Electrolyte for rechargeable lithium battery and rechargeable lithium battery including same

Abstract

The present invention relates to an electrolyte for a rechargeable lithium battery and a rechargeable lithium battery comprising the same, the electrolyte comprising: a non-aqueous organic solvent; a lithium salt; an ionic liquid including a cation represented by Chemical Formula 1 and an anion represented by Chemical Formula 2; and at least one of compounds represented by Chemical Formulae 3 to 6.

Description

Technical Field

[0001] This application relates to an electrolyte for a rechargeable lithium battery and a rechargeable lithium battery including the same. Background Art

[0002] Portable information devices such as cellular phones, laptop computers, smart phones, etc. or electric vehicles have used rechargeable lithium batteries having high energy density and easy portability as a driving power source.

[0003] In general, a rechargeable lithium battery is manufactured by using a material capable of reversibly intercalating and deintercalating lithium ions as a positive electrode active material and a negative electrode active material, and filling an electrolyte between the positive electrode and the negative electrode.

[0004] Lithium transition metal oxides are used as positive electrode active materials of rechargeable lithium batteries, various types of carbon-based materials are used as negative electrode active materials, and the electrolyte uses a lithium salt dissolved in a non-aqueous organic solvent.

[0005] In particular, since a rechargeable lithium battery exhibits battery characteristics through complex reactions (such as a positive electrode and an electrolyte, a negative electrode and an electrolyte, etc.), using an appropriate electrolyte is one of important parameters for improving the performance of the rechargeable lithium battery.

[0006] The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. Summary of the invention

[0007] Technical issues

[0008] One embodiment provides an electrolyte for a rechargeable lithium battery that exhibits excellent thermal safety while maintaining the performance of the battery.

[0009] Another embodiment provides a rechargeable lithium battery including an electrolyte.

[0010] Technical Solution

[0011] The electrolyte for a rechargeable lithium battery may include: a nonaqueous organic solvent; a lithium salt; an ionic liquid including a cation represented by Chemical Formula 1 and an anion represented by Chemical Formula 2; and an additive including at least one of the compounds represented by Chemical Formulas 3 to 6.

[0012] [Chemical formula 1]

[0013]

[0014] (wherein, R1 and R2 are the same or different and are substituted or unsubstituted C1-C6 alkyl)

[0015] [Chemical formula 2]

[0016] PF6 -

[0017] [Chemical formula 3]

[0018]

[0019] (Wherein, X1 is a substituted or unsubstituted C1-C3 alkylene or (-C2H4-O-C2H4-) n1 , and n1 is an integer ranging from 1 to 10)

[0020] [Chemical formula 4]

[0021]

[0022] (Wherein, X2 is a substituted or unsubstituted C1-C2 alkylene or (-C2H4-O-C2H4-) n2 , and n2 is an integer ranging from 1 to 10, and

[0023] R7 is -CN, -N=C=O, -N=C=S, -OSO2CH3, -OSO2C2H5, -OSO2F or -OSO2CF3. )

[0024] [Chemical formula 5]

[0025]

[0026] (in,

[0027] X3 is a fluoro group, a chloro group, a bromo group or an iodo group,

[0028] R8~R 13 are the same or different and are hydrogen, cyano, substituted or unsubstituted C1-C20 alkyl, substituted or unsubstituted C1-C20 alkoxy, substituted or unsubstituted C2-C20 alkenyl, substituted or unsubstituted C2-C20 alkynyl, substituted or unsubstituted C3-C20 cycloalkyl, substituted or unsubstituted C6-C20 aryl or substituted or unsubstituted C2-C20 heteroaryl, and

[0029] n3 is an integer of 0 or 1. )

[0030] [Chemical formula 6]

[0031]

[0032] (Among them, R 14 ~R 16are the same or different and are substituted or unsubstituted C1-C10 alkylene, substituted or unsubstituted C3-C30 cycloalkylene, substituted or unsubstituted C6-C30 arylene or substituted or unsubstituted C2-C30 heteroarylene).

[0033] The amount of the ionic liquid may be 0.05 wt % to 30 wt % based on 100 wt % in total of the electrolyte.

[0034] The amount of the additive may be 0.05 wt% to 10 wt% or 0.05 wt% to 8 wt% based on 100 wt% in total of the electrolyte.

[0035] According to one embodiment, in Chemical Formula 4, R7 may be -CN, and in Chemical Formula 5, X3 may be F.

[0036] In addition, the compound of Chemical Formula 5 may be represented by Chemical Formula 5a or Chemical Formula 5b.

[0037] [Chemical Formula 5a]

[0038]

[0039] [Chemical Formula 5b]

[0040]

[0041] (in,

[0042] X3 is a fluoro group, a chloro group, a bromo group or an iodo group, and

[0043] R8~R 13 Each is independently hydrogen, cyano, substituted or unsubstituted C1-C20 alkyl, substituted or unsubstituted C1-C20 alkoxy, substituted or unsubstituted C2-C20 alkenyl, substituted or unsubstituted C2-C20 alkynyl, substituted or unsubstituted C3-C20 cycloalkyl, substituted or unsubstituted C6-C20 aryl or substituted or unsubstituted C2-C20 heteroaryl.)

[0044] A rechargeable lithium battery according to one embodiment may include a negative electrode, a positive electrode, and an electrolyte.

[0045] Beneficial effects

[0046] An electrolyte for a rechargeable lithium battery according to one embodiment may realize a rechargeable lithium battery that exhibits improved thermal safety while maintaining electrical characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 is a schematic diagram of a rechargeable lithium battery according to an embodiment. DETAILED DESCRIPTION

[0048] Hereinafter, the present invention will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. The present invention may be embodied in many different forms and should not be construed as limited to the exemplary embodiments set forth herein.

[0049] In order to clearly illustrate the present invention, parts irrelevant to the description are omitted, and the same or similar components are denoted by the same reference numerals throughout the specification.

[0050] In addition, the sizes and thicknesses of components in the drawings are arbitrarily represented for the convenience of description, and thus the present invention is not limited by the drawings.

[0051] In addition, unless explicitly described to the contrary, the word “comprise” and variations such as “comprises” or “comprising” will be understood to imply the inclusion of stated elements but not the exclusion of any other elements.

[0052] As used herein, when no limitation is otherwise provided, the term "substituted" refers to a case in which a hydrogen of a compound is replaced by a halogen atom (F, Br, Cl or I), a hydroxyl group, an alkoxy group, a nitro group, a cyano group, an amino group, an azido group, an amidino group, a hydrazine group, a hydrazone group, a carbonyl group, a carbamoyl group, a thiol group, an ester group, a carboxyl group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphate group or a salt thereof, a C1-C20 alkyl group, a C2-C20 alkenyl group, a C2-C20 alkynyl group, a C6-C30 aryl group, a C7-C30 aralkyl group, a C1-C4 alkoxy group, a C1-C20 heteroalkyl group, a C3-C20 heteroaralkyl group, a C3-C30 cycloalkyl group, a C3-C15 cycloalkenyl group, a C6-C15 cycloalkynyl group, a C2-C20 heterocycloalkyl group and combinations thereof.

[0053] In the specification, when no definition is otherwise provided, the term "hetero" means a case where 1 to 3 hetero atoms selected from N, O, S and P are included.

