Lithium secondary battery

Abstract

The present invention relates to a 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 loading of the positive electrode is 450 mg / 25 cm 2 ~740mg / 25cm 2 The non-aqueous electrolyte comprises a lithium salt, an organic solvent, and an additive, the organic solvent comprises a cyclic carbonate solvent and a linear carbonate solvent, the cyclic carbonate solvent comprises ethylene carbonate, the linear carbonate solvent comprises dimethyl carbonate, the dimethyl carbonate is contained in the organic solvent at 5% by volume to 75% by volume, and the additive comprises vinylene carbonate, and a ratio of the weight of the vinylene carbonate to the weight of the dimethyl carbonate is greater than 0 and equal to or less than 0.2.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0146438, filed November 4, 2022, and all contents disclosed in the documents of this Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a lithium secondary battery. [Background technology]

[0003] With the development of the information society, personal IT devices and computer networks have become more prevalent, and as a result, society as a whole has become more dependent on electrical energy, which has created a demand for the development of technologies to efficiently store and utilize electrical energy.

[0004] Of all the technologies developed, secondary batteries are the most suitable for a variety of applications. Among these secondary batteries, interest is growing in lithium secondary batteries, which not only can be miniaturized to a degree that makes them suitable for personal IT devices, but also have the highest energy density.

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

[0006] Possible negative electrode active materials for such lithium secondary batteries include carbon-based active materials and silicon-based active materials, while possible positive electrode active materials include lithium-containing cobalt oxide, LiMnO2 with a layered crystal structure, LiMn2O4 with a spinel crystal structure, and lithium-containing nickel oxide (LiNiO2).

[0007] Recently, lithium iron phosphate (for example, LiFePO4)-based active materials have been considered for use as positive electrode active materials because they have excellent thermal stability and are relatively inexpensive.

[0008] However, the lithium iron phosphate-based active material has a lower specific capacity than lithium cobalt oxide, lithium nickel oxide, etc., and therefore, in order to increase the energy density of a positive electrode and a lithium secondary battery containing the same, it is necessary to use a lithium iron phosphate-based active material at a high loading amount. However, a high-loading lithium iron phosphate positive electrode has problems such as difficulty in fully impregnating the non-aqueous electrolyte into the positive electrode, making it difficult to exhibit capacity, increasing resistance, and shortening lifespan. Summary of the Invention [Problem to be solved by the invention]

[0009] In order to solve the above problems, an object of the present invention is to provide a lithium secondary battery including a positive electrode containing lithium iron phosphate particles as a positive electrode active material and having a specific loading amount or more, which has excellent capacity development effect, excellent life performance, and resistance reduction effect by improving the impregnation ability of the positive electrode with a non-aqueous electrolyte and improving the reduction stability of the negative electrode. [Means for solving the problem]

[0010] One embodiment of the present invention includes 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 loading of the positive electrode is 450 mg / 25 cm. 2 ~740mg / 25cm 2 The non-aqueous electrolyte comprises a lithium salt, an organic solvent, and an additive, the organic solvent comprises a cyclic carbonate solvent and a linear carbonate solvent, the cyclic carbonate solvent comprises ethylene carbonate, the linear carbonate solvent comprises dimethyl carbonate, the dimethyl carbonate is contained in the organic solvent at 5% by volume to 75% by volume, and the additive comprises vinylene carbonate, and a weight ratio of the vinylene carbonate to the dimethyl carbonate is greater than 0 and equal to or less than 0.2. [Effects of the Invention]

[0011] The lithium secondary battery according to the present invention includes a positive electrode having a specific loading or more, the positive electrode including lithium iron phosphate particles as a positive electrode active material, and a non-aqueous electrolyte including ethylene carbonate and dimethyl carbonate as an organic solvent and vinylene carbonate as an additive, the contents and ratio of the dimethyl carbonate and vinylene carbonate being controlled within a specific range. The lithium secondary battery according to the present invention uses excellent dimethyl carbonate as an organic solvent component to improve electrolyte impregnation of a positive electrode having a high loading, and uses vinylene carbonate additive in a specific content ratio relative to dimethyl carbonate to improve anode reduction stability, thereby achieving excellent capacity, life performance, and resistance characteristics of the lithium secondary battery. DETAILED DESCRIPTION OF THE INVENTION

[0012] First, before describing the present invention, the terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as having meanings and concepts that are consistent with the technical idea of ​​the present invention, based on the principle that an inventor can appropriately define the concepts of terms in order to best describe his or her invention.

[0013] Meanwhile, the terms used in this specification are merely used to describe exemplary embodiments and are not intended to limit the present invention. The singular expressions include the plural expressions unless the context clearly indicates otherwise.

[0014] In this specification, the terms "comprises," "includes," "has," and the like are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, but are not intended to preclude the possible presence or addition of one or more different features, numbers, steps, components, or combinations thereof.

[0015] In this specification, "%" means % by weight unless expressly indicated otherwise.

[0016] Before describing the present invention, in the description of "number of carbon atoms a to b" in the specification, "a" and "b" mean the number of carbon atoms contained in a specific functional group. That is, the functional group can contain "a" to "b" carbon atoms.

[0017] Furthermore, in this specification, unless otherwise defined, the term "substituted" means that at least one hydrogen atom bonded to a carbon atom has been substituted with an element other than hydrogen, for example, with an alkyl group having 1 to 5 carbon atoms or a fluorine atom.

[0018] 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 ) can be measured using, for example, a laser diffraction method. The laser diffraction method generally enables measurement of particle sizes from the submicron range to several mm, and can provide results with high reproducibility and high resolution.

[0019] The present invention will now be described in further detail.

