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

Abstract

To provide an electrolyte solution for a lithium secondary battery, in which even if a charging voltage increases and / or quick charging is performed, the growth of lithium dendrite and / or the deterioration of the lithium secondary battery can be suppressed.SOLUTION: An electrolyte solution for a lithium secondary battery includes a nonaqueous organic solvent, lithium salt, and an additive. The additive includes a first additive represented by Chemical Formula 1 below and a second additive represented by Chemical Formula 2 below. R1 and R2 express halogen or the like, and R3 and R4 express an aryl group with 6 to 20 carbons.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Lithium secondary batteries are rechargeable and have an energy density per unit weight that is more than three times higher than conventional lead-acid batteries, nickel-cadmium batteries, nickel-metal hydride batteries, and nickel-zinc batteries, and they can be charged quickly. As a result, they have been commercialized for use in laptops, mobile phones, power tools, and electric bicycles, and research and development is actively underway to further improve their energy density.

[0003] Such a lithium secondary battery is used by injecting an electrolyte into an electrode assembly including a positive electrode including a positive electrode active material capable of lithium intercalation and deintercalation and a negative electrode including a negative electrode active material capable of lithium intercalation and deintercalation.

[0004] During the charging process of a lithium secondary battery, if lithium ions are reduced instead of being inserted into the negative electrode active material, lithium dendrites grow on the surface of the negative electrode. Lithium dendrites can cause internal short circuits and / or deterioration in the lithium secondary battery, and the charging voltage increases. Furthermore, the growth of lithium dendrites deepens during rapid charging.

[0005] One method for suppressing the growth of lithium dendrites is to use a low-viscosity ester-based solvent as the electrolyte solvent. However, ester-based solvents have low oxidation resistance, and when charged at high voltages (e.g., 4.5 V or higher), they can cause degradation of lithium secondary batteries. Summary of the Invention [Problem to be solved by the invention]

[0006] One embodiment of the present invention provides an electrolyte solution for a lithium secondary battery that can suppress the growth of lithium dendrites and / or the deterioration of the lithium secondary battery even when the charging voltage increases and / or rapid charging is performed. [Means for solving the problem]

[0007] One embodiment of the present invention provides an electrolyte solution for a lithium secondary battery, comprising a non-aqueous organic solvent, a lithium salt, and an additive, the additive comprising a first additive represented by the following Chemical Formula 1 and a second additive represented by the following Chemical Formula 2:

[0008] [ka]

[0009] Another embodiment provides a lithium secondary battery including an electrolyte solution for a lithium secondary battery. [Effects of the Invention]

[0010] The electrolyte for a lithium secondary battery according to one embodiment of the present invention can suppress the growth of lithium dendrites and / or the deterioration of the lithium secondary battery even when the charging voltage increases and / or rapid charging is performed. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment. [Figure 2] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment. [Figure 3] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment. [Figure 4] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] DETAILED DESCRIPTION OF THE INVENTION The following detailed description of the present invention is provided by way of example only and is not intended to limit the scope of the present invention, which is defined solely by the scope of the claims that follow.

[0013] Unless otherwise specified in this specification, when a layer, film, region, plate, or other part is said to be "on" another part, this includes not only the case where it is "directly on" the other part, but also the case where there is another part in between.

[0014] Unless otherwise specified herein, singular terms can also include plural terms. At the same time, unless otherwise specified, "A or B" means "including A, including B, or including A and B."

