Lithium secondary battery

Abstract

Lithium secondary battery, comprehensive a positive electrode, a negative electrode, a separator and a non-aqueous electrolyte, wherein: the positive electrode comprises a positive electrode active material, wherein the positive electrode active material comprises lithium iron phosphate particles and the positive electrode has a loading amount of 450 mg / 25 cm² 2 up to 740 mg / 25 cm 2 exhibits; and the non-aqueous electrolyte comprises a lithium salt, an organic solvent and an additive, wherein the organic solvent comprises a solvent based on a cyclic carbonate and a solvent based on a linear carbonate, wherein the solvent based on a cyclic carbonate comprises ethylene carbonate and the solvent based on a linear carbonate comprises dimethyl carbonate, the additive comprises vinylene carbonate and the dimethyl carbonate is present in an amount of 5 vol% to 75 vol% in the organic solvent and the weight ratio of vinylene carbonate to dimethyl carbonate is greater than 0 to 0.2 or less.

Description

TECHNICAL AREA REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority over Korean patent application No. 10-2022-0146438, filed on November 4, 2022, the disclosure of which is hereby incorporated by reference. TECHNICAL AREA

[0002] The present disclosure relates to a lithium secondary battery. BACKGROUND OF THE INVENTION

[0003] As personal IT devices and computer networks have evolved with the development of an information society, and society's overall dependence on electrical energy has increased, there is a need to develop a technology for the efficient storage and use of electrical energy.

[0004] A secondary battery is a technology that is best suited for various applications among the developed technologies, and among these secondary batteries, there is growing interest in a lithium secondary battery that can be manufactured small enough to be used in personal IT devices and the like, and which also has the highest energy density.

[0005] In general, a lithium secondary battery is manufactured by injecting or impregnating a non-aqueous electrolyte into an electrode assembly consisting of a positive electrode, a negative electrode, and a porous separator.

[0006] Suitable materials for the negative electrodes of a lithium secondary battery include carbon-based, silicon-based, or similar materials. For the positive electrodes, lithium-containing cobalt oxide, LiMnO2 with a layered crystal structure, LiMn2O4 with a spinel crystal structure, lithium-containing nickel oxide (LiNiO2), or similar materials are being considered.

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

[0008] However, lithium iron phosphate-based active material has a lower specific capacity than lithium cobalt oxide, lithium nickel oxide, and the like. Therefore, to increase the energy density of a positive electrode and a lithium secondary battery containing it, the lithium iron phosphate-based active material should be used in a high loading quantity. However, a highly loaded lithium iron phosphate positive electrode has the problem that it is difficult to sufficiently impregnate the positive electrode with a non-aqueous electrolyte, making it difficult to maintain capacity, increasing resistance, and reducing lifespan. REVELATION OF THE INVENTIONAL PROBLEM

[0009] One aspect of the present invention relates to a lithium secondary battery comprising lithium iron phosphate particles as a positive electrode active material and a positive electrode with a certain charge amount or more, wherein the lithium secondary battery exhibits excellent capacity development, excellent lifetime and a resistance reduction effect by improving the reduction stability of the negative electrode while improving the impregnation properties of the positive electrode with respect to the non-aqueous electrolyte. TECHNICAL SOLUTION

[0010] According to one aspect of the present invention, a lithium secondary battery is provided 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, and the positive electrode has a loading of 450 mg / 25 cm². 2 up to 740 mg / 25 cm 2The non-aqueous electrolyte comprises a lithium salt, an organic solvent, and an additive, wherein the organic solvent comprises a cyclic carbonate-based solvent and a linear carbonate-based solvent, wherein the cyclic carbonate-based solvent contains ethylene carbonate and the linear carbonate-based solvent contains dimethyl carbonate, and wherein the dimethyl carbonate is present in the organic solvent in an amount of 5 vol.% to 75 vol.%, and the additive contains vinylene carbonate, and wherein the ratio of the weight of the vinylene carbonate to the weight of the dimethyl carbonate is greater than 0 to 0.2 or less. BENEFICIAL EFFECTS

[0011] The lithium secondary battery according to the disclosure is characterized in that it has a positive electrode having a certain charge quantity or more and containing lithium iron phosphate particles as positive electrode active material, and a non-aqueous electrolyte containing ethylene carbonate and dimethyl carbonate as an organic solvent and vinylene carbonate as an additive, wherein the content and content ratio of dimethyl carbonate and vinylene carbonate are each adjusted to a certain range.In the disclosed lithium secondary battery, excellent dimethyl carbonate is used as an organic solvent component to improve the electrolyte impregnation properties of a positive electrode with a high charge level, and at the same time a vinylene carbonate additive is used which has a specific content ratio with respect to dimethyl carbonate to improve the reduction stability of the negative electrode, so that the capacity of the lithium secondary battery can be maintained at an excellent level and the lifetime properties and resistance properties can be improved. MODE FOR IMPLEMENTING THE INVENTION

[0012] Before describing the present invention, it should first be noted that the terms or words used in the present description and the claims are not to be understood as being limited to the meanings defined in common dictionaries, but should be interpreted as having meanings and concepts that correspond to the technical idea of ​​the present invention, based on the principle that an inventor can adequately define the concepts of the terms in order to explain the invention in the best possible way.

[0013] The terms used here serve only to describe exemplary embodiments and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

[0014] It is further understood that the terms “comprise”, “consist of” or “have”, when used in the present description, specify the presence of the indicated features, numbers, steps, elements or combinations thereof, but do not exclude the presence or addition of one or more other features, numbers, steps, elements or combinations thereof.

[0015] In this description, “%” means weight percent unless otherwise stated.

[0016] Before describing the present invention, it should be noted that in the description of "carbon atoms a to b", "a" and "b" refer to the number of carbon atoms contained in a particular functional group. That is, the functional group can contain a number of "a" to "b" carbon atoms.

[0017] Furthermore, unless otherwise defined, in the present description ‘substituted’ means that at least one hydrogen bonded to carbon is substituted by an element other than hydrogen, for example by an alkyl group with 1 to 5 carbon atoms or a fluorine element.

[0018] In the present description, an average particle diameter (D) can be used. 50 ) is defined as a particle diameter that corresponds to 50% of the accumulated volume in a particle diameter distribution curve of a particle. The average particle diameter (D 50 The particle size can be measured, for example, using a laser diffraction method. Laser diffraction generally allows for the measurement of particle diameters ranging from submicrons to several millimeters, enabling results with high reproducibility and high resolution.

[0019] The present invention will be described in more detail below. Lithium secondary battery

[0020] The present disclosure relates to a lithium secondary battery.

[0021] In particular, the disclosed lithium secondary battery comprises 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, and wherein the positive electrode has a loading amount of 450 mg / 25 cm² 2 up to 740 mg / 25 cm 2comprising, and wherein the non-aqueous electrolyte comprises a lithium salt, an organic solvent and an additive, wherein the organic solvent comprises a solvent based on a cyclic carbonate and a solvent based on a linear carbonate, wherein the solvent based on a cyclic carbonate contains ethylene carbonate and the solvent based on a linear carbonate contains dimethyl carbonate, wherein the dimethyl carbonate is present in an amount of 5 vol.% to 75 vol.% in the organic solvent, wherein the additive contains vinylene carbonate, and wherein the ratio of the weight of the vinylene carbonate to the weight of the dimethyl carbonate is greater than 0 to 0.2 or less.

