Electrolyte solution for lithium secondary battery, and lithium secondary battery

Abstract

To provide an electrolyte solution for a lithium secondary battery with excellent safety against overcharging and under thermal exposure.SOLUTION: An electrolyte solution for a lithium secondary battery in an embodiment includes a nonaqueous organic solvent, a lithium salt, and an additive. The additive includes a first compound expressed by Chemical Formula 1 below, and a second compound that is a nitrile compound containing three or more cyano groups. In Chemical Formula 1, R1 and R2 independently represent a substituted or non-substituted alkyl group with 1 to 20 carbons, or a substituted or non-substituted aryl group with 6 to 30 carbons, and any one or more of R1 and R2 represent a substituted or non-substituted aryl group with 6 to 30 carbons.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an electrolyte for a lithium secondary battery and a lithium secondary battery including the same.

Background Art

[0002] Recently, with the rapid spread of electronic devices using batteries such as mobile phones, notebook computers, and electric vehicles, the demand for secondary batteries with high energy density and high capacity has been rapidly increasing. Accordingly, research and development for improving the performance of lithium secondary batteries have been actively conducted.

[0003] A lithium secondary battery is a battery including a positive electrode and a negative electrode containing an active material capable of insertion (intercalation) and desorption (deintercalation) of lithium ions, and an electrolyte, and produces electrical energy by oxidation and reduction reactions when lithium ions are inserted / desorbed at the positive electrode and the negative electrode.

[0004] Recently, lithium secondary batteries with high capacity, high energy density, and high safety have been actively studied for use as a driving power source for hybrid vehicles and electric vehicles, or a power storage power source.

[0005] In a lithium secondary battery, the electrolyte plays an important role in transmitting lithium ions and can exhibit very high ionic conductivity by containing an organic solvent and a lithium salt. Such an electrolyte plays an important role in determining the safety and performance of a lithium secondary battery.

[0006] When a lithium secondary battery is exposed to an overcharged state or high-temperature heat, the battery rapidly generates heat and gas, and the safety of the battery due to cell explosion or the like has become a problem.

[0007] Therefore, development of an electrolyte for realizing a battery excellent in safety even under overcharge and heat exposure is required.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0009] One embodiment of the present invention provides an electrolyte for a lithium secondary battery that is excellent in safety under overcharge and thermal exposure.

[0010] Another embodiment of the present invention provides a lithium secondary battery including the electrolyte.

Means for Solving the Problems

[0011] One embodiment of the present invention provides an electrolyte for a lithium secondary battery, which includes a non-aqueous organic solvent, a lithium salt, and an additive, wherein the additive includes a first compound represented by the following Chemical Formula 1 and a second compound that is a nitrile compound containing three or more cyano groups.

[0012]

Chem.

[0013] In Chemical Formula 1, R 1 and R 2 are each independently a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms or a substituted or unsubstituted aryl group having 6 to 30 carbon atoms, and at least one of R 1 and R 2 is a substituted or unsubstituted aryl group having 6 to 30 carbon atoms.

[0014] Another embodiment of the present invention provides a lithium secondary battery including a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, a separator positioned between the positive electrode and the negative electrode, and the electrolytic solution.

Advantages of the Invention

[0015] The electrolytic solution for a lithium secondary battery according to one embodiment of the present invention can realize a battery excellent in safety under overcharge and thermal exposure.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Modes for Carrying Out the Invention

[0017] Hereinafter, embodiments of the present invention will be described in detail. However, this is presented as an example, and the present invention is not limited thereby. The present invention is defined only by the scope of the claims described later.

[0018] Unless otherwise specifically mentioned in this specification, when a part such as a layer, a film, a region, a plate, etc. is "on" another part, this includes not only the case where it is "directly on" another part but also the case where there are other parts in between.

[0019] Unless otherwise specified in this specification, singular forms can include plural forms. At the same time, unless otherwise specified, "A or B" can mean "including A, or including B, or including both A and B".

[0020] As used herein, "these combinations" can mean a mixture of components, a laminate, a composite, a copolymer, an alloy, a blend, and a reaction product, etc.

[0021] Unless otherwise defined herein, the particle size can be the average particle size. Also, the particle size means the average particle size (D50) which is the diameter of the particle with a cumulative volume of 50% in the particle size distribution. The average particle size (D50) measurement can be carried out by methods widely known to those skilled in the art. For example, it can be measured with a particle size analyzer, or it can also be measured from a transmission electron microscope (TEM) photograph or a scanning electron microscope (SEM) photograph. As another method, it can be measured using a measuring device employing the dynamic light-scattering method. After measuring and performing data analysis to count the number of particles for each particle size range, the average particle size (D50) value can then be calculated. Or it can be measured using the laser diffraction method. When measuring by the laser diffraction method, more specifically, after dispersing the particles to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (for example, MT3000 manufactured by Microtrac), irradiated with ultrasonic waves of about 28 kHz at an output of 60 W, and then the average particle size (D50) at the 50% standard of the particle size distribution in the measuring device can be calculated.

