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. The additive includes a first compound and a second compound.

Description

Technical Field

[0001] The present application discloses an electrolyte for a rechargeable lithium battery and a rechargeable lithium battery including the same. Background Art

[0002] As the use of electronic devices using batteries (such as, for example, mobile phones, laptop computers, electric vehicles, etc.) increases, the demand for rechargeable batteries having high energy density and high capacity increases.

[0003] A rechargeable lithium battery generally includes positive and negative electrodes including an active material capable of intercalating and deintercalating lithium ions, and an electrolyte, and generates electric energy through oxidation and reduction reactions when lithium ions are intercalated and deintercalated from the positive and negative electrodes.

[0004] There is increasing interest in rechargeable lithium batteries having high capacity, high energy density, and high safety for use as a driving power source for hybrid vehicles or electric vehicles or as a power storage power source.

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

[0006] When rechargeable lithium batteries are exposed to overcharge, rechargeable lithium battery cells may explode, raising safety concerns about the batteries. When exposed to high temperatures, the increase in the internal resistance of the battery may pose a challenge.

[0007] Accordingly, it would be advantageous to develop electrolytes to achieve batteries with desired or improved safety even under overcharge and exposure to high temperatures. Summary of the invention

[0008] Some example embodiments include an electrolyte for a rechargeable lithium battery having desired or improved safety under overcharge and desired or improved high temperature storage characteristics.

[0009] Some example embodiments include a rechargeable lithium battery including an electrolyte.

[0010] In some example embodiments, an electrolyte for a rechargeable lithium battery includes a non-aqueous organic solvent, a lithium salt, and an additive, wherein the additive includes a first compound represented by Chemical Formula 1 and a second compound represented by Chemical Formula 2.

[0011] Chemical formula 1:

[0012]

[0013] Chemical formula 2:

[0014]

[0015] 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,

[0016] In Chemical Formula 2, A1, A2, A3 and A4 are each independently or include a single bond, an unsubstituted or substituted C1-C5 alkylene group, a carbonyl group or a sulfinyl group, provided that A1 and A2 are not simultaneously or concurrently single bonds, and A3 and A4 are not simultaneously or concurrently single bonds.

[0017] 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.

[0018] An electrolyte for a rechargeable lithium battery according to some example embodiments may result in a rechargeable lithium battery having desired or improved safety under overcharge and desired or improved high temperature storage characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 to Figure 4 is a schematic diagram of a rechargeable lithium battery according to some example embodiments.

[0020] Figure 5 1 is a graph showing the evaluation results of overcharge of the rechargeable lithium battery cells manufactured in Example 1 and Comparative Examples 1 to 3.

[0021] Figure 6 1 is a graph showing the evaluation results of high temperature storage characteristics of the rechargeable lithium battery cells manufactured in Example 1 and Comparative Examples 1 to 3.

[0022] Description of Reference Numerals

[0023] 100: Rechargeable lithium battery 10: Positive electrode

[0024] 11: Positive electrode lead lug 12: Positive electrode terminal

[0025] 20: Negative electrode 21: Negative electrode lead lug

[0026] 22: Negative electrode terminal 30: Separator

[0027] 40: electrode assembly 50: shell

[0028] 60: Sealing member 70: Electrode terminal piece

[0029] 71: Positive electrode terminal tab 72: Negative electrode terminal tab DETAILED DESCRIPTION

[0030] Hereinafter, exemplary embodiments of the present disclosure will be described in detail. However, these embodiments are presented as examples, the present disclosure is not limited thereto, and the present disclosure is defined by the scope of the claims.

[0031] As used herein, when specific definitions are otherwise provided, 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), the element (such as a layer, film, region, or substrate) can be directly on the other element (such as a layer, film, region, or substrate), or intervening elements may also be present.

[0032] Unless otherwise specified in this specification, contents indicated 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".

[0033] As used herein, "combinations thereof" means mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like, of the components.