[0054] An electrolyte for a rechargeable lithium battery according to one embodiment may include: a non-aqueous organic solvent; a lithium salt; an ionic liquid including a cation and an anion; and an additive.

[0055] The ionic liquid may include a cation represented by Chemical Formula 1 and an anion represented by Chemical Formula 2.

[0056] [Chemical formula 1]

[0057]

[0058] In Chemical Formula 1, R1 and R2 are the same or different and are substituted or unsubstituted C1-C6 alkyl groups.

[0059] [Chemical formula 2]

[0060] PF6 -

[0061] The additive according to one embodiment may include at least one of the compounds represented by Chemical Formulae 3 to 6.

[0062] [Chemical formula 3]

[0063]

[0064] In Chemical Formula 3, X1 is a substituted or unsubstituted C1-C3 alkylene group, or (-C2H4-O-C2H4-) n1 , and n1 is an integer ranging from 1 to 10. X1 may be an unsubstituted C1-C3 alkylene group.

[0065] [Chemical formula 4]

[0066]

[0067] In Chemical Formula 4, X2 is a substituted or unsubstituted C1-C2 alkylene group, or (-C2H4-O-C2H4-) n2 , and n2 is an integer ranging from 1 to 10, and

[0068] R7 is -CN, -N=C=O, -N=C=S, -OSO2CH3, -OSO2C2H5, -OSO2F or -OSO2CF3.

[0069] In one embodiment, X2 may be a substituted or unsubstituted C1-C2 alkylene group, and R7 may be -CN.

[0070] [Chemical formula 5]

[0071]

[0072] In Chemical Formula 5,

[0073] X3 is a fluoro group, a chloro group, a bromo group or an iodo group,

[0074] R8~R 13 are the same or different and are hydrogen, cyano, substituted or unsubstituted C1-C20 alkyl, substituted or unsubstituted C1-C20 alkoxy, substituted or unsubstituted C2-C20 alkenyl, substituted or unsubstituted C2-C20 alkynyl, substituted or unsubstituted C3-C20 cycloalkyl, substituted or unsubstituted C6-C20 aryl or substituted or unsubstituted C2-C20 heteroaryl, and n3 is an integer of 0 or 1.

[0075] X3 can be F, and R8~R 13 It may be hydrogen.

[0076] The compound of Chemical Formula 5 may be represented by Chemical Formula 5a or Chemical Formula 5b.

[0077] [Chemical Formula 5a]

[0078]

[0079] [Chemical Formula 5b]

[0080]

[0081] In Chemical Formula 5a or Chemical Formula 5b,

[0082] X3 is a fluoro group, a chloro group, a bromo group or an iodo group, and

[0083] R8~R 13 Each is independently hydrogen, cyano, substituted or unsubstituted C1-C20 alkyl, substituted or unsubstituted C1-C20 alkoxy, substituted or unsubstituted C2-C20 alkenyl, substituted or unsubstituted C2-C20 alkynyl, substituted or unsubstituted C3-C20 cycloalkyl, substituted or unsubstituted C6-C20 aryl or substituted or unsubstituted C2-C20 heteroaryl.

[0084] [Chemical formula 6]

[0085]

[0086] In Chemical Formula 6,

[0087] R 14 ~R 16 are the same or different and are substituted or unsubstituted C1-C10 alkylene, substituted or unsubstituted C3-C30 cycloalkylene, substituted or unsubstituted C6-C30 arylene, or substituted or unsubstituted C2-C30 heteroarylene.

[0088] R 14 ~R 16 The same or different, and may be unsubstituted C1-C10 alkylene.

[0089] As such, the electrolyte for a rechargeable lithium battery includes at least one additive of the compounds represented by Chemical Formula 3 to Chemical Formula 6, and an ionic liquid including a cation of Chemical Formula 1 and an anion of Chemical Formula 2.

[0090] In one embodiment, inclusion of the ionic liquid may allow for improvement of overcharge safety and thermal safety, and inclusion of the additive may allow for appropriate maintenance of charge and discharge capacity.

[0091] The effect of using an ionic liquid together with an additive can be achieved by using an ionic liquid including a cation of Chemical Formula 1 and an anion of Chemical Formula 2 together with at least one additive among compounds represented by Chemical Formulas 3 to 6. If the cation of Chemical Formula 1 and the anion of Chemical Formula 2 are not included, the thermal safety effect cannot be obtained even if the ionic liquid is used.

[0092] In one embodiment, the amount of the ionic liquid may be 0.05 wt% to 30 wt% based on a total of 100 wt% of the electrolyte. According to another embodiment, the amount of the ionic liquid may be 1 wt% to 30 wt%, 2 wt% to 30 wt%, 2 wt% to 20 wt%, or 2 wt% to 10 wt%. When the amount of the ionic liquid is within this range, the effect of improving thermal safety can be more fully obtained.

[0093] The amount of the additive may be 0.05 wt % to 10 wt %, 0.05 wt % to 8 wt %, or 0.05 wt % to 5 wt % based on 100 wt % of the total electrolyte. When the amount of the additive satisfies the range, thermal safety may be more improved while maintaining battery characteristics.

[0094] In one embodiment, the ionic liquid and the additive may be present in a weight ratio of 2:1 to 20:1, and within the above range, thermal safety may be more improved.

[0095] The cation represented by Chemical Formula 1 may be represented by Chemical Formula 1-1, and the anion represented by Chemical Formula 2 may be represented by Chemical Formula 2-1.

[0096] [Chemical formula 1-1]

[0097]

[0098] The ionic liquid according to one embodiment may be 1-methyl-1-propylpiperidinium hexafluorophosphate).

[0099] The compound represented by Chemical Formula 3 may be ethane-1,2-diylbis(difluorophosphite).

[0100] [Chemical formula 3-1]

[0101]

[0102] The compound represented by Chemical Formula 4 may be 2-cyanoethyl difluorophosphite represented by Chemical Formula 4-1.

[0103] [Chemical formula 4-1]

[0104]

[0105] The compound represented by Chemical Formula 5 may be 2-fluoro-1,3,2-dioxaphospholane represented by Chemical Formula 5-1, or 2-fluoro-4-methyl-1,3,2-dioxaphospholane represented by Chemical Formula 5-2.

[0106] [Chemical formula 5-1]

[0107]

[0108] [Chemical formula 5-2]

[0109]

[0110] The compound represented by Chemical Formula 6 may be a cyanoalkyl phosphate represented by Chemical Formula 6-1.

[0111] [Chemical formula 6-1]

[0112]

[0113] The nonaqueous organic solvent serves as a medium for transporting ions participating in the electrochemical reaction of the battery.

[0114] The non-aqueous organic solvent may include carbonates, esters, ethers, ketones, alcohols or aprotic solvents. Carbonate solvents may include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), ethyl methyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. Esters may include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, decalactone, valerolactone, mevalonolactone, caprolactone, etc. Ether solvents may include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc. Ketone solvents may include cyclohexanone, etc. In addition, alcohol solvents may include ethanol, isopropanol, etc., and aprotic solvents may include: nitriles, such as R-CN (wherein R is a C2~C20 straight chain, branched or cyclic hydrocarbon group, and may include a double bond, an aromatic ring or an ether bond); amides (such as dimethylformamide); dioxolanes (such as 1,3-dioxolane); cyclopentane sulfone, etc.

