have a multilayer separator such as a polyethylene / polypropylene bilayer separator, a polyethylene / polypropylene / polyethylene trilayer separator, and a polypropylene / polyethylene / polypropylene trilayer separator.

[0067] The separator 30 may include a porous substrate and a coating on one or opposite surfaces of the porous substrate, the coating including an organic material, an inorganic material, or a combination thereof.

[0068] The porous substrate may be a polymer layer including a copolymer or mixture of one or two or more selected from the following: polyolefins (such as polyethylene and polypropylene), polyesters (such as polyethylene terephthalate and polybutylene terephthalate), polyacetals, polyamides, polyimides, polycarbonates, polyether ketones, polyaryl ether ketones, polyether imides, polyamide imides, polybenzimidazoles, polyether sulfones, polyphenylene ethers, cycloolefin copolymers, polyphenylene sulfides, polyethylene naphthalate, glass fiber, and polytetrafluoroethylene (e.g., Teflon).

[0069] The organic material may include polyvinylidene fluoride-based copolymers and / or (meth)acrylic acid-based copolymers.

[0070] Inorganic materials may include inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite or combinations thereof, but this disclosure is not limited thereto.

[0071] Organic and inorganic materials can be mixed in a single coating or exist as a stack of coatings containing organic materials and coatings containing inorganic materials.

[0072] Electrolyte ELL

[0073] Electrolytes (ELLs) used in rechargeable lithium batteries may include non-aqueous organic solvents and lithium salts.

[0074] Non-aqueous organic solvents can be used as media for transporting ions that participate in the electrochemical reactions of a battery.

[0075] Non-aqueous organic solvents may include carbonate solvents, ester solvents, ether solvents, ketone solvents, alcohol solvents, aprotic solvents, or combinations thereof.

[0076] Carbonate solvents may include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), and / or butyl carbonate (BC).

[0077] Ester solvents may include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanoic acid lactone, mevalonate lactone, valproic acid lactone, and / or caprolactone.

[0078] 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. Alcohol solvents may include ethanol and / or isopropanol, and aprotic solvents may include nitriles (such as R-CN, where R is a hydrocarbon group having a C2-C20 straight-chain, branched, or cyclic structure, and may include double bonds, aromatic rings, and / or ether bonds); amides (such as dimethylformamide); dioxolane (such as 1,3-dioxolane and / or 1,4-dioxolane); and / or sulfolane.

[0079] Non-aqueous organic solvents can be used alone or in combination of two or more substances.

[0080] In embodiments, if (for example, when) a carbonate solvent is used, cyclic carbonates and chain carbonates can be mixed and used, and cyclic carbonates and chain carbonates can be mixed in a volume ratio of about 1:1 to about 1:9.

[0081] Lithium salts are materials that can be dissolved in non-aqueous organic solvents to serve as a source of lithium ions in batteries, and play a role in ensuring the basic operation of rechargeable lithium batteries and facilitating the transport of lithium ions between the positive and negative electrodes. Lithium salts may include, for example, those 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 (where x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluoro(oxalate)borate (LiDFOB), lithium difluorobis(oxalate)phosphate (LiDFBOP), and lithium bis(oxalate)borate (LiBOB).

[0082] Rechargeable lithium batteries

[0083] Based on their shape, rechargeable lithium batteries can be classified into cylindrical, prismatic, pouch, and coin-shaped (or different types). Figures 2 to 5 To illustrate a simplified diagram of a rechargeable lithium battery according to an embodiment, Figure 2 A cylindrical battery is shown. Figure 3 A prismatic battery is shown, and Figures 4 to 5 A pouch-type battery is shown. (Reference) Figures 2 to 5 The rechargeable lithium battery 100 may include an electrode assembly 40 (with a separator 30 between a positive electrode 10 and a negative electrode 20) and may also include a housing 50 (containing the electrode assembly 40). The positive electrode 10, negative electrode 20, and separator 30 may be impregnated with an electrolyte. Figure 2 The text explains that the rechargeable lithium battery 100 may include a sealing member 60 of a sealed housing 50. In some embodiments, such as... Figure 3 The text explains that the rechargeable lithium battery 100 may include a positive electrode lead connector 11, a positive electrode terminal 12, a negative electrode lead connector 21, and a negative electrode terminal 22. For example... Figures 4 to 5 As shown, the rechargeable lithium battery 100 may include electrode terminals 70. Figure 5 ), or positive electrode terminal 71 and negative electrode terminal 72 ( Figure 4), which serves as an electrical path for guiding the current generated in the electrode assembly 40 to the outside.

