WO2024096701A1 - Lithium secondary battery - Google Patents

Abstract

The present invention provides a lithium secondary battery comprising a cathode, an anode, a separator and a nonaqueous electrolyte, wherein the cathode comprises a cathode active material, the cathode active material comprises lithium iron phosphate particles, the loading amount of the cathode is 450 mg/25 cm2 to 740 mg/25 cm2, the nonaqueous electrolyte comprises a lithium salt, an organic solvent and an additive, the organic solvent comprises a cyclic carbonate-based solvent and a linear carbonate-based solvent, the cyclic carbonate-based solvent includes ethylene carbonate, the linear carbonate-based solvent includes dimethyl carbonate, the dimethyl carbonate is included in an amount of 5-75 vol% in the organic solvent, the additive includes vinylene carbonate, and the ratio of the weight of the vinylene carbonate to the weight of the dimethyl carbonate is greater than 0 and less than or equal to 0.2.

Description

Lithium secondary battery

Cross-citation with related applications

This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0146438, dated November 4, 2022, and all contents disclosed in the document of the Korean Patent Application are incorporated as part of this specification.

Technology field

The present invention relates to lithium secondary batteries.

As personal IT devices and computer networks develop due to the development of the information society, and the overall society's dependence on electrical energy increases, there is a need to develop technologies to efficiently store and utilize electrical energy.

Among the developed technologies, secondary batteries are the most suitable for various purposes. Among these secondary batteries, interest is growing in lithium secondary batteries, which are not only capable of being miniaturized to the point where they can be applied to personal IT devices, but also have the highest energy density.

Generally, lithium secondary batteries are 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.

Carbon-based active materials, silicon-based active materials, etc. are considered as negative electrode active materials for these lithium secondary batteries. Meanwhile, the use of lithium-containing cobalt oxide, layered crystal structure LiMnO ₂ , spinel crystal structure LiMn ₂ O ₄ , and lithium-containing nickel oxide (LiNiO ₂ ) is being considered as the positive electrode active material.

Recently, the use of lithium iron phosphate (for example, LiFePO ₄ )-based active material, which has excellent thermal stability and is relatively inexpensive, has been considered as a positive electrode active material.

However, in the case of the lithium iron phosphate-based active material, it has a lower specific capacity compared to lithium cobalt oxide, lithium nickel oxide, etc., and therefore, in order to increase the energy density of the positive electrode and lithium secondary battery containing it, the lithium iron phosphate-based active material must be used at a high loading amount. However, the high-loading lithium iron phosphate anode has problems in that it is difficult to fully impregnate the anode with the non-aqueous electrolyte, making capacity development difficult, resistance increasing, and lifespan being reduced.

One object of the present invention is to solve the above problems, in a lithium secondary battery including lithium iron phosphate particles as a positive electrode active material and a positive electrode with a specific loading amount or more, the impregnation of the positive electrode into the non-aqueous electrolyte By improving the cathode reduction stability while improving the cathode reduction stability, a lithium secondary battery having excellent capacity development effect, excellent life performance, and resistance reduction effect is provided.

The present invention includes a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, wherein the positive electrode includes a positive electrode active material, the positive electrode active material includes lithium iron phosphate particles, and the loading amount of the positive electrode is 450 mg/25 cm ² to 740 mg/ 25 cm ² , the non-aqueous electrolyte includes a lithium salt, an organic solvent and an additive, the organic solvent includes a cyclic carbonate-based solvent and a linear carbonate-based solvent, the cyclic carbonate-based solvent includes ethylene carbonate, and the linear The carbonate-based solvent includes dimethyl carbonate, and the dimethyl carbonate is included in the organic solvent in an amount of 5% to 75% by volume. The additive includes vinylene carbonate, and the weight of the vinylene carbonate relative to the weight of the dimethyl carbonate is A lithium secondary battery having a weight ratio of more than 0 and less than or equal to 0.2 is provided.

The lithium secondary battery according to the present invention includes a positive electrode having a loading amount greater than a certain level and containing lithium iron phosphate particles as a positive electrode active material; and a non-aqueous electrolyte comprising ethylene carbonate and dimethyl carbonate as an organic solvent and vinylene carbonate as an additive, and in which the content and content ratio of dimethyl carbonate and vinylene carbonate are adjusted to a specific range. According to the lithium secondary battery of the present invention, excellent dimethyl carbonate is used as an organic solvent component to improve electrolyte impregnation of a positive electrode with a high loading amount, and a vinylene carbonate additive is added to have a specific content ratio in relation to dimethyl carbonate. Since the cathode reduction stability can be improved by using , the capacity of the lithium secondary battery can be developed at an excellent level, and the lifespan performance and resistance characteristics can be improved.

First, before describing the present invention, the terms or words used in the specification and claims should not be construed as limited to their usual or dictionary meanings, and the inventor must explain his/her invention in the best way possible. Based on the principle that the concept of a term can be appropriately defined, it must be interpreted with a meaning and concept consistent with the technical idea of the present invention.

Meanwhile, the terms used in this specification are merely used to describe exemplary embodiments and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

In this specification, terms such as “comprise,” “comprise,” or “have” are intended to designate the presence of implemented features, numbers, steps, components, or a combination thereof, and are intended to indicate the presence of one or more other features or It should be understood that this does not exclude in advance the possibility of the presence or addition of numbers, steps, components, or combinations thereof.

In this specification, “%” means weight percent unless explicitly stated otherwise.

Before explaining the present invention, in the description of “carbon numbers a to b” in the specification, “a” and “b” refer to the number of carbon atoms included in a specific functional group. That is, the functional group may include “a” to “b” carbon atoms.

In addition, in this specification, unless otherwise defined, “substitution” means that at least one hydrogen bonded to carbon is replaced with an element other than hydrogen, for example, an alkyl group having 1 to 5 carbon atoms or a fluorine element. It means replaced with .

