Lithium-ion rechargeable battery

Abstract

The present invention provides a lithium secondary battery comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, wherein the positive electrode comprises a positive electrode active material, the positive electrode active material comprising lithium iron phosphate particles, the non-aqueous electrolyte comprises a lithium salt, an organic solvent, and an additive, and the additive comprises a compound represented by a specific chemical formula.

Description

[Technical Field]

[0001] This application claims priority under Korean Patent Application No. 10-2022-0146435 dated November 4, 2022, and all content disclosed in the said Korean Patent Application is incorporated herein by reference.

[0002] The present invention relates to a lithium secondary battery, and more specifically to a lithium secondary battery that can suppress an increase in initial resistance and improve output characteristics and lifespan performance by including a non-aqueous electrolyte containing an additive that can form a strong SEI film on the positive / negative electrodes. [Background technology]

[0003] With the development of the information society, personal IT devices and computer networks have advanced, and consequently, society as a whole has become more dependent on electrical energy. As a result, there is a growing need for technologies to efficiently store and utilize electrical energy.

[0004] Rechargeable batteries are the most suitable technology among the developed technologies for a wide range of applications, and among these rechargeable batteries, there is growing interest in lithium-ion batteries, which not only can be miniaturized to a degree that makes them applicable to personal IT devices, but also have the highest energy density.

[0005] Generally, lithium secondary batteries are manufactured by injecting or impregnating an electrode assembly, which consists of a positive electrode, a negative electrode, and a porous separator, with a non-aqueous electrolyte.

[0006] Possible negative electrode active materials for such lithium secondary batteries include carbon-based active materials and silicon-based active materials. On the other hand, possible positive electrode active materials include lithium-containing cobalt oxide, layered crystalline LiMnO2, spinel crystalline LiMn2O4, and lithium-containing nickel oxide (LiNiO2).

[0007] Recently, as a positive electrode active material, the use of a lithium iron phosphate (e.g., LiFePO4) - based active material with excellent thermal stability and relatively low cost has been considered.

[0008] On the other hand, from lithium salts such as LiPF6 contained in the non - aqueous electrolyte, PF6 ,

[0010] , , , , , , , anions may be thermally decomposed to form Lewis acids such as PF5, and PF5 may react with moisture to generate HF. Such substances as PF5 or HF can not only destroy the film formed on the surface of the electrode, but also cause decomposition reactions of the organic solvent. In particular, when lithium iron phosphate is used as the positive electrode active material, there is a problem that Fe elutes from the surface of the positive electrode active material exposed by the above - mentioned HF and PF5. Such elution of Fe destabilizes the lattice structure of lithium iron phosphate, thereby generating active oxygen and promoting the decomposition of the organic solvent in the non - aqueous electrolyte, and accelerating gas generation. Further, after the eluted Fe moves to the negative electrode through the non - aqueous electrolyte, it electrodeposits on the surface of the negative electrode and destroys the Solid Electrolyte Interface layer (hereinafter referred to as the SEI film). In the process of regenerating the destroyed SEI film, it causes further consumption of lithium ions, resulting in an increase in resistance and a decrease in capacity.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0010] One problem of the present invention is to solve the above - mentioned problems, and to provide a lithium secondary battery containing lithium iron phosphate particles as a positive electrode active material, in which side reactions caused by Fe eluted from lithium iron phosphate are suppressed, and an SEI film with low resistance is formed on the negative electrode, thereby improving the output characteristics and life characteristics simultaneously. [Means for solving the problem]

[0011] The present invention provides a lithium secondary battery comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, wherein the positive electrode comprises a positive electrode active material, the positive electrode active material comprises lithium iron phosphate particles, and the non-aqueous electrolyte comprises a lithium salt, an organic solvent, and an additive, the additive comprising a compound represented by the following chemical formula 1. [ka] In the above chemical formula 1, R1 and R2 are each independently an alkylene group having 1 to 10 carbon atoms, and R3 is an alkyl group having 1 to 20 carbon atoms substituted with one or more fluorine atoms. [Effects of the Invention]

[0012] The present invention relates to a lithium secondary battery in which the positive electrode contains a positive electrode active material containing lithium iron phosphate particles, and the non-aqueous electrolyte contains, as an additive, a compound represented by the chemical formula 1. The compound represented by the chemical formula 1 has a propargyl group in its structure. H Because it contains a fluorocarbon functional group substituted with C≡C- and one or more fluorine elements, it is reduced before organic solvents, and a low-resistance SEI film containing fluorocarbon components can be formed on the surface of the negative electrode. The SEI film formed on the negative electrode by the compound represented by chemical formula 1 not only prevents side reactions caused by Fe eluted from lithium iron phosphate particles, but also has low resistance, which simultaneously improves the lifespan and output characteristics (specifically, room temperature output characteristics and low-temperature output characteristics) of the lithium secondary battery. [Modes for carrying out the invention]

[0013] First, before describing the present invention, the terms and words used in this specification and in the claims should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather in a manner consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors may define the concepts of terms as appropriate to best describe their invention.

