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

Abstract

To provide an electrolyte solution for a lithium secondary battery, which contains a non-aqueous organic solvent having a low reduction potential and high oxidation resistance.SOLUTION: The present invention relates to an electrolyte solution for a lithium secondary battery and a lithium secondary battery including the same, the electrolyte includes a non-aqueous organic solvent and a lithium salt, the non-aqueous organic solvent includes two or more propionate-based solvents, and the propionate-based solvent includes an alkyl fluorinated propionate and a propyl propionate.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] In recent years, the demand for high-energy-density, high-capacity secondary batteries has increased rapidly with the rapid spread of electronic devices that use batteries, such as mobile phones, laptops, and electric vehicles. This has led to active research and development into improving the performance of lithium secondary batteries.

[0003] A lithium secondary battery is a battery that includes a positive electrode, a negative electrode, and an electrolyte, each of which includes an active material capable of intercalating and deintercalating lithium ions, and generates electrical energy through oxidation and reduction reactions that occur when lithium ions are intercalated and deintercalated from the positive electrode and the negative electrode.

[0004] The electrolytes widely known up to now are those using carbonate-based non-aqueous organic solvents, but carbonate-based non-aqueous organic solvents have a high tendency to be electrochemically oxidized and decomposed under high charging voltage conditions, and therefore electrolytes using carbonate-based non-aqueous organic solvents not only cause side reactions on the surface of the positive electrode to form a resistance layer, but also cause problems such as gas generation and electrolyte depletion, thereby persistently impairing the life characteristics of lithium secondary batteries. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2018 / 061301 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of one embodiment of the present invention is to provide an electrolyte for a lithium secondary battery, which contains a non-aqueous organic solvent having a low reduction potential and high oxidation resistance. [Means for solving the problem]

[0007] One embodiment of the present invention provides an electrolyte for a lithium secondary battery, comprising a non-aqueous organic solvent and a lithium salt, the non-aqueous organic solvent comprising two or more propionate-based solvents, the propionate-based solvent comprising an alkyl fluorinated propionate and a propyl propionate.

[0008] Another embodiment of the present invention provides a lithium secondary battery including an electrolyte. Effect of the Invention

[0009] The electrolyte for lithium secondary batteries of the present invention can form a stable SEI film on the surface of a negative electrode and can also suppress side reactions on the surface of a positive electrode.

[0010] Therefore, a lithium secondary battery using the electrolyte solution can exhibit excellent life characteristics even when the charging voltage is increased. [Brief description of the drawings]

[0011] [Figure 1] 1 is a schematic diagram showing a lithium secondary battery according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, embodiments of the present invention will be described in detail, but they are given by way of example only and are not intended to limit the present invention, which is defined by the scope of the following claims.

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

[0014] 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."

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

[0016] (electrolyte) One embodiment provides an electrolyte for a lithium secondary battery, comprising a non-aqueous organic solvent having a low reduction potential and high oxidation resistance.

[0017] Specifically, one embodiment provides an electrolyte for a lithium secondary battery, comprising a non-aqueous organic solvent and a lithium salt, the non-aqueous organic solvent comprising two or more propionate-based solvents, the propionate-based solvent comprising an alkyl fluorinated propionate and a propyl propionate.

[0018] The electrolyte solution for a lithium secondary battery of one embodiment can form a stable SEI film on the surface of a negative electrode and can suppress side reactions on the surface of a positive electrode.

[0019] Therefore, a lithium secondary battery using the electrolyte solution can exhibit excellent life characteristics even when the charging voltage is increased.

[0020] <Propionate-based solvents> The non-aqueous organic solvent comprises two or more propionate-based solvents, and the propionate-based solvents include an alkyl fluorinated propionate and a propyl propionate.

[0021] Propionate-based solvents have higher electrochemical stability than carbonate-based solvents, and side reactions are reduced even when the lithium secondary battery is repeatedly charged and discharged. This can be confirmed by the battery capacity retention rate and the amount of decomposition products of the lithium salt after a long charge and discharge cycle of the lithium secondary battery.