[0022] Here, unless otherwise defined, "substituted" means that at least one hydrogen in a substituent or a compound is substituted with deuterium, a halogen group, a hydroxy group, an amino group, an amine group having 1 to 30 carbon atoms, a nitro group, a silyl group having 1 to 40 carbon atoms, an alkyl group having 1 to 30 carbon atoms, an alkylsilyl group having 1 to 10 carbon atoms, an arylsilyl group having 6 to 30 carbon atoms, a cycloalkyl group having 3 to 30 carbon atoms, a heterocycloalkyl group having 3 to 30 carbon atoms, an aryl group having 6 to 30 carbon atoms, a heteroaryl group having 2 to 30 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a fluoroalkyl group having 1 to 10 carbon atoms, a cyano group, or a combination thereof.

[0023] Specifically, "substituted" can mean that at least one hydrogen in a substituent or a compound is substituted with deuterium, a halogen group, an alkyl group having 1 to 30 carbon atoms, an alkylsilyl group having 1 to 10 carbon atoms, an arylsilyl group having 6 to 30 carbon atoms, a cycloalkyl group having 3 to 30 carbon atoms, a heterocycloalkyl group having 3 to 30 carbon atoms, an aryl group having 6 to 30 carbon atoms, a heteroaryl group having 2 to 30 carbon atoms, a fluoroalkyl group having 1 to 10 carbon atoms, or a cyano group. For example, "substituted" can mean that at least one hydrogen in a substituent or a compound is substituted with deuterium, a halogen group, an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 30 carbon atoms, a fluoroalkyl group having 1 to 10 carbon atoms, or a cyano group. Or, "substituted" can mean that at least one hydrogen in a substituent or a compound is substituted with deuterium, a halogen group, an alkyl group having 1 to 5 carbon atoms, an aryl group having 6 to 18 carbon atoms, a fluoroalkyl group having 1 to 5 carbon atoms, or a cyano group. As an example, "substituted" can mean that at least one hydrogen in a substituent or a compound is substituted with deuterium, a cyano group, a halogen group, a methyl group, an ethyl group, a propyl group, a butyl group, a phenyl group, a biphenyl group, a terphenyl group, a trifluoromethyl group, or a naphthyl group.

[0024] The electrolyte for a lithium secondary battery according to an embodiment includes a non-aqueous organic solvent, a lithium salt, and an additive, and the additive includes a first compound and a second compound. The first compound and the second compound will be described in detail below.

[0025] When the first compound and the second compound are used in combination, it is possible to effectively realize both the stability of the battery under overcharge and the safety of the battery under thermal exposure.

[0026] Compound 1 The first compound is a sulfoxide-based compound and plays a role in effectively suppressing the heat generation temperature of the battery under overcharge driving conditions.

[0027] The first compound is represented by the following Chemical Formula 1.

[0028]

Chemical Formula

[0029] In Chemical Formula 1, R 1 and R 2 are each independently a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 30 carbon atoms, and one or more of R 1 and R 2 is a substituted or unsubstituted aryl group having 6 to 30 carbon atoms.

[0030] In one embodiment, Chemical Formula 1 is represented by the following Chemical Formula 1-1 or Chemical Formula 1-2. As the most specific example, Chemical Formula 1 is represented by the following Chemical Formula 1-1.

[0031]

Chemical Formula

[0032] In Chemical Formula 1-1, R 1ais a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, H a ~H e each independently may be hydrogen, a halogen group, a hydroxy group, a cyano group, a nitro group, a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 20 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 20 carbon atoms, a substituted or unsubstituted alkynyl group having 2 to 20 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 20 carbon atoms, a substituted or unsubstituted aryl group having 6 to 20 carbon atoms or a substituted or unsubstituted heteroaryl group having 2 to 20 carbon atoms.

[0033] As a specific example, H a ~H e each independently may be hydrogen, a halogen group, a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, or a substituted or unsubstituted alkoxy group having 1 to 20 carbon atoms.