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

[0021] Specifically, the lithium secondary battery according to the present invention includes 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 loading of the positive electrode is 450 mg / 25 cm. 2 ~740mg / 25cm 2the non-aqueous electrolyte comprises a lithium salt, an organic solvent, and an additive; the organic solvent comprises a cyclic carbonate solvent and a linear carbonate solvent; the cyclic carbonate solvent comprises ethylene carbonate; the linear carbonate solvent comprises dimethyl carbonate; the dimethyl carbonate is contained in the organic solvent at 5% by volume to 75% by volume; the additive comprises vinylene carbonate; and the ratio of the weight of the vinylene carbonate to the weight of the dimethyl carbonate is greater than 0 and equal to or less than 0.2.

[0022] The lithium secondary battery according to the present invention includes a positive electrode having a specific loading or more, the positive electrode including lithium iron phosphate particles as a positive electrode active material, and a non-aqueous electrolyte including ethylene carbonate and dimethyl carbonate as an organic solvent and vinylene carbonate as an additive, the contents and ratio of the dimethyl carbonate and vinylene carbonate being controlled within a specific range. The lithium secondary battery according to the present invention uses excellent dimethyl carbonate as an organic solvent component to improve electrolyte impregnation of the positive electrode having a high loading, and uses vinylene carbonate additive in a specific content ratio relative to the dimethyl carbonate to improve anode reduction stability, thereby achieving excellent capacity, life performance, and resistance characteristics of the lithium secondary battery.

[0023] The lithium secondary battery according to the present invention may have a capacity retention rate of 90% or more, preferably 90% to 95%, and a resistance increase rate of 20% or less, preferably 15% or less, when the cell (or lithium secondary battery) has a design capacity of at least 500 mAh and an initial discharge capacity of at least 500 mAh, after 200 charge / discharge cycles. Here, the positive electrode contains lithium iron phosphate particles as an active material, and the loading amount is 450 mg / 25 cm. 2 ~740mg / 25cm 2the non-aqueous electrolyte comprises a lithium salt, an organic solvent, and an additive, the organic solvent comprises a cyclic carbonate solvent and a linear carbonate solvent, the cyclic carbonate solvent comprises ethylene carbonate, the linear carbonate solvent comprises dimethyl carbonate, the dimethyl carbonate is contained in the organic solvent at 5% by volume to 75% by volume, the additive comprises vinylene carbonate, and the ratio of the weight of the vinylene carbonate to the weight of the dimethyl carbonate is greater than 0 and 0.2 or less. The design capacity, initial discharge capacity, capacity retention, and resistance increase rate of the cell are measured by the methods described in the examples below.

[0024] 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.

[0025] The lithium secondary battery may be manufactured by a method including the steps of: preparing an electrode assembly including a positive electrode, a negative electrode, and a separator; housing the electrode assembly in a battery case; preparing a non-aqueous electrolyte including a lithium salt, an organic solvent, and an additive; and injecting or impregnating the non-aqueous electrolyte into the battery case.

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

[0027] The lithium iron phosphate particles may include 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, 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.

[0030] The chemical formula A can be specifically represented as LiFePO4 (a=0, s=0, and b=0).

[0031] The lithium iron phosphate particles may be in the form of primary particles or secondary particles formed by aggregation of two or more primary particles. Specifically, the lithium iron phosphate particles may be in the form of primary particles.

[0032] The lithium iron phosphate particles may be composed of primary particles, secondary particles formed by agglomeration of two or more primary particles, or a mixture of primary particles and secondary particles formed by agglomeration of two or more primary particles.

[0033] Here, when the lithium iron phosphate particles are in the form of primary particles, the average particle size (D 50 ) can be 0.2 μm to 3.0 μm, specifically 0.2 μm to 2.0 μm, and more specifically 0.3 μm to 1.5 μm. In addition, when the lithium iron phosphate particles are in the form of secondary particles formed by agglomeration of two or more primary particles, the primary particles have an average particle size (D 50 ) can be 0.2 μm to 3.0 μm, specifically 0.2 μm to 2.0 μm, and more specifically 0.3 μm to 1.5 μm, and the secondary particles have an average particle size (D 50 ) may be 7 μm to 25 μm, particularly 10 μm to 20 μm.

[0034] The positive electrode active material may further include a carbon coating layer disposed on the surface of the lithium iron phosphate particles for the purposes of protecting the lithium iron phosphate particles and improving electrical conductivity.

[0035] The positive electrode active material may not contain 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, the loading amount (450 mg / 25 cm) described below is 2 ~740mg / 25cm 2 ) and non-aqueous electrolytes may be applied, it may be difficult to achieve the desired effect.

[0036] The loading amount of the positive electrode is 450 mg / 25 cm 2 ~740mg / 25cm 2 is.

[0037] The lithium iron phosphate particles have advantages of excellent thermal stability and relatively low cost compared to other positive electrode active materials such as lithium cobalt oxide and lithium nickel-cobalt-manganese oxide. However, they have a problem of low specific capacity, which requires an increased loading amount to achieve high energy density. Increasing the loading amount of the positive electrode (for example, 450 mg / 25 cm) 2 ~740mg / 25cm 2 ) it is possible to realize a battery with a high energy density (for example, a lithium secondary battery with a cell design capacity of at least 500 mAh and an initial discharge capacity of at least 500 mAh), but the non-aqueous electrolyte cannot be sufficiently impregnated into the positive electrode, which makes it difficult for the lithium secondary battery to realize its capacity, increases resistance, and reduces life performance.

[0038] In order to solve these problems, the lithium secondary battery according to the present invention is characterized by using a non-aqueous electrolyte in which dimethyl carbonate is used as an organic solvent component and vinylene carbonate is used as an additive, and the contents and content ratios of these components are adjusted within specific ranges. 2 ~740mg / 25cm 2This improves the electrolyte impregnation of the positive electrode having a loading amount of 0.01g, and improves the reduction stability of the negative electrode, thereby enabling the capacity of the lithium secondary battery to be exhibited at an excellent level and improving the life performance and resistance characteristics.