[0115] The organic solvent may be used alone or in a mixture, and when the organic solvent is used in a mixture, the mixing ratio may be controlled according to desired battery performance, and this is well known to those skilled in the relevant art.

[0116] When the non-aqueous organic solvent is mixed and used, a mixed solvent of a cyclic carbonate and a chain carbonate, a mixed solvent of a cyclic carbonate and a propionate solvent, or a mixed solvent of a cyclic carbonate, a chain carbonate and a propionate solvent can be used. The propionate solvent can be methyl propionate, ethyl propionate, propyl propionate or a combination thereof.

[0117] Herein, when a mixture of a cyclic carbonate and a linear carbonate is used, or a mixture of a cyclic carbonate and a propionate solvent is used, it is desirable to use it in a volume ratio of about 1:1 to about 1:9 in consideration of performance. In addition, a cyclic carbonate, a linear carbonate, and a propionate solvent may be mixed and used in a volume ratio of 1:1:1 to 3:3:4. The mixing ratio of the solvent may also be appropriately controlled according to the desired performance.

[0118] The organic solvent may further include an aromatic hydrocarbon solvent and a carbonate solvent. Herein, the carbonate solvent and the aromatic hydrocarbon solvent may be mixed together in a volume ratio of 1:1 to 30:1.

[0119] The aromatic hydrocarbon organic solvent may be an aromatic hydrocarbon compound represented by Chemical Formula 7.

[0120] [Chemical formula 7]

[0121]

[0122] (In Chemical Formula 7, R 20 ~R 25 are the same or different and are selected from hydrogen, halogen, C1-C10 alkyl, haloalkyl and combinations thereof.

[0123] Specific examples of aromatic hydrocarbon organic solvents may be selected from benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene, 1,2,4-triiodobenzene, toluene, fluoroform, Benzene, 2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,3,4-trifluorotoluene, 2,3,5-trifluorotoluene, chlorotoluene, 2,3-dichlorotoluene, 2,4-dichlorotoluene, 2,5-dichlorotoluene, 2,3,4-trichlorotoluene, 2,3,5-trichlorotoluene, iodotoluene, 2,3-diiodotoluene, 2,4-diiodotoluene, 2,5-diiodotoluene, 2,3,4-triiodotoluene, 2,3,5-triiodotoluene, xylene, and combinations thereof.

[0124] The electrolyte may further include vinyl ethyl carbonate, vinylene carbonate, or an ethylene carbonate-based compound.

[0125] [Chemical formula 8]

[0126]

[0127] (In Chemical Formula 8, R 26 and R 27 The same or different and may be independently hydrogen, halogen, cyano (CN), nitro (NO2) or C1-C5 fluoroalkyl, provided that at least one of R7 and R8 is halogen, cyano (CN), nitro (NO2) or C1-C5 fluoroalkyl, and R7 and R8 are not hydrogen at the same time.)

[0128] Examples of the ethylene carbonate-based compound may include difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, fluoroethylene carbonate, etc. The amount of the additive for improving the cycle life characteristics may be used within an appropriate range.

[0129] The lithium salt dissolved in the organic solvent supplies the battery with lithium ions, makes the rechargeable lithium battery basically operate, and improves the transport of lithium ions between the positive electrode and the negative electrode. Examples of lithium salts include those selected from LiPF6, LiBF4, LiSbF6, LiAsF6, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiN(SO3C2F5)2, LiC4F9SO3, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (wherein x and y are natural numbers, for example, integers of 0 to 20), at least one or two carrier salts of lithium difluoro(bisoxalate)phosphate, LiCl, LiI, LiB(C2O4)2 (lithium bis(oxalate)borate: LiBOB) and lithium difluoro(oxalate)borate (LiDFOB). The concentration of the lithium salt may be in the range of about 0.1M to about 2.0M. When the lithium salt is included in the above concentration range, the electrolyte may have excellent performance and lithium ion mobility due to optimal electrolyte conductivity and viscosity.

[0130] Another embodiment provides a rechargeable lithium battery including a nonaqueous electrolyte.

[0131] A rechargeable lithium battery includes a non-aqueous electrolyte, a negative electrode, and a positive electrode.

[0132] In one embodiment, the negative electrode includes: a negative active material layer including a negative active material and a current collector supporting the negative active material layer.

[0133] The negative electrode active material includes a material that reversibly intercalates / deintercalates lithium ions, lithium metal, a lithium metal alloy, a material capable of doping / de-doping lithium, or a transition metal oxide.

[0134] The material that reversibly intercalates / deintercalates lithium ions can be a carbon material, and the carbon material can be any commonly used carbon-based negative electrode active material used in a rechargeable lithium battery. Examples thereof can be crystalline carbon, amorphous carbon, or a combination thereof. The crystalline carbon can be shapeless (unspecified shape), or can be flaky, lamellar, spherical, or fibrous natural graphite or artificial graphite, and the amorphous carbon can be soft carbon, hard carbon, mesophase pitch carbonization product, calcined coke, etc.

[0135] The lithium metal alloy can be an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn.

[0136] The material capable of doping / de-doping lithium can be Si, SiO x (0 < x < 2), an Si-Q alloy (where Q is an element selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof, and is not Si), Sn, SnO2, an Sn-R alloy (where R is an element selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof, and is not Sn), etc., and at least one of these materials can be mixed with SiO2. The element Q and the element R can be Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

[0137] The transition element oxide can be a lithium titanium oxide.

[0138] The negative electrode active material according to one embodiment can include: an Si-C composite including an Si-based active material and a carbon-based active material.

[0139] The Si-based active material is Si, SiO x (0 < x < 2) or an Si-Q alloy (where Q is an element selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof, and is not Si).

[0140] The average particle size of the Si-based active material may be 50 nm to 200 nm.

[0141] When the particle diameter of the Si particles is within this range, volume expansion caused during charge and discharge can be suppressed, and damage to the conductive path due to particle crushing can be prevented.

[0142] The Si-based active material may be included in an amount of 1 wt % to 60 wt %, and for example, may be 3 wt % to 60 wt %, based on the total weight of the Si—C composite.

[0143] The negative active material according to another embodiment may further include crystalline carbon in addition to the Si—C composite.

[0144] If the negative electrode active material includes both the Si-C composite and the crystalline carbon, the negative electrode active material may include the Si-C composite and the crystalline carbon in a mixture, and herein, the weight ratio of the Si-C composite and the crystalline carbon included may be 1:99 to 50:50. More specifically, the weight ratio of the Si-C composite and the crystalline carbon included may be 5:95 to 20:80.

[0145] The crystalline carbon may include, for example, graphite, and more specifically, may include natural graphite, artificial graphite, or a mixture thereof.

[0146] The crystalline carbon may have an average particle size of 5 μm to 30 μm.

[0147] In the specification, the average particle diameter refers to the particle size (D50) at which the cumulative volume is 50 volume % in a cumulative size distribution curve.

[0148] The Si-C composite may further include a shell surrounding a surface of the Si-C composite, and the shell may include amorphous carbon. The shell may have a thickness of 5 nm to 100 nm.

