Lithium secondary battery

Abstract

The present invention provides a lithium secondary battery with improved high-temperature cycle characteristics. Specifically, the present invention relates to a lithium secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode comprises lithium iron phosphate, the loading amount of the positive electrode is 32 mg / cm2 to 60 mg / cm2, and the electrolyte comprises a lithium salt; a first organic solvent; a second organic solvent; a first additive; and a second additive, wherein the first organic solvent is a cyclic lactone compound, the second organic solvent is a carbonate organic solvent, the first additive is lithium nitrate (LiNO3), and the second additive is a sulfonylimide compound.

Description

Technology Field

[0001] The present invention relates to a lithium secondary battery, and more specifically to a lithium secondary battery with improved high-temperature cycle characteristics. Background Technology

[0002] Recently, lithium-ion batteries are being used in various fields, including portable electronic devices such as mobile phones, PDAs, and laptop computers. In particular, with growing concern for environmental issues, research on lithium-ion batteries with high energy density and discharge voltage is actively underway as a power source for electric vehicles that can replace fossil fuel-using vehicles, such as gasoline and diesel cars—which are one of the major causes of air pollution—and some are already in the commercialization stage.

[0003] Meanwhile, in order to use the above-mentioned lithium secondary battery as a driving source for electric vehicles, it must be able to stably maintain high output at high temperatures and high voltages. To this end, the use of carbon materials, lithium metal, sulfur compounds, silicon compounds, tin compounds, etc., is being considered as the main components of the negative electrode active material for the above-mentioned lithium secondary battery, and lithium-containing cobalt oxide (LiCoO2) or nickel-based lithium transition metal oxide is mainly used as the positive electrode active material.

[0004] However, in the case of the above-mentioned lithium-containing cobalt oxide, energy density and power characteristics have reached practical limits, and especially when used in high-energy-density applications, due to its structural instability, it causes structural deformation under high-temperature charging conditions, along with the release of oxygen within the structure and exothermic reactions with the electrolyte within the battery, thereby causing secondary battery explosions. In the case of the above-mentioned nickel-based lithium transition metal oxide, since the power output drops sharply in the low SOC range (e.g., SOC 30% or less), there is a disadvantage that the usable SOC range is significantly limited, which limits its application in fields where power characteristics are particularly important, such as electric vehicles. In particular, the above-mentioned nickel-based lithium transition metal oxide has low structural stability, so when exposed to high temperature or high voltage, the transition metal within the cathode active material may leach out or side reactions with the electrolyte may occur, leading to a problem where battery performance deteriorates rapidly.

[0005] Recently, to address these issues, research is being conducted on methods using lithium iron phosphate with an olivine structure, which offers excellent high-temperature stability, instead of nickel-based lithium transition metal oxides.

[0006] However, since the aforementioned lithium iron phosphate has a lower theoretical capacity compared to the conventionally used nickel-based lithium transition metal oxide, it has the disadvantage of having a relatively lower energy density compared to nickel-based lithium transition metal oxide when designing electrodes under the same conditions.

[0007] To address these issues, high-loading electrodes are being attempted recently, in which the amount of electrode active material applied per unit area (loading amount) is increased when lithium iron phosphate is applied.

[0008] However, high-loading electrodes not only feature a high degree of active material coating but are also designed to increase electrode density. Consequently, the degree of electrode compression is very high, leading to a lack of porous structure within the electrode and a disadvantage of reduced electrolyte impregnation. This decrease in electrolyte impregnation causes a reduction in "charge transport," which is the reaction between lithium ions and electrons, and can manifest as an increase in battery resistance.

[0009] Accordingly, there is a need to develop a new secondary battery configuration that can improve electrolyte impregnation and simultaneously enhance charge mobility when manufacturing secondary batteries using high-loading electrodes. Prior art literature

[0010] Japanese Registered Patent Publication No. 2680685 The problem to be solved

[0011] The present invention aims to solve the above-mentioned problems by using an electrolyte of a specific composition in combination when applying a high-loading cathode, thereby improving electrolyte impregnation and simultaneously forming a stable film on the electrode surface to enhance charge transfer phenomena, which in turn suppresses the increase in resistance during high-temperature storage and secures an excellent cycle capacity retention rate. means of solving the problem

[0012] According to one embodiment, the present invention relates to a lithium secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode comprises lithium iron phosphate as a positive electrode active material, and the loading amount of the positive electrode is 32 mg / cm² 2 to 60 mg / cm² 2The present invention provides a lithium secondary battery comprising: a lithium salt; a first organic solvent; a second organic solvent; a first additive; and a second additive, wherein the first organic solvent is a cyclic lactone compound, the second organic solvent is a carbonate-based organic solvent, the first additive is lithium nitrate (LiNO3), and the second additive is a sulfonylimide compound.

[0013] The above lithium iron phosphate may include a compound represented by the following chemical formula 1.

[0014] [Chemical Formula 1]

[0015] Li 1+a Fe x M y (PO 4-b )X' b

[0016] In the above [Chemical Formula 1], M is any one selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y, and X' is one or more elements selected from the group consisting of F, S, and N, and -0.5≤a≤0.5, 0 <x≤1, 0≤y≤1 및 0≤b≤0.3이다.

[0017] The above cyclic lactone compound may include gamma-butyrolactone.

[0018] The above carbonate organic solvent may include a cyclic carbonate organic solvent.

[0019] The above sulfonylimide compound may include a compound represented by the following chemical formula 2.

[0020] [Chemical Formula 2]

[0021]

[0022] In the above [Chemical Formula 2],

[0023] R1 is hydrogen or an alkyl group having 1 to 4 carbon atoms, and

[0024] R2 is an alkylene group having 1 to 10 carbon atoms, an oxyalkylene group having 1 to 10 carbon atoms, a cycloalkylene group having 5 to 10 carbon atoms, and It is any one selected from the group consisting of, and R3 is a fluoro group, an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, or However, in the above R2 and R3, alkyl group, alkylene group, alkoxy group, oxyalkylene group, cycloalkylene group, and One or more of the hydrogens included in may be substituted with fluorine atoms, A is an oxygen atom (O) or -NR4, R4 is hydrogen or a carbon-1 to carbon-4 alkyl group, M1 is any one selected from the group consisting of lithium, sodium, potassium, carbon-1 to carbon-4 tetraalkylammonium and carbon-1 to carbon-4 tetraalkylphosphonium, l is an integer from 1 to 6, and m and n are each independently integers from 1 to 20. Effects of the invention

[0025] A lithium secondary battery according to the present invention comprises an organic solvent containing a cyclic lactone compound as a main solvent and two types of additives, lithium nitrate (LiNO3) and sulfonylimide (-S(=O)2-N - By applying an electrolyte containing an ionic compound containing -S(=O)2-) units, the electrolyte impregnation properties of the high-loading anode are improved, and at the same time, a film having low resistance is formed on the surface of the high-loading anode, thereby improving charge mobility on the surface of the high-loading anode. Accordingly, the lithium secondary battery of the present invention can have improved cycle characteristics and storage characteristics at high temperatures. Specific details for implementing the invention

[0026] The terms and words used in this specification and claims are used merely to describe exemplary embodiments and should not be interpreted as being limited to their ordinary or dictionary meanings, and should be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0027] For example, in this specification, terms such as “comprising,” “having,” or “having” are intended to specify the existence of the implemented features, numbers, steps, components, or combinations thereof, and should be understood as not excluding in advance the existence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0028] In addition, in the description of "a to b carbon atoms" within this specification, "a" and "b" refer to the number of carbon atoms included in a specific functional group. That is, the functional group may include "a" to "b" carbon atoms. For example, "alkylene group having 1 to 5 carbon atoms" refers to an alkylene group containing 1 to 5 carbon atoms, namely -CH2-, -CH2CH2-, -CH2CH2CH2-, -CH2(CH2)CH-, -CH2CH2CH2CH2CH2-, and -CH(CH2)CH2CH2-, etc.

[0029] Additionally, in this specification, the term "alkylene group" refers to a branched or unbranched aliphatic hydrocarbon group or a functional group in which one hydrogen atom is removed from each carbon atom located at both ends of the aliphatic hydrocarbon group. In one embodiment, the alkylene group may be substituted or unsubstituted. The alkylene group includes, but is not limited to, methylene groups, ethylene groups, propylene groups, isopropylene groups, butylene groups, isobutylene groups, tert-butylene groups, pentylene groups, 3-pentylene groups, etc., and each of these may be optionally substituted in other embodiments.

[0030] Additionally, in this specification, "substitution" means that one or more hydrogen atoms bonded to carbon are substituted with other elements such as fluorine, unless otherwise defined.

[0031] In addition, in this specification, "loading amount" refers to the amount of active material per unit area obtained by measuring a positive active material layer comprising lithium iron phosphate with an olivine structure formed on a current collector, and "mg / cm²" 2 It is indicated as ". In this specification, "loading amount" means the total sum of the loading amounts of both positive and negative sides.

[0033] The present invention will be described in detail below.

[0034] A lithium secondary battery according to the present invention comprises at least one of the configurations disclosed below, and may comprise any combination of technically feasible configurations among the configurations below.

[0036] lithium secondary battery

[0037] The present invention relates to a lithium secondary battery.

[0038] Specifically, the present invention provides a lithium secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte.

[0039] The above anode may include lithium iron phosphate as an anode active material.

[0040] The loading amount of the above anode is 32 mg / cm² 2 to 60 mg / cm² 2 It could be.

[0041] The above electrolyte may include a lithium salt; a first organic solvent; a second organic solvent; a first additive; and a second additive.

[0042] The first organic solvent may include a cyclic lactone compound.

[0043] The second organic solvent mentioned above may include a carbonate organic solvent.

[0044] The first additive above may include lithium nitrate (LiNO3).

[0045] The second additive above may include a sulfonylimide compound.