[0039] The loading of the positive electrode is 450 mg / 25 cm 2 If the thickness is less than this, the above-mentioned problem of decreased electrolyte impregnation does not occur, and the effect of the present invention on the use of the non-aqueous electrolyte is not exhibited.

[0040] The loading amount of the positive electrode is 740 mg / 25 cm 2 If the loading amount of the positive electrode is more than 740 mg / 25 cm, even if the nonaqueous electrolyte according to the present invention is applied to a positive electrode containing lithium iron phosphate particles, the electrolyte impregnation may not be sufficiently ensured. 2 For example, when the average particle size (D 50 When lithium iron phosphate particles having the above structure are used for a positive electrode, the size of the voids formed between the lithium iron phosphate particles is small. In this case, during the drying process of manufacturing the positive electrode, the slurry solvent evaporates from the voids formed between the lithium iron phosphate particles, which may cause cracks in the positive electrode, making it difficult to manufacture or realize the positive electrode.

[0041] Specifically, the loading amount of the positive electrode is 450 mg / 25 cm 2 ~740mg / 25cm 2 , 450mg / 25cm 2 ~730mg / 25cm 2 , 450mg / 25cm 2 ~720mg / 25cm 2 , 450mg / 25cm 2 ~710mg / 25cm 2 , or 450 mg / 25 cm 2 ~700mg / 25cm 2 , more specifically, 500mg / 25cm 2 ~680mg / 25cm 2 , 500mg / 25cm 2 ~650mg / 25cm2 , 500mg / 25cm 2 ~625mg / 25cm 2 , or 500mg / 25cm 2 ~600mg / 25cm 2 It can be.

[0042] 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, wherein the positive electrode active material layer may include the positive electrode active material described above.

[0043] 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 may be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, or an aluminum-cadmium alloy.

[0044] The positive electrode current collector can usually have a thickness of 3 μm to 500 μm.

[0045] The positive electrode current collector may have a surface with fine irregularities to enhance the bonding strength of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, a sheet, a foil, a mesh, a porous material, a foam, or a nonwoven fabric.

[0046] The positive electrode active material layer may be disposed on at least one surface of the positive electrode current collector. Specifically, the positive electrode active material layer may be disposed on one or both surfaces of the positive electrode current collector.

[0047] The positive electrode active material may be contained in the positive electrode active material layer in an amount of 80 to 99% by weight, taking into consideration the sufficient capacity of the positive electrode active material.

[0048] The positive electrode active material layer may further include a binder and / or a conductive material in addition to the positive electrode active material.

[0049] The binder is a component that helps bind the active material and conductive material together and to the current collector, and specifically includes at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluororubber, preferably polyvinylidene fluoride.

[0050] The binder may be contained 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 strength between components such as the positive electrode active material.

[0051] The conductive material can be used to supplement and improve the conductivity of the secondary battery, and is not particularly limited as long as it does not cause chemical changes and has conductivity. Specifically, the positive electrode conductive material can include at least one selected from the group consisting of graphite such as natural graphite and artificial graphite; carbon black such as carbon black, acetylene black, KETJENBLACK (registered trademark), 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, the positive electrode conductive material can include carbon black in order to improve conductivity.

[0052] In order to ensure sufficient electrical conductivity, the conductive material may be contained in the positive electrode active material layer in an amount of 1 to 20% by weight, preferably 1.2 to 10% by weight.

[0053] The thickness of the positive electrode active material layer can be 100 μm to 300 μm, and preferably 150 μm to 250 μm.

[0054] The positive electrode may be manufactured by coating a positive electrode slurry containing a positive electrode active material and, optionally, a binder, a conductive material, and a solvent for forming the positive electrode slurry on the positive electrode current collector, followed by drying and rolling.

[0055] The solvent for forming the positive electrode slurry may include an organic solvent such as N-methyl-2-pyrrolidone (NMP). The solid content of the positive electrode slurry may be 40% by weight to 90% by weight, specifically 50% by weight to 80% by weight.

[0056] (2) Negative electrode The negative electrode can face the positive electrode.

[0057] The negative electrode includes a negative electrode active material.

[0058] 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, wherein the negative electrode active material may be included in the negative electrode active material layer.

[0059] 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 may be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, or an aluminum-cadmium alloy.

[0060] The negative electrode current collector can usually have a thickness of 3 μm to 500 μm.

[0061] The negative electrode current collector may have a surface with fine irregularities to enhance the bonding strength of the negative electrode active material. For example, the negative electrode current collector may be used in various forms such as a film, a sheet, a foil, a mesh, a porous material, a foam, or a nonwoven fabric.

[0062] The negative electrode active material layer may be disposed on at least one surface of the negative electrode current collector. Specifically, the negative electrode active material layer may be disposed on one or both surfaces of the negative electrode current collector.

[0063] The negative electrode active material layer may include a negative electrode active material.

[0064] The negative electrode active material may include at least one material selected from the group consisting of a carbon-based active material, a (semi)metal-based active material, and lithium metal, as a material capable of reversibly inserting / extracting lithium ions. Specifically, the negative electrode active material may include at least one material selected from the group consisting of a carbon-based active material and a (semi)metal-based active material.

[0065] The carbon-based active material may include at least one selected from the group consisting of graphite, hard carbon, soft carbon, carbon black, graphene, and fibrous carbon, and preferably includes graphite. The graphite may include at least one selected from the group consisting of artificial graphite and natural graphite.

[0066] The average particle size (D 50 ) can be 10 μm to 30 μm, preferably 15 μm to 25 μm, in order to ensure structural stability and reduce side reactions with the electrolyte during charge and discharge.

[0067] 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 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.

[0068] More specifically, the (semi)metallic active material can include a silicon-based active material.

[0069] The silicon-based active material is SiO x (0≦x<2) In the case of SiO2, since it does not react with lithium ions and therefore cannot store lithium, it is preferable that x is within the above range, and more preferably, the silicon-based active material can be SiO.

