Lithium secondary battery

Abstract

A lithium secondary battery includes: a positive electrode; a negative electrode; a separator interposed between the positive electrode and the negative electrode; and a nonaqueous electrolyte. The positive electrode includes a positive electrode active material including a lithium-rich manganese-rich oxide containing 50 mol% or more of Mn among all metal elements other than lithium and having a molar ratio of lithium to a transition metal of more than 1, and the non-aqueous electrolyte includes a lithium salt, an organic solvent, and an additive, the organic solvent contains a first organic solvent and a second organic solvent, the first organic solvent contains ethylene carbonate, the second organic solvent contains diethyl carbonate and ethyl methyl carbonate, and the additive contains a cyclic sulfur oxide represented by a specific chemical formula.

Description

[0001] Cross-reference to related applications

[0002] This application is based on and claims the benefit of priority from Korean Patent Application No. 10-2023-0040007, filed on March 27, 2023, and Korean Patent Application No. 10-2023-0183782, filed on December 15, 2023, in the Korean Intellectual Property Office, the disclosures of which are incorporated herein in their entirety by reference. Technical Field

[0003] The present invention relates to a lithium secondary battery. Background Art

[0004] In recent years, the application of lithium secondary batteries has rapidly expanded from power supply for electronic devices such as electricity, electronics, communications, and computers to energy storage and power supply for large-scale equipment such as automobiles and energy storage systems. As a result, the demand for secondary batteries with high capacity, high power, and high stability is increasing.

[0005] Lithium secondary batteries typically include a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, an electrolyte as a lithium ion transport medium, and a separator. In this case, the negative electrode active material can be a carbon-based active material or a silicon-based active material. In addition, the positive electrode active material can be a lithium transition metal oxide, such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a lithium nickel cobalt manganese composite oxide.

[0006] At the same time, improvements are being made to the respective characteristics of the positive electrode, negative electrode, electrolyte, and separator to construct high-capacity secondary batteries. Summary of the Invention

[0007] Technical issues

[0008] The present invention provides a lithium secondary battery comprising an over-lithium manganese-rich oxide as a positive electrode active material, which reduces the generation of gases such as CO2 at the positive electrode interface during high-voltage or high-temperature operation, reduces gas generation during initial activation and charge and discharge, and inhibits the dissolution of transition metals from the positive electrode active material, thereby simultaneously improving life at high temperatures, reducing resistance, improving durability, and preventing gas generation.

[0009] Technical Solution

[0010] The present invention provides a lithium secondary battery comprising: a positive electrode; a negative electrode; a separator interposed between the positive electrode and the negative electrode; and a non-aqueous electrolyte, wherein the positive electrode comprises a positive electrode active material, the positive electrode active material comprising a perlithium manganese-rich oxide containing about 50 mol % or more of Mn in all metal elements other than lithium and a molar ratio of lithium to transition metal exceeding about 1, the non-aqueous electrolyte comprising a lithium salt, an organic solvent, and an additive, the organic solvent comprising a first organic solvent and a second organic solvent, the first organic solvent comprising ethylene carbonate, the second organic solvent comprising diethyl carbonate and ethyl methyl carbonate, and the additive comprising a compound represented by Chemical Formula 1:

[0011] (Chemical Formula 1)

[0012]

[0013] In Chemical Formula 1, n is 1 or 2; L1 and L2 are each independently a direct bond or an alkylene group having 1 to 6 carbon atoms which may be substituted or unsubstituted; R1 and R2 are each independently selected from a substituent represented by the following Chemical Formula 2, an alkyl group having 1 to 10 carbon atoms, an alkyl group having 1 to 10 carbon atoms substituted with one or more fluorine atoms, an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, a phosphate group, and a nitrile group; and at least one of R1 and R2 is a substituent represented by Chemical Formula 2:

[0014] (Chemical Formula 2)

[0015]

[0016] In Chemical Formula 2, m is 1 or 2; X1 and X2 are each independently -O- or -C(R 31 )(R 32 )-, provided that at least one of X1 and X2 is -O-; R 31 to R 36Each of the following is independently hydrogen, an alkyl group having 1 to 6 carbon atoms, -C(=O)-R4 or -R5-OC(=O)-R6; R4 and R6 are each independently a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, an alkynyl group having 2 to 20 carbon atoms or an aryl group having 6 to 20 carbon atoms; R5 is a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms; alkylene group having from 1 to 6 carbon atoms; each substituent of L1, L2, R4, R5 and R6 is at least one independently selected from the group consisting of deuterium, -F, -Cl, -Br, -I, -CN, -NO2 and -SO3; * is the bonding position to L1 or L2, when L1 and L2 are both directly bonded, then R1 and R2 are not simultaneously CS-7 below; when L1 and L2 are both methylene and n is 2, then R1 and R2 are not simultaneously CS-2 below.

[0017]

[0018] Beneficial effects

[0019] The lithium secondary battery of the present invention adopts perlithium manganese-rich oxide as the positive electrode active material, and the non-aqueous electrolyte comprises a lithium salt, an organic solvent and an additive, wherein the organic solvent comprises ethylene carbonate, diethyl carbonate and ethyl methyl carbonate, and the additive comprises a cyclic sulfur oxide represented by a specific chemical formula. According to the present invention, the combination of the above-mentioned organic solvents makes it possible to significantly reduce the amount of gas generated at the positive electrode interface containing perlithium manganese-rich oxide, improve the life performance of the negative electrode, and thus provide a lithium secondary battery with excellent capacity retention and gas generation reduction performance. For example, the cyclic sulfur oxide included as an additive has a low consumption rate in the secondary battery, so that the long-term durability can be continuously improved when the secondary battery is in operation. Therefore, the lithium secondary battery of the present invention can simultaneously improve life, reduce resistance, improve durability and prevent gas generation, especially at high temperature and high voltage. DETAILED DESCRIPTION

[0020] In the following detailed description, reference is made to the accompanying drawings which form a part hereof. The illustrative embodiments described in the detailed description, drawings, and claims are not intended to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented herein.

[0021] In this specification, terms such as "comprising", "setting" or "having" are intended to specify the existence of stated features, numbers, steps, operations, ingredients, parts or their combinations, but should not be interpreted as excluding the possibility of the existence or addition of one or more other features, numbers, steps, operations, ingredients, parts or their combinations.

[0022] As used herein, the average particle size (D50) can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve. The average particle size (D50) can be measured using, for example, laser diffraction. Laser diffraction methods are generally capable of measuring particle sizes from the submicron range to several millimeters, and can produce results with high reproducibility and resolution.

[0023] The words "about," "approximately," and "substantially" as used herein are used to indicate a range or approximation of values ​​or degrees taking into account inherent manufacturing and material tolerances, and are used to prevent infringers from improperly taking advantage of the present disclosure where precise or absolute values ​​are provided to aid in understanding the present disclosure.

[0024] Over-lithium manganese-rich oxides have attracted much attention as the next generation of positive electrode active materials for building high-capacity batteries. Over-lithium manganese-rich oxides are a relatively cheap and abundant source of manganese (Mn), and lithium secondary batteries using over-lithium manganese-rich oxides have the advantage of high capacity. However, the application of these over-lithium manganese-rich oxides has the problem of significantly increasing the production of gases such as CO2 due to electrolyte side reactions at the positive electrode interface when operating at high voltage (for example, above 4.35V) or high temperature. In addition, in the case of over-lithium manganese-rich oxides, the active oxygen generated by the phase transition of the positive electrode active material during activation (formation), charging and discharging will aggravate the decomposition of the electrolyte and greatly increase the production of gases such as CO2. The transition metal dissolved from the positive electrode active material is electrodeposited on the negative electrode, thereby destroying the solid electrolyte interface (SEI) film of the negative electrode, and the application of this material is limited.

[0025] The present invention provides a lithium secondary battery, which solves the aforementioned gas generation problem and SEI film destruction problem of the negative electrode while using over-lithium manganese-rich oxide as the positive electrode active material of the lithium secondary battery.

[0026] Hereinafter, the present invention will be described in more detail.

[0027] lithium secondary batteries

[0028] The present invention relates to a lithium secondary battery.

