Electrolyte for rechargeable lithium battery and rechargeable lithium battery including same

Abstract

The invention relates to an electrolyte for a rechargeable lithium battery and a rechargeable lithium battery including the same. An electrolyte for a rechargeable lithium battery according to some example embodiments includes a non-aqueous organic solvent, a lithium salt, and an additive, where the additive includes a first compound and a second compound, the second compound being or including a nitrile-based compound containing three or more cyano groups.

Description

Technical Field

[0001] Disclosed are an electrolyte for a rechargeable lithium battery and a rechargeable lithium battery including the electrolyte. Background Art

[0002] As the use of electronic devices using batteries increases, such as, for example, mobile phones, laptop computers, electric vehicles, etc., the demand for rechargeable lithium batteries with high energy density and high capacity is also increasing. Accordingly, it may be advantageous to improve the performance of rechargeable lithium batteries.

[0003] Rechargeable lithium batteries generally include positive and negative electrodes (including active materials capable of intercalating and deintercalating lithium ions) and an electrolyte, and are configured to generate electrical energy through oxidation and reduction reactions when lithium ions are intercalated and deintercalated into and from the positive and negative electrodes.

[0004] A rechargeable lithium battery having high capacity, high energy density, and high safety may be advantageous for use as a driving power source for a hybrid vehicle or an electric vehicle or as an energy storage power source.

[0005] In a rechargeable lithium battery, the electrolyte plays a role in transferring lithium ions, and can exhibit significantly higher ion conductivity by including a non-aqueous organic solvent and a lithium salt. These electrolytes play a role in determining the safety and performance of the rechargeable lithium battery.

[0006] When a rechargeable lithium battery is subjected to an overcharge condition or a high temperature, the rechargeable lithium battery rapidly generates heat and produces gas, causing safety problems such as, for example, battery cell explosion.

[0007] Therefore, the development of electrolytes may facilitate the implementation of batteries with desired or improved safety even under overcharge and heat exposure conditions. Summary of the invention

[0008] Some example embodiments include electrolytes for rechargeable lithium batteries having desired or improved safety under overcharge and heat exposure conditions.

[0009] Some example embodiments include a rechargeable lithium battery that includes the electrolyte discussed above.

[0010] In some example embodiments, an electrolyte for a rechargeable lithium battery includes a nonaqueous organic solvent, a lithium salt, and an additive, wherein the additive includes a first compound represented by Chemical Formula 1 and a second compound, the second compound being or including a nitrile compound containing three or more cyano groups.

[0011] Chemical formula 1:

[0012]

[0013] In Chemical Formula 1, R 1 and R 2 are each independently a substituted or unsubstituted C1-C20 alkyl group or a substituted or unsubstituted C6-C30 aryl group, provided that R 1 and R 2 At least one of them is a substituted or unsubstituted C6-C30 aryl group.

[0014] In some example embodiments, a rechargeable lithium battery includes a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, a separator between the positive electrode and the negative electrode, and the aforementioned electrolyte.

[0015] An electrolyte for a rechargeable lithium battery according to some example embodiments may be suitable for a battery having desired or improved safety under overcharge and heat exposure. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 to Figure 4 is a schematic diagram of a rechargeable lithium battery according to some example embodiments.

[0017] Figure 5 Graphs illustrating evaluation results of overcharge of rechargeable lithium battery cells manufactured in Example 1 and Comparative Examples 1 to 3.

[0018] Figure 6 Graphs illustrating heat exposure evaluation results of rechargeable lithium battery cells manufactured in Example 1 and Comparative Examples 1 to 3.

[0019] Description of reference numerals:

[0020] 100: Rechargeable lithium battery 10: Positive electrode

[0021] 11: Positive electrode lead lug 12: Positive electrode terminal

[0022] 20: Negative electrode 21: Negative electrode lead lug

[0023] 22: Negative electrode terminal 30: Separator

[0024] 40: electrode assembly 50: shell

[0025] 60: Sealing member 70: Electrode terminal piece

[0026] 71: Positive electrode terminal tab 72: Negative electrode terminal tab DETAILED DESCRIPTION

[0027] Hereinafter, exemplary embodiments of the present disclosure will be described in detail. However, these embodiments are presented as examples, and the present disclosure is not limited thereto, and the present disclosure is defined by the scope of the claims.

[0028] As used herein, when no specific limitations are provided otherwise, it will be understood that when an element (such as a layer, film, region, or substrate) is referred to as being "on" another element (such as a layer, film, region, or substrate), it can be directly on the other element (such as a layer, film, region, or substrate), or intervening elements may also be present.