[0034] As used herein, when no other definition is provided, the particle size may be the average particle size. In addition, the particle size means the average particle size (D 50 ), which means 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, for example, by a particle size analyzer, or by transmission electron microscope images or scanning electron microscope images. Alternatively, 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 ) value can be measured using a laser diffraction method. When measuring by the laser diffraction method, more specifically, 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 with an output of 60 W are irradiated to calculate the average particle size (D ) based on 50 volume % of the cumulative volume in the particle size distribution in the measuring device. 50 ).

[0035] As used herein, when no limitation is otherwise provided, "substituted" refers to the replacement of at least one hydrogen of a substituent or a compound by deuterium, halogen, hydroxyl, amino, C1-C30 amine, nitro, C1-C40 silyl, C1-C30 alkyl, C1-C10 alkylsilyl, C6-C30 arylsilyl, C3-C30 cycloalkyl, C3-C30 heterocycloalkyl, C6-C30 aryl, C2-C30 heteroaryl, C1-C20 alkoxy, C1-C10 fluoroalkyl, cyano or a combination thereof.

[0036] 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, "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 a substituent or compound is replaced by deuterium, cyano, halogen, methyl, ethyl, propyl, butyl, phenyl, biphenyl, terphenyl, trifluoromethyl, or naphthyl.

[0037] When the term "about" or "substantially" is used in conjunction with a numerical value in this specification, it means that the relevant numerical value includes a tolerance of ±10% around the stated numerical value. When a range is specified, the range includes all values ​​therebetween, such as an increment of 0.1%.

[0038] An electrolyte for a rechargeable lithium battery according to some example embodiments includes: a non-aqueous 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.

[0039] In example embodiments, when the first compound and the second compound are used in combination, a rechargeable lithium battery having desired or improved safety under overcharge and desired or improved high temperature storage characteristics may be realized.

[0040] First Compound

[0041] The first compound is a sulfoxide compound, which effectively reduces or suppresses the heating temperature of the battery under overcharge operation conditions.

[0042] The first compound is represented by Chemical Formula 1.

[0043] Chemical formula 1:

[0044]

[0045] In Chemical Formula 1, R 1 and R 2 Each independently is or includes 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.

[0046] In some example embodiments, the first compound represented by Chemical Formula 1 may be represented by Chemical Formula 1-1 or Chemical Formula 1-2. For example, the first compound represented by Chemical Formula 1 may be represented by Chemical Formula 1-1.

[0047] Chemical formula 1-1:

[0048]

[0049] In Chemical Formula 1-1,

[0050] R 1a may be or include a substituted or unsubstituted C1-C20 alkyl group, and

[0051] 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.

[0052] 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.

[0053] Chemical formula 1-2:

[0054]

[0055] In Chemical Formula 1-2,

[0056] H a ~H jEach 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.

[0057] As a specific example, H a ~H j Each independently may be or include hydrogen, halogen, substituted or unsubstituted C1-C20 alkyl, or substituted or unsubstituted C1-C20 alkoxy.

[0058] As an example, the first compound represented by Chemical Formula 1 may be or include one or more of the compounds listed in Group 1.

[0059] Group 1:

[0060]

[0061]

[0062] 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.

[0063] As a specific example, the first compound can be included in an amount 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.

[0064] When the first compound is included in an amount of less than or equal to about 0.05 wt % based on the total weight of the electrolyte for a rechargeable lithium battery, the improvement in battery safety during overcharge is minimal, and when the first compound is included in an amount of greater than or equal to about 6 wt %, the resistance of the battery may increase excessively, thereby shortening the cycle life of the battery.

[0065] Second compound

[0066] The second compound is or includes a bicyclic sulfate compound that forms a solid electrolyte interface (SEI) layer on the surface of the negative electrode or a protective layer on the surface of the positive electrode, thereby improving the thermal stability of the battery, thereby enhancing the cycle life characteristics of the rechargeable lithium battery at high temperatures.

[0067] The second compound is represented by Chemical Formula 2.

[0068] Chemical formula 2:

[0069]

[0070] In Chemical Formula 2, A1, A2, A3 and A4 may each independently be or include a single bond, an unsubstituted or substituted C1-C5 alkylene group, a carbonyl group or a sulfinyl group, provided that A1 and A2 are not simultaneously or concurrently single bonds, and A3 and A4 are not simultaneously or concurrently single bonds.