[0014] On the other hand, the terms used herein are used solely to describe exemplary embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

[0015] In this specification, terms such as “includes,” “equip,” or “have” indicate the presence of implemented features, figures, steps, components, or combinations thereof, but should be understood not to preclude the existence or possibility of adding one or more different features, figures, steps, components, or combinations thereof.

[0016] In this specification, "%" means weight percent unless otherwise explicitly indicated.

[0017] Before describing the present invention, in the description of "carbon number a to b" in the specification, "a" and "b" refer to the number of carbon atoms contained in a specific functional group. That is, the functional group may contain "a" to "b" carbon atoms.

[0018] Furthermore, in this specification, "substitution" means, unless otherwise defined, that at least one hydrogen atom bonded to a carbon atom is substituted with an element other than hydrogen, for example, by an alkyl group having 1 to 5 carbon atoms or by a fluorine element.

[0019] In this specification, the average particle size (D 50 The average particle size (D) can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve. 50 The particle size can be measured, for example, using the laser diffraction method. This laser diffraction method can generally measure particle sizes from the submicron region to several millimeters in size, and can yield highly reproducible and high-resolution results.

[0020] The present invention will be described in more detail below.

[0021] Lithium-ion rechargeable battery The present invention provides a lithium secondary battery comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, wherein the positive electrode comprises a positive electrode active material, the positive electrode active material comprises lithium iron phosphate particles, and the non-aqueous electrolyte comprises a lithium salt, an organic solvent, and an additive, the additive comprising a compound represented by the following chemical formula 1.

[0022] [ka]

[0023] In the above chemical formula 1, R1 and R2 are each independently an alkylene group having 1 to 10 carbon atoms, and R3 is an alkyl group having 1 to 20 carbon atoms substituted with one or more fluorine atoms.

[0024] The present invention relates to a lithium secondary battery in which the positive electrode contains a positive electrode active material containing lithium iron phosphate particles, and the non-aqueous electrolyte contains, as an additive, a compound represented by the chemical formula 1. The compound represented by the chemical formula 1 has a propargyl group in its structure. H Because it contains a fluorocarbon functional group substituted with C≡C- and one or more fluorine elements, it is reduced before organic solvents, and a low-resistance SEI film containing fluorocarbon components can be formed on the surface of the negative electrode. The SEI film formed on the negative electrode by the compound represented by chemical formula 1 not only prevents side reactions caused by Fe eluted from lithium iron phosphate particles, but also has low resistance, which simultaneously improves the lifespan and output characteristics (specifically, room temperature output characteristics and low-temperature output characteristics) of the lithium secondary battery.

[0025] The lithium secondary battery includes a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte. Specifically, the lithium secondary battery includes a positive electrode, a negative electrode facing the positive electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. The lithium secondary battery can be manufactured by housing an electrode assembly including the positive electrode, a negative electrode facing the positive electrode, and a separator interposed between the positive electrode and the negative electrode in a battery case and then injecting a non-aqueous electrolyte.

[0026] (1) Positive electrode The positive electrode includes a positive electrode active material. The positive electrode active material includes lithium iron phosphate particles.

[0027] The lithium iron phosphate particles can contain a compound represented by the following chemical formula A.

[0028] [Chemical formula A] Li 1+a Fe 1-s M s (PO 4-b )X b

[0029] In the chemical formula A, M is one or more elements selected from Co, Ni, Al, Mg, Ti, and V, X is F, S, or N, 0 ≦ s ≦ 0.5; -0.5 ≦ a ≦ +0.5; 0 ≦ b ≦ 0.1.

[0030] Specifically, the chemical formula A can be represented by LiFePO4 (a = 0, s = 0, and b = 0).

[0031] The lithium iron phosphate particles can be composed of primary particles, or secondary particles formed by aggregation of two or more primary particles, or a mixture of primary particles and secondary particles formed by aggregation of two or more primary particles.

[0032] Here, the primary particles can have an average particle size (D 50 ) of 0.2 μm to 3.0 μm, specifically 0.2 μm to 1.0 μm, and more specifically 0.3 μm to 0.8 μm, and the secondary particles can have an average particle size (D50 The size of the sprockets can range from 7 μm to 25 μm, and more specifically, from 10 μm to 20 μm.

[0033] The positive electrode active material may further include, but is not limited to, a carbon coating layer located on the lithium iron phosphate particles. The carbon coating layer may be introduced for purposes such as protecting the lithium iron phosphate particles or improving electrical conductivity.

[0034] The positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector. Here, the positive electrode active material layer may include the positive electrode active material described above.

[0035] The positive electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. Specifically, the positive electrode current collector can be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloy.

[0036] The positive electrode current collector can typically have a thickness of 3 μm to 500 μm.

[0037] The positive electrode current collector can also have fine irregularities formed on its surface to strengthen the bonding force of the positive electrode active material. For example, the positive electrode current collector can be used in various forms such as film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0038] The positive electrode active material layer is disposed on at least one surface of the positive electrode current collector. Specifically, the positive electrode active material layer can be disposed on one or both surfaces of the positive electrode current collector.