[0029] Unless otherwise specified in the specification, what is expressed in the singular may also include the plural. In addition, unless otherwise specified, "A or B" may mean "including A", "including B", or "including A and B".

[0030] As used herein, "combinations thereof" refers to mixtures, stacks, composites, copolymers, alloys, blends, reaction products, and the like, of the components.

[0031] As used herein, when no further limitation is provided, the particle size may be an average particle size. In addition, the particle size refers to the average particle size (D 50 ), which represents the diameter of particles with a cumulative volume of 50% by volume in the particle size distribution. Average particle size (D 50 ) can be measured by methods well known to those skilled in the art (e.g., by a particle size analyzer or by transmission electron microscope images or scanning electron microscope images). Optionally, a dynamic light scattering measurement device is used to perform data analysis and count the number of particles in each particle size range. Thus, the average particle size (D) can be easily obtained by calculation 50 ) value. Optionally, the average particle size (D 50 ) can be measured using a laser diffraction method. When measuring by the laser diffraction method, for example, the particles to be measured are dispersed in a dispersion medium, then introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), and ultrasonic waves of about 28 kHz are irradiated at an output of 60 W to calculate the average particle size (D ) based on 50% of the particle size distribution in the measuring device. 50 ).

[0032] As used herein, when no limitation is otherwise provided, "substituted" refers to a substituent or at least one hydrogen of a compound being replaced by deuterium, halo, hydroxyl, amino, C1-C30 amine, nitro, C1-C40 silyl, C1-C30 alkyl, C1-C10 alkylsilyl, C6-C30 arylsilyl, C3-C30 cycloalkyl, C3-C30 heterocycloalkyl, C6-C30 aryl, C2-C30 heteroaryl, C1-C20 alkoxy, C1-C10 fluoroalkyl, cyano or a combination thereof.

[0033] For example, "substituted" may refer to at least one hydrogen of a substituent or compound being replaced by deuterium, halogen, C1-C30 alkyl, C1-C10 alkylsilyl, C6-C30 arylsilyl, C3-C30 cycloalkyl, C3-C30 heterocycloalkyl, C6-C30 aryl, C2-C30 heteroaryl, C1-C10 fluoroalkyl or cyano. For example, "substituted" may refer to at least one hydrogen of a substituent or compound being replaced by deuterium, halogen, C1-C20 alkyl, C6-C30 aryl, C1-C10 fluoroalkyl or cyano. Alternatively, the term "substituted" may refer to at least one hydrogen of a substituent or compound being replaced by deuterium, halogen, C1-C5 alkyl, C6-C18 aryl, C1-C5 fluoroalkyl or cyano. For example, "substituted" may mean that at least one hydrogen of the substituent or compound is replaced by deuterium, cyano, halo, methyl, ethyl, propyl, butyl, phenyl, biphenyl, terphenyl, trifluoromethyl, or naphthyl.

[0034] When the term "about" or "substantially" is used with a numerical value in this specification, it means that the relevant numerical value includes the stated numerical value with a tolerance of about ±10%. When a range is specified, the range includes all values ​​therebetween, such as an increment of 0.1%.

[0035] An electrolyte for a rechargeable lithium battery according to some example embodiments includes a nonaqueous organic solvent, a lithium salt, and an additive, wherein the additive includes a first compound and a second compound. The first compound and the second compound are described in detail below.

[0036] When the first compound and the second compound are used in combination, both the stability of the battery under overcharge and the safety of the battery under heat exposure can be effectively achieved.

[0037] First Compound

[0038] The first compound is or includes a sulfoxide compound, which effectively reduces or suppresses the heating temperature of the battery under overcharge operation conditions.

[0039] The first compound is represented by Chemical Formula 1.

[0040] Chemical formula 1:

[0041]

[0042] In Chemical Formula 1, R 1 and R 2 are each independently a substituted or unsubstituted C1-C20 alkyl group or a substituted or unsubstituted C6-C30 aryl group, provided that R 1 and R 2At least one of them is a substituted or unsubstituted C6-C30 aryl group.

[0043] In some example embodiments, Chemical Formula 1 may be represented by Chemical Formula 1-1 or Chemical Formula 1-2. As an example, Chemical Formula 1 may be represented by Chemical Formula 1-1.

[0044] Chemical formula 1-1:

[0045]

[0046] In Chemical Formula 1-1,

[0047] R 1a may be or include a substituted or unsubstituted C1-C20 alkyl group, and

[0048] H a ~H e Each may independently be or include hydrogen, halogen, hydroxyl, cyano, nitro, 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.

[0049] As an example, H a ~H e Each independently may be or include hydrogen, halogen, substituted or unsubstituted C1-C20 alkyl, or substituted or unsubstituted C1-C20 alkoxy.