[0047] (1) positive electrode

[0048] The positive electrode of the present invention may include lithium iron phosphate as a positive electrode active material. Specifically, the lithium iron phosphate may include a compound represented by the following chemical formula 1.

[0049] [Chemical Formula 1]

[0050] Li 1+a Fe x M y (PO 4-b )X' b

[0051] In the above [Chemical Formula 1],

[0052] M is any one selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y, and

[0053] X' is one or more elements selected from the group consisting of F, S and N, and

[0054] -0.5≤a≤0.5, 0 <x≤1, 0≤y≤1 및 0≤b≤0.3이다.

[0056] Lithium iron phosphate represented by the above chemical formula 1 may include, as representative examples, lithium iron phosphate (LiFePO4, LFP) or lithium manganese iron phosphate (LiFeMnPO4, LMFP).

[0057] The lithium iron phosphate represented by the above chemical formula 1 may use primary particles of nanometer size for high lithium ion input / output, or it is possible to use secondary particles formed by assembling these primary particles. For example, when primary particles are used as the above olivine-structured phosphate, the particle size may be 50 to 2000 nm, more specifically 200 to 1100 nm. In addition, when secondary particles formed by assembling these primary particles are used, the average particle size (D50) of the secondary particles may be 0.5 μm to 30 μm.

[0058] The lithium iron phosphate represented by Chemical Formula 1 above can ensure structural and thermal stability even under volume changes caused by charging and discharging because phosphorus and oxygen form strong covalent bonds within the tetrahedral structure of PO4. Additionally, the lithium iron phosphate represented by Chemical Formula 1 above may have an amorphous layer of carbon or metal oxide coated on its surface. In this case, since the amorphous layer of carbon or metal oxide coated on the surface is not crystalline, the insertion and extraction of lithium ions into and out of the lithium iron phosphate in the core portion occurs through the amorphous layer of the shell. The amorphous layer of carbon or metal oxide coated on the surface allows lithium ions to pass through while also possessing excellent electronic conductivity, so it can act as a current path to the lithium iron phosphate core, which is the active material, thereby enabling charging and discharging at a high rate. Furthermore, safety can be further enhanced by controlling unnecessary reactions between the core material and the electrolyte when the surface of the lithium iron phosphate is coated with the amorphous layer of carbon or metal oxide.

[0059] Meanwhile, in the present invention, for the design of a high-capacity electrode, the loading amount of the anode containing the lithium iron phosphate represented by Chemical Formula 1 is 32 mg / cm² 2 Above (Single-sided loading amount: 16 mg / cm² 2 (above), specifically 32 mg / cm² 2 to 60 mg / cm² 2 , more preferably 40 mg / cm² 2 to 60 mg / cm² 2 It may be possible. If the loading amount of the anode satisfies the above range, high capacity characteristics can be realized.

[0061] The above-mentioned positive electrode may include a positive electrode current collector; and a positive electrode composite layer disposed on at least one surface of the positive electrode current collector. In this case, the positive electrode composite layer may include the aforementioned lithium iron phosphate as a positive electrode active material.

[0062] The thickness of the above positive current collector can typically be 3 to 500 μm.

[0063] The above positive current collector may form fine irregularities on its surface to strengthen the bonding force of the positive active material. For example, the above positive current collector can be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0064] The above positive composite layer may be disposed on at least one surface of the positive current collector, and specifically, may be disposed on one or both surfaces of the positive current collector.

[0065] In addition, the lithium iron phosphate represented by the above chemical formula 1 may be included in the anode composite layer in an amount of 80% to 99% by weight, taking into consideration sufficient capacity performance.

[0067] Meanwhile, the above-mentioned anode composite layer may further include a binder and / or a conductive material together with the aforementioned anode active material.

[0068] The above binder serves to improve adhesion between positive active material particles and adhesion between the positive active material and the current collector. Examples of such binders include fluoropolymer-based binders such as polyvinylidene fluoride (PVDF); rubber-based binders including styrene butadiene rubber (SBR), acrylonitrile-butadiene rubber, and styrene-isoprene rubber; cellulose-based binders including carboxyl methyl cellulose (CMC), starch, hydroxypropyl cellulose, and regenerated cellulose; polyalcohol-based binders including polyvinyl alcohol; polyolefin-based binders including polyethylene and polypropylene; polyimidazole-based binders; polyester-based binders; and silane-based binders, either alone or as a mixture of two or more.

[0069] The above binder may be included in the anode composite layer in an amount of 0.1 to 15 weight%, preferably 0.1 to 10 weight%.

[0070] Next, the conductive material is used to impart conductivity to the electrode, and in the battery being constructed, it can be used without special limitations as long as it has electronic conductivity without causing chemical changes. Specifically, the conductive material may be carbon black such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powder such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; conductive fibers such as carbon fibers or metal fibers; conductive powders such as carbon fluoride powder, aluminum powder, or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; polyphenylene derivatives, etc.

[0071] The above conductive material may be added to the anode composite layer in an amount of 1 to 30 weight percent.

[0073] The anode may be manufactured by coating an anode slurry comprising an anode active material and optionally a binder, a conductive material, and a solvent for forming an anode slurry onto the anode current collector, and then drying and rolling. Alternatively, the anode may be manufactured by mixing an anode active material and optionally a binder, a conductive material, etc. to produce a film, and then laminating it onto an anode current collector.

[0074] The solvent for forming the anode slurry may include, for example, at least one selected from the group consisting of distilled water, N-methylpyrrolidone, ethanol, methanol, and isopropyl alcohol, preferably N-methylpyrrolidone, in order to facilitate the dispersion of the anode active material, binder, and / or conductive material.

[0076] (2) Negative electrode

[0077] Next, the cathode is explained.

[0078] The above cathode may include a cathode active material.

[0079] As the above-mentioned negative electrode active material, a carbon-based active material, a silicon-based active material, or a mixture of a carbon-based active material and a silicon-based active material may be used.

[0080] The above carbon-based active material may include various carbon-based active materials used in the industry, such as graphite-based materials like natural graphite, artificial graphite, and Kish graphite; pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon, soft carbon, and hard carbon such as petroleum or coal tar pitch-derived cokes. The shape of the above carbon-based active material is not particularly limited, and materials of various shapes such as amorphous, plate-like, flake-like, spherical, or fibrous can be used.

[0081] Specifically, the carbon-based active material may be either natural graphite or artificial graphite, and natural graphite and artificial graphite may be used together to increase adhesion with the current collector and suppress the detachment of the active material.

[0082] In addition, the silicon-based active material is, for example, metallic silicon (Si) or silicon oxide (SiO). x, here 0 <x<2) 실리콘 탄화물(SiC) 및 Si-Y 합금(상기 Y는 알칼리 금속, 알칼리 토금속, 13족 원소, 14족 원소, 전이금속, 희토류 원소 및 이들의 조합으로 이루어진 군에서 선택되는 원소이며, Si은 아님)로 이루어진 군으로부터 선택된 1종 이상을 포함할 수 있다. 상기 원소 Y로는 Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db (dubnium), Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, Se, Te, Po, 및 이들의 조합으로 이루어진 군에서 선택될 수 있다.

[0083] Average particle size (D) of the above silicon-based active material 50 ) can be 1㎛ to 30㎛, preferably 2㎛ to 15㎛, in terms of reducing adverse reactions with the electrolyte while ensuring structural stability during charging and discharging.

[0084] In addition, the cathode of the present invention may include at least one selected from the carbon-based active material and the silicon-based active material.

[0085] Specifically, the cathode of the present invention may include the carbon-based active material and the silicon-based active material.

[0086] At this time, the weight ratio of the silicon-based active material and the carbon-based active material may be 1:99 to 30:70, specifically 3:97 to 15:85. When the mixing ratio of the silicon-based active material and the carbon-based active material satisfies the above range, excellent cycle performance can be secured by suppressing the volume expansion of the silicon-based active material while improving capacity characteristics.

[0088] The above cathode may include a cathode current collector; and a cathode composite layer disposed on at least one surface of the cathode current collector. In this case, the cathode active material may be included in the cathode composite layer.

[0089] The above-mentioned negative current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. Specifically, the above-mentioned negative current collector may be copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface treated with carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloy.

[0090] The above-mentioned cathode current collector can typically have a thickness of 3 to 500 μm.

[0091] The above-mentioned negative current collector may form fine irregularities on its surface to strengthen the bonding force of the negative active material. For example, the above-mentioned negative current collector can be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0092] The above cathode composite layer is disposed on at least one surface of the cathode current collector. Specifically, the cathode composite layer may be disposed on one or both surfaces of the cathode current collector.

[0093] The above-mentioned negative electrode active material may be included in the above-mentioned negative electrode composite layer in an amount of 60% to 99% by weight in order to sufficiently express capacity in the secondary battery while minimizing the effect of volume expansion / contraction on the battery.

[0094] The above cathode composite layer may further include a conductive material and / or a binder together with the cathode active material.

[0095] The above conductive material is a component for further improving the conductivity of the negative electrode active material, and is not particularly limited as long as it is conductive without causing chemical changes in the battery. For example, carbon black such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powder such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; conductive fibers such as carbon fibers or metal fibers; conductive powders such as carbon fluoride powder, aluminum powder, or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives may be used.

[0096] The above conductive material may be added to the above cathode composite layer in an amount of 10 weight% or less, preferably 5 weight% or less.

[0097] The above binder is a component that assists in the bonding between a conductive material, an active material, and a current collector, and typically includes fluoropolymer-based binders such as polyvinylidene fluoride (PVDF); rubber-based binders including styrene butadiene rubber (SBR), acrylonitrile-butadiene rubber, and styrene-isoprene rubber; cellulose-based binders including carboxyl methyl cellulose (CMC), starch, hydroxypropyl cellulose, and regenerated cellulose; polyalcohol-based binders including polyvinyl alcohol; polyolefin-based binders including polyethylene and polypropylene; polyimidazole-based binders; polyester-based binders; and silane-based binders.

