Electrolyte for rechargeable lithium battery and rechargeable lithium battery including same

Abstract

The invention discloses an electrolyte for a rechargeable lithium battery and a rechargeable lithium battery including the same. The electrolyte includes: a non-aqueous organic solvent; a lithium salt; a first additive including a borate lithium salt having a double bond between carbon atoms; and a second additive including a dithioketone compound.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to and the benefit of Korean Patent Application No. 10-2023-0153635 filed on November 8, 2023 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 same. Background Art

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

[0005] The rechargeable lithium battery includes a positive electrode, a negative electrode, and an electrolyte, the positive electrode and the negative electrode include an active material in which lithium ions can be intercalated and deintercalated, and if the lithium ions are intercalated and deintercalated, electric energy caused by oxidation reaction and reduction reaction is generated.

[0006] Lithium salts dissolved in non-aqueous organic solvents are 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 one of the variables for improving rechargeable lithium batteries. Summary of the invention

[0007] Embodiments of the present disclosure provide an electrolyte for a rechargeable lithium battery that can suppress or reduce the generation of gas by reducing oxidative decomposition and has increased high-temperature lifespan and high-temperature retention characteristics.

[0008] An embodiment of the present disclosure provides a rechargeable lithium battery including the above-mentioned electrolyte.

[0009] According to an embodiment of the present disclosure, an electrolyte for a rechargeable lithium battery may include: a nonaqueous organic solvent; a lithium salt; a first additive including a borate-based lithium salt having a double bond between carbon atoms; and a second additive including a dithione-based compound.

[0010] 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 an electrolyte for a rechargeable lithium battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] 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.

[0012] Figure 1 A simplified conceptual diagram showing a rechargeable lithium battery according to some embodiments of the present disclosure is illustrated.

[0013] Figure 2 is a simplified perspective view showing a rechargeable lithium battery according to some embodiments of the present disclosure.

[0014] Figure 3 1 is a simplified cross-sectional view showing a rechargeable lithium battery according to some embodiments of the present disclosure.

[0015] Figure 4-5 is a simplified perspective view showing a rechargeable lithium battery according to some embodiments of the present disclosure. DETAILED DESCRIPTION

[0016] In order to fully understand the configuration and effects of the embodiments 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 forms. On the contrary, the example embodiments are provided only to illustrate the embodiments of the present disclosure and to fully inform the scope of the present disclosure to those skilled in the art.

[0017] 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 them. In the accompanying drawings, some component sizes (e.g., thickness) may be exaggerated in order to effectively explain the technical content of the present disclosure. The same reference numerals refer to the same elements throughout the specification.

[0018] Unless otherwise specifically stated in the description, expressions in the singular may include expressions in the plural. 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.

[0019] In the present description, the term "combination thereof" may refer to a mixture, stack, composite, copolymer, alloy, blend or reaction product of the indicated components.

[0020] Figure 1 A simplified conceptual diagram showing a rechargeable lithium battery according to some embodiments 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.

[0021] 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 impregnated with the electrolyte ELL.

[0022] The electrolyte ELL may be a medium through which lithium ions are transferred between the positive electrode 10 and the negative electrode 20. In the electrolyte ELL, the lithium ions may move toward one of the positive electrode 10 and the negative electrode 20 through the separator 30.

[0023] Positive electrode 10

[0024] 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).

[0025] For example, the positive electrode 10 may further include an additive that may function as a sacrificial positive electrode.

[0026] The amount of the positive electrode active material may be in the range of about 90 wt % to about 99.5 wt % based on 100 wt % of the positive electrode active material layer AML1. The amount of the binder and the conductive material may be about 0.5 wt % and about 5 wt % respectively based on 100 wt % of the positive electrode active material layer AML1.

[0027] The binder can be used to improve the attachment of the positive electrode active material particles to each other, and also to improve the attachment of the positive electrode active material to the positive electrode current collector COL1. 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.

[0028] The conductive material can be used to provide electrode conductivity (e.g., electrical conductivity), and any suitable conductive material (e.g., conductive material) that 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 the conductive material. The conductive material may include, for example: 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 of copper, nickel, aluminum, and silver; a conductive polymer (e.g., conductive polymer) such as a polyphenylene derivative; or a mixture thereof.

[0029] An Al foil may be used as the positive electrode current collector COL1 , but the present disclosure is not limited thereto.