[0034]

Chemical formula

[0035] In the above Chemical formula 1-2, H a ~H j each independently may be hydrogen, a halogen group, a hydroxy group, a cyano group, a nitro group, a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 20 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 20 carbon atoms, a substituted or unsubstituted alkynyl group having 2 to 20 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 20 carbon atoms, a substituted or unsubstituted aryl group having 6 to 20 carbon atoms, or a substituted or unsubstituted heteroaryl group having 2 to 20 carbon atoms.

[0036] As a specific example, H a ~H jEach may independently be hydrogen, a halogen group, a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, or a substituted or unsubstituted alkoxy group having 1 to 20 carbon atoms.

[0037] As an example, the first compound may be any one or more selected from the compounds listed in Group 1 below.

[0038]

Chemical formula

[0039] In one embodiment, the first compound may be contained in an amount of more than 0.05% by weight or 0.1% by weight or more, and less than 6% by weight or 5% by weight or less, based on the total weight of the electrolyte for a lithium secondary battery.

[0040] As a specific example, the first compound may be contained in an amount of more than 0.05% by weight and less than 6% by weight, for example, more than 0.05% by weight and 5% by weight or less, 0.1% by weight or more and less than 6% by weight, or 0.1% by weight or more and 5% by weight or less, based on the total weight of the electrolyte for a lithium secondary battery.

[0041] When the first compound is contained in an amount of 0.05% by weight or less based on the total weight of the electrolyte for a lithium secondary battery, the effect of improving the battery safety during overcharging is negligible. When it is contained in an amount of 6% by weight or more, there are problems such as excessive increase in the battery thickness or excessive increase in the battery resistance.

[0042] Compound 2 The second compound is a nitrile compound containing three or more cyano groups (-CN), and plays a role in improving the battery safety when the lithium secondary battery is exposed to high temperatures.

[0043] The second compound is represented by the following Chemical formula 2.

[0044]

Chemical formula

[0045] In Chemical Formula 2, L is a substituted linear or branched alkylene group having 1 to 20 carbon atoms, and the substituted alkylene group may be one in which at least one hydrogen of the alkylene is substituted with a cyano group (-CN).

[0046] As an example, the substituted alkylene group may be one in which at least one hydrogen of the alkylene is further substituted with an isocyano group (-NC) or a thiocyanato group (-SCN).

[0047] As an example, the second compound may be any one or more selected from the compounds listed in Group 2 below.

[0048]

Chemical Formula

[0049] According to a most specific embodiment, the additive contained in the electrolyte for a lithium secondary battery may be a composition containing at least one of the compounds listed in Group 1 as the first compound and at least one of the compounds listed in Group 2 as the second compound.

[0050] As an example, the additive contained in the electrolyte for a lithium secondary battery may be a composition containing Compound 1-a in Group 1 as the first compound and Compound 2-a as the second compound.

[0051] In one embodiment, the second compound may be contained in an amount of more than 0.05% by weight or 0.1% by weight or more, and less than 6% by weight or 5% by weight or less based on the total weight of the electrolyte for a lithium secondary battery.

[0052] As a specific example, the second compound may be contained in an amount of more than 0.05% by weight and less than 6% by weight based on the total weight of the electrolyte for a lithium secondary battery. For example, it may be contained in an amount of more than 0.05% by weight and 5% by weight or less, more than 0.1% by weight and less than 6% by weight, or more than 0.1% by weight and 5% by weight or less.

[0053] When the second compound is contained in an amount of 0.05% by weight or less based on the total weight of the electrolyte for a lithium secondary battery, the effect of improving the safety of the battery during thermal exposure is negligible. When it is contained in an amount of 6% by weight or more, there is a problem that the resistance of the battery increases excessively.

[0054] In one embodiment, the first compound and the second compound may be contained in a weight ratio of 0.01:1 to 50:1, 0.01:1 to 40:1, 0.05:1 to 40:1, or 0.05:1 to 20:1.

[0055] When the weight ratio of the first compound and the second compound satisfies the above numerical range, a battery with excellent safety under overcharge and thermal exposure can be realized.

[0056] The electrolyte for a lithium secondary battery contains a non-aqueous organic solvent and a lithium salt.

[0057] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0058] The non-aqueous organic solvent may be a carbonate-based, ester-based, ether-based, ketone-based, or alcohol-based solvent, an aprotic solvent, or a combination thereof.

[0059] As the carbonate solvent, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. can be used. As the ester solvent, methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate (EP), propyl propionate (PP), decanolide, mevalonolactone, valerolactone, caprolactone, etc. can be used. As the ether solvent, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. can be used. Further, as the ketone solvent, cyclohexanone, etc. can be used. As the alcohol solvent, ethyl alcohol, isopropyl alcohol, etc. can be used, and as the aprotic solvent, nitriles such as R-CN (R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may contain a double bond, an aromatic ring, or an ether group), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, 1,4-dioxolane, sulfolane, etc. can be used.