[0084] The electrolyte for rechargeable lithium batteries according to some embodiments of the present disclosure will be described in more detail below.

[0085] The electrolyte for a rechargeable lithium battery according to the embodiments may include a non-aqueous organic solvent, a lithium salt, and additives.

[0086] The additives according to embodiments of this disclosure may be represented by chemical formula 1-1 or chemical formula 1-2.

[0087] Chemical Formula 1-1

[0088]

[0089] Chemical formula 1-2

[0090]

[0091] In chemical formula 1-1, L1 can be independently substituted or unsubstituted C1-C10 alkylene groups. R1 can be independently hydrogen, substituted or unsubstituted C1-C20 alkyl, substituted or unsubstituted C2-C20 alkenyl, substituted or unsubstituted C2-C20 alkynyl, substituted or unsubstituted C3-C20 cycloalkyl, or substituted or unsubstituted C6-C20 aryl, and at least one R1 can be a substituted or unsubstituted C2-C20 alkenyl.

[0092] In chemical formulas 1-2, R2 can be hydrogen, substituted or unsubstituted C1-C20 alkyl, substituted or unsubstituted C2-C20 alkenyl, substituted or unsubstituted C2-C20 alkynyl, substituted or unsubstituted C3-C20 cycloalkyl, or substituted or unsubstituted C6-C20 aryl, and at least one R2 can be a substituted or unsubstituted C6-C20 aryl.

[0093] Additives according to embodiments of this disclosure may include structures in which oxygen atoms are double-bonded to disulfide bonds (SS=O) (e.g., including double bonds between oxygen atoms and sulfur atoms in disulfide bonds). This bonding structure can stabilize the positive electrode by eliminating unstable oxygen (e.g., reactive oxygen species) generated around the positive electrode active material due to positive electrode degradation. In embodiments, this bonding structure can stabilize the positive electrode by facilitating the formation of a robust cathode electrolyte interface (CEI) on the positive electrode surface.

[0094] In rechargeable lithium batteries, unstable oxygen can be generated internally with repeated charge and discharge cycles. This unstable oxygen corrodes the surface of the positive electrode, leading to its degradation. This bonding structure can effectively remove unstable oxygen (or reduce its concentration), thereby significantly improving the degradation of the positive electrode (e.g., significantly reducing its degradation). Therefore, the additive according to embodiments of this disclosure can cause improvements in battery performance. The positive electrode stability effect of this bonding structure becomes more pronounced at high temperatures. For example, in embodiments, the high temperature may be equal to or greater than about 50°C or equal to or greater than about 135°C.

[0095] In Formula 1-1, at least one R1 may comprise a carbon atom having a double bond (e.g., a carbon atom double-bonded to another atom). For example, in Formula 1-1, all R1 may comprise an allyl structure. For example, in Formula 1-1, only one R1 may comprise an allyl structure.

[0096] In embodiments, the additive represented by chemical formula 1-1 may be a compound represented by chemical formula 1-1A, chemical formula 1-1B, or chemical formula 1-1C. For example, the additive represented by chemical formula 1-1 may be at least one selected from S-allyl prop-2-ene-1-sulfinothioate (allicin), S-propyl prop-2-ene-1-sulfinothioate, and S-allylethanesulfinothioate.

[0097] Chemical formula 1-1A

[0098]

[0099] Chemical formula 1-1B

[0100]

[0101] Chemical formula 1-1C

[0102]

[0103] The additives according to embodiments of the present disclosure may include allyl groups. For example, an additive represented by chemical formula 1-1 may include an allyl group located at one end (e.g., at the terminal end), thus allowing for easy and continuous polymerization (e.g., chain polymerization) during SEI film formation. Therefore, due to the chain polymerization reaction, the additives according to embodiments of the present disclosure can form relatively thick and high-density SEI films.

[0104] In formula 1-2, at least one R2 may comprise an aryl group. For example, in formula 1-2, all R2 may comprise a phenyl structure. For example, in formula 1-2, only one R2 may comprise a phenyl structure.

