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

Abstract

To provide an electrolyte for a lithium secondary battery, which can improve charge / discharge characteristics and / or high-temperature storage characteristics, and a lithium secondary battery.SOLUTION: An electrolyte for a lithium secondary battery includes an aprotic organic solvent, a lithium salt, a first additive represented by the following Chemical Formula 1, and a second additive represented by the following Chemical Formula 2.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 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, nickel-zinc batteries, etc., and they are capable of fast charging, so they have been commercialized as power sources for laptops, mobile phones, power tools, and electric bicycles. In addition, research and development is being actively conducted to further improve energy density.

[0003] Such lithium secondary batteries are used by injecting an electrolyte into an electrode assembly including a positive electrode containing a positive electrode active material capable of lithium intercalation and deintercalation, and a negative electrode containing a negative electrode active material capable of lithium intercalation and deintercalation. During continuous charge / discharge of a lithium secondary battery or storage at high temperatures, HF, a product of the decomposition of LiPF6 salt at high temperatures, reacts with the positive electrode active material, resulting in the elution of transition metal (e.g., Fe) ions from the active material. The transition metal ions eluted from the positive electrode active material can migrate through the electrolyte and precipitate as transition metals on the surface of the negative electrode. The electrolyte decomposes continuously on the surface of the precipitates, generating gas, and the precipitates increase the resistance of the negative electrode, accelerating the degradation of the lithium secondary battery. Furthermore, moisture present in the battery accelerates the decomposition reaction of LiPF6 salt at high temperatures, increasing the generation of HF, an acidic substance, and thus accelerating the degradation reaction. Summary of the Invention [Problem to be solved by the invention]

[0004] One embodiment of the present invention provides an electrolyte solution for a lithium secondary battery that can remove moisture from within the lithium secondary battery and suppress decomposition of salts and generation of acidic substances at high temperatures, thereby reducing elution of transition metals from active materials, thereby improving the charge / discharge characteristics and / or high-temperature storage characteristics of the lithium secondary battery.

[0005] Another embodiment of the present invention provides a lithium secondary battery including the above-mentioned electrolyte solution for lithium secondary batteries. [Means for solving the problem]

[0006] One embodiment of the present invention provides an electrolyte solution for a lithium secondary battery, comprising an aprotic 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:

[0007] [ka]

[0008] Another embodiment of the present invention provides a lithium secondary battery including a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and the above-described electrolyte solution. [Effects of the Invention]

[0009] The electrolyte for a lithium secondary battery according to one embodiment of the present invention removes moisture from within the lithium secondary battery, suppressing salt decomposition and generation of acidic substances at high temperatures, thereby reducing leaching of transition metals from active materials, thereby improving the charge / discharge characteristics and / or high-temperature storage characteristics of the lithium secondary battery. [Brief explanation of the drawings]

[0010] [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

[0011] 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.

[0012] 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.

[0013] Unless otherwise specified herein, the singular can also include the plural. At the same time, unless otherwise specified, "A or B" means "including A, including B, or including A and B."

[0014] As used herein, "combinations thereof" refers to mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0015] 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 carbon It means that the 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 of a combination thereof.

[0016] Unless otherwise specified in this specification, the terms "heterocycloalkyl group," "heterocycloalkenyl group," "heterocycloalkynyl group," and "heterocycloalkylene group" refer to cycloalkyl, cycloalkenyl, cycloalkynyl, and cycloalkylene groups, respectively, in which at least one N, O, S, or P heteroatom is present in the ring compound.

[0017] Unless otherwise defined in the chemical formulas herein, when 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.

[0018] (electrolyte) One embodiment provides an electrolyte solution for a lithium secondary battery, comprising an aprotic 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:

[0019] [ka]

[0020] The first additive represented by Chemical Formula 1 is an alkane sultone-based compound, which is decomposed from the electrode surface to form a strong film containing -SO3- based components that is stable at high temperatures and has high heat resistance.