In this specification, the average particle size (D ₅₀ ) can be defined as the particle size corresponding to 50% of the volume accumulation in the particle size distribution curve. The average particle diameter (D ₅₀ ) can be measured using, for example, a laser diffraction method. The laser diffraction method is generally capable of measuring particle diameters ranging from the submicron region to several millimeters, and can obtain results with high reproducibility and high resolution.

Hereinafter, the present invention will be described in more detail.

Lithium secondary battery

The present invention relates to lithium secondary batteries.

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, and the loading amount of the positive electrode is 450 mg/25 cm ² to 740 mg/25 cm ² , the non-aqueous electrolyte includes a lithium salt, an organic solvent and an additive, the organic solvent includes a cyclic carbonate-based solvent and a linear carbonate-based solvent, and the cyclic carbonate-based solvent is It includes ethylene carbonate, the linear carbonate-based solvent includes dimethyl carbonate, the dimethyl carbonate is included in the organic solvent in an amount of 5% to 75% by volume, and the additive includes vinylene carbonate, and the dimethyl carbonate. The weight ratio of the vinylene carbonate to the weight of is characterized in that it exceeds 0 and is 0.2 or less.

The lithium secondary battery according to the present invention includes a positive electrode having a loading amount greater than a certain level and containing lithium iron phosphate particles as a positive electrode active material; and a non-aqueous electrolyte comprising ethylene carbonate and dimethyl carbonate as an organic solvent and vinylene carbonate as an additive, and in which the content and content ratio of dimethyl carbonate and vinylene carbonate are adjusted to a specific range. According to the lithium secondary battery of the present invention, excellent dimethyl carbonate is used as an organic solvent component to improve electrolyte impregnation of a positive electrode with a high loading amount, and a vinylene carbonate additive is added to have a specific content ratio in relation to dimethyl carbonate. Since the cathode reduction stability can be improved by using , the capacity of the lithium secondary battery can be developed at an excellent level, and the lifespan performance and resistance characteristics can be improved.

The lithium secondary battery according to the present invention has a capacity retention rate of 90% or more, preferably 90% to 95%, when the design capacity of the cell (or lithium secondary battery) is at least 500 mAh and the initial discharge capacity is at least 500 mAh. %, and the resistance increase rate may be 20% or less, preferably 15% or less. At this time, the positive electrode includes lithium iron phosphate-based particles as an active material, the loading amount is 450 mg/25 cm ² to 740 mg/25 cm ² , the non-aqueous electrolyte includes lithium salt, an organic solvent, and an additive, and the organic solvent is a cyclic carbonate-based solvent. and a linear carbonate-based solvent, wherein the cyclic carbonate-based solvent includes ethylene carbonate, the linear carbonate-based solvent includes dimethyl carbonate, and the dimethyl carbonate is included in the organic solvent in an amount of 5% to 75% by volume. The additive includes vinylene carbonate, and the weight ratio of the vinylene carbonate to the weight of the dimethyl carbonate is greater than 0 and less than or equal to 0.2. The design capacity, initial discharge capacity, capacity maintenance rate, and resistance increase rate of the cell were measured according to the methods described in the examples below.

The lithium secondary battery includes a positive electrode; cathode; separation membrane; and non-aqueous electrolytes. Specifically, the lithium secondary battery includes a positive electrode; a cathode opposite the anode; a separator interposed between the anode and the cathode; and non-aqueous electrolytes.

The lithium secondary battery includes manufacturing an electrode assembly including a positive electrode, a negative electrode, and a separator; Storing the electrode assembly in a battery case; Preparing a non-aqueous electrolyte comprising a lithium salt, an organic solvent, and additives; and injecting or impregnating the non-aqueous electrolyte into the battery case.

(1) anode

The positive electrode includes a positive electrode active material. The positive electrode active material includes lithium iron phosphate particles.

The lithium iron phosphate particles may include a compound represented by the following formula (A).

[Formula A]

Li _1+a Fe _1-s M _s (PO _4-b )X _b

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

The formula A may be specifically expressed as LiFePO ₄ (a=0, s=0, and b=0).

The lithium iron phosphate particles may be in the form of primary particles or may be in the form of secondary particles in which two or more primary particles are aggregated. Specifically, the lithium iron phosphate particles may be in the form of primary particles.

The lithium iron phosphate particles may be made of primary particles, may be made of secondary particles in which two or more primary particles are aggregated, or may be a mixture of primary particles and secondary particles in which two or more primary particles are aggregated.

At this time, when the lithium iron phosphate particles are in the form of primary particles, the average particle diameter (D ₅₀ ) of the lithium iron phosphate particles may be 0.2 to 3.0 μm, specifically 0.2 to 2.0 μm, and more specifically, It may be 0.3 to 1.5㎛. In addition, when the lithium iron phosphate particles are in the form of secondary particles in which two or more primary particles are aggregated, the primary particles may have an average particle diameter (D ₅₀ ) of 0.2 to 3.0 ㎛, specifically 0.2 to 2.0 ㎛. and, more specifically, may be 0.3 to 1.5 ㎛, and the secondary particles may have an average particle diameter (D ₅₀ ) of 7 to 25 ㎛, specifically 10 to 20 ㎛.

The positive electrode active material may further include a carbon coating layer located on the surface of the lithium iron phosphate particles. The carbon coating layer may be introduced for the purpose of protecting lithium iron phosphate particles and improving electrical conductivity.

The positive electrode active material may not contain lithium nickel-based oxide, for example, lithium nickel-cobalt-manganese oxide or lithium nickel-cobalt-aluminum oxide. In the case of the positive electrode containing the lithium nickel-based oxide, it may be difficult to achieve the effect even if the loading amount (450 mg/25 cm ² to 740 mg/25 cm ² ) and the non-aqueous electrolyte described later are applied.

The loading amount of the anode is 450mg/25cm ² to 740mg/25cm ² .