[0098] The above binder may be included in the cathode composite layer in an amount of 0.1 to 15 weight%, preferably 0.1 to 10 weight%.

[0099] The above cathode may be manufactured by coating a cathode slurry comprising a cathode active material and optionally a binder, a conductive material, and a solvent for forming a cathode slurry onto the cathode current collector, and then drying and rolling. Alternatively, the cathode may be manufactured by mixing a cathode active material and optionally a binder, a conductive material, etc. to produce a film, and then laminating it onto a cathode current collector.

[0100] The solvent for forming the above cathode slurry may include, for example, at least one selected from the group consisting of distilled water, N-methylpyrrolidone, ethanol, methanol, and isopropyl alcohol, preferably distilled water, in order to facilitate the dispersion of the cathode active material, binder, and / or conductive material.

[0102] (3) Separator

[0103] The above separator separates the negative and positive electrodes and provides a pathway for the movement of lithium ions. It can be used without any specific restrictions as long as it is typically used as a separator in a lithium secondary battery, and it is particularly desirable that it has low resistance to the movement of ions of a non-aqueous electrolyte and excellent moisture retention capacity for the non-aqueous electrolyte.

[0104] Specifically, as a separator, a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, a coated separator containing a ceramic component or a polymer material may be used to ensure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

[0106] (4) Electrolyte

[0107] Next, the electrolyte of the present invention may comprise a lithium salt; a first organic solvent; a second organic solvent; a first additive; and a second additive, and specific examples of each component are as described below.

[0109] (4-1) Lithium salt

[0110] First, the above lithium salt can be any that are commonly used in electrolytes for lithium secondary batteries without limitation, for example, Li as a cation + It includes, and as anion, F - , Cl - , Br - , I - , N(CN)2 - , BF4 - , ClO4 - , B 10 Cl 10 - , AlCl4 - , AlO2 - , PF6 - , CF3SO3 - , CH3CO2 - , CF3CO2 - , AsF6 - , SbF6 - , CH3SO3 - , (CF3CF2SO2)2N - , (CF3SO2)2N - , (FSO2)2N - , BF2C2O4 - , BC4O8 - , PF4C2O4 - , PF2C4O8 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , C4F9SO3 - , CF3CF2SO3 - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - and CF3(CF2)7SO3- One can be selected from the group consisting of

[0111] Specifically, the lithium salt is LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10 It may include a single substance or a mixture of two or more substances selected from the group consisting of LiAlCl4, LiAlO2, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiN(SO2F)2(Lithium bis(fluorosulfonyl)imide, LiFSI), LiN(SO2CF2CF3)2(lithium bis(pentafluoroethanesulfonyl)imide, LiBETI), and LiN(SO2CF3)2(lithium bis(trifluoromethanesulfonyl)imide, LiTFSI), and specifically LiBF4, LiPF6, LiN(SO2F)2(Lithium bis(fluorosulfonyl)imide, LiFSI), LiN(SO2CF2CF3)2(lithium bis(pentafluoroethanesulfonyl)imide, LiBETI), and LiN(SO2CF3)2(lithium It may include any one selected from the group consisting of bis(trifluoromethane sulfonyl)imide, LiTFSI). In addition to these, lithium salts commonly used in the electrolyte of lithium secondary batteries may be used without limitation.

[0112] The above lithium salt can be appropriately modified within a range that is typically usable, but in order to obtain the effect of forming a corrosion-preventing film on the optimal electrode surface, it may be included in the electrolyte at a concentration of 0.8M to 3.0M, specifically 1.0M to 2.0M, preferably 1.0M to 1.8M.

[0113] When the concentration of the lithium salt is within the above range, the viscosity of the electrolyte can be controlled to achieve optimal impregnation, and the mobility of lithium ions can be improved to obtain the effect of improving the capacity characteristics and cycle characteristics of the lithium secondary battery.

[0115] (4-2) First organic solvent

[0116] Next, the first organic solvent is described.

[0117] The first organic solvent may include a cyclic lactone compound.

[0118] The above-mentioned cyclic lactone compound is a compound having high dielectric constant and ionic conductivity, and can improve the charge transfer degradation caused during high-loading electrode operation.

[0119] The above cyclic lactone compound may include gamma-butyrolactone.

[0120] The first organic solvent may be included in an amount of 39% to 80% by weight based on the total weight of the electrolyte, specifically in an amount of 48% to 80% by weight based on weight, and more preferably in an amount of 52% to 70% by weight.

[0121] When the content of the first organic solvent of the present invention satisfies the above range, the lithium ion transfer characteristics can be improved to achieve a battery resistance reduction effect.

[0123] (4-3) Second organic solvent

[0124] Next, the second organic solvent is described.

[0125] The above second organic solvent may include a carbonate organic solvent so that decomposition due to oxidation reactions, etc., during the charging and discharging process of the secondary battery can be minimized and desired characteristics can be exhibited together with the additive.

[0126] Specifically, the carbonate organic solvent preferably comprises one selected from the group consisting of a cyclic carbonate-based organic solvent having high ionic conductivity and high dielectric constant and a linear carbonate-based organic solvent having low viscosity and low dielectric constant, and specifically, may comprise a cyclic carbonate-based organic solvent.

[0127] The above-mentioned cyclic carbonate-based organic solvent may specifically include at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, and fluoroethylene carbonate (FEC), among which ethylene carbonate is preferred as it can maintain stable SEI film passivation ability.

[0128] In addition, the above-mentioned linear carbonate-based organic solvent may be any one or more of the organic solvents selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), methylpropyl carbonate, and ethylpropyl carbonate. Among these, dimethyl carbonate (DMC) or ethylmethyl carbonate (EMC), which have a small molecular size and low viscosity characteristics, may be cited as linear carbonate-based organic solvents.

[0129] Meanwhile, when the cyclic carbonate and linear carbonate are mixed and used as the second organic solvent, in order to secure low viscosity characteristics, the cyclic carbonate organic solvent and the linear carbonate organic solvent may be mixed and used in a volume ratio of about 1:99 to 50:50, or in a volume ratio of 20:80 to 40:60.

[0130] In the present invention, the first organic solvent and the second organic solvent may be included in a volume ratio of 50:50 to 99:1, specifically in a volume ratio of 70:30 to 99:1, and more specifically in a volume ratio of 70:30 to 90:10.

[0131] When the mixing ratio of the first organic solvent and the second organic solvent satisfies the above range, a high ion transfer characteristic effect can be achieved, and battery performance with low resistance characteristics can be secured. That is, when the volume ratio of the first organic solvent is 50 or more, an ion transfer characteristic effect can be secured, and when the volume ratio is 99 or less, a stable film can be formed to improve battery life characteristics.

[0133] Meanwhile, the electrolyte of the present invention may additionally include a third organic solvent as needed.

[0134] The above third organic solvent may include a linear ester-based organic solvent.

[0135] Representative examples of the above linear ester-based organic solvents include at least one organic solvent selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate, and specifically, may include at least one of ethyl propionate and propyl propionate.

[0137] (4-4) 1st additive

[0138] Next, the first additive is described.

[0139] The first additive above may include lithium nitrate (LiNO3).

[0140] The lithium nitrate (LiNO3) included as the first additive above can form an inorganic film containing lithium-nitrogen and lithium-oxygen bonds on the surface of the cathode during the activation step. Since this inorganic film increases surface energy and acts as an ion carrier capable of uniformly transporting lithium ions, it can improve the electrode impregnation properties of the electrolyte and induce a more effective charge transfer reaction.

[0141] In addition, the lithium nitrate (LiNO3) included as the first additive can form a coordination bond with a transition metal leached from the anode under a high-temperature environment, or form a coordination bond with a Lewis acid generated by the decomposition product of the lithium salt, thereby inhibiting the electrodeposition of transition metal ions on the cathode surface and preventing reversible lithium loss, thus improving the degradation of cycle characteristics.

[0142] Meanwhile, the first additive may be included in the electrolyte in a specific amount. Specifically, the first additive may be included in an amount of 0.05% to 3.0% by weight based on the total weight of the electrolyte, specifically in an amount of 0.05% to 2.0% by weight, more specifically in an amount of 0.1% to 2.0% by weight, and preferably in an amount of 0.1% to 1.5% by weight.

[0143] When the content of the first additive of the present invention satisfies the above range, an inorganic film containing lithium-nitrogen and lithium-oxygen bonds is uniformly formed on the surface of the negative electrode, so that it can function as an effective ion carrier instead of functioning as a resistor. That is, when the first additive is included in an amount of 0.05 wt% or more, the increase in battery resistance can be suppressed to prevent the deterioration of battery performance, and when it is included in an amount of 3.0 wt% or less, the formation of a robust film suppresses side reactions between the electrolyte and the electrode, thereby preventing the generation of unnecessary activating gases, etc., thus preventing deterioration of high-temperature cycle and high-temperature storage characteristics.

[0144] Meanwhile, it is desirable that the content of the first additive (f) and the anode loading amount in the electrolyte satisfy the following relationship 1.

[0145] [Equation 1]

[0146] 0.0001 ≤ ≤ 0.050

[0147] In the above Equation 1,

[0148] A is the total amount of electrolyte (g) injected into the lithium secondary battery, and

[0149] B is the content (weight%) of lithium nitrate (LiNO3) contained in the above-mentioned electrolyte, and

[0150] C is the anode loading amount (g / cm²) 2 ) and,

[0151] D is the total surface area of ​​the positive current collector (cm²) 2 )am.

[0153] When the content of the first additive in the electrolyte of the present invention satisfies the above relationship, an effective inorganic film can be formed that can increase the electrolyte impregnation of the cathode and improve ion transfer characteristics, thereby ensuring excellent battery performance.

[0155] (4-5) Second additive

[0156] Next, the second additive is described.

[0157] In the present invention, a sulfonylimide compound may be included as a second additive.