[0022] Alkyl fluorinated propionate has a low reduction potential and can form a robust LiF-rich solid electrolyte interphase (SEI) on the negative electrode to protect the negative electrode. In addition, alkyl fluorinated propionate has high oxidation resistance, suppresses side reactions between the positive electrode and the electrolyte, and prevents deterioration of the positive electrode. Therefore, alkyl fluorinated propionate suppresses deterioration of not only the negative electrode but also the positive electrode even in a high-voltage environment, improving the life of lithium secondary batteries.

[0023] Specifically, the alkyl fluorinated propionate is represented by the following chemical formula 1:

[0024] [ka]

[0025] In chemical formula 1, R 1 can be a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms.

[0026] For example, R 1 can be a methyl group.

[0027] In chemical formula 1, X 1 ~X 5 may be the same or different and each independently may be a hydrogen atom or a fluorine atom.

[0028] For example, X 1 ~X 5 Three or more of may be fluorine atoms.

[0029] Representative examples of Formula 1 are represented by Formulas 1-1, 1-2, or 1-3 below:

[0030] [ka]

[0031] [ka]

[0032] [ka]

[0033] The alkyl fluorinated propionate represented by chemical formula 1-1 is methyl 3,3,3-trifluoropropionate (MTIP), the alkyl fluorinated propionate represented by chemical formula 1-2 is methyl 2,2,3,3,3-pentafluoropropanoate, and the alkyl fluorinated propionate represented by chemical formula 1-3 is methyl 2,3,3-trifluoropropanoate. When at least one of these is used, the deterioration of not only the negative electrode but also the positive electrode can be suppressed, and the life of the lithium secondary battery can be improved.

[0034] Relative to 100% by volume of the non-aqueous organic solvent, the alkyl fluorinated propionate is contained at 1% by volume to 30% by volume, 5% by volume to 30% by volume, 10% by volume to 30% by volume, or 15% by volume to 30% by volume; and the propyl propionate is contained at 30% by volume to 90% by volume, 40% by volume to 80% by volume, 50% by volume to 65% by volume, or 50% by volume to 60% by volume.

[0035] In the propionate-based solvent, the volume ratio of alkyl fluorinated propionate and propyl propionate can be 1:1 to 1:9, 1:1.5 to 1:8, 1:2 to 1:7, or 1:2 to 1:4.

[0036] Even if the charging voltage is increased within the above range, the oxidative decomposition of the propionate-based solvent can be suppressed.

[0037] The propionate-based solvent may contain only two of the alkyl fluorinated propionate and the propyl propionate, but may selectively further contain methyl propionate, ethyl propionate, or a combination thereof.

[0038] The propionate-based solvent is contained in an amount of 50% to 90% by volume relative to 100% by volume of the non-water-soluble organic solvent.

[0039] <Carbonate-based solvent> The non-aqueous organic solvent may further include a carbonate-based solvent.

[0040] The carbonate-based non-aqueous organic solvent includes a cyclic carbonate-based non-aqueous organic solvent and a linear carbonate-based non-aqueous organic solvent. Specifically, the carbonate-based non-aqueous organic solvent may include at least one selected from a cyclic carbonate-based non-aqueous organic solvent including ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), or a combination thereof; and a linear carbonate-based non-aqueous organic solvent including dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), or a combination thereof. In addition, when using a carbonate-based solvent, a cyclic carbonate and a chain carbonate may be mixed and used, and the cyclic carbonate and the chain carbonate may be mixed at a volume ratio of 1:1 to 1:9.

[0041] The volume ratio of the carbonate-based solvent to the propionate-based solvent may be 1:2 to 1:3, where the propionate-based solvent functions as a "main solvent" and the carbonate-based solvent functions as an "auxiliary solvent".