The lithium iron phosphate particles have the advantage of excellent thermal stability and relatively low cost compared to other cathode active materials such as lithium cobalt oxide and lithium nickel-cobalt-manganese oxide, but due to their small specific capacity, the loading amount is required to realize high energy density. There is a problem that needs to be increased. When increasing the loading amount of the positive electrode (e.g., 450 mg/25 cm ² to 740 mg/25 cm ² ), a high energy density battery (e.g., a lithium battery with a design capacity of the cell of at least 500 mAh and an initial discharge capacity of at least 500 mAh) Although it is possible to implement a secondary battery, the non-aqueous electrolyte cannot be sufficiently impregnated into the positive electrode, making it difficult to develop the capacity of the lithium secondary battery, increasing resistance, and deteriorating lifespan performance.

In order to solve this problem, the lithium secondary battery according to the present invention uses dimethyl carbonate as an organic solvent component, vinylene carbonate as an additive, and a non-aqueous electrolyte whose content and content ratio are adjusted to a specific range. It is characterized by Through these features, it is possible to improve the electrolyte impregnation of the positive electrode with a loading amount of 450mg/25cm2 to 740mg/25cm2 and at the same time improve the negative electrode reduction stability, so that the capacity of the lithium secondary battery is developed at an excellent level and the lifespan is improved. Performance and resistance characteristics can be improved.

The loading amount of the anode was 450mg/25cm ² If it is less than that, the above-described problem of deterioration of electrolyte impregnability does not occur, so the effect of using the non-aqueous electrolyte according to the present invention is not expressed.

In addition, if the loading amount of the positive electrode exceeds 740 mg/25 cm ² , there is a possibility that electrolyte impregnation may not be sufficiently secured even if the non-aqueous electrolyte according to the present invention is applied to the positive electrode containing lithium iron phosphate particles. In addition, when the loading amount of the positive electrode exceeds 740 mg/25cm ² , for example, when lithium iron phosphate particles having a small average particle diameter (D ₅₀ ) are applied to the positive electrode, the voids formed between the lithium iron phosphate particles The size is small, and in this case, cracking of the anode may occur as the slurry solvent evaporates in the voids formed between lithium iron phosphate particles during the drying process during anode production, which may make it difficult to manufacture or implement the anode. There is.

Specifically, the loading amount of the positive electrode is specifically 450mg/25cm ² to 740mg/25cm ² , 450mg/25cm ² to 730mg/25cm ² , 450mg/25cm ² to 720mg/25cm ² , 450mg/25cm ² to 710mg/25cm ² , or 450mg/25cm ² to 700mg/25cm ² , more specifically 500mg/25cm ² to 680mg/25cm ² , 500mg/25cm ² to 650mg/25cm ² , 500mg/25cm ² to 625mg/25cm ² , or 500mg/25cm ² It may be from 600mg/25cm ² .

The positive electrode includes a positive electrode current collector; and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector. At this time, the positive electrode active material layer may include the above-described positive electrode active material.

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

The thickness of the positive electrode current collector may typically range from 3 to 500 ㎛.

The positive electrode current collector may form fine irregularities on the surface to strengthen the bonding force of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven materials.

The positive electrode active material layer is disposed on at least one side of the positive electrode current collector. Specifically, the positive electrode active material layer may be disposed on one or both sides of the positive electrode current collector.

The positive electrode active material may be included in the positive electrode active material layer in an amount of 80% to 99% by weight in consideration of sufficient capacity of the positive active material.

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

The binder is a component that helps bind active materials and conductive materials and bind to the current collector, and is specifically made of polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, and hydroxypropyl cellulose. From the group consisting of wood, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber and fluoroelastomer. It may include at least one selected type, preferably polyvinylidene fluoride.

The binder may be included in the positive electrode active material layer in an amount of 1% to 20% by weight, preferably 1.2% to 10% by weight, in terms of ensuring sufficient binding force between components such as the positive electrode active material.

The conductive material can be used to assist and improve conductivity in secondary batteries, and is not particularly limited as long as it has conductivity without causing chemical changes. Specifically, the anode conductive material includes graphite such as natural graphite or artificial graphite; Carbon black such as carbon black, acetylene black, KETJENBLACK®, channel black, panel black, lamp black, thermal black; Conductive fibers such as carbon fiber and metal fiber; Conductive tubes such as carbon nanotubes; fluorocarbon; 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, and may preferably include carbon black in terms of improving conductivity.

In terms of ensuring sufficient electrical conductivity, the conductive material may be included in the positive electrode active material layer in an amount of 1% to 20% by weight, preferably 1.2% to 10% by weight.

The thickness of the positive electrode active material layer may be 100 ㎛ to 300 ㎛, preferably 150 ㎛ to 250 ㎛.

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 a positive electrode slurry on the positive electrode current collector, followed by drying and rolling.

The solvent for forming the positive electrode slurry may include an organic solvent such as NMP (N-methyl-2-pyrrolidone). 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.

(2) cathode

The cathode may face the anode.

The negative electrode includes a negative electrode active material.

The negative electrode includes a negative electrode current collector; and a negative electrode active material layer disposed on at least one side of the negative electrode current collector. At this time, the negative electrode active material may be included in the negative electrode active material layer.

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

The negative electrode current collector may typically have a thickness of 3 to 500 μm.

The negative electrode current collector may form fine irregularities on the surface to strengthen the bonding force of the negative electrode active material. For example, the negative electrode current collector may be used in various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven fabrics.

The negative electrode active material layer is disposed on at least one side of the negative electrode current collector. Specifically, the negative electrode active material layer may be disposed on one or both sides of the negative electrode current collector.

The negative electrode active material layer may include a negative electrode active material.

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

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 may preferably include graphite. The graphite may include at least one selected from the group consisting of artificial graphite and natural graphite.

The average particle diameter (D ₅₀ ) of the carbon-based active material may be 10 ㎛ to 30 ㎛, preferably 15 ㎛ to 25 ㎛, in terms of ensuring structural stability during charging and discharging and reducing side reactions with the electrolyte solution.