[0060] The non-aqueous organic solvent can be used alone or in combination of two or more.

[0061] Also, when using a carbonate solvent, a cyclic carbonate and a chain carbonate can be mixed and used, and the cyclic carbonate and the chain carbonate can be mixed at a volume ratio of 1:1 to 1:9.

[0062] The lithium salt is dissolved in an organic solvent, acts as a source of lithium ions in the battery to enable the operation of a basic lithium secondary battery, and plays a role in promoting the movement of lithium ions between the positive electrode and the negative electrode. Representative examples of lithium salts include LiPF 6 、LiBF 4 、LiSbF 6 、LiAsF 6 、LiClO 4 、LiAlO 2 、LiAlCl 4 、LiPO 2 F 2 、LiCl、LiI、LiN(SO 3 C 2 F 5 ) 2 、Li(FSO 2 ) 2 N (lithium bis(fluorosulfonyl)imide (LiFSI), LiC 4 F 9 SO 3 、LiN(C x F 2x+1 SO 2 )(C y F 2y+1 SO 2 )(x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalate)phosphate (LiDFOB), and lithium bis(oxalate)borate (LiBOB), and can include one or more selected therefrom.

[0063] A lithium secondary battery according to another embodiment includes a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, a separator positioned between the positive electrode and the negative electrode, and the electrolyte described above.

[0064] Positive electrode active material As the positive electrode active material, a compound capable of reversible intercalation and deintercalation of lithium (lithiated intercalation compound) can be used. Specifically, one or more of composite oxides of metals selected from cobalt, manganese, nickel, and combinations thereof and lithium can be used.

[0065] The composite oxide may be a lithium transition metal composite oxide. Specific examples include lithium nickel-based oxides, lithium cobalt-based oxides, lithium manganese-based oxides, lithium iron phosphate-based compounds, cobalt-free nickel-manganese-based oxides, or combinations thereof.

[0066] As an example, a compound represented by any one of the following chemical formulas can be used. Li a A 1-b X b O 2-c D c (0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05), Li a Mn 2-b X b O 4-c D c (0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05), Li a Ni 1-b-c Co b X c O 2-α D α (0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.5, 0 < α < 2), Li a Ni 1-b-c Mn b X c O 2-α D α (0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.5, 0 < α < 2), Li a Ni b Co c L 1 d GeO 2 (0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.9, 0 ≦ c ≦ 0.5, 0 ≦ d ≦ 0.5, 0 ≦ e ≦ 0.1), Lia NiG b O 2 (0.90 ≦ a ≦ 1.8, 0.001 ≦ b ≦ 0.1), Li a CoG b O 2 (0.90 ≦ a ≦ 1.8, 0.001 ≦ b ≦ 0.1), Li a Mn 1-b G b O 2 (0.90 ≦ a ≦ 1.8, 0.001 ≦ b ≦ 0.1), Li a Mn 2 G b O 4 (0.90 ≦ a ≦ 1.8, 0.001 ≦ b ≦ 0.1), Li a Mn 1-g G g PO 4 (0.90 ≦ a ≦ 1.8, 0 ≦ g ≦ 0.5), Li (3-f) Fe 2 (PO 4 ) 3 (0 ≦ f ≦ 2), Li a FePO 4 (0.90 ≦ a ≦ 1.8).

[0067] In the above chemical formula, A is Ni, Co, Mn, or a combination thereof, X is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof, D is O, F, S, P, or a combination thereof, G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof, and L 1 is Mn, Al, or a combination thereof.

[0068] As an example, the positive electrode active material may be a high-nickel-based positive electrode active material in which the content of nickel with respect to 100 mol% of the metal excluding lithium in the lithium transition metal composite oxide is 80 mol% or more, 85 mol% or more, 90 mol% or more, 91 mol% or more, or 94 mol% or more and 99 mol% or less. The high-nickel-based positive electrode active material can achieve a high capacity and can be applied to a high-capacity, high-density lithium secondary battery.

[0069] Positive electrode The positive electrode for a lithium secondary battery can include a current collector and a positive electrode active material layer formed on the current collector. The positive electrode active material layer contains a positive electrode active material and can further contain a binder and / or a conductive material.

[0070] As an example, the positive electrode can further contain an additive that can serve as a sacrificial positive electrode.

[0071] The content of the positive electrode active material is 90% by weight or more and 99.5% by weight or less based on 100% by weight of the positive electrode active material layer, and the contents of the binder and the conductive material may each be 0.5% by weight or more and 5% by weight or less based on 100% by weight of the positive electrode active material layer.

