Electrolyte for lithium secondary battery and lithium secondary battery including the same

Abstract

To provide an electrolyte for a lithium secondary battery which is highly safe and has a normal-temperature life characteristic.SOLUTION: The electrolyte for a lithium secondary battery includes a non-aqueous organic solvent, lithium salt, and an additive. The additive contains a first compound represented by Chemical Formula 1 and a second compound represented by Chemical Formula 2: Chemical Formula 1 is O=S(R1)(R2) and Chemical Formula 2 is as follows. R1 and R2 are each independently a C1-C20 alkyl group or a C6-C30 aryl group, provided that at least one of R1 and R2 is a C6-C30 aryl group; M is B or P; R3 and R4 are each independently hydrogen, a halogen group, or a C1-C10 alkyl group, n is 1 to 3, and m is 0 or 1.SELECTED DRAWING: None

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] 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. Therefore, 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 from the positive electrode and the negative electrode.

[0004] Recently, active research has been conducted on lithium secondary batteries with high capacity, high energy density, and high safety 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 contains an organic solvent and a lithium salt, showing significantly 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 battery generates gas while rapidly heating, so the safety of the battery due to cell explosion or the like becomes a problem. Also, when a lithium secondary battery is in a rapid charging state, there is a problem that lithium is electrodeposited on the negative electrode and the resistance inside the battery increases.

[0007] Therefore, the development of an electrolyte for realizing a battery excellent in safety even under overcharging and rapid charging is required.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0009] One embodiment aims to provide an electrolyte for a lithium secondary battery that is excellent in safety even under overcharge and rapid charging and has excellent normal-temperature life characteristics.

[0010] One embodiment aims to provide a lithium secondary battery including the above electrolyte for a lithium secondary battery.

Means for Solving the Problems

[0011] The electrolyte for a lithium secondary battery according to one embodiment includes a non-aqueous organic solvent, a lithium salt, and an additive, The additive includes a first compound represented by the following Chemical Formula 1 and a second compound represented by the following Chemical Formula 2.

[0012] [Chemical Formula 1]

Chem.

[0013] [Chemical Formula 2]

Chem.

[0014] In the above Chemical Formula 1, R 1 and R 2 are each independently a substituted or unsubstituted C1-C20 alkyl group or a substituted or unsubstituted C6-C30 aryl group, and R 1 and R2 One or more of them are substituted or unsubstituted C6-C30 aryl groups, In Chemical Formula 2, M is B (boron) or P (phosphorus), R 3 and R 4 are each independently hydrogen, a halogen group (F, Cl, Br, or I), or a substituted or unsubstituted C1-C10 alkyl group, n is an integer from 1 to 3, and m is 0 or 1.

[0015] A lithium secondary battery according to an 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 an electrolytic solution for the lithium secondary battery.

Advantages of the Invention

[0016] An electrolytic solution for a lithium secondary battery according to an embodiment is excellent in safety even under overcharge and rapid charge, and can realize a lithium secondary battery having excellent normal temperature life characteristics.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Best Mode for Carrying Out the Invention

[0018] 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 below.

[0019] In this specification, unless otherwise specified, when a part such as a layer, film, region, plate, etc. is “above” another part, this includes not only the case where it is “directly above” another part, but also the case where there are other parts in between.

[0020] In this specification, unless otherwise specified, those expressed in the singular can also include the plural. Also, unless otherwise specified, “A or B” can mean “including A, including B, or including both A and B”.

[0021] In this specification, “these combinations” can mean a mixture of components, a laminate, a composite, a copolymer, an alloy, a blend, and a reaction product, etc.