[0030] Positive electrode active material

[0031] The positive electrode active material in the positive electrode active material layer AML1 may include a compound capable of reversibly inserting and extracting lithium (e.g., a lithiated inserting compound). For example, the positive electrode active material may include at least one composite oxide of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof.

[0032] The composite oxide may include a lithium transition metal composite oxide, for example, a lithium nickel-based oxide (eg, a nickel cobalt aluminum (NCA)-based lithium composite oxide), a lithium cobalt-based oxide, a lithium manganese-based oxide, a lithium iron phosphate-based compound, a cobalt-free nickel manganese-based oxide, or a combination thereof.

[0033] For example, the positive electrode active material may include a compound represented by one of the following chemical formulas. 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 O2-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), Li a 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).

[0034] 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.

[0035] For example, based on 100 mol% of metals other than 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 energy density rechargeable lithium batteries.

[0036] Negative electrode 20

[0037] 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).

[0038] For example, based on 100 wt % of the total weight of the negative electrode active material layer AML2, the negative electrode active material layer AML2 may include about 90 wt % to about 99 wt % of the negative electrode active material, about 0.5 wt % to about 5 wt % of the binder, and about 0 wt % to about 5 wt % of the conductive material (e.g., conductive material).

[0039] The binder may be used to improve the attachment of the negative electrode active material particles to each other and also to improve the attachment 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.

[0040] 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.

[0041] The aqueous binder may include styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, 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.

[0042] 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 of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, and alkali metal salts thereof. The alkali metal may include Na, K, and / or Li.

[0043] The dry binder may include a polymer material capable of fiberization such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0044] Conductive materials can be used to provide electrode conductivity (e.g., electrical conductivity), and any suitable conductive material (e.g., electrically conductive material) that 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 can include: carbonaceous materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal powders and / or metal fibers including one or more of copper, nickel, aluminum, and silver; conductive polymers (e.g., electrically conductive polymers) such as polyphenylene derivatives; or mixtures thereof.

[0045] The negative electrode current collector COL2 can include copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal (e.g., electrically conductive metal), and / or combinations thereof.

[0046] Negative electrode active material

[0047] The negative electrode active material in the negative electrode active material layer AML2 can include: materials that can reversibly intercalate and deintercalate lithium ions, lithium metal, lithium metal alloys, materials that can be doped and dedoped with lithium, and / or transition metal oxides.

[0048] Materials that can reversibly intercalate and deintercalate lithium ions can include carbonaceous negative electrode active materials, e.g., crystalline carbon, amorphous carbon, or combinations thereof. For example, crystalline carbon can include graphite such as amorphous, flaky, lamellar, spherical, and / or fibrous natural or artificial graphite, and amorphous carbon can include soft carbon, hard carbon, mesophase pitch carbon, and / or calcined coke.

[0049] Lithium metal alloys can 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.

[0050] 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, 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 can include Sn, SnO k (0 < k ≤ 2) (e.g., SnO2), Sn-based alloys, or combinations thereof.

[0051] The silicon-carbon composite may be a composite of silicon and amorphous carbon. According to an embodiment, the silicon-carbon composite may be in the form of silicon particles and amorphous carbon coated on the surface of the 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 primary silicon particles, and, for example, primary silicon particles may be coated with amorphous carbon. Secondary particles may be dispersed in an amorphous carbon matrix.

[0052] The silicon-carbon composite may further include crystalline carbon. For example, the silicon-carbon composite may include a core including crystalline carbon and silicon particles, and may further include an amorphous carbon coating on a surface of the core.

[0053] The Si-based negative electrode active material and / or the Sn-based negative electrode active material may be used in combination with the carbon-based negative electrode active material.

[0054] Diaphragm 30

[0055] 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 have a multilayer separator thereof (such as a polyethylene / polypropylene double-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, and a polypropylene / polyethylene / polypropylene three-layer separator).

[0056] The separator 30 may include a porous substrate and a coating on one or opposite surface of the porous substrate, the coating including an organic material, an inorganic material, or a combination thereof.

[0057] The porous substrate may be a polymer layer comprising: one selected from polyolefins (such as polyethylene and / or polypropylene), polyesters (such as polyethylene terephthalate and / or 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); and / or copolymers and / or mixtures comprising two or more of the above-mentioned materials.

[0058] The organic material may include a polyvinylidene fluoride-based copolymer and / or a (meth)acrylic acid copolymer.