[0021] In addition, the second additive represented by chemical formula 2 is a compound in which two cyclohexyl compounds substituted with an isocyanate group are linked by a linker (*-(C(R 3 It has a structure in which two isocyanate groups are linked via )-*), and two isocyanate groups in one molecule have the effect of effectively removing moisture.

[0022] Therefore, the electrolyte solution for a lithium secondary battery according to one embodiment contains two types of additives, which removes moisture from within the lithium secondary battery, thereby suppressing the leaching of transition metals from the positive electrode active material and the accompanying side reactions, thereby improving the charge / discharge characteristics and / or high-temperature storage characteristics of the lithium secondary battery.

[0023] The electrolyte according to one embodiment will be described in more detail below.

[0024] First Additive The explanation for Chemical Formula 1 representing the first additive is as follows:

[0025] X 1 ~X 4 may each independently be a single bond, O, or X.

[0026] For example, X 1 and X 2 One of them is O and the other is X 3 and X 4 One of them may be O.

[0027] L 1 ~L 4 may each independently be a single bond, a carbonyl group, a sulfinyl group, or a substituted or unsubstituted alkylene group having 1 to 10 carbon atoms.

[0028] For example, L 1 ~L 4 may each independently be a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms.

[0029] Chemical formula 1 can also be represented by the following chemical formula 1-1 or 1-2.

[0030] [ka]

[0031] Second Additive The explanation for Chemical Formula 2, which represents the second additive, is as follows:

[0032] R 1 are the same or different and each independently represent a hydrogen atom, a halogen atom, an alkyl group having 1 to 10 carbon atoms, or an isocyanate group; R 1 At least one of them may be an isocyanate group.

[0033] For example, R 1 One of the R is an isocyanate group. 1 are the same or different and may each independently be a hydrogen atom, a halogen atom, or an alkyl group having 1 to 10 carbon atoms.

[0034] For example, R 1 R excluding the isocyanate group 1 may all be hydrogen atoms.

[0035] R 2 are the same or different and each independently represent a hydrogen atom, a halogen atom, an alkyl group having 1 to 10 carbon atoms, or an isocyanate group; R 2 One of them may be an isocyanate group.

[0036] For example, R 2 One of the R is an isocyanate group. 2are the same or different and may each independently be a hydrogen atom, a halogen atom, or an alkyl group having 1 to 10 carbon atoms.

[0037] For example, R 2 R excluding the isocyanate group 2 may all be hydrogen atoms.

[0038] R 3 are the same or different and may each independently be a hydrogen atom or a cyclohexyl isocyanate residue.

[0039] For example, R 3 may be a hydrogen atom.

[0040] n may be an integer of 1-10.

[0041] For example, n may be 1.

[0042] Chemical formula 2 is represented by the following chemical formula 2-1, and the definitions of each substituent are as described above.

[0043] [ka]

[0044] Content / mixing ratio of first additive and second additive The first additive represented by Chemical Formula 1 may be present in an amount of 0.01 to 10 wt %, 0.1 to 5 wt %, or 0.1 to 1 wt % relative to 100 wt % of the total amount of the electrolyte for a lithium secondary battery.

[0045] The second additive represented by Chemical Formula 2 may be present in an amount of 0.01 to 10 wt %, 0.1 to 5 wt %, or 0.1 to 1 wt % relative to the total amount (100 wt %) of the electrolyte for a lithium secondary battery.

[0046] The weight ratio of the first additive represented by Chemical Formula 1 to the second additive represented by Chemical Formula 2 may be 1:10 to 10:1, 1:5 to 5:1, or 2:1 to 1:2.

[0047] When each range is satisfied, the effects of the first additive represented by Chemical Formula 1 and the second additive represented by Chemical Formula 2 can be optimized.

[0048] Additional Additives In addition to the first additive represented by Chemical Formula 1 and the second additive represented by Chemical Formula 2, the additive may further include other compounds (hereinafter referred to as "additional additives").

[0049] The additional additive may include a cyclic carbonate. 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 ethylene carbonate derivatives include fluoroethylene carbonate (FEC), difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, and cyanoethylene carbonate.