[0015] As used herein, "combinations thereof" refers to mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0016] Unless otherwise specified in this specification, "substituted" means that at least one hydrogen atom of the compound has been replaced with a halogen atom (F, Cl, Br, I), a hydroxy group, an alkoxy group having 1 to 20 carbon atoms, a nitro group, a cyano group, an amino group, an imino group, an azide group, an amidino group, a hydrazino group, a hydrazono group, a carbonyl group, a carbamoyl group, a thiol group, an ester group, an ether group, a carboxyl group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a carbonyl group, a hydroxyl ... a thiol group, an ester group, an ether group, a carboxyl group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a phosphonic acid group, a phosphonic acid group, a phosphonic acid group, a phosphonic acid group, a phosphonic acid group, a phosphonic acid group, a phosphonic acid group, a phosphonic acid group, a phosphonic acid group, a phosphonic acid group, a phosphonic acid group, a phosphonic acid group, a phosphonic acid group, a phosphonic acid group, a phosphonic acid group, a phosphonic acid group, a phosphonic acid group, a phosphonic acid group, a phosphonic acid group, a phosphonic acid group, a phosphonic acid group, a phosphonic acid group, a phosphonic acid group, a phosphonic acid group, a phosphonic acid group, It means that the alkyl group is substituted with an alkyl group having 1 to 20 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, an alkynyl group having 2 to 20 carbon atoms, an aryl group having 6 to 30 carbon atoms, a cycloalkyl group having 3 to 20 carbon atoms, a cycloalkenyl group having 3 to 20 carbon atoms, a cycloalkynyl group having 3 to 20 carbon atoms, a heterocycloalkyl group having 2 to 20 carbon atoms, a heterocycloalkenyl group having 2 to 20 carbon atoms, a heterocycloalkynyl group having 2 to 20 carbon atoms, or a substituent that is a combination thereof.

[0017] Unless otherwise specified in this specification, the terms "heterocycloalkyl group," "heterocycloalkenyl group," "heterocycloalkynyl group," and "heterocycloalkylene group" mean that at least one N, O, S, or P heteroatom is present in the ring system of a cycloalkyl, cycloalkenyl, cycloalkynyl, and cycloalkylene, respectively.

[0018] Unless otherwise defined in a chemical formula herein, if no chemical bond is drawn at a position where a chemical bond should be drawn, this means that a hydrogen atom is bonded at that position.

[0019] (electrolyte) One embodiment provides an electrolyte solution for a lithium secondary battery, comprising a non-aqueous organic solvent, a lithium salt, and an additive, the additive comprising a first additive represented by the following Chemical Formula 1 and a second additive represented by the following Chemical Formula 2:

[0020] [ka]

[0021] The electrolyte for a lithium secondary battery according to one embodiment can suppress the growth of lithium dendrites and / or the deterioration of the lithium secondary battery even when the charging voltage increases and / or rapid charging is performed.

[0022] [Electrolyte Additives] First Additive The first additive represented by Chemical Formula 1 includes a lithium oxalatoborate-based compound substituted with a halogen group (e.g., a fluoro group), and the halogen group can stabilize a lithium salt (e.g., LiPF6) in a high-voltage environment.

[0023] Therefore, the use of an electrolyte containing the first additive suppresses the generation of HF, and can prevent the elution of transition metals from the positive electrode active material and damage to the SEI film at the interface between the negative electrode and the electrolyte.

[0024] In chemical formula 1, R1 and R 2 may each independently be a halogen or a halogen-substituted or unsubstituted alkyl group having 1 to 20 carbon atoms.

[0025] Preferably, R 1 and R 2 may each independently be a fluoro group or an unsubstituted or fluoro-substituted alkyl group having 1 to 10 carbon atoms.

[0026] For example, R 1 and R 2 may all be fluoro groups.

[0027] Representative examples of the first additive are as follows:

[0028] [ka]

[0029] The first additive is contained in an amount of 0.1 to 10 wt %, 0.5 to 7 wt %, or 1 to 5 wt % relative to the total amount of the electrolyte. An electrolyte containing the first additive in this range can effectively suppress the formation and growth of lithium dendrites.

[0030] Second Additive The second additive represented by Chemical Formula 2 includes a diallyl sulfate-based compound, which is more advantageous than dialkyl sulfate-based compounds or dialkenyl sulfate-based compounds in suppressing the formation and growth of lithium dendrites.

[0031] Therefore, the second additive can suppress the formation and growth of lithium dendrites on the surface of the negative electrode, and can uniformly insert lithium ions into the negative electrode active material.