[0072] The binder serves to well adhere the positive electrode active material particles to each other and also to well adhere the positive electrode active material to the current collector. Representative examples of the binder include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, 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.

[0073] The conductive material is used to impart conductivity to the electrode, and in the configured battery, any material can be used as long as it is an electron conductive material that does not cause a chemical change. Examples of the conductive material include carbon-based substances such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, carbon nanotube, etc., metal-based substances in the form of metal powder or metal fiber containing copper, nickel, aluminum, silver, etc., conductive polymers such as polyphenylene derivatives, or mixtures thereof.

[0074] As the current collector, Al can be used, but it is not limited thereto.

[0075] Negative electrode active material The negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and undoping lithium, or a transition metal oxide.

[0076] The material capable of reversibly intercalating / deintercalating the lithium ions can be a carbon-based negative electrode active material, and can include, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, fired coke, and the like.

[0077] As the alloy of the lithium metal, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0078] As the material capable of doping and undoping lithium, an Si-based negative electrode active material or an Sn-based negative electrode active material can be used. The Si-based negative electrode active material can be silicon, a silicon-carbon composite, SiO x (0 < x < 2), an Si-Q alloy (wherein Q is selected from an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element (excluding Si), a Group 15 element, a Group 16 element, a transition metal, a rare earth element, and combinations thereof), or a combination thereof. As the Sn-based negative electrode active material, Sn, SnO 2 , an Sn-based alloy, or a combination thereof may be used.

[0079] The silicon-carbon composite may be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite may be in a form in which silicon particles are coated with amorphous carbon on the surface of the silicon particles. For example, it may include secondary particles (cores) formed by granulating primary silicon particles and an amorphous carbon coating layer (shell) located on the surface of the secondary particles. The amorphous carbon is also located between the primary silicon particles, for example, the primary silicon particles are coated with amorphous carbon. The secondary particles may be dispersed and present in an amorphous carbon matrix.

[0080] 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 an amorphous carbon coating layer located on the surface of the core.

[0081] The Si-based negative electrode active material or the Sn-based negative electrode active material can be used by mixing with a carbon-based negative electrode active material.

[0082] Negative electrode The negative electrode for a lithium secondary battery includes a current collector and a negative electrode active material layer located on the current collector. The negative electrode active material layer contains a negative electrode active material and may further contain a binder and / or a conductive material.

[0083] For example, the negative electrode active material layer can contain 90% by weight or more and 99% by weight or less of the negative electrode active material, 0.5% by weight or more and 5% by weight or less of the binder, and 0% by weight or more and 5% by weight or less of the conductive material.

[0084] The binder serves to well adhere the negative electrode active material particles to each other and also well adhere the negative electrode active material to the current collector. As the binder, a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof can be used.

[0085] Examples of the non-aqueous binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene-propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

[0086] The aqueous binder may be selected from 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, and combinations thereof.

[0087] When an aqueous binder is used as the negative electrode binder, a cellulose-based compound capable of imparting viscosity can be further included. Examples of the cellulose-based compound include carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or alkali metal salts thereof, and one or more of these can be mixed and used. As the alkali metal, Na, K, or Li can be used.

[0088] The dry binder is a polymer substance capable of being fibrillated, and may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or combinations thereof.

[0089] The conductive material is used to impart conductivity to the electrode, and in the configured battery, any material can be used as long as it is an electron conductive material that does not cause a chemical change. Specific examples include carbon-based substances such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, carbon nanotube, etc., metal-based substances in the form of metal powder or metal fiber including copper, nickel, aluminum, silver, etc., conductive polymers such as polyphenylene derivatives, or mixtures thereof.

[0090] As the negative electrode current collector, those selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof can be used.

[0091] Separator Depending on the type of lithium secondary battery, a separator may exist between the positive electrode and the negative electrode. As such a separator, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof can be used. Of course, mixed multilayer films such as a two-layer separator of polyethylene / polypropylene, a three-layer separator of polyethylene / polypropylene / polyethylene, and a three-layer separator of polypropylene / polyethylene / polypropylene can be used.

[0092] The separator can include a porous substrate and a coating layer located on one or both sides of the porous substrate and containing an organic substance, an inorganic substance, or a combination thereof.

[0093] The porous substrate may be a polymer film formed from any one polymer selected from polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyether ketone, polyaryl ether ketone, polyether imide, polyamide imide, polybenzimidazole, polyether sulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon (registered trademark), and polytetrafluoroethylene, or a copolymer or mixture of two or more of these.