[0022] In this specification, unless otherwise defined, 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 with a cumulative volume of 50% in the particle size distribution. The measurement of the average particle size (D50) may be measured 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 photograph or a scanning electron microscope photograph. As another method, it can be measured using a measuring device that utilizes the dynamic light-scattering method. After performing data analysis and counting the number of particles for each particle size range, the average particle size (D50) value 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, it is introduced into a commercially available laser diffraction particle size measuring device (for example, MT3000 of Microtrac), irradiated with ultrasonic waves of about 28 kHz at an output of 60 W, and then the average particle size (D50) based on the 50% standard of the particle size distribution in the measuring device can be calculated.

[0023] In this specification, "substitution" means that, unless otherwise defined, at least one hydrogen in the substituent or compound is substituted with a deuterium, halogen group, hydroxyl group, amino group, C1-C30 amine group, nitro group, C1-C40 silyl group, C1-C30 alkyl group, C1-C10 alkylsilyl group, C6-C30 arylsilyl group, C3-C30 cycloalkyl group, C3-C30 heterocycloalkyl group, C6-C30 aryl group, C2-C30 heteroaryl group, C1-C20 alkoxy group, C1-C10 fluoroalkyl group, cyano group, or a substituent combination thereof.

[0024] Specifically, "substituted" may mean that at least one hydrogen in a substituent or a compound is substituted with deuterium, a halogen group, a C1-C30 alkyl group, a C1-C10 alkylsilyl group, a C6-C30 arylsilyl group, a C3-C30 cycloalkyl group, a C3-C30 heterocycloalkyl group, a C6-C30 aryl group, a C2-C30 heteroaryl group, a C1-C10 fluoroalkyl group or a cyano group. For example, "substituted" may mean that at least one hydrogen in a substituent or a compound is substituted with deuterium, a halogen group, a C1-C20 alkyl group, a C6-C30 aryl group, a C1-C10 fluoroalkyl group or a cyano group. Or, "substituted" may mean that at least one hydrogen in a substituent or a compound is substituted with deuterium, a halogen group, a C1-C5 alkyl group, a C6-C18 aryl group, a C1-C5 fluoroalkyl group or a cyano group. As an example, "substituted" may 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.

[0025] 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.

[0026] When the first compound, the second compound, and the lithium salt are used in combination, a lithium secondary battery excellent in safety even under overcharge and rapid charge and excellent in normal temperature life characteristics can be realized.

[0027] [First Compound] The first compound is a sulfoxide-based compound and plays a role of effectively suppressing the heat generation temperature of the battery under overcharge driving conditions.

[0028] The first compound is represented by the following Chemical Formula 1.

[0029] [Chemical Formula 1] [Chemical formula]

[0030] In Chemical formula 1, R 1 and R 2 are each independently a substituted or unsubstituted C1-C20 alkyl group or a substituted or unsubstituted C6-C30 aryl group, and one or more of R 1 and R 2 is a substituted or unsubstituted C6-C30 aryl group.

[0031] As an example, one or more of R 1 and R 2 may be a substituted or unsubstituted C6-C30 aryl group.

[0032] In one embodiment, Chemical formula 1 may be represented by the following Chemical formula 1-1 or Chemical formula 1-2. As the most specific example, Chemical formula 1 may be represented by the following Chemical formula 1-1.

[0033] [Chemical formula 1-1] [Chemical formula]

[0034] In Chemical formula 1-1, R 1a is a substituted or unsubstituted C1-C20 alkyl group, H a ~H e are each independently hydrogen, a halogen group, a hydroxyl group, a cyano group, a nitro group, a substituted or unsubstituted C1-C20 alkyl group, a substituted or unsubstituted C1-C20 alkoxy group, a substituted or unsubstituted C2-C20 alkenyl group, a substituted or unsubstituted C2-C20 alkynyl group, a substituted or unsubstituted C3-C20 cycloalkyl group, a substituted or unsubstituted C6-C20 aryl group, or a substituted or unsubstituted C2-C20 heteroaryl group.

[0035] As a specific example, H a ~H e may each independently be hydrogen, a halogen group, a substituted or unsubstituted C1-C20 alkyl group, or a substituted or unsubstituted C1-C20 alkoxy group.