[0071] For example, the above-mentioned A1, A2, A3 and A4 may each independently be or include unsubstituted C1~C5 alkylene or substituted C1~C5 alkylene, and the substituent of the substituted C1~C5 alkylene may be or include at least one of halogen, unsubstituted or halogen-substituted C1~C20 alkyl, unsubstituted or halogen-substituted C2~C20 alkenyl, unsubstituted or halogen-substituted C2~C20 alkynyl, unsubstituted or halogen-substituted C3~C20 cycloalkenyl, unsubstituted or halogen-substituted C3~C20 heterocyclyl, unsubstituted or halogen-substituted C6~C40 aryl and unsubstituted or halogen-substituted C2~C40 heteroaryl.

[0072] For example, A1, A2, A3 and A4 may each independently be or include an unsubstituted C1-C5 alkylene group or a substituted C1-C5 alkylene group, and the substituent of the substituted C1-C5 alkylene group may be or include at least one of halogen, methyl, ethyl, propyl, isopropyl, butyl, tert-butyl, trifluoromethyl, tetrafluoroethyl, phenyl, naphthyl, tetrafluorophenyl, pyrrolyl and pyridyl, but is not necessarily limited thereto, and may be any group that can be used as a substituent of an alkylene group in the relevant technical field.

[0073] In some example embodiments, the second compound represented by Chemical Formula 2 may include one or more of the compounds represented by Chemical Formula 2-1 to Chemical Formula 2-7.

[0074] Chemical formula 2-1:

[0075]

[0076] Chemical formula 2-2:

[0077]

[0078] Chemical formula 2-3:

[0079]

[0080] Chemical formula 2-4:

[0081]

[0082] Chemical formula 2-5:

[0083]

[0084] Chemical formula 2-6:

[0085]

[0086] Chemical formula 2-7:

[0087]

[0088] 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.

[0089] As an example, the second compound can be included in an amount 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.

[0090] When the second compound is included in an amount of less than or equal to about 0.05 wt % based on the total weight of the electrolyte for a rechargeable lithium battery, it can be challenging to improve the high temperature cycle life characteristics of the battery, and when the second compound is included in an amount of greater than or equal to about 6 wt %, the resistance of the battery may increase excessively, thereby reducing the cycle life of the battery.

[0091] In some example embodiments, the first compound and the second compound may be included in a weight ratio of about 0.01:1 to about 100:1, e.g., a weight ratio of about 0.05:1 to about 100:1, a weight ratio of about 0.01:1 to about 40:1, a weight ratio of about 0.05:1 to about 40:1, a weight ratio of about 0.05:1 to about 20:1, or a weight ratio of about 0.1:1 to about 20:1.

[0092] When the weight ratio of the first compound to the second compound satisfies any one of the above numerical ranges, a battery having desired or improved stability under overcharge and desired or improved high temperature cycle-life characteristics can be obtained.

[0093] The electrolyte for a rechargeable lithium battery includes a non-aqueous organic solvent and a lithium salt.

[0094] The nonaqueous organic solvent may constitute a medium for transporting ions participating in the electrochemical reaction of the battery.

[0095] The non-aqueous organic solvent may be or include a carbonate solvent, an ester solvent, an ether solvent, a ketone solvent, an alcohol solvent, an aprotic solvent or a combination thereof.

[0096] 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), butylene carbonate (BC), etc. The ester solvent may include at least one of methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanoic acid lactone, mevalonate lactone, valerolactone, caprolactone, etc. 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, tetrahydrofuran, etc. In addition, the ketone solvent may include cyclohexanone, etc. The alcohol solvent may include at least one of ethanol, isopropanol, etc., and the aprotic solvent may include at least one of 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, etc.)); amides (such as dimethylformamide); dioxolanes (such as 1,3-dioxolane, 1,4-dioxolane, etc.); sulfolane, etc.

[0097] The nonaqueous organic solvent may be used alone or in combination of two or more solvents.

[0098] In an example, when a carbonate-based solvent is used, a cyclic carbonate and a chain carbonate may be mixed and used, and the cyclic carbonate and the chain carbonate may be mixed in a volume ratio of about 1:1 to about 1:9.