[0149] The amorphous carbon may be soft carbon, hard carbon, mesophase pitch carbide, sintered carbon, or a mixture thereof.

[0150] The amorphous carbon may be included in an amount of 1 to 50 parts by weight, for example, 5 to 50 parts by weight or 10 to 50 parts by weight, based on 100 parts by weight of the carbon-based active material.

[0151] The negative active material layer may include a binder, and optionally a conductive material.

[0152] In the negative electrode active material layer, the amount of the negative electrode active material may be about 95 wt% to about 99 wt% based on the total weight of the negative electrode active material layer. In the negative electrode active material layer, the amount of the binder may be 1 wt% to 5 wt% based on the total weight of the negative electrode active material layer. In addition, in the case of further including a conductive material, the amount of the negative electrode active material included may be 90 wt% to 98 wt%, the amount of the binder included may be 1 wt% to 5 wt%, and the amount of the conductive material included may be 1 wt% to 5 wt%.

[0153] The binder improves the bonding properties between the negative electrode active material particles and the bonding properties between the negative electrode active material particles and the current collector. The binder may be a non-aqueous binder, an aqueous binder or a combination thereof.

[0154] The non-aqueous binder may be ethylene propylene copolymer, polyacrylonitrile, polystyrene, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0155] The aqueous binder may include styrene-butadiene rubber, acrylated styrene-butadiene rubber, acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyepichlorohydrin, polyphosphazene, ethylene propylene diene copolymer, polyvinyl pyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol or a combination thereof.

[0156] When an aqueous binder is used as a negative electrode binder, a cellulose compound may be further used as a thickener to provide viscosity. The cellulose compound includes one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose or an alkali metal salt thereof. The alkali metal may be Na, K or Li. Based on 100 parts by weight of the negative electrode active material, the amount of the thickener included may be about 0.1 parts by weight to about 3 parts by weight.

[0157] The conductive material is included to provide the electrode with conductivity, and any conductive material can be used as the conductive material unless it causes a chemical change. Examples of the conductive material may be carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.; metal-based materials including metal powder or metal fiber of copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0158] The current collector may include one selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof, but is not limited thereto.

[0159] The positive electrode includes a positive electrode active material layer including a positive electrode active material and a current collector supporting the positive electrode active material layer.

[0160] The positive electrode active material may include a lithiated intercalation compound that reversibly intercalates and deintercalates lithium ions, and specifically, one or more composite oxides of a metal selected from cobalt, manganese, nickel, and a combination thereof and lithium may be used. More specifically, a compound represented by one of the following chemical formulas may be used. Li a A 1-b X b D2(0.90≤a≤1.8, 0≤b≤0.5); Li a A 1- b X b O 2-c D c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); Li a E 1-b X b O 2-c D c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); Li a E 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 D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, 0<α≤2); Li a Ni 1-b-c Co b X c O 2-α T α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, 0<α<2); Li a Ni 1-b-c Co b X c O 2-α T2(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 D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, 0<α≤2); Lia Nor 1-b- c Mn b X c O 2-α T α (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.5,0<α<2);Li a Nor 1-b-c Mn b X c O 2-α T2(0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.5,0<α<2);Li a Nor b E c G d O2(0.90≤a≤1.8,0≤b≤0.9,0≤c≤0.5,0.001≤d≤0.1);Li a Nor b Co c Mn d G e O2(0.90≤a≤1.8,0≤b≤0.9,0≤c≤0.5,0≤d≤0.5,0.001≤e≤0.1);Li a NiG b O2(0.90≤a≤1.8,0.001≤b≤0.1)Li a CoG b O2(0.90≤a≤1.8,0.001≤b≤0.1);Li a Mn 1-b G b O2(0.90≤a≤1.8,0.001≤b≤0.1);Li a Mn2G b O4(0.90≤a≤1.8,0.001≤b≤0.1);Li a Mn 1-g G g PO4(0.90≤a≤1.8,0≤g≤0.5);QO2;QS2;LiQS2;V2O5;LiV2O5;LiZO2;LiVO4;Li (3-f) J2(PO4)3(0≤f≤2);Li (3-f) Fe2(PO4)3(0≤f≤2);Li a FePO4(0.90≤a≤1.8)

[0161] In the above chemical formula, A is selected from Ni, Co, Mn and combinations thereof; X is selected from Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements and combinations thereof; D is selected from O, F, S, P and combinations thereof; E is selected from Co, Mn and combinations thereof; T is selected from F, S, P and combinations thereof; G is selected from Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V and combinations thereof; Q is selected from Ti, Mo, Mn and combinations thereof; Z is selected from Cr, V, Fe, Sc, Y and combinations thereof; and J is selected from V, Cr, Mn, Co, Ni, Cu and combinations thereof.

[0162] Furthermore, the compound may have a coating on the surface, or may be mixed with another compound having a coating. The coating may include at least one coating element compound selected from the group consisting of an oxide of a coating element, a hydroxide of a coating element, an oxyhydroxide of a coating element, an oxycarbonate of a coating element, and a basic carbonate of a coating element. The compound for the coating may be amorphous or crystalline. The coating elements included in the coating may include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof. By using these elements in the compound, the coating may be provided in a method that has no adverse effect on the characteristics of the positive active material, and for example, the method may include any coating method, such as spraying, dipping, etc., but since it is well known in the relevant art, it is not explained in more detail.

[0163] In the positive electrode, the amount of the positive active material may be about 90 wt % to about 98 wt % based on the total weight of the positive active material layer.

[0164] In one embodiment, the positive active material layer may further include a binder and a conductive material. Herein, the amount of the binder and the conductive material may be 1 wt % to 5 wt % based on the total amount of the positive active material.

[0165] The binder improves the bonding properties between the positive electrode active material particles and the bonding properties between the positive electrode active material particles and the current collector, and examples of the binder may be 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, acrylated styrene butadiene rubber, epoxy resin, nylon, etc., but are not limited thereto.

[0166] A conductive material is included to provide electrode conductivity, and any conductive material can be used as the conductive material unless it causes a chemical change. Examples of the conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.; metal-based materials including metal powders or metal fibers of copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0167] The current collector may use aluminum foil, nickel foil or a combination thereof, but is not limited thereto.

[0168] The positive electrode active material layer and the negative electrode active material layer can be formed by mixing an active material, a binder and an optional conductive material in a solvent to prepare an active material composition, and coating the active material composition on a current collector. This method for preparing an active material layer is well known and is therefore not described in detail in this specification. The solvent includes N-methylpyrrolidone and the like, but is not limited thereto. In addition, when the binder is a water-soluble binder, the solvent may be water.

[0169] In addition, depending on the type of rechargeable lithium battery, a separator may be provided between the positive electrode and the negative electrode. The separator may use polyethylene, polypropylene, polyvinylidene fluoride or a multilayer having two or more layers thereof, and may be a mixed multilayer (such as a polyethylene / polypropylene double-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, a polypropylene / polyethylene / polypropylene three-layer separator, etc.).

[0170] The separator may also include a porous substrate and a ceramic-containing coating on one side of the porous substrate. The ceramic may include SiO2, Al2O3, Al(OH)3, AlO(OH), TiO2, BaTiO2, ZnO2, Mg(OH)2, MgO, Ti(OH)4, ZrO2, aluminum nitride, silicon carbide, boron nitride, or a combination thereof.