[0094] The organic substance may include a polyvinylidene fluoride-based polymer or a (meth)acrylic-based polymer.

[0095] The inorganic substance is Al 2 O 3 、SiO 2 、TiO 2 、SnO 2 、CeO 2 、MgO, NiO, CaO, GaO, ZnO, ZrO 2 、Y 2 O 3 、SrTiO 3 、BaTiO 3 、Mg(OH) 2 、boehmite, and inorganic particles selected from combinations thereof, but not limited thereto.

[0096] The organic substance and the inorganic substance may be present mixed in one coating layer, or may be present in a form in which a coating layer containing the organic substance and a coating layer containing the inorganic substance are laminated.

[0097] Lithium secondary battery Lithium secondary batteries are classified into cylindrical, square, pouch, coin, etc. according to their form. FIGS. 1 to 4 are schematic views showing a lithium secondary battery according to an embodiment, where FIG. 1 shows a cylindrical form, FIG. 2 shows a square form, and FIGS. 3 and 4 can show a pouch form of the battery. Referring to FIGS. 1 to 4, the lithium secondary battery 100 can include an electrode assembly 40 with a separator 30 interposed between a positive electrode 10 and a negative electrode 20, and a case 50 in which the electrode assembly 40 is built-in. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolytic solution (not shown). The lithium secondary battery 100 can include a sealing member 60 for sealing the case 50 as shown in FIG. 1. Also, in FIG. 2, the lithium secondary battery 100 can include a positive electrode lead tab 11, a positive electrode terminal 12, a negative electrode lead tab 21, and a negative electrode terminal 22. As shown in FIGS. 3 and 4, the lithium secondary battery 100 can include electrode tabs 70, i.e., a positive electrode tab 71 and a negative electrode tab 72, which serve as electrical paths for guiding the current formed by the electrode assembly 40 to the outside.

[0098] The lithium secondary battery according to an embodiment of the present invention can be applied to automobiles, mobile phones, and / or various forms of electrical devices, etc., and the present invention is not limited thereto.

[0099] Hereinafter, examples and comparative examples of the present invention will be described. However, the following examples are merely one embodiment of the present invention, and the present invention is not limited to the following embodiments.

Example

[0100] Example 1 1.3 M LiPF was added to a non-aqueous organic solvent in which ethylene carbonate (EC), propylene carbonate (PC), ethyl propionate (EP), and propyl propionate (PP) were mixed in a volume ratio of 10:15:30:45 in sequence. 6 A lithium salt was dissolved to prepare a basic electrolytic solution.

[0101] The following Compound 1-a was added as the first compound and the following Compound 2-a was added as the second compound to the basic electrolyte to prepare an electrolyte.

[0102]

Chemical formula

Chemical formula

[0103] At this time, the first compound is contained at 2% by weight and the second compound is contained at 3% by weight with respect to the entire electrolyte.

[0104] LiCoO as the positive electrode active material 2 , polyvinylidene fluoride as the binder, and Ketjen black as the conductive material were mixed at a weight ratio of 97:2:1, respectively, and dispersed in N-methylpyrrolidone to produce a positive electrode active material slurry.

[0105] The positive electrode active material slurry was coated on an Al foil with a thickness of 10 μm, dried at 110 °C, and then rolled to produce a positive electrode.

[0106] Artificial graphite as the negative electrode active material, styrene-butadiene rubber as the binder, and carboxymethyl cellulose as the thickener were mixed at a weight ratio of 97:1:2, respectively, and dispersed in distilled water to produce a negative electrode active material slurry. The negative electrode active material slurry was coated on a Cu foil current collector with a thickness of 10 μm, dried at 100 °C, and then rolled to produce a negative electrode.

[0107] An electrode assembly was manufactured with a separator having a polyethylene-polypropylene multilayer structure with a thickness of 25 μm between the positive electrode and the negative electrode manufactured above, inserted into a pouch-type battery case, and then the manufactured electrolyte was injected to fabricate the lithium secondary battery of Example 1.

[0108] Examples 2 to 9 Lithium secondary batteries according to Examples 2 to 9 were manufactured in the same manner as in Example 1, except that the contents of the first compound and the second compound were adjusted as shown in Table 1 below with respect to the entire electrolyte.

[0109] Comparative Example 1 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the first compound and the second compound were not added to the electrolyte.

[0110] Comparative Example 2 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the second compound was not added during the production of the electrolyte.

[0111] Comparative Example 3 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the first compound was not added during the production of the electrolyte.