[0036] [Chemical Formula 1-2]

Chem.

[0037] In the Chemical Formula 1-2, H a ~H j may each independently be hydrogen, a halogen group, a hydroxyl group, a cyano group, a nitro group, a substituted or unsubstituted C1-C20 alkyl group, a substituted or unsubstituted C1-C20 alkoxy group, a substituted or unsubstituted C2-C20 alkenyl group, a substituted or unsubstituted C2-C20 alkynyl group, a substituted or unsubstituted C3-C20 cycloalkyl group, a substituted or unsubstituted C6-C20 aryl group, or a substituted or unsubstituted C2-C20 heteroaryl group.

[0038] As a specific example, H a ~H j may each independently be hydrogen, a halogen group, a substituted or unsubstituted C1-C20 alkyl group, or a substituted or unsubstituted C1-C20 alkoxy group.

[0039] As an example, the first compound may be any one or more selected from the compounds listed in Group 1 below.

[0040] [Group 1]

Chem.

Chem.

[0041] In one embodiment, the first compound may be contained in an amount exceeding 0.05% by weight or 0.1% by weight or more, and may be contained in an amount less than 10% by weight or 5% by weight or less, based on the total weight of the electrolyte for a lithium secondary battery.

[0042] As a specific example, the first compound may be contained in an amount exceeding 0.05% by weight and less than 10% by weight, for example, exceeding 0.05% by weight and 5% by weight or less, 0.1% by weight or more and less than 10% 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.

[0043] 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 weak, and when it is contained in an amount of 10% by weight or more, there is a problem that the resistance of the battery increases excessively.

[0044] [Second Compound] The second compound is a lithium salt having an oxalate group, and by rapidly undergoing reductive decomposition during battery operation to form a SEI (solid electrolyte interface) film on the negative electrode, it can prevent lithium from being electrodeposited on the negative electrode, thereby preventing an increase in the internal resistance of the battery.

[0045] The second compound is represented by the following Chemical Formula 2.

[0046] [Chemical Formula 2] [Chemical Structure]<

[0047] In Chemical Formula 2, M is B (boron) or P (phosphorus), R 3 and R 4 are each independently hydrogen, a halogen group (F, Cl, Br, or I), or a substituted or unsubstituted C1-C10 alkyl group, n is an integer from 1 to 3, and m is 0 or 1.

[0048] As an example, M may be B, and R 1 and R 2 may each independently be hydrogen or a halogen group (F, Cl, Br, or I), n may be an integer from 1 to 2, and m may be 0 or 1.

[0049] In one embodiment, Chemical Formula 2 can include any one or more of the compounds represented by the following Chemical Formulas 2-1 to 2-8. As a specific example, Chemical Formula 2 can include any one or more of the compounds represented by the following Chemical Formulas 2-1 to 2-4.

[0050] [Chemical Formula 2-1] [Chemical Structure]

[0051] [Chemical Formula 2-2] [Chemical Structure]

[0052] [Chemical Formula 2-3] [Chemical Structure]

[0053] [Chemical Formula 2-4] [Chemical Structure]

[0054] [Chemical Formula 2-5] [Chemical Structure]

[0055] [Chemical Formula 2-6] [Chemical Structure]

[0056] [Chemical Formula 2-7] [Chemistry]

[0057] [Chemical Formula 2-8] [Chemistry]

[0058] In one embodiment, the second compound may be contained in an amount exceeding 0.05% by weight or 0.1% by weight or more, and may be contained in an amount less than 5% by weight or 3% by weight or less, based on the total weight of the electrolyte for a lithium secondary battery.

[0059] As a specific example, the second compound may be contained in an amount exceeding 0.05% by weight and less than 5% by weight, for example, exceeding 0.05% by weight and 3% by weight or less, 0.1% by weight or more and less than 5% by weight, or 0.1% by weight or more and 3% by weight or less, based on the total weight of the electrolyte for a lithium secondary battery.