[0042] <Lithium salt> Lithium salts are substances that dissolve in organic solvents and act as a source of lithium ions in the battery to enable basic lithium secondary battery operation and facilitate 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 p F 2p+1 SO2)(C q F 2q+1 SO2) (p and q are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFOB), and lithium bis(oxalato)borate (LiBOB).

[0043] The lithium salt is preferably used at a concentration within the range of 0.1 M to 2.0 M. If the lithium salt concentration is within the above range, the electrolyte has appropriate ion conductivity and viscosity, and therefore can exhibit excellent performance and allow lithium ions to migrate effectively.

[0044] <Additives> The electrolyte may further include a carbonate-based additive, a sultone-based additive, a nitrile-based additive, a lithium salt-based additive, or a combination thereof to improve battery life.

[0045] The carbonate based additive may also include vinylene carbonate or ethylene carbonate based compounds.

[0046] Representative examples of the ethylene carbonate-based compounds include fluoroethylene carbonate, difluoroethylene carbonate, vinylethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, and cyanoethylene carbonate.

[0047] The nitrile additive may also include a dinitrile compound, a polynitrile compound, or a combination thereof.

[0048] Representative examples of dinitrile compounds include succinonitrile (SN), glutaronitrile, adiponitrile (AN), pimelonitrile, octanedinitrile, nonanedinitrile, caprylnitrile, ethylene glycol (bispropionitrile) ether (nitrile ether), and fumaronitrile.

[0049] Representative examples of polynitrile compounds include 1,3,6-hexanetrinitrile (HTCN), 1,2,6-hexanetrinitrile, 1,3,5-pentanetrinitrile, nonanetrinitrile, 1,3,5-benzotrinitrile, 2,4,6-trifluorobenzene-1,3,5-trinitrile, 1,3,5-cyclohexanetrinitrile, 1,2,3-propionitrile, 1,3,5-benzotricyano, and 1,2,3-tris(2-cyanooxy)propane.

[0050] Sulfone-based additives include propene sultone (PST), propane sultone (PS), and the like; lithium salt-based additives include lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium difluoro(fluoromalonate)borate (LFMB), and the like.

[0051] (lithium secondary battery) Another embodiment provides a lithium secondary battery comprising: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and an electrolyte according to an embodiment of the present invention.

[0052] <Lithium secondary battery> FIG. 1 is an exploded perspective view of a lithium secondary battery 100 according to one embodiment of the present invention.

[0053] Referring to FIG. 1, a lithium secondary battery 100 according to an embodiment of the present invention includes a positive electrode 10, a negative electrode 20, and a separator 30. The separator 30 is disposed between the positive electrode 10 and the negative electrode 20, and the positive electrode 10, the negative electrode 20, and the separator are wound or folded to form an electrode assembly 40. The formed electrode assembly 40 is housed in a case 50. An electrode tab 70 that serves as an electrical path for inducing the electrodes formed by the electrode assembly 40 to the outside may be included. An electrolyte according to an embodiment of the present invention is injected into the case 50 and sealed to complete the lithium secondary battery 100. The case 50 is rectangular, but is not necessarily limited to such a shape, and may be, for example, cylindrical or pouch-shaped.

[0054] The lithium secondary battery may have a charging voltage of 4.5 V or more, or 4.53 V or more. The lithium secondary battery using the electrolyte solution can exhibit excellent life characteristics even when the charging voltage is increased as described above.

[0055] <Positive electrode> The positive electrode for a lithium secondary battery may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material, and may further include a binder and / or a conductive material.

[0056] As an example, the positive electrode can further include an additive that can act as a sacrificial positive electrode.

[0057] 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.

[0058] The binder serves to make the positive electrode active material particles adhere well to each other and to the current collector. Representative examples of the binder include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, nylon, etc.

[0059] The conductive material is used to impart electrical conductivity to the electrodes, and any material that does not cause chemical changes in the battery that is constructed 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 containing copper, nickel, aluminum, silver, etc., in the form of metal powder or metal fiber; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0060] The positive electrode current collector can be made of Al, but is not limited to this.

