WO2024035170A1 - Non-aqueous electrolyte and lithium secondary battery comprising same - Google Patents

Abstract

The present invention provides a non-aqueous electrolyte comprising: a lithium salt; an organic solvent; and additives, wherein the additives comprise a first additive including a compound represented by a specific chemical formula and a second additive including lithium difluorophosphate. In the non-aqueous electrolyte according to the present invention, by forming a film that is stable for an electrode, the storage characteristic and resistance characteristic of a lithium secondary battery comprising same can be improved at high temperature.

Description

Non-aqueous electrolyte and lithium secondary battery containing the same

[Cross-citation with related applications]

This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0101642 filed on August 12, 2022, and all contents disclosed in the Korean Patent Application document are included as part of this specification.

[Technology field]

The present invention relates to a non-aqueous electrolyte and a lithium secondary battery containing the same.

Recently, the application area of lithium secondary batteries has rapidly expanded not only to supply power to electronic devices such as electricity, electronics, communication, and computers, but also to supply power storage to large-area devices such as automobiles and power storage devices, leading to high capacity, high output, and high stability. Demand for secondary batteries is increasing.

In particular, as interest in solving environmental problems and realizing a sustainable, cyclical society grows, research on power storage devices such as lithium-ion batteries and electric double-layer capacitors is being conducted extensively. Among battery technologies, lithium secondary batteries are attracting attention as a battery system with theoretically the highest energy density.

The lithium secondary battery is largely composed of a positive electrode composed of a transition metal oxide containing lithium, a negative electrode capable of storing lithium, an electrolyte solution that serves as a medium for transferring lithium ions, and a separator. In the case of the double electrolyte solution, the stability of the battery ( It is known to be a component that has a significant impact on stability, safety, etc., and much research is being conducted on it.

In this regard, generally, the electrolyte of a lithium secondary battery is a non-aqueous electrolyte containing a lithium salt and an organic solvent, and the organic solvent is a carbonate-based organic solvent. At this time, for example, LiPF ₆ can be used as the lithium salt. In the case of PF ₆ ^- anion, it is very vulnerable to heat, so when the battery is exposed to high temperature, thermal decomposition of the lithium salt causes Lewis acids such as HF and PF ₅ . There is a problem with acid being generated. Lewis acids such as HF and PF ₅ cause decomposition of the organic solvent itself and destroy the solid electrolyte interface layer (SEI layer) formed on the surface of the negative electrode active material, increasing the resistance of lithium secondary batteries, reducing their lifespan, and reducing storage. There is a problem that causes performance problems.

One object of the present invention is to provide a non-aqueous electrolyte that can reduce electrolyte side reactions by forming a stable film on an electrode and can provide excellent storage and resistance characteristics at high temperatures when applied to a lithium secondary battery.

In addition, another object of the present invention is to provide a lithium secondary battery containing the above-described non-aqueous electrolyte.

The present invention relates to a lithium salt; organic solvent; and an additive; wherein the additive includes a first additive and a second additive, wherein the first additive includes a compound represented by the following formula (1), and the second additive includes lithium difluorophosphate. Provide non-aqueous electrolyte.

[Formula 1]

In Formula 1, R ₁ is an alkoxy group having 1 to 10 carbon atoms substituted with one or more fluorines or an aryloxy group having 6 to 20 carbon atoms with one or more fluorine substituted, and R ₂ and R ₃ are independently hydrogen and carbon atoms. It is an alkyl group with 1 to 10 carbon atoms or an aryl group with 6 to 20 carbon atoms.

In addition, the present invention is an anode; a cathode opposite the anode; a separator interposed between the anode and the cathode; and a lithium secondary battery containing the above-described non-aqueous electrolyte.

The non-aqueous electrolyte of the present invention is characterized by comprising a first additive containing a sulfonamide-based compound having a specific structural formula as an additive and a second additive containing lithium difluorophosphate. The non-aqueous electrolyte according to the present invention can reduce electrolyte side reactions by forming a stable film on the electrode, and can achieve excellent storage and resistance characteristics at high temperatures when applied to a lithium secondary battery.

Terms or words used in this specification and claims should not be construed as limited to their common or dictionary meanings, and the inventor may appropriately define the concept of terms in order to explain his or her invention in the best way. It should be interpreted with meaning and concept consistent with the technical idea of the present invention based on the principle that it is.

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, but are intended to indicate the presence of one or more other features or numbers. It should be understood that this does not exclude in advance the possibility of the presence or addition of steps, components, or combinations thereof.

Meanwhile, before explaining the present invention, unless otherwise specified in the present invention, "*" means a connected portion (bonding site) between terminal parts of the same or different atoms or chemical formulas.