[0158] The above sulfonylimide compound may include a compound represented by the following chemical formula 2.

[0159] [Chemical Formula 2]

[0160]

[0161] In the above chemical formula 2,

[0162] R1 is hydrogen or an alkyl group having 1 to 4 carbon atoms, and

[0163] R2 is an alkylene group having 1 to 10 carbon atoms, an oxyalkylene group having 1 to 10 carbon atoms, a cycloalkylene group having 5 to 10 carbon atoms, and It is any one selected from the group consisting of, and

[0164] R3 is a fluoro group, a C1- to C10 alkyl group, a C1- to C10 alkoxy group, or However,

[0166] In the above R2 and R3, alkyl group, alkylene group, alkoxy group, oxyalkylene group, cycloalkylene group, and One or more of the hydrogen atoms contained in can be replaced with fluorine atoms, and

[0167] A is an oxygen atom (O) or -NR4, and R4 is hydrogen or an alkyl group having 1 to 4 carbon atoms, and

[0168] M1 is any one selected from the group consisting of lithium, sodium, potassium, tetraalkylammonium having 1 to 4 carbon atoms, and tetraalkylphosphonium having 1 to 4 carbon atoms, and

[0169] l is an integer from 1 to 6, and

[0170] m and n are each independently integers from 1 to 20.

[0172] Specifically, the sulfonylimide compound represented by Chemical Formula 2 included as the second additive is sulfonylimide (disulfonimide, -S(=O)2-N - It may be an ionic compound in which a vinyl group is bonded to one side of a -S(=O)2-) unit through functional groups (A and R1) that extend the conjugation of the sulfonylimide group. Since this ionic compound contains a negative charge within its molecular structure, it can easily migrate to the anode upon activation and undergo oxidative decomposition, thereby uniformly forming an organic film and / or a robust inorganic film containing lithium-nitrogen / oxygen / sulfur bonds on the surface of the anode.

[0173] As such, the compound represented by Chemical Formula 2 is a lithium ion (Li + Since it has the characteristic of being electrochemically oxidized at a potential near 4.0V, when used as an electrolyte additive in a secondary battery with a lithium iron phosphate electrode, it is reduced before the organic solvent and can form a solid film on the anode surface during the initial activation phase. This can block additional oxidative decomposition of the electrolyte on the anode surface during repeated cycle operation, thereby suppressing the increase in resistance and improving the overall performance degradation of the lithium secondary battery.

[0175] Meanwhile, in the above chemical formula 2, R1 is hydrogen or a methyl group, and R2 is a methylene group, an ethylene group, a propylene group, an oxymethylene group, an oxyethylene group, an oxypropylene group, a cyclophenylene group, a cyclohexylene group, a cycloheptylene group, and It is any one selected from the group consisting of, and R3 is a fluoro group, methyl group, ethyl group, propyl group, trifluoromethyl group, methoxy group, ethoxy group, or A is an oxygen atom (O), -NH or -NCH3, M1 is lithium, l is an integer of 1 or 2, and m and n can each independently be integers from 1 to 10.

[0176] Alternatively, in the above formula 2, m and n may each independently be integers from 1 to 5, and preferably integers from 2 to 5.

[0178] More specifically, the compound represented by Chemical Formula 2 may be at least one selected from the group consisting of compounds represented by Chemical Formulas 2-1 to 2-80 below. More preferably, it may be a compound having a fluorine-substituted alkyl group substituted at the terminal end to form a robust film with superior durability containing a fluorine element on the surface of the cathode and anode, or a compound in which an oxygen / nitrogen element and a sulfur (S) element are connected through an alkylene group. That is, in the case of a compound in which an oxygen / nitrogen element and a sulfur (S) element are connected through an alkylene group, compared to a compound connected through an ether group or a cyclic alkylene group, it forms a more stable chemical bond, thereby making it easier to form a negatively charged organic film, and also makes it easier to form a reducing material having a lithium-nitrogen / oxygen / sulfur bond, thus having the advantage of being able to form a thinner and more robust film on the surface of the cathode and anode.

[0179] [Chemical Formula 2-1]

[0180]

[0181] [Chemical Formula 2-2]

[0182]

[0183] [Chemical Formula 2-3]

[0184]

[0185] [Chemical Formula 2-4]

[0186]

[0187] [Chemical Formula 2-5]

[0188]

[0189] In the above chemical formula 2-5, n is as defined in the above chemical formula 2.

[0190] [Chemical Formula 2-6]

[0191]

[0192] In the above chemical formula 2-6, n is as defined in the above chemical formula 2.

[0193] [Chemical Formula 2-7]

[0194]

[0195] In the above chemical formula 2-7, n is as defined in the above chemical formula 2.

[0196] [Chemical Formula 2-8]

[0197]

[0198] In the above chemical formula 2-8, n is as defined in the above chemical formula 2.

[0199] [Chemical Formula 2-9]

[0200]

[0201] [Chemical Formula 2-10]

[0202]

[0203] [Chemical Formula 2-11]

[0204]

[0205] [Chemical Formula 2-12]

[0206]

[0207] [Chemical Formula 2-13]

[0208]

[0209] In the above chemical formula 2-13, n is as defined in the above chemical formula 2.

[0210] [Chemical Formula 2-14]

[0211]

[0212] In the above chemical formula 2-14, n is as defined in the above chemical formula 2.

[0213] [Chemical Formula 2-15]

[0214]

[0215] In the above chemical formula 2-15, n is as defined in the above chemical formula 2.

[0216] [Chemical Formula 2-16]

[0217]

[0218] In the above chemical formula 2-16, n is as defined in the above chemical formula 2.

[0219] [Chemical Formula 2-17]

[0220]

[0221] In the above chemical formula 2-17, m is as defined in the above chemical formula 2.

[0222] [Chemical Formula 2-18]

[0223]

[0224] In the above chemical formula 2-18, m is as defined in the above chemical formula 2.

[0225] [Chemical Formula 2-19]

[0226]

[0227] In the above chemical formula 2-19, m is as defined in the above chemical formula 2.

[0228] [Chemical Formula 2-20]

[0229]

[0230] In the above chemical formula 2-20, m is as defined in the above chemical formula 2.

[0231] [Chemical Formula 2-21]

[0232]

[0233] In the above chemical formula 2-21, n and m are as defined in the above chemical formula 2.

[0234] [Chemical Formula 2-22]

[0235]

[0236] In the above chemical formula 2-22, n and m are as defined in the above chemical formula 2.

[0237] [Chemical Formula 2-23]

[0238]

[0239] In the above chemical formula 2-23, n and m are as defined in the above chemical formula 2.

[0240] [Chemical Formula 2-24]

[0241]

[0242] In the above chemical formula 2-24, n and m are as defined in the above chemical formula 2.

[0243] [Chemical Formula 2-25]

[0244]

[0245] In the above chemical formula 2-25, m is as defined in the above chemical formula 2.

[0246] [Chemical Formula 2-26]

[0247]

[0248] In the above chemical formula 2-26, m is as defined in the above chemical formula 2.

[0249] [Chemical Formula 2-27]

[0250]

[0251] In the above chemical formula 2-27, m is as defined in the above chemical formula 2.

[0252] [Chemical Formula 2-28]

[0253]

[0254] In the above chemical formula 2-28, m is as defined in the above chemical formula 2.

[0255] [Chemical Formula 2-29]

[0256]

[0257] In the above chemical formula 2-29, n and m are as defined in the above chemical formula 2.

[0258] [Chemical Formula 2-30]

[0259]

[0260] In the above chemical formula 2-30, n and m are as defined in the above chemical formula 2.

[0261] [Chemical Formula 2-31]

[0262]

[0263] In the above chemical formula 2-31, n and m are as defined in the above chemical formula 2.

[0264] [Chemical Formula 2-32]

[0265]

[0266] In the above chemical formula 2-32, n and m are as defined in the above chemical formula 2.

[0267] [Chemical Formula 2-33]

[0268]

[0269] [Chemical Formula 2-34]

[0270]

[0271] [Chemical Formula 2-35]

[0272]

[0273] [Chemical Formula 2-36]

[0274]

[0275] [Chemical Formula 2-37]

[0276]

[0277] In the above chemical formula 2-37, n is as defined in the above chemical formula 2.

[0278] [Chemical Formula 2-38]

[0279]

[0280] In the above chemical formula 2-38, n is as defined in the above chemical formula 2.

[0281] [Chemical Formula 2-39]

[0282]

[0283] In the above chemical formula 2-39, n is as defined in the above chemical formula 2.

[0284] [Chemical Formula 2-40]

[0285]

[0286] In the above chemical formula 2-40, n is as defined in the above chemical formula 2.

[0287] [Chemical Formula 2-41]

[0288]

[0289] [Chemical Formula 2-42]

[0290]

[0291] [Chemical Formula 2-43]

[0292]

[0293] [Chemical Formula 2-44]

[0294]

[0295] [Chemical Formula 2-45]

[0296]

[0297] In the above chemical formula 2-45, n is as defined in the above chemical formula 2.

[0298] [Chemical Formula 2-46]

[0299]

[0300] In the above chemical formula 2-45, n is as defined in the above chemical formula 2.

[0301] [Chemical Formula 2-47]

[0302]

[0303] In the above chemical formula 2-47, n is as defined in the above chemical formula 2.

[0304] [Chemical Formula 2-48]

[0305]

[0306] In the above chemical formula 2-48, n is as defined in the above chemical formula 2.

[0307] [Chemical Formula 2-49]

[0308]

[0309] In the above chemical formula 2-49, m is as defined in the above chemical formula 2.

[0310] [Chemical Formula 2-50]

[0311]

[0312] In the above chemical formula 2-50, m is as defined in the above chemical formula 2.

[0313] [Chemical Formula 2-51]

[0314]

[0315] In the above Chemical Formula 2-51, m is as defined in the above Chemical Formula 2.