[0029] The lithium secondary battery of the present invention includes: a positive electrode; a negative electrode; a separator inserted between the positive electrode and the negative electrode; and a non-aqueous electrolyte, wherein the positive electrode includes a positive electrode active material, the positive electrode active material includes a perlithium manganese-rich oxide containing about 50 mol% or more of Mn in all metal elements other than lithium and a molar ratio of lithium to transition metal exceeding about 1, the non-aqueous electrolyte includes a lithium salt, an organic solvent and an additive, the organic solvent includes a first organic solvent and a second organic solvent, the first organic solvent includes ethylene carbonate, the second organic solvent includes diethyl carbonate and ethyl methyl carbonate, and the additive includes a compound represented by Chemical Formula 1:

[0030] (Chemical Formula 1)

[0031]

[0032] In Chemical Formula 1, n is 1 or 2; L1 and L2 are each independently a direct bond or an alkylene group having 1 to 6 carbon atoms which may be substituted or unsubstituted; R1 and R2 are each independently selected from a substituent represented by the following Chemical Formula 2, an alkyl group having 1 to 10 carbon atoms, an alkyl group having 1 to 10 carbon atoms substituted with one or more fluorine atoms, an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, a phosphate group, and a nitrile group; and at least one of R1 and R2 is a substituent represented by Chemical Formula 2:

[0033] (Chemical Formula 2)

[0034]

[0035] In Chemical Formula 2, m is 1 or 2; X1 and X2 are each independently -O- or -C(R 31 )(R 32 )-, provided that at least one of X1 and X2 is -O-; R 31 to R 36 Each of the following is independently hydrogen, an alkyl group having 1 to 6 carbon atoms, -C(=O)-R4 or -R5-OC(=O)-R6; R4 and R6 are each independently a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, an alkynyl group having 2 to 20 carbon atoms or an aryl group having 6 to 20 carbon atoms; R5 is a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms; alkylene group having from 1 to 6 carbon atoms; each substituent of L1, L2, R4, R5 and R6 is at least one independently selected from the group consisting of deuterium, -F, -Cl, -Br, -I, -CN, -NO2 and -SO3; * is the bonding position to L1 or L2, when L1 and L2 are both directly bonded, then R1 and R2 are not simultaneously CS-7 below; when L1 and L2 are both methylene and n is 2, then R1 and R2 are not simultaneously CS-2 below.

[0036]

[0037] The lithium secondary battery comprises a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte. For example, the lithium secondary battery comprises a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. The lithium secondary battery can be manufactured by housing an electrode assembly comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode in a battery housing, and injecting a non-aqueous electrolyte into the battery housing.

[0038] (1) Positive electrode

[0039] The positive electrode contains a positive electrode active material.

[0040] The positive electrode active material of the present invention comprises an over-lithiated manganese-rich oxide containing about 50 mol % or more of Mn in all metal elements except lithium and a molar ratio of lithium to transition metal exceeding about 1.

[0041] Over-lithium manganese-rich oxide has attracted much attention as a next-generation high-capacity positive electrode active material, but its application is limited due to the inherent structural degradation of the material. For example, when over-lithium manganese-rich oxide is used as a positive electrode active material, there is a problem of electrolyte side reactions occurring at the positive electrode interface and a significant increase in the amount of gases such as carbon dioxide (CO2) produced. In addition, during the initial activation process of a lithium secondary battery containing over-lithium manganese-rich oxide, the active oxygen released from the over-lithium manganese-rich oxide decomposes and consumes the organic solvent (such as ethylene carbonate) contained in the non-aqueous electrolyte, thereby producing gaseous by-products, resulting in a decrease in life performance, an increase in resistance, and a decrease in safety. In addition, there is a problem of manganese (Mn) being dissolved to balance the charge due to the release of active oxygen during the charge and discharge process of a lithium secondary battery containing over-lithium manganese-rich oxide. At this time, the dissolved manganese is electrodeposited on the negative electrode and destroys the solid electrolyte interface (SEI) film, and the active oxygen released during the charge and discharge process continuously decomposes and consumes the organic solvent in the non-aqueous electrolyte, thereby increasing the generation of gaseous by-products. The depletion of non-aqueous electrolytes, the structural collapse of over-lithiation manganese-rich oxides, and the increase in gas by-products significantly reduce the lifespan, resistance characteristics, and safety of lithium secondary batteries. Furthermore, these problems are exacerbated under high temperature and high voltage conditions.

[0042] In order to solve these problems, as described later, the lithium secondary battery of the present invention contains ethylene carbonate, diethyl carbonate and ethyl methyl carbonate as organic solvents of the non-aqueous electrolyte, and the additive includes a compound represented by Chemical Formula 1. According to the present invention, the combination of the components of the non-aqueous electrolyte makes it possible to significantly reduce the amount of gas generated at the positive electrode interface containing excessive lithium manganese-rich oxide, improve the life performance of the negative electrode, and thus provide a lithium secondary battery with excellent capacity retention and gas generation reduction performance compared to conventional lithium secondary batteries. The lithium secondary battery of the present invention can have excellent life performance and gas reduction performance, especially at high temperature and high voltage.

[0043] The perlithium manganese-rich oxide may include a compound represented by Chemical Formula X:

[0044] (Chemical Formula X)

[0045] Li 1+s [Ni t Cou Mn v M 1 w ]O 2+z

[0046] In chemical formula X, M 1 is at least one selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo; and s, t, u, v, w, and z satisfy 0.05≤s≤1, 0≤t≤0.5, 0≤u≤0.3, 0.5≤v<1.0, 0≤w≤0.2, and 0≤z≤1. For example, in the chemical formula X, s, t, u, v, w, and z may satisfy 0.05≤s≤1.0, 0.1≤t≤0.5, 0≤u≤0.1, 0.5≤v<1.0, 0≤w≤0.2, and 0≤z≤1. Alternatively, in the chemical formula X, s, t, u, v, w, and z may satisfy 0.10≤s≤0.50, 0.1≤t≤0.5, 0≤u≤0.1, 0.6≤v<1.0, 0≤w≤0.1, and 0≤z≤0.50.

[0047] According to one embodiment, the perlithiated manganese-rich oxide may include a compound represented by Chemical Formula Y:

[0048] (Chemical formula Y)

[0049] XLi2MnO3·(1-X)Li[Ni 1-y-z-w Mn y Co z M 1 w ]O2

[0050] In chemical formula Y, M 1 is at least one selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo. Furthermore, in the chemical formula Y, X, y, z, and w may satisfy 0.1≤X≤0.5, 0.5≤y<1, 0≤z≤0.3, and 0≤w≤0.2, for example, 0.2≤X≤0.5, 0.5≤y<1, 0≤z≤0.1, and 0≤w≤0.2, or 0.3≤X≤0.5, 0.6≤y<1, 0≤z≤0.1, and 0≤w≤0.2.

[0051] The positive electrode may include a positive electrode current collector and a positive electrode active material layer provided on at least one side of the positive electrode current collector. In this case, the positive electrode active material layer may contain a positive electrode active material.

[0052] The positive electrode current collector is not particularly limited and may be any positive electrode current collector having high conductivity and not causing chemical changes in the battery. For example, the positive electrode current collector may include at least one selected from the group consisting of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, and aluminum-cadmium alloy. According to one embodiment, the positive electrode current collector may include aluminum.

[0053] The thickness of the positive electrode current collector may generally be about 3 μm to 500 μm.

[0054] The positive electrode current collector may have fine concavoconvexities formed on the surface to enhance the binding force of the positive electrode active material. For example, the positive electrode current collector can be used in various forms such as film, sheet, foil, mesh, porous body, foam and non-woven fabric.

[0055] The positive electrode active material layer may be provided on at least one side of the positive electrode current collector, for example, on one side or both sides of the positive electrode current collector.

[0056] Considering sufficient capacity of the positive electrode active material, the content of the positive electrode active material in the positive electrode active material layer may be about 80 wt % to 99 wt %, for example, about 92 wt % to 98.5 wt %.

[0057] Since the positive electrode active material has been described above, further description will be omitted.

[0058] The positive electrode active material layer may further include a binder and / or a conductive material together with the positive electrode active material.

[0059] The binder is a component that assists in combining the active material with the conductive material and with the current collector, and for example, may include at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluororubber. According to one embodiment, the binder may include polyvinylidene fluoride.