[0171] Figure 1 2 is an exploded perspective view of a rechargeable lithium battery according to an embodiment of the present invention. The rechargeable lithium battery according to the embodiment is illustrated as a pouch type battery, but is not limited thereto and may include batteries of various shapes such as a cylindrical battery and a prismatic battery.

[0172] refer to Figure 1 According to an embodiment, a rechargeable lithium battery 100 includes: a battery assembly including a positive electrode 114, a negative electrode 112 facing the positive electrode 114, a separator 113 disposed between the positive electrode 114 and the negative electrode 112, and an electrolyte (not shown) in which the positive electrode 114, the negative electrode 112 and the separator 113 are immersed; a battery case 120 that accommodates the battery assembly; and a sealing member 140 that seals the battery case 120.

[0173] Detailed description of the invention

[0174] Hereinafter, examples of the present invention and comparative examples are described. However, these examples are not to be construed as limiting the scope of the present invention in any sense.

[0175] (Comparative Example 1)

[0176] (1) Preparation of electrolyte

[0177] 1.5 M of LiPF 6 was dissolved in a nonaqueous organic solvent in which ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate were mixed at 20:10:70 volume % to prepare an electrolyte for a rechargeable lithium battery cell.

[0178] (2) Preparation of positive and negative electrodes

[0179] 98wt% LiNi 0.8 Co 0.1 Mn 0.1 O2 positive active material, 1wt% polyvinylidene fluoride binder and 1wt% Ketjen black conductive material were mixed in N-methylpyrrolidone solvent to prepare positive active material slurry. The positive active material slurry was coated on aluminum foil, dried, and then pressed to prepare a positive electrode.

[0180] 97 wt% of artificial graphite negative active material, 1 wt% of Ketjen black conductive material, 1 wt% of styrene-butadiene rubber binder and 1 wt% of carboxymethyl cellulose thickener were mixed in a distilled water solvent to prepare a negative active material slurry. The negative active material slurry was coated on a copper foil and dried, followed by pressing to prepare a negative electrode.

[0181] Using the electrolyte, the positive electrode and the negative electrode, a 18650 cylindrical rechargeable lithium battery cell was manufactured according to conventional procedures.

[0182] (Comparative Example 2)

[0183] 1.5 M of LiPF 6 was dissolved in a nonaqueous organic solvent in which ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate were mixed at 20:10:70 volume % to prepare an electrolyte precursor.

[0184] An ionic liquid including a cation of Chemical Formula 1-1 and an anion of Chemical Formula 2 is added to an electrolyte precursor to prepare an electrolyte for a rechargeable lithium battery cell. Herein, the amount of the ionic liquid is set to 10 wt % based on a total of 100 wt % of the electrolyte.

[0185] [Chemical formula 1-1]

[0186]

[0187] [Chemical formula 2]

[0188] PF6 -

[0189] Using the electrolyte, the positive electrode of Comparative Example 1, and the negative electrode of Comparative Example 1, a 18650 cylindrical rechargeable lithium battery cell was manufactured according to conventional procedures.

[0190] (Comparative Example 3)

[0191] The cation of formula 1-1 and BF4 - The ionic liquid of anion and the additive of Chemical Formula 3-1 were added to the electrolyte precursor of Comparative Example 2 to prepare an electrolyte for a rechargeable lithium battery cell. Herein, the amount of the ionic liquid was set to 10 wt % based on 100 wt % of the total electrolyte, and the amount of the additive was set to 1 wt % based on 100 wt % of the total electrolyte.

[0192] [Chemical formula 1-1]

[0193]

[0194] [Chemical formula 3-1]

[0195]

[0196] (Comparative Example 4)

[0197] An ionic liquid including a triethylsulfonium cation and an anion of Chemical Formula 2-1 and an additive of Chemical Formula 3-1 were added to the electrolyte precursor of Comparative Example 2 to prepare an electrolyte for a rechargeable lithium battery cell. Herein, the amount of the ionic liquid was set to 10 wt % based on a total of 100 wt % of the electrolyte, and the amount of the additive was set to 1 wt % based on a total of 100 wt % of the electrolyte.

[0198] [Chemical formula 2]

[0199] PF6 -

[0200] [Chemical formula 3-1]

[0201]

[0202] (Comparative Example 5)

[0203] The additive of Chemical Formula 3-1 was added to the electrolyte precursor of Comparative Example 2 to prepare an electrolyte for a rechargeable lithium battery cell. Herein, the amount of the additive was set to 0.5 wt % based on 100 wt % of the total electrolyte.

[0204] [Chemical formula 3-1]

[0205]

[0206] Using the electrolyte, the positive electrode of Comparative Example 1, and the negative electrode of Comparative Example 1, a 18650 cylindrical rechargeable lithium battery cell was manufactured according to conventional procedures.

[0207] (Comparative Example 6)

[0208] The additive of Chemical Formula 4-1 was added to the electrolyte precursor of Comparative Example 2 to prepare an electrolyte for a rechargeable lithium battery cell. Herein, the amount of the additive was set to 0.5 wt % based on 100 wt % of the total electrolyte.

[0209] [Chemical formula 4-1]

[0210]

[0211] Using the electrolyte, the positive electrode of Comparative Example 1, and the negative electrode of Comparative Example 1, a 18650 cylindrical rechargeable lithium battery cell was manufactured according to conventional procedures.

[0212] (Comparative Example 7)

[0213] The additive of Chemical Formula 5-1 was added to the electrolyte precursor of Comparative Example 2 to prepare an electrolyte for a rechargeable lithium battery cell. Herein, the amount of the additive was set to 0.5 wt % based on 100 wt % of the total electrolyte.

[0214] [Chemical formula 5-1]

[0215]

[0216] Using the electrolyte, the positive electrode of Comparative Example 1, and the negative electrode of Comparative Example 1, a 18650 cylindrical rechargeable lithium battery cell was manufactured according to conventional procedures.

[0217] (Comparative Example 8)

[0218] The additive of Chemical Formula 5-2 was added to the electrolyte precursor of Comparative Example 2 to prepare an electrolyte for a rechargeable lithium battery cell. Herein, the amount of the additive was set to 0.75 wt % based on 100 wt % of the total electrolyte.

[0219] [Chemical formula 5-2]

[0220]

[0221] Using the electrolyte, the positive electrode of Comparative Example 1, and the negative electrode of Comparative Example 1, a 18650 cylindrical rechargeable lithium battery cell was manufactured according to conventional procedures.

[0222] (Comparative Example 9)

[0223] The additive of Chemical Formula 6-1 was added to the electrolyte precursor of Comparative Example 2 to prepare an electrolyte for a rechargeable lithium battery cell. Herein, the amount of the additive was set to 0.5 wt % based on 100 wt % of the total electrolyte.

[0224] [Chemical formula 6-1]

[0225]

[0226] Using the electrolyte, the positive electrode of Comparative Example 1, and the negative electrode of Comparative Example 1, a 18650 cylindrical rechargeable lithium battery cell was manufactured according to conventional procedures.