[0022] The lithium secondary battery according to the disclosure is characterized in that it comprises a positive electrode having a certain charge quantity or greater and containing lithium iron phosphate particles as positive electrode active material, and a non-aqueous electrolyte containing ethylene carbonate and dimethyl carbonate as organic solvents and vinylene carbonate as an additive, wherein the content and ratio of dimethyl carbonate and vinylene carbonate are each adjusted to be within a certain range.In the disclosed lithium secondary battery, dimethyl carbonate is used as an organic solvent component to improve the electrolyte impregnation properties of a positive electrode with a high charge level, and at the same time a vinylene carbonate additive is used such that it has a specific content ratio with respect to dimethyl carbonate to improve the reduction stability of the negative electrode, so that the capacity of the lithium secondary battery can be expressed at an excellent level and the lifetime performance and resistance properties can be improved.

[0023] The disclosed lithium secondary battery can only exhibit a capacity retention rate of 90% or greater, preferably 90% to 95%, at the 200th cycle and a resistance increase rate of 20% or less, preferably 15% or less, at the 200th cycle, while maintaining a nominal capacity of at least 500 mAh, specifically at least 550 mAh, and an initial discharge capacity of at least 500 mAh, specifically at least 540 mAh, provided by the positive electrode, which comprises lithium iron phosphate particles as active material and has a loading of 450 mg / 25 cm². 2 up to 740 mg / 25 cm 2The cell has a capacity of 0 to 0.2 if the electrolyte comprises an organic solvent including ethylene carbonate and dimethyl carbonate, and an additive including vinylene carbonate, wherein the dimethyl carbonate is present in the organic solvent in 5 to 75 vol% and the weight ratio of vinylene carbonate to dimethyl carbonate is greater than 0 to 0.2 or less. The nominal capacity of the cell, the initial discharge capacity, the capacity maintenance rate, and the resistance increase rate are measured according to the procedures described in the following examples.

[0024] The lithium secondary battery comprises a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte. Specifically, the lithium secondary battery comprises a positive electrode, a negative electrode opposite the positive electrode, a separator arranged between the positive and negative electrodes, and a non-aqueous electrolyte.

[0025] The lithium secondary battery can be manufactured by preparing an electrode assembly comprising a positive electrode, a negative electrode and a separator; housing the electrode assembly in a battery casing; preparing a non-aqueous electrolyte comprising a lithium salt, an organic solvent and an additive; and injecting or impregnating the prepared non-aqueous electrolyte into the battery casing. (1) Positive electrode

[0026] The positive electrode comprises a positive electrode active material. The positive electrode active material comprises lithium iron phosphate particles.

[0027] The lithium iron phosphate particles may contain a compound represented by formula A below. Li 1+a Fe 1-s M s (PO 4-b )X b [Formula A]

[0028] In the formula above, A is one or more element(s) selected from the group consisting of Co, Ni, Mn, Al, Mg, Ti and V, and X is F, S or N, where 0≤s≤0.5, -0.5≤a≤+0.5 and 0≤b≤0.1.

[0029] The above formula A can be specifically represented by LiFePO4 (a=0, s=0 and b=0).

[0030] The lithium iron phosphate particles can exist in the form of a primary particle or as a secondary particle, in which two or more primary particles are aggregated. In particular, the lithium iron phosphate particles can exist in the form of a primary particle.

[0031] The lithium iron phosphate particles can be formed from primary particles, from secondary particles in which two or more primary particles are aggregated, or from a mixture of primary particles and secondary particles in which two or more primary particles are aggregated.

[0032] If the lithium iron phosphate particles are in the form of a primary particle, the average particle diameter (D) can be 50) of the lithium iron phosphate particles are 0.2 µm to 3.0 µm, in particular 0.2 µm to 2.0 µm, and even more precisely 0.3 µm to 1.5 µm. If the lithium iron phosphate particles are present in the form of secondary particles in which two or more primary particles are aggregated, the primary particles can have an average particle diameter (D 50 ) from 0.2 µm to 3.0 µm, in particular from 0.2 µm to 2.0 µm and even more precisely from 0.3 µm to 1.5 µm, and the secondary particles can have an average particle diameter (D 50 ) from 7 µm to 25 µm, especially from 10 µm to 20 µm.

[0033] The positive electrode active material can further comprise a carbon coating layer arranged on the surface of the lithium iron phosphate particles. The carbon coating layer can be incorporated to protect the lithium iron phosphate particles, improve electrical conductivity, and for similar purposes.

[0034] The positive electrode active material can be free of a lithium-nickel-based oxide, for example, lithium-nickel-cobalt-manganese oxide or lithium-nickel-cobalt-aluminum oxide. In the case of a positive electrode containing the lithium-nickel-based oxide, it can be difficult to achieve the desired effect, even with a loading amount (450 mg / 25 cm²). 2 or more) and a non-aqueous electrolyte as described below is used.

[0035] The loading amount of the positive electrode can be 450 mg / 25 cm². 2 up to 740 mg / 25 cm 2 be.

[0036] Compared to other positive electrode active materials such as lithium cobalt oxide and lithium nickel cobalt manganese oxide, lithium iron phosphate particles have the advantage of excellent thermal stability and relatively low cost. However, the problem is that the loading amount needs to be increased to achieve a high energy density due to their low specific capacity. Increasing the loading amount of the positive electrode (e.g., to 450 mg / 25 cm²) 2 up to 740 mg / 25 cm 2), it is possible to realize a battery with high energy density (e.g., a lithium secondary battery with a cell nominal capacity of at least 500 mAh, more precisely at least 550 mAh, and an initial discharge capacity of at least 500 mAh, more precisely at least 540 mAh), but it is difficult to sufficiently impregnate the positive electrode with a non-aqueous electrolyte, so the problem is that it is difficult to access the capacity of the lithium secondary battery, the resistance is increased, and the lifetime performance is impaired.

[0037] To solve this problem, the disclosed lithium secondary battery uses a non-aqueous electrolyte containing dimethyl carbonate as an organic solvent component and vinylene carbonate as an additive, with their content and ratio adjusted to within a specific range. This feature makes it possible to control the electrolyte impregnation properties of a positive electrode with a loading of 450 mg / 25 cm². 2 up to 740 mg / 25 cm 2 to improve and simultaneously improve the reduction stability of the negative electrode, so that the capacity of a lithium secondary battery can be accessed at an excellent level and the lifetime performance and resistance characteristics can be improved.

[0038] If the loading amount of the positive electrode is less than 450 mg / 25 cm² 2Since the above-described problem of deterioration of the electrolyte impregnation properties does not occur, the effect of using the non-aqueous electrolyte as disclosed does not come into play.

[0039] However, if the loading amount of the positive electrode is greater than 740 mg / 25 cm² 2 If the electrolyte impregnation properties are not sufficiently guaranteed, even when the disclosed non-aqueous electrolyte containing lithium iron phosphate particles is used at the positive electrode, there is a possibility that the electrolyte impregnation properties will not be adequately ensured. This is especially true if the loading amount of the positive electrode is greater than 740 mg / 25 cm². 2 is, for example, when lithium iron phosphate particles have a small average particle diameter (D 50) used in a positive electrode, the size of the pores formed between the lithium iron phosphate particles is small, and in this case, during a drying process in the manufacture of the positive electrode, a slurry solvent evaporates from the pores formed between the lithium iron phosphate particles, which can lead to cracks in the positive electrode, making it difficult to manufacture or implement the positive electrode.