[0060] To ensure sufficient binding force between the positive electrode active material and other components, the content of the binder in the positive electrode active material layer may be about 1 wt % to 20 wt %, for example, about 1.2 wt % to 10 wt %.

[0061] Conductive materials can be used to assist and improve the conductivity of secondary batteries. There are no particular limitations and they can be any material that is conductive and does not cause chemical changes. For example, the positive electrode conductive material may include at least one selected from the group consisting of: graphite, such as natural graphite or artificial graphite; carbon black, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers, such as carbon fibers and metal fibers; conductive tubes, such as carbon nanotubes; fluorocarbons; metal powders, such as aluminum and nickel powders; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium dioxide; and polyphenylene derivatives. According to one embodiment, in terms of improving conductivity, the positive electrode conductive material may include carbon nanotubes.

[0062] In terms of ensuring sufficient electrical conductivity, the conductive material may be contained in the positive electrode active material layer in an amount of about 1 wt % to 20 wt %, for example, about 1.2 wt % to 10 wt %.

[0063] The thickness of the positive active material layer may be about 30 μm to 400 μm, for example, about 40 μm to 110 μm.

[0064] 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 a positive electrode current collector, followed by drying and rolling.

[0065] The positive electrode slurry forming solvent may include an organic solvent, such as N-methyl-2-pyrrolidone (NMP). The positive electrode slurry may have a solid content of about 40 wt % to 90 wt %, for example, about 50 wt % to 80 wt %.

[0066] (2) Negative electrode

[0067] The negative electrode may be opposite the positive electrode.

[0068] The negative electrode contains a negative electrode active material.

[0069] The negative electrode active material is a material capable of reversibly intercalating and deintercalating lithium ions, and may include at least one selected from the group consisting of a carbon-based active material, a (quasi)metallic active material, and lithium metal. For example, the negative electrode active material may include at least one selected from a carbon-based active material and a (quasi)metallic active material.

[0070] The carbon-based active material may include at least one selected from the group consisting of artificial graphite, natural graphite, hard carbon, soft carbon, carbon black, graphene, and fibrous carbon. For example, the carbon-based active material may include at least one selected from the group consisting of artificial graphite and natural graphite.

[0071] In terms of ensuring structural stability during charge and discharge and reducing side reactions with the electrolyte, the average particle size (D50 ) may be about 10 μm to 30 μm, for example about 15 μm to 25 μm.

[0072] For example, the (quasi)metallic active material may include at least one selected from the group consisting of (quasi)metallic, alloys of (quasi)metallic and lithium, (quasi)metallic oxides, lithium titanium oxide (LTO), and lithium vanadium oxide.

[0073] The (quasi)metal may include at least one 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.

[0074] The alloy of a (quasi)metal and lithium may include an alloy of lithium and at least one (quasi)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.

[0075] The oxide of a (quasi)metal may include an oxide of at least one (quasi)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.

[0076] According to one embodiment, the (quasi)metal-based active material may include a silicon-based active material.

[0077] Silicon-based active materials may include SiO x (0≤x<2) represents a compound. In the case of SiO2, since SiO2 does not react with lithium ions, it cannot store lithium. Therefore, x is selected to be within the above range except 2. According to one embodiment, the silicon-based active material may be SiO.

[0078] In terms of ensuring structural stability during charge and discharge and reducing side reactions with the electrolyte, the average particle size (D 50 ) may be about 1 μm to 30 μm, for example, about 2 μm to 15 μm.

[0079] The negative electrode may include a negative electrode current collector and a negative electrode active material layer provided on at least one side of the negative electrode current collector. In this case, the negative electrode active material layer may contain a negative electrode active material.

[0080] The negative electrode current collector is not particularly limited and may be any negative electrode current collector having high conductivity and not causing chemical changes in the battery. For example, 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, or silver, and aluminum-cadmium alloy.

[0081] The thickness of the negative electrode current collector may generally be about 3 μm to 500 μm.

[0082] The negative electrode current collector may have fine concavoconvexities formed on its surface to enhance the binding 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 bodies, foams, and non-woven fabrics.

[0083] The negative electrode active material layer may be provided on at least one side of the negative electrode current collector, for example, on one side or both sides of the negative electrode current collector.

[0084] The content of the negative electrode active material in the negative electrode active material layer may be about 60 wt % to 99 wt %, for example, about 75 wt % to 95 wt %.

[0085] Since the positive electrode active material has been described above, further description will be omitted.

[0086] The negative electrode active material layer may further include a binder and / or a conductive material together with the negative electrode active material.

[0087] The binder is used to improve the battery performance by improving the adhesion between the negative electrode active material layer and the negative electrode collector, thereby improving the battery performance, and may include, for example, at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene propylene diene monomer rubber (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber and substances in which hydrogen is replaced by Li, Na or Ca, and may also include various copolymers thereof.

[0088] The binder may be present in the negative active material layer in an amount of about 0.5 wt % to 10 wt %, for example, about 1 wt % to 5 wt %.

[0089] The conductive material is not particularly limited and can be any material that is conductive and does not cause chemical changes within the battery. Examples include: graphite, such as natural graphite or artificial graphite; carbon black, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers, such as carbon fibers and metal fibers; conductive tubes, such as carbon nanotubes; fluorocarbons; metal powders, such as aluminum and nickel powders; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium dioxide; and conductive materials, such as polyphenylene derivatives.

[0090] The conductive material may be included in an amount of about 0.5 wt % to 10 wt %, for example, about 1 wt % to 5 wt %.

[0091] The thickness of the negative active material layer may be about 10 μm to 200 μm, for example, about 20 μm to 150 μm.

[0092] The negative electrode can be manufactured by coating a negative electrode slurry containing a negative electrode active material, a binder, a conductive material, and a solvent for forming a negative electrode slurry on at least one side of a negative electrode current collector, followed by drying and rolling.

[0093] In terms of promoting the dispersion of the negative electrode active material, binder and / or conductive material, 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 isopropanol. According to one embodiment, the solvent may include distilled water. The solid content of the negative electrode slurry may be about 30% to 80% by weight, for example, about 40% to 70% by weight.

[0094] (3) Diaphragm

[0095] A separator may be inserted between the positive electrode and the negative electrode.

[0096] In addition, operable barrier film can be any porous polymer film commonly used as barrier film, for example, the porous polymer film made of polyolefin polymer (such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer), it can be used alone or laminated.Or, operable barrier film here can be any porous nonwoven fabric, for example, the nonwoven fabric made of high melting point glass fiber or polyethylene terephthalate fiber etc., but is not limited thereto.In addition, the coating barrier film comprising ceramic component or polymer material can be used to ensure heat resistance or mechanical strength, and can alternatively be used with single layer or multilayer structure.

[0097] (4) Non-aqueous electrolytes

[0098] The nonaqueous electrolyte includes a lithium salt and an organic solvent.

[0099] 1) Lithium salt

[0100] As the lithium salt used here, various lithium salts commonly used in non-aqueous electrolytes for lithium secondary batteries can be used without limitation. For example, the lithium salt includes Li + , and as an anion selected from 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 - 、(FSO2)2N - CF3CF2(CF3)2CO - 、(CF3SO2)2CH - 、CH3SO3 - CF3(CF2)7SO3 - CF3CO2 - 、CH3CO2 - 、SCN - and (CF3CF2SO2)2N - At least one of the group consisting of.

[0101] For example, the lithium salt may include a salt 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, LiFSI (LiN (SO2F) 2), LiCH3SO3, LiCF3CO2, LiCH3CO2 and LiBETI (LiN (SO2CF2CF3) 2). For example, the lithium salt may include at least one 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).

[0102] The concentration of the lithium salt contained in the non-aqueous electrolyte may be about 0.5 M to 5 M, for example, about 0.8 M to 4 M, or about 0.8 M to 2.0 M. When the concentration of the lithium salt satisfies the above range, the lithium ion yield (Li + The transference number) and the dissociation degree of lithium ions are improved, thereby improving the output characteristics of the battery.

[0103] 2) Organic solvents

[0104] The organic solvent includes a first organic solvent and a second organic solvent.

[0105] The first organic solvent includes ethylene carbonate.