[0099] The lithium salt dissolved in the non-aqueous organic solvent can supply lithium ions in the battery, can ensure the basic operation of the rechargeable lithium battery, and can improve the transmission of lithium ions between the positive electrode and the negative electrode. For example, the lithium salt 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 F 2y+1SO2) (x and y are integers of 1 to 20), at least one of lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFBOP) and lithium bis(oxalato)borate (LiBOB).

[0100] 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.

[0101] Positive electrode active material

[0102] 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 including cobalt, manganese, nickel, or a combination thereof may be used.

[0103] The composite oxide may be or include a lithium transition metal composite oxide, and specific examples thereof may include lithium nickel-based oxides, lithium cobalt-based oxides, lithium manganese-based oxides, lithium iron phosphate-based compounds, cobalt-free lithium nickel manganese-based oxides, or combinations thereof.

[0104] As an example, any one or more of the compounds represented by any one of the following chemical formulas may be used: Li 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 L 1 d G eO2 (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, 0≤g≤0.5); Li (3-f) Fe2(PO4)3(0≤f≤2); and Li a FePO4(0.90≤a≤1.8).

[0105] In the above chemical formula, A is or includes Ni, Co, Mn or a combination thereof; X is or includes Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element or a combination thereof; D is or includes O, F, S, P or a combination thereof; G is or includes Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V or a combination thereof; and L 1 It is or includes Mn, Al or a combination thereof.

[0106] For example, the positive electrode active material may be or include a high nickel positive electrode active material, which has 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 positive electrode active material can achieve high capacity and can be applied to high capacity, high density rechargeable lithium batteries.

[0107] Positive electrode

[0108] 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.

[0109] For example, the positive electrode may further include a component that may constitute a sacrificial positive electrode.

[0110] The amount of the positive electrode active material may be about 90 wt % to about 99.5 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.

[0111] 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, nylon, etc. At least one, but not limited thereto.

[0112] The conductive material is configured to impart conductivity to the electrode, and any material that does not cause chemical changes and conducts electrons may be used in the battery. Examples of the conductive material may include: a carbon-based material (such as at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube); a metal-based material containing at least one of copper, nickel, aluminum, silver, etc. in the form of a metal powder or metal fiber; a conductive polymer (such as a polyphenylene derivative); or a mixture thereof.

[0113] Al foil may be included in the positive electrode current collector, but is not limited thereto.

[0114] Negative electrode active material

[0115] The negative electrode active material may include a material that reversibly intercalates / deintercalates lithium ions, lithium metal, a lithium metal alloy, a material capable of doping / dedoping lithium, or a transition metal oxide.

[0116] 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 or include graphite (such as amorphous, flaky, sheet-like, 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, calcined coke, etc.

[0117] Lithium metal alloys include alloys of lithium and at least one of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al and Sn.

[0118] The material capable of doping / de-doping lithium may be or include at least one of Si-based negative electrode active materials and Sn-based negative electrode active materials. The Si-based negative electrode active material may include silicon, silicon-carbon composite, SiO x (0 < x ≤ 2), at least one of Si-Q alloys (where Q is or includes 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, a rare earth element, or a combination thereof). The Sn-based negative electrode active material may include Sn, SnO2, SnO x (0 < x < 2), Sn-based alloys, or a combination thereof.

[0119] The silicon-carbon composite may be or include at least one of composites of silicon and amorphous carbon. According to an exemplary embodiment, the silicon-carbon composite may be in the following form or may include the following: silicon particles and amorphous carbon coated on the surface of the silicon particles. For example, the silicon-carbon composite may include secondary particles (cores) in which primary silicon particles are assembled 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 the amorphous carbon coating.

[0120] The silicon-carbon composite may further include crystalline carbon. For example, the silicon-carbon composite may include a core containing crystalline carbon and silicon particles, and amorphous carbon coated on the surface of the core.

[0121] 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.

[0122] Negative electrode

[0123] 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.

[0124] For example, 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.

[0125] The binder is configured to attach the negative electrode active material particles to each other and also 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.

[0126] The non-aqueous binder may be or include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide imide, polyimide, or a combination thereof.