[0316] [Chemical Formula 2-52]

[0317]

[0318] In the above chemical formula 2-52, m is as defined in the above chemical formula 2.

[0319] [Chemical Formula 2-53]

[0320]

[0321] In the above chemical formula 2-53, n and m are as defined in the above chemical formula 2.

[0322] [Chemical Formula 2-54]

[0323]

[0324] In the above chemical formula 2-54, n and m are as defined in the above chemical formula 2.

[0325] [Chemical Formula 2-55]

[0326]

[0327] In the above chemical formula 2-55, n and m are as defined in the above chemical formula 2.

[0328] [Chemical Formula 2-56]

[0329]

[0330] In the above chemical formula 2-56, n and m are as defined in the above chemical formula 2.

[0331] [Chemical Formula 2-57]

[0332]

[0333] In the above chemical formula 2-57, m is as defined in the above chemical formula 2.

[0334] [Chemical Formula 2-58]

[0335]

[0336] In the above chemical formula 2-58, m is as defined in the above chemical formula 2.

[0337] [Chemical Formula 2-59]

[0338]

[0339] In the above chemical formula 2-59, n and m are as defined in the above chemical formula 2.

[0340] [Chemical Formula 2-60]

[0341]

[0342] In the above chemical formula 2-60, n and m are as defined in the above chemical formula 2.

[0343] [Chemical Formula 2-61]

[0344]

[0345] In the above chemical formula 2-61, n and m are as defined in the above chemical formula 2.

[0346] [Chemical Formula 2-62]

[0347]

[0348] In the above chemical formula 2-62, n and m are as defined in the above chemical formula 2.

[0349] [Chemical Formula 2-63]

[0350]

[0351] In the above chemical formula 2-63, n and m are as defined in the above chemical formula 2.

[0352] [Chemical Formula 2-64]

[0353]

[0354] In the above chemical formula 2-64, n and m are as defined in the above chemical formula 2.

[0355] [Chemical Formula 2-65]

[0356]

[0357] [Chemical Formula 2-66]

[0358]

[0359] [Chemical Formula 2-67]

[0360]

[0361] [Chemical Formula 2-68]

[0362]

[0363] [Chemical Formula 2-69]

[0364]

[0365] In the above chemical formula 2-69, n is as defined in the above chemical formula 2.

[0366] [Chemical Formula 2-70]

[0367]

[0368] In the above chemical formula 2-70, n is as defined in the above chemical formula 2.

[0369] [Chemical Formula 2-71]

[0370]

[0371] In the above chemical formula 2-71, n is as defined in the above chemical formula 2.

[0372] [Chemical Formula 2-72]

[0373]

[0374] In the above Chemical Formula 2-72, n is as defined in Chemical Formula 2.

[0375] [Chemical Formula 2-73]

[0376]

[0377] [Chemical Formula 2-74]

[0378]

[0379] [Chemical Formula 2-75]

[0380]

[0381] [Chemical Formula 2-76]

[0382]

[0383] [Chemical Formula 2-77]

[0384]

[0385] In the above chemical formula 2-77, n is as defined in the above chemical formula 2.

[0386] [Chemical Formula 2-78]

[0387]

[0388] In the above chemical formula 2-78, n and m are as defined in the above chemical formula 2.

[0389] [Chemical Formula 2-79]

[0390]

[0391] In the above chemical formula 2-79, n and m are as defined in the above chemical formula 2.

[0392] [Chemical Formula 2-80]

[0393]

[0394] In the above chemical formula 2-80, n and m are as defined in the above chemical formula 2.

[0396] In the electrolyte of the present invention, the first additive and the second additive may be included in a weight ratio of 1:0.05 to 1:2, in a weight ratio of 1:0.1 to 1:2, and more preferably in a weight ratio of 1:0.1 to 1:1.

[0397] When the composition ratio of the first additive and the second additive satisfies the above range, a stable film can be formed on the surfaces of the anode and cathode, thereby improving overall high-temperature performance (cycle characteristics, OCV stabilization, etc.). That is, when the second additive is included in a weight ratio of 2 or less, a uniform film is formed on the surface of the cathode, which prevents it from acting as a resistor and prevents corrosion of the anode and cathode current collectors. On the other hand, when the second additive is included in a somewhat large amount, the film thickness increases due to the increased content of the second additive that undergoes reductive decomposition on the cathode surface, which may cause it to act as a resistor, and the second additive remaining after activation without decomposing may cause corrosion of the anode current collector.

[0399] (4-6) Other additives

[0400] Meanwhile, the lithium secondary battery of the present invention may additionally include other additives in the electrolyte as needed to prevent the decomposition of the electrolyte in a high-power environment from causing negative electrode collapse, or to further improve low-temperature high-rate discharge characteristics, high-temperature stability, prevention of overcharging, and suppression of battery expansion at high temperatures. If other additives are included, the other additives may be referred to as third additives.

[0401] These other additives may include any one selected from the group consisting of cyclic carbonate compounds, sulfonate compounds, phosphate compounds, borate compounds, nitrile compounds, benzene compounds, amine compounds, silane compounds, and lithium salt compounds as representative examples.

[0402] Examples of the above-mentioned cyclic carbonate compounds include vinylene carbonate (VC).

[0403] The above sulfone-based compound may be any one compound selected from the group consisting of 1,3-propane sulfone (PS), 1,4-butane sulfone, ethen sulfone, 1,3-propene sulfone (PRS), 1,4-butene sulfone, and 1-methyl-1,3-propene sulfone.

[0404] The above phosphate-based compound may include one or more compounds selected from the group consisting of lithium difluoro(bisoxalato)phosphate, lithium difluorophosphate, tris(trimethylsilyl)phosphate, tris(2,2,2-trifluoroethyl)phosphate, and tris(trifluoroethyl)phosphate.

[0405] The above borate-based compounds may include tetraphenylborate and lithium oxalyl difluoroborate.

[0406] The above nitrile-based compound may include any one compound selected from the group consisting of succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanitrile, cyclopentane carbonitrile, cyclohexane carbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

[0407] The above benzene-based compound may include fluorobenzene, the above amine-based compound may include triethanolamine or ethylenediamine, etc., and the above silane-based compound may include tetravinylsilane.

[0408] The above lithium salt-based compound is a compound different from the lithium salt included in the electrolyte, and may include one or more compounds selected from the group consisting of LiPO2F2, LiODFB, LiBOB (lithium bisoxalate toborate (LiB(C2O4)2)), LiBF4, and LiDFOP.

[0410] Meanwhile, the above other additives may be used in a mixture of two or more types, and may be included in an amount of less than 10% by weight based on the total weight of the electrolyte, specifically 0.01% by weight or more and less than 8.0% by weight, and preferably 0.05% by weight to 5.0% by weight. If the content of the above other additives satisfies the above range, the induction of side reactions caused by unreacted additives can be suppressed, and the effects of improving low-temperature output, high-temperature storage characteristics, and high-temperature life characteristics of the battery can be further enhanced.

[0412] The lithium secondary battery according to the present invention as described above can be usefully applied in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in the field of electric vehicles such as hybrid electric vehicles (HEVs).

[0413] The external shape of the lithium secondary battery of the present invention is not particularly limited, but can be a cylindrical shape using a can, a prismatic shape, a pouch shape, or a coin shape.

[0414] The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for a small device, but can also preferably be used as a unit cell in a medium-to-large battery module comprising a plurality of battery cells.

[0416] Hereinafter, the present invention will be described in detail with reference to examples in order to specifically explain the invention. However, the embodiments according to the present invention may be modified in various different forms, and the scope of the present invention should not be interpreted as being limited to the embodiments described below. The embodiments of the present invention are provided to more completely explain the invention to those with average knowledge in the art.

[0418] [Example]

[0419] Example 1.

[0420] (Electrolyte manufacturing)

[0421] The electrolyte of the present invention was prepared by dissolving LiPF6 in an organic solvent mixed with gamma-butyrolactone and ethylene carbonate in a volume ratio of 70:30 to a concentration of 1.0 M, adding 0.05 wt% of lithium nitrate (LiNO3) as a first additive and 0.1 wt% of a sulfonylimide compound represented by chemical formula 2-41 as a second additive (weight ratio of the first additive and the second additive = 1:2), and adding 3.0 wt% of vinylene carbonate (VC) and 1.0 wt% of ethylene sulfate (Esa) as other additives.

[0423] (Anode manufacturing)

[0424] A positive active material slurry (solid content 67 wt%) was prepared by adding a positive active material (LiFePO4), a conductive material (carbon black), and a binder (polyvinylidene fluoride, PVDF) to a solvent, N-methyl-2-pyrrolidone (NMP), in a weight ratio of 96:1:3. The positive active material slurry was applied to a positive current collector (Al thin film) with a thickness of 15 μm, dried, and rolled to produce a positive electrode (double-sided loading amount: 48 mg / cm², single-sided loading amount: 24 mg / cm²).

[0426] (Cathode manufacturing)

[0427] A cathode active material slurry (solid content: 53 wt%) was prepared by adding a cathode active material (synthetic graphite), CMC-SBR as a binder, and carbon black as a conductive material to distilled water as a solvent in a weight ratio of 96:3.5:0.5. The cathode active material slurry was coated onto a cathode current collector (Cu thin film) with a thickness of 8 μm, dried, and then rolled to produce a cathode.

[0429] (Secondary battery manufacturing)

[0430] An electrode assembly was manufactured by sequentially laminating the positive and negative electrodes prepared by the aforementioned method together with a polyethylene porous film using a conventional method, and then the assembly was housed in a pouch-type secondary battery case, and the lithium secondary battery electrolyte prepared above was injected to manufacture a lithium secondary battery.

[0432] Example 2.