[0059] 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, or combinations thereof, but the present disclosure is not limited thereto.

[0060] The organic material and the inorganic material may be present mixed 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.

[0061] Electrolyte ELL

[0062] The electrolyte ELL for a rechargeable lithium battery may include a non-aqueous organic solvent, a lithium salt, a first additive, and a second additive.

[0063] The nonaqueous organic solvent may be used as a medium for transporting ions participating in the electrochemical reaction of the battery.

[0064] 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.

[0065] The carbonate-based solvent may include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), propylene carbonate (PC) and / or butylene carbonate (BC).

[0066] The ester solvent may include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanoic acid lactone, mevalonolactone, valerolactone and / or caprolactone.

[0067] Ether solvents may include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran and / or tetrahydrofuran. Ketone solvents may include cyclohexanone. Alcohol solvents may include ethanol and / or isopropanol. 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 or an ether group); amides (such as dimethylformamide); dioxolanes (such as 1,3-dioxolanes and / or 1,4-dioxolanes); and / or sulfolane.

[0068] The nonaqueous organic solvent may be used alone or in mixture of two or more.

[0069] 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.

[0070] The lithium salt may be a material dissolved in a non-aqueous organic solvent, used as a lithium ion supply source in the battery, and plays a role in ensuring 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, bis(fluorosulfonyl)imide lithium (LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (wherein x and y are each an integer of 1 to 20), at least one of lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFBOP) and lithium bis(oxalato)borate (LiBOB).

[0071] Rechargeable lithium battery

[0072] Rechargeable lithium batteries may be classified into cylindrical batteries, prismatic batteries, pouch type (or similar) batteries, and coin type (or similar) batteries based on their shapes. Figure 2 to Figure 5 A simplified view showing a rechargeable lithium battery according to an embodiment. Figure 2 A cylindrical battery is shown, Figure 3 A prismatic cell is shown, and Figure 4-5 Pouch type battery is shown. Figure 2 to Figure 4 , the rechargeable lithium battery 100 may include an electrode assembly 40 in which a separator 30 is between a positive electrode 10 and a negative electrode 20, and may also 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 impregnated with an electrolyte. Figure 2 As illustrated, the rechargeable lithium battery 100 may include a sealing member 60 that seals the housing 50. In an embodiment, as shown in FIG. Figure 3 As illustrated, 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, 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 ), which serves as an electrical path for guiding the current generated in the electrode assembly 40 to the outside.

[0073] Hereinafter, an electrolyte for a rechargeable lithium battery according to some embodiments of the present disclosure will be described in more detail.

[0074] According to an embodiment, an electrolyte for a rechargeable lithium battery may include: a nonaqueous organic solvent; a lithium salt; a first additive including a borate-based lithium salt having a double bond between carbon atoms; and a second additive including a dithioketone-based compound.

[0075] The non-aqueous organic solvent may be a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC).

[0076] For example, based on the total volume of the non-aqueous organic solvent, the amount of ethylene carbonate (EC) included may be about 10 vol% to about 30 vol%. Based on the total volume of the non-aqueous organic solvent, the amount of ethyl methyl carbonate (EMC) included may be about 30 vol% to about 50 vol%. Based on the total volume of the non-aqueous organic solvent, the amount of dimethyl carbonate (DMC) included may be about 40 vol% to about 70 vol%. In an embodiment, the rechargeable lithium battery can improve high voltage characteristics and / or high temperature characteristics.

[0077] The lithium salt may include, for example, LiPF6.

[0078] 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 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 an embodiment of the present disclosure, if the lithium salt has a concentration of about 0.1 M to about 2.0 M, the electrolyte may properly or appropriately maintain its conductivity and viscosity.

[0079] additive

[0080] The first additive may be represented by the following Chemical Formula 1:

[0081] [Chemical formula 1]

[0082]

[0083] In Chemical Formula 1, R1 and R2 may include the same or different halogen elements. The halogen elements may include fluorine, bromine, chlorine, iodine, and the like.

[0084] For example, the first additive may be represented by the following chemical formula 1-1:

[0085] [Chemical formula 1-1]

[0086]

[0087] Since the first additive has such a structure (the structure has double bonds between carbon atoms), compared with lithium salt additives having ordinary ester bonds, the first additive can have the effect of reducing gas generation by inhibiting or reducing free radical decomposition reactions, and can increase high temperature characteristics and output characteristics.

