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 an excellent high-temperature preservation characteristic.SOLUTION: An electrolyte solution for a lithium secondary battery includes a nonaqueous organic solvent, a lithium salt, and an additive. The additive includes a first compound expressed by Chemical Formula 1, and a second compound expressed by Chemical Formula 2.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 containing the same.

Background Art

[0002] In recent years, 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. For this reason, research and development for improving the performance of lithium secondary batteries have been actively carried out.

[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 between the positive electrode and the negative electrode.

[0004] Recently, in order to be used as a power source for driving hybrid vehicles and electric vehicles, or as a power storage power source, etc., active research has been conducted on lithium secondary batteries with high capacity, high energy density, and high safety.

[0005] In a lithium secondary battery, the electrolyte plays an important role in transmitting lithium ions, contains an organic solvent and a lithium salt, and exhibits very high ionic conductivity. 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 in an overcharged state, the cell may explode, and the safety of the battery has become a problem. Also, when exposed to high temperatures, there is a problem that the internal resistance of the battery increases.

[0007] For this reason, the development of an electrolyte for realizing a battery excellent in safety even under overcharging and high temperatures is required.

Summary of the Invention

Problems to be Solved by the Invention

[0008] One embodiment of the present invention is an electrolyte for a lithium secondary battery that is excellent in safety under overcharge and excellent in high-temperature storage characteristics.

[0009] Another embodiment of the present invention is a lithium secondary battery including the above electrolyte.

Means for Solving the Problems

[0010] One embodiment of the present invention is an electrolyte for a lithium secondary battery, which includes a non-aqueous organic solvent, a lithium salt, and an additive, and the additive includes a first compound represented by the following Chemical Formula 1 and a second compound represented by the following Chemical Formula 2.

[0011]

Chem.

[0012] 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 any one or more of R 1 and R 2 is a substituted or unsubstituted aryl group having 6 to 30 carbon atoms. In Chemical Formula 2, A 1 , A 2 , A 3 and A 4 are each independently a single bond, a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms, a carbonyl group, or a sulfinyl group. However, A 1 and A 2 are not simultaneously a single bond, and A 3 and A 4 are not simultaneously a single bond.

[0013] Another embodiment of the present invention is 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 above-described electrolytic solution.

Advantages of the Invention

[0014] The electrolytic solution for a lithium secondary battery according to one embodiment of the present invention can realize a lithium secondary battery that is excellent in safety under overcharge and excellent in high-temperature storage characteristics.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Modes for Carrying Out the Invention

[0016] 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, and the present invention is defined only by the scope of the claims described later.

[0017] 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.

[0018] Unless otherwise specified in this specification, singular terms can include plural ones. At the same time, unless otherwise specified, "A or B" can mean "including A, or including B, or including both A and B".

[0019] As used herein, "these combinations" can mean mixtures of components, laminates, composites, copolymers, alloys, blends, reaction products, and the like.

[0020] Unless otherwise defined herein, the particle size may be the average particle size. Also, the particle size means the average particle size (D50) which is the diameter of the particle at which the cumulative volume is 50% by volume in the particle size distribution. The average particle size (D50) measurement can be performed by methods widely known to those skilled in the art. For example, the average particle size (D50) can be measured with a particle size analyzer, or can also be measured using a transmission electron microscope (TEM) photograph or a scanning electron microscope (SEM) photograph. As another method, a measuring device using the dynamic light-scattering method can be used, and after performing data analysis to count the number of particles for each particle size range, the average particle size (D50) can be calculated therefrom. 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, the dispersion liquid 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.

[0021] Here, unless otherwise defined, "substituted" means that at least one hydrogen in the substituent or compound is substituted with deuterium, halogen, hydroxy group, amino group, an amine group having 1 to 30 carbon atoms, 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, cyano group, or a combination thereof.

[0022] Specifically, "substituted" can mean that at least one hydrogen in the substituent or compound is substituted with deuterium, halogen, 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 cyano group. For example, "substituted" can mean that at least one hydrogen in the substituent or compound is substituted with deuterium, halogen, 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 cyano group. Or, "substituted" can mean that at least one hydrogen in the substituent or compound is substituted with deuterium, halogen, 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 cyano group. As an example, "substituted" can mean that at least one hydrogen in the substituent or compound is substituted with deuterium, cyano group, halogen, methyl group, ethyl group, propyl group, butyl group, phenyl group, biphenyl group, terphenyl group, trifluoromethyl group or naphthyl group.