Specifically, the (semi-)metal-based active materials include Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, At least one (semi-)metal selected from the group consisting of V, Ti, and Sn; From the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn. An alloy of lithium and at least one selected (semi-)metal; 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 selected (semi-)metal; Lithium Titanium Oxide (LTO); lithium vanadium oxide; It may include etc.

More specifically, the (semi-)metal-based active material may include a silicon-based active material.

The silicon-based active material may include a compound represented by SiO _x (0≤x<2). In the case of SiO ₂ , since lithium cannot be stored because it does not react with lithium ions, x is preferably within the above range, and more preferably, the silicon-based active material may be SiO.

The average particle diameter (D ₅₀ ) of the silicon-based active material may be 1 ㎛ to 30 ㎛, preferably 2 ㎛ to 15 ㎛ in terms of reducing side reactions with the electrolyte solution while ensuring structural stability during charging and discharging.

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

The negative electrode active material layer may further include a binder and/or a conductive material along with the negative electrode active material.

The binder is used to improve battery performance by improving adhesion between the negative electrode active material layer and the negative electrode current collector, for example, polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co- HFP), polyvinylidenefluoride (PVDF), polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, recycled Cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluoroelastomer, and hydrogen thereof. It may include at least one selected from the group consisting of substances substituted with Li, Na, or Ca, and may also include various copolymers thereof.

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

The conductive material is not particularly limited as long as it has conductivity without causing chemical changes in the battery. For example, graphite such as natural graphite or artificial graphite; Carbon black such as carbon black, acetylene black, KETJENBLACK®, channel black, panel black, lamp black, thermal black; Conductive fibers such as carbon fiber and metal fiber; Conductive tubes such as carbon nanotubes; fluorocarbon; Metal powders such as aluminum 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 may be used.

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

The thickness of the negative electrode active material layer may be 50㎛ to 300㎛, preferably 100㎛ to 200㎛.

The loading amount of the negative electrode active material layer may be 200mg/25cm ² to 500mg/25cm ² , preferably 250mg/25cm ² to 400mg/25cm ² .

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

The solvent for forming the negative electrode slurry is, for example, distilled water, NMP (N-methyl-2-pyrrolidone), ethanol, methanol, and isopropyl alcohol in terms of facilitating dispersion of the negative electrode active material, binder, and/or conductive material. It may contain at least one selected from the group, preferably distilled water. 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.

(3) Separator

The separator may be interposed between the anode and the cathode.

The separator includes typical porous polymer films conventionally used as separators, such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer. Porous polymer films made of polyolefin-based polymers can be used alone or by laminating them, or conventional porous non-woven fabrics, such as high-melting point glass fibers, polyethylene terephthalate fibers, etc., can be used, but are limited to these. It doesn't work. Additionally, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

(4) Non-aqueous electrolyte

1) Lithium salt

First, the lithium salt is explained as follows.

In the non-aqueous electrolyte for lithium secondary batteries according to an embodiment of the present invention, the lithium salt may be those commonly used in electrolytes for lithium secondary batteries without limitation, and for example, includes Li ⁺ as a cation and Li + as an anion. F ^- , Cl ^- , Br ^- , I ^- , NO ₃ ^- , N(CN) ₂ ^- , BF ₄ ^- , ClO ₄ ^- , AlO ₄ ^- , AlCl ₄ ^- , PF ₆ ^- , SbF ₆ ^- , AsF ₆ ^- , B ₁₀ Cl ₁₀ ^- , BF ₂ C ₂ O ₄ ^- , BC ₄ O ₈ ^- , PF ₄ C ₂ O ₄ ^- , PF ₂ C ₄ O ₈ ^- , (CF ₃ ) ₂ PF ₄ ^- , (CF ₃ ) ₃ PF ₃ ^- , (CF ₃ ) ₄ PF ₂ ^- , (CF ₃ ) ₅ PF ^- , (CF ₃ ) ₆ P ^- , CF ₃ SO ₃ ^- , C ₄ F ₉ SO ₃ ^- , CF ₃ CF ₂ SO ₃ ^- , (CF ₃ SO ₂ ) ₂ N ^- , (FSO ₂ ) ₂ N ^- , CF ₃ CF ₂ (CF ₃ ) ₂ CO ^- , (CF ₃ SO ₂ ) ₂ CH ^- , CH ₃ SO ₃ ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- , CF ₃ CO ₂ ^- , CH ₃ CO ₂ ^- , SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- at least one selected from the group consisting of. Specifically, the lithium salt is LiCl, LiBr, LiI, 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 At least one or more selected from the group consisting of CF ₂ CF ₃ ) ₂ ) may be mentioned. The lithium salt is specifically LiBF ₄ , LiClO ₄ , LiPF ₆ , LiBOB (LiB(C ₂ O ₄ ) ₂ ), LiCF ₃ SO ₃ , LiTFSI (LiN(SO ₂ CF ₃ ) ₂ ), LiFSI (LiN(SO ₂ ) F) ₂ ) and LiBETI (LiN(SO ₂ CF ₂ CF ₃ ) ₂ ) may contain a single substance or a mixture of two or more types selected from the group consisting of LiPF ₆ .

The lithium salt can be appropriately changed within the range commonly used, but in order to obtain the optimal effect of forming an anti-corrosion film on the electrode surface, it should be included in the electrolyte solution at a concentration of 0.8 M to 3.0 M, specifically at a concentration of 1.0 M to 3.0 M. You can. At this time, the unit “M” may mean molar concentration, specifically “mol/L”.

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 to improve the capacity characteristics and cycle characteristics of the lithium secondary battery. there is.

2) Organic solvent

The organic solvent may include a cyclic carbonate-based solvent and a linear carbonate-based solvent. The organic solvent may be composed of a cyclic carbonate-based solvent and a linear carbonate-based solvent.