[0061] <Cathode active material> The positive electrode active material may be a compound capable of reversible intercalation and deintercalation of 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.

[0062] The composite oxide may be a lithium transition metal composite oxide, and specific examples include lithium nickel-based oxides, lithium cobalt-based oxides, lithium manganese-based oxides, lithium iron phosphate-based compounds, cobalt-free nickel-manganese-based oxides, or combinations thereof.

[0063] As an example, a compound represented by any one of the following chemical formulas can be used. 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);Lia 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, 0.001b≦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).

[0064] In the chemical formula, A is Ni, Co, Mn, or a combination thereof; X is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is O, F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; L 1 is Mn, Al or a combination thereof.

[0065] Specifically, the positive electrode active material may include a lithium nickel-based composite oxide represented by the following chemical formula 2:

[0066] [Chemical formula 2] Li x M 1 y M 2 z M 3 1-y-z O 2±a X a

[0067] In chemical formula 2, 0.5≦x≦1.8, 0≦a≦0.1, 0 <y≦1、0≦z≦1、0<y+z≦1、M 1 , M 2 and M. 3each independently comprises one or more elements selected from metals such as Ni, Co, Mn, Al, B, Ba, Ca, Ce, Cr, Fe, Mo, Nb, Si, Sr, Mg, Ti, V, W, Zr, or La, and combinations thereof, and X comprises one or more elements selected from F, S, P, or Cl.

[0068] The positive electrode active material corresponding to chemical formula 2 is LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi a Mn b Co c O2(a+b+c=1), LiNi a Mn b Co c Al d O2(a+b+c+d=1) and LiNi e Co f Al g O2 (e+f+g=1).

[0069] As an example, the positive electrode active material may be a high-nickel-based positive electrode active material in which the nickel content relative to 100 mol% of metals excluding lithium in a lithium transition metal composite oxide is 80 mol% or more, 85 mol% or more, 90 mol% or more, 91 mol% or more, or 94 mol% or more and 99 mol% or less. The high-nickel-based positive electrode active material can achieve high capacity and can be applied to high-capacity, high-density lithium secondary batteries.

[0070] <Negative electrode> The negative electrode for a lithium secondary battery includes a negative electrode current collector and a negative electrode active material layer located on the negative electrode 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.

[0071] 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.

[0072] The binder serves to adhere the negative electrode active material particles to each other and to the negative electrode current collector well. The binder may be a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0073] Non-aqueous binders include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymers, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

[0074] 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.

[0075] When an aqueous binder is used as the negative electrode binder, a cellulose-based compound capable of imparting viscosity may be further included. As the cellulose-based compound, one or more of carboxymethylcellulose, hydroxypropylmethylcellulose, methylcellulose, or alkali metal salts thereof may be mixed and used. As the alkali metal, Na, K, or Li may be used.

[0076] The dry binder may be a polymeric material capable of being fiberized, such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0077] The conductive material is used to impart electrical conductivity to the electrodes, and any material that does not cause chemical changes in the battery that is constructed and is electronically conductive 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 the form of metal powder or metal fiber, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0078] 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.

[0079] <Negative electrode active material> The negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of being doped and dedoped with lithium, or a transition metal oxide.

[0080] The material capable of reversibly intercalating / deintercalating lithium ions may be a carbon-based negative electrode active material, and may include, for example, 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 graphite or artificial graphite, and examples of amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, and calcined coke.

[0081] As the alloy of lithium metal, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al and Sn can be used.

[0082] As the substance capable of doping and undoping lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used. The Si-based negative electrode active material may be silicon, a silicon-carbon composite, SiOx (0 < x < 2), a Si-Q alloy (Q is selected from an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element (excluding Si), a Group 15 element, a Group 16 element, a transition metal, a rare earth element, and combinations thereof), or a combination thereof. The Sn-based negative electrode active material may be Sn, SnO2, a Sn-based alloy, or a combination thereof.