[0127] The aqueous binder may be or include 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, polyvinyl alcohol or a combination thereof.

[0128] When the aqueous binder is used as the negative electrode binder, a cellulose compound (thickener) configured to impart 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.

[0129] The dry binder may be or include a polymer material that can be in fibrous form, and may be or include, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0130] The conductive material is configured to impart conductivity to the electrode, and any material that does not cause chemical changes and conducts electrons can be used for the battery. Examples of the conductive material may include: a carbon-based material (such as at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube); a metal-based material including at least one of copper, nickel, aluminum, silver, etc. in the form of a metal powder or metal fiber; a conductive polymer (such as a polyphenylene derivative); or a mixture thereof.

[0131] The negative electrode current collector may include copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or a combination thereof.

[0132] Diaphragm

[0133] 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 a polyethylene separator, a polypropylene separator, a polyvinylidene fluoride separator, or a multilayer film of two or more layers thereof (such as at least one of a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, a polypropylene / polyethylene / polypropylene three-layer separator, etc.).

[0134] 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.

[0135] 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 (such as Teflon), or copolymers or mixtures of two or more thereof.

[0136] The organic material may include a polyvinylidene fluoride-based polymer or a (meth)acrylic polymer.

[0137] The inorganic material may include inorganic particles including Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, or a combination thereof, but is not limited thereto.

[0138] 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.

[0139] Rechargeable lithium battery

[0140] The rechargeable lithium batteries may be classified into cylindrical batteries, prismatic batteries, pouch type batteries, coin type batteries, etc. according to their shapes. Figure 1 to Figure 4 A schematic diagram illustrating a rechargeable lithium battery according to some example embodiments. Figure 1 The cylindrical battery was explained. Figure 2 A prismatic battery is described, and Figure 3 and Figure 4 Pouch cell batteries are explained. Figure 1 to Figure 4 , the rechargeable lithium battery 100 includes an electrode assembly 40 and a case 50 including the electrode assembly 40, the battery assembly 40 including a separator 30 between a positive electrode 10 and a negative electrode 20. 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 4As shown in FIG. 1 , the rechargeable lithium battery 100 includes Figure 4 The electrode tab 70 is illustrated and may include Figure 3 The illustrated positive electrode tab 71 and the negative electrode tab 72 , the electrode tab 70 , the positive electrode tab 71 , and the negative electrode tab 72 form an electrical path for guiding current generated in the electrode assembly 40 to the outside of the battery 100 .

[0141] A rechargeable lithium battery according to example embodiments may be applied to, for example, automobiles, mobile phones, and / or various types of electronic devices, but the present disclosure is not limited thereto.

[0142] Examples and comparative examples of the present disclosure are described below. However, the following examples are merely examples of the present disclosure, and the present disclosure is not limited to the following examples.

[0143] Example:

[0144] Example 1

[0145] 1.15 M LiPF6 lithium salt was dissolved in a non-aqueous organic solvent of ethylene carbonate (EC), ethyl methyl carbonate (MEC), and diethyl carbonate (DEC) mixed in a volume ratio of 20:40:40 to prepare a basic electrolyte.

[0146] The electrolyte solution was prepared by adding Compound 1-a as a first compound and a compound represented by Chemical Formula 2-1 as a second compound to the above-mentioned basic electrolyte solution.

[0147] Compound 1-a:

[0148]

[0149] Chemical formula 2-1:

[0150]

[0151] Herein, 2 wt % of the first compound and 1 wt % of the second compound were added based on the total weight of the electrolyte.

[0152] LiNi as the positive electrode active material 0.91 Co 0.07 Al 0.02 O2, polyvinylidene fluoride as a binder, and Ketjen black as a conductive material were mixed at a weight ratio of 97:2:1, and then dispersed in N-methylpyrrolidone to prepare a positive electrode active material slurry.

[0153] The positive electrode active material slurry was coated on a 14 μm thick Al foil, dried at 110° C., and pressed, thereby manufacturing a positive electrode.

[0154] 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, thereby manufacturing a negative electrode.

[0155] 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 prismatic battery case and injecting the prepared electrolyte therein.