[0088] In an embodiment, since the first additive has a halogen component such as fluorine, LiF generated during the charge / discharge process can form a strong film on both the positive electrode and the negative electrode. Therefore, the first additive can effectively contribute to the cycle life characteristics of the rechargeable lithium battery.

[0089] The second additive may be represented by the following Chemical Formula 2:

[0090] [Chemical formula 2]

[0091]

[0092] If the second additive is used in combination with a fluorinated lithium salt additive (e.g., the first additive), a synergistic effect may be produced. The combination of the first additive and the second additive may result in: inhibiting or reducing gas generation, increasing high temperature storage characteristics, and improving high temperature and room temperature cycle stability of a rechargeable lithium battery.

[0093] Based on the total weight of the electrolyte, the amount of the first additive included may be about 0.05wt% to about 1wt%. For example, based on the total weight of the electrolyte, the first additive may be present in an amount of about 0.1wt% to about 0.7wt%. Based on the total weight of the electrolyte, the first additive may be present in an amount of about 0.2wt% to about 0.5wt%. If the first additive has the aforementioned concentration in the electrolyte, a protective film having an appropriate or suitable film resistance may be formed on the surface of the positive electrode in the rechargeable lithium battery, thereby improving the cycle characteristics of the rechargeable lithium battery and reducing gas generation during high temperature storage.

[0094] Based on the total weight of the electrolyte, the amount of the second additive included may be about 0.05wt% to about 3wt%. For example, based on the total weight of the electrolyte, the second additive may be present in an amount of about 0.1wt% to about 2wt%. Based on the total weight of the electrolyte, the second additive may be present in an amount of about 0.5wt% to about 1wt%. If the second additive has the aforementioned concentration in the electrolyte, the increase in the internal resistance of the battery can be prevented or reduced. In an embodiment, the second additive can improve the high temperature characteristics of the battery.

[0095] In an embodiment of the present disclosure, the concentration (or weight ratio) of the second additive may be greater than the concentration (or weight ratio) of the first additive. The ratio of the concentration of the second additive to the concentration of the first additive may be in the range of about 1.5 to about 10. For example, the ratio of the concentration of the second additive to the concentration of the first additive may be in the range of about 2 to about 5.

[0096] In an embodiment, a rechargeable lithium battery may be provided, including: a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, and the electrolyte discussed above.

[0097] A rechargeable lithium battery according to an embodiment of the present disclosure may use a nickel-cobalt-aluminum (NCA)-based lithium composite oxide as a positive electrode active material. In embodiments, high voltage and / or high temperature characteristics of the battery may be significantly improved.

[0098] The rechargeable lithium battery according to an embodiment of the present disclosure may be applied to a motor vehicle (eg, an electric car), a mobile phone, and / or any other electronic device (eg, a laptop computer), but the present disclosure is not limited thereto.

[0099] Hereinafter, embodiments and comparative examples of the present disclosure will be described. However, the embodiments described below are merely examples, and the present disclosure is not limited to the embodiments described below.

[0100] Examples and Comparative Examples

[0101] Example 1

[0102] (1) Preparation of electrolyte

[0103] About 1.25 M of LiPF6 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 20:30:50), and about 0.2 wt % of a first additive and about 0.5 wt % of a second additive were added based on the total weight of the electrolyte to prepare an electrolyte.

[0104] A material represented by the following Chemical Formula 1-1 is used as the first additive:

[0105] [Chemical formula 1-1]

[0106]

[0107] For example, the first additive of Chemical Formula 1-1 can be prepared by the following reaction.

[0108] The compound of Chemical Formula 1-1 is synthesized through the reaction route of Formula 1 below.

[0109] [Equation 1]

[0110]

[0111] First, 1 mmol of maleic acid and 0.1 M sulfuric acid were added dropwise to a Schlenk flask in which 100 ml of methanol was present, and the mixture was stirred at a temperature of 0° C. for 30 minutes and then at room temperature for 24 hours.

[0112] Thereafter, the mixture was extracted with MC / H 2 O, and the solvent was removed to obtain Intermediate 1-1.

[0113] 1 mmol of Intermediate 1-1 and 2.5 mmol of lithium hydroxide were added dropwise to a Schlenk flask in which 100 ml of H 2 O was present, and the mixture was stirred at a temperature of 80° C. for 1 hour. The compound obtained by filtering the reaction precipitate was washed with acetone to obtain Intermediate 1-2.