[0083] The silicon-carbon composite may be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite may be in a form in which amorphous carbon is coated on the surface of silicon particles. For example, it may include secondary particles (cores) formed by granulating primary silicon particles and an amorphous carbon coating layer (shell) located on the surface of the secondary particles. The amorphous carbon is also located between the primary silicon particles, and for example, the primary silicon particles can be coated with amorphous carbon. The secondary particles may be dispersed and present in the amorphous carbon matrix.

[0084] The silicon-carbon composite may further include crystalline carbon. For example, the silicon-carbon composite can include a core containing crystalline carbon and silicon particles and an amorphous carbon coating layer located on the surface of the core.

[0085] The Si-based negative electrode active material or the Sn-based negative electrode active material can be used in mixture with a carbon-based negative electrode active material.

[0086] <Separator> Depending on the type of lithium secondary battery, a separator may be present between the positive and negative electrodes. As such a separator, polyethylene, polypropylene, polyvinylidene fluoride, or a multi-layer film of two or more layers of these may be used, and it is of course possible to use a mixed multi-layer film such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator.

[0087] 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.

[0088] 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 fibers, Teflon (registered trademark), and polytetrafluoroethylene, or a copolymer or mixture of two or more of these.

[0089] The organic material may include a polyvinylidene fluoride-based polymer or a (meth)acrylic-based polymer.

[0090] The inorganics can include, but are 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.

[0091] The organic material and the inorganic material may be mixed in one coating layer, or a coating layer containing an organic material and a coating layer containing an inorganic material may be laminated.

[0092] (electrolyte) The electrolyte solution according to one embodiment of the present invention can be used as the electrolyte solution. The lithium secondary battery using the electrolyte solution according to one embodiment of the present invention can have a charging voltage of 4.5 V or more, or 4.53 V or more. The lithium secondary battery using the electrolyte solution can exhibit excellent life characteristics even when the charging voltage is increased as described above.

[0093] The lithium secondary battery according to an embodiment of the present invention may be applied to automobiles, mobile phones, and / or various types of electric devices, but the present invention is not limited thereto. EXAMPLES

[0094] Examples and comparative examples of the present invention will be described below. However, the following examples are merely examples of the present invention, and the present invention is not limited to the following examples.

[0095] Example 1 (1) Electrolyte production An electrolyte solution was prepared by mixing the components as shown in Table 1 below. In the electrolyte solution compositions below, the lithium salt content "M" indicates the amount (mol) of lithium salt in the volume (L) of the entire electrolyte solution (lithium salt + non-aqueous organic solvent + additives); the non-aqueous organic solvent content "volume %" is based on 100 volume % of the entire non-aqueous organic solvent; and the additive content "weight %" is based on 100 weight % of the entire electrolyte solution (lithium salt + non-aqueous organic solvent + additives).

[0096] [Table 1]

[0097] The substances used in Table 1 above are as follows: 1) Lithium salt LiPF6: Lithium hexafluorophosphate

[0098] 2) Carbonate-based solvents EC: Ethylene carbonate PC: Propylene carbonate

[0099] 3) Propionate Solvents PP: Propyl propionate MP: Methyl propionate MTIP: Methyl 3,3,3-trifluoropropionate

[0100] 4) Other additives FEC: Fluoroethylene carbonate VEC: Vinyl ethylene carbonate LiBF4: Lithium tetrafluoroborate PS: Propane sultone SN: Succinonitrile HTCN: 1,3,6-Hexanetrinitrile LFMB: Lithium difluoro(fluoromalonate)borate

[0101] (2) Manufacture of lithium secondary batteries LiCoO2 as a positive electrode active material, polyvinylidene fluoride as a binder, and Ketjen black as a conductive material were mixed in a weight ratio of 98.5:0.75:0.75, respectively, and dispersed in N-methylpyrrolidone to produce a positive electrode active material slurry.