[0040] Specifically, the loading amount of the positive electrode can be 450 mg / 25 cm². 2 up to 740 mg / 25 cm 2 , 450 mg / 25 cm 2 up to 730 mg / 25 cm 2 , 450 mg / 25 cm 2 up to 720 mg / 25 cm 2 , 450 mg / 25 cm 2 up to 710 mg / 25 cm 2 or 450 mg / 25 cm 2 up to 700 mg / 25 cm 2 amount to, specifically 500 mg / 25 cm² 2 up to 680 mg / 25 cm 2 , 500 mg / 25 cm 2 up to 650 mg / 25 cm 2, 500 mg / 25 cm 2 up to 625 mg / 25 cm 2 or 500 mg / 25 cm 2 up to 600 mg / 25 cm 2 .

[0041] The positive electrode can comprise a positive electrode current collector and a positive electrode active material layer arranged on at least one surface of the positive electrode current collector. At this stage, the positive electrode active material layer can comprise the positive electrode active material described above.

[0042] The positive electrode current collector is not particularly restricted as long as it is conductive without causing a chemical change in the battery. In particular, copper, stainless steel, aluminum, nickel, titanium, burnt carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy or the like may be used as a positive electrode current collector.

[0043] The positive electrode current collector can typically have a thickness of 3 µm to 500 µm.

[0044] The positive electrode current collector may have microscopic irregularities on its surface to improve the adhesion of the positive electrode active material. The positive electrode current collector can be used in various forms, such as a film, a sheet, a mesh, a porous body, a foam, and a non-woven fabric.

[0045] The positive electrode active material layer is arranged on at least one surface of the positive electrode current collector. In particular, the positive electrode active material layer can be arranged on one surface or on both surfaces of the positive electrode current collector.

[0046] Taking into account the need to maintain sufficient capacity of the positive electrode active material, the positive electrode active material can be contained in the positive electrode active material layer in an amount of 80 wt.% to 99 wt.%.

[0047] The positive electrode active material layer may also contain a binder and / or a conductive material together with the positive electrode active material described above.

[0048] The binder is a component to support the bonding of an active material, a conductive material and the like, as well as the bonding to a current collector, and may specifically comprise at least one of polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, an ethylene propylene diene monomer (EPDM), a sulfonated EPDM, styrene-butadiene rubber or fluororubber, preferably polyvinylidene fluoride.

[0049] The binder can be contained in the positive electrode active material layer in an amount of 1 wt.% to 20 wt.%, preferably 1.2 wt.% to 10 wt.%, to ensure sufficient bonding strength between components such as the positive electrode active material.

[0050] The conductive material can be used to support and enhance conductivity in the secondary battery and is not particularly limited as long as it exhibits conductivity without causing a chemical change. Specifically, the conductive material of the positive electrode can include graphite, such as natural graphite and synthetic graphite; a carbon-based material, such as carbon black, acetylene carbon black, KETJENBLACK®, sewer carbon black, furnace carbon black, lamp carbon black, and thermal carbon black; conductive fibers, such as carbon fibers and metal fibers; conductive tubes, such as carbon nanotubes; fluorocarbon; metal powders, such as aluminum powder and nickel powder; conductive whiskers, such as zinc oxide and potassium titanate; a conductive metal oxide, such as titanium oxide; and a polyphenylene derivative, and it may preferably include carbon black to enhance conductivity.

[0051] To ensure sufficient electrical conductivity, the conductive material can be contained in the positive electrode active material layer in an amount of 1 wt.% to 20 wt.%, preferably 1.2 wt.% to 10 wt.%.

[0052] The thickness of the positive electrode active material layer can be 100 µm to 300 µm, preferably 150 µm to 250 µm.

[0053] The positive electrode can be produced by applying a positive electrode slurry, containing a positive electrode active material and selectively a binder, a conductive material and a solvent to form a positive electrode slurry, to the positive electrode current collector, followed by drying and roller pressing.

[0054] The solvent used to form a positive electrode slurry can include an organic solvent such as N-methyl-2-pyrrolidone (NMP). The solids content of the positive electrode slurry can be between 40 wt% and 90 wt%, particularly between 50 wt% and 80 wt%. (2) Negative electrode

[0055] The negative electrode can be opposite the positive electrode.

[0056] The negative electrode comprises a negative electrode active material.

[0057] The negative electrode can comprise a negative electrode current collector and a negative electrode active material layer arranged on at least one surface of the negative electrode current collector. At this stage, the negative electrode active material can be contained within the negative electrode active material layer.

[0058] The negative electrode current collector is not particularly restricted as long as it is conductive without causing a chemical change in the battery. In particular, copper, stainless steel, aluminum, nickel, titanium, burnt carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy or the like can be used as a negative electrode current collector.

[0059] The negative electrode current collector can typically have a thickness of 3 µm to 500 µm.

[0060] The negative electrode current collector may have microscopic irregularities on its surface to improve the adhesion of the negative electrode active material. The negative electrode current collector can be used in various forms, such as film, sheet, foil, mesh, porous body, foam, and nonwoven fabric.

[0061] The negative electrode active material layer is arranged on at least one surface of the negative electrode current collector. Specifically, the negative electrode active material layer can be arranged on one surface or on both surfaces of the negative electrode current collector.

[0062] The negative electrode active material layer may contain a negative electrode active material.

[0063] The negative electrode active material is a material that can reversibly intercalate / de-intercalate lithium ions and may comprise at least one of a carbon-based active material, a (semi-)metal-based active material or a lithium metal, and may specifically comprise at least one of a carbon-based active material or a (semi-)metal-based active material.

[0064] The carbon-based active material can comprise at least one of graphite, hard carbon, soft carbon, carbon black, graphene, or fibrous carbon, and can preferably comprise graphite. The graphite can comprise at least one of natural or synthetic graphite.

[0065] The average particle diameter (D 50 The thickness of the carbon-based active material can be 10 µm to 30 µm, preferably 15 µm to 25 µm, to ensure structural stability during charging / discharging and to reduce side reactions with an electrolyte solution.

[0066] In particular, the (semi-)metal-based active material may comprise at least one (semi-)metal of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti or Sn, an alloy of lithium and at least one (semi-)metal of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti or Sn, an oxide of at least one (semi-)metal of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti or Sn, lithium titanium oxide (LTO), lithium vanadium oxide or the like.

[0067] More specifically, the (semi-)metal-based active material can include a silicon-based active material.

[0068] The silicon-based active material can include a compound consisting of SiO₂ x(0≤x<2) is represented. Since SiO2 does not react with lithium ions and therefore cannot store lithium, it is advantageous that x lies in the above-mentioned range, and the silicon-based active material SiO can be even more advantageous.

[0069] The average particle diameter (D 50 ) of the silicon-based active material can be 1 µm to 30 µm, preferably 2 µm to 15 µm, to ensure structural stability during charging / discharging and to reduce side reactions with an electrolyte solution.

[0070] The negative electrode active material can be contained in the negative electrode active material layer in an amount of 60 wt.% to 99 wt.%, preferably 75 wt.% to 95 wt.%.

[0071] The negative electrode active material layer may contain a binder and / or a conductive material in addition to the negative electrode active material.

[0072] In this case, the binder is used to improve battery performance by enhancing the adhesion between the negative electrode active material layer and the negative electrode current collector, and may, for example, contain at least one of the following materials: polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or a material in which hydrogen is substituted by Li, Na, Ca, or the like, and may also contain various copolymers thereof.