[0106] Ethylene carbonate is an organic solvent with high viscosity and high dielectric constant, which can facilitate the dissociation of lithium salts in the electrolyte.

[0107] In addition to ethylene carbonate, the first organic solvent may further include at least one selected from the group consisting of fluoroethylene carbonate (FEC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone and ε-caprolactone, but is not limited thereto.

[0108] The second organic solvent includes diethyl carbonate and ethyl methyl carbonate.

[0109] In the lithium secondary battery of the present invention, owing to comprising diethyl carbonate as the second organic solvent, the oxidative stability of the nonaqueous electrolyte is improved, thereby enhancing the effect of reducing gas generation. Therefore, the life performance of the lithium secondary battery comprising excessive lithium manganese-rich oxide can be significantly improved. Meanwhile, when using diethyl carbonate alone as straight-chain carbonate ester, there is the problem that ionic conductivity is relatively low, electrolyte impregnation is relatively low due to viscosity increase, and initial resistance increases. However, these shortcomings can be offset by using ethyl methyl carbonate with relatively low viscosity and excellent ionic conductivity. When using ethyl methyl carbonate, compared with the situation of using other straight-chain carbonate esters other than ethyl methyl carbonate such as dimethyl carbonate, better effect is achieved.

[0110] Moreover, by using a first organic solvent (comprising ethylene carbonate) and a second organic solvent (comprising diethyl carbonate and ethyl methyl carbonate), the present invention can have an excellent capacity retention rate and reduce the amount of gas generated, thereby preventing, for example, volume expansion of the battery cell. Although a combination of diethyl carbonate and ethyl methyl carbonate is used as the second organic solvent in this embodiment, any solvent or any combination of solvents that can reduce the amount of carbon dioxide (CO2) generated when the over-lithium manganese-rich oxide is used as a positive electrode component and has low reactivity with the active oxygen that may be released by the over-lithium manganese-rich oxide can be used as the second organic solvent.

[0111] Although the effects of the present invention, such as the feature of reducing the amount of gas generated in lithium secondary batteries as described above, are uniquely manifested when using lithium-rich manganese oxide as a positive electrode active material, the organic solvent of the present invention can be combined for limited purposes in other positive electrode active materials such as high-nickel lithium nickel manganese cobalt transition metal oxides (for example, NCM-type active materials containing 80 mol% or more of Ni as a transition metal) where the generation of active oxygen and excessive dissolution of Mn are not significant problems.

[0112] Meanwhile, the second organic solvent may further contain other additional organic solvents together with diethyl carbonate at a level that does not impair the above-mentioned effects.

[0113] For example, the second organic solvent may further include at least one selected from the group consisting of dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate.

[0114] The volume ratio of the first organic solvent to the second organic solvent may be about 10:90 to 50:50, for example, about 15:85 to 40:60, or about 15:85 to 35:65. When the volume ratio is within the above range, high ion transportability and an appropriate viscosity level of the non-aqueous electrolyte can be achieved while reducing gas generation of the above-mentioned over-lithiation manganese-rich oxide, thereby further improving the life performance of the positive and negative electrodes.

[0115] In addition, the organic solvent can include about 10% to 50% by volume of ethylene carbonate, about 5% to 80% by volume of diethyl carbonate and about 5% to 80% by volume of ethyl methyl carbonate. For example, the organic solvent can include about 15% to 40% by volume of ethylene carbonate, about 8% to 75% by volume of diethyl carbonate and about 8% to 75% by volume of ethyl methyl carbonate. Alternatively, the organic solvent can include about 15% to 35% by volume of ethylene carbonate, about 30% to 50% by volume of diethyl carbonate and about 30% to 50% by volume of ethyl methyl carbonate. Within the above range, the high ion transportability and appropriate viscosity level of nonaqueous electrolyte can be achieved, while reducing the gas generation of the above-mentioned excessive lithium manganese-rich oxide, thereby further improving the life performance of the positive and negative electrodes.

[0116] Meanwhile, if necessary, the organic solvent may further include an organic solvent commonly used in non-aqueous electrolytes without limitation. For example, the organic solvent may include at least one other organic solvent selected from the group consisting of ether organic solvents, glycol ether solvents, and nitrile organic solvents.

[0117] The ether solvent used here can be any one selected from the group consisting of dimethyl ether, ethyl 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.

[0118] The glycol ether solvent has a high dielectric constant and low surface tension compared to the linear carbonate organic solvent, and has low reactivity with metals, and may include at least one selected from the group consisting of dimethoxyethane (glyme dimethyl ether, DME), diethoxyethane, diethylene glycol ether, triethylene glycol ether, and tetraethylene glycol ether (TEGDME), but is not limited thereto.

[0119] The nitrile solvent may include at least one selected from the group consisting of acetonitrile, propionitrile, butyronitrile, valeronitrile, octanonitrile, heptanecarbonitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, benzyl acetonitrile, 2-fluorophenyl acetonitrile and 4-fluorophenyl acetonitrile, but is not limited thereto.

[0120] 3) Additives

[0121] The nonaqueous electrolyte contains additives.

[0122] The additive may include a compound represented by Chemical Formula 1:

[0123] (Chemical Formula 1)

[0124]

[0125] In Chemical Formula 1, n is 1 or 2; L1 and L2 are each independently a direct bond or an alkylene group having 1 to 6 carbon atoms which may be substituted or unsubstituted; R1 and R2 are each independently selected from a substituent represented by the following Chemical Formula 2, an alkyl group having 1 to 10 carbon atoms, an alkyl group having 1 to 10 carbon atoms substituted with one or more fluorine atoms, an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, a phosphate group, and a nitrile group; and at least one of R1 and R2 is a substituent represented by Chemical Formula 2:

[0126] (Chemical Formula 2)

[0127]

[0128] In Chemical Formula 2, m is 1 or 2, X1 and X2 are each independently -O- or -C(R 31 )(R 32 )-, provided that at least one of X1 and X2 is -O-; R 31 to R 36 Each of the following is independently hydrogen, an alkyl group having 1 to 6 carbon atoms, -C(=O)-R4 or -R5-OC(=O)-R6; R4 and R6 are each independently a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, an alkynyl group having 2 to 20 carbon atoms or an aryl group having 6 to 20 carbon atoms; R5 is a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms; alkylene group having from 1 to 6 carbon atoms; each substituent of L1, L2, R4, R5 and R6 is at least one independently selected from the group consisting of deuterium, -F, -Cl, -Br, -I, -CN, -NO2 and -SO3; * is the bonding position to L1 or L2, when L1 and L2 are both directly bonded, then R1 and R2 are not simultaneously CS-7 below; when L1 and L2 are both methylene and n is 2, then R1 and R2 are not simultaneously CS-2 below.

[0129]

[0130] The compound represented by Chemical Formula 1 has a sulfur oxide structure in the center and a cyclic sulfur oxide structure at at least one of the two ends. By adopting such a chemical structure, the compound can induce the stable formation of anions when used as an additive for a non-aqueous electrolyte, and can further ensure the formation of a stable SEI layer. For example, the compound represented by Chemical Formula 1 has a lower consumption rate in a secondary battery than other cyclic sulfur oxides (e.g., 1,3-propane sultone), so it is retained during the operation of the secondary battery, thereby continuously improving the high-temperature durability of the secondary battery.

[0131] Thus, when a perlithium-rich manganese oxide, which generates a large amount of gas and releases a significant amount of reactive oxygen or manganese at high temperatures and high voltages, is used as a positive electrode active material, the compound represented by Chemical Formula 1 can continue to form a stable and robust film on the positive electrode, thereby contributing to improved high-temperature durability, gas reduction, and lifespan performance of secondary batteries using the perlithium-rich manganese oxide. For example, the effects of improving lifespan performance, durability, and gas reduction at high temperatures of the secondary battery of the present invention are achieved using a combination of the organic solvent and additives of the non-aqueous electrolyte described above.

[0132] Furthermore, the effects of the present invention are demonstrated in over-lithiated manganese-rich oxides, whereas the generation of active oxygen and excessive dissolution of Mn are not a problem in other positive electrode active materials, such as lithium nickel manganese cobalt transition metal oxides containing high nickel content (e.g., NCM-type active materials containing approximately 80 mol% or more of Ni in the transition metal). Therefore, even if the aforementioned organic solvents are used in combination, the desired effects will not be achieved. Conversely, when a non-aqueous electrolyte containing the aforementioned organic solvents and additives is applied to a positive electrode active material other than over-lithiated manganese-rich oxides, the components of the non-aqueous electrolyte may act as a resistor, reducing lifespan performance.