[0039] The positive electrode active material can be included in the positive electrode active material layer at an amount of 80% to 99% by weight, taking into consideration the sufficient capacity of the positive electrode active material.

[0040] The positive electrode active material layer may further include a binder and / or a conductive material along with the positive electrode active material described above.

[0041] The binder is a component that helps in binding the active material to conductive materials and to the current collector, and specifically includes at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluororubber, preferably polyvinylidene fluoride.

[0042] The binder can be included in the positive electrode active material layer in an amount of 1% to 20% by weight, preferably 1.2% to 10% by weight, in order to ensure sufficient binding force between components such as the positive electrode active material.

[0043] The conductive material can be used in a secondary battery to assist and improve conductivity, and is not particularly limited as long as it does not cause chemical changes and is conductive. Specifically, the positive electrode conductive material may include at least one selected from the group consisting of graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; fluorocarbons; metal powders such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and polyphenylene derivatives. Preferably, carbon nanotubes can be included in terms of improving conductivity.

[0044] The conductive material can be included in the positive electrode active material layer in an amount of 1% to 20% by weight, preferably 1.2% to 10% by weight, in order to ensure sufficient electrical conductivity.

[0045] The thickness of the positive electrode active material layer may be 10 μm to 500 μm, preferably 200 μm to 400 μm.

[0046] The loading amount of the positive electrode active material layer is 2.5 mAh / cm². 2 ~5.0mAh / cm 2 Preferably 3mAh / cm² 2 ~4mAh / cm 2 It can be.

[0047] The positive electrode can be manufactured by coating the positive electrode current collector with a positive electrode active material and a positive electrode slurry containing a binder, conductive material, and solvent for forming the positive electrode slurry, followed by drying and rolling.

[0048] The solvent for forming the positive electrode slurry may include organic solvents such as NMP (N-methyl-2-pyrrolidone). The solid content of the positive electrode slurry can be 40% to 90% by weight, specifically 50% to 80% by weight.

[0049] (2) Negative electrode The negative electrode can face the positive electrode.

[0050] The aforementioned negative electrode includes a negative electrode active material.

[0051] The negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. Here, the negative electrode active material may be included in the negative electrode active material layer.

[0052] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. Specifically, the negative electrode current collector can be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloy.

[0053] The negative electrode current collector can typically have a thickness of 3 μm to 500 μm.

[0054] The negative electrode current collector can also have fine irregularities formed on its surface to strengthen the bonding force of the negative electrode active material. For example, the negative electrode current collector can be used in various forms such as film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0055] The negative electrode active material layer is disposed on at least one surface of the negative electrode current collector. Specifically, the negative electrode active material layer can be disposed on one or both surfaces of the negative electrode current collector.

[0056] The negative electrode active material layer may contain a negative electrode active material.

[0057] The negative electrode active material may include at least one selected from the group consisting of carbon-based active materials, (semi)metallic active materials, and lithium metal, as a material capable of reversibly inserting / deinserting lithium ions. Specifically, it may include at least one selected from carbon-based active materials and (semi)metallic active materials.

[0058] The carbon-based active material may include at least one selected from the group consisting of artificial graphite, natural graphite, hard carbon, soft carbon, carbon black, graphene, and fibrous carbon, and preferably may include at least one selected from the group consisting of artificial graphite and natural graphite.

[0059] The average particle size (D) of the carbon-based active material 50The thickness of the ) can be 10 μm to 30 μm, preferably 15 μm to 25 μm, in order to ensure structural stability during charging and discharging and to reduce side reactions with the electrolyte.

[0060] Specifically, the (semi)metallic active material may include: at least one (semi)metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn; an alloy of lithium with at least one (semi)metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn; an oxide of at least one (semi)metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn; lithium titanium oxide (LTO); lithium vanadium oxide; and the like.

[0061] More specifically, the (semi)metallic active material may include a silicon-based active material.

[0062] The silicon-based active material is SiO x The compound may include compounds represented by (0 ≤ x < 2). In the case of SiO2, lithium cannot be stored because it does not react with lithium ions, so it is preferable that x is within the above range, and more preferably the silicon-based active material can be SiO.

[0063] The average particle size (D) of the silicon-based active material 50 The thickness of the ) can be 1 μm to 30 μm, preferably 2 μm to 15 μm, in order to ensure structural stability during charging and discharging and to reduce side reactions with the electrolyte.

[0064] The negative electrode active material can be contained in the negative electrode active material layer in an amount of 60% to 99% by weight, preferably 75% to 95% by weight.

[0065] The negative electrode active material layer may further include a binder and / or a conductive material together with the negative electrode active material.

[0066] The binder is used to improve the adhesion between the negative electrode active material layer and the negative electrode current collector, thereby improving the performance of the battery. For example, it may contain at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and substances in which the hydrogen atoms of these are substituted with Li, Na, or Ca, and may also contain various copolymers thereof.