[0070] The average particle size (D 50 ) can be 1 μm to 30 μm, preferably 2 μm to 15 μm, in order to ensure structural stability and reduce side reactions with the electrolyte during charge and discharge.

[0071] The negative electrode active material may be contained in the negative electrode active material layer in an amount of 60% by weight to 99% by weight, preferably 75% by weight to 95% by weight.

[0072] The negative electrode active material layer may further include a binder and / or a conductive material in addition to the negative electrode active material.

[0073] The binder is used to improve the adhesive strength between the negative electrode active material layer and the negative electrode current collector, thereby improving battery performance. For example, the binder may include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethylmethacrylate, 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, and substances in which hydrogen is substituted with Li, Na, Ca, or the like, or may include various copolymers thereof.

[0074] The binder may be contained in the negative electrode active material layer in an amount of 0.5% by weight to 10% by weight, preferably 1% by weight to 5% by weight.

[0075] The conductive material is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. For example, graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, KETJENBLACK, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber and metal fiber; 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 may be used.

[0076] The conductive material may be contained in the negative electrode active material layer in an amount of 0.5% by weight to 10% by weight, preferably 1% by weight to 5% by weight.

[0077] The thickness of the negative electrode active material layer can be 50 μm to 300 μm, and preferably 100 μm to 200 μm.

[0078] The loading amount of the negative electrode active material layer is 200 mg / 25 cm 2 ~500mg / 25cm 2 , preferably 250 mg / 25 cm 2 ~400mg / 25cm 2 It can be.

[0079] The negative electrode may be prepared by coating at least one surface of a negative electrode current collector with a negative electrode slurry including 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.

[0080] The solvent for forming the negative electrode slurry may include, for example, at least one selected from the group consisting of distilled water, N-methyl-2-pyrrolidone (NMP), ethanol, methanol, and isopropyl alcohol, preferably distilled water, in order to facilitate dispersion of the negative electrode active material, binder, and / or conductive material. The solid content of the negative electrode slurry may be 30% by weight to 80% by weight, specifically 40% by weight to 70% by weight.

[0081] (3) Separator The separator may be interposed between the positive electrode and the negative electrode.

[0082] The separator may be a conventional porous polymer film, such as a porous polymer film made of a polyolefin polymer such as ethylene homocopolymer, propylene homocopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, or ethylene / methacrylate copolymer, either alone or in a laminate, or a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. Furthermore, to ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymer material may be used, and may be used in a single-layer or multi-layer structure.

[0083] (4) Nonaqueous electrolyte 1) Lithium salt First, the lithium salt will be described below.

[0084] In the non-aqueous electrolyte for a lithium secondary battery according to one embodiment of the present invention, the lithium salt may be any of those commonly used in electrolytes for lithium secondary batteries, without limitation. For example, a lithium salt containing Li as a cation may be used. + 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 - Specifically, the lithium salt may be at least one selected 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 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, LiPF6.

[0085] The lithium salt can be appropriately changed within a range that is normally usable, but in order to obtain an optimal effect of forming a corrosion prevention coating on the surface of the electrode, it can be contained in the electrolyte at a concentration of 0.8 M to 3.0 M, specifically 1.0 M to 3.0 M. Here, the unit "M" represents molar concentration, specifically, "mol / L."

[0086] When the concentration of the lithium salt satisfies the above range, the viscosity of the non-aqueous electrolyte can be controlled to achieve optimal impregnation, and the mobility of lithium ions can be improved, thereby improving the capacity characteristics and cycle characteristics of the lithium secondary battery.

[0087] 2) Organic solvents The organic solvent may include a cyclic carbonate solvent and a linear carbonate solvent, and may consist of a cyclic carbonate solvent and a linear carbonate solvent.

[0088] The volume ratio of the cyclic carbonate solvent to the linear carbonate solvent may be 10:90 to 50:50, specifically 15:85 to 50:50, and more specifically 20:80 to 35:65, and when it is in this range, it is preferable in terms of achieving high ion transport properties and low viscosity of the electrolyte.

[0089] The cyclic carbonate solvent includes ethylene carbonate, which is a highly viscous organic solvent with a high dielectric constant and can effectively dissociate the lithium salt in the electrolyte.

[0090] The cyclic carbonate solvent may not contain a fluorinated cyclic carbonate, such as fluoroethylene carbonate (FEC). Specifically, the cyclic carbonate solvent may consist of only ethylene carbonate and may not contain other cyclic carbonate solvents (such as propylene carbonate).

[0091] The linear carbonate solvent includes dimethyl carbonate. Dimethyl carbonate is an organic solvent with low viscosity and low dielectric constant, and has particularly excellent electrolyte impregnation properties, allowing for high loading and excellent impregnation of the positive electrode containing lithium iron phosphate particles according to the present invention. Meanwhile, as an organic solvent, dimethyl carbonate has the problem of forming an unstable negative electrode coating, which reduces the reduction stability of the negative electrode. However, as described below, by using dimethyl carbonate and vinylene carbonate in a specific content ratio, both electrolyte impregnation and reduction stability of the negative electrode can be improved. Furthermore, the nonaqueous electrolyte of the present invention is particularly suitable for a positive electrode containing lithium iron phosphate particles with a loading of 450 mg / 25 cm. 2 ~740mg / 25cm 2 The desired effect can be achieved when the loading of the positive electrode is 450 mg / 25 cm 2 Less than or 740 mg / 25 cm 2 If the temperature exceeds 100°C, the effect of improving the electrolyte impregnation property due to the use of dimethyl carbonate cannot be obtained.