[0114] 1 mmol of Intermediate 1-2 and 2.1 mmol of boron trifluoride ether were added dropwise to a Schlenk flask in which 100 ml of acetonitrile was present, and the mixture was stirred at room temperature overnight (12 to 16 hours).

[0115] Thereafter, the compound obtained by filtering the reaction precipitate was purified by reprecipitation in a small amount of dimethyl carbonate, and dried under vacuum to obtain the compound represented by Chemical Formula 1-1.

[0116] A material represented by the following Chemical Formula 2 is used as the second additive:

[0117] [Chemical formula 2]

[0118]

[0119] (2) Preparation of rechargeable lithium batteries

[0120] LiNiCoAlO2 as a positive electrode active material, polyvinylidene fluoride as a binder, and acetylene black as a conductive material were mixed together at a weight ratio of 96:3:1, and the mixture was distributed in N-methylpyrrolidone to prepare a positive electrode active material slurry.

[0121] The positive electrode active material slurry was coated on an Al foil positive electrode current collector having a thickness of 15 μm, dried at a temperature of 100° C., and then pressed to prepare a positive electrode.

[0122] The silicon negative electrode active material, the styrene-butadiene rubber binder, and the carboxymethyl cellulose were mixed together at a weight ratio of 98:1:1, and dispersed in distilled water to prepare a negative electrode active material slurry.

[0123] The negative electrode active material slurry was coated on a Cu foil negative electrode current collector having a thickness of 10 μm, dried at a temperature of 100° C., and then pressed to prepare a negative electrode.

[0124] The positive electrode, the negative electrode, and a 10 μm thick polyethylene separator were assembled to prepare an electrode assembly, and an electrolyte was introduced to prepare a rechargeable lithium battery.

[0125] Example 2

[0126] An electrolyte and a rechargeable lithium battery were prepared by substantially the same method as Example 1, except that 1.0 wt % of the second additive was used.

[0127] Example 3

[0128] An electrolyte and a rechargeable lithium battery were prepared by substantially the same method as Example 1, except that 0.5 wt % of the first additive and 1.0 wt % of the second additive were used.

[0129] Comparative Example 1

[0130] An electrolyte and a rechargeable lithium battery were prepared by substantially the same method as in Example 1, except that neither the first additive nor the second additive was added when the electrolyte was prepared.

[0131] Comparative Example 2

[0132] An electrolyte and a rechargeable lithium battery were prepared by substantially the same method as in Example 1, except that 0.2 wt % of lithium bis(oxalate)borate (LiBOB) was used instead of the first additive when preparing the electrolyte.

[0133] LiBOB can be represented by the following chemical formula 3:

[0134] [Chemical formula 3]

[0135]

[0136] Comparative Example 3

[0137] An electrolyte and a rechargeable lithium battery were prepared by substantially the same method as in Example 2, except that 0.5 wt % of LiBOB was used instead of the first additive when preparing the electrolyte.

[0138] Comparative Example 4

[0139] An electrolyte and a rechargeable lithium battery were prepared by substantially the same method as in Example 3, except that 1 wt % of propylene sulfite (PS) was used instead of the second additive when preparing the electrolyte.

[0140] PS can be represented by the following chemical formula 4:

[0141] [Chemical formula 4]

[0142]

[0143] Evaluation Example

[0144] The rechargeable lithium battery was evaluated by the following method.

[0145] Evaluation 1: Evaluation of storage at high temperature (60°C)

[0146] After the prepared battery cell is charged to 4.2V at a 1C charge rate and then discharged to SOC50% at a 1C discharge rate, the prepared battery cell is discharged for 10 seconds to measure the initial DC internal resistance (initial DC-IR), and after being charged to 4.2V at a 1C charge rate, it is stored at a high temperature (60°C) for 60 days, and then the process of 1C charging to 4.2V and 1C discharging twice is basically the same as the initial DC internal resistance measurement method to measure the DC internal resistance (DC-IR) after storage at high temperature (60°C), and the DC-IR increase rate is calculated according to "DC-IR increase rate = DC-IR after high temperature storage (60°C, 60 days) / initial DC-IR", and the evaluation results are listed in the following Table 1.

[0147] Table 1

[0148]

[0149]

[0150] Assessment 2: Assessment of gas generation at high temperatures

[0151] The rechargeable lithium batteries according to the examples and comparative examples were subjected to evaluation of gas generation characteristics at high temperatures.The rechargeable lithium batteries according to the examples and comparative examples were stored at 60°C for 28 days.