[0050] Additionally, the additional additives may further include 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 combinations thereof.

[0051] The additional additive may be 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 additional additive is within the above range, it does not adversely affect the battery, improves the life characteristics, and effectively reduces the amount of gas generation and the increase in resistivity.

[0052] Aprotic Organic Solvents The aprotic organic solvent serves as a medium through which ions involved in the electrochemical reactions of the battery can migrate.

[0053] The aprotic organic solvent may be a carbonate, ester, ether, ketone, or alcohol solvent, an aprotic solvent, or a combination thereof.

[0054] 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), and butylene carbonate (BC). Examples of ester solvents that can be used include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, and caprolactone. 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 alcoholic solvents that can be used include ethyl alcohol and isopropyl alcohol, and examples of aprotic solvents that can be used include nitriles represented by R-CN (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.

[0055] The aprotic organic solvents can be used alone or in combination of two or more.

[0056] 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.

[0057] For example, the aprotic organic solvent may be a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC), with no particular limitation on the volume ratio.

[0058] lithium salts 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(oxalato)phosphate (LiDFOB), and lithium bis(oxalato)borate (LiBOB).

[0059] For example, LiPF6 can be used as the lithium salt.

[0060] The molar concentration of the lithium salt in the electrolyte may be 0.8 to 1.0M, for example, 1.0 to 2.0M.

[0061] (lithium secondary battery) Another embodiment provides a lithium secondary battery including the electrolyte solution for a lithium secondary battery according to the above embodiment.

[0062] By including the electrolyte solution for a lithium secondary battery according to the embodiment described above, moisture in the lithium secondary battery is removed, thereby suppressing the elution of transition metals from the positive electrode active material and the accompanying side reactions, and as a result, the charge / discharge characteristics and / or high-temperature storage characteristics of the lithium secondary battery are improved.

[0063] Hereinafter, the description overlapping with the above content will be omitted, and the configuration of the lithium secondary battery will be described.

[0064] positive electrode 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.

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

[0066] As an example, a compound represented by any one of the following chemical formulas can be used: Li a A 1-b X b O 2-c D c (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05), Li a Mn 2-b X b O 4-c D c (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05), Li a Ni 1-b-c Co b Xc 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 a FePO4(0.90≦a≦1.8).

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

[0068] 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.

[0069] [Chemical formula 11] Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1

[0070] 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.

[0071] 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 be satisfied.

[0072] [Chemical formula 12] Li a2 Co x2 M 3 y2 O 2-b2 X b2

[0073] 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 3is 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.

[0074] [Chemical formula 13] Li a3 Fe x3 M 4 y3 PO 4-b3 X b3

[0075] 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.

[0076] [Chemical formula 14] Li a4 Ni x4 Mn y4 M 5 z4 O 2-b4 X b4

[0077] 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.

[0078] For example, a lithium iron phosphate compound represented by Chemical Formula 13 can be used as the positive electrode active material.

[0079] When a large amount of moisture is present in a lithium secondary battery, decomposition of the LiPF salt is accelerated (especially under high temperature conditions), generating acidic by-products such as HF. When this HF reacts with the lithium iron phosphate compound represented by Chemical Formula 13, Fe ions may be eluted. Therefore, when the electrolyte solution of the above-described embodiment, which is capable of scavenging moisture, is used, the generation of HF, a decomposition product of the salt, is suppressed, and as a result, the elution of Fe can be reduced.

[0080] 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.

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

[0082] 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.

[0083] The binder serves to firmly bond the positive electrode active material particles to each other and to firmly bond 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.

[0084] Any electrically conductive material can be used as long as it can impart electrical conductivity to the electrode and does not cause chemical changes in the battery that is constructed. Examples of the electrically 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.

[0085] The current collector may be made of Al, but is not limited to this.

[0086] 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.

[0087] The material capable of reversibly intercalating / deintercalating lithium ions may be a carbon-based negative electrode active material, such as crystalline carbon, amorphous carbon, or a combination thereof. Examples of crystalline carbon include graphite, such as amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, and examples of amorphous carbon include soft or hard carbon, mesophase pitch carbide, and calcined coke.