[0133] In Chemical Formula 1, R1 and R2 are each independently selected from a substituent represented by Chemical Formula 2, an alkyl group having 1 to 10 carbon atoms, an alkyl group having 1 to 10 carbon atoms substituted with one or more fluorine atoms, an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, a phosphate group, and a nitrile group, and at least one of R1 and R2 is a substituent represented by Chemical Formula 2. For example, in Chemical Formula 1, R1 and R2 may be a substituent represented by Chemical Formula 2.

[0134] The alkyl group having 1 to 10 carbon atoms may be selected from, for example, alkyl groups having 1 to 3 carbon atoms, ie, methyl, ethyl, and propyl.

[0135] The alkyl group having 1 to 10 carbon atoms substituted with one or more fluorine atoms may be an alkyl group having 1 to 3 carbon atoms substituted with one or more fluorine atoms, for example, *-CF3, *-CH2CF3, *-CF2CF3, *-CH2CH2CF3, *-CH2CF2CF3 and *-CF2CF2CF3. In the present invention, the symbol "*" may refer to a binding site.

[0136] In addition, the substituent represented by Chemical Formula 2 may be selected from the group consisting of CS-1 to CS-15:

[0137]

[0138]

[0139] The substituent structures CS-1 to CS-15 are preferred examples of the substituents represented by Chemical Formula 2 or R1 and R2 in Chemical Formula 1. When the substituents represented by CS-1 to CS-15 are used as R1 and R2 in Chemical Formula 1, the overall compound has good structural stability and can be used as an additive for non-aqueous electrolytes. For example, R1 and R2 can each be independently selected from the group consisting of CS-1, CS-2, CS-5, CS-8, CS-10, and CS-11, which may be preferred in terms of structural stability and ease of synthesis.

[0140] At the same time, in the compound represented by Chemical Formula 1 of the present invention, when L1 and L2 are both directly bonded and R1 and R2 are CS-7, or when L1 and L2 are both methylene, n is 2 and R1 and R2 are both CS-2, the compound itself may be easily decomposed due to low structural stability, so the synthesis of the compound itself may be difficult. For example, the compound that meets the above conditions has the disadvantage that the cyclic R1 and R2 structures are easily decomposed during the synthesis process, and even if the compound is finally synthesized, it is easy to decompose during storage, and the synthesis yield is significantly low. Therefore, the present invention excludes compounds in which L1 and L2 are both directly bonded and R1 and R2 are CS-7, as well as compounds in which n is 2 and R1 and R2 are both CS-2.

[0141] In the compound represented by Chemical Formula 1, L1 and L2 can each independently be a direct bond, a methylene group, or an ethylene group, such as a methylene group. When L1 and L2 are methylene groups, the synthesis of the compound is facilitated and the decomposition of the compound after synthesis can be suppressed.

[0142] The compound represented by Chemical Formula 1 may include at least one compound selected from the group consisting of the following compounds A to U, for example, at least one compound selected from the group consisting of compound A, compound F, and compound J:

[0143]

[0144]

[0145]

[0146] When the compound represented by Chemical Formula 1 has the above structure, the compound has an advantage of being able to form a stable SEI layer with low resistance even in a small amount, compared to commonly used additives.

[0147] The content of the compound represented by Chemical Formula 1 in the non-aqueous electrolyte may be about 0.01 to 10 wt %, for example, about 0.1 to 5 wt %, about 0.2 to 3 wt %, about 0.5 to 2 wt %, or about 0.7 to 1.5 wt %. Within the above range, it is desirable to achieve the above-mentioned effect of improving the high-temperature durability of the secondary battery while preventing an increase in resistance due to excessive use of the additive.

[0148] At the same time, in addition to the compound represented by Chemical Formula 1, the above-mentioned additive can be any substance that can continue to play a role in forming a stable and strong film on the positive electrode when the over-lithium manganese-rich oxide, which generates a large amount of gas and releases a serious amount of active oxygen or manganese at high temperature and high voltage, is used as the positive electrode active material, thereby helping to improve the high-temperature durability, gas reduction and life performance of the secondary battery using the over-lithium manganese-rich oxide.

[0149] The non-aqueous electrolyte may further include a supplementary additive together with the compound represented by Chemical Formula 1. The supplementary additive may be included in the non-aqueous electrolyte to strengthen the SEI film on the positive and negative electrodes to prevent gas generation due to electrolyte side reactions, to prevent decomposition of the non-aqueous electrolyte under high power conditions and the collapse of the negative electrode, or for improving low-temperature high-rate discharge characteristics, high-temperature stability, overcharge protection, and suppression of battery expansion at high temperatures.

[0150] For example, the supplementary additive may include at least one selected from the group consisting of sulfate ester or salt compounds, phosphate ester or salt compounds, borate ester or salt compounds, nitrile compounds, benzene compounds, and lithium salt compounds.

[0151] The sulfate ester or salt compound may be ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS), and its content may be less than about 5 wt % based on the total weight of the electrolyte.

[0152] The phosphate or salt compound may be at least one selected from the group consisting of lithium difluorobisoxalatophosphate, lithium difluorophosphate, tetramethyltrimethylsilyl phosphate, trimethylsilyl phosphite, tris(2,2,2-trifluoroethyl) phosphate and tris(trifluoroethyl) phosphite compounds, and its content may be 5 wt% or less based on the total weight of the electrolyte.

[0153] The borate ester or salt compound may include tetraphenyl borate and lithium oxalyldifluoroborate, and the content thereof may be 5 wt % or less based on the total weight of the electrolyte.

[0154] The nitrile compound is a nitrile compound other than decanenitrile (DN) and 1,4-dicyano-2-butene (DCB), and representative examples thereof include at least one compound selected from the group consisting of succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, octanonitrile, heptonitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, benzyl acetonitrile, 2-fluorophenylacetonitrile, 4-fluorophenylacetonitrile and 1,3,6-hexanetonitrile.

[0155] The content of the nitrile compound may be about 5 wt % to 8 wt %, for example, about 6 wt % to 8 wt %. When the content of the nitrile compound in the electrolyte exceeds 8 wt %, the resistance may increase due to the increase of the film formed on the electrode surface, and thus the battery performance may deteriorate.

[0156] The benzene compound may be fluorobenzene, the amine compound may be triethanolamine or ethylenediamine, and the silane compound may be tetravinylsilane.

[0157] The lithium salt compound is a compound different from the lithium salt contained in the non-aqueous electrolyte, and may include one or more compounds selected from the group consisting of LiPO2F2, LiODFB, LiBOB (lithium bis(oxalatoborate) (LiB(C2O4)2)), and LiBF4. The content thereof may be 5 wt% or less based on the total weight of the electrolyte.

[0158] For example, the supplementary additive may include at least one selected from the group consisting of coumarin, vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, propane sultone, propylene sultone, succinonitrile, adiponitrile, ethylene sulfate, lithium difluorophosphate (LiDFP), lithium tetrafluoroborate (LiBF4), lithium difluorooxalatoborate (LiODFB), lithium dioxalatoborate (LiBOB), 3-trimethoxysilyl-propyl-N-aniline (TMSPa), tris(trimethylsilyl) phosphite (TMSPi), and a compound represented by Chemical Formula 3:

[0159] (Chemical Formula 3)

[0160]

[0161] The additive may include at least one selected from the group consisting of vinylene carbonate, propane sultone, ethylene sulfate, LiDFP, LiBF 4 , and a compound represented by Chemical Formula 1.

[0162] The additive may be present in an amount of about 0.1 wt % to 15 wt % in the non-aqueous electrolyte.

[0163] The supplementary additive may be present in an amount of about 0.1 wt % to 15 wt % in the non-aqueous electrolyte.

[0164] The shape of the lithium secondary battery of the present invention is not particularly limited, and may be cylindrical using a can, square, pouch, or coin-shaped.