[0032] In chemical formula 2, R 3 and R 4 may each independently be a substituted or unsubstituted aryl group having 6 to 20 carbon atoms.

[0033] Preferably, R 3 and R 4 may each independently be a substituted or unsubstituted aryl group having 6 to 10 carbon atoms.

[0034] For example, R 3 and R 4 may all be phenyl groups.

[0035] Representative examples of the second additive are as follows:

[0036] [ka]

[0037] The first additive is contained in an amount of 0.1 to 10 wt %, 0.5 to 7 wt %, or 1 to 5 wt % relative to the total amount of the electrolyte. An electrolyte containing the second additive in this range can effectively suppress the formation and growth of lithium dendrites.

[0038] Content ratio (weight ratio) of the first additive and the second additive The weight ratio of the first additive to the second additive may be 10:1 to 1:10, 5:1 to 1:5, or 2:1 to 1:2. Within this range, the effects of the first additive and the second additive are well balanced, so that the growth of lithium dendrites and / or degradation of the lithium secondary battery can be suppressed even when the charging voltage increases and / or rapid charging is performed.

[0039] Third Additive The additive may further include another compound (hereinafter referred to as a "third additive") in addition to the first additive and the second additive.

[0040] The third additive may include a cyclic carbonate, succinonitrile (SN), adiponitrile (AN), 1,3,6-hexanetricyanide (HTCN), propene sultone (PST), propane sultone (PS), lithium tetrafluoroborate (LiBF), lithium difluorophosphate (LiPOF), 2-fluorobiphenyl (2-FBP), or a combination thereof.

[0041] The cyclic carbonate may be, for example, vinyl ethylene carbonate (VEC), vinylene carbonate (VC), ethylene carbonate, a derivative thereof, or a combination thereof. Examples of the derivative of ethylene carbonate include fluoroethylene carbonate (FEC), difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, and cyanoethylene carbonate.

[0042] The third additive is included in an amount of 0.1 wt % to 10 wt %, 0.5 wt % to 9 wt %, 1 wt % to 8 wt %, 1 wt % to 7 wt %, 1 wt % to 6 wt %, or 2 wt % to 5 wt % relative to the total weight of the electrolyte (100 wt %). When the content of the third additive is within the above range, it does not adversely affect the battery, improves the life characteristics, and effectively controls the amount of gas generation and the increase in resistivity.

[0043] [Non-aqueous organic solvent] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reactions of the battery can migrate.

[0044] The non-aqueous organic solvent may be a carbonate, ester, ether, ketone, or alcohol solvent, an aprotic solvent, or a combination thereof.

[0045] Examples of carbonate solvents that can be used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. Examples of ester solvents that can be used include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, propyl propionate, decanolide, mevalonolactone, valerolactone, caprolactone, etc. Examples of ether solvents that can be used include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran. Examples of ketone solvents that can be used include cyclohexanone. Examples of alcohol solvents that can be used include ethyl alcohol and isopropyl alcohol. Examples of aprotic solvents that can be used include nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, which 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, and sulfolanes.

[0046] The non-aqueous organic solvents can be used alone or in combination of two or more kinds.

[0047] When a carbonate-based solvent is used, a cyclic carbonate and a chain carbonate can be mixed and used, and the cyclic carbonate and the chain carbonate can be mixed in a volume ratio of 1:1 to 1:9.

[0048] For example, the non-aqueous organic solvent can include ethylene carbonate (EC), propylene carbonate (PC), and propyl propionate (PP).

[0049] Based on the total volume of the non-aqueous organic solvent, ethylene carbonate (EC) is contained in an amount of 1 to 20 volume %, 1 to 15 volume %, or 5 to 15 volume %, propylene carbonate (PC) is contained in an amount of 5 to 30 volume %, 5 to 20 volume %, or 10 to 20 volume %, and propyl propionate (PP) is contained in an amount of 50 to 90 volume %, 65 to 80 volume %, or 70 to 80 volume %.