[0092] The dimethyl carbonate is contained in the organic solvent in an amount of 5 to 75% by volume. In one embodiment, the dimethyl carbonate can be contained in the organic solvent in an amount of 5 to 55% by volume, more specifically 7 to 45% by volume, and even more specifically 35 to 45% by volume. If the dimethyl carbonate is contained in the organic solvent in an amount of less than 5% by volume, the impregnation of the positive electrode with the electrolyte cannot be improved. If the dimethyl carbonate is contained in the organic solvent in an amount of more than 75% by volume, an unstable SEI coating is formed, which is undesirable as it can lead to a problem of reduced cell performance.

[0093] The linear carbonate solvent may further include ethyl methyl carbonate in addition to the dimethyl carbonate. When the linear carbonate further includes ethyl methyl carbonate, the stability of the SEI coating can be further improved, which is preferable.

[0094] When the linear carbonate solvent further contains ethyl methyl carbonate, the organic solvent may contain 10 to 50% by volume of the ethylene carbonate, 5 to 55% by volume of the dimethyl carbonate, and 20 to 70% by volume of the ethyl methyl carbonate; more specifically, the organic solvent may contain 20 to 40% by volume of the ethylene carbonate, 7 to 45% by volume of the dimethyl carbonate, and 25 to 65% by volume of the ethyl methyl carbonate; even more specifically, the organic solvent may contain 25 to 35% by volume of the ethylene carbonate, 30 to 45% by volume of the dimethyl carbonate, and 25 to 50% by volume of the ethyl methyl carbonate; or the organic solvent may contain 30 to 35% by volume of the ethylene carbonate, 35 to 45% by volume of the dimethyl carbonate, and 25 to 50% by volume of the ethyl methyl carbonate. When the content is within the above range, it is preferable in terms of improving the electrolyte impregnation property and improving the stability of the negative electrode SEI coating.

[0095] Meanwhile, the organic solvent may be any organic solvent commonly used in non-aqueous electrolytes, and may further include at least one organic solvent selected from the group consisting of ester-based solvents, ether-based solvents, glyme-based solvents, and nitrile-based solvents, if necessary.

[0096] The ester solvent may include at least one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0097] The ether solvent may be any 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 thereof, but is not limited thereto.

[0098] The glyme-based solvent has a higher dielectric constant and lower surface tension than linear carbonate-based solvents, and is less reactive with metals. The glyme-based solvent may include, but is not limited to, at least one selected from the group consisting of dimethoxyethane (DME), diethoxyethane, diglyme, triglyme, and tetraglyme (TEGDME).

[0099] The nitrile solvent may be at least one selected from the group consisting of acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile, but is not limited thereto.

[0100] On the other hand, the remainder of the non-aqueous electrolyte other than the lithium salt and the additive may be an organic solvent unless otherwise specified.

[0101] (3) Additives The non-aqueous electrolyte of the present invention contains an additive.

[0102] The additive includes vinylene carbonate.

[0103] Vinylene carbonate can be used as an additive in the nonaqueous electrolyte of the present invention to form a stable SEI film on the negative electrode. In particular, when dimethyl carbonate is used as an organic solvent, the stability of the negative electrode SEI film is poor when exposed to high temperatures. However, the use of vinylene carbonate as an additive can improve the reduction stability of the negative electrode.

[0104] In the present invention, the ratio of the weight of the vinylene carbonate to the weight of the dimethyl carbonate is more than 0 and 0.2 or less. If the ratio of the weight of the vinylene carbonate to the weight of the dimethyl carbonate exceeds 0.2, an excessive amount of the negative electrode SEI coating is formed, which may increase the resistance and reduce the life performance.

[0105] Specifically, the weight ratio of the vinylene carbonate to the weight of the dimethyl carbonate may be 0.01 to 0.18, more specifically 0.016 to 0.130, and even more specifically 0.02 to 0.08. When the weight ratio is within this range, the effect of simultaneously improving the electrolyte impregnation property of the positive electrode and the reduction stability of the negative electrode can be suitably achieved.

[0106] The ratio of the weight of the vinylene carbonate to the weight of the dimethyl carbonate can be calculated based on the total weight or volume of the non-aqueous electrolyte, the volume content, weight content, density information, etc. of the dimethyl carbonate.

[0107] The vinylene carbonate may be included in the non-aqueous electrolyte in an amount of 0.01 wt % to 7 wt %, specifically 0.3 wt % to 6 wt %, more specifically 0.4 wt % to 3 wt %, and even more specifically 0.6 wt % to 2 wt %. When the amount is within this range, not only is an SEI coating on the negative electrode properly formed, preventing electrolyte side reactions, but an increase in resistance due to the use of an excessive amount of additives is also prevented, which is preferable.

[0108] Meanwhile, the additive may contain additional additives in addition to vinylene carbonate as needed to prevent the non-aqueous electrolyte from being decomposed in a high-power environment, which may cause the collapse of the negative electrode, or to further improve low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, and the effect of suppressing battery expansion at high temperatures.

[0109] Examples of such additional additives include at least one selected from the group consisting of cyclic carbonate-based compounds, halogen-substituted carbonate-based compounds, sultone-based compounds, sulfonate-based compounds, sulfate-based compounds, phosphate-based or phosphite-based compounds, borate-based compounds, nitrile-based compounds, benzene-based compounds, amine-based compounds, silane-based compounds, and lithium salt-based compounds.

[0110] The cyclic carbonate compound may be, for example, vinyl ethylene carbonate.

[0111] The halogen-substituted carbonate compound may be, for example, fluoroethylene carbonate (FEC).

[0112] The sultone compound may be, for example, at least one compound selected from the group consisting of 1,3-propane sultone (PS), 1,4-butane sultone, ethene sultone, 1,3-propene sultone (PRS), 1,4-butene sultone, and 1-methyl-1,3-propene sultone.

[0113] The sulfonate-based compound may include a saturated or unsaturated hydrocarbon group, such as an alkenyl or alkynyl group.