[0050] Chemical formula 1-2:

[0051]

[0052] In Chemical Formula 1-2,

[0053] H a ~H j Each may independently be or include hydrogen, halogen, hydroxyl, cyano, nitro, 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.

[0054] As an example, H a ~H jEach independently may be or include hydrogen, halogen, substituted or unsubstituted C1-C20 alkyl, or substituted or unsubstituted C1-C20 alkoxy.

[0055] As an example, the first compound may be or include any one or more of the compounds listed in Group 1.

[0056] Group 1:

[0057]

[0058] In some example embodiments, the first compound may be included in an amount greater than about 0.05 wt % or greater than or equal to about 0.1 wt % and less than about 6 wt % or less than or equal to about 5 wt % based on the total weight of the electrolyte for a rechargeable lithium battery.

[0059] As an example, the amount of the first compound included may be greater than about 0.05wt% and less than about 6wt%, for example, greater than about 0.05wt% and less than or equal to about 5wt%, greater than or equal to about 0.1wt% and less than about 6wt%, or about 0.1wt% to about 5wt%.

[0060] When the amount of the first compound included is less than or equal to about 0.05 wt % based on the total weight of the electrolyte for a rechargeable lithium battery, the effect of improving battery safety during overcharge is minimal, and when the amount of the first compound is greater than or equal to about 6 wt %, the thickness of the battery may excessively increase, or the resistance of the battery excessively increases.

[0061] Second compound

[0062] The second compound is or includes a nitrile compound containing three or more cyano groups (—CN), and helps improve the safety of the rechargeable lithium battery when the battery is subjected to high temperature.

[0063] The second compound may be represented by Chemical Formula 2.

[0064] Chemical formula 2:

[0065] N≡CLC≡N

[0066] In Chemical Formula 2, L is a substituted linear or branched C1-C20 alkylene group, wherein at least one hydrogen in the linear or branched C1-C20 alkylene group may be replaced by a cyano group (—CN).

[0067] For example, the substituted linear or branched C1-C20 alkylene group may be a group in which at least one hydrogen is further replaced by an isocyano group (—NC) or a thiocyano group (—SCN).

[0068] For example, the second compound may be or include at least one of the compounds listed in Group 2.

[0069] Group 2:

[0070]

[0071] According to example embodiments, the additive included in the electrolyte for a rechargeable lithium battery may be or include a composition including at least one of the compounds listed in Group 1 as a first compound and at least one of the compounds listed in Group 2 as a second compound.

[0072] For example, the additive included in the electrolyte for a rechargeable lithium battery may be or include a composition including Compound 1-a of Group 1 as the first compound and Compound 2-a as the second compound.

[0073] In some example embodiments, the second compound may be included in an amount greater than about 0.05 wt % or greater than or equal to about 0.1 wt % and less than about 6 wt % or less than or equal to about 5 wt % based on the total weight of the electrolyte for a rechargeable lithium battery.

[0074] As an example, the amount of the second compound included may be greater than about 0.05 wt % and less than about 6 wt %, e.g., greater than about 0.05 wt % and less than or equal to about 5 wt %, greater than or equal to about 0.1 wt % and less than about 6 wt %, or about 0.1 wt % to about 5 wt %, based on the total weight of the electrolyte for a rechargeable lithium battery.

[0075] When the amount of the second compound included is less than or equal to about 0.05 wt % based on the total weight of the electrolyte for a rechargeable lithium battery, the effect of improving battery safety during heat exposure is minimal, and when the amount of the second compound included is greater than or equal to about 6 wt %, the resistance of the battery may increase excessively.

[0076] In some example embodiments, the weight ratio of the first compound and the second compound may be within a range of about 0.01:1 to about 50:1, the weight ratio of the first compound and the second compound may be about 0.01:1 to about 40:1, the weight ratio of the first compound and the second compound may be about 0.05:1 to about 40:1, or the weight ratio of the first compound and the second compound may be about 0.05:1 to about 20:1.

[0077] When the weight ratio of the first compound to the second compound satisfies any one of the above ranges, a battery having desired or improved safety under both overcharge and heat exposure may be achieved.

[0078] The electrolyte for a rechargeable lithium battery includes a non-aqueous organic solvent and a lithium salt.

[0079] The nonaqueous organic solvent constitutes a medium for transporting ions participating in the electrochemical reaction of the battery.

[0080] The non-aqueous organic solvent may be or include at least one of a carbonate solvent, an ester solvent, an ether solvent, a ketone solvent, an alcohol solvent and an aprotic solvent.