[0152] In order to determine the gas reduction effect, the initial thickness of the battery cell and the thickness of the battery cell after storage for 28 days were each measured, and the results are listed in Table 2 below. For example, a compression thickness gauge commercially available from MITUTOYO Corporation was used so that the pouch-type battery cell was located between the press plates, and then the thickness was measured while being pressed with a weight of 300 g. In Table 2 below, the initial thickness shows the thickness measured immediately after being taken out of an oven at 60°C to exclude the cooling effect, and the same method was performed to measure the thickness after being stored in a thermostat at 60°C for 28 days.

[0153] Table 2

[0154]

[0155] Portfolio Assessment

[0156] Referring to Table 1, the use of the electrolyte to which the first additive and the second additive are added according to the embodiment of the present disclosure (Examples 1 to 3) can be confirmed to improve the DC-IR according to high temperature storage (60° C.) compared with the use of the electrolyte to which no additive is added (Comparative Example 1) and compared with the use of the electrolyte to which the combination of the borate-based lithium salt and the dithioketone compound having a double bond between carbon atoms is not added (Comparative Examples 2 to 4). Therefore, if the combination of the first additive and the second additive according to the present disclosure is added to the electrolyte for use, it can be confirmed that the cycle characteristics and life of the battery under the high temperature storage (60° C.) environment are improved.

[0157] Referring to Table 2, in the use of the electrolyte to which the first additive and the second additive are added according to the embodiment of the present disclosure (Examples 1 to 3), compared with the use of the electrolyte to which no additive is added (Comparative Example 1) and compared with the use of the electrolyte to which the combination of the borate-based lithium salt and the dithioketone-based compound having a double bond between carbon atoms is not added (Comparative Examples 2 to 4), it can be determined that the improvement in the change in the thickness of the battery cell according to high temperature storage (60° C.) can be determined. Therefore, in the rechargeable lithium battery using the compounds represented by Chemical Formula 1 and Chemical Formula 2 according to the embodiment of the present disclosure, it can be determined that the gas generation at high temperature (60° C.) is effectively suppressed compared with Comparative Examples 1 to 4.

[0158] In the electrolyte according to the embodiment, borate-based lithium salts and dithioketone-based compounds having double bonds between carbon atoms may be used as additives to prevent or reduce the generation of a large amount of gas under high temperature conditions if the rechargeable lithium battery is activated. Moreover, the electrolyte according to the embodiment of the present disclosure may have the effect of improving the high temperature storage and high temperature life characteristics of the rechargeable lithium battery.

[0159] Although the subject matter of the present disclosure has been described in conjunction with example embodiments that are presently considered to be practical, it should be understood that the disclosure is not limited to the disclosed embodiments and is intended to cover various suitable modifications and equivalent arrangements included within the spirit and scope of the claims and their equivalents, and therefore the aforementioned embodiments should be understood as examples and not limiting the disclosure in any way.

Claims

1. An electrolyte for a rechargeable lithium battery, the electrolyte comprising: Non-aqueous organic solvents; Lithium salts; A first additive includes a borate-type lithium salt having double bonds between carbon atoms; and The second additive includes a dithioketone compound.

2. The electrolyte of claim 1, wherein the first additive is represented by Chemical Formula 1, [Chemical formula 1] In Chemical Formula 1, R1 and R2 include the same or different halogen elements.

3. The electrolyte of claim 1, wherein the first additive is represented by Chemical Formula 1-1, [Chemical formula 1-1] 4 . The electrolyte of claim 1 , wherein the first additive is included in an amount of 0.05 wt % to 1 wt % based on the total weight of the electrolyte.

5. The electrolyte of claim 1, wherein the second additive is represented by Chemical Formula 2, [Chemical formula 2] 6 . The electrolyte of claim 1 , wherein the second additive is included in an amount of 0.05 wt % to 3 wt % based on the total weight of the electrolyte.

7. The electrolyte according to claim 1, wherein the non-aqueous organic solvent comprises a carbonate solvent, The carbonate solvent includes one or more selected from the group consisting of ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, propylene carbonate and butylene 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), one or more of lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate and lithium bis(oxalato)borate, wherein x and y are each an integer of 1 to 20.

9. The electrolyte of 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 nickel-cobalt-aluminum-based lithium composite oxide. 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, or a combination thereof.

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