[0050] [Lithium salt] Lithium salts are substances that dissolve in organic solvents and act as a source of lithium ions within the battery, enabling basic lithium secondary battery operation and facilitating the movement of lithium ions between the positive and negative electrodes. Representative examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide (LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (x and y are integers of 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalate)phosphate (LiDFOB), and lithium bis(oxalate)borate (LiBOB).

[0051] For example, LiPF6 can be used as the lithium salt.

[0052] The molar concentration of the lithium salt in the electrolyte may be 1.0 to 2.0M.

[0053] (lithium secondary battery)

[0054] Another embodiment provides a lithium secondary battery including the electrolyte solution for a lithium secondary battery according to the above embodiment.

[0055] By including the electrolyte solution for a lithium secondary battery according to the embodiment described above, it is possible to suppress the growth of lithium dendrites and / or the deterioration of the lithium secondary battery even when the charging voltage increases and / or rapid charging is performed.

[0056] The configuration of the lithium secondary battery will be described below, excluding any overlapping description with the above content.

[0057] [Maximum charging voltage] When a lithium secondary battery is charged at a high voltage, the amount of transition metal ions eluted from the positive electrode active material increases.

[0058] However, if a rigid coating is formed on the surface of the positive electrode using the electrolyte solution of the above-described embodiment, it is possible to prevent the transition metal ions in the positive electrode active material from eluting even when the battery is charged at a high voltage.

[0059] For example, the upper charging voltage limit of a lithium secondary battery can be 4.3 V or higher, 4.4 V or higher, or 4.45 V or higher.

[0060] [Cathode active material] The positive electrode active material may be a compound capable of reversibly intercalating and deintercalating lithium (lithiated intercalation compound). Specifically, one or more of composite oxides of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof may be used.

[0061] 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.

[0062] 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 O2 (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 O2 (0.90≦a≦1.8, 0.001≦b≦0.1), Li a CoG b O2 (0.90≦a≦1.8, 0.001≦b≦0.1), Li a Mn 1-b G b O2 (0.90≦a≦1.8, 0.001≦b≦0.1), Li a Mn2G b O4 (0.90≦a≦1.8, 0.001≦b≦0.1), Li a Mn 1-g G g PO4(0.90≦a≦1.8, 0≦g≦0.5), Li (3-f) Fe2(PO4)3(0≦f≦2), Li aFePO4(0.90≦a≦1.8).

[0063] 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.

[0064] The positive electrode active material may include, for example, a lithium nickel-based oxide represented by the following Chemical Formula 11, a lithium cobalt-based oxide represented by the following Chemical Formula 12, a lithium iron phosphate-based compound represented by the following Chemical Formula 13, a cobalt-free lithium nickel-manganese-based oxide represented by the following Chemical Formula 14, or a combination thereof.

[0065] [Chemical formula 11] Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1

[0066] In Chemical Formula 11, 0.9≦a1≦1.8, 0.3≦x1≦1, 0≦y1≦0.7, 0≦z1≦0.7, 0.9≦x1+y1+z1≦1.1, and 0≦b1≦0.1; M 1 and M 2 are each independently one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

[0067] In Chemical Formula 11, 0.6≦x1≦1, 0≦y1≦0.4, and 0≦z1≦0.4, or 0.8≦x1≦1, 0≦y1≦0.2, and 0≦z1≦0.2 may also be satisfied.

[0068] [Chemical formula 12] Li a2 Co x2 M 3 y2 O 2-b2 X b2

[0069] In Chemical Formula 12, 0.9≦a2≦1.8, 0.7≦x2≦1, 0≦y2≦0.3, 0.9≦x2+y2≦1.1, and 0≦b2≦0.1; M 3 is one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Se, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

[0070] [Chemical formula 13] Li a3 Fe x3 M 4 y3 PO 4-b3 X b3

[0071] In Chemical Formula 13, 0.9≦a3≦1.8, 0.6≦x3≦1, 0≦y3≦0.4, and 0≦b3≦0.1; M 4 is one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Co, Cr, Cu, Mg, Mn, Mo, Ni, Se, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

[0072] [Chemical formula 14] Li a4 Ni x4 Mn y4 M 5 z4 O 2-b4 X b4

[0073] In chemical formula 14, 0.9≦a4≦1.8, 0.8≦x4<1, 0 <y4≦0.2、0≦z4≦0.2、0.9≦x4+y4+z4≦1.1、および0≦b4≦0.1であり、M 5 is one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

[0074] For example, the positive electrode active material may be a lithium-cobalt-based oxide represented by Chemical Formula 12, but is not limited thereto.