[0081] The carbonate solvent may include at least one of 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), and butylene carbonate (BC). The ester solvent may include at least one of methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate (EP), propyl propionate (PP), decanoic acid lactone, mevalonate lactone, valerolactone, and caprolactone. The ether solvent may include at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran. In addition, the ketone solvent may include cyclohexanone, etc. The alcohol solvent may include at least one of ethanol and isopropanol, etc., and the aprotic solvent may include at least one of the following: nitriles, such as R-CN (wherein R is a C2 to C20 straight chain, branched or cyclic hydrocarbon group and may include a double bond, an aromatic ring or an ether bond), etc.; amides, such as dimethylformamide; dioxolanes, such as 1,3-dioxolane, 1,4-dioxolane, etc.; and cyclopentane sulfone, etc.

[0082] The nonaqueous organic solvent may be used alone or in combination of two or more nonaqueous organic solvents.

[0083] In addition, when a carbonate-based solvent is used, a cyclic carbonate and a chain carbonate may be mixed, and the cyclic carbonate and the chain carbonate may be mixed in a volume ratio of about 1:1 to about 1:9.

[0084] Lithium salts dissolved in non-aqueous organic solvents can supply lithium ions in batteries, can ensure the basic operation of rechargeable lithium batteries, and can improve the transport of lithium ions between positive electrodes and negative electrodes. For example, lithium salts may include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide, LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F2y+1 SO2) (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).

[0085] A rechargeable lithium battery according to some example embodiments includes a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, a separator between the positive electrode and the negative electrode, and the aforementioned electrolyte.

[0086] Positive electrode active material

[0087] The positive electrode active material may include a compound capable of intercalating and deintercalating lithium (lithiated intercalation compound). For example, at least one of a composite oxide of lithium and a metal such as or including at least one of cobalt, manganese, and nickel may be used.

[0088] The composite oxide may be or include a lithium transition metal composite oxide, and examples thereof may include at least one of a lithium nickel oxide, a lithium cobalt oxide (e.g., LiCoO2), a lithium manganese oxide, a lithium iron phosphate compound, and a cobalt-free lithium nickel manganese oxide.

[0089] As an example, a compound represented by any one of the following chemical formulas may be used. a A 1-b X b O 2-c D c (0.90≤a≤1.8, 0≤b≤0.5, and 0≤c≤0.05); Li a Mn 2-b X b O 4-c D c (0.90≤a≤1.8, 0≤b≤0.5, and 0≤c≤0.05); Li a Ni 1-b-c Co b X c O 2-α D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, and 0<α<2); Li a Ni 1-b-c Mn b X c O 2-α D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, and 0<α<2); Li a Ni b Co c L1 d G e O2 (0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5, and 0≤e≤0.1); Li a NeG b O2(0.90≤a≤1.8 and 0.001≤b≤0.1); Li a CoG b O2(0.90≤a≤1.8 and 0.001≤b≤0.1); Li a Mn 1-b G b O2(0.90≤a≤1.8 and 0.001≤b≤0.1); Li a Mn b O4 (0.90≤a≤1.8 and 0.001≤b≤0.1); Li a Mn 1- g G g PO4(0.90≤a≤1.8, and 0≤g≤0.5); Li (3-f) Fe2(PO4)3(0≤f≤2); and Li a FePO4(0.90≤a≤1.8).

[0090] In the above chemical formula, A is or includes at least one of Ni, Co and Mn; X is or includes at least one of Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V and rare earth elements; D is or includes at least one of O, F, S and P; G is or includes at least one of Al, Cr, Mn, Fe, Mg, La, Ce, Sr and V; and L 1 It is or includes at least one of Mn and Al.

[0091] For example, the positive electrode active material may be or include a high nickel-based positive electrode active material having a nickel content of greater than or equal to about 80 mol%, greater than or equal to about 85 mol%, greater than or equal to about 90 mol%, greater than or equal to about 91 mol%, or greater than or equal to about 94 mol% and less than or equal to about 99 mol%, based on 100 mol% of metals other than lithium in the lithium transition metal composite oxide. The high nickel-based positive electrode active material can achieve high capacity and can be applied to high capacity, high density rechargeable lithium batteries.

[0092] Positive electrode

[0093] A positive electrode for a rechargeable lithium battery may include a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector. The positive electrode active material layer may include a positive electrode active material, and may further include a binder and / or a conductive material.

[0094] For example, the positive electrode may further include a component that may constitute a sacrificial positive electrode.

[0095] The amount of the positive electrode active material may be about 90 wt % to about 99 wt % based on 100 wt % of the positive electrode active material layer, and the amount of the binder and the conductive material may be about 0.5 wt % to about 5 wt % based on 100 wt % of the positive electrode active material layer, respectively.