[0156] Example 2 to Example 15

[0157] Each rechargeable lithium battery cell according to Examples 2 to 15 was manufactured in substantially the same manner as Example 1, except that the contents of the first compound and the second compound were respectively changed as shown in Table 1 based on the total weight of the electrolyte.

[0158] Comparative Example 1

[0159] 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.

[0160] Comparative Example 2

[0161] 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.

[0162] Comparative Example 3

[0163] 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.

[0164] Evaluation example:

[0165] Evaluation Example 1: Evaluation of overcharge safety

[0166] The rechargeable lithium battery cells manufactured in Examples 1 to 15 and Comparative Examples 1 to 3 were evaluated for overcharge, and the results are shown in Table 1.

[0167] In addition, the overcharge evaluation results of the rechargeable lithium battery cells manufactured in Example 1 and Comparative Examples 1 to 3 are as follows: Figure 5shown.

[0168] After attaching a safety protection device to the negative electrode of each rechargeable lithium battery cell by welding and attaching a tab to the positive electrode, a thermocouple was attached and fixed to the center of the rechargeable lithium battery cell to measure the temperature.

[0169] Then, the rechargeable lithium battery cell prepared in a 4.2V fully charged state was charged to 6V at a rate of 1.0C and exposed at this voltage for 50 minutes. When the rechargeable lithium battery cell did not catch fire during the above exposure time and was in the same state as the rechargeable lithium battery cell before the evaluation, the rechargeable lithium battery cell was evaluated as "qualified", and when the rechargeable lithium battery cell caught fire during the above exposure time, the rechargeable lithium battery cell was evaluated as "unqualified". The results are shown in Table 1.

[0170] Referring to Table 1, in the case of Comparative Examples 1 and 3 in which the first compound was not added to the electrolyte, the rechargeable lithium battery cells caught fire when overcharged.

[0171] refer to Figure 5 In the case of Example 1, even if exposed in an overcharged state for 50 minutes, the temperature of the rechargeable lithium battery cell did not increase and remained constant, while in the cases of Comparative Examples 1 to 3, the temperature of the rechargeable lithium battery cell reached about 600°C in about 35 minutes, confirming that the rechargeable lithium battery cell caught fire.

[0172] Evaluation Example 2: Evaluation of high temperature (60°C) storage characteristics

[0173] For the rechargeable lithium battery cells according to Examples 1 to 15 and Comparative Examples 1 to 3, the initial direct current resistance (DC-IR) was measured as a ΔV / ΔI (voltage change / current change) value, such that the maximum energy state inside the rechargeable lithium battery cell became a fully charged state (SOC 100), and in this state, the rechargeable lithium battery cell was stored at a high temperature (60°C) for 90 days.

[0174] In addition, every 30 days, the rechargeable lithium battery cells were fully charged at room temperature (25°C), DC-IR was measured, and the high temperature DC-IR increase rate (%) was calculated according to the following equation 1. The rechargeable lithium battery cells for which DC-IR was measured were fully charged to 4.2V, SOC 100, and stored at high temperature (60°C).

[0175] Equation 1:

[0176] High temperature DC-IR increase rate = (DC-IR after (30 × n) days / initial DC-IR) × 100%

[0177] (n is a natural number in the range of 1 to 3)

[0178] The evaluation results of the high temperature storage characteristics measured above are shown in Tables 1 and Figure 6 The results of the high temperature DC-IR increase rate (%) in Table 1 show the case where n is 3.

[0179] Referring to Table 1, in the case of the rechargeable lithium battery cells of Comparative Examples 1 to 3, the high-temperature DC-IR increase rate of the rechargeable lithium battery cells after high-temperature storage is higher than that of the embodiment.

[0180] However, in the case of Comparative Example 3, due to the second compound, the high-temperature DC-IR increase rate is lower than those of the other Comparative Examples.

[0181] refer to Figure 6 , the rechargeable lithium battery cell of Example 1 has a high-temperature DC-IR increase rate significantly lower than those of Comparative Examples 1 to 3 after high-temperature storage.