[0073] The binder can be present in the negative electrode active material layer in an amount of 0.5 wt.% to 10 wt.%, preferably 1 wt.% to 5 wt.%.

[0074] The conductive material is not particularly limited as long as it exhibits conductivity without causing a chemical change in the battery, and includes, for example, graphite, such as natural graphite and synthetic graphite; a carbon-based material such as carbon black, acetylene carbon black, KETJEN BLACK®, sewer carbon black, furnace carbon black, lamp carbon black and thermal carbon black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; fluorocarbon; metal powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives and the like.

[0075] The conductive material can be contained in the negative electrode active material layer in an amount of 0.5 wt.% to 10 wt.%, preferably 1 wt.% to 5 wt.%.

[0076] The thickness of the negative electrode active material layer can be 50 µm to 300 µm, preferably 100 µm to 200 µm.

[0077] The loading amount of the negative electrode active material layer can be 200 mg / 25 cm². 2 up to 500 mg / 25 cm 2 , preferably 250 mg / 25 cm² 2 up to 400 mg / 25 cm 2 , amount to.

[0078] The negative electrode can be produced by applying a negative electrode slurry comprising a negative electrode active material, a binder, a conductive material and / or a solvent for forming a negative electrode slurry to at least one surface of a negative electrode current collector, followed by drying and roller pressing.

[0079] The solvent for forming a negative electrode slurry can, for example, comprise at least one of distilled water, N-methyl-2-pyrrolidone (NMP), ethanol, methanol, or isopropyl alcohol, preferably distilled water, to facilitate the slurrying of the negative electrode active material, the binder, and / or the conductive material. The solids content of the negative electrode slurry can be 30 wt% to 80 wt%, specifically 40 wt% to 70 wt%. (3) Separator

[0080] The separator can be positioned between the positive electrode and the negative electrode.

[0081] A common porous polymer film typically used as a separator, such as a porous polymer film made of a polyolefin-based polymer like an ethylene homocopolymer, a propylene homocopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, can be used alone or as a laminate. Alternatively, a common porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fibers or polyethylene terephthalate fibers, can be used, although this disclosure is not limited to such uses. Furthermore, a coated separator with a ceramic component or a polymer material can be used to ensure heat resistance or mechanical strength and can optionally be used in a single-layer or multi-layer structure. (4) Non-aqueous electrolyte1) Lithium salt

[0082] First, the lithium salt is described as follows.

[0083] In the non-aqueous electrolyte solution for a lithium secondary battery according to an embodiment of the present invention, any lithium salt can be used as a lithium salt without any particular restriction, as long as it is typically used in an electrolyte solution for a lithium secondary battery, and for example the lithium salt Li + as a cation and at least one of 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 - , or (CF3CF2SO2)2N - as an anion. In particular, the lithium salt can contain at least one anion from the group consisting of LiCl, LiBr, LiI, LiBF4, LiClO4, LiAlO4, LiAlCl4, LiPF6, LiSbF6, LiAsF6, LiB 10 Cl 10 , 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 contain a single material of LiBF4, LiClO4, LiPF6, LiBOB (LiB(C2O4)2), LiCF3SO3, LiTFSI (LiN(SO2CF3)2), LiFSI (LiN(SO2F)2), or LiBETI (LiN(SO2CF2CF3)2), or a mixture of two or more of these, and it may in particular contain LiPF6.

[0084] The lithium salt content can be varied within a typical range for the use of lithium salts, but to achieve optimal effectiveness in forming a corrosion-resistant layer on the electrode surface, the lithium salt can be present in a concentration of 0.8 M to 3.0 M, specifically 1.0 M to 3.0 M. Here, the unit "M" represents a molar concentration and can specifically mean "mol / L".

[0085] If the concentration of the lithium salt falls into the aforementioned range, the viscosity of the non-aqueous electrolyte solution can be controlled to achieve optimal impregnation, and the mobility of the lithium ions can be improved to enhance the capacity and cycle characteristics of a lithium secondary battery. 2) Organic solvent

[0086] The organic solvent can comprise a cyclic carbonate-based solvent and a linear carbonate-based solvent. The organic solvent can consist of a cyclic carbonate-based solvent and a linear carbonate-based solvent.

[0087] The volume ratio of the cyclic carbonate-based solvent and the linear carbonate-based solvent can be 10:90 to 50:50, in particular 15:85 to 50:50 and even more specifically 20:80 to 35:65, and if it is in the above range, this is preferred with regard to achieving high ion transfer properties and low electrolyte viscosity.

[0088] The cyclic carbonate-based solvent contains ethylene carbonate. Ethylene carbonate is a highly viscous organic solvent with a high dielectric constant and can therefore readily dissociate a lithium salt in an electrolyte.

[0089] The cyclic carbonate-based solvent can be free of a fluorinated cyclic carbonate such as fluoroethylene carbonate (FEC). In particular, the cyclic carbonate-based solvent can consist only of ethylene carbonate and can be free of any other cyclic carbonate-based solvent, such as propylene carbonate.

[0090] Furthermore, the linear carbonate-based solvent includes dimethyl carbonate. Dimethyl carbonate is an organic solvent with low viscosity and low dielectric constant, and is characterized in particular by very good electrolyte impregnation properties, enabling it to impregnate the disclosed highly charged positive electrode, which contains lithium iron phosphate particles, to an excellent degree. However, as an organic solvent, dimethyl carbonate has the problem of forming an unstable negative electrode film, which leads to a deterioration of the negative electrode's reduction stability. As described below, however, the electrolyte impregnation properties and the reduction stability of the negative electrode can be improved simultaneously by using dimethyl carbonate and vinylene carbonate in a specific ratio.Furthermore, the non-aqueous electrolyte as disclosed can be used, in particular, if the loading amount of a positive electrode containing lithium iron phosphate particles is 450 mg / 25 cm. 2 up to 740 mg / 25 cm 2 to achieve the desired effect, and if the loading amount of a positive electrode is less than 450 mg / 25 cm 2 or more than 740 mg / 25 cm 2 Given the amount, it is not possible to achieve the effect of improving the electrolyte impregnation properties by using dimethyl carbonate.

[0091] The dimethyl carbonate is present in the organic solvent at a concentration of 5 to 75 vol%. In one embodiment, the dimethyl carbonate can be present in the organic solvent at a concentration of 5 to 55 vol%, specifically at 7 to 45 vol%, and even more specifically at 35 to 45 vol%. If the dimethyl carbonate concentration is less than 5 vol% in the organic solvent, it is not possible to improve the impregnation properties of the positive electrode with respect to the electrolyte. If the dimethyl carbonate concentration is greater than 75 vol% in the organic solvent, this is not advantageous because an unstable SEI film forms and cell performance is impaired.

[0092] The linear carbonate-based solvent can also contain ethyl methyl carbonate in addition to dimethyl carbonate. The presence of ethyl methyl carbonate in the linear carbonate is advantageous because it further improves the stability of the SEI film.