[0075] [Positive electrode] A 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 includes a positive electrode active material and can further include a binder and / or a conductive material.

[0076] As an example, the positive electrode may further include an additive that can act as a sacrificial positive electrode.

[0077] The content of the positive electrode active material may be 90% by weight to 99.5% by weight relative to 100% by weight of the positive electrode active material layer, and the contents of the binder and conductive material may each be 0.5% by weight to 5% by weight relative to 100% by weight of the positive electrode active material layer.

[0078] The binder serves to firmly adhere the positive electrode active material particles to each other and to firmly adhere the positive electrode active material to the current collector. Representative examples of binders 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, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, and nylon.

[0079] The conductive material is used to impart conductivity to the electrode, and any material that does not cause a chemical change in the constructed battery and is electronically conductive can be used. Examples of the conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0080] The current collector may be made of Al, but is not limited to this.

[0081] [Negative electrode active material] The negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, a lithium metal alloy, a material capable of being doped and dedoped with lithium, or a transition metal oxide.

[0082] As a substance capable of reversibly intercalating / deintercalating lithium ions, a carbon-based negative electrode active material can be used, 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, and examples of amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, fired coke, and the like.

[0083] As an alloy of lithium metal, an alloy of lithium and a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, Sn can be used.

[0084] As a 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 (where 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, SnO2, a Sn-based alloy, or a combination thereof.

[0085] 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 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. Amorphous carbon may also be located between the primary silicon particles, and for example, the primary silicon particles may be coated with amorphous carbon. The secondary particles may be dispersed and present in the amorphous carbon matrix. [[ID=第十三条]]

[0086] The silicon-carbon composite may further comprise crystalline carbon. For example, the silicon-carbon composite may comprise a core comprising crystalline carbon and silicon particles, and an amorphous carbon coating layer disposed on the core.

[0087] The Si-based negative electrode active material or the Sn-based negative electrode active material can be used in combination with a carbon-based negative electrode active material.

[0088] [Negative electrode] A 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 includes a negative electrode active material and may further include a binder and / or a conductive material.

[0089] 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.

[0090] The binder serves to firmly adhere the negative electrode active material particles to each other and to the current collector. The binder may be a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0091] 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.

[0092] The water-based 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, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0093] When an aqueous binder is used as the negative electrode binder, a cellulose-based compound that can impart viscosity may be further included. The cellulose-based compound may be a mixture of one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or alkali metal salts thereof. The alkali metal may be sodium, potassium, or lithium.

[0094] The dry binder may be a fiberizable polymeric material such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0095] The conductive material is used to impart conductivity to the electrode and may be any material that is electronically conductive and does not cause chemical changes in the battery. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0096] The negative electrode current collector may 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.

[0097] [Separator] Depending on the type of lithium secondary battery, a separator may be present between the positive and negative electrodes. Such separators may be made of polyethylene, polypropylene, polyvinylidene fluoride, or multilayer films of two or more of these. Of course, mixed multilayer films such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may also be used.

[0098] The separator can include a porous substrate and a coating layer comprising an organic material, an inorganic material, or a combination thereof located on one or both sides of the porous substrate.

[0099] The porous substrate may be a polymer membrane 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, polyetherimide, polyamide imide, polybenzimidazole, polyethersulfone, 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.

[0100] The organic material may include a polyvinylidene fluoride polymer or a (meth)acrylic polymer.