[0023] The electrolyte for a lithium secondary battery according to one 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.

[0024] When the first compound and the second compound are used in combination, a lithium secondary battery excellent in stability under overcharge and excellent in high-temperature storage characteristics can be realized.

[0025] 1. First compound The first compound is a sulfoxide-based compound and plays a role in effectively suppressing the heat generation of the battery under overcharge driving conditions.

[0026] The first compound is represented by the following Chemical Formula 1.

[0027]

Chem.

[0028] 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 any one or more of R 1 and R 2 is a substituted or unsubstituted aryl group having 6 to 30 carbon atoms.

[0029] 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.

[0030]

Chem.

[0031] In Chemical Formula 1-1, R 1a is a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, H a ~H emay each independently be hydrogen, halogen, 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.

[0032] As a specific example, H a ~H e may each independently be hydrogen, halogen, 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.

[0033] [Chemical formula]

[0034] In Chemical formula 1-2, H a ~H j may each independently be hydrogen, halogen, 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.

[0035] As a specific example, H a ~H j may each independently be hydrogen, halogen, 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.

[0036] As an example, the first compound may be any one or more selected from the compounds listed in Group 1 below.

[0037]

Chemical formula

[0038] In one embodiment, the first compound may be contained in an amount exceeding 0.05% by weight, or 0.1% by weight or more, based on the total weight of the electrolyte for a lithium secondary battery, and may be contained in an amount less than 6% by weight, or 5% by weight or less.

[0039] As a specific example, the first compound may be contained in an amount exceeding 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 exceeding 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 to 5% by weight.

[0040] 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 safety of the battery during overcharge is low. 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 and the battery life decreases.

[0041] 2. The second compound The second compound is a bicyclic sulfate-based compound, which forms a SEI (solid electrolyte interface) layer on the surface of the negative electrode or forms a protective layer on the surface of the positive electrode to improve the thermal stability of the battery, thereby playing a role in improving the life characteristics of the lithium secondary battery at high temperatures.

[0042] The second compound is represented by the following Chemical formula 2.

[0043]

Chemical formula

[0044] In Chemical formula 2, A 1 , A2 and A 3 and A 4 are each independently a single bond, a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms, a carbonyl group, or a sulfinyl group. However, A 1 and A 2 are not simultaneously a single bond, and A 3 and A 4 are not simultaneously a single bond.

[0045] As an example, one or more of A 1 , A 2 , A 3 , and A 4 are an unsubstituted alkylene group having 1 to 5 carbon atoms or a substituted alkylene group having 1 to 5 carbon atoms, and the substituent of the substituted alkylene group having 1 to 5 carbon atoms may be a halogen-substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, a halogen-substituted or unsubstituted alkenyl group having 2 to 20 carbon atoms, a halogen-substituted or unsubstituted alkynyl group having 2 to 20 carbon atoms, a halogen-substituted or unsubstituted cycloalkenyl group having 3 to 20 carbon atoms, a halogen-substituted or unsubstituted heterocyclyl group having 3 to 20 carbon atoms, a halogen-substituted or unsubstituted aryl group having 6 to 40 carbon atoms, or a halogen-substituted or unsubstituted heteroaryl group having 2 to 40 carbon atoms.

[0046] As an example, one or more of A 1 , A 2 , A 3 and A 4 are an unsubstituted alkylene group having 1 to 5 carbon atoms or a substituted alkylene group having 1 to 5 carbon atoms, and the substituent of the substituted alkylene group having 1 to 5 carbon atoms may be a halogen, a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, a tert-butyl group, a trifluoromethyl group, a tetrafluoroethyl group, a phenyl group, a naphthyl group, a tetrafluorophenyl group, a pyrrolyl group, or a pyridinyl group, but the substituent is not necessarily limited to these, and all are possible as long as they can be used as a substituent of an alkylene group in the technical field.

[0047] In one embodiment, Chemical Formula 2 can include any one or more of the compounds represented by the following Chemical Formulas 2-1 to 2-7.

[0048]

Chemical Formula

Chemical Formula

[0049] In one embodiment, the second compound may be contained in an amount exceeding 0.05% by weight, or 0.1% by weight or more, based on the total weight of the electrolyte for a lithium secondary battery, and may be contained in an amount less than 6% by weight, or 5% by weight or less.

[0050] As a specific example, the second compound may be contained in an amount exceeding 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, exceeding 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 to 5% by weight.