[0067] The binder can be included in the negative electrode active material layer in an amount of 0.5% to 10% by weight, preferably 1% to 5% by weight.

[0068] The conductive material is not particularly limited as long as it does not cause a chemical change in the battery and is conductive. Examples of such materials include graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; fluorocarbons; metal powders such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0069] The conductive material can be included in the negative electrode active material layer in an amount of 0.5% to 10% by weight, preferably 1% to 5% by weight.

[0070] The thickness of the negative electrode active material layer may be 5 μm to 500 μm, preferably 100 μm to 300 μm.

[0071] The loading amount of the negative electrode active material layer is 3.0 mAh / cm². 2 ~5.5mAh / cm 2 Preferably 3.5 mAh / cm² 2 ~4.5mAh / cm 2 It can be.

[0072] The negative electrode can be manufactured by coating at least one surface of a negative electrode current collector with a negative electrode slurry containing a negative electrode active material, a binder, a conductive material and / or a solvent for forming the negative electrode slurry, followed by drying and rolling.

[0073] The solvent for forming the negative electrode slurry may include, for example, at least one selected from the group consisting of distilled water, NMP (N-methyl-2-pyrrolidone), ethanol, methanol, and isopropyl alcohol, preferably distilled water, in terms of facilitating the dispersion of the negative electrode active material, binder, and / or conductive material. The solid content of the negative electrode slurry can be 30% to 80% by weight, specifically 40% to 70% by weight.

[0074] (3) Separator The separator can be interposed between the positive electrode and the negative electrode.

[0075] As the separator, conventional porous polymer films that have been used as separators, such as porous polymer films made from polyolefin polymers such as ethylene monopolymer, propylene monopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, can be used alone or in laminated form. Alternatively, conventional porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers, can be used, but are not limited to these. Furthermore, to ensure heat resistance or mechanical strength, coated separators containing ceramic components or polymeric substances may be used, and can be selectively used in single-layer or multi-layer structures.

[0076] (4) Non-aqueous electrolytes 1) Lithium salt First, let me explain lithium salts as follows:

[0077] In a non-aqueous electrolyte for a lithium secondary battery according to one embodiment of the present invention, the lithium salt can be any one that is commonly used in lithium secondary battery electrolytes, for example, Li as a cation. + It contains, and as an anion, F - Cl - , Br - , I - NO3 - , N(CN)2 - BF4 - ClO4 - AlO4 - AlCl4 - PF6 - SbF6 - AsF6 - B 10 Cl 10 - BF2C2O4 - BC4O8 - PF4C2O4 - PF2C4O8 - (CF3)2PF4 - (CF3)3PF3 -(CF3)4PF2 - (CF3)5PF - (CF3)6P - CF3SO3 - , C4F9SO3 - CF3CF2SO3 - (CF3SO2)2N - , (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2) 2CH - CH3SO3 - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N - At least one selected from the group consisting of the following is mentioned. Specifically, the lithium salt is LiCl, LiBr, LiI, LiBF4, LiClO4, LiAlO4, LiAlCl4, LiPF6, LiSbF6, LiAsF6, LiB 10 Cl 10 The lithium salt may be at least one selected from the group consisting of LiBOB(LiB(C2O4)2), LiCF3SO3, LiTFSI(LiN(SO2CF3)2), LiFSI(LiN(SO2F)2), LiCH3SO3, LiCF3CO2, LiCH3CO2, and LiBETI(LiN(SO2CF2CF3)2). Specifically, the lithium salt may include a single substance or a mixture of two or more substances selected from the group consisting of LiBF4, LiClO4, LiPF6, LiBOB(LiB(C2O4)2), LiCF3SO3, LiTFSI(LiN(SO2CF3)2), LiFSI(LiN(SO2F)2), and LiBETI(LiN(SO2CF2CF3)2), and more specifically, it may include LiPF6.

[0078] The lithium salt can be appropriately modified within a range of normal use, but in order to obtain the optimal effect of forming a corrosion-preventive coating on the electrode surface, it can be included in the electrolyte at a concentration of 0.8 M to 3.0 M, specifically 1.0 M to 3.0 M.

[0079] When the concentration of the lithium salt satisfies the aforementioned range, the viscosity of the non-aqueous electrolyte can be controlled to achieve optimal impregnation, thereby improving the mobility of lithium ions and obtaining an improvement in the capacity characteristics and cycle characteristics of the lithium secondary battery.

[0080] 2) Organic solvents The aforementioned organic solvent is not particularly limited as long as it is a non-aqueous solvent commonly used in lithium secondary batteries that can minimize decomposition due to oxidation reactions during the charging and discharging process of the secondary battery.

[0081] Specifically, the organic solvent may include cyclic carbonate organic solvents and linear carbonate organic solvents.

[0082] The cyclic carbonate-based organic solvent is a highly viscous organic solvent that has a high dielectric constant and can effectively dissociate lithium salts in the electrolyte. Specifically, it can include at least one organic solvent 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, and vinylene carbonate. More specifically, it can include ethylene carbonate.