[0227] (Example 1)

[0228] The ionic liquid used in Comparative Example 2 and the additive of Chemical Formula 3-1 were added to the electrolyte precursor of Comparative Example 2 to prepare an electrolyte for a rechargeable lithium battery cell. Herein, the amount of the ionic liquid was set to 2 wt % based on a total of 100 wt % of the electrolyte, and the amount of the additive was set to 0.5 wt % based on a total of 100 wt % of the electrolyte.

[0229] [Chemical formula 3-1]

[0230]

[0231] Using the electrolyte, the positive electrode of Comparative Example 1, and the negative electrode of Comparative Example 1, a 18650 cylindrical rechargeable lithium battery cell was manufactured according to conventional procedures.

[0232] (Example 2)

[0233] The electrolyte was prepared by the same procedure as in Example 1, except that the amount of the ionic liquid was set to 10 wt % based on 100 wt % of the total electrolyte, and the amount of the additive was set to 0.5 wt % based on 100 wt % of the total electrolyte.

[0234] Using the electrolyte, the positive electrode of Comparative Example 1, and the negative electrode of Comparative Example 1, a 18650 cylindrical rechargeable lithium battery cell was manufactured according to conventional procedures.

[0235] (Example 3)

[0236] The electrolyte was prepared by the same procedure as in Example 1, except that the amount of the ionic liquid was set to 2 wt % based on 100 wt % of the total electrolyte, and the amount of the additive was set to 1 wt % based on 100 wt % of the total electrolyte.

[0237] Using the electrolyte, the positive electrode of Comparative Example 1, and the negative electrode of Comparative Example 1, a 18650 cylindrical rechargeable lithium battery cell was manufactured according to conventional procedures.

[0238] (Example 4)

[0239] The electrolyte was prepared by the same procedure as in Example 1, except that the amount of the ionic liquid was set to 10 wt % based on 100 wt % of the total electrolyte, and the amount of the additive was set to 1 wt % based on 100 wt % of the total electrolyte.

[0240] Using the electrolyte, the positive electrode of Comparative Example 1, and the negative electrode of Comparative Example 1, a 18650 cylindrical rechargeable lithium battery cell was manufactured according to conventional procedures.

[0241] (Example 5)

[0242] The ionic liquid used in Example 1 and the additive of Chemical Formula 4-1 were added to the electrolyte precursor of Comparative Example 2 to prepare an electrolyte for a rechargeable lithium battery cell. Herein, the amount of the ionic liquid was set to 2 wt % based on a total of 100 wt % of the electrolyte, and the amount of the additive was set to 0.5 wt % based on a total of 100 wt % of the electrolyte.

[0243] [Chemical formula 4-1]

[0244]

[0245] Using the electrolyte, the positive electrode of Comparative Example 1, and the negative electrode of Comparative Example 1, a 18650 cylindrical rechargeable lithium battery cell was manufactured according to conventional procedures.

[0246] (Example 6)

[0247] The electrolyte was prepared by the same procedure as in Example 5, except that the amount of the ionic liquid was set to 10 wt % based on 100 wt % of the total electrolyte, and the amount of the additive was set to 0.5 wt % based on 100 wt % of the total electrolyte.

[0248] Using the electrolyte, the positive electrode of Comparative Example 1, and the negative electrode of Comparative Example 1, a 18650 cylindrical rechargeable lithium battery cell was manufactured according to conventional procedures.

[0249] (Example 7)

[0250] The electrolyte was prepared by the same procedure as in Example 5, except that the amount of the ionic liquid was set to 2 wt % based on 100 wt % of the total electrolyte, and the amount of the additive was set to 1 wt % based on 100 wt % of the total electrolyte.

[0251] Using the electrolyte, the positive electrode of Comparative Example 1, and the negative electrode of Comparative Example 1, a 18650 cylindrical rechargeable lithium battery cell was manufactured according to conventional procedures.

[0252] (Example 8)

[0253] The electrolyte was prepared by the same procedure as in Example 5, except that the amount of the ionic liquid was set to 10 wt % based on 100 wt % of the total electrolyte, and the amount of the additive was set to 1 wt % based on 100 wt % of the total electrolyte.

[0254] Using the electrolyte, the positive electrode of Comparative Example 1, and the negative electrode of Comparative Example 1, a 18650 cylindrical rechargeable lithium battery cell was manufactured according to conventional procedures.

[0255] (Example 9)

[0256] The ionic liquid used in Example 1 and the additive of Chemical Formula 5-1 were added to the electrolyte precursor of Comparative Example 2 to prepare an electrolyte for a rechargeable lithium battery cell. Herein, the amount of the ionic liquid was set to 2 wt % based on a total of 100 wt % of the electrolyte, and the amount of the additive was set to 0.5 wt % based on a total of 100 wt % of the electrolyte.

[0257] [Chemical formula 5-1]

[0258]

[0259] Using the electrolyte, the positive electrode of Comparative Example 1, and the negative electrode of Comparative Example 1, a 18650 cylindrical rechargeable lithium battery cell was manufactured according to conventional procedures.

[0260] (Example 10)

[0261] The electrolyte was prepared by the same procedure as Example 9, except that the amount of the ionic liquid was set to 10 wt % based on 100 wt % of the total electrolyte, and the amount of the additive was set to 0.5 wt % based on 100 wt % of the total electrolyte.

[0262] Using the electrolyte, the positive electrode of Comparative Example 1, and the negative electrode of Comparative Example 1, a 18650 cylindrical rechargeable lithium battery cell was manufactured according to conventional procedures.

[0263] (Example 11)

[0264] The electrolyte was prepared by the same procedure as Example 9, except that the amount of the ionic liquid was set to 2 wt % based on 100 wt % of the total electrolyte, and the amount of the additive was set to 1 wt % based on 100 wt % of the total electrolyte.

[0265] Using the electrolyte, the positive electrode of Comparative Example 1, and the negative electrode of Comparative Example 1, a 18650 cylindrical rechargeable lithium battery cell was manufactured according to conventional procedures.

[0266] (Example 12)

[0267] The electrolyte was prepared by the same procedure as Example 9, except that the amount of the ionic liquid was set to 10 wt % based on 100 wt % of the total electrolyte, and the amount of the additive was set to 1 wt % based on 100 wt % of the total electrolyte.

[0268] (Example 13)

[0269] The ionic liquid used in Example 1 and the additive of Chemical Formula 5-2 were added to the electrolyte precursor of Comparative Example 2 to prepare an electrolyte for a rechargeable lithium battery cell. Herein, the amount of the ionic liquid was set to 2 wt % based on a total of 100 wt % of the electrolyte, and the amount of the additive was set to 0.75 wt % based on a total of 100 wt % of the electrolyte.

[0270] [Chemical formula 5-2]

[0271]

[0272] Using the electrolyte, the positive electrode of Comparative Example 1, and the negative electrode of Comparative Example 1, a 18650 cylindrical rechargeable lithium battery cell was manufactured according to conventional procedures.

[0273] (Example 14)

[0274] An electrolyte was prepared by the same procedure as in Example 13, except that the amount of the ionic liquid was set to 10 wt % based on 100 wt % of the total electrolyte, and the amount of the additive was set to 0.75 wt % based on 100 wt % of the total electrolyte.