[0060] When the second compound is contained in an amount of 0.05% by weight or less or 5% by weight or more based on the total weight of the electrolyte for a lithium secondary battery, the normal temperature life characteristics of the battery may deteriorate.

[0061] In one embodiment, the first compound and the second compound may be contained in a weight ratio of 0.05:1 to 50:1, for example, a weight ratio of 0.05:1 to 40:1, a weight ratio of 0.1:1 to 50:1, or a weight ratio of 0.1:1 to 40:1.

[0062] When the weight ratio of the first compound and the second compound satisfies the above numerical range, a lithium secondary battery excellent in safety and normal temperature life characteristics can be realized even under overcharge and rapid charging.

[0063] [Lithium salt] The lithium salt is dissolved in an organic solvent and 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.

[0064] The concentration of the lithium salt can be from 0.1 M to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance due to having appropriate conductivity and viscosity, and lithium ions can move effectively.

[0065] As an example, the lithium salt is 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, or a combination thereof may be included.

[0066] [Non-aqueous organic solvent] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0067] The non-aqueous organic solvent may be a carbonate solvent, an ester solvent, an ether solvent, a ketone solvent, an alcohol solvent, an aprotic solvent, or a combination thereof.

[0068] 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, 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. Also, 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 and 1,4-dioxolane, sulfolane, etc. can be used.

[0069] The non-aqueous organic solvent can be used alone or in a mixture of two or more.

[0070] In addition, 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 may be mixed at a volume ratio of 1:1 to 1:9.

[0071] [Lithium secondary battery] In one embodiment, a lithium secondary battery including the aforementioned electrolyte is provided.

[0072] A lithium secondary battery according to one embodiment includes a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, a separator positioned between the positive electrode and the negative electrode, and the electrolyte for the lithium secondary battery described above.

[0073] Lithium secondary batteries can be 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 one embodiment, FIG. 1 is a cylindrical type, FIG. 2 is a square 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, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte (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, that is, a positive electrode tab 71 and a negative electrode tab 72, which serve as an electrical path for guiding the current formed by the electrode assembly 40 to the outside.

[0074] The lithium secondary battery according to one embodiment of the present invention may be applied to an automobile, a mobile phone, and / or various forms of electrical devices, etc., and the present invention is not limited thereto.

[0075] [Positive electrode active material] As the positive electrode active material, a compound capable of reversible insertion and extraction of lithium (lithiated insertion 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.

[0076] The composite oxide may be a lithium transition metal composite oxide. As a specific example, 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 can be mentioned.

[0077] As an example, 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 Any one of the compounds represented by the chemical formula (0.90 ≤ a ≤ 1.8) can be used.

[0078] 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; L 1 is Mn, Al, or a combination thereof.

[0079] As an example, the positive electrode active material may be a high-nickel positive electrode active material in which the nickel content 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, based on 100 mol% of the metal excluding lithium in the lithium transition metal composite oxide. Since the high-nickel positive electrode active material can achieve a high capacity, it can be applied to a high-capacity and high-density lithium secondary battery.

[0080] [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 can include a positive electrode active material and can further include a binder and / or a conductive agent.

[0081] As an example, the positive electrode can further include an additive that can serve as a sacrificial positive electrode.

[0082] The content of the positive electrode active material is 90% by weight 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 agent can be 0.5% by weight to 5% by weight respectively based on 100% by weight of the positive electrode active material layer.

[0083] The binder serves to make the positive electrode active material particles adhere well to each other and also make the positive electrode active material adhere well 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.

[0084] The conductive agent is used to impart conductivity to the electrode, and in the battery being constructed, any electron conductive material that does not cause a chemical change can be used. Examples of the conductive agent 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 containing copper, nickel, aluminum, silver, etc., conductive polymers such as polyphenylene derivatives, or mixtures thereof.

[0085] As the current collector, Al can be used, but it is not limited thereto.