[0093] If the linear carbonate-based solvent also contains ethyl methyl carbonate, the organic solvent may contain 10 vol.% to 50 vol.% ethylene carbonate, 5 vol.% to 55 vol.% dimethyl carbonate and 20 vol.% to 70 vol.% ethyl methyl carbonate; more specifically, 20 vol.% to 40 vol.% ethylene carbonate, 7 vol.% to 45 vol.% dimethyl carbonate and 25 vol.% to 65 vol.% ethyl methyl carbonate; even more specifically, 25 vol.% to 35 vol.% ethylene carbonate, 30 vol.% to 45 vol.% dimethyl carbonate and 25 vol.% to 50 vol.% ethyl methyl carbonate; or 30 vol.% to 35 vol.% ethylene carbonate, 35 vol.% to 45 vol.% dimethyl carbonate and 25 vol.% to 50 vol.% ethyl methyl carbonate. If they are located in the above range, this is preferable with regard to improving the electrolyte impregnation properties and improving the stability of a negative electrode SEI film.

[0094] If necessary, the organic solvent may additionally include, without restriction, any organic solvent commonly used in a non-aqueous electrolyte. For example, at least one organic solvent from the group of ester-based solvents, ether-based solvents, glycerin-based solvents, or nitrile-based solvents may be additionally included.

[0095] The ester-based solvent may contain at least one of the following compounds: methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate and butyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone or ε-caprolactone.

[0096] Any ether-based solvent 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 thereof, may be used, however the present invention is not limited thereto.

[0097] The glyme-based solvent is a solvent with a higher dielectric constant and a lower surface tension than linear carbonate-based solvents, and exhibits lower reactivity with metals, and it may include at least one of dimethoxyethane (glyme, DME), diethoxyethane, diglyme, triglyme or tetraglyme (TEGDME), but is not limited to these.

[0098] The nitrile-based solvent may be one or more selected from the group consisting of acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile and 4-fluorophenylacetonitrile, but is not limited to these.

[0099] Unless otherwise specified, the remainder of the non-aqueous electrolyte, with the exception of the lithium salt and the additive, may consist entirely of the organic solvent. (3) Additive

[0100] The non-aqueous additive revealed comprises an additive.

[0101] The additive includes vinylene carbonate.

[0102] Vinylene carbonate can be used as an additive to the disclosed non-aqueous electrolyte to form a stable SEI film on the negative electrode. In particular, when dimethyl carbonate is used as the organic solvent, the stability of the negative electrode SEI film deteriorates under high temperatures, but by using vinylene carbonate as an additive, it is possible to improve the reduction stability of the negative electrode.

[0103] In the present disclosure, the ratio of the weight of vinylene carbonate to the weight of dimethyl carbonate is greater than 0 to 0.2 or less. If the ratio of the weight of vinylene carbonate to the weight of dimethyl carbonate is greater than 0.2, the SEI film of the negative electrode is excessively formed, which can lead to problems such as increased resistance and reduced service life.

[0104] Specifically, the ratio of the weight of vinylene carbonate to the weight of dimethyl carbonate can be 0.01 to 0.18, more specifically 0.016 to 0.130, and even more specifically 0.02 to 0.08, and if it is in the above range, a preferred effect of simultaneously improving the electrolyte impregnation properties of a positive electrode and the reduction stability of a negative electrode can be achieved.

[0105] The ratio of the weight of vinylene carbonate to the weight of dimethyl carbonate can be calculated from the weight or volume of the entire non-aqueous electrolyte, the volume fraction, the weight fraction, the density data, and the like of dimethyl carbonate.

[0106] The vinylene carbonate can be present in the non-aqueous electrolyte in amounts ranging from 0.01 wt% to 7 wt%, specifically 0.3 wt% to 6 wt%, even more specifically 0.4 wt% to 3 wt%, and even more specifically 0.6 wt% to 2 wt%, and being within the above-mentioned range is advantageous in that the SEI film of the negative electrode is properly formed to prevent electrolyte side reactions, and an increase in resistance due to the excessive use of additives is prevented.

[0107] At the same time, the additive may, if necessary, contain an additional additive besides vinylene carbonate to prevent the non-aqueous electrolyte solution from decomposing in a high-power environment and causing a breakdown of the negative electrode, or to further improve the properties during high-rate discharge at low temperatures, stability at high temperatures, protection against overcharging, the effect of suppressing battery expansion at high temperatures, and the like.

[0108] Examples of the additional additive may include at least one of the following: a compound based on a cyclic carbonate, a compound based on a halogen-substituted carbonate, a compound based on a sultane, a compound based on a sulfonate, a compound based on a sulfate, a compound based on a phosphate or phosphite, a compound based on a borate, a compound based on a nitrile, a compound based on a benzene, a compound based on an amine, a compound based on a silane, or a compound based on a lithium salt.

[0109] The compound based on a cyclic carbonate can be, for example, vinylethylene carbonate or the like.

[0110] The compound based on a halogen-substituted carbonate can be, for example, fluoroethylene carbonate (FEC) and the like.

[0111] The compound based on a sultone can, for example, be at least one compound selected from the group consisting of 1,3-propanesultone (PS), 1,4-butanesultone, ethenesulfone, 1,3-propenesultone (PRS), 1,4-butenesultone and 1-methyl-1,3-propenesultone.

[0112] The compound based on a sulfonate can contain a saturated hydrocarbon group or an unsaturated hydrocarbon group such as an alkenylene or an alkynylene group.

[0113] The compound based on a sulfate can be, for example, ethylene sulfate (ESA), trimethylene sulfate (TMS), methyl trimethylene sulfate (MTMS) or the like.

[0114] The phosphate- or phosphite-based compound may, for example, be one or more compounds selected from the group consisting of lithium difluoro(bisoxalato)phosphate, lithium difluorophosphate, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite, tris(2,2,2-trifluoroethyl)phosphate and tris(trifluoroethyl)phosphite.

[0115] The borate-based compound can be tetraphenyl borate, lithium difluoro(oxalato)borate (LiODFB), lithium bisoxalate borate (LiB(C2O4)2, LiBOB) or the like.

[0116] The nitrile-based compound may, for example, be at least one compound selected from the group consisting of succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile and 4-fluorophenylacetonitrile.

[0117] The benzene-based compound can be, for example, fluorobenzene or the like, the amine-based compound can be triethanolamine, ethylenediamine or the like, and the silane-based compound can be tetravinylsilane or the like.

[0118] The lithium salt-based compound is a compound that differs from the lithium salt contained in the non-aqueous electrolyte solution and may be lithium difluorophosphate (LiPO2F2), LiBF4, or the like.

[0119] The additional additive can be used in combination with two or more compounds, and the total content of vinylene carbonate and the additional additive can range from 0.05 wt% to 20 wt%, specifically 0.05 wt% to 10 wt%, based on the total weight of the non-aqueous electrolyte. If the total additive content falls within the aforementioned range, it is possible to effectively further improve the high-temperature storage and high-temperature lifetime properties and prevent side reactions in the battery caused by additives remaining after a reaction.

[0120] The non-aqueous electrolyte can be prepared by producing an organic solvent by mixing ethylene carbonate (EC), dimethyl carbonate (DMC), and optionally ethyl methyl carbonate (EMC) in an amount as described above, wherein, in particular, the dimethyl carbonate (DMC) is present in the organic solvent in an amount of 5 vol% to 75 vol%, more precisely 5 vol% to 55 vol%, 7 vol% to 45 vol%, or 35 vol% to 45 vol%. Subsequently, a lithium salt, as described above, is dissolved in the organic solvent to achieve a concentration of 0.8 M to 3.0 M, in particular 1.0 M to 3.0 M. Next, vinylene carbonate (VC) is added to the organic solvent in which the lithium salt has been dissolved, with the vinylene carbonate (VC) being present in an amount of 0.01 wt% to 7 wt%, more specifically 0.3 wt% to 6 wt%, even more specifically 0.4 wt% to 3 wt% and even more specifically 0.6 wt% to 2 wt%.-% is contained, based on the weight of the non-aqueous electrolyte, and wherein the weight ratio of vinylene carbonate to dimethyl carbonate is greater than 0 to 0.2 or less, specifically 0.01 to 0.18, 0.016 to 0.130 and even more specifically 0.02 to 0.08. The non-aqueous electrolyte may contain additional solvents and / or additives, as described above.