In addition, in the description of “carbon numbers a to b” in this 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. For example, “alkyl group having 1 to 5 carbon atoms” refers to an alkyl group containing 1 to 5 carbon atoms, i.e. CH ₃ -, CH ₃ CH ₂ -, CH ₃ CH ₂ CH ₂ -, (CH ₃ ) ₂ CH -, CH ₃ CH ₂ CH ₂ CH ₂ -, (CH ₃ ) ₂ CHCH ₂ -, CH ₃ CH ₂ CH ₂ CH ₂ CH ₂ -, (CH ₃ ) ₂ CHCH ₂ CH ₂ -, etc.

Additionally, in this specification, all alkyl groups or aryl groups may be substituted or unsubstituted. Unless otherwise defined, the term "substitution" means that at least one hydrogen bonded to carbon is replaced with an element other than hydrogen, for example, an alkyl group with 1 to 20 carbon atoms, an alkene with 2 to 20 carbon atoms. Nyl group, alkynyl group of 2 to 20 carbon atoms, alkoxy group of 1 to 20 carbon atoms, cycloalkyl group of 3 to 12 carbon atoms, cycloalkenyl group of 3 to 12 carbon atoms, cycloalkynyl group of 3 to 12 carbon atoms, hetero group of 3 to 12 carbon atoms Cycloalkyl group, heterocycloalkenyl group with 3 to 12 carbon atoms, heterocycloalkynyl group with 2 to 12 carbon atoms, aryloxy group with 6 to 12 carbon atoms, halogen atom, fluoroalkyl group with 1 to 20 carbon atoms, nitro group, 6 to 12 carbon atoms It means substituted with an aryl group of 20, a heteroaryl group of 2 to 20 carbon atoms, a haloaryl group of 6 to 20 carbon atoms, etc.

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

non-aqueous electrolyte

The present invention relates to non-aqueous electrolytes. More specifically, the non-aqueous electrolyte may be a non-aqueous electrolyte for a lithium secondary battery.

The non-aqueous electrolyte according to the present invention includes a lithium salt; organic solvent; and an additive; wherein the additive includes a first additive and a second additive, wherein the first additive includes a compound represented by the following formula (1), and the second additive includes lithium difluorophosphate. It is characterized by

[Formula 1]

In Formula 1, R ₁ is an alkoxy group having 1 to 10 carbon atoms substituted with one or more fluorines or an aryloxy group having 6 to 20 carbon atoms with one or more fluorine substituted, and R ₂ and R ₃ are independently hydrogen and carbon atoms. It is an alkyl group with 1 to 10 carbon atoms or an aryl group with 6 to 20 carbon atoms.

The non-aqueous electrolyte of the present invention is characterized by comprising a first additive containing a sulfonamide-based compound having a specific structural formula as an additive and a second additive containing lithium difluorophosphate. The non-aqueous electrolyte according to the present invention can reduce electrolyte side reactions by forming a stable film on the electrode, and can achieve excellent storage and resistance characteristics at high temperatures when applied to a lithium secondary battery.

(1) Lithium salt

As the lithium salt used in the present invention, 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 ⁺ as a cation, and F ^- , Cl ^- , Br ^- , I ^- , NO ₃ ^- , N(CN) ₂ ^- , BF ₄ ^- , and ClO ₄ ^- as anions. , 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 ^- , (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 ^- selected from the group consisting of It may include at least one of them.

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 , LiFSI (LiN(SO ₂ F) ₂ ), LiCH ₃ SO ₃ , LiCF ₃ CO ₂ , LiCH ₃ CO ₂ and LiBETI (LiN(SO ₂ CF ₂ CF ₃ ) ₂ ). It may include at least one type. Specifically, the lithium salt is 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 ).

The lithium salt may be included in the non-aqueous electrolyte at a concentration of 0.5M to 5M, specifically 0.8M to 4M, and more specifically 0.8M to 2.0M. When the concentration of the lithium salt satisfies the above range, the lithium ion yield (Li ⁺ transference number) and the degree of dissociation of lithium ions are improved, thereby improving the output characteristics of the battery.

(2) Organic solvent

The organic solvent is a non-aqueous solvent commonly used in lithium secondary batteries, and is not particularly limited as long as it can minimize decomposition due to oxidation reactions, etc. during the charging and discharging process of the secondary battery.

Specifically, the organic solvent may include at least one selected from the group consisting of cyclic carbonate-based organic solvents, linear carbonate-based organic solvents, linear ester-based organic solvents, and cyclic ester-based organic solvents.

Specifically, the organic solvent may include a cyclic carbonate-based organic solvent, a linear carbonate-based organic solvent, or a mixture thereof.