[0086] [Negative electrode active material] The negative electrode active material includes a material capable of reversibly inserting / desorbing lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, or a transition metal oxide.

[0087] Examples of the material capable of reversibly inserting / desorbing lithium ions include carbon-based negative electrode active materials, which can include, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite. Examples of amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0088] As the alloy of 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.

[0089] As the material capable of doping and dedoping 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. The Sn-based negative electrode active material may be Sn, SnO 2 , a Sn-based alloy, or a combination thereof.

[0090] 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. Amorphous carbon may also be located between the primary silicon particles. For example, the primary silicon particles may be coated with amorphous carbon. The secondary particles may be dispersed and present in an amorphous carbon matrix.

[0091] 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.

[0092] 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.

[0093] [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 agent.

[0094] 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 agent.

[0095] The binder serves to make the negative electrode active material particles adhere well to each other and also make the negative electrode active material adhere well to the current collector. As the binder, a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof can be used.

[0096] Examples of non-aqueous binders include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene-propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

[0097] Examples of aqueous binders may include 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, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0098] When an aqueous binder is used as the negative electrode binder, it may further contain a cellulose-based compound capable of imparting viscosity. 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.

[0099] Dry binders are polymer substances that can be fibrillated and may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or combinations thereof.

[0100] A conductive agent is used to impart conductivity to an electrode, and in the configured battery, any electron conductive material that does not cause a chemical change can be used. 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.

[0101] 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.

[0102] [Separator] Depending on the type of lithium secondary battery, a separator can also be present 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, and a mixed multilayer film such as a two-layer separator of polyethylene / polypropylene, a three-layer separator of polyethylene / polypropylene / polyethylene, a three-layer separator of polypropylene / polyethylene / polypropylene can be used.

[0103] The separator can include a porous substrate and a coating layer including an organic substance, an inorganic substance or a combination thereof located on one or both surfaces of the porous substrate.

[0104] The porous substrate may be a polymer membrane formed of 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.

[0105] The organic substance may include a polyvinylidene fluoride polymer or a (meth)acrylic polymer.

[0106] The inorganic substance is Al 2 O 3 , SiO 2 , TiO 2 , SnO 2 , CeO 2 It may include, but is not limited to, inorganic particles selected from MgO, NiO, CaO, GaO, ZnO, ZrO 2 Y 2 O 3 , SrTiO 3 , BaTiO 3 , Mg(OH) 2 , boehmite, and combinations thereof.

[0107] 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.

[0108] Hereinafter, examples and comparative examples of the present invention will be described. However, the following examples are merely examples of the present invention, and the present invention is not limited to the following examples.

Examples

[0109] (Example 1) In 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 that order, 1.15 M LiPF is used as a lithium salt 6 and dissolved to prepare a basic electrolyte solution.

[0110] To the above basic electrolyte solution, a first compound represented by the following Compound 1-a and a second compound represented by the following Chemical Formula 2-2 are added to prepare an electrolyte solution.

[0111] [Compound 1-a] [Chemical formula]

[0112] [Chemical Formula 2-2] [Chemical formula]

[0113] At this time, with respect to the entire electrolyte solution, the first compound is contained at 2% by weight and the second compound is contained at 0.5% by weight.

[0114] As a 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 agent are mixed in a weight ratio of 97:2:1, respectively, and dispersed in N-methylpyrrolidone to produce a positive electrode active material slurry.

[0115] The positive electrode active material slurry is coated on an aluminum foil with a thickness of 14 μm, dried at 110 °C, and then rolled to produce a positive electrode.

[0116] As the negative electrode active material, artificial graphite, as the binder, styrene-butadiene rubber, and as the thickener, carboxymethyl cellulose are 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 is coated on a copper (Cu) foil current collector with a thickness of 10 μm, dried at 100 °C, and then rolled to produce a negative electrode.