[0096] The binder is configured to attach the positive electrode active material particles to each other and also to attach the positive electrode active material to the positive electrode current collector. Examples of the binder may include 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 nylon, etc. At least one, but not limited thereto.

[0097] The conductive material may be configured to impart conductivity to the electrode, and any material that does not cause chemical changes and conducts electrons may be used for the battery. Examples of the conductive material may include carbon-based materials (such as at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube); metal-based materials containing at least one of copper, nickel, aluminum, and silver, etc. in the form of metal powder or metal fiber; conductive polymers (such as polyphenylene derivatives); or mixtures thereof.

[0098] Al foil may be used as the positive electrode current collector, but the positive electrode current collector is not limited thereto.

[0099] Negative electrode active material

[0100] The negative electrode active material may include at least one of a material that reversibly intercalates / deintercalates lithium ions, lithium metal, a lithium metal alloy, a material capable of doping / dedoping lithium, and a transition metal oxide.

[0101] The material that reversibly intercalates / deintercalates lithium ions may include a carbon-based negative electrode active material, such as crystalline carbon, amorphous carbon, or a combination thereof. The crystalline carbon may be graphite, such as amorphous, flaky, flaky, spherical, or fibrous natural graphite or artificial graphite, and the amorphous carbon may be or include at least one of soft carbon, hard carbon, mesophase pitch carbonization product, and calcined coke, etc.

[0102] The lithium metal alloy includes an alloy of lithium and a metal (such as or including at least one of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn).

[0103] The material capable of doping / dedoping lithium may be or include at least one of Si-based negative electrode active materials or Sn-based negative electrode active materials. The Si-based negative electrode active material may include silicon, a silicon-carbon composite, SiO x (0 < x ≤ 2) and at least one of Si-Q alloys (where Q is or includes at least one of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element (except Si), a Group 15 element, a Group 16 element, a transition metal, and a rare earth element). The Sn-based negative electrode active material may include Sn, SnO x (0 < x ≤ 2, for example, SnO2) and at least one of Sn-based alloys.

[0104] The silicon-carbon composite may be or include a composite of silicon and amorphous carbon. According to an exemplary embodiment, the silicon-carbon composite may be in the form of silicon particles and an amorphous carbon coating 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. The amorphous carbon may also be between the primary silicon particles, and, for example, the primary silicon particles may be coated with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0105] 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 an amorphous carbon coating on the surface of the core.

[0106] The Si-based negative electrode active material or the Sn-based negative electrode active material may be used in combination with a carbon-based negative electrode active material.

[0107] Negative electrode

[0108] The negative electrode for a rechargeable lithium battery includes a negative electrode current collector and a negative electrode active material layer on the negative electrode current collector. The negative electrode active material layer may include a negative electrode active material and may further include a binder and / or a conductive material.

[0109] For example, based on 100 wt% of the negative electrode active material layer, the negative electrode active material layer 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.

[0110] The binder is configured to attach the negative electrode active material particles to each other and also to attach the negative electrode active material to the negative electrode current collector. The binder may include a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0111] The non-aqueous binder may include at least one of polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide imide, and polyimide.

[0112] The aqueous binder may be or include at least one of styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-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 and polyvinyl alcohol.

[0113] When an aqueous binder is used as a binder in the negative electrode active material layer, a cellulose compound capable of imparting viscosity may be further included. The cellulose compound may include at least one of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, and an alkali metal salt thereof. The alkali metal may include at least one of Na, K, and Li.

[0114] The dry binder may be or include a polymer material capable of becoming fibrous, and may be or include, for example, at least one of polytetrafluoroethylene, polyvinylidene fluoride, a polyvinylidene fluoride-hexafluoropropylene copolymer, and polyethylene oxide.

[0115] The conductive material may be configured to impart conductivity to the electrode, and any material that does not cause chemical changes and conducts electrons may be used for the battery. Examples thereof may include carbon-based materials (such as or including at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube); metal-based materials including at least one of copper, nickel, aluminum, and silver, etc. in the form of metal powder or metal fiber; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0116] The negative electrode current collector may include at least one of a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, and a polymer substrate coated with a conductive metal.

[0117] Diaphragm

[0118] Depending on the type of rechargeable lithium battery, the separator may be present between the positive electrode and the negative electrode. The separator may include at least one of a polyethylene separator, a polypropylene separator, a polyvinylidene fluoride separator, and a multilayer film of two or more layers thereof (such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, a polypropylene / polyethylene / polypropylene three-layer separator, etc.).

[0119] The separator may include a porous substrate and a coating on one or both surfaces of the porous substrate, the coating including an organic material, an inorganic material, or a combination thereof.