[0088] As the 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 and Sn can be used.

[0089] 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 (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.

[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, and 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 material.

[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 material.

[0095] 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.

[0096] 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] 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.

[0098] 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.

[0099] The dry binder is a polymeric material that can be fiberized, and may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0100] The conductive material is used to impart conductivity to the electrodes, and any material that is electron-conductive and does not cause chemical changes in the battery that is constructed can be used. 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 powder or fiber form, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0101] 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.

[0102] Separator Depending on the type of lithium secondary battery, a separator may be present between the positive and negative electrodes. Such separators can be made of polyethylene, polypropylene, polyvinylidene fluoride, or multilayer films of two or more of these. 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 can also be used.

[0103] 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.

[0104] 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 copolymers, 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 material may include a polyvinylidene fluoride-based polymer or a (meth)acrylic-based polymer.

[0106] 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.

[0107] The organic material and the inorganic material may be mixed in one coating layer, or may be present in a form in which a coating layer containing an organic material and a coating layer containing an inorganic material are laminated.

[0108] 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 a lithium secondary battery according to an embodiment, with FIG. 1 representing a cylindrical battery, FIG. 2 representing a prismatic battery, and FIGS. 3 and 4 representing pouch battery types. 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.

[0109] 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]

[0110] 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.

[0111] Example 1 (1) Preparation of electrolyte An organic solvent was prepared by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 2:4:4, and LiPF6 lithium salt was mixed at a concentration of 1.5M. 0.5 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 were added to prepare an electrolyte solution.

[0112] [ka]

[0113] In chemical formula 2-1, R 1 ~R 2 are all hydrogen atoms and n is 1.

[0114] However, the composition of the electrolyte solution is based on the content of the entire electrolyte solution (lithium salt + aprotic organic solvent + first additive + second additive), and the same applies hereinafter.

[0115] (2) Preparation of the positive electrode A positive electrode active material layer slurry was prepared by mixing 97.7 wt% LiFePO4, 1.3 wt% polyvinylidene fluoride binder, and 1.0 wt% carbon nanotube conductive material as the positive electrode active material. This was coated onto an aluminum foil current collector, dried, and rolled to prepare a positive electrode.

[0116] (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.

[0117] (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, which was then housed in a prismatic case and injected with an electrolyte to prepare a lithium secondary battery.

[0118] Example 2 The electrolyte solution and lithium secondary battery of Example 2 were prepared and fabricated in the same manner as in Example 1, except that 0.5 wt % of the first additive represented by Chemical Formula 1-1 and 0.1 wt % of the second additive represented by Chemical Formula 2-1 were used.

[0119] Example 3 The electrolyte solution and lithium secondary battery of Example 3 were prepared and fabricated in the same manner as in Example 1, except that 0.5 wt % of the first additive represented by Chemical Formula 1-1 and 0.3 wt % of the second additive represented by Chemical Formula 2-1 were used.

[0120] Example 4 The electrolyte solution and lithium secondary battery of Example 4 were prepared and fabricated in the same manner as in Example 1, except that 0.1 wt % of the first additive represented by Chemical Formula 1-1 and 0.5 wt % of the second additive represented by Chemical Formula 2-1 were used.

[0121] Example 5 The electrolyte solution and lithium secondary battery of Example 5 were prepared and fabricated in the same manner as in Example 1, except that 0.3 wt % of the first additive represented by Chemical Formula 1-1 and 0.5 wt % of the second additive represented by Chemical Formula 2-1 were used.

[0122] Example 6 The same electrolyte as in Example 1 was used. In addition, LiNi was used as the positive electrode active material instead of LiFePO4. 0.9 Co 0.08 Al 0.02 A lithium secondary battery of Example 6 was produced in the same manner as in Example 1, except that O2 was used.