[0165] Hereinafter, the present invention will be described in more detail by way of examples. However, the following examples are intended to illustrate the present invention and are not intended to limit the scope of the invention. It will be apparent to those skilled in the art that various changes and modifications may be made within the scope of the present invention and the technical concept, and such changes and modifications fall within the scope of the appended claims.

[0166] Examples and Comparative Examples

[0167] Example 1

[0168] (Preparation of non-aqueous electrolyte)

[0169] A mixture of ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate in a volume ratio of 20:10:70 was used as the organic solvent.

[0170] The non-aqueous electrolyte is prepared by adding LiPF6 as a lithium salt and the compound represented by Chemical Formula A as an additive, propane sultone (PS), ethylene sulfate (ESa), LiDFP, LiBF4 and the compound represented by Chemical Formula 3 as supplementary additives to an organic solvent.

[0171] LiPF6 is contained in the non-aqueous electrolyte at a molar concentration of 1.2M.

[0172] The non-aqueous electrolyte contained 1 wt % of the compound represented by Chemical Formula A.

[0173] In addition, the nonaqueous electrolyte contains 0.5 wt % of vinylene carbonate, 0.8 wt % of propane sultone, 1.0 wt % of ethylene sulfate, 1.0 wt % of LiDFP, 0.5 wt % of LiBF 4 , and 0.1 wt % of the compound represented by Chemical Formula 1.

[0174] (Preparation of lithium secondary battery)

[0175] The positive electrode active material (Li 1.3 [Ni 0.35 Mn 0.65 ]O 2.33 A positive electrode mixture slurry (48 wt% solids) was prepared by adding a conductive material (carbon nanotubes, lithium-rich manganese oxide), a conductive material (carbon nanotubes), and a binder (PVdF) to a solvent (N-methyl-2-pyrrolidone (NMP)) in a weight ratio of 97.4:0.6:2.0. This slurry was applied to one side of a 12 μm thick positive electrode current collector (Al film), dried, and rolled to prepare a positive electrode.

[0176] A negative electrode mixture slurry (70% solids by weight) was prepared by adding the negative electrode active material (a mixture of artificial graphite, natural graphite, and SiO), a conductive material (carbon black), and a binder (PVdF) to distilled water as a solvent at a weight ratio of 95.7:1.0:3.3. This slurry was applied to one side of an 8 μm thick negative electrode current collector (Cu film), dried, and rolled to prepare a negative electrode.

[0177] A separator made of a porous polyethylene film was inserted between the prepared positive electrode and negative electrode in a dry room, and then the prepared nonaqueous electrolyte was injected, thereby preparing a secondary battery.

[0178] Example 2

[0179] A lithium secondary battery was prepared in the same manner as in Example 1, except that the amount of the compound represented by Chemical Formula A added to the non-aqueous electrolyte was 0.5 wt % instead of 1 wt %. That is, in Example 2, ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate were used as organic solvents, and a different amount of the compound represented by Chemical Formula A from that in Example 1 was used as an additive to prepare a lithium secondary battery.

[0180] Example 3

[0181] A lithium secondary battery was prepared in the same manner as in Example 1, except that the amount of the compound represented by Chemical Formula A added to the non-aqueous electrolyte was 2.0 wt % instead of 1 wt %. That is, in Example 3, a lithium secondary battery was prepared using ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate as organic solvents and using the compound represented by Chemical Formula A as an additive at a different content from that in Examples 1 and 2.

[0182] Example 4

[0183] A lithium secondary battery was prepared in the same manner as in Example 1, except that the compound represented by Chemical Formula S was used instead of the compound represented by Chemical Formula A. That is, in Example 4, ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate were used as organic solvents, and the compound represented by Chemical Formula S was used instead of the compound represented by Chemical Formula A in Example 1 to prepare a lithium secondary battery.

[0184] Comparative Example 1

[0185] A lithium secondary battery was prepared in the same manner as in Example 1, except that the compound represented by Chemical Formula A was not added to the non-aqueous electrolyte. That is, in Example 1, in addition to ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate as organic solvents, the compound represented by Chemical Formula A was used as an additive, whereas in Comparative Example 1, a lithium secondary battery was prepared without using any additives other than these three organic solvents.

[0186] Comparative Example 2

[0187] A lithium secondary battery was prepared in the same manner as in Example 1, except that 1,3-propane sultone (PS) was used instead of the compound represented by Chemical Formula A. That is, in Comparative Example 2, in addition to using ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate as organic solvents, a lithium secondary battery was prepared using 1,3-propane sultone (PS) as an additive instead of the compound represented by Chemical Formula A as an additive.

[0188] Comparative Example 3

[0189] A lithium secondary battery was prepared in the same manner as in Example 1, except that ethylene carbonate and ethyl methyl carbonate were used in a volume ratio of 20:80 as the organic solvent for the non-aqueous electrolyte. That is, in Comparative Example 3, a lithium secondary battery was prepared using only two organic solvents, ethylene carbonate and ethyl methyl carbonate, and a compound represented by Chemical A as an additive.

[0190] Comparative Example 4

[0191] A lithium secondary battery was prepared in the same manner as in Example 1, except that ethylene carbonate and diethyl carbonate were used in a volume ratio of 20:80 as the organic solvent for the non-aqueous electrolyte. That is, in Comparative Example 4, a lithium secondary battery was prepared using only two organic solvents, ethylene carbonate and diethyl carbonate, and a compound represented by Chemical A as an additive.

[0192] Comparative Example 5

[0193] A lithium secondary battery was prepared in the same manner as in Example 1, except that ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate were used in a volume ratio of 20:10:70 as the organic solvent for the non-aqueous electrolyte. That is, in Comparative Example 5, dimethyl carbonate was used instead of diethyl carbonate among the three organic solvents in Example 1 to prepare a lithium secondary battery.

[0194] Experimental example

[0195] Experimental Example 1: High-temperature cyclic charge-discharge performance evaluation

[0196] Using an electrochemical charge and discharge device, the lithium secondary batteries of Examples 1 to 4 and Comparative Examples 1 to 5 prepared above were each subjected to 200 cycles of charge and discharge, each comprising charging to 4.35 V and 1 / 40 C at 45° C. under constant current / constant voltage (CC / CV) and 0.33 C, and discharging to 2.0 V under constant current (CC) and 0.33 C.

[0197] Experimental Example 1-A: Capacity Retention Evaluation

[0198] The capacity retention ratio was calculated using the following mathematical formula, and the results are shown in Table 1 below.

[0199] Capacity retention (%) = {(discharge capacity after 200 cycles / discharge capacity after 1 cycle)} × 100

[0200] Experimental Example 1-B: Evaluation of Resistance Increase Rate

[0201] After one charge and discharge cycle, the discharge capacity after one cycle was measured using an electrochemical charge and discharge device. The state of charge (SOC) was adjusted to 50% SOC, a 2.5C pulse was applied for 10 seconds, and the initial resistance was calculated by the difference between the voltage before and after the pulse application.

[0202] After 200 charge and discharge cycles, the resistance after 200 cycles was calculated in the same manner as above, and the resistance increase rate was calculated using the following mathematical formula. The results are shown in Table 1 below.

[0203] Resistance increase rate (%) = (resistance after 200 cycles - initial resistance) / initial resistance × 100

[0204] Table 1

[0205]

[0206] Referring to Table 1, it can be seen that the lithium secondary batteries of Examples 1 to 4 comprising a combination of the non-aqueous electrolyte of the present invention and a positive electrode containing an over-lithium manganese-rich oxide have higher capacity retention and lower resistance increase rate during high-temperature cyclic charge and discharge compared to Comparative Examples 1 to 5.

[0207] Experimental Example 2: High-temperature storage performance evaluation

[0208] The lithium secondary batteries of Examples 1 to 5 and Comparative Examples 1 to 5 prepared above were each subjected to initial charge and discharge, including charging to 4.35 V and 1 / 40 C under CC / CV and 0.33 C conditions at 25° C., and then discharging to 2.0 V under CC and 0.33 C conditions. Then, the lithium secondary batteries were charged to 4.35 V and 1 / 40 C under CC / CV and 0.33 C conditions at 25° C., and then stored at 60° C. for 8 weeks.