[0120] The porous substrate may be or include a polymer film formed from or including polyolefins (such as polyethylene and polypropylene), polyesters (such as polyethylene terephthalate and polybutylene terephthalate), polyacetals, polyamides, polyimides, polycarbonates, polyether ketones, polyaryletherketones, polyetherimides, polyamideimides, polybenzimidazoles, polyethersulfones, polyphenylene oxides, cyclic olefin copolymers, polyphenylene sulfide, polyethylene naphthalate, glass fibers, and polytetrafluoroethylene (e.g., Teflon), or copolymers or mixtures of two or more thereof.

[0121] The organic material may include a polyvinylidene fluoride-based polymer or a (meth)acrylic-based polymer.

[0122] The inorganic material may include inorganic particles (such as or including at least one of Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2 and boehmite), but is not limited thereto.

[0123] An organic material and an inorganic material may be mixed in one coating layer, or a coating layer including an organic material and a coating layer including an inorganic material may be stacked.

[0124] Rechargeable lithium battery

[0125] The rechargeable lithium battery may be classified into a cylindrical battery, a prismatic battery, a pouch type battery, a coin type battery, etc., depending on the shape of the rechargeable lithium battery. Figure 1 to Figure 4 A schematic diagram illustrating a rechargeable lithium battery according to some example embodiments. Figure 1 Explain cylindrical batteries, Figure 2 Explain prismatic cells, and Figure 3 and Figure 4 Explain the pouch cell. Figure 1 to Figure 4, the rechargeable lithium battery 100 includes: an electrode assembly 40 including a separator 30 between a positive electrode 10 and a negative electrode 20; and 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 (not shown). Figure 1 As shown, the rechargeable lithium battery 100 may include a sealing member 60 that seals the housing 50. Figure 2 In the embodiment, 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 3 and Figure 4 As shown, the rechargeable lithium battery 100 includes Figure 4 The electrode tab 70 explained in Figure 3 The positive electrode tab 71 and the negative electrode tab 72 illustrated in FIG. 7A and 7B , the electrode tabs 70 / 71 / 72 form an electrical path for introducing current formed in the electrode assembly 40 to the outside of the battery 100 .

[0126] A rechargeable lithium battery according to example embodiments may be applicable to, for example, vehicles, mobile phones, and / or other various types of electronic devices, but the present disclosure is not limited thereto.

[0127] The following describes embodiments and comparative examples of the present disclosure. However, the following embodiments are merely examples of the present disclosure, and the present disclosure is not limited to the following embodiments.

[0128] Example:

[0129] Example 1

[0130] 1.3 M LiPF6 lithium salt was dissolved in a non-aqueous organic solvent mixed with ethylene carbonate (EC), propylene carbonate (PC), ethyl propionate (EP) and propyl propionate (PP) in a volume ratio of 10:15:30:45 to prepare a basic electrolyte.

[0131] The electrolyte solution was prepared by adding Compound 1-a as a first compound and Compound 2-a as a second compound to a basic electrolyte solution.

[0132] Compound 1-a

[0133]

[0134] Compound 2-a

[0135]

[0136] exist Example 1 In the electrolyte, 2 wt % of the first compound and 3 wt % of the second compound were added based on the total weight of the electrolyte.

[0137] LiCoO 2 as a positive electrode active material, polyvinylidene fluoride as a binder, and Ketjen black as a conductive material were mixed at a weight ratio of 97:2:1 and dispersed in N-methylpyrrolidone to prepare a positive electrode active material slurry.

[0138] The positive electrode active material slurry was coated on a 10 μm thick Al foil, dried at 110° C., and pressed to produce a positive electrode.

[0139] In addition, a negative electrode active material slurry was prepared by mixing artificial graphite as a negative electrode active material, styrene-butadiene rubber as a binder, and carboxymethyl cellulose as a thickener at a weight ratio of 97:1:2 and dispersing the mixture in distilled water. The negative electrode active material slurry was coated on a 10 μm thick Cu foil current collector, dried at 100°C, and pressed to manufacture a negative electrode.

[0140] A 25 μm thick separator having a polyethylene-polypropylene multilayer structure was inserted between the positive electrode and the negative electrode to manufacture an electrode assembly, and a rechargeable lithium battery cell was manufactured by inserting the electrode assembly into a pouch type battery case and injecting the prepared electrolyte therein.

[0141] Embodiment 2 to Embodiment 9

[0142] Each rechargeable lithium battery cell according to Examples 2 to 9 was manufactured in substantially the same manner as Example 1, except that the content of the first compound and the content of the second compound based on the total weight of the electrolyte solution were respectively changed as shown in Table 1 below.