[0112]

Table 1

[0113] (Evaluation Example) Evaluation Example 1: Overcharge safety evaluation Overcharge evaluation was performed on the lithium secondary batteries manufactured in Examples 1 to 9 and Comparative Examples 1 to 3, and the results are shown in Table 2 and FIG. 5 below.

[0114] A safety protection element is welded to the negative electrode portion of the lithium secondary battery cell, a tab is welded to the positive electrode portion, and a thermocouple is attached to the middle portion of the cell and fixed so that temperature measurement is possible.

[0115] Thereafter, after surrounding the cell well with a heat insulating material, the cell is charged at a rate-determining rate of 2.0C until it reaches 10V, and is exposed at the said voltage for 450 minutes.

[0116] After conducting a total of three experiments, if the battery does not catch fire during the exposure time and is in the same state as the battery before evaluation, it is evaluated as "P (Pass)", and if the battery catches fire, it is evaluated as "F (Fail)", as shown in Table 2 below.

[0117] Also, the overcharge evaluation results of the lithium secondary batteries of Example 1 and Comparative Examples 1 to 3 are shown graphically in Figure 5. In Figure 5, the line located relatively at the upper end indicates the voltage change over time, and the line located relatively at the lower end indicates the temperature change over time.

[0118] Referring to Table 2, in the case of Comparative Examples 1 and 3 where the first compound was not added to the electrolytic solution, it can be confirmed that the temperature of the cell increased to 200 °C between about 350 and 400 minutes, and the voltage of the cell reached 10 V. When the voltage of the cell reaches 10 V, it means that the cell explodes and the potential difference between the positive electrode and the negative electrode cannot be measured.

[0119] Referring to Figure 5, in the case of Example 1, even when exposed to an overcharged state for 450 minutes, the temperature of the battery does not increase and remains constant. On the other hand, in Comparative Example 1, the temperature of the battery increased to about 200 °C at about 370 minutes, and in Comparative Example 3, the temperature of the battery increased to about 175 °C at about 380 minutes.

[0120] Evaluation Example 2: Thermal exposure safety evaluation For the lithium secondary batteries manufactured in Examples 1 to 9 and Comparative Examples 1 to 3, after being fully charged at a charging rate of 0.5C in a discharged state of 3.0V under a cut-off condition of 4.47V / 3hr, a thermal exposure evaluation was conducted.

[0121] After placing the lithium secondary batteries manufactured in Examples 1 to 9 and Comparative Examples 1 to 3 in a chamber, starting from room temperature (25 °C), the temperature was increased at a rate of 5 °C per minute to 140 °C, 141 °C, 142 °C, 143 °C, 144 °C, and 145 °C, and the changes in the lithium secondary batteries were observed while maintaining the temperature at the above temperatures for about 1 hour.

[0122] After conducting a total of three experiments, if thermal runaway does not occur while maintaining the temperature, it is displayed as "P (Pass)", and if it is exposed to high temperature and rapid thermal runaway occurs, it is displayed as "F (Fail)" and shown in Table 2 below.

[0123] In addition, the thermal exposure evaluation results at 143 °C for the lithium secondary batteries manufactured in Example 1 and Comparative Examples 1 to 3 are shown graphically in Fig. 6. In Fig. 6, the line located relatively at the upper end indicates the voltage change over time, and the line located relatively at the lower end indicates the temperature change over time.

[0124] Referring to Table 2, in the case of Comparative Examples 1 and 2 where the second compound is not added to the electrolyte, it can be confirmed that thermal runaway occurs during thermal exposure at 141 °C.

[0125] Referring to Fig. 6, a rapid voltage drop is observed in the lithium secondary batteries according to Example 1 and Comparative Examples 1 to 3. If the pouch-type battery is rapidly exposed to high temperature, gas is generated and the internal pressure increases, causing the battery protection circuit (CID) to operate and the voltage to drop rapidly. From the occurrence of the rapid voltage drop, it can be seen that the protection circuit of the lithium secondary batteries according to Example 1 and Comparative Examples 1 to 3 has operated due to gas generation caused by high temperature exposure.

[0126] Specifically, it can be confirmed that the lithium secondary battery according to Example 1 does not experience thermal runaway while maintaining the temperature at 143 °C even when exposed to a temperature of 143 °C.

[0127] On the contrary, it can be confirmed that in Comparative Example 1, the battery temperature rises to about 450 °C or more at about 35 minutes, and in Comparative Example 2, the battery temperature rises to about 370 °C or more at about 36 minutes.

[0128]

Table 2

[0129] (In Table 2 above, the parts marked with "-" mean that it is not necessary to conduct further evaluation after thermal runaway (Fail), or that thermal runaway does not occur at a specific temperature (Pass) and it is not necessary to conduct evaluation at temperatures below that.)