[0051] 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, it is difficult to improve the high-temperature life characteristics of the battery. When it is contained in an amount of 6% by weight or more, there is a problem that the resistance of the battery excessively increases and the life of the battery decreases.

[0052] In one embodiment, the first compound and the second compound may be contained in a weight ratio of 0.01:1 to 100:1, for example, a weight ratio of 0.05:1 to 100:1, a weight ratio of 0.01:1 to 40:1, a weight ratio of 0.05:1 to 40:1, a weight ratio of 0.05:1 to 20:1, or a weight ratio of 0.1:1 to 20:1.

[0053] When the weight ratio of the first compound and the second compound satisfies the above numerical range, a battery excellent in safety under overcharge and excellent in high-temperature life characteristics can be realized.

[0054] The electrolyte for a lithium secondary battery contains a non-aqueous organic solvent and a lithium salt.

[0055] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0056] 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.

[0057] As the carbonate-based 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-based solvent, methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, caprolactone, etc. can be used. As the ether-based solvent, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. can be used. Also, as the ketone-based solvent, cyclohexanone, etc. can be used. As the alcohol-based solvent, ethyl alcohol, isopropyl alcohol, etc. can be used, and as the aprotic solvent, nitriles represented by 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.

[0058] The non-aqueous organic solvent can be used alone or in a mixture of two or more. When using a carbonate-based 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.

[0059] The lithium salt dissolves in the organic solvent and acts as a source of lithium ions in the battery, playing a role in enabling the operation of a basic lithium secondary battery. 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 ) (where 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 one or more selected therefrom can be mentioned.

[0060] 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.

[0061] 3. Cathode active material As the cathode 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 with lithium can be used.

[0062] The composite oxide may be a lithium transition metal composite oxide, and 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.

[0063] 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 G e O 2(0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, 0 ≤ e ≤ 0.1), Li a 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).

[0064] 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.

[0065] As an example, the positive electrode active material may be a high-nickel type positive electrode active material in which the nickel content 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 type positive electrode active material can achieve a high capacity and can be applied to a high-capacity and high-density lithium secondary battery.

[0066] 4. 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.

[0067] As an example, the positive electrode can further contain an additive that can serve as a sacrificial positive electrode.

[0068] The content of the positive electrode active material is 90% to 99.5% by weight based on 100% by weight of the positive electrode active material layer, and the contents of the binder and the conductive material can each be 0.5% to 5% by weight based on 100% by weight of the positive electrode active material layer.

[0069] The binder serves to firmly adhere the positive electrode active material particles to each other and also to firmly adhere the positive electrode active material to the current collector. Representative examples of the binder include 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., but are not limited thereto.

[0070] The conductive material is used to impart conductivity to the electrode, and in the battery being configured, 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, metal-based substances containing copper, nickel, aluminum, silver, etc. in the form of metal powder or metal fiber, conductive polymers such as polyphenylene derivatives, or mixtures thereof.

[0071] Al can be used as the current collector, but it is not limited thereto.

[0072] 5. Anode active material The anode active material includes substances that can reversibly intercalate / deintercalate lithium ions, lithium metal, alloys of lithium metal, substances that can be doped and undoped with lithium, or transition metal oxides.

[0073] Substances that can reversibly intercalate / deintercalate lithium ions can include carbon-based anode active materials, for example, crystalline carbon, amorphous carbon, or combinations thereof. Examples of crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical or fibrous natural graphite or artificial graphite, and examples of amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, fired coke, etc.

[0074] As alloys of lithium metal, alloys of lithium and metals 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.

[0075] As the substance capable of doping and undoping lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used. The Si-based negative electrode active material may be silicon, a silicon-carbon composite, SiOx (0 < x < 2), a Si-Q alloy (Q is selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements (excluding Si), group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof), or a combination thereof. As the Sn-based negative electrode active material, Sn, SnO 2 , a Sn-based alloy, or a combination thereof may be used.

[0076] 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 amorphous carbon is coated on the surface of silicon particles. For example, it can 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 in the amorphous carbon matrix.

[0077] The silicon-carbon composite may further contain crystalline carbon. For example, the silicon-carbon composite can include a core containing crystalline carbon and silicon particles, and an amorphous carbon coating layer located on the surface of the core.

[0078] 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.

[0079] 6. 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.

[0080] For example, the negative electrode active material layer can contain 90% to 99% by weight of the negative electrode active material, 0.5% to 5% by weight of the binder, and 0% to 5% by weight of the conductive material.