[0209] Experimental Example 2-A: Capacity Retention Evaluation

[0210] After storage for 8 weeks, the lithium secondary battery was charged to 4.35 V, 1 / 40 C at 25° C. under the conditions of CC / CV and 0.33 C, and then discharged to 2.0 V under the conditions of CC and 0.33 C to measure the capacity during discharge.

[0211] The capacity retention ratio was calculated according to the following mathematical formula, and the results are shown in Table 2 below.

[0212] Capacity retention (%) = (discharge capacity after 8 weeks of storage / initial discharge capacity) × 100

[0213] Experimental Example 2-B: Evaluation of Resistance Increase Rate

[0214] After the initial charge and discharge, the capacity was checked at room temperature. Afterwards, the lithium secondary battery was charged to an SOC of 50% based on the discharge capacity and discharged at a current of 2.5C for 10 seconds. The resistance was then measured using the voltage drop difference at this time, which was used as the initial resistance. After storage at 60°C for 8 weeks, the resistance was measured in the same manner and used as the final resistance. The resistance increase rate was then calculated using the following mathematical formula. The results are shown in Table 2 below.

[0215] Resistance increase rate (%) = (final resistance - initial resistance) / initial resistance × 100

[0216] Table 2

[0217]

[0218] Referring to Table 2, it can be seen that the lithium secondary batteries of Examples 1 to 4 comprising a combination of the nonaqueous electrolyte of the present invention and a positive electrode containing an over-lithium manganese-rich oxide have higher capacity retention and lower resistance increase rate during high-temperature cyclic charge and discharge compared to the cases of Comparative Examples 1 to 5.

[0219] Reference Example

[0220] Reference Example 1

[0221] Preparation of non-aqueous electrolyte

[0222] In the same manner as in Example 1, a non-aqueous electrolyte was prepared.

[0223] Preparation of lithium secondary batteries

[0224] The positive electrode active material (LiNi 0.85 Co 0.05 Mn 0.07 Al 0.03 O2), a conductive material (carbon nanotubes), and a binder (polyvinylidene fluoride) were added to N-methyl-2-pyrrolidone (NMP) as a solvent in a weight ratio of 98.0:0.7:1.3 to prepare a positive electrode mixture slurry (76.5% solids by weight). The positive electrode mixture slurry was coated on one side of a positive electrode current collector (Al film) with a thickness of 12 μm, dried, and rolled to prepare a positive electrode. That is, in Reference Example 1, a different type of positive electrode active material from Example 1, such as lithium nickel cobalt manganese oxide containing high nickel, was used to prepare the positive electrode.

[0225] A negative electrode mixture slurry (50% solids by weight) was prepared by adding the negative electrode active material (artificial graphite), conductive material (carbon black), and binder (styrene-butadiene rubber) to distilled water as a solvent at a weight ratio of 96.5:1.5:2.0. The negative electrode mixture slurry was coated on one side of a negative electrode current collector (Cu film) with a thickness of 8 μm, dried, and rolled to prepare a negative electrode.

[0226] A separator made of a porous polyethylene film was inserted between the prepared positive electrode and negative electrode in a dry room, and then the prepared nonaqueous electrolyte was injected, thereby preparing a secondary battery.

[0227] Reference Example 2

[0228] A lithium secondary battery was prepared in the same manner as in Reference Example 1, except that the nonaqueous electrolyte prepared in Comparative Example 1 was used instead of the nonaqueous electrolyte prepared in Example 1.

[0229] Reference Experiment 1: Evaluation of High-Temperature Cycling Capacity Retention

[0230] Using an electrochemical charge and discharge apparatus, the lithium secondary batteries of Reference Examples 1 and 2 prepared above were each subjected to 200 cycles of charge and discharge, each comprising charging to 4.2 V and 1 / 40 C at 45° C. under constant current / constant voltage (CC / CV) and 0.33 C, and discharging to 2.5 V at 0.33 C.

[0231] Reference Experiment 1-A: Capacity Retention Evaluation

[0232] The capacity retention ratio was calculated using the following mathematical formula, and the results are shown in Table 3 below.

[0233] Capacity retention (%) = {(discharge capacity after 200 cycles / discharge capacity after 1 cycle)} × 100

[0234] Reference Experiment 1-B: Evaluation of Resistance Increase Rate

[0235] After one charge and discharge cycle, the discharge capacity after one cycle was measured using an electrochemical charge and discharge device, the SOC was adjusted to 50% SOC, a 2.5C pulse was applied for 10 seconds, and the initial resistance was calculated by the difference between the voltage before and after the pulse application.

[0236] After 200 charge and discharge cycles, the resistance after 200 cycles was calculated in the same manner as above, and the resistance increase rate was calculated using the following mathematical formula. The results are shown in Table 3 below.

[0237] Resistance increase rate (%) = (resistance after 200 cycles - initial resistance) / initial resistance × 100

[0238] Table 3

[0239]

[0240] Referring to Table 3, it can be seen that in the case of Reference Example 1, which uses a high-nickel lithium nickel cobalt manganese oxide instead of a perlithium-rich manganese oxide, even when the same non-aqueous electrolyte as that of Example 1 is used, the effect of improving the high-temperature cycle charge-discharge performance is limited. In contrast, in the case of Reference Example 1, due to the use of the compound represented by Chemical Formula A as a non-aqueous electrolyte additive, problems such as a decrease in capacity retention and an increase in resistance occurred compared to Reference Example 2, which did not use the compound represented by Chemical Formula A. This shows that the non-aqueous electrolyte of the present invention exhibits a unique effect when using a perlithium-rich manganese oxide as the positive electrode active material.

[0241] Reference Experiment 2: High-temperature storage performance evaluation

[0242] Using an electrochemical charge and discharge device, the lithium secondary batteries of Reference Examples 1 and 2 prepared above were each subjected to initial charge and discharge, including charging to 4.2 V and 1 / 40 C under CC / CV and 0.33 C conditions at 25° C., and then discharging to 2.5 V under 0.33 C conditions. The lithium secondary batteries were then charged to 4.2 V and 1 / 40 C under CC / CV and 0.33 C conditions at 25° C., and then stored at 60° C. for 8 weeks.

[0243] Reference Experiment 2-A: Capacity Retention Evaluation

[0244] After storage for 8 weeks, the lithium secondary battery was charged to 4.2 V, 1 / 40 C at 25° C. under the conditions of CC / CV and 0.33 C, and discharged to 2.5 V under the condition of 0.33 C to measure the capacity during discharge.

[0245] The capacity retention ratio was calculated according to the following mathematical formula, and the results are shown in Table 4 below.

[0246] Capacity retention (%) = (discharge capacity after 8 weeks of storage / initial discharge capacity) × 100

[0247] Reference Experiment 2-B: Evaluation of Resistance Increase Rate

[0248] After the initial charge and discharge, the capacity was checked at room temperature. Afterwards, the lithium secondary battery was charged to an SOC of 50% based on the discharge capacity and discharged at a current of 2.5C for 10 seconds. The resistance was then measured using the voltage drop difference at this time, which was used as the initial resistance. After storage at 60°C for 8 weeks, the resistance was measured in the same manner and used as the final resistance. The resistance increase rate was then calculated using the following mathematical formula. The results are shown in Table 4 below.

[0249] Resistance increase rate (%) = (final resistance - initial resistance) / initial resistance × 100

[0250] Table 4

[0251]

[0252] As shown in Table 4, in Reference Example 1, which uses a high-nickel lithium nickel cobalt manganese oxide instead of an over-lithiated manganese-rich oxide, even with the same non-aqueous electrolyte as that used in Example 1, the effect of improving high-temperature storage performance is limited. In contrast, in Reference Example 1, due to the use of the compound represented by Chemical Formula A as a non-aqueous electrolyte additive, problems such as increased resistance occurred compared to Reference Example 2, which did not use the compound represented by Chemical Formula A. This demonstrates that the non-aqueous electrolyte of the present invention exhibits unique effects when using an over-lithiated manganese-rich oxide as the positive electrode active material.

[0253] As will be appreciated from the foregoing, various embodiments of the present invention have been described herein for illustrative purposes, and various modifications may be made without departing from the scope and spirit of the invention. Therefore, the various embodiments disclosed herein are not intended to be limiting, with the true scope and spirit being indicated by the appended claims.