[0083] Furthermore, the linear carbonate-based organic solvent is an organic solvent having low viscosity and low dielectric constant, and specifically includes at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate, and ethyl propyl carbonate. In the case of a positive electrode containing lithium iron phosphate particles as the positive electrode active material, the thickness must be increased to achieve the required energy density, and therefore, in terms of further improving electrolyte impregnation, the linear carbonate-based organic solvent can specifically include dimethyl carbonate and ethyl methyl carbonate, and more specifically, it can contain dimethyl carbonate and ethyl methyl carbonate in a volume ratio of 60:40 to 90:10.

[0084] The organic solvent may be a mixture of a cyclic carbonate organic solvent and a linear carbonate organic solvent. Here, the cyclic carbonate organic solvent and the linear carbonate organic solvent may be mixed in a volume ratio of 10:90 to 40:60, specifically, in a volume ratio of 15:85 to 35:65.

[0085] On the other hand, the organic solvent may be further used without limitation by adding any organic solvents commonly used for non-aqueous electrolytes, as needed. For example, it may further contain at least one or more organic solvents from among ester-based organic solvents, ether-based organic solvents, glyme-based solvents, and nitrile-based organic solvents.

[0086] The ester-based organic solvent may include at least one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0087] As the ether-based solvent, one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, ethyl propyl ether, 1,3-dioxolane (DOL), and 2,2-bis(trifluoromethyl)-1,3-dioxolane (TFDOL), or a mixture of two or more of these, may be used, but is not limited thereto.

[0088] The aforementioned glyme-based solvent has a higher dielectric constant and lower surface tension compared to linear carbonate-based organic solvents, and is less reactive with metals. It may include, but is not limited to, at least one selected from the group consisting of dimethoxyethane (Glyme, DME), diethoxyethane, diglyme, triglyme, and tetraglyme (TEGDME).

[0089] The nitrile solvent may be one or more selected from the group consisting of acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonile, cyclohexanecarbonile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile, but is not limited thereto.

[0090] On the other hand, the remainder of the non-aqueous electrolyte, excluding the lithium salt and additives, may be organic solvents unless otherwise specified.

[0091] (3) Additives The non-aqueous electrolyte of the present invention contains additives.

[0092] The aforementioned additive contains a compound represented by the following chemical formula 1.

[0093] [ka]

[0094] In the aforementioned chemical formula 1, R1 and R2 are each independently alkylene groups having 1 to 10 carbon atoms. R3 is an alkyl group having 1 to 20 carbon atoms that is substituted with one or more fluorine atoms.

[0095] Specifically, the compound represented by chemical formula 1, by containing a propargyl functional group in its structure, is easily reductively decomposed on the surface of the negative electrode, forming a SEI film with low resistance and high passivation capacity, thereby improving the durability of the negative electrode itself. Furthermore, when a component derived from the compound represented by chemical formula 1 is included in the SEI film, the problem of Fe eluted from the lithium iron phosphate particles of the positive electrode electrodepositing onto the surface of the negative electrode and damaging the negative electrode SEI film can be prevented to a significant degree. Therefore, when a non-aqueous electrolyte containing the compound represented by chemical formula 1 as an electrolyte additive is used together with a positive electrode using lithium iron phosphate particles as the positive electrode active material, it is possible to prevent the self-discharge reaction of the negative electrode caused by further reductive decomposition of the electrolyte due to the instability of the SEI film.

[0096] Furthermore, the compound represented by chemical formula 1 contains a fluorocarbon functional group substituted with one or more fluorine elements at the end of its structure, thereby forming a coating on the positive electrode surface that ensures oxidation resistance, suppressing the elution of Fe from lithium iron phosphate at the positive electrode, preventing the eluted Fe from electrodepositing and depositing on the negative electrode, and thus preventing internal short circuits.

[0097] Thus, the compound represented by chemical formula 1 contains a fluorocarbon functional group and a propargyl group substituted with one or more fluorine elements, which have excellent flame retardancy and non-flammability. This allows for the formation of a strong SEI film with low resistance, which not only suppresses additional reductive decomposition reactions of the electrolyte but also prevents self-discharge reactions of the negative electrode, thereby suppressing the increase in initial resistance and providing a lithium secondary battery with improved output characteristics at room temperature and low temperatures.

[0098] On the other hand, in the above chemical formula 1, R1 and R2 are each independently an alkylene group having 1 to 5 carbon atoms, and R3 can be an alkyl group having 3 to 20 carbon atoms substituted with one or more fluorine atoms.

[0099] Furthermore, in the above chemical formula 1, R1 and R2 are each independently an alkylene group having 1 to 3 carbon atoms, and R3 can be an alkyl group having 3 to 15 carbon atoms substituted with one or more fluorine atoms.

[0100] Specifically, in the above chemical formula 1, R3 can be an alkyl group having 4 to 8 carbon atoms substituted with one or more fluorine atoms.