[0105] In embodiments, the additives represented by chemical formulas 1-2 may be compounds represented by chemical formulas 1-2A and 1-2B. For example, the additives represented by chemical formulas 1-2 may be at least one selected from S-phenylbenzenesulfonothioate and S-phenylethanesulfinothioate.

[0106] Chemical formula 1-2A

[0107]

[0108] Chemical formula 1-2B

[0109]

[0110] The additives according to embodiments of this disclosure may include at least one phenyl group. For example, additives represented by chemical formulas 1-2 may include a phenyl group located at one end (e.g., the terminal end) to facilitate the formation of a robust cathode electrolyte interface (CEI) on the surface of the positive electrode, thereby stabilizing the positive electrode.

[0111] Because the additives according to embodiments of this disclosure include a structure in which oxygen atoms are double-bonded to disulfide bonds (e.g., oxygen atoms are double-bonded to sulfur atoms in disulfide bonds) (SS=O) and a set or specific functional group located at one end (e.g., the terminal), the effects discussed above can be achieved even more effectively. Compared to additives containing only allyl or phenyl groups, the additives according to embodiments of this disclosure with this structural feature exhibit significantly superior positive electrode stability.

[0112] The amount of additives included relative to the total weight of the electrolyte may be from about 0.01 wt% to about 10 wt% (e.g., from about 0.01 wt% to about 5 wt%), from about 0.03 wt% to about 8 wt%, from about 0.05 wt% to about 7 wt%, or from about 0.1 wt% to about 5 wt%. In embodiments, the amount of additives included relative to the total weight of the electrolyte may be from about 0.1 wt% to about 5 wt%.

[0113] The amount of additive can refer to the weight of the additive included in the electrolyte relative to the total weight of the electrolyte. If, for example, the amount of additive falls within the above range, the effect of suppressing or reducing the increase of impedance (e.g., resistance) at high temperatures and during high-temperature storage can be maximized or increased due to positive electrode stability. If, for example, the amount of additive is less than the lower limit of the above range, the additive may not be able to sufficiently remove unstable oxygen, resulting in a lack of positive electrode stability effect. If, for example, the amount of additive is greater than the upper limit of the above range, the additive itself may act as a material that causes impedance, resulting in a lack of positive electrode stability effect.

[0114] Non-aqueous organic solvents may include at least one selected from ethylene carbonate (EC), methyl ethyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate (PC), propyl propionate (PP), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), and butyl carbonate (BC).

[0115] In this embodiment, the non-aqueous organic solvent may be a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC).

[0116] For example, the amount of ethylene carbonate (EC) included may be about 10 vol% to about 40 vol% relative to the total volume of the non-aqueous organic solvent. The amount of ethyl methyl carbonate (EMC) included may be about 20 vol% to about 70 vol% relative to the total volume of the non-aqueous organic solvent. The amount of dimethyl carbonate (DMC) included may be about 20 vol% to about 70 vol% relative to the total volume of the non-aqueous organic solvent.

[0117] The lithium salt may include at least one selected from LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, lithium bis(fluorosulfonyl)imide (LiFSI), and LiC4F9SO3. According to embodiments, the lithium salt may include LiPF6.

[0118] The lithium salt may have a concentration of about 0.1 M to about 2.0 M. For example, the lithium salt may have a concentration equal to or greater than about 0.5 M or equal to or greater than about 1.0 M. The lithium salt may have a concentration equal to or less than about 2.0 M, equal to or less than about 1.7 M, or equal to or less than about 1.5 M. In embodiments of this disclosure, if (for example, when) the lithium salt has a concentration of about 0.1 M to about 2.0 M, the electrolyte may suitably or appropriately maintain its conductivity (e.g., electronic conductivity) and viscosity.

[0119] In embodiments of this disclosure, a rechargeable lithium battery may include: a positive electrode comprising a positive electrode active material, a negative electrode comprising a negative electrode active material, and an electrolyte, wherein the electrolyte may include a non-aqueous organic solvent, a lithium salt, and an additive represented by chemical formula 1-1 or chemical formula 1-2.

[0120] The positive electrode active material may include lithium composite oxide represented by chemical formula 2.

[0121] Chemical formula 2

[0122] Li x M 1 y M 2 z M 3 1-y-z O 2-a X a

[0123] In chemical formula 2,

[0124] x, a, y, and z can satisfy the relationships 0.5≤x≤1.8, 0≤a≤0.05, 0≤y≤1, 0≤z≤1, and 0≤y+z≤1.