The volume ratio of the cyclic carbonate-based solvent and the linear carbonate-based solvent may be 10:90 to 50:50, specifically 15:85 to 50:50, more specifically 20:80 to 35:65, and may be within the above range. This is desirable in terms of achieving high ion transport properties and low viscosity of the electrolyte.

The cyclic carbonate-based solvent includes ethylene carbonate. The ethylene carbonate is a high viscosity organic solvent and has a high dielectric constant, so it can easily dissociate the lithium salt in the electrolyte.

The cyclic carbonate-based solvent may not include a fluorinated cyclic carbonate, for example, fluoroethylene carbonate (FEC). Specifically, the cyclic carbonate-based solvent may consist only of ethylene carbonate and may not include other cyclic carbonate-based solvents (eg, propylene carbonate).

Additionally, the linear carbonate-based solvent includes dimethyl carbonate. The dimethyl carbonate is an organic solvent with low viscosity and low dielectric constant, and is particularly excellent in electrolyte impregnation, so it can impregnate the positive electrode containing lithium iron phosphate particles at a high loading level according to the present invention to an excellent level. On the other hand, dimethyl carbonate as an organic solvent has the problem of forming an unstable negative electrode film, which reduces the reduction stability of the negative electrode. However, as described later, by using dimethyl carbonate and vinylene carbonate in a specific content ratio, the electrolyte impregnation property and the negative electrode are improved. The reduction stability of can be improved at the same time. In addition, the non-aqueous electrolyte of the present invention can achieve the desired effect especially when the loading amount of the positive electrode containing lithium iron phosphate particles is 450mg/25cm2 to 740mg/25cm2, and if the loading amount of the positive electrode is less than 450mg/ ^25cm2 or If it exceeds 740 mg/25cm ² , the effect of improving electrolyte impregnation by using dimethyl carbonate cannot be obtained.

The dimethyl carbonate is included in the organic solvent in an amount of 5% to 75% by volume. In one embodiment, the dimethyl carbonate may be included 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 dimethyl carbonate is included in the organic solvent in an amount of less than 5% by volume, the impregnability of the positive electrode into the electrolyte cannot be improved. If dimethyl carbonate is included in the organic solvent in an amount exceeding 75% by volume, an unstable SEI film is formed and cell performance is deteriorated, which is not desirable.

The linear carbonate-based solvent may further include ethylmethyl carbonate along with the dimethyl carbonate. It is preferable that the linear carbonate further includes ethylmethyl carbonate in that the stability of the SEI film can be further improved.

When the linear carbonate-based solvent further includes ethylmethyl carbonate, the organic solvent contains 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 ethylmethyl carbonate. It may include % by volume, and more specifically, it may include 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 ethylmethyl carbonate. , more specifically, it may include 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 ethylmethyl carbonate, or 30% by volume of the ethylene carbonate. % to 35% by volume, 35% to 45% by volume of dimethyl carbonate, and 25% to 50% by volume of ethylmethyl carbonate. When it is within the above range, it is desirable in terms of improving electrolyte impregnation and improving the stability of the negative SEI film.

Meanwhile, the organic solvent can be used by adding organic solvents commonly used in non-aqueous electrolytes without limitation, if necessary. For example, it may further include at least one organic solvent selected from ester-based solvents, ether-based solvents, glyme-based solvents, and nitrile-based solvents.

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

The ether-based solvents include dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, ethyl propyl ether, 1,3-dioxolane (DOL), and 2,2-bis (trifluoromethyl )-1,3-dioxolane (TFDOL) or a mixture of two or more of these may be used, but are not limited thereto.

The glyme-based solvent has a high dielectric constant and low surface tension compared to the linear carbonate-based solvent, and is a solvent with low reactivity with metal, such as dimethoxyethane (glyme, DME), diethoxyethane, digylme, and trimethylamine. -It may include at least one selected from the group consisting of triglyme and tetra-glyme (TEGDME), but is not limited thereto.

The nitrile-based solvents include acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentane carbonitrile, cyclohexane carbonitrile, 2-fluorobenzonitrile, and 4-fluorobenzonitrile. , difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile, but is not limited thereto.

Meanwhile, the remainder of the non-aqueous electrolyte, excluding lithium salts and additives, may be organic solvents unless otherwise specified.

(3) Additives

The non-aqueous electrolyte of the present invention contains additives.

The additive includes vinylene carbonate.

The vinylene carbonate can be used as an additive in the non-aqueous electrolyte of the present invention to form a stable SEI film on the cathode. In particular, when dimethyl carbonate is used as an organic solvent, there is a problem that the stability of the anode SEI film is poor when exposed to high temperatures, but the cathode reduction stability can be improved by using vinylene carbonate as an additive.

In the present invention, the weight ratio of the vinylene carbonate to the weight of the dimethyl carbonate is greater than 0 and less than or equal to 0.2. If the weight ratio of the vinylene carbonate to the weight of the dimethyl carbonate exceeds 0.2, the negative SEI film may be excessively formed, which may cause problems such as increased resistance and decreased lifespan performance.

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, and when in the above range, the positive electrode The effect of simultaneously improving electrolyte impregnation and reduction stability of the cathode can be preferably implemented.

The weight ratio of vinylene carbonate to the weight of dimethyl carbonate can be calculated through the weight or volume of the entire non-aqueous electrolyte, volume content of dimethyl carbonate, weight content, density information, etc.

The vinylene carbonate is added to the non-aqueous electrolyte in an amount of 0.01% to 7% by weight, specifically 0.3% to 6% by weight, more specifically 0.4% to 3% by weight, and even more specifically 0.6% to 2% by weight. It may be included in the above range, and is preferable because the negative SEI film is properly formed to prevent electrolyte side reactions and to prevent an increase in resistance due to excessive use of additives.

On the other hand, the additive is necessary to prevent the non-aqueous electrolyte from decomposing in a high-output environment and causing cathode collapse, or to further improve low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, and battery expansion suppression at high temperatures. Accordingly, other additional additives may be included in addition to vinylene carbonate.