[0123] Example 7 The same electrolyte as in Example 1 was used. In addition, LiNi was used as the positive electrode active material instead of LiFePO4. 0.8 Co 0.1 Mn 0.1 An electrolyte solution and a lithium secondary battery of Example 7 were produced in the same manner as in Example 1, except that O2 was used.

[0124] Comparative example 1 (Ref.) The electrolyte solution and lithium secondary battery of Comparative Example 1 were prepared and fabricated in the same manner as in Example 1, except that the first additive represented by Chemical Formula 1-1 and the second additive represented by Chemical Formula 2-1 were not used at all.

[0125] 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 Example 1, except that only the first additive represented by Chemical Formula 1-1 was used in an amount of 0.5 wt% among the additives.

[0126] 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 Example 1, except that only the second additive represented by Chemical Formula 2-1 was used in an amount of 0.5 wt % among the additives.

[0127] For reference, the positive electrode active materials and additives of Examples 1 to 6 and Comparative Examples 1 to 3 are summarized in Table 1 below.

[0128] [Table 1]

[0129] Evaluation example 1: Life characteristics (1) Life characteristics at room temperature The lithium secondary batteries according to Examples 1 to 7 and Comparative Examples 1 to 3 were subjected to 400 charge / discharge cycles under the conditions of 25°C, 0.5C charge (CC / CV, 3.65V, 0.025C cut-off) / 0.5C discharge (CC, 2.5V cut-off), and then the capacity retention ratio (CRR) at room temperature was calculated using the following formula 1.

[0130] (2) Life characteristics at high temperatures The lithium secondary batteries of Examples 1 to 7 and Comparative Examples 1 to 3 were subjected to 400 charge / discharge cycles under the conditions of 45°C, 0.5C charge (CC / CV, 3.65V, 0.025C cut-off) / 0.5C discharge (CC, 2.5V cut-off), and then the capacity retention ratio (CRR) at high temperature was calculated using the following equation 1.

[0131] [Formula 1] Capacity retention rate [%]=(Discharge capacity after 200 cycles / Discharge capacity after 1 cycle)*100

[0132] [Table 2]

[0133] Evaluation example 2: High temperature storage characteristics (1) DC-IR increase rate For the lithium secondary batteries of Examples 1 to 7 and Comparative Examples 1 to 3, the initial DC resistance (DCIR) was measured using the ΔV / ΔI (change in voltage / change in current) value, and then the maximum energy state inside the battery was set to a fully charged state (SOC 100%). After storing the batteries in this state at high temperature (60°C) for 60 days, the DC resistance was measured and the DC-IR increase rate (%) was calculated using the following formula 2. The results are shown in Table 3 below.

[0134] [Formula 2] DC-IR increase rate [%] = (DC-IR after 60 days of high temperature storage / initial DC-IR) * 100

[0135] (2) Lifespan (capacity maintenance rate) The lithium secondary batteries of Examples 1 to 7 and Comparative Examples 1 to 3 were subjected to one cycle immediately after fabrication, and then the discharge capacity was measured (initial discharge capacity). The maximum energy state inside the battery was then set to a fully charged state (SOC 100%), and the battery was stored in this state at a high temperature (60°C) for 60 days. After one cycle, the discharge capacity was measured (discharge capacity after high-temperature storage), and the capacity retention rate (%) was calculated using the following formula 3. The results are shown in Table 3 below.

[0136] [Formula 3] Capacity retention rate [%]=(Discharge capacity after high temperature storage / Initial discharge capacity)*100

[0137] (3) Amount of gas generated The amount of gas generated immediately after production was measured for the lithium secondary batteries of Examples 1 to 7 and Comparative Examples 1 to 3. The results are shown in Table 3 below.

[0138] [Table 3]

[0139] Results and Discussion According to Tables 2 and 3, when LiFePO4 is used as the positive electrode active material, the lithium secondary batteries using the electrolyte solutions of Examples 1 to 5 have improved room temperature and high temperature life characteristics (increased capacity retention rate) and improved high temperature storage characteristics (decreased DC-IR increase rate, increased capacity retention rate, and reduced amount of gas generation) compared to Comparative Examples 1 to 3.