[0125] M 1 M 2 and M 3 Each of these metals may independently include metals such as Ni, Co, Mn, Al, B, Ba, Ca, Ce, Cr, Fe, Mo, Nb, Si, Sr, Mg, Ti, V, W, Zr, La, Y, or combinations thereof.

[0126] X may include at least one element selected from F, S, P, and Cl.

[0127] In the implementation method, in chemical formula 2, M 1 It can be Ni, y can satisfy 0.8≤y≤1, and z can satisfy 0≤z≤0.2. In the implementation, in chemical formula 2, M 1 It can be Ni, M 2 It can be Co, and M 3 It can be Al. In the implementation method, in chemical formula 2, M 1 It can be Ni, M 2 It can be Co, and M 3 It can be Mn.

[0128] The negative electrode active material may include at least one selected from graphite and silicon composites.

[0129] If (e.g., when) the negative electrode active material includes both a silicon composite and graphite, the silicon composite and graphite may be included in a mixture form, and in an embodiment, the weight ratio of the included silicon composite and graphite may be about 1:99 to about 50:50. For example, the weight ratio of the included silicon composite and graphite may be about 3:97 to about 20:80 or about 5:95 to about 20:80.

[0130] The silicon composite may include a core containing silicon-based particles and an amorphous carbon coating, and the silicon-based particles may include at least one selected from a silicon-carbon composite, SiO x (where 0 < x ≤ 2) and a silicon alloy. For example, the silicon-carbon composite may include a core containing silicon particles and crystalline carbon, and may also include an amorphous carbon coating on the surface of the core. The crystalline carbon may include graphite, for example, natural graphite, artificial graphite, or a mixture thereof.

[0131] In a rechargeable lithium battery, due to the erosion of the acid generated inside the battery, deterioration of the positive electrode film and the negative electrode film may occur. In the rechargeable lithium battery according to an embodiment of the present disclosure, the electrolyte may decompose during initial charge-discharge to form a film having a passivation ability on the surface of the positive electrode and the surface of the negative electrode to improve the high-temperature storage characteristics. Since acids such as HF and PF5 generated by the thermal decomposition of lithium salts (such as LiPF6) widely used in lithium ion batteries deteriorate the film. In an embodiment, such acid erosion may dissolve transition metal elements (transition metal ions) from the positive electrode and increase the electrode surface impedance (e.g., resistance) caused by the structural change on the surface. Therefore, due to the loss of the metal element as a redox (reduction and oxidation) center, the theoretical capacity may be reduced, which may lead to a reduction in capacity. The dissolved transition metal ions may be electrodeposited on the negative electrode that reacts within a strong reduction potential range. The transition metal ions consume electrons when electrodeposited on the negative electrode and may break or damage the film to expose the negative electrode surface. This may lead to an additional decomposition reaction of the electrolyte. Therefore, the impedance (e.g., resistance) and irreversible capacity of the negative electrode may increase, and as a result, there may be a problem that the capacity of the battery cell continuously decreases.

[0132] Since the additive according to an embodiment of the present disclosure includes a structure (S-S=O) in which an oxygen atom is double-bonded to a disulfide bond (e.g., the oxygen atom is double-bonded to the sulfur atom of the disulfide bond) and a set or specific functional group located at one end (e.g., the terminal), reactive oxygen species can be removed (or the concentration of reactive oxygen species can be reduced) and the positive electrode film can be strengthened. Therefore, deterioration of the positive electrode can be effectively prevented or reduced. As a result, the rechargeable lithium battery according to an embodiment of the present disclosure can exhibit excellent electrochemical performance. The above effects can become more obvious at high temperatures.

[0133] Rechargeable lithium batteries can be used in motor vehicles, mobile phones and / or any other suitable electronic devices, but this disclosure is not limited thereto.

[0134] Some embodiments and comparative examples of this disclosure will be described below. However, the embodiments described below are merely examples, and this disclosure is not limited to the embodiments discussed below.