[0130] Evaluation Example 3: Alternative Current-Internal Resistance (AC-IR) evaluation For the pouch cell-shaped lithium secondary batteries manufactured in Examples 1 to 9, the cell thickness (mm) and the alternating current - internal resistance (AC-IR, mΩ) at a state of charge (SOC, state of charge = 100%) were measured and are shown in Table 3 below.

[0131]

Table 3

[0132] Referring to Table 3, in the case of the examples, it can be confirmed that the cell thickness is 6.04 mm or less. In particular, it can be confirmed that the cell thickness characteristics are excellent in Examples 2, 3, 8, and 9.

[0133] Also, referring to Table 3, it can be confirmed that the alternating current - internal resistance (AC-IR) of the examples is 29.3 mΩ or less. In particular, it can be confirmed that the AC-IR is low in Examples 2, 3, 6, and 7.

[0134] As described above, the preferred embodiments of the present invention have been explained. However, the present invention is not limited thereto, and various modifications can be made and implemented within the scope of the claims, the detailed description of the invention, and the attached drawings, and it is natural that this also belongs to the scope of the present invention.

Description of Reference Numerals

[0135] 100: Lithium secondary battery 10: Positive electrode 11: Positive electrode lead tab 12: Positive electrode terminal 20: Negative electrode 21: Negative electrode lead tab 22: Negative electrode terminal 30: Separator 40: Electrode assembly 50: Case 60: Sealing member 70: Electrode tab 71: Positive electrode tab 72: Negative electrode tab

Claims

1. A non-aqueous organic solvent, a lithium salt, and an additive, The additive comprises a first compound represented by the following chemical formula 1, and a second compound which is a nitrile-based compound having three or more cyano groups. 【Chemistry 1】 In the above formula 1, R １ and R ２ are each independently a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms or a substituted or unsubstituted aryl group having 6 to 30 carbon atoms; R １ and R ２ At least one of them is a substituted or unsubstituted aryl group having 6 to 30 carbon atoms.

2. The electrolyte for a lithium secondary battery according to claim 1 , wherein the second compound is represented by the following Chemical Formula 2: 【Chemistry 2】 In the above Chemical Formula 2, L is a substituted linear or branched alkylene group having 1 to 20 carbon atoms, and the substituted alkylene group is one in which at least one hydrogen atom of the alkylene is replaced with a cyano group (-CN).

3. The electrolyte for a lithium secondary battery according to claim 1, wherein the formula 1 is represented by the following formula 1-1 or 1-2. 【Chemistry 3】 In the above Chemical Formula 1-1, R １ａ is a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, H ａ ~H ｅ each independently represents a hydrogen atom, a halogen group, a hydroxy group, a cyano group, a nitro group, a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 20 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 20 carbon atoms, a substituted or unsubstituted alkynyl group having 2 to 20 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 20 carbon atoms, a substituted or unsubstituted aryl group having 6 to 20 carbon atoms, or a substituted or unsubstituted heteroaryl group having 2 to 20 carbon atoms, 【Chemistry 4】 In the above Chemical Formula 1-2, H ａ ~H ｊ are each independently a hydrogen atom, a halogen group, a hydroxyl group, a cyano group, a nitro group, a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 20 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 20 carbon atoms, a substituted or unsubstituted alkynyl group having 2 to 20 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 20 carbon atoms, a substituted or unsubstituted aryl group having 6 to 20 carbon atoms, or a substituted or unsubstituted heteroaryl group having 2 to 20 carbon atoms.

4. The electrolyte for a lithium secondary battery according to claim 1 , wherein the first compound is at least one selected from the compounds listed in Group 1 below: 【Chemistry 5】

5. The electrolyte for a lithium secondary battery according to claim 1 , wherein the second compound is at least one selected from the compounds listed in Group 2 below. 【Chemistry 6】

6. The electrolyte for a lithium secondary battery according to claim 1 , wherein the first compound is contained in an amount of more than 0.05 wt % and less than 6 wt % based on a total weight of the electrolyte for a lithium secondary battery.

7. The electrolyte for a lithium secondary battery according to claim 1 , wherein the second compound is contained in an amount of more than 0.05 wt % and less than 6 wt % based on a total weight of the electrolyte for a lithium secondary battery.

8. 2. The electrolyte for a lithium secondary battery according to claim 1, wherein the first compound and the second compound are contained in a weight ratio of 0.01:1 to 50:

1.

9. a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; a separator located between the positive electrode and the negative electrode; A lithium secondary battery comprising the electrolyte solution according to any one of claims 1 to 8.

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