[0114] The sulfate-based compound may be, for example, ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS).

[0115] The phosphate- or phosphite-based 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.

[0116] Examples of the borate-based compound include tetraphenylborate, lithium difluoro(oxalate)borate (LiODFB), and lithium bisoxalateborate (LiB(C2O4)2, LiBOB).

[0117] The nitrile compound may be, for example, at least one compound selected from the group consisting of succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

[0118] The benzene-based compound may be, for example, fluorobenzene, the amine-based compound may be, for example, triethanolamine or ethylenediamine, and the silane-based compound may be, for example, tetravinylsilane.

[0119] The lithium salt-based compound is a compound different from the lithium salt contained in the non-aqueous electrolyte, and examples thereof include lithium difluorophosphate (LiPO2F2) and LiBF4.

[0120] The additional additives may be used in combination of two or more compounds, and the total content of the vinylene carbonate and the additional additives may be 0.05 wt % to 20 wt %, specifically 0.05 wt % to 10 wt %, based on the total weight of the non-aqueous electrolyte. When the total content of the additives satisfies this range, high-temperature storage characteristics and high-temperature life characteristics can be more effectively improved, and side reactions in the battery due to residual additives after the reaction can be prevented.

[0121] The nonaqueous electrolyte can be prepared, for example, by the following method. First, ethylene carbonate (EC), dimethyl carbonate (DMC), and optionally ethyl methyl carbonate (EMC) are mixed to prepare an organic solvent in the above-described amounts, specifically, 5% to 75% by volume, more specifically, 5% to 55% by volume, 7% to 45% by volume, or 35% to 45% by volume. Next, the lithium salt is dissolved in the organic solvent to a lithium salt concentration of 0.8M to 3.0M, specifically, 1.0M to 3.0M. Next, vinylene carbonate (VC) is added to the organic solvent in which the lithium salt has been dissolved, where the content of the vinylene carbonate is 0.01 wt % to 7 wt %, specifically 0.3 wt % to 6 wt %, more specifically 0.4 wt % to 3 wt %, and even more specifically 0.6 wt % to 2 wt %, based on the total weight of the non-aqueous electrolyte, and the weight ratio of the vinylene carbonate to the dimethyl carbonate is greater than 0 and 0.2 or less, specifically 0.01 to 0.18, more specifically 0.016 to 0.130, and even more specifically 0.02 to 0.08. The above-mentioned additional solvent and / or additive may be included in the non-aqueous electrolyte.

[0122] The lithium secondary battery according to the present invention can be usefully used in portable devices such as mobile phones, notebook computers, and digital cameras, and in electric vehicles such as hybrid electric vehicles (HEVs).

[0123] Therefore, according to another embodiment of the present invention, there is provided a battery module including the lithium secondary battery as a unit cell, and a battery pack including the same.

[0124] The battery module or battery pack may be used as a power source for one or more medium- to large-sized devices, including power tools; electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0125] The external shape of the lithium secondary battery of the present invention is not particularly limited, and may be a cylindrical shape using a can, a square shape, a pouch shape, a coin shape, or the like.

[0126] The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for a small device, but also as a unit battery in a medium- to large-sized battery module including a large number of battery cells.

[0127] The present invention will be specifically described below with reference to examples.

[0128] The present invention can be embodied in various other forms, and the scope of the present invention should not be construed as being limited to the following detailed examples. The following examples are provided to more completely explain the present invention to those skilled in the art.

[0129] The present invention will be specifically described below with reference to specific examples.

[0130] Example Example 1 (Production of non-aqueous electrolyte) 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.

[0131] LiPF6 was dissolved as a lithium salt in the organic solvent to a molar concentration of 1.0M.

[0132] A non-aqueous electrolyte was prepared by adding vinylene carbonate (VC) to the organic solvent in which the lithium salt was dissolved. The vinylene carbonate was contained in the non-aqueous electrolyte at a content of 1 wt %.

[0133] (Secondary battery manufacturing) A positive electrode slurry was prepared by adding lithium iron phosphate (LiFePO4) particles with a carbon coating layer as a positive electrode active material, carbon black as a conductive material, and polyvinylidene fluoride (PVdF) as a binder in a weight ratio of 94:3:3 to N-methyl-2-pyrrolidone (NMP) as a solvent. The positive electrode slurry was applied to a 15 μm-thick positive electrode current collector (Al thin film) at a concentration of 600 mg / 25 cm. 2 After being applied and dried, a roll press was carried out to prepare a positive electrode (thickness of the positive electrode active material: 220 μm). 50 The particle size of the lithium iron phosphate (LiFePO4) particles on which the carbon coating layer was formed was 1.1 μm, and the lithium iron phosphate (LiFePO4) particles on which the carbon coating layer was formed were in the form of primary particles.

[0134] Anode slurry was prepared by adding artificial graphite as anode active material, SBR-CMC as binder, and carbon black as conductive material to water as solvent in a weight ratio of 97:2:1. The anode slurry was applied to a copper (Cu) thin film as anode current collector with a thickness of 15 μm at a concentration of 300 mg / 25 cm. 2After drying, a roll press was carried out to prepare a negative electrode (thickness of negative electrode active material: 170 μm).

[0135] The positive electrode, the polyolefin-based porous separator, and the negative electrode were stacked in this order to prepare an electrode assembly.

[0136] The assembled electrode assembly was placed in a battery case, and the prepared non-aqueous electrolyte was poured into the battery case to prepare a lithium secondary battery.

[0137] Example 2 A lithium secondary battery was manufactured in the same manner as in Example 1, except that a non-aqueous electrolyte was prepared using a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 30:60:10 as the organic solvent.

[0138] Example 3 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 of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 30:70 as the organic solvent.

[0139] Example 4 A lithium secondary battery was manufactured in the same manner as in Example 1, except that the non-aqueous electrolyte was prepared by adding 0.5 wt % of vinylene carbonate as an additive to the non-aqueous electrolyte instead of 1 wt %.