[0135] Implementation methods and comparative examples

[0136] Implementation Method 1

[0137] (1) Preparation of electrolyte

[0138] An electrolyte was prepared by dissolving 1.15 M LiPF6 in a non-aqueous organic solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) mixed in a volume ratio of approximately 20:40:40, and adding additives. The amount of additives included was 0.1 wt% relative to the total weight of the electrolyte. The material represented by chemical formula 1-1A was used as the additive.

[0139] Chemical formula 1-1A

[0140]

[0141] (2) Manufacturing of rechargeable lithium batteries

[0142] 97 wt% LiNi was used as the positive electrode active material. 0.91 Co 0.08 Al 0.01 O2 (NCA), 0.5 wt% artificial graphite powder as a conductive material, 0.8 wt% carbon black, 0.2 wt% acrylonitrile rubber, and 1.5 wt% polyvinylidene fluoride (PVDF) were mixed and added to N-methyl-2-pyrrolidone (NMP). The mixture was then stirred for 30 minutes using a mechanical stirrer to prepare a slurry for the positive electrode active material. The slurry was coated onto an aluminum current collector with a thickness of 20 μm to a thickness of 60 μm using a doctor blade, dried in a hot air dryer at 100 °C for 0.5 hours, and then dried again under vacuum at 120 °C for 4 hours. Finally, it was rolled to manufacture the positive electrode.

[0143] A negative electrode active material slurry was prepared by mixing 98 wt% of a mixture of artificial graphite and silicon composite in a weight ratio of 95.8:4.2, 1 wt% of styrene-butadiene rubber (SBR), and 1 wt% of carboxymethyl cellulose (CMC) in distilled water and stirring for 60 minutes using a mechanical stirrer. The slurry was then coated onto a copper current collector with a thickness of 10 μm to a thickness of 60 μm using a doctor blade, dried in a hot air dryer at 100 °C for 0.5 hours, and then dried again under vacuum at 120 °C for 4 hours. Finally, the material was rolled to fabricate the negative electrode.

[0144] The positive electrode, negative electrode, and 16μm thick polyethylene separator are assembled to manufacture the electrode assembly, and an electrolyte is introduced to manufacture the rechargeable lithium battery.

[0145] Implementation Method 2

[0146] The electrolyte and rechargeable lithium battery are manufactured according to essentially the same method as in Embodiment 1, except that when preparing the electrolyte, 1.0 wt% of an additive represented by chemical formula 1-1A is applied.

[0147] Implementation Method 3

[0148] The electrolyte and rechargeable lithium battery are manufactured according to essentially the same method as in Embodiment 1, except that when preparing the electrolyte, 5.0 wt% of an additive represented by chemical formula 1-1A is applied.

[0149] Implementation Method 4

[0150] The electrolyte and rechargeable lithium battery are manufactured according to essentially the same method as in Embodiment 1, except that when preparing the electrolyte, 0.1 wt% of the additive represented by chemical formula 1-2A is used instead of the additive represented by chemical formula 1-1A.

[0151] Chemical formula 1-2A

[0152]

[0153] Implementation Method 5

[0154] The electrolyte and rechargeable lithium battery are manufactured according to essentially the same method as in Embodiment 1, except that when preparing the electrolyte, 1.0 wt% of the additive represented by chemical formula 1-2A is used instead of the additive represented by chemical formula 1-1A.

[0155] Implementation Method 6

[0156] The electrolyte and rechargeable lithium battery are manufactured according to essentially the same method as in Embodiment 1, except that when preparing the electrolyte, 5.0 wt% of the additive represented by chemical formula 1-2A is used instead of the additive represented by chemical formula 1-1A.

[0157] Comparative Example 1

[0158] The electrolyte and rechargeable lithium battery are manufactured according to a method substantially the same as that in Embodiment 1, except that no additives represented by chemical formula 1-1A are added when preparing the electrolyte.

[0159] Comparative Example 2

[0160] The electrolyte and rechargeable lithium battery are manufactured according to essentially the same method as in Embodiment 1, except that when preparing the electrolyte, 0.1 wt% of a compound represented by Chemical Formula 3-1 is added instead of an additive represented by Chemical Formula 1-1A.

[0161] Chemical formula 3-1

[0162]

[0163] Comparative Example 3

[0164] The electrolyte and rechargeable lithium battery are manufactured according to essentially the same method as in Embodiment 1, except that when preparing the electrolyte, 1.0 wt% of a compound represented by Chemical Formula 3-1 is added instead of an additive represented by Chemical Formula 1-1A.