[0101] The inorganic material may include, but is not limited to, inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof.

[0102] The organic material and the inorganic material may be mixed in one coating layer, or may be stacked in a form in which a coating layer containing an organic material and a coating layer containing an inorganic material are laminated.

[0103] [Lithium secondary battery] Lithium secondary batteries can be classified into cylindrical, prismatic, pouch, and coin types depending on their shape. FIGS. 1 to 4 are schematic diagrams showing lithium secondary batteries according to an embodiment, with FIG. 1 representing a cylindrical battery, FIG. 2 representing a prismatic battery, and FIGS. 3 and 4 representing pouch-type batteries. Referring to FIGS. 1 to 4, a lithium secondary battery 100 may include an electrode assembly 40 having a positive electrode 10 and a negative electrode 20 with a separator 30 interposed therebetween, and a case 50 housing the electrode assembly 40. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte (not shown). As shown in FIG. 1, the lithium secondary battery 100 may include a sealing member 60 that seals the case 50. Also, in FIG. 2, the lithium secondary battery 100 may include a positive electrode lead tab 11, a positive electrode terminal 12, a negative electrode lead tab 21, and a negative electrode terminal 22. As shown in FIGS. 3 and 4, the lithium secondary battery 100 may include electrode tabs 70, i.e., a positive electrode tab 71 and a negative electrode tab 72, which serve as electrical paths for conducting the current generated in the electrode assembly 40 to the outside.

[0104] The lithium secondary battery according to an embodiment of the present invention may be applied to automobiles, mobile phones, and / or various types of electrical devices, but the present invention is not limited thereto. [Example]

[0105] Examples of the present invention and comparative examples are described below. However, the following examples are merely examples of the present invention, and the present invention is not limited to the following examples.

[0106] Example 1 (1) Preparation of electrolyte An organic solvent was prepared by mixing ethylene carbonate (EC), propylene carbonate (PC), and propyl propionate (PP) in a volume ratio of 10:15:75, and LiPF6 lithium salt was mixed at a concentration of 1.3 M. An electrolyte solution was prepared by adding 1 wt % of a first additive represented by the following chemical formula 1-1 and 0.5 wt % of a second additive represented by the following chemical formula 2-1.

[0107] [ka]

[0108] Lithium difluoro(oxalato)borate(Cas No.:409071-16-5)

[0109] [ka]

[0110] Diphenyl sulfone(Cas No.:127-63-9)

[0111] However, in the above electrolyte composition, "% by weight" is based on the content of the entire electrolyte (lithium salt + non-aqueous organic solvent + additives), and the same applies hereinafter.

[0112] (2) Preparation of the positive electrode A positive electrode active material layer slurry was prepared by mixing 97.7 wt% of LiCoO2 positive electrode active material, 1.3 wt% of polyvinylidene fluoride binder, and 1.0 wt% of carbon nanotube conductive material. This was then coated onto an aluminum foil current collector, dried, and rolled to produce a positive electrode.

[0113] (3) Preparation of the negative electrode A negative electrode active material layer slurry was prepared by mixing 97.5 wt% graphite negative electrode active material, 1.5 wt% carboxymethyl cellulose, and 1 wt% styrene-butadiene rubber in an aqueous solvent. The negative electrode active material layer slurry was coated onto a copper foil current collector, dried, and rolled to prepare a negative electrode.

[0114] (4) Fabrication of lithium secondary batteries The cathode and anode prepared as described above and a 25 μm thick polyethylene separator were assembled to prepare an electrode assembly, and the electrode assembly was placed in a prismatic case, after which an electrolyte solution was injected to prepare a lithium secondary battery.

[0115] Example 2 An electrolyte solution and a lithium secondary battery of Example 2 were prepared and fabricated in the same manner as in Example 1, except that the content of the second additive represented by Chemical Formula 2-1 was changed to 1 wt %.

[0116] Example 3 An electrolyte solution and a lithium secondary battery of Example 3 were prepared and fabricated in the same manner as in Example 1, except that the content of the second additive represented by Chemical Formula 2-1 was changed to 2 wt %.