[0140] Example 5 A lithium secondary battery was manufactured in the same manner as in Example 1, except that the non-aqueous electrolyte was prepared by adding 5 wt % of vinylene carbonate as an additive to the non-aqueous electrolyte instead of 1 wt %.

[0141] Example 6 Positive electrode slurry loading: 600 mg / 25 cm 2 Instead of 500mg / 25cm 2 A lithium secondary battery was produced in the same manner as in Example 1, except that the positive electrode was produced using the above-mentioned method.

[0142] Example 7 Positive electrode slurry loading: 600 mg / 25 cm 2 Instead of 700mg / 25cm 2 A lithium secondary battery was produced in the same manner as in Example 1, except that the positive electrode was produced using the above-mentioned method.

[0143] Example 8 Positive electrode slurry loading: 600 mg / 25 cm 2 Instead of 450mg / 25cm 2 A lithium secondary battery was produced in the same manner as in Example 1, except that the positive electrode was produced using the above-mentioned method.

[0144] Comparative Example 1 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 of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 30:70 as the organic solvent.

[0145] Comparative Example 2 A lithium secondary battery was produced in the same manner as in Example 1, except that the non-aqueous electrolyte was produced without adding vinylene carbonate as an additive.

[0146] Comparative Example 3 A lithium secondary battery was produced in the same manner as in Example 1, except that 8 wt % of vinylene carbonate was added as an additive to the non-aqueous electrolyte instead of 1 wt % to produce the non-aqueous electrolyte.

[0147] Comparative Example 4 A lithium secondary battery was produced in the same manner as in Example 6, except that a non-aqueous electrolyte was produced using a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 30:70 as the organic solvent.

[0148] Comparative Example 5 A non-aqueous electrolyte was prepared using an organic solvent consisting of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) mixed in a volume ratio of 30:30:40. The loading amount of the positive electrode slurry was 600 mg / 25 cm. 2 Instead of 500mg / 25cm 2 A lithium secondary battery was produced in the same manner as in Example 1, except that the positive electrode was produced using the above-mentioned method.

[0149] Comparative Example 6 Positive electrode slurry loading: 600 mg / 25 cm 2 Instead of 750mg / 25cm 2 A lithium secondary battery was produced in the same manner as in Example 1, except that the positive electrode was produced using the above-mentioned method.

[0150] Comparative Example 7 A non-aqueous electrolyte was prepared using a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 30:70 as an organic solvent, and the loading amount of the positive electrode slurry was set to 600 mg / 25 cm. 2 Instead of 400mg / 25cm 2 A lithium secondary battery was produced in the same manner as in Example 1, except that the positive electrode was produced using the above-mentioned method.

[0151] Comparative Example 8 Positive electrode slurry loading: 600 mg / 25 cm 2 Instead of 400mg / 25cm 2 A lithium secondary battery was produced in the same manner as in Example 1, except that the positive electrode was produced using the above-mentioned method.

[0152] Comparative Example 9 A non-aqueous electrolyte was prepared using an organic solvent consisting of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) mixed in a volume ratio of 30:30:40. The loading amount of the positive electrode slurry was 600 mg / 25 cm. 2 Instead of 400mg / 25cm 2A lithium secondary battery was produced in the same manner as in Example 1, except that the positive electrode was produced using the above-mentioned method.

[0153] [Table 1]

[0154] Experimental Example Experimental Example 1: Measurement of initial capacity development rate The lithium secondary batteries of Examples 1 to 8 and Comparative Examples 1 to 9 prepared above were initially charged and discharged at 25°C under CC / CV and 0.33C conditions up to 3.65V, and then discharged at 0.33C down to 2.5V, and the initial discharge capacity (unit: mAh) was measured.

[0155] The initial discharge capacity was divided by the cell design capacity (based on 0.33 C) and then multiplied by 100 to evaluate the capacity development rate (%). The results are shown in Table 2 below.

[0156] Experimental Example 2: Evaluation of cycle charge / discharge capacity retention rate The lithium secondary batteries of Examples 1 to 8 and Comparative Examples 1 to 9 prepared above were charged to 3.65 V C at 25° C. under CC / CV conditions at 0.33 C and then discharged to 2.5 V at 0.33 C, which constituted one cycle, and the discharge capacity and resistance after one cycle were measured. Here, the resistance was measured by checking the capacity at room temperature, charging to 50% SOC as the discharge capacity standard, and then discharging at a current of 2.5 C for 10 seconds, using the difference in voltage drop obtained.

[0157] After 200 charge / discharge cycles under the same conditions, the capacity retention rate (%) and resistance increase rate (%) were measured. The capacity retention rate (%) was calculated using the following formula 1, and the resistance increase rate (%) was calculated using the following formula 2. The measurement results are shown in Table 2.

[0158] [Formula 1] Capacity retention rate (%) = (discharge capacity after 200 cycles / discharge capacity after 1 cycle) x 100

[0159] [Formula 2] Resistance increase rate (%) = {(resistance after 200 cycles - resistance after 1 cycle) / resistance after 1 cycle} x 100

[0160] [Table 2]

[0161] Referring to Table 2, it can be seen that the lithium secondary batteries of Examples 1 to 8 according to the present invention exhibit excellent capacity development effect, excellent life performance, and a low resistance increase rate compared to the batteries of Comparative Examples 1 to 6.

[0162] In addition, the positive electrode loading amount is 500 mg / 25 cm 2 It can be seen that Example 6, which is designed as above, exhibits excellent capacity development effect, excellent life performance, and a low resistance increase rate compared to Comparative Example 4, which does not use dimethyl carbonate.