Examples of such additional additives include 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, and benzene-based compounds. , amine-based compounds, silane-based compounds, and lithium salt-based compounds.

The cyclic carbonate-based compound may be, for example, vinylethylene carbonate.

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

The sultone-based compounds include, for example, 1,3-propane sultone (PS), 1,4-butane sultone, ethenesultone, 1,3-propene sultone (PRS), 1,4-butene sultone, and 1- It may be at least one compound selected from the group consisting of methyl-1,3-propene sultone.

The sulfonate-based compound may contain a saturated hydrocarbon group or an unsaturated hydrocarbon group, for example, an alkenyl group or an alkynyl group.

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

The phosphate-based or phosphite-based compounds include, for example, lithium difluoro(bisoxalato)phosphate, lithium difluorophosphate, tris(trimethylsilyl) phosphate, tris(trimethylsilyl) phosphite, and tris(2). , 2,2-trifluoroethyl) phosphate and tris (trifluoroethyl) phosphite.

The borate-based compound may include tetraphenylborate, lithium difluoro(oxalato)borate (LiODFB), or lithium bisoxalatoborate (LiB(C ₂ O ₄ ) ₂ , LiBOB).

The nitrile-based compounds include, for example, succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentane carbonitrile, cyclohexane carbonitrile, From the group consisting of 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile. It may be at least one compound selected.

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

The lithium salt-based compound is a compound different from the lithium salt contained in the non-aqueous electrolyte solution, and may include lithium difluorophosphate (LiPO ₂ F ₂ ) or LiBF ₄ .

The additional additive may be used in combination of two or more types of compounds, and the total content of the vinylene carbonate and the additional additive may be 0.05 to 20% by weight, specifically 0.05 to 10% by weight, based on the total weight of the non-aqueous electrolyte. . When the total content of the additives satisfies the above range, high-temperature storage characteristics and high-temperature lifespan characteristics can be more effectively improved, and side reactions in the battery due to additives remaining after the reaction can be prevented.

The non-aqueous electrolyte can be prepared, for example, by the following method. First, ethylene carbonate (EC), dimethyl carbonate (EMC), and optionally ethylmethyl carbonate (EMC) are added in the above-described amounts, for example, dimethyl carbonate (DMC) in an organic solvent, specifically 5% to 75% by volume, or more. Specifically, the organic solvent is prepared by mixing to contain 5% to 55% by volume, 7% to 45% by volume, or 35% to 45% by volume. Next, the above-described lithium salt is dissolved in the organic solvent so that the concentration of the lithium salt is 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 is dissolved, and the content of vinylene carbonate is 0.01% to 7% by weight, specifically 0.3% by weight, based on the total weight of the non-aqueous electrolyte. to 6% by weight, more specifically 0.4% to 3% by weight, even more specifically 0.6% to 2% by weight, and the weight ratio of the vinylene carbonate to the dimethyl carbonate is greater than 0 and less than or equal to 0.2, specifically 0.01. to 0.18, more specifically 0.016 to 0.130, and even more specifically 0.02 to 0.08. Additional solvents and/or additives described above may be included in the non-aqueous electrolyte.

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

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

The battery module or battery pack is a power tool; Electric vehicles, including electric vehicles (EV), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEV); Alternatively, it can be used as a power source for any one or more mid- to large-sized devices among power storage systems.

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

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

Hereinafter, the present invention will be described in detail through examples.

At this time, the embodiments according to the present invention may be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described in detail below. Examples of the present invention are provided to more completely explain the present invention to those with average knowledge in the art.

Hereinafter, the present invention will be described in detail through specific examples.

Example

Example 1

(Non-aqueous electrolyte preparation)

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

LiPF ₆ as a lithium salt was dissolved in the organic solvent to a molar concentration of 1.0M.

Additionally, 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 included in an amount of 1% by weight in the non-aqueous electrolyte.

(Secondary battery manufacturing)

Lithium iron phosphate (LiFePO ₄ ) particles with a carbon coating layer formed as the 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 and N-methyl-2- as a solvent. A positive electrode slurry was prepared by adding pyrrolidone (NMP). The positive electrode slurry was applied and dried at a loading amount of 600 mg/25 cm ² on a positive electrode current collector (Al thin film) with a thickness of 15 μm, and then roll pressed to prepare a positive electrode (thickness of positive electrode active material: 220 ㎛). The average particle diameter (D ₅₀ ) of the positive electrode active material was 1.1 ㎛, and the lithium iron phosphate (LiFePO ₄ ) particles on which the carbon coating layer was formed were in the form of primary particles.

A cathode slurry was prepared by adding artificial graphite as a cathode active material, SBR-CMC as a binder, and carbon black as a conductive material to water as a solvent at a weight ratio of 97:2:1. The negative electrode slurry was applied and dried at a loading amount of 300 mg/25 cm ² to a 15 ㎛ thick copper (Cu) thin film, which is a negative electrode current collector, and then roll pressed to prepare a negative electrode (thickness of the negative electrode active material: 170 ㎛).

An electrode assembly was manufactured by sequentially stacking the positive electrode, polyolefin-based porous separator, and negative electrode.

The assembled electrode assembly was stored in a battery case, and then the prepared non-aqueous electrolyte solution was injected to manufacture a lithium secondary battery.

Example 2

The same method as Example 1 except that a non-aqueous electrolyte was prepared using a mixture of ethylene carbonate (EC), ethylmethyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 30:60:10 as an organic solvent. A lithium secondary battery was manufactured.

Example 3

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) and dimethyl carbonate (DMC) at a volume ratio of 30:70 as an organic solvent.

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 vinylene carbonate as an additive to the non-aqueous electrolyte at 0.5 wt% instead of 1 wt%.

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 vinylene carbonate as an additive to the non-aqueous electrolyte at 5 wt% instead of 1 wt%.