[0101] Preferably, the compound represented by chemical formula 1 may be the compound represented by the following chemical formula 1a.

[0102] [ka]

[0103] On the other hand, the compound represented by chemical formula 1 can be included in the non-aqueous electrolyte in an amount of 0.01% to 10.0% by weight.

[0104] When the content of the compound represented by chemical formula 1 falls within the range, drawbacks such as side reactions due to additives, decreased capacity, and increased resistance can be suppressed to the greatest extent possible, and a low-resistance SEI film can be formed on the surface of the negative electrode, improving the lithium transfer effect in the film, suppressing additional reductive decomposition reactions of the electrolyte, and preventing self-discharge reactions of the negative electrode.

[0105] Specifically, when the content of the compound represented by chemical formula 1 is 0.01% by weight or more, a stable film is formed during the battery's operating time, forming a low-resistance SEI film on the negative electrode surface, thereby improving battery output performance. Furthermore, when the content of the compound represented by chemical formula 1 is 10.0% by weight or less, the viscosity of the non-aqueous electrolyte can be controlled to achieve optimal impregnation, effectively suppressing the increase in battery resistance due to the decomposition of additives, further increasing the ionic conductivity within the battery, and preventing a decrease in output characteristics.

[0106] Specifically, the compound represented by chemical formula 1 can be contained in a non-aqueous electrolyte in an amount of 0.05% to 6.0% by weight, more specifically, 0.08% to 0.5% by weight.

[0107] On the other hand, the additive may, if necessary, include additional additives in addition to the compound represented by Chemical Formula 1, in order to prevent the non-aqueous electrolyte from decomposing in a high-power environment and causing negative electrode collapse, or to further improve low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, and suppression of battery swelling at high temperatures.

[0108] Examples of such additional additives include at least one selected from the group consisting of cyclic carbonate compounds, halogen-substituted carbonate compounds, sultone compounds, sulfate compounds, phosphate or phosphite compounds, borate compounds, nitrile compounds, benzene compounds, amine compounds, silane compounds, and lithium salt compounds.

[0109] The cyclic carbonate compound may be, for example, vinylene carbonate (VC) or vinylethylene carbonate.

[0110] The halogen-substituted carbonate compound can be, for example, fluoroethylene carbonate (FEC).

[0111] The sultone compound can be, for example, at least one compound selected from the group consisting of 1,3-propanesultone (PS), 1,4-butanesultone, ethensultone, 1,3-propensultone (PRS), 1,4-butensultone, and 1-methyl-1,3-propensultone.

[0112] The sulfate compound may be, for example, ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS).

[0113] The phosphate or phosphite compound can be, for example, one or more compounds selected from the group consisting of lithium difluoro(bisoxalate) phosphate, lithium difluorophosphate, tris(trimethylsilyl) phosphate, tris(trimethylsilyl) phosphite, tris(2,2,2-trifluoroethyl) phosphate, and tris(trifluoroethyl) phosphite.

[0114] Examples of the borate compounds include tetraphenyl borate, lithium difluoro(oxalate) borate (LiODFB), or lithium bisoxalate borate (LiB(C2O4)2, LiBOB).

[0115] The nitrile compound can be, for example, at least one compound selected from the group consisting of succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonile, cyclohexanecarbonile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

[0116] The benzene-based compound may be, for example, fluorobenzene, the amine-based compound may be triethanolamine or ethylenediamine, and the silane-based compound may be tetravinylsilane.

[0117] The lithium salt compound is a compound different from the lithium salt contained in the non-aqueous electrolyte, and examples include lithium difluorophosphate (LiPO2F2) or LiBF4.

[0118] If such additional additives include at least one selected from the group consisting of vinylethylene carbonate, 1,3-propanesultone, fluoroethylene carbonate, succinonitrile, and lithium difluoro(oxalate) borate, a stronger SEI film can be formed on the surface of the negative electrode during the initial activation process of the secondary battery.

[0119] The aforementioned additional additive can be used by mixing two or more compounds, and the total content of the compound represented by chemical formula 1 and the additional additive may be 50% by weight or less, specifically 0.05% to 20% by weight, or specifically 0.05% to 10% by weight, relative to the total weight of the non-aqueous electrolyte. When the total content of the additive satisfies the above range, the low-temperature power characteristics of the battery can be improved, the high-temperature storage characteristics and high-temperature life characteristics can be improved more effectively, and the occurrence of side reactions of the battery due to additives remaining after the reaction can be prevented.

[0120] The lithium secondary battery according to the present invention, as described above, can be usefully used in portable devices such as mobile phones, notebook computers, and digital cameras, as well as in the field of electric vehicles such as hybrid electric vehicles (HEVs).

[0121] Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

[0122] The aforementioned battery module or battery pack can be used as a power source for one or more medium-to-large devices, including power tools; electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0123] The external shape of the lithium secondary battery of the present invention is not particularly limited, but may be cylindrical, rectangular, pouch-type, or coin-type, using a can.