[0165] Comparative Example 4

[0166] The electrolyte and rechargeable lithium battery are manufactured according to a method substantially the same as in Embodiment 1, except that when preparing the electrolyte, 5.0 wt% of a compound represented by Chemical Formula 3-1 is added instead of an additive represented by Chemical Formula 1-1A.

[0167] Comparative Example 5

[0168] The electrolyte and rechargeable lithium battery are manufactured according to essentially the same method as in Embodiment 1, except that when preparing the electrolyte, 0.1 wt% of a compound represented by chemical formula 3-2 is added instead of an additive represented by chemical formula 1-1A.

[0169] Chemical formula 3-2

[0170]

[0171] Table 1 lists the composition of the electrolyte according to the embodiments and comparative examples.

[0172] Table 1

[0173]

[0174]

[0175] For reference, in Table 1, the molar concentration (M) of lithium salts can refer to the amount of lithium salts dissolved in 1 liter of electrolyte (in moles), the volume ratio of non-aqueous organic solvents can refer to the volume ratio of EC:EMC:DMC, and the amount of additives can refer to the weight of the additives relative to the total 100 wt% of the electrolyte.

[0176] Evaluation Example

[0177] The rechargeable lithium batteries of the embodiments and comparative examples were evaluated using the following methods.

[0178] Evaluation 1: High-Temperature Impedance Test

[0179] Each of the rechargeable lithium batteries manufactured in the embodiments and comparative examples was charged to 4.3V at 45°C, and the initial battery impedance (Re(Z) / Ohm) and the impedance after 7 days at 60°C (battery impedance after 7 days of high-temperature storage (Re(Z) / Ohm)) were measured, and the results are shown in Table 2. The impedance values ​​were measured using electrochemical impedance spectroscopy (EIS).

[0180] Table 2

[0181]

[0182] Assessment 2: Heat Exposure

[0183] Each of the rechargeable lithium batteries manufactured according to the embodiments and comparative examples was exposed to a target temperature (high temperature) for one hour, and the battery was evaluated for ignition. The results are shown in Table 3. When the temperature rose from room temperature to the target temperature, the heating rate was maintained at 5°C / min. At this time, the occurrence of fire was checked, and the results are shown in Table 3.

[0184] Table 3

[0185] Target temperature 134℃ 136℃ 138℃ 140℃ Comparative Example 1 No fire Fire - - Comparative Example 2 No fire Fire - - Comparative Example 3 No fire Fire - - Comparative Example 4 No fire Fire - - Comparative Example 5 No fire Fire - - Example 1 No fire No fire No fire No fire Example 2 No fire No fire No fire No fire Example 3 No fire No fire No fire No fire Example 4 No fire No fire Fire - Example 5 No fire No fire Fire - Example 6 No fire No fire Fire -

[0186] Evaluation 3: Charge / discharge characteristics at room temperature

[0187] At 25°C, each of the rechargeable lithium batteries manufactured according to the embodiments and comparative examples was subjected to 100 charge and discharge cycles under 0.5C charging (CC / CV, 4.25V, 0.05C cutoff) and 0.5C discharging (CC, 2.8V cutoff) conditions to obtain the initial discharge capacity and the discharge capacity after 100 cycles. The capacity retention rate was calculated and listed in Table 4. The capacity retention rate was calculated according to Equation 1.

[0188] Equation 1

[0189] Capacity retention (%) = (Discharge capacity after 100 cycles / Initial discharge capacity) × 100%

[0190] Table 4

[0191] Category Capacity retention rate (%) Comparative Example 1 90.6 Comparative Example 2 90.4 Comparative Example 3 91.2 Comparative Example 4 92.7 Comparative Example 5 90.5 Example 1 93.2 Example 2 93.7 Example 3 95.7 Example 4 92.7 Example 5 93.1 Example 6 94.9

[0192] Comprehensive assessment

[0193] Referring to Table 2, it can be seen that, compared with the comparative example, in the embodiments (Embodiments 1 to 6) in which an electrolyte containing an additive according to an embodiment of the present invention was added, the impedance at high temperature (60°C) was effectively suppressed.