[0143] Comparative Example 1

[0144] A rechargeable lithium battery cell was manufactured in substantially the same manner as Example 1, except that the first compound and the second compound were not added to the electrolyte.

[0145] Comparative Example 2

[0146] A rechargeable lithium battery cell was manufactured in substantially the same manner as Example 1, except that the second compound was not added when the electrolyte was prepared.

[0147] Comparative Example 3

[0148] A rechargeable lithium battery cell was manufactured in substantially the same manner as in Example 1, except that the first compound was not added when the electrolyte was prepared.

[0149] Table 1:

[0150]

[0151]

[0152] Evaluation example:

[0153] Evaluation Example 1: Evaluation of overcharge safety

[0154] The overcharge safety of the rechargeable lithium battery cells of Examples 1 to 9 and Comparative Examples 1 to 3 were evaluated, and the results are shown in Tables 2 and 3 below. Figure 5 Shown in.

[0155] After attaching a safety protection device to the negative electrode of each of the rechargeable lithium battery cells by welding and attaching a tab to the positive electrode of each of the rechargeable lithium battery cells by welding, a thermocouple is attached and fixed to the center of each battery cell to measure temperature.

[0156] Subsequently, after wrapping the battery cell with a heat insulating material, the battery cell was charged to 10 V at a rate of 0.2 C and then subjected to the voltage for 450 minutes.

[0157] After a total of three experiments, when the battery cell did not catch fire during the test but remained in the same state as before the evaluation, "P (Pass)" was given, but when the battery cell caught fire, "F (Fail)" was given, and the results are shown in Table 2.

[0158] In addition, the overcharge evaluation results of the rechargeable lithium battery cells of Example 1 and Comparative Examples 1 to 3 are as follows: Figure 5 As shown in the curve graph. Figure 5 , the line at the top relatively represents the change of voltage over time, and the line at the bottom relatively represents the change of temperature over time.

[0159] Refer to Table 2 and Figure 5 For Comparative Examples 1 and 3 in which the first compound was not added to the electrolyte, as the temperature increased to about 200° C. between about 350 minutes and 400 minutes, the battery cell voltage reached 10 V. When the battery cell voltage reached 10 V, the battery cell exploded, which prevented the measurement of the potential difference between the positive electrode and the negative electrode.

[0160] refer to Figure 5 In Example 1, in which the battery cell was subjected to the overcharge state for 450 minutes, the battery cell maintained a constant temperature and had substantially no temperature increase, but Comparative Example 1 exhibited a temperature increase to approximately 200° C. at approximately 370 minutes, and Comparative Example 3 exhibited a temperature increase to approximately 175° C. at approximately 380 minutes.

[0161] Evaluation Example 2: Evaluation of thermal exposure safety

[0162] The rechargeable lithium battery cells of Examples 1 to 9 and Comparative Examples 1 to 3 in a discharged state of 3.0 V were fully charged at a charge rate of 0.5 C under a cut-off condition of 4.47 V / 3 hours and subjected to heat exposure evaluation.

[0163] The rechargeable lithium battery cells of Examples 1 to 9 and Comparative Examples 1 to 3 were placed in a chamber, and the battery changes were examined by raising the temperature from room temperature (25°C) to 140°C, 141°C, 142°C, 143°C, 144°C and 145°C at a rate of 5°C / min and maintaining each temperature for 1 hour.

[0164] After conducting the experiment three times in total, when thermal runaway did not occur while maintaining each temperature as described above, "P (Pass)" was given, but when rapid thermal runaway occurred during being subjected to each high temperature as described above, "F (Fail)" was given, and the results are shown in Table 2 below.

[0165] In addition, the heat exposure results of the rechargeable lithium battery cells according to Example 1 and Comparative Examples 1 to 3 at 143° C. are as follows: Figure 6 As shown in the curve graph. Figure 6 In FIG. 1 , a relatively thicker line (relatively a line at the top) represents a change in voltage over time, and a relatively thinner line (relatively a line at the bottom) represents a change in temperature over time.

[0166] Referring to Table 2, Comparative Examples 1 and 2 in which the second compound was not added to the electrolyte exhibited thermal runaway when subjected to heat at 141°C.

[0167] refer to Figure 6 , the rechargeable lithium battery cells according to Example 1 and Comparative Examples 1 to 3 exhibit a sharp voltage drop. When the pouch-type battery is suddenly exposed to high temperature, gas is generated thereby and the internal pressure increases, thereby activating the current cut-off device (CID), resulting in a sharp voltage drop. The sharp voltage drop of the rechargeable lithium battery cells of Example 1 and Comparative Examples 1 to 3 confirms that the current cut-off device (CID) is activated due to gas generation caused by being subjected to high temperature.