[0117] An electrode assembly is produced with a separator having a polyethylene - polypropylene multi - layer structure with a thickness of 25 μm between the produced positive electrode and negative electrode, inserted into a rectangular battery case (57 Ah), and then the produced electrolyte is injected to produce the lithium secondary battery of Example 1.

[0118] (Example 2) A lithium secondary battery of Example 2 is produced in the same manner as in Example 1, except that the compound represented by the following Chemical Formula 2 - 1 is used as the second compound.

[0119] [Chemical Formula 2 - 1]

Chemical Structure

[0120] (Examples 3 to 14) A lithium secondary battery is produced in the same manner as in Example 1, except that the contents of the first compound and the second compound in the whole electrolyte are adjusted as shown in Table 1 below.

[0121] (Examples 15 to 19) A lithium secondary battery is produced in the same manner as in Example 2, except that the contents of the first compound and the second compound in the whole electrolyte are adjusted as shown in Table 1 below.

[0122] (Comparative Example 1) A lithium secondary battery is produced in the same manner as in Example 1, except that the first compound and the second compound are not added to the electrolyte.

[0123] (Comparative Example 2) A lithium secondary battery is manufactured in the same manner as in Example 1, except that the second compound is not added to the electrolyte solution.

[0124] (Comparative Example 3) A lithium secondary battery is manufactured in the same manner as in Example 1, except that the first compound is not added to the electrolyte solution.

[0125] (Comparative Example 4) A lithium secondary battery is manufactured in the same manner as in Example 2, except that the first compound is not added to the electrolyte solution.

[0126]

Table 1

[0127] (Evaluation Example 1: Overcharge / Rapid Charge Safety Evaluation) An overcharge evaluation was performed on some of the examples (Examples 1 to 2, Examples 4 to 8, Examples 10 to 13, and Examples 15 to 18) and the lithium secondary batteries manufactured in Comparative Examples 1 to 4. The results of the overcharge evaluation are shown in Table 2 and FIG. 5 below.

[0128] A safety protection element is welded and attached to the negative electrode portion of the lithium secondary battery cell, a tab is welded and attached 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.

[0129] Thereafter, the cell is charged at a rate of 1.0C until it reaches 6V, and the cell is exposed to the voltage for 50 minutes to overcharge / rapidly charge the cell.

[0130] The results of the evaluation where it is evaluated as "Pass" if the battery does not catch fire during the exposure time and remains in the same state as the battery before the evaluation, and "Fail" if the battery catches fire are shown in Table 2 below.

[0131] Also, the results of the overcharge evaluation of the lithium secondary batteries of Examples 1 to 2 and Comparative Examples 1 to 4 are shown graphically in FIG. 5.

[0132] The line located relatively higher in FIG. 5 indicates the voltage change over time, and the line located relatively lower indicates the temperature change over time.

[0133] (Evaluation Example 2: Normal Temperature Life Characteristic Evaluation) For the lithium secondary batteries manufactured in some of the examples (Examples 1 to 2, Examples 4 to 8, Examples 10 to 13, and Examples 15 to 18) and Comparative Examples 1 to 4, the life characteristics at normal temperature (25 °C) were evaluated.

[0134] Specifically, charging at 0.05C and discharging at 0.5C were carried out 465 cycles between 2.8V and 4.2V, and the capacity retention rate (%) after 465 cycles with respect to the discharge capacity per cycle was calculated. The results are shown in Table 2 below.

[0135] Also, the results of the normal temperature life evaluation of the lithium secondary batteries of Examples 1 to 2 and Comparative Examples 1 to 4 are shown graphically in FIG. 6.

[0136]

Table 2

[0137] Referring to Table 2, in the cases of Comparative Examples 1, 3, and 4 where the electrolyte does not contain the first lithium salt, it can be confirmed that the battery caught fire during overcharging.