[0117] Example 4 An electrolyte solution and a lithium secondary battery of Example 4 were prepared and fabricated in the same manner as in Example 2, except that the content of the first additive represented by Chemical Formula 1-1 was changed to 0.5 wt %.

[0118] Example 5 An electrolyte solution and a lithium secondary battery of Example 5 were prepared and fabricated in the same manner as in Example 2, except that the content of the first additive represented by Chemical Formula 1-1 was changed to 2 wt %.

[0119] Comparative example 1 (Ref.) An electrolyte solution and a lithium secondary battery of Comparative Example 1 were prepared and fabricated in the same manner as in Example 1, except that no additives were added.

[0120] Comparative Example 2 An electrolyte solution and a lithium secondary battery of Comparative Example 2 were prepared and fabricated in the same manner as in Comparative Example 1, except that 0.5 wt % of the first additive represented by Chemical Formula 1-1 was added.

[0121] Comparative Example 3 An electrolyte solution and a lithium secondary battery of Comparative Example 3 were prepared and fabricated in the same manner as in Comparative Example 1, except that 1 wt % of the first additive represented by Chemical Formula 1-1 was added.

[0122] Comparative Example 4 An electrolyte solution and a lithium secondary battery of Comparative Example 4 were prepared and fabricated in the same manner as in Comparative Example 1, except that 2 wt % of the first additive represented by Chemical Formula 1-1 was added.

[0123] Comparative Example 5 An electrolyte solution and a lithium secondary battery of Comparative Example 5 were prepared and fabricated in the same manner as in Comparative Example 1, except that 0.5 wt % of the second additive represented by Chemical Formula 1-2 was added.

[0124] Comparative Example 6 An electrolyte solution and a lithium secondary battery of Comparative Example 6 were prepared and fabricated in the same manner as in Comparative Example 1, except that 1 wt % of the second additive represented by Chemical Formula 1-2 was added.

[0125] Comparative Example 7 An electrolyte solution and a lithium secondary battery of Comparative Example 7 were prepared and fabricated in the same manner as in Comparative Example 1, except that 1.5 wt % of the second additive represented by Chemical Formula 1-2 was added.

[0126] For reference, the contents of the additives in each of the electrolyte solutions in Examples 1 to 5 and Comparative Examples 1 to 7 are summarized in Table 1 below.

[0127] [Table 1]

[0128] Evaluation example 1: Rapid charging characteristics of a lithium secondary battery The lithium secondary batteries according to Examples 1 to 5 and Comparative Examples 1 to 7 were subjected to 400 charge / discharge cycles at 25°C under the conditions of 3.0C charge (CC / CV, 4.5V, 0.01C cut-off) / 0.5C discharge (CC, 3.0V cut-off), and then the capacity retention ratio (CRR) and DC-IR increase rate were calculated using the following equation 2. DC-IR for each cycle was calculated based on the voltage change when a current of SOC 50C was applied for 30 seconds to discharge the battery.

[0129] [Formula 2] Capacity retention rate [%]=(Discharge capacity after 400 cycles / Discharge capacity after 1 cycle)*100

[0130] [Formula 3] DC-IR increase rate [%] = (DC-IR after 400 cycles / DC-IR after 1 cycle) * 100

[0131] [Table 2]

[0132] According to Table 2 above, the lithium secondary batteries according to Examples 1 to 5 have an improved life span and suppressed increase in DC-IR even when they are rapidly charged at a high voltage.

[0133] The electrolyte solution according to an embodiment represented by Examples 1 to 5 is believed to suppress the growth of lithium dendrites and / or the deterioration of the lithium secondary battery even when the charging voltage increases and / or rapid charging is performed.

[0134] It should be noted that by adjusting the contents of the first additive and the second additive with reference to Examples 1 to 5, it is possible to control the effect.