[0433] (Electrolyte manufacturing)

[0434] The electrolyte for a lithium secondary battery of the present invention was prepared by dissolving LiPF6 in an organic solvent mixed with gamma-butyrolactone and ethylene carbonate in a 70:30 volume ratio so that the concentration was 1.0 M, then adding 0.1 wt% of lithium nitrate (LiNO3) as a first additive and 0.1 wt% of a sulfonylimide compound represented by chemical formula 2-41 as a second additive (weight ratio of the first additive and the second additive = 1:1), and adding 3.0 wt% of vinylene carbonate (VC) and 1.0 wt% of ethylene sulfate (Esa) as other additives.

[0436] (Secondary battery manufacturing)

[0437] A lithium secondary battery was manufactured in the same manner as in Example 1, except for injecting the electrolyte manufactured above.

[0439] Example 3.

[0440] (Electrolyte manufacturing)

[0441] The electrolyte for a lithium secondary battery of the present invention was prepared by dissolving LiPF6 in an organic solvent mixed with gamma-butyrolactone and ethylene carbonate in a 70:30 volume ratio to make the concentration 1.0 M, adding 1.5 wt% of lithium nitrate (LiNO3) as a first additive and 0.15 wt% of a sulfonylimide compound represented by chemical formula 2-41 as a second additive (weight ratio of the first additive and the second additive = 1:0.1), and adding 3.0 wt% of vinylene carbonate (VC) and 1.0 wt% of ethylene sulfate (Esa) as other additives.

[0443] (Secondary battery manufacturing)

[0444] A lithium secondary battery was manufactured in the same manner as in Example 1, except for injecting the electrolyte manufactured above.

[0446] Example 4.

[0447] (Electrolyte manufacturing)

[0448] The electrolyte for a lithium secondary battery of the present invention was prepared by dissolving LiPF6 in an organic solvent mixed with gamma-butyrolactone and ethylene carbonate in a 70:30 volume ratio to make the concentration 1.0 M, adding 3.0 wt% of lithium nitrate (LiNO3) as a first additive and 0.15 wt% of a sulfonylimide compound represented by chemical formula 2-41 as a second additive (weight ratio of the first additive and the second additive = 1:0.05), and adding 3.0 wt% of vinylene carbonate (VC) and 1.0 wt% of ethylene sulfate (Esa) as other additives.

[0450] (Secondary battery manufacturing)

[0451] A lithium secondary battery was manufactured in the same manner as in Example 1, except for injecting the electrolyte manufactured above.

[0453] Example 5.

[0454] (Electrolyte manufacturing)

[0455] The electrolyte for a lithium secondary battery of the present invention was prepared by dissolving LiPF6 in an organic solvent mixed with gamma-butyrolactone and ethylene carbonate in a 70:30 volume ratio so that the concentration was 1.0 M, adding 1.0 wt% of lithium nitrate (LiNO3) as a first additive and 0.1 wt% of a sulfonylimide compound represented by chemical formula 2-41 as a second additive (weight ratio of the first additive and the second additive = 1:0.1), and adding 3.0 wt% of vinylene carbonate (VC) and 1.0 wt% of ethylene sulfate (Esa) as other additives.

[0457] (Secondary battery manufacturing)

[0458] A lithium secondary battery was manufactured in the same manner as in Example 1, except for injecting the electrolyte manufactured above.

[0460] Example 6.

[0461] (Electrolyte manufacturing)

[0462] The electrolyte for a lithium secondary battery of the present invention was prepared by dissolving LiPF6 in an organic solvent mixed with gamma-butyrolactone and ethylene carbonate in a 70:30 volume ratio to make the concentration 1.0 M, adding 1.0 wt% of lithium nitrate (LiNO3) as a first additive and 0.5 wt% of a sulfonylimide compound represented by chemical formula 2-41 as a second additive (weight ratio of the first additive and the second additive = 1:0.5), and adding 3.0 wt% of vinylene carbonate (VC) and 1.0 wt% of ethylene sulfate (Esa) as other additives.

[0464] (Secondary battery manufacturing)

[0465] A lithium secondary battery was manufactured in the same manner as in Example 1, except for injecting the electrolyte manufactured above.

[0467] Example 7.

[0468] (Electrolyte manufacturing)

[0469] The electrolyte for a lithium secondary battery of the present invention was prepared by dissolving LiPF6 in an organic solvent mixed with gamma-butyrolactone and ethylene carbonate in a volume ratio of 70:30 to a concentration of 1.0 M, adding 1.0 wt% of lithium nitrate (LiNO3) as a first additive and 2.0 wt% of a sulfonylimide compound represented by chemical formula 2-41 as a second additive (weight ratio of the first additive and the second additive = 1:2), and adding 3.0 wt% of vinylene carbonate (VC) and 1.0 wt% of ethylene sulfate (Esa) as other additives.

[0471] (Secondary battery manufacturing)

[0472] A lithium secondary battery was manufactured in the same manner as in Example 1, except for injecting the electrolyte manufactured above.

[0474] Example 8.

[0475] (Electrolyte manufacturing)

[0476] The electrolyte for a lithium secondary battery of the present invention was prepared by dissolving LiPF6 in an organic solvent mixed with gamma-butyrolactone and ethylene carbonate in a volume ratio of 70:30 to a concentration of 1.0 M, adding 1.0 wt% of lithium nitrate (LiNO3) as a first additive and 0.5 wt% of a sulfonylimide compound represented by chemical formula 2-9 as a second additive (weight ratio of the first additive and the second additive = 1:0.5), and adding 3.0 wt% of vinylene carbonate (VC) and 1.0 wt% of ethylene sulfate (Esa) as other additives.

[0478] (Secondary battery manufacturing)

[0479] A lithium secondary battery was manufactured in the same manner as in Example 1, except for injecting the electrolyte manufactured above.

[0481] Example 9.

[0482] (Electrolyte manufacturing)

[0483] The electrolyte for a lithium secondary battery of the present invention was prepared by dissolving LiPF6 in an organic solvent mixed with gamma-butyrolactone and ethylene carbonate in a volume ratio of 70:30 to a concentration of 1.0 M, adding 1.0 wt% of lithium nitrate (LiNO3) as a first additive and 0.5 wt% of a sulfonylimide compound represented by chemical formula 2-10 as a second additive (weight ratio of the first additive and the second additive = 1:0.5), and adding 3.0 wt% of vinylene carbonate (VC) and 1.0 wt% of ethylene sulfate (Esa) as other additives.

[0485] (Secondary battery manufacturing)

[0486] A lithium secondary battery was manufactured in the same manner as in Example 1, except for injecting the electrolyte manufactured above.

[0488] Example 10.

[0489] (Electrolyte manufacturing)

[0490] The electrolyte for a lithium secondary battery of the present invention was prepared by dissolving LiPF6 in an organic solvent mixed with gamma-butyrolactone and ethylene carbonate in a volume ratio of 70:30 to a concentration of 1.0 M, adding 1.0 wt% of lithium nitrate (LiNO3) as a first additive and 0.5 wt% of a sulfonylimide compound represented by chemical formula 2-25 as a second additive (weight ratio of the first additive and the second additive = 1:0.5), and adding 3.0 wt% of vinylene carbonate (VC) and 1.0 wt% of ethylene sulfate (Esa) as other additives.

[0492] (Secondary battery manufacturing)

[0493] A lithium secondary battery was manufactured in the same manner as in Example 1, except for injecting the electrolyte manufactured above.

[0495] Example 11.

[0496] (Electrolyte manufacturing)

[0497] The electrolyte for a lithium secondary battery of the present invention was prepared by dissolving LiPF6 in an organic solvent mixed with gamma-butyrolactone and ethylene carbonate in a volume ratio of 70:30 to a concentration of 1.0 M, adding 1.0 wt% of lithium nitrate (LiNO3) as a first additive and 0.5 wt% of a sulfonylimide compound represented by chemical formula 2-26 as a second additive (weight ratio of the first additive and the second additive = 1:0.5), and adding 3.0 wt% of vinylene carbonate (VC) and 1.0 wt% of ethylene sulfate (Esa) as other additives.

[0499] (Secondary battery manufacturing)

[0500] A lithium secondary battery was manufactured in the same manner as in Example 1, except for injecting the electrolyte manufactured above.

[0502] Example 12.

[0503] (Electrolyte manufacturing)

[0504] The electrolyte for a lithium secondary battery of the present invention was prepared by dissolving LiPF6 in an organic solvent mixed with gamma-butyrolactone and ethylene carbonate in a volume ratio of 70:30 to a concentration of 1.0 M, adding 1.0 wt% of lithium nitrate (LiNO3) as a first additive and 0.5 wt% of a sulfonylimide compound represented by chemical formula 2-42 as a second additive (weight ratio of the first additive and the second additive = 1:0.5), and adding 3.0 wt% of vinylene carbonate (VC) and 1.0 wt% of ethylene sulfate (Esa) as other additives.

[0506] (Secondary battery manufacturing)

[0507] A lithium secondary battery was manufactured in the same manner as in Example 1, except for injecting the electrolyte manufactured above.

[0509] Example 13.

[0510] (Electrolyte manufacturing)

[0511] The electrolyte for a lithium secondary battery of the present invention was prepared by dissolving LiPF6 in an organic solvent mixed with gamma-butyrolactone and ethylene carbonate in a volume ratio of 70:30 to a concentration of 1.0 M, adding 1.0 wt% of lithium nitrate (LiNO3) as a first additive and 0.5 wt% of a sulfonylimide compound represented by chemical formula 2-57 as a second additive (weight ratio of the first additive and the second additive = 1:0.5), and adding 3.0 wt% of vinylene carbonate (VC) and 1.0 wt% of ethylene sulfate (Esa) as other additives.

[0513] (Secondary battery manufacturing)

[0514] A lithium secondary battery was manufactured in the same manner as in Example 1, except for injecting the electrolyte manufactured above.

[0516] Example 14.