[0102] The positive electrode active material slurry was coated on a positive electrode current collector (a 14 μm-thick Al foil) at a loading amount of 36.72 mg / cm, dried at 110° C., and pressed to prepare a positive electrode.

[0103] Artificial graphite was used as the negative electrode active material. The negative electrode active material, styrene-butadiene rubber binder, and carboxymethyl cellulose were mixed in a weight ratio of 97:1:2, respectively, and dispersed in distilled water to prepare a negative electrode active material slurry.

[0104] The negative electrode active material slurry was coated on a negative electrode current collector (a copper foil having a thickness of 10 μm) at a loading amount of 20.76 mg / cm, dried at 100° C., and pressed to prepare a negative electrode.

[0105] The positive and negative electrodes prepared above were assembled with a 16 μm thick polyethylene separator to prepare an electrode assembly, which was then placed in a pouch and the electrolyte solution of Example 1 was injected to prepare a 2032 coin-type lithium secondary battery.

[0106] The lithium secondary batteries of Examples 2 to 7 and Comparative Examples 1 to 3 were produced in the same manner as the lithium secondary battery of Example 1, except that the electrolyte solutions of Examples 2 to 7 and Comparative Examples 1 to 3, respectively, were used as the electrolyte solutions.

[0107] <Evaluation Example 1: Capacity Retention Rate of Lithium Secondary Battery> After undergoing the formation step, the lithium secondary batteries of Examples 1 to 7 and Comparative Examples 1 to 3 were charged at a constant current of 1.5 C rate at 25° C. until the voltage reached 4.53 V (vs. Li), and then cut-off at a current of 0.075 C rate while maintaining 4.53 V in constant voltage mode. Next, during discharge, the batteries were discharged at a constant current of 0.75 C rate until the voltage reached 3 V (vs. Li). This charge-discharge cycle was repeated 200 times.

[0108] In all charge / discharge cycles, a rest period of 10 minutes was allowed after one charge / discharge cycle.

[0109] The results of the charge and discharge experiments are shown in Table 2 below. th The capacity retention rate during cycling is defined by the following formula 1.

[0110] <Formula 1> Capacity retention rate=[n th Discharge capacity in cycles / 1 st Discharge capacity in cycles x 100

[0111] [Table 2]

[0112] According to Table 2 above, it was found that the longer the charge / discharge cycle of the lithium secondary battery was, the more rapidly the lifespan of Comparative Examples 1-3 decreased compared to Examples 1-7.

[0113] This is presumably because propionate-based solvents, including alkyl fluorinated propionate and propyl propionate, have higher electrochemical stability than carbonate-based solvents, and reduce side reactions even when the lithium secondary battery is subjected to repeated charge-discharge cycles.

[0114] <Evaluation Example 2: Confirmation of decomposition products of lithium salt after high-temperature life of lithium secondary battery> The positive electrode of the lithium secondary battery after high-temperature life was disassembled and analyzed by XPS to confirm whether the decomposition products of the lithium salt in the electrolyte had adhered to the negative electrode surface.

[0115] Representatively, only Comparative Examples 1 to 3 and Examples 1 and 3 were checked, and the results are shown in Table 3 below.

[0116] [Table 3] (Unit: weight %)

[0117] According to Table 3 above, compared to Comparative Examples 1 and 3, the amounts of F and P, which are decomposition products of the lithium salt (LiPF6), detected in Example 3 are smaller.

[0118] These results indicate that propionate-based solvents, including alkyl fluorinated propionate and propyl propionate, have higher electrochemical stability than carbonate-based solvents and reduce side reactions on the positive electrode surface.

[0119] Although the above describes a preferred embodiment of the present invention, the present invention is not limited thereto, and various modifications and variations can be made within the scope of the claims, the detailed description of the invention, and the accompanying drawings, which of course also fall within the scope of the present invention. [Explanation of symbols]

[0120] 100 Lithium secondary battery 10 positive electrode 20 negative electrode 30 Separator 40 Electrode assembly 50 cases 70 Electrode tab

Claims

1. a non-aqueous organic solvent and a lithium salt; The non-aqueous organic solvent comprises two or more propionate solvents, The electrolyte for a lithium secondary battery, wherein the propionate-based solvent includes an alkyl fluorinated propionate and a propyl propionate.