[0140] Furthermore, by adjusting the compounding ratio (weight ratio) of the first additive represented by chemical formula 1 and the second additive represented by chemical formula 2 with reference to Examples 1 to 5, the effect can also be controlled.

[0141] On the other hand, the characteristics of the lithium secondary batteries of Examples 6 and 7, which used the same electrolyte as in Example 1 but changed the positive electrode active material, were improved compared to Comparative Example 1, but were less effective than Examples 1 to 5. This shows that the electrolyte for a lithium secondary battery of one embodiment represented by Example 1 can be used in combination with any positive electrode active material, but is optimized when LiFePO4 is used as the positive electrode active material.

[0142] 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 to be understood that these modifications also fall within the scope of the present invention. [Explanation of symbols]

[0143] 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. aprotic 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 1: 【Chemistry 1】 In the above Chemical Formula 1, X １ ~X ４ are each independently a single bond, O, or X; L １ ~L ４ each independently represents a single bond, a carbonyl group, a sulfinyl group, or a substituted or unsubstituted alkylene group having 1 to 10 carbon atoms, 【Chemistry 2】 In the above Chemical Formula 2, R １ are the same or different and each independently represent a hydrogen atom, a halogen atom, an alkyl group having 1 to 10 carbon atoms, or an isocyanate group, The R １ at least one of which is an isocyanate group; R ２ are the same or different and each independently represent a hydrogen atom, a halogen atom, an alkyl group having 1 to 10 carbon atoms, or an isocyanate group, The R ２ one of which is an isocyanate group, R ３ are the same or different and each independently represent a hydrogen atom or a cyclohexyl isocyanate residue, An electrolyte for a lithium secondary battery, wherein n is an integer of 1 to 10.

2. L １ ~L ４ and each independently represent a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms.

3. X １ and X ２ One of them is O and the other is X. ３ and X ４ 2. The electrolyte for a lithium secondary battery according to claim 1, wherein one of the groups is O.

4. 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 or 1-2: 【Transformation 3】

5. The chemical formula 2 is represented by the following chemical formula 2-1: 【Chemistry 4】 In the above chemical formula 2-1, R １ are the same or different and each independently represent a hydrogen atom, a halogen atom, or an alkyl group having 1 to 10 carbon atoms, R ２ and are the same or different and each independently represent a hydrogen atom, a halogen atom, or an alkyl group having 1 to 10 carbon atoms.

6. 2. The electrolyte solution for a lithium secondary battery according to claim 1, wherein the first additive represented by Chemical Formula 1 is contained in an amount of 0.01 to 10 wt % based on 100 wt % of the total amount of the electrolyte solution for a lithium secondary battery.

7. 2. The electrolyte solution for a lithium secondary battery according to claim 1, wherein the second additive represented by Chemical Formula 2 is contained in an amount of 0.01 to 10 wt % based on 100 wt % of the total amount of the electrolyte solution for a lithium secondary battery.

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

1.

9. 2. The electrolyte solution for a lithium secondary battery according to claim 1, wherein the aprotic organic solvent comprises ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate.

10. The lithium salt is LiPF ６ The electrolyte solution for a lithium secondary battery according to claim 1, comprising:

11. 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 10.

12. 12. The lithium secondary battery according to claim 11, wherein the positive electrode active material is 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.

13. The positive electrode active material is a lithium iron phosphate-based compound represented by the following chemical formula 13: [Chemical formula 13] Li ａ３ Fe ｘ３ M ４ ｙ３ PO ４－ｂ３ X ｂ３ In the above 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; 13. The lithium secondary battery according to claim 12, wherein X is one or more elements selected from the group consisting of F, P, and S.

14. The lithium secondary battery according to claim 11 , wherein the negative electrode active material is a Si-based negative electrode active material, a carbon-based negative electrode active material, or a combination thereof.

15. The lithium secondary battery according to claim 14 , wherein the negative electrode active material is a carbon-based negative electrode active material.

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