[0182] Table 1

[0183]

[0184] Evaluation Example 3: Evaluation of cycle life characteristics at room temperature (25°C)

[0185] For the rechargeable lithium battery cells manufactured in Examples 1 to 15, the cycle life characteristics at room temperature (25°C) were evaluated. Specifically, the rechargeable lithium battery cells were charged at 0.33C and discharged at 0.5C for 800 cycles in the range of 2.8V to 4.2V to calculate the ratio of the discharge capacity after the 800th cycle to the discharge capacity after the 1st cycle as the room temperature capacity retention rate (%), and the results are shown in Table 2.

[0186] Table 2

[0187] Room temperature (25°C) capacity retention rate (%) Example 1 90.2 Example 2 90.3 Example 3 90.4 Example 4 90.3 Example 5 90.4 Example 6 90.1 Example 7 89.5 Example 8 81.3 Example 9 90.2 Example 10 90.3 Embodiment 11 90.2 Example 12 90.1 Example 13 90.3 Embodiment 14 88.7 Embodiment 15 79.1

[0188] Referring to Table 2, the rechargeable lithium battery cells manufactured in Examples 1 to 15 have the desired or improved overcharge safety and high temperature storage characteristics as described above, while the room temperature cycle life characteristics (i.e., room temperature capacity retention rate) are mostly advantageously maintained at about 90%.

[0189] While the disclosure has been described in connection with what are presently considered to be practical example embodiments, it is to be understood that the disclosure is not limited to the disclosed 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 represented by Chemical Formula 2: Chemical formula 1: Chemical formula 2: Wherein, in Chemical Formula 1, R 1 and R 2 Each independently includes 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, The term "substituted" refers to the replacement of at least one hydrogen of the substituent by deuterium, halogen, hydroxyl, amino, C1-C30 amine, nitro, C1-C40 silyl, C1-C30 alkyl, C1-C10 alkylsilyl, C6-C30 arylsilyl, C3-C30 cycloalkyl, C3-C30 heterocycloalkyl, C6-C30 aryl, C2-C30 heteroaryl, C1-C20 alkoxy, C1-C10 fluoroalkyl, cyano or a combination thereof, In Chemical Formula 2, A1, A2, A3 and A4 each independently include a single bond, an unsubstituted or substituted C1-C5 alkylene group, a carbonyl group or a sulfinyl group, provided that A1 and A2 are not single bonds at the same time or simultaneously, and A3 and A4 are not single bonds at the same time or simultaneously, The substituents of the C1-C5 alkylene are selected from halogen, C1-C20 alkyl unsubstituted or substituted by halogen, C2-C20 alkenyl unsubstituted or substituted by halogen, C2-C20 alkynyl unsubstituted or substituted by halogen, C3-C20 cycloalkenyl unsubstituted or substituted by halogen, C3-C20 heterocyclyl unsubstituted or substituted by halogen, C6-C40 aryl unsubstituted or substituted by halogen and C2-C40 heteroaryl unsubstituted or substituted by halogen.

2. The electrolyte according to claim 1, wherein The compound represented by 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 1a including substituted or unsubstituted C1-C20 alkyl groups, and H a ~H e Each independently includes 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 independently includes 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.

3. The electrolyte according to claim 1, wherein The first compound represented by Chemical Formula 1 includes one or more of the compounds listed in Group 1: Group 1:

4. The electrolyte according to claim 1, wherein the second compound represented by Chemical Formula 2 comprises one or more of the compounds represented by Chemical Formula 2-1 to Chemical Formula 2-7: Chemical formula 2-1: Chemical formula 2-2: Chemical formula 2-3: Chemical formula 2-4: Chemical formula 2-5: Chemical formula 2-6: Chemical formula 2-7: 5 . The electrolyte of claim 1 , wherein the first compound is included in an amount of greater than 0.05 wt % and less than 6 wt % based on the total weight of the electrolyte. 6 . The electrolyte of claim 1 , wherein the second compound is included in an amount of greater than 0.05 wt % and less than 6 wt % based on the total weight of the electrolyte. 7 . The electrolyte of claim 1 , wherein the first compound and the second compound are included in a weight ratio of 0.01:1 to 100:

1.

8. 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; and The electrolyte according to any one of claims 1 to 7.

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