[0138] Also referring to FIG. 5, in the cases of Examples 1 and 2, even when exposed in the overcharged state for 50 minutes, the temperature of the battery is maintained constant, whereas in the cases of Comparative Examples 1, 3, and 4, it can be confirmed that the temperature of the battery rose to about 400 °C at about 35 minutes and the battery caught fire.

[0139] Referring to Table 2 and FIG. 6, it can be confirmed that, as described above, the examples are excellent in overcharging characteristics and the normal temperature life characteristics are also at the same level as those of the comparative examples.

[0140] Although the preferred embodiments of the present invention have been described above, 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

[0141] 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 is an electrolyte for a lithium secondary battery, comprising a first compound represented by the following Chemical Formula 1 and a second compound represented by the following Chemical Formula 2: [Chemical formula 1] 【Chemistry 20】 [Chemical formula 2] 【Chemistry 21】 In the above Chemical Formula 1, R １ and R ２ are each independently a substituted or unsubstituted C1 to C20 alkyl group or a substituted or unsubstituted C6 to C30 aryl group; R １ and R ２ at least one of which is a substituted or unsubstituted C6 to C30 aryl group; In the above Chemical Formula 2, M is B (boron) or P (phosphorus); R ３ and R ４ are each independently a hydrogen, a halogen group (F, Cl, Br, or I), or a substituted or unsubstituted C1-C10 alkyl group; n is an integer of 1 to 3, and m is 0 or 1.

2. 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: [Chemical formula 1-1] 【Chemical 22】 In the above Chemical Formula 1-1, R １ａ is a substituted or unsubstituted C1 to C20 alkyl group, H ａ ~H ｅ are each independently a hydrogen, a halogen group, a hydroxyl group, a cyano group, a nitro group, a substituted or unsubstituted C1 to C20 alkyl group, a substituted or unsubstituted C1 to C20 alkoxy group, a substituted or unsubstituted C2 to C20 alkenyl group, a substituted or unsubstituted C2 to C20 alkynyl group, a substituted or unsubstituted C3 to C20 cycloalkyl group, a substituted or unsubstituted C6 to C20 aryl group, or a substituted or unsubstituted C2 to C20 heteroaryl group; [Chemical formula 1-2] 【Chemistry 23】 In the above Chemical Formula 1-2, H ａ ~H ｊ are each independently a hydrogen, a halogen group, a hydroxyl group, a cyano group, a nitro group, a substituted or unsubstituted C1 to C20 alkyl group, a substituted or unsubstituted C1 to C20 alkoxy group, a substituted or unsubstituted C2 to C20 alkenyl group, a substituted or unsubstituted C2 to C20 alkynyl group, a substituted or unsubstituted C3 to C20 cycloalkyl group, a substituted or unsubstituted C6 to C20 aryl group, or a substituted or unsubstituted C2 to C20 heteroaryl group.

3. The electrolyte for a lithium secondary battery according to claim 1 , wherein the first compound is at least one selected from the group consisting of the compounds listed in Group 1 below: [Group 1] 【Chemistry 24】 【Chemistry 25】

4. The electrolyte for a lithium secondary battery according to claim 1, wherein the formula 2 includes at least one of compounds represented by the following formulas 2-1 to 2-8: [Chemical formula 2-1] 【Chemistry 26】 [Chemical formula 2-2] 【Chemical 27】 [Chemical formula 2-3] 【Chemistry 28】 [Chemical formula 2-4] 【Chemical 29】 [Chemical formula 2-5] 【Chemistry 30】 [Chemical formula 2-6] 【Chemistry 31】 [Chemical formula 2-7] 【Chemistry 32】 [Chemical formula 2-8] 【Chemical 33】

5. The lithium salt is 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 2. The electrolyte for a lithium secondary battery according to claim 1, comprising lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, or a combination thereof, wherein x and y are integers from 1 to 20.

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 10 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 5 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 0.05:1 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; and A lithium secondary battery comprising the electrolyte solution according to any one of claims 1 to 8.

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