[0124] The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for small devices, but also suitably as a unit battery in medium- and large-sized battery modules containing a large number of battery cells.

[0125] The present invention will be specifically described below with reference to examples.

[0126] Herein, the embodiments of the present invention can be modified in various other forms, and the scope of the invention should not be construed as being limited to the embodiments detailed below. The embodiments of the present invention are provided to give a more complete explanation of the invention to a person of average skill in the art.

[0127] The present invention will be described in detail below with reference to specific examples.

[0128] Examples Example 1 (Manufacturing of non-aqueous electrolytes) An organic solvent was prepared by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 30:10:60.

[0129] LiPF6 was dissolved in the aforementioned organic solvent to a molar concentration of 1.0 M as a lithium salt.

[0130] Furthermore, a non-aqueous electrolyte was produced by adding the compound represented by chemical formula 1a and additional additives to the organic solvent in which the lithium salt was dissolved.

[0131] The compound represented by chemical formula 1a was present in the non-aqueous electrolyte at a concentration of 0.1% by weight.

[0132] The aforementioned additional additives include vinylethylene carbonate (VEC), 1,3-propanesultone (PS), fluoroethylene carbonate (FEC), succinonitrile (SN), and LiODFB. The non-aqueous electrolyte was to be mixed with 0.5% by weight of vinylethylene carbonate (VEC), 1.0% by weight of 1,3-propanesultone (PS), 5.0% by weight of fluoroethylene carbonate (FEC), 1.0% by weight of succinonitrile (SN), and 0.5% by weight of LiODFB.

[0133] (Manufacturing of secondary batteries) A positive electrode slurry (solid content: 50% by weight) was prepared by adding lithium iron phosphate particles (LiFePO4) as the positive electrode active material, carbon nanotubes as the conductive material, and polyvinylidene fluoride (PVdF) as the binder in a weight ratio of 94:3:3 to the solvent N-methyl-2-pyrrolidone (NMP). The positive electrode slurry was then applied to a 20 μm thick positive electrode current collector (a thin aluminum film) at a rate of 3.7 mAh / cm². 2 After coating and drying with the specified loading amount, the positive electrode was manufactured by roll pressing (thickness of positive electrode active material: 220 μm).

[0134] A negative electrode slurry (solid content: 60% by weight) was prepared by adding graphite as the negative electrode active material, SBR-CMC as the binder, and carbon black as the conductive material in a weight ratio of 96:3:1 to water as the solvent. This negative electrode slurry was then applied to a copper (Cu) thin film, which was a negative electrode current collector with a thickness of 10 μm, to a current discharge rate of 4.2 mAh / cm². 2 After coating and drying with the specified loading amount, the negative electrode was manufactured by roll pressing (thickness of negative electrode active material: 170 μm).

[0135] An electrode assembly was manufactured by sequentially stacking the positive electrode, a polyolefin-based porous separator coated with inorganic particles (Al2O3), and a negative electrode.

[0136] After placing the assembled electrode assembly inside the battery case, the manufactured non-aqueous electrolyte was poured in to produce a lithium secondary battery.

[0137] Example 2 A non-aqueous electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the compound represented by chemical formula 1a was added in a content of 1.0% by weight based on the weight of the non-aqueous electrolyte to produce the non-aqueous electrolyte.

[0138] Example 3 A non-aqueous electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the compound represented by chemical formula 1a was added in a content of 5.0% by weight based on the weight of the non-aqueous electrolyte to produce the non-aqueous electrolyte.

[0139] Comparative Example 1 A non-aqueous electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the compound represented by chemical formula 1a was not added to produce the non-aqueous electrolyte.

[0140] Comparative Example 2 A non-aqueous electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the compound represented by Chemical Formula 2 below was added in a content of 0.1% by weight based on the weight of the non-aqueous electrolyte, instead of the compound represented by Chemical Formula 1a, to produce the non-aqueous electrolyte.

[0141] [ka]

[0142] Comparative Example 3 A non-aqueous electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the compound represented by chemical formula 2 was added in a content of 1.0% by weight based on the weight of the non-aqueous electrolyte, instead of the compound represented by chemical formula 1a, to produce the non-aqueous electrolyte.

[0143] Comparative Example 4 A non-aqueous electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the compound represented by Chemical Formula 3 below was added in a content of 0.1% by weight based on the weight of the non-aqueous electrolyte, instead of the compound represented by Chemical Formula 1a, to produce the non-aqueous electrolyte.

[0144] [ka]

[0145] Experimental example Experimental Example 1: Evaluation of initial capacity and cycle capacity retention rate The lithium secondary batteries of Examples 1 to 3 and Comparative Examples 1 to 4, manufactured as described above, were charged to 3.65V and 0.05C at 25°C under CC / CV and 0.33C conditions using an electrochemical charger / discharger. One cycle consisted of charging to 2.5V under CC and 0.33C conditions, and 300 charge / discharge cycles were performed to measure the capacity retention rate.

[0146] The capacity retention rate was calculated using the following formula, and the results are shown in Table 1 below.