[0121] The disclosed lithium secondary battery described above can be usefully used in portable devices such as mobile phones, laptops and digital cameras, in electric cars such as hybrid electric vehicles (HEVs) and the like.

[0122] Accordingly, according to a further embodiment of the present invention, a battery module containing the lithium secondary battery as a unit cell and a battery pack containing the battery module are provided.

[0123] The battery module or battery pack can be used as a power source for one or more medium and large devices such as power tools, electric cars including electric vehicles (EVs), hybrid electric vehicles (HEVs) and plug-in hybrid electric vehicles (PHEVs), or energy storage systems.

[0124] The external shape of the disclosed lithium secondary battery is not particularly restricted, but may be cylindrical using a can, square, pouch, coin, or the like.

[0125] The disclosed lithium secondary battery can be used in a battery cell that serves as a power source for a small device, and can preferably also be used as a unit cell for a medium and large battery module comprising several battery cells.

[0126] The present invention will now be described in detail using examples.

[0127] The examples according to the invention can be modified to various other forms at this time, and the scope of the present invention should not be interpreted as being limited to the examples described below. The examples according to the invention serve to describe the present invention in more detail to those skilled in the art.

[0128] The present invention will now be described in detail with reference to specific examples. Examples Example 1 (Production of a non-aqueous electrolyte)

[0129] An organic solvent was prepared by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) in a volume ratio of 30:30:40.

[0130] LiPF6, a lithium salt, was dissolved in the organic solvent at a molar concentration of 1.0 M.

[0131] Additionally, a non-aqueous electrolyte was prepared by adding vinylene carbonate (VC) to the organic solvent in which the lithium salt had been dissolved. The vinylene carbonate was present in the non-aqueous electrolyte at a concentration of 1 wt%. (Manufacturing a secondary battery)

[0132] Lithium iron phosphate (LiFePO4) particles formed with a carbon coating layer as the positive electrode active material, carbon black as the conductive material, and polyvinylidene fluoride (PVdF) as a binder were added to N-methyl-2-pyrrolidone (NMP) as the solvent in a weight ratio of 94:3:3 to produce a positive electrode slurry. The positive electrode slurry was loaded with 600 mg / 25 cm². 2The material is applied to a positive electrode current collector (an aluminum thin film) with a thickness of 15 µm, dried, and then roll-pressed to produce a positive electrode (thickness of the positive electrode active material: 220 µm). The average particle diameter (D 50 The diameter of the positive electrode active material was 1.1 µm, and the lithium iron phosphate (LiFePO4) particles formed with the carbon coating layer were in the form of primary particles.

[0133] Artificial graphite (as the negative electrode active material), SBR-CMC (as a binder), and carbon black (as a conductive material) were added to water (as a solvent) in a weight ratio of 97:2:1 to produce a negative electrode slurry. The negative electrode slurry was loaded with 300 mg / 25 cm². 2applied to a copper (Cu) thin film, which is a negative electrode current collector with a thickness of 15 µm, and dried, and then roll-pressed to produce a negative electrode (thickness of the negative electrode active material: 170 µm).

[0134] The positive electrode, a porous polyolefin-based separator, and the negative electrode were stacked sequentially to create an electrode array.

[0135] The assembled electrode array was placed into a battery casing, and then the prepared non-aqueous electrolyte solution was injected to produce a lithium secondary battery. Example 2

[0136] A lithium secondary battery was prepared in the same manner as in Example 1, except that a non-aqueous electrolyte was prepared using a mixture in which ethylene carbonate (EC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) were mixed in a volume ratio of 30:60:10 as an organic solvent. Example 3

[0137] A lithium secondary battery was produced in the same manner as in Example 1, except that a non-aqueous electrolyte was produced using a mixture in which ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed in a volume ratio of 30:70 as the organic solvent. Example 4

[0138] A lithium secondary battery was manufactured in the same manner as in Example 1, except that a non-aqueous electrolyte was produced by adding 0.5 wt%, instead of 1 wt%, vinylene carbonate as an additive to the non-aqueous electrolyte. Example 5

[0139] A lithium secondary battery was manufactured in the same manner as in Example 1, except that a non-aqueous electrolyte was produced by adding 5 wt% instead of 1 wt% vinylene carbonate as an additive to the non-aqueous electrolyte. Example 6

[0140] A lithium secondary battery was produced in the same way as in Example 1, except that a positive electrode was produced by increasing the loading amount of the positive electrode slurry to 600 mg / 25 cm². 2 to 500 mg / 25 cm 2 was changed. Example 7

[0141] A lithium secondary battery was produced in the same way as in Example 1, except that a positive electrode was produced by increasing the loading amount of the positive electrode slurry to 600 mg / 25 cm². 2 to 700 mg / 25 cm 2 was changed. Example 8

[0142] A lithium secondary battery was produced in the same way as in Example 1, except that a positive electrode was produced by increasing the loading amount of the positive electrode slurry to 600 mg / 25 cm². 2 to 450 mg / 25 cm 2 was changed. Comparative example 1

[0143] A lithium secondary battery was produced in the same manner as in Example 1, except that a non-aqueous electrolyte was produced using a mixture in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 30:70 as the organic solvent. Comparative example 2

[0144] A lithium secondary battery was produced in the same way as in Example 1, except that a non-aqueous electrolyte was produced to which no vinylene carbonate was added as an additive. Comparative example 3

[0145] A lithium secondary battery was manufactured in the same manner as in Example 1, except that a non-aqueous electrolyte was produced by adding 8 wt% instead of 1 wt% vinylene carbonate as an additive to the non-aqueous electrolyte. Comparative example 4

[0146] A lithium secondary battery was produced in the same way as in Example 6, except that a non-aqueous electrolyte was produced by using a mixture in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 30:70 as an organic solvent. Comparative example 5

[0147] A lithium secondary battery was prepared in the same manner as in Example 1, except that a non-aqueous electrolyte was prepared using a mixture in which ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) were mixed in a volume ratio of 30:30:40 as an organic solvent, and that a positive electrode was prepared by applying a positive electrode slurry loading of 600 mg / 25 cm³. 2 to 500 mg / 25 cm 2 was changed. Comparative example 6

[0148] A lithium secondary battery was produced in the same way as in Example 1, except that a positive electrode was produced by increasing the loading amount of the positive electrode slurry to 600 mg / 25 cm². 2 to 750 mg / 25 cm 2 was changed. Comparative example 7

[0149] A lithium secondary battery was prepared in the same manner as in Example 1, except that a non-aqueous electrolyte was prepared using a mixture in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 30:70 as the organic solvent, and that a positive electrode was prepared by applying a positive electrode slurry loading of 600 mg / 25 cm³. 2 to 400 mg / 25 cm 2 was changed. Comparative example 8