Claims

1. A lithium secondary battery comprising: positive electrode; negative electrode; a separator interposed between the positive electrode and the negative electrode; and non-aqueous electrolytes, in, The positive electrode comprises a positive electrode active material, The positive electrode active material comprises an over-lithium manganese-rich oxide, wherein the over-lithium manganese-rich oxide contains 50 mol % or more of Mn in all metal elements except lithium, and the molar ratio of lithium to transition metal exceeds 1. The non-aqueous electrolyte comprises a lithium salt, an organic solvent and an additive, The organic solvent comprises a first organic solvent and a second organic solvent, The first organic solvent comprises ethylene carbonate, The second organic solvent comprises diethyl carbonate and ethyl methyl carbonate, and The additive comprises a compound represented by Chemical Formula 1: (Chemical Formula 1) in, n is 1 or 2, L1 and L2 are each independently a direct bond or a substituted or unsubstituted alkylene group having 1 to 6 carbon atoms, R1 and R2 are each independently selected from a substituent represented by the following Chemical Formula 2, an alkyl group having 1 to 10 carbon atoms, an alkyl group having 1 to 10 carbon atoms substituted with one or more fluorine atoms, an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, a phosphate group, and a nitrile group, and At least one of R1 and R2 is a substituent represented by Chemical Formula 2: (Chemical Formula 2) in, m is 1 or 2, X1 and X2 are each independently -O- or -C(R 31 )(R 32 )-, provided that at least one of X1 and X2 is -O-, R 31 to R 36 are each independently hydrogen, an alkyl group having 1 to 6 carbon atoms, -C(=O)-R4 or -R5-OC(=O)-R6, R4 and R6 are each independently a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, an alkynyl group having 2 to 20 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 20 carbon atoms, R5 is a substituted or unsubstituted alkylene group having 1 to 6 carbon atoms, Each substituent of L1, L2, R4, R5 and R6 is at least one independently selected from the group consisting of deuterium, -F, -Cl, -Br, -I, -CN, -NO2 and -SO3, * is the binding site with L1 or L2, When L1 and L2 are both directly bonded, then R1 and R2 are not both CS-7 below, and When L1 and L2 are both methylene and n is 2, then R1 and R2 are not the following CS-2 2. The lithium secondary battery according to claim 1, wherein The perlithium manganese-rich oxide is a compound represented by the chemical formula X: (Chemical Formula X) Li 1+s [Ni t Co u Mr v M 1 w ]O 2+z Among them, M 1 is at least one selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and s, t, u, v, w and z satisfy 0.05≤s≤1, 0≤t≤0.5, 0≤u≤0.3, 0.5≤v<1.0, 0≤w≤0.2, 0≤z≤1.

3. The lithium secondary battery according to claim 1, wherein The volume ratio of the first organic solvent to the second organic solvent is 10:90 to 50:

50.

4. The lithium secondary battery according to claim 1, wherein The substituent represented by Chemical Formula 2 is selected from the group consisting of CS-1 to CS-15:

5. The lithium secondary battery according to claim 4, wherein R1 and R2 are each independently selected from the group consisting of CS-1, CS-2, CS-5, CS-8, CS-10 and CS-11.

6. The lithium secondary battery according to claim 1, wherein L1 and L2 are methylene groups.

7. The lithium secondary battery according to claim 1, wherein The compound represented by Chemical Formula 1 includes at least one compound selected from the group consisting of compounds A to U:

8. The lithium secondary battery according to claim 1, wherein The content of the compound represented by Chemical Formula 1 in the non-aqueous electrolyte is 0.01 wt % to 10 wt %.

9. The lithium secondary battery according to claim 1, wherein The lithium salt includes a salt 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, LiFSI (LiN (SO2F) 2), LiCH3SO3, LiCF3CO2, LiCH3CO2 and LiBETI (LiN (SO2CF2CF3) 2) At least one of the group consisting of.

10. The lithium secondary battery according to claim 1, wherein The lithium salt is contained in the non-aqueous electrolyte at a molar concentration of 0.5M to 5.0M.

11. The lithium secondary battery according to claim 1, wherein The additive includes at least one selected from the group consisting of coumarin, vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, propane sultone, propylene sultone, succinonitrile, adiponitrile, ethylene sulfate, lithium difluorophosphate (LiDFP), lithium tetrafluoroborate (LiBF4), lithium difluorooxalatoborate (LiODFB), lithium bisoxalatoborate (LiBOB), 3-trimethoxysilyl-propyl-N-aniline (TMSPa), tris(trimethylsilyl) phosphite (TMSPi) and a compound represented by Chemical Formula 3: (Chemical Formula 3) 12. A method for manufacturing a lithium secondary battery, the method comprising: housing an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode in a battery case; and injecting a non-aqueous electrolyte into the battery case housing the electrode assembly, wherein the positive electrode comprises a positive electrode active material, The positive electrode active material comprises an over-lithium manganese-rich oxide, wherein the over-lithium manganese-rich oxide contains 50 mol % or more of Mn in all metal elements except lithium, and the molar ratio of lithium to transition metal exceeds 1. The non-aqueous electrolyte comprises a lithium salt, an organic solvent and an additive, The organic solvent comprises a first organic solvent and a second organic solvent, The first organic solvent comprises ethylene carbonate, The second organic solvent comprises diethyl carbonate and ethyl methyl carbonate, and The additive comprises a compound represented by Chemical Formula 1: (Chemical Formula 1) in, n is 1 or 2, L1 and L2 are each independently a direct bond or a substituted or unsubstituted alkylene group having 1 to 6 carbon atoms, R1 and R2 are each independently selected from a substituent represented by the following Chemical Formula 2, an alkyl group having 1 to 10 carbon atoms, an alkyl group having 1 to 10 carbon atoms substituted with one or more fluorine atoms, an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, a phosphate group, and a nitrile group, and At least one of R1 and R2 is a substituent represented by Chemical Formula 2: (Chemical Formula 2) in, m is 1 or 2, X1 and X2 are each independently -O- or -C(R 31 )(R 32 )-, provided that at least one of X1 and X2 is -O-, R 31 to R 36 are each independently hydrogen, an alkyl group having 1 to 6 carbon atoms, -C(=O)-R4 or -R5-OC(=O)-R6, R4 and R6 are each independently a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, an alkynyl group having 2 to 20 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 20 carbon atoms, R5 is a substituted or unsubstituted alkylene group having 1 to 6 carbon atoms, Each substituent of L1, L2, R4, R5 and R6 is at least one independently selected from the group consisting of deuterium, -F, -Cl, -Br, -I, -CN, -NO2 and -SO3, * is the binding site with L1 or L2, When L1 and L2 are both directly bonded, then R1 and R2 are not both CS-7 below, and When L1 and L2 are both methylene and n is 2, then R1 and R2 are not the following CS-2 13. The method of claim 12, wherein: The perlithium manganese-rich oxide is a compound represented by the chemical formula X: (Chemical Formula X) Li 1+s [Ni t Co u Mr v M 1 w ]O 2+z Among them, M 1 is at least one selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and s, t, u, v, w and z satisfy 0.05≤s≤1, 0≤t≤0.5, 0≤u≤0.3, 0.5≤v<1.0, 0≤w≤0.2, 0≤z≤1.

14. The method of claim 12, wherein: The volume ratio of the first organic solvent to the second organic solvent is 10:90 to 50:

50.

15. The method of claim 12, wherein: The substituent represented by Chemical Formula 2 is selected from the group consisting of CS-1 to CS-15:

16. The method of claim 15, wherein: R1 and R2 are each independently selected from the group consisting of CS-1, CS-2, CS-5, CS-8, CS-10 and CS-11.

17. The method of claim 12, wherein: L1 and L2 are methylene groups.

18. The method of claim 12, wherein: The compound represented by Chemical Formula 1 includes at least one compound selected from the group consisting of compounds A to U:

19. The method of claim 12, wherein: The content of the compound represented by Chemical Formula 1 in the non-aqueous electrolyte is 0.01 wt % to 10 wt %.

20. The method of claim 12, wherein: The lithium salt includes a salt 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, LiFSI (LiN (SO2F) 2), LiCH3SO3, LiCF3CO2, LiCH3CO2 and LiBETI (LiN (SO2CF2CF3) 2) At least one of the group consisting of.

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