[0168] For example, even when the rechargeable lithium battery cell of Example 1 was exposed to a temperature of 143° C., it was confirmed that thermal runaway was not exhibited while maintaining the temperature of 143° C.

[0169] refer to Figure 6On the other hand, the rechargeable lithium battery cell of Comparative Example 1 showed a battery temperature increase to about 450°C or higher at about 35 minutes, and the rechargeable lithium battery cell of Comparative Example 2 also showed a battery temperature increase to about 370°C or higher at about 36 minutes.

[0170] Table 2:

[0171]

[0172]

[0173] In Table 2 above, the mark "-" indicates that no evaluation is required after thermal runaway occurs (failure), and also indicates that no evaluation is required at a given temperature or lower because no thermal runaway occurs at the given temperature (pass).

[0174] Evaluation Example 3: Evaluation of AC Internal Resistance (AC-IR)

[0175] The thickness (mm) and AC-internal resistance (AC-IR, mΩ) of the rechargeable lithium battery pouch-type battery cells according to Examples 1 to 9 in a fully charged state (SOC=100%) were measured, and the results are shown in Table 3 below.

[0176] Table 3:

[0177] Battery cell thickness (mm) AC-IR(mΩ) Example 1 5.43 25.2 Example 2 5.24 24.7 Example 3 5.26 24.8 Example 4 5.82 26.8 Example 5 6.04 27.9 Example 6 5.74 24.4 Example 7 5.69 24.7 Example 8 5.18 27.7 Example 9 5.15 29.3

[0178] Referring to Table 3, the battery cells of Examples had a thickness of 6.04 mm or less, and in particular, the battery cells of Examples 2, 3, 8, and 9 exhibited desirable or improved thickness characteristics.

[0179] In addition, referring to Table 3, the Examples exhibited AC-internal resistance (AC-IR) of 29.3 mΩ or less, and in particular, Example 2, Example 3, Example 6, and Example 7 exhibited small AC-IR.

[0180] While the disclosure has been described in conjunction with what are presently considered to be example embodiments, it should be understood that the disclosure is not limited to the disclosed example embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the claims.

Claims

1. An electrolyte for a rechargeable lithium battery, the electrolyte comprising: Non-aqueous organic solvents; Lithium salts; and additive, The additive includes a first compound represented by Chemical Formula 1, and a second compound including a nitrile compound containing three or more cyano groups: Chemical formula 1: Wherein, in Chemical Formula 1, R 1 and R 2 are each independently a substituted or unsubstituted C1-C20 alkyl group or a substituted or unsubstituted C6-C30 aryl group, provided that R 1 and R 2 At least one of them is a substituted or unsubstituted C6-C30 aryl group.

2. The electrolyte of claim 1, wherein the second compound is represented by Chemical Formula 2: Chemical formula 2: NC—CN in, In chemical formula 2, L is a substituted straight or branched C1-C20 alkylene group, and at least one hydrogen in the straight or branched C1-C20 alkylene group is replaced by a cyano group.

3. The electrolyte according to claim 1, wherein Chemical Formula 1 is represented by Chemical Formula 1-1 or Chemical Formula 1-2: Chemical formula 1-1: in, In Chemical Formula 1-1, R 1 a is a substituted or unsubstituted C1-C20 alkyl group, and Ha to He are each independently hydrogen, halogen, hydroxyl, cyano, nitro, 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; Chemical formula 1-2: Wherein, in Chemical Formula 1-2, H a ~H j Each is independently hydrogen, halogen, hydroxyl, cyano, nitro, 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.

4. The electrolyte of claim 1, wherein the first compound comprises any one or more of the compounds listed in Group 1: Group 1:

5. The electrolyte of claim 1, wherein the second compound comprises at least one of the compounds listed in Group 2: Group 2: 6 . The electrolyte of claim 1 , wherein the first compound is included in an amount greater than 0.05 wt % and less than 6 wt % based on the total weight of the electrolyte for a rechargeable lithium battery. 7 . The electrolyte of claim 1 , wherein the second compound is included in an amount greater than 0.05 wt % and less than 6 wt % based on the total weight of the electrolyte for a rechargeable lithium battery. 8 . The electrolyte according to claim 1 , wherein a weight ratio of the first compound to the second compound is in a range of 0.01:1 to 50:

1.

9. A rechargeable lithium battery comprising: a positive electrode, including a positive electrode active material; a negative electrode, including a negative electrode active material; a separator between the positive electrode and the negative electrode; as well as The electrolyte according to any one of claims 1 to 8.

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