[0275] Using the electrolyte, the positive electrode of Comparative Example 1, and the negative electrode of Comparative Example 1, a 18650 cylindrical rechargeable lithium battery cell was manufactured according to conventional procedures.

[0276] (Example 15)

[0277] An electrolyte was prepared by the same procedure as in Example 13, except that the amount of the ionic liquid was set to 2 wt % based on 100 wt % of the total electrolyte, and the amount of the additive was set to 1 wt % based on 100 wt % of the total electrolyte.

[0278] Using the electrolyte, the positive electrode of Comparative Example 1, and the negative electrode of Comparative Example 1, a 18650 cylindrical rechargeable lithium battery cell was manufactured according to conventional procedures.

[0279] (Example 16)

[0280] An electrolyte was prepared by the same procedure as in Example 13, except that the amount of the ionic liquid was set to 10 wt % based on 100 wt % of the total electrolyte, and the amount of the additive was set to 1 wt % based on 100 wt % of the total electrolyte.

[0281] (Example 17)

[0282] The ionic liquid used in Example 1 and the additive of Chemical Formula 6-1 were added to the electrolyte precursor of Comparative Example 2 to prepare an electrolyte for a rechargeable lithium battery cell. Herein, the amount of the ionic liquid was set to 2 wt % based on a total of 100 wt % of the electrolyte, and the amount of the additive was set to 0.5 wt % based on a total of 100 wt % of the electrolyte.

[0283] [Chemical formula 6-1]

[0284]

[0285] Using the electrolyte, the positive electrode of Comparative Example 1, and the negative electrode of Comparative Example 1, a 18650 cylindrical rechargeable lithium battery cell was manufactured according to conventional procedures.

[0286] (Example 18)

[0287] An electrolyte was prepared by the same procedure as in Example 17, except that the amount of the ionic liquid was set to 10 wt % based on 100 wt % of the total electrolyte, and the amount of the additive was set to 0.5 wt % based on 100 wt % of the total electrolyte.

[0288] Using the electrolyte, the positive electrode of Comparative Example 1, and the negative electrode of Comparative Example 1, a 18650 cylindrical rechargeable lithium battery cell was manufactured according to conventional procedures.

[0289] (Example 19)

[0290] An electrolyte was prepared by the same procedure as in Example 17, except that the amount of the ionic liquid was set to 2 wt % based on 100 wt % of the total electrolyte, and the amount of the additive was set to 1 wt % based on 100 wt % of the total electrolyte.

[0291] Using the electrolyte, the positive electrode of Comparative Example 1, and the negative electrode of Comparative Example 1, a 18650 cylindrical rechargeable lithium battery cell was manufactured according to conventional procedures.

[0292] (Example 20)

[0293] The electrolyte was prepared by the same procedure as Example 9, except that the amount of the ionic liquid was set to 10 wt % based on 100 wt % of the total electrolyte, and the amount of the additive was set to 1 wt % based on 100 wt % of the total electrolyte.

[0294] Using the electrolyte, the positive electrode of Comparative Example 1, and the negative electrode of Comparative Example 1, a 18650 cylindrical rechargeable lithium battery cell was manufactured according to conventional procedures.

[0295] The compositions of the ionic liquids and additives used in Comparative Examples 1 to 7 and Examples 1 to 20 are summarized in Table 1.

[0296] Table 1

[0297]

[0298]

[0299] Experimental Example 1) Measurement of room temperature capacity retention rate

[0300] For the rechargeable lithium battery cells according to Examples 1 to 20 and Comparative Examples 1 to 9, charging and discharging were performed at 0.5C at room temperature of 25°C, and the discharge capacity was measured. The capacity retention rate relative to the discharge capacity of the first cycle at 200 cycles was calculated. Among these results, the results of Comparative Examples 1 to 5 and Examples 1 to 4 are shown in Table 2, the results of Comparative Examples 1, 2 and 6 and Examples 5 to 8 are shown in Table 3, and the results of Comparative Examples 1, 2 and 7 and Examples 9 to 12 are shown in Table 4. In addition, the results of Comparative Examples 1, 2 and 8 and Examples 13 to 16 are shown in Table 5, and the results of Comparative Examples 1, 2 and 9 and Examples 17 to 20 are shown in Table 6.

[0301] Experimental Example 2) Measurement of Self-Extinguishing Time (SET Time)

[0302] The electrolytes prepared according to Examples 1 to 20 and Comparative Examples 1 to 9 were ignited with a torch to measure the self-extinguishing time, and the results are shown as SET time. The capacity retention rate relative to the discharge capacity of the first cycle at 200 cycles was calculated. Among these results, the results of Comparative Examples 1 to 5 and Examples 1 to 4 are shown in Table 2, the results of Comparative Examples 1, 2 and 6 and Examples 5 to 8 are shown in Table 3, and the results of Comparative Examples 1, 2 and 7 and Examples 9 to 12 are shown in Table 4. In addition, the results of Comparative Examples 1, 2 and 8 and Examples 13 to 16 are shown in Table 5, and the results of Comparative Examples 1, 2 and 9 and Examples 17 to 20 are shown in Table 6.

[0303] Experimental Example 3) Differential Scanning Calorimetry (DSC) Measurement

[0304] The rechargeable lithium battery cells of Examples 1 to 20 and Comparative Examples 1 to 9 were charged and discharged twice (formation) at 0.2C and at a cut-off voltage of 3.0V to 4.3V, and then charged once at 0.2C and at a cut-off voltage of 4.3V. The positive electrode was collected from the fully charged battery cell under an argon atmosphere, and 5 mg of the positive active material was obtained from the positive electrode, and the calorimetric change was measured using a differential scanning calorimetry (DSC) device. The differential scanning calorimetry was measured by increasing the temperature from 40°C to 400°C at a heating rate of 10°C / min.

[0305] The calculated calorific value (the integral value of the calorific value curve of DSC with respect to the temperature) is shown in the following table. Among these results, the results of Comparative Examples 1 to 5 and Examples 1 to 4 are shown in Table 2, the results of Comparative Examples 1, 2 and 6 and Examples 5 to 8 are shown in Table 3, and the results of Comparative Examples 1, 2 and 7 and Examples 9 to 12 are shown in Table 4. In addition, the results of Comparative Examples 1, 2 and 8 and Examples 13 to 16 are shown in Table 5, and the results of Comparative Examples 1, 2 and 9 and Examples 17 to 20 are shown in Table 6.

[0306] Table 2

[0307]

[0308]

[0309] As shown in Table 2, compared with Comparative Example 1 without both the ionic liquid and the additive or Comparative Example 2 and Comparative Example 5 with only one of the ionic liquid and the additive, Examples 1 to 4 including the ionic liquid and the additive of Chemical Formula 3-1 showed better capacity retention at room temperature. In addition, even if both the ionic liquid and the additive are included, the capacity retention rate of the additive including BF4 - Comparative Example 3 of the ionic liquid of the anion or Comparative Examples 3 and 4 including the ionic liquid having the sulfonium cation exhibited extremely low capacity retention at room temperature, as well as high SET time and DSC calorific value.