[0194] Referring to Table 3, when using the electrolyte according to the embodiments of this disclosure (Embodiments 1 to 6), it can withstand heat up to 140°C. Therefore, it is confirmed that, compared with the comparative examples, the thermal stability characteristics (thermal runaway and positive electrode degradation) are improved in the embodiments using electrolytes with additives according to the embodiments of this disclosure.

[0195] Referring to Table 4, it can be seen that, compared with the comparative example, the capacity retention rate based on charge / discharge cycles at room temperature is improved in the respective embodiments using the electrolyte according to the present disclosure.

[0196] If (for example, when) a rechargeable lithium battery is activated, the electrolyte according to the embodiment can improve cycle life characteristics due to the positive electrode stability at high temperatures.

[0197] Although the subject matter of this disclosure has been described in conjunction with what is now regarded as exemplary embodiments, it should be understood that this disclosure is not limited to the disclosed embodiments, but is intended to cover various suitable modifications and equivalent arrangements included within the spirit and scope of the claims and their equivalents. Therefore, the foregoing embodiments should be understood as examples and not as limiting this disclosure in any way.

Claims

1. An electrolyte for a rechargeable lithium battery, the electrolyte comprising: Non-aqueous organic solvents; Lithium salts; and Additives, represented by chemical formula 1-1 or chemical formula 1-2, Chemical Formula 1-1 Chemical formula 1-2 In chemical formula 1-1, L1 is independently a substituted or unsubstituted C1-C10 alkylene group. R1 is independently hydrogen, a substituted or unsubstituted C1-C20 alkyl, a substituted or unsubstituted C2-C20 alkenyl, a substituted or unsubstituted C2-C20 alkynyl, a substituted or unsubstituted C3-C20 cycloalkyl, or a substituted or unsubstituted C6-C20 aryl, and At least one R1 is a substituted or unsubstituted C2-C20 alkenyl group, and Among them, in chemical formulas 1-2, R2 is independently hydrogen, a substituted or unsubstituted C1-C20 alkyl, a substituted or unsubstituted C2-C20 alkenyl, a substituted or unsubstituted C2-C20 alkynyl, a substituted or unsubstituted C3-C20 cycloalkyl, or a substituted or unsubstituted C6-C20 aryl, and At least one R2 is a substituted or unsubstituted C6-C20 aryl group.

2. The electrolyte of claim 1, wherein the additive represented by chemical formula 1-1 comprises at least one compound selected from chemical formulas 1-1A, 1-1B, and 1-1C. Chemical formula 1-1A Chemical formula 1-1B Chemical formula 1-1C 3. The electrolyte of claim 1, wherein the additive represented by chemical formulas 1-2 comprises at least one compound selected from chemical formulas 1-2A and 1-2B. Chemical formula 1-2A Chemical formula 1-2B 4. The electrolyte of claim 1, wherein the additive is present in an amount of 0.01 wt% to 5 wt% relative to the total weight of the electrolyte.

5. The electrolyte of claim 1, wherein the non-aqueous organic solvent comprises at least one selected from methyl ethyl carbonate, ethylene carbonate, dimethyl carbonate, propylene carbonate, propyl propionate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, and butyl carbonate.

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

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

8. A rechargeable lithium battery, comprising: Positive electrode, including positive electrode active material; Negative electrode, including negative electrode active material; and The electrolyte as described in any one of claims 1 to 7.

9. The rechargeable lithium battery of claim 8, wherein the positive electrode active material comprises a lithium composite oxide represented by chemical formula 2. Chemical formula 2 Li x M 1 y M 2 z M 3 1-y-z O 2-a X a in, In chemical formula 2, 0.5≤x≤1.8, 0≤a≤0.05, 0≤y≤1, 0≤z≤1, and 0≤y+z≤1. M 1 M 2 and M 3 Each independently includes metals such as Ni, Co, Mn, Al, B, Ba, Ca, Ce, Cr, Fe, Mo, Nb, Si, Sr, Mg, Ti, V, W, Zr, La, Y, or combinations thereof, and X includes at least one element selected from F, S, P, and Cl.

10. The rechargeable lithium battery of claim 9, wherein M of chemical formula 2 1 For Ni.

11. The rechargeable lithium battery of claim 9, wherein the negative electrode active material comprises at least one selected from graphite and silicon composites.

12. The rechargeable lithium battery of claim 9, wherein the rechargeable lithium battery is a cylindrical, prismatic, pouch-shaped, or coin-shaped battery.

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