[0081] The binder serves to firmly adhere the negative electrode active material particles to each other and also firmly 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.

[0082] 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 a combination thereof.

[0083] Examples of 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, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene-propylene-diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0084] When an aqueous binder is used as the negative electrode binder, a cellulose-based compound capable of imparting viscosity can be further included. As this cellulose-based compound, one or more of carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or alkali metal salts thereof can be mixed and used. As the alkali metal, Na, K, or Li can be used.

[0085] The dry binder is a polymer substance capable of being fibrillated, and for example, it may be polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride - hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0086] The conductive material is used to impart conductivity to the electrode, and in the battery being configured, any material can be used as long as it is an electron - conductive material and 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, 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.

[0087] The negative electrode current collector can be 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.

[0088] 7. Separator Depending on the type of lithium secondary battery, there may be a separator 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.

[0089] The separator can include a porous substrate and a coating layer containing an organic substance, an inorganic substance, or a combination thereof located on one or both sides of the porous substrate.

[0090] 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, and polytetrafluoroethylene, or a copolymer or mixture of two or more of these.

[0091] The organic substance may include a polyvinylidene fluoride-based polymer or a (meth)acrylic-based polymer.

[0092] 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.

[0093] 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.

[0094] Lithium secondary battery Lithium secondary batteries are classified into cylindrical, prismatic, 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 is a cylindrical type, FIG. 2 is a prismatic type, and FIGS. 3 and 4 are pouch type battery forms. 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 incorporated. The positive electrode 10, negative electrode 20, and 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, as shown 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 in the electrode assembly 40 to the outside.

[0095] 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., but the present invention is not limited thereto.

Examples

[0096] Hereinafter, examples and comparative examples of the present invention will be described. However, the following examples are only one embodiment of the present invention, and the present invention is not limited to the following embodiments.

[0097] Example 1 A non-aqueous organic solvent obtained by mixing ethylene carbonate (EC), methyl ethyl carbonate (MEC), and diethyl carbonate (DEC) in a volume ratio of 20:40:40 in this order was used to dissolve 1.15 M of LiPF 6 lithium salt to prepare a basic electrolytic solution.

[0098] To the basic electrolytic solution, a compound 1-a below as the first compound and a compound represented by the following chemical formula 2-1 as the second compound were added to prepare an electrolytic solution.

[0099]

Chem.

[0100] At this time, with respect to the entire electrolyte solution, the first compound was contained at 2% by weight and the second compound was contained at 1% by weight.

[0101] As the positive electrode active material, LiNi 0.91 Co 0.07 Al 0.02 O 2 , polyvinylidene fluoride as a binder, and Ketjen black as a conductive material were mixed at a weight ratio of 97:2:1, respectively, and this mixture was dispersed in N-methylpyrrolidone to prepare a positive electrode active material slurry.

[0102] The positive electrode active material slurry was coated on an Al foil with a thickness of 14 μm, dried at 110 °C, and then rolled to fabricate a positive electrode.

[0103] As the negative electrode active material, artificial graphite, styrene-butadiene rubber as a binder, and carboxymethyl cellulose as a thickener were mixed at a weight ratio of 97:1:2, respectively, and this mixture was dispersed in distilled water to prepare 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 fabricate a negative electrode.

[0104] An electrode assembly was manufactured with a separator having a polyethylene-polypropylene multilayer structure with a thickness of 25 μm between the fabricated positive electrode and negative electrode, inserted this into a rectangular battery case, and then injected the prepared electrolyte solution to fabricate the lithium secondary battery of Example 1.

[0105] Examples 2 to 15 Lithium secondary batteries according to Examples 2 to 15 were fabricated 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 solution.

[0106] 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.

[0107] 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.

[0108] 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.

[0109] (Evaluation Example) Evaluation Example 1: Overcharge Safety Evaluation Overcharge evaluation was performed on the lithium secondary batteries fabricated in Examples 1 to 15 and Comparative Examples 1 to 3, and the results are shown in Table 1 below.

[0110] Also, the overcharge evaluation results of the lithium secondary batteries fabricated in Example 1 and Comparative Examples 1 to 3 are shown in Fig. 5.

[0111] A safety protection element was attached to the negative electrode portion of the lithium secondary battery cell, a tab was welded to the positive electrode portion, and a thermocouple was fixed to the middle portion of the cell so that temperature measurement was possible.