[0147] Capacity retention rate (%) = {(Discharge capacity after 300 cycles / Discharge capacity after 1 cycle)} × 100

[0148] The discharge capacity (initial capacity) after 1 cycle and the capacity retention rate after 300 cycles are shown in Table 1 below.

[0149] Experimental Example 2: Evaluation of Initial Resistance The lithium secondary batteries of Examples 1 to 3 and Comparative Examples 1 to 4 manufactured as described above were charged to 3.65V and 0.05C at 25°C under CC / CV and 0.1C conditions, and then discharged to 2.5V under CC and 0.1C conditions, with each cycle being considered a charge-discharge cycle.

[0150] After one charge-discharge cycle, the discharge capacity after one cycle was measured using an electrochemical charger. After adjusting the SOC to 50%, a 2.5C pulse was applied for 10 seconds, and the initial resistance was calculated from the difference between the voltage before and after pulse application. The results are shown in Table 1 below.

[0151] Experimental Example 3: Evaluation of Metal Dissolution Amount The lithium secondary batteries of Examples 1 to 3 and Comparative Examples 1 to 4, manufactured as described above, were charged to 3.65V and 0.05C at 25°C under CC / CV and 0.33C conditions using an electrochemical charger / discharger. One cycle consisted of charging to 2.5V under CC and 0.33C conditions, and 300 charge / discharge cycles were performed to measure the capacity retention rate.

[0152] Next, the concentration of Fe dissolved in the electrolyte was measured using an inductively coupled plasma optical emission spectrophotometer (ICP-OES). The amount of Fe measured using ICP analysis is shown in Table 1 below.

[0153] [Table 1]

[0154] Referring to Table 1, it can be confirmed that the lithium secondary batteries of Examples 1 to 3 according to the present invention have superior initial capacity, capacity retention rate, and resistance characteristics, and exhibit a low Fe elution rate, compared to Comparative Examples 1 to 4.

Claims

1. It comprises a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte. The positive electrode includes a positive electrode active material. The positive electrode active material includes lithium iron phosphate particles, The non-aqueous electrolyte comprises a lithium salt, an organic solvent, and an additive. The aforementioned additive contains a compound represented by the following chemical formula 1, in a lithium secondary battery: 【Chemistry 1】 In the aforementioned chemical formula 1, R １ and R ２ Each of these is an alkylene group having 1 to 10 carbon atoms, R ３ This is an alkyl group having 1 to 20 carbon atoms that is substituted with one or more fluorine atoms.

2. In the above chemical formula 1, R １ and R ２ Each of these is an alkylene group having 1 to 5 carbon atoms, and R ３ The lithium secondary battery according to claim 1, wherein is an alkyl group having 3 to 20 carbon atoms substituted with one or more fluorines.

3. In the above Chemical Formula 1, R １ and R ２ are each independently an alkylene group having 1 to 3 carbon atoms, and R ３ is an alkyl group having 3 to 15 carbon atoms substituted with one or more fluorines. The lithium secondary battery according to Claim 1.

4. In the above chemical formula 1, R ３ The lithium secondary battery according to claim 1, wherein is an alkyl group having 4 to 8 carbon atoms substituted with one or more fluorines.

5. The lithium secondary battery according to claim 1, wherein the compound represented by the chemical formula 1 is the compound represented by the chemical formula 1a below. 【Chemistry 2】

6. The lithium secondary battery according to any one of claims 1 to 5, wherein the compound represented by chemical formula 1 is contained in the non-aqueous electrolyte in an amount of 0.01% to 10.0% by weight.

7. The lithium secondary battery according to any one of claims 1 to 5, wherein the compound represented by chemical formula 1 is contained in an amount of 0.05% to 6.0% by weight relative to the total weight of the non-aqueous electrolyte for the lithium secondary battery.

8. The lithium secondary battery according to any one of claims 1 to 5, wherein the additive comprises at least one additional additive selected from the group consisting of halogen-substituted or unsubstituted carbonate compounds, sultone compounds, sulfate compounds, phosphate or phosphite compounds, borate compounds, nitrile compounds, amine compounds, silane compounds, and lithium salt compounds.

9. The lithium secondary battery according to any one of claims 1 to 5, wherein the organic solvent includes a cyclic carbonate organic solvent and a linear carbonate organic solvent.

10. The cyclic carbonate-based organic solvent includes ethylene carbonate. The lithium secondary battery according to claim 9, wherein the linear carbonate-based organic solvent comprises ethyl methyl carbonate and dimethyl carbonate.

11. The lithium iron phosphate particles include a compound represented by the following chemical formula A, according to any one of claims 1 to 5: [Chemical formula A] Li １＋ａ Fe １－ｓ M ｓ (PO ４－ｂ )X ｂ In the above chemical formula A, M is one or more elements selected from Co, Ni, Al, Mg, Ti, and V, and X is F, S, or N, with 0 ≤ s ≤ 0.5; -0.5 ≤ a ≤ +0.5; 0 ≤ b ≤ 0.1.

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