Example 6

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode was manufactured by changing the loading amount of the positive electrode slurry to 500 mg/25 cm ² instead of 600 mg/25 cm ² .

Example 7

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode was manufactured by changing the loading amount of the positive electrode slurry to 700 mg/25 cm ² instead of 600 mg/25 cm ² .

Example 8

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode was manufactured by changing the loading amount of the positive electrode slurry to 450 mg/25 cm ² instead of 600 mg/25 cm ² .

Comparative Example 1

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) and ethylmethyl carbonate (EMC) at a volume ratio of 30:70 as an organic solvent.

Comparative Example 2

A lithium secondary battery was manufactured in the same manner as Example 1, except that the non-aqueous electrolyte was prepared without adding vinylene carbonate as an additive.

Comparative Example 3

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the non-aqueous electrolyte was prepared by adding vinylene carbonate as an additive to the non-aqueous electrolyte at 8 wt% instead of 1 wt%.

Comparative Example 4

A lithium secondary battery was manufactured in the same manner as in Example 6, except that a non-aqueous electrolyte was prepared using a mixture of ethylene carbonate (EC) and ethylmethyl carbonate (EMC) at a volume ratio of 30:70 as an organic solvent.

Comparative Example 5

A non-aqueous electrolyte was prepared using a mixture of ethylene carbonate (EC), ethylmethyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 30:30:40 as an organic solvent, and the loading amount of the positive electrode slurry was 600 mg. A lithium secondary battery was manufactured in the same manner as Example 1, except that the positive electrode was manufactured at 500mg/25cm ^{2 instead of /25cm 2 .}

Comparative Example 6

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode was manufactured by changing the loading amount of the positive electrode slurry to 750 mg/25 cm ² instead of 600 mg/25 cm ² .

Comparative Example 7

A non-aqueous electrolyte was prepared using a mixture of ethylene carbonate (EC) and ethylmethyl carbonate (EMC) at a volume ratio of 30:70 as an organic solvent, and the loading amount of the positive electrode slurry was set to 400 mg/25 cm ² instead of 600 mg/25 cm ² . A lithium secondary battery was manufactured in the same manner as Example 1, except that the positive electrode was manufactured.

Comparative Example 8

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode was manufactured by changing the loading amount of the positive electrode slurry to 400 mg/25 cm ² instead of 600 mg/25 cm ² .

Comparative Example 9

A non-aqueous electrolyte was prepared using a mixture of ethylene carbonate (EC), ethylmethyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 30:30:40 as an organic solvent, and the loading amount of the positive electrode slurry was 600 mg. A lithium secondary battery was manufactured in the same manner as Example 1, except that the positive electrode was manufactured at 400mg/25cm ^{2 instead of /25cm 2 .}

	Anode loading amount (mg/25cm 2 )	non-aqueous electrolyte
		organic solvent				lithium salt	additive	VC/DMC weight ratio
		EC (volume %)	EMC (volume%)	DMC (volume %)	DEC (volume %)	LiPF 6 (mol/L)	VC (% by weight)
Example 1	600	30	30	40	-	One	One	0.030
Example 2	600	30	60	10	-	One	One	0.120
Example 3	600	30	-	70	-	One	One	0.018
Example 4	600	30	30	40	-	One	0.5	0.015
Example 5	600	30	30	40	-	One	5	0.159
Example 6	500	30	30	40	-	One	One	0.030
Example 7	700	30	30	40	-	One	One	0.030
Example 8	450	30	30	40	-	One	One	0.030
Comparative Example 1	600	30	70	-	-	One	One	-
Comparative Example 2	600	30	30	40	-	One	-	0
Comparative Example 3	600	30	30	40	-	One	8	0.263
Comparative Example 4	500	30	70	-	-	One	One	-
Comparative Example 5	500	30	30	-	40	One	One	0.030
Comparative Example 6	750	30	30	40	-	One	One	0.030
Comparative Example 7	400	30	70	-	-	One	One	-
Comparative Example 8	400	30	30	40	-	One	One	0.030
Comparative Example 9	400	30	30	-	40	One	One	0.030

Experiment 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 charged to 3.65 VC under CC/CV, 0.33 C conditions at 25°C and discharged to 2.5 V at 0.33 C to perform initial charge and discharge. The initial discharge capacity (unit: mAh) was measured.

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

Experimental Example 2: Cycle charge/discharge capacity maintenance rate evaluation

The lithium secondary batteries of Examples 1 to 8 and Comparative Examples 1 to 9 prepared above were charged to 3.65 VC under CC/CV, 0.33 C conditions at 25°C and discharged to 2.5 V at 0.33 C as one cycle. The subsequent discharge capacity and resistance were measured. At this time, the resistance was measured using the voltage drop difference obtained by checking the capacity at room temperature, charging to SOC 50% based on the discharge capacity, and discharging for 10 seconds at 2.5C current.

Then, after 200 cycles of charging and discharging were performed under the above charging and discharging conditions, the capacity maintenance rate (%) and resistance increase rate (%) were measured. Capacity retention rate (%) was calculated according to [Equation 1] below, and resistance increase rate (%) was calculated according to [Equation 2] below. The measurement results are listed in Table 2 below.

[Equation 1]

Capacity maintenance rate (%) = (discharge capacity after 200 cycles/discharge capacity after 1 cycle) × 100

[Equation 2]

Resistance increase rate (%) = {(resistance after 200 cycles - resistance after 1 cycle)/resistance after 1 cycle}×100

	Experimental Example 1			Experimental Example 2
	Cell design capacity (mAh)	Initial discharge capacity (mAh)	Capacity development rate (%)	Capacity maintenance rate (%, 200th cycle)	resistance increase rate (%, 200th 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
Comparative Example 1	730	973	92.2	81.2	34.4
Comparative Example 2	730	724	99.2	84.0	22.8
Comparative Example 3	730	701	96.0	89.1	23.5
Comparative Example 4	610	588	96.4	85.6	23.7
Comparative Example 5	610	558	91.5	86.1	20.1
Comparative Example 6	916	831	90.7	81.4	35.2
Comparative Example 7	490	486	99.2	93.2	10.4
Comparative Example 8	490	487	99.4	93.4	10.0
Comparative Example 9	490	486	99.2	93.6	10.0

Referring to Table 2, the lithium secondary batteries of Examples 1 to 8 according to the present invention show superior capacity development effect, excellent life performance, and low resistance increase rate compared to Comparative Examples 1 to 6. You can check it.