[0112] Thereafter, the cell prepared in a fully charged state of 4.2 V was charged at a rate of 1.0 C until the charging voltage reached 6 V, and this charging voltage was maintained for 50 minutes. If the battery did not catch fire during the maintenance of the charging voltage and was in the same state as the battery before the evaluation, it was evaluated as "P (Pass)", and if the battery caught fire, it was evaluated as "F (Fail)", and the results are shown in Table 1 below.

[0113] Referring to Table 1, in the case of Comparative Examples 1 and 3 where the first compound was not added to the electrolyte, it was confirmed that the battery caught fire during overcharge.

[0114] Referring to Fig. 5, in the case of Example 1, even when maintained in an overcharged state for 50 minutes, the temperature of the battery remained constant without increasing. On the contrary, in the cases of Comparative Examples 1 to 3, it was confirmed that the temperature of the battery reached about 600 °C and the battery caught fire after about 35 minutes had elapsed.

[0115] Evaluation Example 2: Evaluation of storage characteristics at high temperature (60 °C) For the lithium secondary batteries fabricated in Examples 1 to 15 and Comparative Examples 1 to 3, after measuring the initial DC resistance (DC-IR) with the value of △V / △I (change in voltage / change in current), the maximum energy state inside the battery was set to a fully charged state (SOC 100), and the battery was stored at a high temperature (60 °C) for 90 days in this state.

[0116] Also, the battery was recharged to full charge at room temperature (25 °C) every 30 days and the DC resistance was measured, and the DC-IR increase rate (%) was calculated by the following formula 1. The battery for which the DC resistance was measured was charged again to 4.2 V and SOC 100, and stored at a high temperature (60 °C). [Formula 1] DCIR increase rate = ((DC-IR after (30×n) days / initial DC-IR) × 100%) (n is a natural number from 1 to 3)

[0117] The results of the high-temperature storage characteristics evaluation are shown in Table 1 and Fig. 6 below.

[0118] Referring to Table 1, it can be confirmed that for the lithium secondary batteries of Comparative Examples 1 to 3, the resistance increase rate of the battery after high-temperature storage is higher than that of the examples.

[0119] However, in the case of Comparative Example 3, since the second compound is included, it can be confirmed that the high-temperature resistance increase rate is lower than that of the other comparative examples.

[0120] Referring to Fig. 6, it can be confirmed that for the lithium secondary battery of Example 1, the resistance increase rate after high-temperature storage is much lower than that of Comparative Examples 1 to 3.

[0121]

Table 1

[0122] Evaluation Example 3: Evaluation of Life Characteristics at Room Temperature (25°C) For the lithium secondary batteries fabricated in Examples 1 to 15, the life characteristics at room temperature (25°C) were evaluated. Specifically, charging at 0.33C and discharging at 0.5C were performed 800 cycles between 2.8V and 4.2V, and the capacity retention rate (%) after 800 cycles with respect to the first discharge capacity was calculated. The results are shown in Table 2 below.

[0123] [Table 2]

[0124] Referring to Table 2, in the case of the lithium secondary batteries fabricated in Examples 1 to 15, it was confirmed that, as described above, they are excellent in overcharge safety and high-temperature storage characteristics, and also excellent in life characteristics at room temperature. Specifically, it was confirmed that the capacity retention rate at room temperature was maintained at around 90%.

[0125] 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 appended drawings, and it is natural that this also belongs to the scope of the present invention. [Explanation of Reference Numerals]

[0126] 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 includes a first compound represented by the following formula 1 and a second compound represented by the following formula 2: 【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 the above is a substituted or unsubstituted aryl group having 6 to 30 carbon atoms; In the above Chemical Formula 2, A １ , A ２ , A ３ and A ４ are each independently a single bond, a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms, a carbonyl group, or a sulfinyl group; A １ and A ２ is not a single bond at the same time, A ３ and A ４ At the same time, it is not a single bond, and is used as an electrolyte for lithium secondary batteries.

2. The formula 1 is represented by the following formula 1-1 or 1-2: 【Chemistry 2】 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 atom, 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 3】 In the above Chemical Formula 1-2, H ａ ~H ｊ are each independently a hydrogen atom, a halogen atom, 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.

3. 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 4】

4. The electrolyte for a lithium secondary battery according to claim 1, wherein the formula 2 includes at least one compound represented by the following formulas 2-1 to 2-7: 【Chemistry 5】 【Chemistry 6】

5. 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.

6. 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.

7. 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 100:

1.

8. 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; and A lithium secondary battery comprising the electrolyte solution for lithium secondary batteries according to any one of claims 1 to 7.

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