[0135] Although the preferred embodiment of the present invention has been described above, the present invention is not limited thereto, and various modifications can be made within the scope of the claims, the detailed description of the invention, and the accompanying drawings, and it is natural that these also fall within the scope of the present invention. [Explanation of symbols]

[0136] 100 Lithium secondary battery 10 positive electrode 11 Positive electrode lead tab 12 Positive terminal 20 negative electrode 21 Negative electrode lead tab 22 Negative terminal 30 Separator 40 Electrode assembly 50 cases 60 Sealing member 70 Electrode tab 71 Positive electrode tab 72 Negative electrode tab

Claims

1. non-aqueous organic solvents, lithium salts, and Contains additives, The additive is A first additive represented by the following chemical formula 1, and The second additive is represented by the following chemical formula 2: 【Chemical 1】 In the above formula 1, R １ and R ２ are each independently a halogen or a halogen-substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, 【Chemistry 2】 In the above chemical formula 2, R ３ and R ４ and each independently represent a substituted or unsubstituted aryl group having 6 to 20 carbon atoms.

2. R １ and R ２ and each independently represent a fluoro group or an unsubstituted or fluoro-substituted alkyl group having 1 to 10 carbon atoms.

3. 2. The electrolyte for a lithium secondary battery according to claim 1, wherein the Chemical Formula 1 is represented by the following Chemical Formula 1-1: 【Chemistry 3】

4. 2. The electrolyte solution for a lithium secondary battery according to claim 1, wherein the first additive is contained in an amount of 0.1 to 10 wt % based on the total amount of the electrolyte solution.

5. R ３ and R ４ The electrolyte solution for a lithium secondary battery according to claim 1 , wherein all of are phenyl groups.

6. The electrolyte for a lithium secondary battery according to claim 1, wherein the chemical formula 2 is represented by the following chemical formula 2-1: 【Chemistry 4】

7. 2. The electrolyte solution for a lithium secondary battery according to claim 1, wherein the second additive is contained in an amount of 0.1 to 10 wt % based on the total amount of the electrolyte solution.

8. 2. The electrolyte solution for a lithium secondary battery according to claim 1, wherein a weight ratio of the first additive to the second additive is 10:1 to 1:

10.

9. The additive further comprises a third additive; 2. The electrolyte solution for a lithium secondary battery according to claim 1, wherein the third additive further comprises a cyclic carbonate, succinonitrile, adiponitrile, 1,3,6-hexanetricyanide, propene sultone, propane sultone, lithium tetrafluoroborate, lithium difluorophosphate, 2-fluorobiphenyl, or a combination thereof.

10. 2. The electrolyte for a lithium secondary battery according to claim 1, wherein the non-aqueous organic solvent comprises ethylene carbonate, propylene carbonate, and propyl propionate.

11. 11. The electrolyte solution for a lithium secondary battery according to claim 10, wherein the ethylene carbonate is contained in an amount of 1 to 20% by volume, the propylene carbonate is contained in an amount of 5 to 30% by volume, and the propyl propionate is contained in an amount of 50 to 90% by volume, relative to a total volume of the non-aqueous organic solvent.

12. The lithium salt is LiPF ６ 2. The electrolyte solution for a lithium secondary battery according to claim 1,

13. 2. The electrolyte solution for a lithium secondary battery according to claim 1, wherein the concentration of the lithium salt is 0.1 M to 2.0 M.

14. a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and A lithium secondary battery comprising the electrolyte solution according to any one of claims 1 to 13.

15. 15. The lithium secondary battery according to claim 14, wherein the positive electrode active material comprises a lithium nickel-based oxide, a lithium cobalt-based oxide, a lithium manganese-based oxide, a lithium iron phosphate-based compound, a cobalt-free nickel-manganese-based oxide, or a combination thereof.

16. The lithium secondary battery according to claim 14 , wherein the negative electrode active material comprises a carbon-based negative electrode active material, a Si-based negative electrode active material, or a combination thereof.

17. 15. The lithium secondary battery according to claim 14, wherein the upper limit charging voltage of the lithium secondary battery is 4.5 V or higher.

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