In addition, in the case of Example 6, in which the anode loading amount was designed at 500mg/25cm ² , it can be seen that the capacity development effect is superior to Comparative Example 4 in which dimethyl carbonate is not used, and it shows excellent lifespan performance and a low resistance increase rate. .

Meanwhile, referring to Comparative Examples 7 to 9 in which the anode loading amount was designed at 400 mg/25 cm ² , it can be seen that the loading amount is adjusted low and the electrolyte impregnation is not a major problem, so it is not significantly affected by the components and content of the non-aqueous electrolyte. there is. Specifically, comparing Comparative Examples 7 and 8, it can be seen that even when dimethyl carbonate is used as an organic solvent component, the effect improvement in terms of capacity development, life performance, and resistance increase rate is minimal. In addition, Comparative Example 9, which used a linear carbonate other than dimethyl carbonate, showed the same or similar level of performance as Comparative Examples 7 and 8. Through this, the non-aqueous electrolyte according to the present invention is used in a positive electrode containing lithium iron phosphate at a certain loading amount (for example, 400 mg/25 cm ² or more and less than 750 mg/25 cm ² , more specifically 450 mg/25 cm ² to 740 mg/25 cm ² ). It can be confirmed that it exhibits excellent effects.

Claims (17)

1. Contains an anode, a cathode, 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 anode is 450mg/25cm ² to 740mg/25cm ² ,

   The non-aqueous electrolyte includes lithium salt, organic solvent and additives,

   The organic solvent includes a cyclic carbonate-based solvent and a linear carbonate-based solvent,

   The cyclic carbonate-based solvent includes ethylene carbonate,

   The linear carbonate-based solvent includes dimethyl carbonate,

   The additive includes vinylene carbonate,

   The dimethyl carbonate is contained in the organic solvent in an amount of 5% to 75% by volume,

   A lithium secondary battery wherein the weight ratio of the vinylene carbonate to the weight of the dimethyl carbonate is greater than 0 and less than or equal to 0.2.
2. In claim 1,

   A lithium secondary battery in which the loading amount of the positive electrode is 450mg/25cm ² to 700mg/25cm ² .
3. In claim 1,

   A lithium secondary battery in which the loading amount of the positive electrode is 500mg/25cm ² to 600mg/25cm ² .
4. In claim 1,

   A lithium secondary battery wherein the vinylene carbonate is included in the non-aqueous electrolyte in an amount of 0.01% to 7% by weight.
5. In claim 1,

   A lithium secondary battery wherein the volume ratio of the cyclic carbonate-based solvent and the linear carbonate-based solvent is 10:90 to 50:50.
6. In claim 1,

   A lithium secondary battery wherein the linear carbonate-based solvent further includes ethylmethyl carbonate.
7. In claim 6,

   The organic solvent is a lithium secondary battery comprising 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 ethylmethyl carbonate.
8. In claim 1,

   The lithium salt is LiCl, LiBr, LiI, 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 ) A lithium secondary battery comprising at least one member selected from the group consisting of ₂ ).
9. In claim 1,

   A lithium secondary battery wherein the lithium salt is contained in the non-aqueous electrolyte at a concentration of 0.8 M to 3.0 M.
10. In claim 1,

    The lithium iron phosphate particles are a lithium secondary battery comprising a compound represented by the following formula (A):

    [Formula A]

    Li _1+a Fe _1-s M _s (PO _4-b )X _b

    In the formula A, M is one or more elements selected from Co, Ni, Mn, Al, Mg, Ti and V, X is F, S, or N, 0≤s≤0.5; -0.5≤a≤+0.5; 0≤b≤0.1.
11. In claim 1,

    The lithium iron phosphate particles are a lithium secondary battery containing LiFePO ₄
12. In claim 1,

    The lithium iron phosphate particles are in the form of primary particles,

    A lithium secondary battery wherein the average particle diameter (D ₅₀ ) of the lithium iron phosphate particles is 0.2 to 3.0 ㎛.
13. In claim 1,

    A lithium secondary battery wherein the lithium iron phosphate particles include a carbon coating layer on the surface.
14. In claim 1,

    A lithium secondary battery in which the positive electrode active material does not contain lithium nickel-based oxide.
15. In claim 1,

    The negative electrode is a lithium secondary battery containing a carbon-based active material.
16. In claim 15,

    A lithium secondary battery wherein the carbon-based active material includes at least one selected from the group consisting of natural graphite and artificial graphite.
17. Manufacturing an electrode assembly including an anode, a cathode, and a separator;

    Storing the electrode assembly in a battery case;

    Preparing a non-aqueous electrolyte comprising a lithium salt, an organic solvent, and additives; and

    Including the step of 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 anode is 450mg/25cm ² to 740mg/25cm ² ,

    The non-aqueous electrolyte includes lithium salt, organic solvent and additives,

    The organic solvent includes a cyclic carbonate-based solvent and a linear carbonate-based solvent,

    The cyclic carbonate-based solvent includes ethylene carbonate,

    The linear carbonate-based solvent includes dimethyl carbonate,

    The additive includes vinylene carbonate,

    The dimethyl carbonate is contained in the organic solvent in an amount of 5% to 75% by volume,

    A method of manufacturing a lithium secondary battery, wherein the weight ratio of the vinylene carbonate to the weight of the dimethyl carbonate is greater than 0 and less than or equal to 0.2.