[0150] A lithium secondary battery was manufactured in the same way as in Example 1, except that a positive electrode was manufactured by increasing the loading amount of the positive electrode slurry from 600 mg / 25 cm². 2 to 400 mg / 25 cm 2 was changed. Comparative example 9

[0151] A lithium secondary battery was prepared in the same manner as in Example 1, except that a non-aqueous electrolyte was prepared using a mixture in which ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) were mixed in a volume ratio of 30:30:40 as an organic solvent, and that a positive electrode was prepared by applying a positive electrode slurry loading of 600 mg / 25 cm³. 2 to 400 mg / 25 cm 2 was changed. [Table 1] Loading amount of the positive electrode (mg / 25cm²) 2 ) Non-aqueous electrolyte Organic solvent lithium salt Additive Weight ratio VC / DMC EC (volume percent) EMC (volume percent) DMC (volume percent) DEC (volume percent) LiPF6(mol / L) VC (wt%) Example 1 600 30 30 40 - 1 1 10,030 Example 2 600 30 60 10 - 1 1 0,120 Example 3 600 30 - 70 - 1 1 0,018 Example 4 600 30 30 40 - 1 0,5 0,015 Example 5 600 30 30 40 - 1 5 0,159 Example 6 500 30 30 40 - 1 1 0,030 Example 7 700 30 30 40 - 1 1 0,030 Example 8 450 30 30 40 - 1 1 0,030 See example 1 600 30 70 - - 1 1 - See example 2 600 30 30 40 - 1 - 0 See example 3 600 30 30 40 - 1 8 0,263 See example 4 500 30 70 - - 1 1 - See example 5 500 30 30 - 40 1 1 0,030 See example 6 750 30 30 40 - 1 1 0,030 See example 7 400 30 70 - - 1 1 - See example 8 400 30 30 40 - 1 1 0,030 See example 9 400 30 30 - 40 1 1 0,030 Experimental Examples: Experimental Example 1: Measuring the Initial Capacity Yield

[0152] The initial charge / discharge was performed by charging the lithium secondary batteries of Examples 1 to 8 and Comparison Examples 1 to 9 produced above to 3.65 V and discharging them to 2.5 V at 0.33 C under CC / CV conditions at 25 °C in order to measure their initial discharge capacity (unit: mAh).

[0153] The initial discharge capacity was divided by the cell's nominal capacity (based on 0.33 C) and then multiplied by 100 to assess the capacity yield (%). The results are shown in Table 2 below. Experimental example 2: Evaluation of the cycle charge / discharge capacity maintenance rate

[0154] Charging the lithium secondary batteries produced above, examples 1 to 8 and comparison examples 1 to 9, to 3.65 V under CC / CV conditions and 0.33 C at 25 °C, and discharging them to 2.5 V at 0.33 C, was defined as one cycle, and the discharge capacity and resistance were measured after one cycle. At this point, the resistance was measured based on a voltage drop difference determined by checking the capacity at room temperature, charging the batteries to a state of charge (SOC) of 50% based on the discharge capacity, and then discharging the batteries for 10 seconds at a current of 2.5 C.

[0155] Subsequently, 200 charge / discharge cycles were performed under the above-mentioned charge / discharge conditions, and the capacity retention rate (%) and the resistance increase rate (%) were measured. The capacity retention rate (%) was calculated according to the following [Equation 1], and the resistance increase rate (%) was calculated according to the following [Equation 2]. The measurement results are listed in Table 2 below. Capacity conservation rate (%) = (Discharge capacity after 200 cycles / Discharge capacity after 1 cycle) × 100 Resistance increase rate (%) = {(Resistance after 200 cycles − Resistance after 1 cycle) / Resistance after 1 cycle} × 100 [Table 2] Experimental Example 1 Experimental Example 2 Nominal cell capacity (mAh) Initial discharge capacity (mAh) Capacity utilization (%) Capacity maintenance rate (%, 200 cycles) Resistance increase rate (%, 200 cycle) Example 1 730 724 99,2 92,6 8,5 Example 2 730 719 98,5 92,0 13,7 Example 3 730 726 99,5 92,3 9,8 Example 4 730 722 98,9 91,1 8,1 Example 5 730 718 98,4 93,8 12,7 Example 6 610 608 99,7 91,9 7,3 Example 7 855 850 99,4 92,3 8,0 Example 8 550 546 99,3 92,2 7,1 See example 1 730 973 92,2 81,2 34,4 See example 2 730 724 99,2 84,0 22,8 See example 3 730 701 96,0 89,1 23,5 See example 4 610 588 96,4 85,6 23,7 See example 5 610 558 91,5 86,1 20,1 See example 6 916 831 90,7 81,4 35,2 See example 7 490 486 99,2 93,2 10,4 See example 8 490 487 99,4 93,4 10,0 See example 9 490 486 99,2 93,6 10,0

[0156] Table 2 above shows that the lithium secondary batteries of the disclosed examples 1 to 8 have excellent capacity yield, excellent lifetime and a low resistance increase rate compared to those of the comparison examples 1 to 6.

[0157] Furthermore, Example 6, in which the positive electrode loading amount is set to 500 mg / 25 cm², shows 2 The design, compared to comparison example 4, which did not use dimethyl carbonate, exhibited excellent capacity yield, excellent lifetime and a low resistance increase rate.

[0158] In comparative examples 7 to 9, where the loading amount of the positive electrode is 400 mg / 25 cm² 2The design used a low loading rate, and electrolyte impregnation was not a major issue, indicating that it was not significantly affected by the components and concentration of the non-aqueous electrolyte. In particular, a comparison of examples 7 and 8 shows that even when using dimethyl carbonate as the organic solvent component, the improvement in capacity yield, lifetime, and resistance increase rate is negligible. Furthermore, example 9, which used a different linear carbonate than dimethyl carbonate, exhibited the same or similar performance as examples 7 and 8. This suggests that the disclosed non-aqueous electrolyte, at a specific loading rate (e.g., more than 400 mg / 25 cm³), 2 and less than 750 mg / 25 cm 2 , , specific 450 mg / 25 cm 2up to 740 mg / 25 cm 2 ) a lithium iron phosphate-containing positive electrode has a particularly good effect.