[0517] (Electrolyte manufacturing)

[0518] The electrolyte for a lithium secondary battery of the present invention was prepared by dissolving LiPF6 in an organic solvent mixed with gamma-butyrolactone and ethylene carbonate in a volume ratio of 70:30 to a concentration of 1.0 M, adding 1.0 wt% of lithium nitrate (LiNO3) as a first additive and 0.5 wt% of a sulfonylimide compound represented by chemical formula 2-58 as a second additive (weight ratio of the first additive and the second additive = 1:0.5), and adding 3.0 wt% of vinylene carbonate (VC) and 1.0 wt% of ethylene sulfate (Esa) as other additives.

[0520] (Secondary battery manufacturing)

[0521] A lithium secondary battery was manufactured in the same manner as in Example 1, except for injecting the electrolyte manufactured above.

[0523] Example 15.

[0524] (Electrolyte manufacturing)

[0525] The electrolyte for a lithium secondary battery of the present invention was prepared by dissolving LiPF6 in an organic solvent mixed with gamma-butyrolactone and ethylene carbonate in a volume ratio of 70:30 to a concentration of 1.0 M, adding 1.0 wt% of lithium nitrate (LiNO3) as a first additive and 0.5 wt% of a sulfonylimide compound represented by chemical formula 2-65 as a second additive (weight ratio of the first additive and the second additive = 1:0.5), and adding 3.0 wt% of vinylene carbonate (VC) and 1.0 wt% of ethylene sulfate (Esa) as other additives.

[0527] (Secondary battery manufacturing)

[0528] A lithium secondary battery was manufactured in the same manner as in Example 1, except for injecting the electrolyte manufactured above.

[0530] Example 16.

[0531] (Electrolyte manufacturing)

[0532] The electrolyte for a lithium secondary battery of the present invention was prepared by dissolving LiPF6 in an organic solvent mixed with gamma-butyrolactone and ethylene carbonate in a volume ratio of 70:30 to a concentration of 1.0 M, adding 1.0 wt% of lithium nitrate (LiNO3) as a first additive and 0.5 wt% of a sulfonylimide compound represented by chemical formula 2-66 as a second additive (weight ratio of the first additive and the second additive = 1:0.5), and adding 3.0 wt% of vinylene carbonate (VC) and 1.0 wt% of ethylene sulfate (Esa) as other additives.

[0534] (Secondary battery manufacturing)

[0535] A lithium secondary battery was manufactured in the same manner as in Example 1, except for injecting the electrolyte manufactured above.

[0537] Example 17.

[0538] (Electrolyte manufacturing)

[0539] The electrolyte for a lithium secondary battery of the present invention was prepared by dissolving LiPF6 in an organic solvent mixed with gamma-butyrolactone and ethylene carbonate in a volume ratio of 70:30 to a concentration of 1.0 M, adding 1.0 wt% of lithium nitrate (LiNO3) as a first additive and 0.5 wt% of a sulfonylimide compound represented by the chemical formula 2-73 as a second additive (weight ratio of the first additive and the second additive = 1:0.5), and adding 3.0 wt% of vinylene carbonate (VC) and 1.0 wt% of ethylene sulfate (Esa) as other additives.

[0541] (Secondary battery manufacturing)

[0542] A lithium secondary battery was manufactured in the same manner as in Example 1, except for injecting the electrolyte manufactured above.

[0544] Example 18.

[0545] (Electrolyte manufacturing)

[0546] The electrolyte for a lithium secondary battery of the present invention was prepared by dissolving LiPF6 in an organic solvent mixed with gamma-butyrolactone and ethylene carbonate in a 99:1 volume ratio to make the concentration 1.0 M, adding 1.0 wt% of lithium nitrate (LiNO3) as a first additive and 0.5 wt% of a sulfonylimide compound represented by chemical formula 2-41 as a second additive (weight ratio of the first additive and the second additive = 1:0.5), and adding 3.0 wt% of vinylene carbonate (VC) and 1.0 wt% of ethylene sulfate (Esa) as other additives.

[0548] (Secondary battery manufacturing)

[0549] A lithium secondary battery was manufactured in the same manner as in Example 1, except for injecting the electrolyte manufactured above.

[0551] Example 19.

[0552] (Electrolyte manufacturing)

[0553] The electrolyte for a lithium secondary battery of the present invention was prepared by dissolving LiPF6 in an organic solvent mixed with gamma-butyrolactone and ethylene carbonate in a 50:50 volume ratio so that the concentration was 1.0 M, adding 1.0 wt% of lithium nitrate (LiNO3) as a first additive and 0.5 wt% of a sulfonylimide compound represented by chemical formula 2-41 as a second additive (weight ratio of the first additive and the second additive = 1:0.5), and adding 3.0 wt% of vinylene carbonate (VC) and 1.0 wt% of ethylene sulfate (Esa) as other additives.

[0555] (Secondary battery manufacturing)

[0556] A lithium secondary battery was manufactured in the same manner as in Example 1, except for injecting the electrolyte manufactured above.

[0558] Example 20.

[0559] (Electrolyte manufacturing)

[0560] The electrolyte for a lithium secondary battery of the present invention was prepared by dissolving LiPF6 in an organic solvent mixed with gamma-butyrolactone and ethylene carbonate in a volume ratio of 70:30 to 1.0 M, adding 4.0 wt% of lithium nitrate (LiNO3) as a first additive and 4.0 wt% of a sulfonylimide compound represented by chemical formula 2-41 as a second additive (weight ratio of the first additive and the second additive = 1:1), and adding 3.0 wt% of vinylene carbonate (VC) and 1.0 wt% of ethylene sulfate (Esa) as other additives.

[0562] (Secondary battery manufacturing)

[0563] A lithium secondary battery was manufactured in the same manner as in Example 1, except for injecting the electrolyte manufactured above.

[0565] Example 21.

[0566] (Electrolyte manufacturing)

[0567] The electrolyte for a lithium secondary battery of the present invention was prepared by dissolving LiPF6 in an organic solvent mixed with gamma-butyrolactone and ethylene carbonate in a volume ratio of 70:30 to a concentration of 1.0 M, adding 1.0 wt% of lithium nitrate (LiNO3) as a first additive and 3.0 wt% of a sulfonylimide compound represented by chemical formula 2-41 as a second additive (weight ratio of the first additive and the second additive = 1:3), and adding 3.0 wt% of vinylene carbonate (VC) and 1.0 wt% of ethylene sulfate (Esa) as other additives.

[0569] (Secondary battery manufacturing)

[0570] A lithium secondary battery was manufactured in the same manner as in Example 1, except for injecting the electrolyte manufactured above.

[0572] Example 22.

[0573] (Electrolyte manufacturing)

[0574] The electrolyte for a lithium secondary battery of the present invention was prepared by dissolving LiPF6 in an organic solvent mixed with gamma-butyrolactone and ethylene carbonate in a 40:60 volume ratio so that the concentration was 1.0 M, adding 1.0 wt% of lithium nitrate (LiNO3) as a first additive and 0.5 wt% of a sulfonylimide compound represented by chemical formula 2-41 as a second additive (weight ratio of the first additive and the second additive = 1:0.5), and adding 3.0 wt% of vinylene carbonate (VC) and 1.0 wt% of ethylene sulfate (Esa) as other additives.

[0576] (Secondary battery manufacturing)

[0577] A lithium secondary battery was manufactured in the same manner as in Example 1, except for injecting the electrolyte manufactured above.

[0579] Example 23.

[0580] (Anode manufacturing)

[0581] A positive active material slurry (solid content 67 wt%) was prepared by adding a positive active material (LiFePO4), a conductive material (carbon black), and a binder (polyvinylidene fluoride, PVDF) to a solvent, N-methyl-2-pyrrolidone (NMP), in a weight ratio of 96:1:3. The positive active material slurry was coated onto a positive current collector (Al thin film) with a thickness of 15 μm, dried, and then rolled to produce a positive (double-sided loading amount: 32 mg / cm², single-sided loading amount: 16 mg / cm²).

[0583] (Secondary battery manufacturing)

[0584] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the above-manufactured positive electrode was applied.

[0586] Example 24.

[0587] (Anode manufacturing)

[0588] A positive active material slurry (solid content 67 wt%) was prepared by adding a positive active material (LiFePO4), a conductive material (carbon black), and a binder (polyvinylidene fluoride, PVDF) to a solvent, N-methyl-2-pyrrolidone (NMP), in a weight ratio of 96:1:3. The positive active material slurry was coated onto a positive current collector (Al thin film) with a thickness of 15 μm, dried, and rolled to produce a positive (double-sided loading amount: 60 mg / cm², single-sided loading amount: 30 mg / cm²).

[0590] (Secondary battery manufacturing)

[0591] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the above-manufactured positive electrode was applied.

[0593] Comparative Example 1.

[0594] (Electrolyte manufacturing)

[0595] An electrolyte was prepared by dissolving LiPF6 in an organic solvent mixed with gamma-butyrolactone and ethylene carbonate in a 70:30 volume ratio to achieve a concentration of 1.0 M, adding 1.0 wt% of lithium nitrate (LiNO3) as a first additive, and adding 3.0 wt% of vinylene carbonate (VC) and 1.0 wt% of ethylene sulfate (ESA) as other additives.

[0597] (Secondary battery manufacturing)

[0598] A lithium secondary battery was manufactured in the same manner as in Example 1, except for injecting the electrolyte manufactured above.

[0600] Comparative Example 2.

[0601] (Electrolyte manufacturing)

[0602] An electrolyte was prepared by dissolving LiPF6 in an organic solvent mixed with gamma-butyrolactone and ethylene carbonate in a 70:30 volume ratio to achieve a concentration of 1.0 M, adding 1.0 wt% of a sulfonylimide compound represented by chemical formula 2-41 as a second additive, and adding 3.0 wt% of vinylene carbonate (VC) and 1.0 wt% of ethylene sulfate (ESA) as other additives.

[0604] (Secondary battery manufacturing)

[0605] A lithium secondary battery was manufactured in the same manner as Comparative Example 1, except for the injection of the electrolyte manufactured above.