[0163] On the other hand, the positive electrode loading amount is 400 mg / 25 cm 2 With reference to Comparative Examples 7 to 9, which were designed according to the present invention, it can be seen that the loading amount was adjusted to a low level, making electrolyte impregnation less of an issue, and therefore the components and content of the non-aqueous electrolyte did not have much of an effect. Specifically, comparing Comparative Examples 7 and 8, it can be seen that the use of dimethyl carbonate as an organic solvent component did not significantly improve the effects in terms of capacity development, life performance, and resistance increase rate. Furthermore, Comparative Example 9, which used a different linear carbonate instead of dimethyl carbonate, showed the same or similar level of performance as Comparative Examples 7 and 8. This indicates that the non-aqueous electrolyte according to the present invention can be used at a specific loading amount (e.g., 400 mg / 25 cm). 2 More than 750mg / 25cm 2 Less than 450 mg / 25 cm 2 ~740mg / 25cm 2 ) It can be confirmed that excellent effects are exhibited in the lithium iron phosphate-containing positive electrode.

Claims

1. 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 loading amount of the positive electrode is 450 mg / 25 cm ２ ~740mg / 25cm ２ and the non-aqueous electrolyte contains a lithium salt, an organic solvent, and an additive; the organic solvent includes a cyclic carbonate solvent and a linear carbonate solvent, the cyclic carbonate solvent contains ethylene carbonate, the linear carbonate solvent includes dimethyl carbonate, the additive comprises vinylene carbonate; the dimethyl carbonate is contained in the organic solvent at 5% by volume to 75% by volume; A lithium secondary battery, wherein a ratio of the weight of the vinylene carbonate to the weight of the dimethyl carbonate is greater than 0 and equal to or less than 0.

2.

2. The loading amount of the positive electrode is 450 mg / 25 cm ２ ~700mg / 25cm ２ 2. The lithium secondary battery according to claim 1, wherein

3. The loading amount of the positive electrode is 500 mg / 25 cm ２ ~600mg / 25cm ２ 2. The lithium secondary battery according to claim 1, wherein

4. 2. The lithium secondary battery according to claim 1, wherein the vinylene carbonate is contained in the non-aqueous electrolyte in an amount of 0.01% by weight to 7% by weight.

5. 2. The lithium secondary battery according to claim 1, wherein a volume ratio of the cyclic carbonate solvent to the linear carbonate solvent is 10:90 to 50:

50.

6. The lithium secondary battery according to claim 1 , wherein the linear carbonate solvent further contains ethyl methyl carbonate.

7. 7. The lithium secondary battery according to claim 6, wherein the organic solvent contains 10% by volume to 50% by volume of the ethylene carbonate, 5% by volume to 55% by volume of the dimethyl carbonate, and 20% by volume to 70% by volume of the ethyl methyl carbonate.

8. The lithium salts include LiCl, LiBr, LiI, and LiBF. ４ , LiClO ４ , LiAlO ４ , LiAlCl ４ , LiPF ６ , LiSbF ６ , LiAsF ６ , LiB １０ Cl １０ , LiBOB(LiB(C ２ O ４ ) ２ ), LiCF ３ SO ３ , LiTFSI (LiN(SO ２ CF ３ ) ２ ), LiFSI (LiN(SO ２ F) ２ ), LiCH ３ SO ３ , LiCF ３ CO ２ , LiCH ３ CO ２ and LiBETI(LiN(SO ２ CF ２ CF ３ ) ２ 2. The lithium secondary battery according to claim 1, comprising at least one selected from the group consisting of:

9. 2. The lithium secondary battery according to claim 1, wherein the lithium salt is contained in the non-aqueous electrolyte at a concentration of 0.8 M to 3.0 M.

10. The lithium secondary battery according to claim 1 , wherein the lithium iron phosphate particles include a compound represented by the following chemical formula A: [Chemical formula A] Li １＋ａ Fe １－ｓ M ｓ (PO ４－ｂ )X ｂ In the chemical formula A, M is one or more elements selected from Co, Ni, Mn, Al, Mg, Ti, and V, and X is F, S, or N, and 0≦s≦0.5; −0.5≦a≦0.5; and 0≦b≦0.

1.

11. The lithium iron phosphate particles are LiFePO ４ The lithium secondary battery according to claim 1 , comprising:

12. the lithium iron phosphate particles are in the form of primary particles; The average particle size (D ５０ 2. The lithium secondary battery according to claim 1, wherein the thickness of the first electrode is 0.2 μm to 3.0 μm.

13. The lithium secondary battery according to claim 1 , wherein the lithium iron phosphate particles include a carbon coating layer on the surface thereof.

14. 2. The lithium secondary battery according to claim 1, wherein the positive electrode active material does not contain a lithium nickel-based oxide.

15. The lithium secondary battery according to claim 1 , wherein the negative electrode comprises a carbon-based active material.

16. 16. The lithium secondary battery according to claim 15, wherein the carbon-based active material comprises at least one selected from the group consisting of natural graphite and artificial graphite.

17. manufacturing an electrode assembly including a positive electrode, a negative electrode, and a separator; housing the electrode assembly in a battery case; preparing a non-aqueous electrolyte containing a lithium salt, an organic solvent, and an additive; injecting or impregnating the non-aqueous electrolyte into the battery case; the positive electrode includes a positive electrode active material, the positive electrode active material includes lithium iron phosphate particles, The loading amount of the positive electrode is 450 mg / 25 cm ２ ~740mg / 25cm ２ and the non-aqueous electrolyte contains a lithium salt, an organic solvent, and an additive; the organic solvent includes a cyclic carbonate solvent and a linear carbonate solvent, the cyclic carbonate solvent contains ethylene carbonate, the linear carbonate solvent includes dimethyl carbonate, the additive comprises vinylene carbonate; the dimethyl carbonate is contained in the organic solvent at 5% by volume to 75% by volume; a weight ratio of the vinylene carbonate to the dimethyl carbonate is greater than 0 and not greater than 0.2.

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