[0159] This utility model is derived from European patent application No. 23 886 395.5. The entire subject matter of that application is incorporated herein by reference. The subject matter of the original claims of European patent application No. 23 886 395.5 is further defined below by the preferred embodiments. <1> until <17> revealed: <1> Lithium secondary battery, comprehensive a positive electrode, a negative electrode, a separator and a non-aqueous electrolyte, wherein: the positive electrode comprises a positive electrode active material, wherein the positive electrode active material comprises lithium iron phosphate particles and the positive electrode has a loading amount of 450 mg / 25 cm² 2 up to 740 mg / 25 cm 2 exhibits; and the non-aqueous electrolyte comprises a lithium salt, an organic solvent and an additive, wherein the organic solvent comprises a solvent based on a cyclic carbonate and a solvent based on a linear carbonate, wherein the solvent based on a cyclic carbonate comprises ethylene carbonate and the solvent based on a linear carbonate comprises dimethyl carbonate, the additive vinylencarbonate includes and the dimethyl carbonate is present in an amount of 5 vol% to 75 vol% in the organic solvent and the weight ratio of vinylene carbonate to dimethyl carbonate is greater than 0 to 0.2 or less. <2> Lithium secondary battery according to <1> , wherein the positive electrode has a loading quantity of 450 mg / 25 cm 2 up to 700 mg / 25 cm 2 exhibits. <3> Lithium secondary battery according to <1> , wherein the positive electrode has a loading quantity of 500 mg / 25 cm 2 up to 600 mg / 25 cm 2 exhibits. <4> Lithium secondary battery according to <1> , wherein the vinylene carbonate is contained in an amount of 0.01 wt.% to 7 wt.% in the non-aqueous electrolyte. <5> Lithium secondary battery according to <1> , wherein the volume ratio of the solvent based on a cyclic carbonate to the solvent based on a linear carbonate is 10:90 to 50:50. 6. Lithium secondary battery according to claim 1, wherein the linear carbonate-based solvent further comprises ethyl methyl carbonate. <7> Lithium secondary battery according to <6> , wherein the organic solvent comprises 10 vol.% to 50 vol.% ethylene carbonate, 5 vol.% to 55 vol.% dimethyl carbonate and 20 vol.% to 70 vol.% ethyl methyl carbonate. <8> Lithium secondary battery according to <1> , wherein the lithium salt comprises at least one of LiCl, LiBr, LiI, LiBF4, LiClO4, LiAlO4, LiAlCl4, LiPF6, LiSbF6, LiAsF6, LiB 10 Cl 10 , LiBOB (LiB(C2O4)2), LiCF3SO3, LiTFSI (LiN(SO2CF3)2), LiFSI (LiN(SO2F)2), LiCH3SO3, LiCF3CO2, LiCH3CO2, or LiBETI (LiN(SO2CF2CF3)2). <9> Lithium secondary battery according to <1> , wherein the lithium salt is contained in the non-aqueous electrolyte at a concentration of 0.8 M to 3.0 M. <10> Lithium secondary battery according to <1> , wherein the lithium iron phosphate particles comprise a compound of formula A: Li 1+a Fe 1-s M s (PO 4-b )X b [Formula A] wherein in formula AM is one or more elements selected from the group consisting of Co, Ni, Mn, Al, Mg, Ti and V, and XF, S or N, where: 0≤s≤0.5; -0.5≤a≤+0.5; and 0≤b≤0.1. <11> Lithium secondary battery according to <1> , comprising the lithium iron phosphate particles LiFePO4. <12> Lithium secondary battery according to <1> , in which: the lithium iron phosphate particles are present in the form of primary particles; and The lithium iron phosphate particles have an average particle size D 50 exhibiting dimensions from 0.2 µm to 3.0 µm. <13> Lithium secondary battery according to <1> , wherein the lithium iron phosphate particles have a carbon coating layer on a surface. <14> Lithium secondary battery according to <1> , wherein the positive electrode active material does not include a lithium-nickel-based oxide. <15> Lithium secondary battery according to <1> , wherein the negative electrode comprises a carbon-based active material. <16> Lithium secondary battery according to <15> , wherein the carbon-based active material comprises at least one of natural graphite or synthetic graphite. <17> Method for manufacturing a lithium secondary battery, the method comprising:

[0160] Manufacturing an electrode arrangement comprising a positive electrode, a negative electrode and a separator, wherein the positive electrode comprises a positive electrode active material comprising lithium iron phosphate particles, and wherein the positive electrode has a loading amount of 450 mg / 25 cm² 2 up to 740 mg / 25 cm 2 exhibits;

[0161] Housing the electrode assembly in a battery casing;

[0162] Producing a non-aqueous electrolyte comprising a lithium salt, an organic solvent, and an additive, wherein the organic solvent comprises a cyclic carbonate-based solvent and a linear carbonate-based solvent, the cyclic carbonate-based solvent comprising ethylene carbonate, and the linear carbonate-based solvent comprising dimethyl carbonate, wherein the additive comprises vinylene carbonate, and wherein the dimethyl carbonate is present in the organic solvent in an amount of 5% to 75% by volume, and the weight ratio of vinylene carbonate to dimethyl carbonate is greater than 0 to 0.2 or less; and

[0163] Injecting or impregnating the manufactured non-aqueous electrolyte into the battery casing. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] KR 10-2022-0146438

[0001] EP 23 886 395.5

[0159]

Claims

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 and the positive electrode having a loading of 450 mg / 25 cm² to 740 mg / 25 cm²; and the non-aqueous electrolyte comprises a lithium salt, an organic solvent and an additive, the organic solvent comprising a cyclic carbonate-based solvent and a linear carbonate-based solvent, the cyclic carbonate-based solvent comprising ethylene carbonate and the linear carbonate-based solvent comprising dimethyl carbonate, the additive comprising vinylene carbonate and the dimethyl carbonate in an amount of 5 vol.% to 75 vol.%.-% is contained in the organic solvent and the weight ratio of vinylene carbonate to dimethyl carbonate is greater than 0 to 0.2 or less. Lithium secondary battery according to claim 1, wherein the positive electrode has a loading quantity of 450 mg / 25 cm2 to 700 mg / 25 cm2. Lithium secondary battery according to claim 1, wherein the positive electrode has a loading quantity of 500 mg / 25 cm2 to 600 mg / 25 cm2. Lithium secondary battery according to claim 1, wherein the vinylene carbonate is contained in an amount of 0.01 wt.% to 7 wt.% in the non-aqueous electrolyte. Lithium secondary battery according to claim 1, wherein the volume ratio of the solvent based on a cyclic carbonate to the solvent based on a linear carbonate is 10:90 to 50:

50. Lithium secondary battery according to claim 1, wherein the linear carbonate-based solvent further comprises ethyl methyl carbonate. Lithium secondary battery according to claim 6, wherein the organic solvent comprises 10 vol.% to 50 vol.% ethylene carbonate, 5 vol.% to 55 vol.% dimethyl carbonate and 20 vol.% to 70 vol.% ethyl methyl carbonate. Lithium secondary battery according to claim 1, wherein the lithium salt comprises at least one of LiCl, LiBr, LiI, LiBF4, LiClO4, LiAlO4, LiAlCl4, LiPF6, LiSbF6, LiAsF6, LiB10Cl10, LiBOB (LiB(C2O4)2), LiCF3SO3, LiTFSI (LiN(SO2CF3)2), LiFSI (LiN(SO2F)2), LiCH3SO3, LiCF3CO2, LiCH3CO2, or LiBETI (LiN(SO2CF2CF3)2). Lithium secondary battery according to claim 1, wherein the lithium salt is contained in the non-aqueous electrolyte in a concentration of 0.8 M to 3.0 M. Lithium secondary battery according to claim 1, wherein the lithium iron phosphate particles comprise a compound of formula A: Li1+aFe1-sMs(PO4-b)Xb[formula A] wherein formula AM is one or more elements selected from the group consisting of Co, Ni, Mn, Al, Mg, Ti and V, and XF, S or N, wherein: 0≤s≤0.5; -0.5≤a≤+0.5; and 0≤b≤0.

1. Lithium secondary battery according to claim 1, wherein the lithium iron phosphate particles comprise LiFePO4. Lithium secondary battery according to claim 1, wherein: the lithium iron phosphate particles are in the form of primary particles; and the lithium iron phosphate particles have an average particle size D50 of 0.2 µm to 3.0 µm. Lithium secondary battery according to claim 1, wherein the lithium iron phosphate particles have a carbon coating layer on a surface. Lithium secondary battery according to claim 1, wherein the positive electrode active material does not comprise a lithium nickel-based oxide. Lithium secondary battery according to claim 1, wherein the negative electrode comprises a carbon-based active material.