2. The electrolyte for a lithium secondary battery according to claim 1 , wherein the alkyl fluorinated propionate is represented by the following Chemical Formula 1: 【Chemistry 1】 (In the above Chemical Formula 1, R １ is a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, X １ ~X ５ are the same or different and each independently represents a hydrogen atom or a fluorine atom.

3. R １ The electrolyte for a lithium secondary battery according to claim 2 , wherein is a methyl group.

4. X １ ~X ５ The electrolyte for a lithium secondary battery according to claim 2 , wherein three or more of the above are fluorine atoms.

5. The electrolyte for a lithium secondary battery according to claim 2, wherein the formula 1 is represented by the following formula 1-1, 1-2, or 1-3. 【Chemistry 2】 【Chemistry 3】 【Chemistry 4】

6. 2. The electrolyte for a lithium secondary battery according to claim 1, wherein the alkyl fluorinated propionate is contained in an amount of 1% by volume to 30% by volume relative to 100% by volume of the non-aqueous organic solvent.

7. 2. The electrolyte for a lithium secondary battery according to claim 1, wherein the propyl propionate is contained in an amount of 30% by volume to 80% by volume based on 100% by volume of the non-aqueous organic solvent.

8. 2. The electrolyte for a lithium secondary battery according to claim 1, wherein a volume ratio of the alkyl fluorinated propionate to the propyl propionate is 1:1 to 1:

9.

9. 2. The electrolyte for a lithium secondary battery according to claim 1, wherein the propionate-based solvent further comprises methyl propionate, ethyl propionate, or a combination thereof.

10. 2. The electrolyte for a lithium secondary battery according to claim 1, wherein the propionate-based solvent is contained in an amount of 50% by volume to 90% by volume relative to 100% by volume of the non-aqueous organic solvent.

11. The electrolyte for a lithium secondary battery according to claim 1 , wherein the non-aqueous organic solvent further comprises a carbonate-based solvent.

12. The electrolyte for lithium secondary batteries according to claim 11, wherein a volume ratio of the carbonate-based solvent to the propionate-based solvent is 1:2 to 1:

3.

13. The lithium salt is LiPF ６ , LiBF ４ , LiSbF ６ , LiAsF ６ , LiClO ４ , LiAlO ２ , LiAlCl ４ , LiPO ２ F ２ , LiCl, LiI, LiN(SO ３ C ２ F ５ ) ２ , Li(FSO ２ ) ２ N (lithium bis(fluorosulfonyl)imide (LiFSI), LiC ４ F ９ SO ３ , LiN (C ｐ F ２ｐ＋１ SO ２ ) (C ｑ F ２ｑ＋１ SO ２ 2. The electrolyte for a lithium secondary battery according to claim 1, comprising one or more selected from the group consisting of lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalate)phosphate (LiDFOB), and lithium bis(oxalate)borate (LiBOB).

14. 2. The electrolyte for a lithium secondary battery according to claim 1, further comprising a carbonate-based additive, a sultone-based additive, a nitrile-based additive, a lithium salt-based additive, or a combination thereof.

15. a positive electrode comprising a positive electrode active material; a negative electrode comprising a negative electrode active material; and The lithium secondary battery according to claim 1, comprising the electrolyte solution according to any one of claims 1 to 14.

16. The lithium secondary battery according to claim 15, wherein the charging voltage of the lithium secondary battery is 4.5 V or more.

17. The lithium secondary battery according to claim 15 , wherein the positive electrode active material comprises lithium cobalt oxide.

18. The lithium secondary battery according to claim 15 , wherein the negative electrode active material comprises graphite.

Images