[0607] Comparative Example 3.

[0608] (Electrolyte manufacturing)

[0609] An electrolyte was prepared by dissolving LiPF6 to a concentration of 1.0 M in an organic solvent mixed with ethylene carbonate and ethyl methyl carbonate in a volume ratio of 30:70, adding 1.0 wt% of lithium nitrate (LiNO3) as a first additive and 0.5 wt% of a sulfonylimide compound represented by chemical formula 2-41 as a second additive (weight ratio of the first additive and the second additive = 1:0.5), and adding 3.0 wt% of vinylene carbonate (VC) and 1.0 wt% of ethylene sulfate (Esa) as other additives.

[0611] (Secondary battery manufacturing)

[0612] A lithium secondary battery was manufactured in the same manner as Comparative Example 1, except for the injection of the electrolyte manufactured above.

[0614] Comparative Example 4.

[0615] (Electrolyte manufacturing)

[0616] An electrolyte was prepared by dissolving LiPF6 to a concentration of 1.0 M in an organic solvent mixed with gamma-butyrolactone and ethylene carbonate in a volume ratio of 70:30, then adding 41.0 wt% of LiBF as a first additive and 1.0 wt% of a sulfonylimide compound represented by chemical formula 2-41 as a second additive (weight ratio of the first additive and the second additive = 1:1), and adding 3.0 wt% of vinylene carbonate (VC) and 1.0 wt% of ethylene sulfate (ESA) as other additives.

[0618] (Secondary battery manufacturing)

[0619] A lithium secondary battery was manufactured in the same manner as Comparative Example 1, except for the injection of the electrolyte manufactured above.

[0621] Comparative Example 5.

[0622] (Electrolyte manufacturing)

[0623] An electrolyte was prepared by dissolving LiPF6 to a concentration of 1.0 M in an organic solvent mixed with gamma-butyrolactone and ethylene carbonate in a 70:30 volume ratio, then adding 0.1 wt% of lithium nitrate (LiNO3) as a first additive and 0.1 wt% of lithium bis(trifluoromethane sulfonyl)imide (LiN(SO2CF3)2, LiTFSI) as a second additive (weight ratio of the first additive and the second additive = 1:1), and adding 3.0 wt% of vinylene carbonate (VC) and 1.0 wt% of ethylene sulfate (ESA) as other additives.

[0625] (Secondary battery manufacturing)

[0626] A lithium secondary battery was manufactured in the same manner as Comparative Example 1, except for the injection of the electrolyte manufactured above.

[0628] Comparative Example 6.

[0629] (Anode manufacturing)

[0630] A positive active material slurry (solid content 67 wt%) was prepared by adding a positive active material (LiFePO4), a conductive material (carbon black), and a binder (polyvinylidene fluoride, PVDF) to a solvent, N-methyl-2-pyrrolidone (NMP), in a weight ratio of 96:1:3. The positive active material slurry was coated onto a positive current collector (Al thin film) with a thickness of 15 μm, dried, and rolled to produce a positive (double-sided loading amount: 62 mg / cm², single-sided loading amount: 31 mg / cm²).

[0632] (Secondary battery manufacturing)

[0633] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the above-manufactured positive electrode was applied.

[0635] [Experimental Example]

[0636] Experimental Example 1. Evaluation of High Temperature (45℃) Cycle Characteristics

[0637] In the above examples and comparative examples, the lithium secondary batteries prepared were each charged to SOC 64% at a high temperature (55℃) at a rate of 0.1 C, followed by an aging (48 hours) and degassing process to perform an activation process.

[0638] After the activation process was completed, each lithium secondary battery was charged to 3.8V at a constant current / constant voltage condition at a rate of 0.1 C at room temperature (25℃), and discharged at a constant current condition of 2.5V at a rate of 0.33 C to check the initial capacity.

[0639] Next, each lithium secondary battery was charged to 3.8V at a constant current / constant voltage condition at a rate of 0.33 C at a high temperature (45℃), and discharged to 2.5V at a constant current condition at a rate of 0.33 C. This was performed for 100 cycles, and then the discharge capacity was measured. The lithium secondary battery operation was performed using a PNE-0506 charge / discharger (Manufacturer: PNE solution).

[0640] The high-temperature cycle capacity retention rate was calculated using the 100th discharge ratio relative to the obtained initial capacity, and the results are shown in Table 1 below.

[0641] High-temperature cycle capacity characteristics Example 1 91.4 Example 2 91.7 Example 3 91.5 Example 4 91.3 Example 5 91.2 Example 6 91.8 Example 7 91.3 Example 8 91.4 Example 9 91.6 Example 10 91.8 Example 11 91.5 Example 12 91.7 Example 13 91.9 Example 14 91.7 Example 15 91.6 Example 16 91.5 Example 17 91.4 Example 18 90.7 Example 19 90.7 Example 20 90.7 Example 21 90.1 Example 22 89.2 Example 23 90.7 Example 24 90.8 Comparative Example 1 87.9 Comparative Example 2 87.7 Comparative Example 3 87.5 Comparative Example 4 87.3 Comparative Example 5 87.2 Comparative Example 6 85.7

[0643] Referring to Table 1 above, it can be seen that in the case of the lithium secondary batteries manufactured in Examples 1 to 24 of the present invention, the capacity retention rate (%) after high-voltage high-temperature cycling is improved compared to the lithium secondary batteries of Comparative Examples 1 to 6.

[0645] Although the present invention has been described above with reference to preferred embodiments, those skilled in the art or those with ordinary knowledge in the relevant technical field will understand that various modifications and changes can be made to the invention without departing from the spirit and technical scope of the invention as set forth in the claims below. Accordingly, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be determined by the claims.

Claims

Claim 1 A lithium secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode comprises lithium iron phosphate as a positive electrode active material, and the loading amount of the positive electrode is 32 mg / cm² 2 to 60 mg / cm² 2 A lithium secondary battery comprising: an electrolyte comprising a lithium salt; a first organic solvent; a second organic solvent; a first additive; and a second additive, wherein the first organic solvent is a cyclic lactone compound, the second organic solvent is a carbonate-based organic solvent, the first additive is lithium nitrate (LiNO3), the second additive is a sulfonylimide compound, and the first organic solvent and the second organic solvent are included in a volume ratio of 50:50 to 99:

1. Claim 2 In claim 1, the lithium secondary battery is a compound represented by the following chemical formula 1, wherein the lithium iron phosphate is a compound: [Chemical Formula 1]Li 1+a Fe x M y (PO 4-b )X' b In the above [Chemical Formula 1], M is any one selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y, X' is one or more elements selected from the group consisting of F, S, and N, and -0.5≤a≤0.5, 0 <x≤1, 0≤y≤1 및 0≤b≤0.3이다. Claim 3 In paragraph 2, the lithium secondary battery wherein the lithium iron phosphate is lithium iron phosphate (LiFePO4) or lithium manganese iron phosphate (LiFeMnPO4). Claim 4 In claim 1, the loading amount of the anode is 40 mg / cm² 2 to 60 mg / cm² 2 lithium secondary battery. Claim 5 A lithium secondary battery according to claim 1, wherein the cyclic lactone compound comprises gamma-butyrolactone. Claim 6 A lithium secondary battery according to claim 1, wherein the carbonate organic solvent is a cyclic carbonate organic solvent. Claim 7 delete Claim 8 A lithium secondary battery according to claim 1, wherein the first organic solvent and the second organic solvent are included in a volume ratio of 70:30 to 90:

10. Claim 9 A lithium secondary battery according to claim 1, wherein the first additive is included in an amount of 0.05 weight% to 3.0 weight% based on the total weight of the electrolyte. Claim 10 In claim 1, the lithium secondary battery comprising a compound represented by the following chemical formula 2, wherein the sulfonylimide compound is: [Chemical Formula 2] In the above chemical formula 2, R1 is hydrogen or an alkyl group having 1 to 4 carbon atoms, R2 is an alkylene group having 1 to 10 carbon atoms, an oxyalkylene group having 1 to 10 carbon atoms, a cycloalkylene group having 5 to 10 carbon atoms, and Any one selected from the group consisting of, and R3 is a fluoro group, an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, or However, the above R2 and In R3 , Alkyl group, alkylene group, alkoxy group, oxyalkylene group, cycloalkylene group, and One or more of the hydrogens included in may be substituted with fluorine atoms, A is an oxygen atom (O) or -NR4, R4 is hydrogen or a carbon-1 to carbon-4 alkyl group, M1 is any one selected from the group consisting of lithium, sodium, potassium, carbon-1 to carbon-4 tetraalkylammonium and carbon-1 to carbon-4 tetraalkylphosphonium, l is an integer from 1 to 6, and m and n are each independently integers from 1 to 20. Claim 11 In claim 10, in the above chemical formula 2, R1 is hydrogen or a methyl group, and R2 is a methylene group, an ethylene group, a propylene group, an oxymethylene group, an oxyethylene group, an oxypropylene group, a cyclophenylene group, a cyclohexylene group, a cycloheptylene group, and It is any one selected from the group consisting of, and R3 is a fluoro group, methyl group, ethyl group, propyl group, trifluoromethyl group, methoxy group, ethoxy group, or A lithium secondary battery in which A is an oxygen atom (O), -NH or -NCH3, M1 is lithium, l is an integer of 1 or 2, and m and n are each independently integers from 1 to 10. Claim 12 A lithium secondary battery according to claim 1, wherein the first additive and the second additive are included in a weight ratio of 1:0.05 to 1:

2. Claim 13 A lithium secondary battery according to claim 1, wherein the first additive and the second additive are included in a weight ratio of 1:0.1 to 1:

2. Claim 14 A lithium secondary battery according to claim 1, wherein the negative electrode comprises a carbon-based active material, a silicon-based active material, or a mixture of a carbon-based active material and a silicon-based active material.

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