[0310] In addition, Examples 1 to 4 show lower DSC calorific values ​​than Comparative Examples 1 and Comparative Examples 3 to 5, and in particular, Example 4 shows lower DSC calorific values ​​than Comparative Examples 1 to 5, and thus thermal stability is also excellent. In addition, the SET times of Examples 2 and 4 are lower than those of Comparative Examples 1 to 5, and the SET times of Examples 1 and 3 are lower than those of Comparative Examples 1 and 3 to 5, and thus thermal stability is also excellent.

[0311] Table 3

[0312]

[0313] As shown in Table 3, compared with Comparative Example 1 without both the ionic liquid and the additive or Comparative Example 2 and Comparative Example 6 having only one of the ionic liquid and the additive, Examples 5 to 8 including the ionic liquid and the additive of Chemical Formula 4-1 exhibited better capacity retention at room temperature. In addition, Examples 5 to 8 exhibited lower DSC calorific values ​​than Comparative Example 1 and Comparative Example 6, and thus the thermal stability was also excellent. In addition, the SET time of Examples 6 to 8 was lower than that of Comparative Example 1 and Comparative Example 6, and the SET time of Example 5 was lower than that of Comparative Example 1 and Comparative Example 6, and thus the thermal stability was also excellent.

[0314] Table 4

[0315]

[0316] As shown in Table 4, Examples 9 to 12 including the ionic liquid and the additive of Chemical Formula 5-1 exhibited better capacity retention at room temperature than Comparative Example 1 without both the ionic liquid and the additive or Comparative Example 2 and Comparative Example 7 having only one of the ionic liquid and the additive. In addition, Examples 9 to 12 exhibited lower DSC calorific values ​​than Comparative Examples 1 and 7, and thus thermal stability was also excellent. In addition, the SET time of Examples 9 to 12 was lower than that of Comparative Examples 1 and 7.

[0317] Table 5

[0318]

[0319] As shown in Table 5, compared with Comparative Example 1 without both the ionic liquid and the additive or Comparative Example 2 and Comparative Example 8 having only one of the ionic liquid and the additive, Examples 13 to 16 including the ionic liquid and the additive of Chemical Formula 5-1 exhibited better capacity retention at room temperature. In addition, Examples 13 to 15 exhibited lower DSC calorific values ​​than Comparative Examples 1 and 8, and Example 16 exhibited lower DSC calorific values ​​than Comparative Examples 1, 2, and 8, and thus thermal stability was also excellent. In addition, the SET time of Examples 13 to 16 was lower than the SET time of Comparative Examples 1 to 8, and the SET time of Examples 14 and 16 was lower than the SET time of Comparative Example 2.

[0320] Table 6

[0321]

[0322] As shown in Table 6, Examples 17 to 20 including an ionic liquid and an additive of Chemical Formula 6-1 exhibited better capacity retention at room temperature than Comparative Example 1 without both an ionic liquid and an additive or Comparative Example 2 and Comparative Example 9 having only one of the ionic liquid and the additive. In addition, Examples 17 to 20 exhibited lower DSC calorific values ​​than Comparative Examples 1 and 9, indicating better thermal stability. In addition, the SET times of Examples 18 and 20 were lower than those of Comparative Examples 1, 2, and 9, and the SET times of Examples 17 and 19 were lower than those of Comparative Examples 1 and 9.

[0323] Although the present invention has been described in conjunction with the exemplary embodiments currently considered to be practiced, it should be understood that the present invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included in the spirit and scope of the claims. Therefore, the aforementioned embodiments should be understood as exemplary, rather than limiting the present invention in any way.

Claims

1. An electrolyte for a rechargeable lithium battery, comprising: Non-aqueous organic solvents; Lithium salts; An ionic liquid comprising a cation represented by Chemical Formula 1 and an anion represented by Chemical Formula 2; and The additive includes at least one compound represented by Chemical Formula 3 to Chemical Formula 6: [Chemical formula 1] (In Chemical Formula 1, R1 and R2 are the same or different and are substituted or unsubstituted C1-C6 alkyl) [Chemical formula 2] PF6 - [Chemical formula 3] (In Chemical Formula 3, X1 is a substituted or unsubstituted C1-C3 alkylene group or (-C2H4-O-C2H4-) n1 , and n1 is an integer ranging from 1 to 10); [Chemical formula 4] (In Chemical Formula 4, X2 is a substituted or unsubstituted C1-C2 alkylene or (-C2H4-O-C2H4-) n2 , and n2 is an integer ranging from 1 to 10, and R7 is -CN, -N=C=O, -N=C=S, -OSO2CH3, -OSO2C2H5, -OSO2F or -OSO2CF3) [Chemical formula 5] (In Chemical Formula 5, X3 is a fluoro group, a chloro group, a bromo group or an iodo group, R8~R 13 are each independently hydrogen, cyano, substituted or unsubstituted C1-C20 alkyl, substituted or unsubstituted C1-C20 alkoxy, substituted or unsubstituted C2-C20 alkenyl, substituted or unsubstituted C2-C20 alkynyl, substituted or unsubstituted C3-C20 cycloalkyl, substituted or unsubstituted C6-C20 aryl, or substituted or unsubstituted C2-C20 heteroaryl, and n3 is an integer of 0 or 1) [Chemical formula 6] (In Chemical Formula 6, R 14 ~R 16 are the same or different and are substituted or unsubstituted C1-C10 alkylene, substituted or unsubstituted C3-C30 cycloalkylene, substituted or unsubstituted C6-C30 arylene or substituted or unsubstituted C2-C30 heteroarylene). 2 . The electrolyte for a rechargeable lithium battery as claimed in claim 1 , wherein the amount of the ionic liquid is 0.05 wt % to 30 wt % based on a total of 100 wt % of the electrolyte. 3 . The electrolyte for a rechargeable lithium battery as claimed in claim 1 , wherein the amount of the additive is 0.05 wt % to 10 wt % based on a total of 100 wt % of the electrolyte. 4 . The electrolyte for a rechargeable lithium battery as claimed in claim 1 , wherein the amount of the additive is 0.05 wt % to 8 wt % based on a total of 100 wt % of the electrolyte.

5. The electrolyte for a rechargeable lithium battery as claimed in claim 1, wherein in Chemical Formula 4, R7 is -CN.

6. The electrolyte for a rechargeable lithium battery as claimed in claim 1, wherein in Chemical Formula 5, X3 is F.

7. The electrolyte for a rechargeable lithium battery as claimed in claim 1, wherein the compound of Chemical Formula 5 is represented by Chemical Formula 5a or Chemical Formula 5b: [Chemical Formula 5a] [Chemical Formula 5b] (In Chemical Formula 5a or Chemical Formula 5b, X3 is a fluoro group, a chloro group, a bromo group or an iodo group, and R8~R 13 Each is independently hydrogen, cyano, substituted or unsubstituted C1-C20 alkyl, substituted or unsubstituted C1-C20 alkoxy, substituted or unsubstituted C2-C20 alkenyl, substituted or unsubstituted C2-C20 alkynyl, substituted or unsubstituted C3-C20 cycloalkyl, substituted or unsubstituted C6-C20 aryl or substituted or unsubstituted C2-C20 heteroaryl).

8. A rechargeable lithium battery comprising: Negative electrode; Positive electrode; and The electrolyte according to any one of claims 1 to 7.

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