The cyclic carbonate-based organic solvent is a high-viscosity organic solvent that has a high dielectric constant and can easily dissociate lithium salts in the electrolyte. Specifically, ethylene carbonate (EC), propylene carbonate (PC), and 1,2-butylene carbonate. , 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, and vinylene carbonate, and may include at least one organic solvent selected from the group consisting of ethylene. May contain carbonate.

In addition, the linear carbonate-based organic solvent is an organic solvent having low viscosity and low dielectric constant, specifically dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, and ethylmethyl carbonate (EMC). ), and may include at least one member selected from the group consisting of methylpropyl carbonate and ethylpropyl carbonate, and more specifically, may include ethylmethyl carbonate (EMC).

The organic solvent may be a mixture of a cyclic carbonate-based organic solvent and a linear carbonate-based organic solvent. At this time, the cyclic carbonate-based organic solvent and the linear carbonate-based organic solvent have a volume ratio of 10:90 to 40:60, specifically 10:90 to 30:70, and more specifically 15:85 to 30:70. Can be mixed. When the mixing ratio of the cyclic carbonate-based organic solvent and the linear carbonate-based organic solvent satisfies the above range, high dielectric constant and low viscosity characteristics can be simultaneously satisfied, and excellent ionic conductivity characteristics can be realized.

In addition, in order to prepare an electrolyte having high ionic conductivity, the organic solvent may be added to at least one carbonate-based organic solvent selected from the group consisting of a cyclic carbonate-based organic solvent and a linear carbonate-based organic solvent, a linear ester-based organic solvent, and a cyclic organic solvent. It may further include at least one type of ester-based organic solvent selected from the group consisting of ester-based organic solvents.

The linear ester-based organic solvent may specifically include at least one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate. there is.

In addition, the cyclic ester-based organic solvent may specifically include at least one selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone. You can.

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 the group consisting of an ether-based organic solvent, a glyme-based solvent, and a nitrile-based organic solvent.

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 linear carbonate-based organic solvents, and is a solvent with low reactivity with metals, such as dimethoxyethane (glyme, DME), diethoxyethane, digylme, It may include, but is not limited to, at least one selected from the group consisting of triglyme and tetra-glyme (TEGDME).

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.

(3) Additives

The non-aqueous electrolyte according to the invention contains additives. The additive includes a first additive and a second additive. The first additive includes a compound represented by Formula 1. The second additive includes lithium difluorophosphate (LiDFP).

In the present invention, the second additive includes lithium difluorophosphate, and the lithium difluorophosphate reacts with an organic solvent (e.g., ethylene carbonate) to form an SEI film containing an organic component on the cathode. However, when only lithium difluorophosphate is used as an additive, the SEI film lacks inorganic components (e.g., LiF, etc.), so the lithium difluorophosphate decomposes first at the anode, resulting in insufficient formation of the SEI film on the cathode. There is. Meanwhile, the compound represented by Formula 1 included in the first additive is a sulfonamide-based compound in which an alkoxy group or aryloxy group is substituted with one or more fluorines, and the alkoxy group or aryloxy group with one or more fluorines is substituted is F Since it is a relatively weak electron withdrawing group compared to -, CF ₃ -, etc., it is easily reduced at the cathode and can easily form a film containing an inorganic component (for example, LiF). Therefore, the non-aqueous electrolyte of the present invention using a combination of the first additive and the second additive can form an SEI film containing both organic and inorganic components on the negative electrode, and is excellent in preventing electrolyte side reactions and suppressing gas generation, and is excellent in preventing electrolyte side reactions and gas generation. Storage properties and resistance properties at high temperatures can be improved to an excellent level.

In addition, in the case of the non-aqueous electrolyte of the present invention using a combination of the first additive and the second additive, it is possible to form an SEI film in which an inorganic component such as LiF is distributed in an SEI film containing an organic component with flexible properties, thereby providing flexibility and Since an SEI film with improved durability can be formed on the electrode, the overall performance of lithium secondary batteries, including high-temperature performance, can be improved to an excellent level. If only the first additive is included as an additive in the non-aqueous electrolyte or only the second additive is included in the non-aqueous electrolyte, durability or flexibility may be reduced, making it difficult to achieve the high-temperature performance improvement effect of the lithium secondary battery targeted by the present invention. I can't.

The first additive includes a compound represented by the following formula (1).

[Formula 1]

In Formula 1, R ₁ is an alkoxy group having 1 to 10 carbon atoms substituted with one or more fluorines or an aryloxy group having 6 to 20 carbon atoms with one or more fluorine substituted, and R ₂ and R ₃ are independently hydrogen and carbon atoms. It is an alkyl group with 1 to 10 carbon atoms or an aryl group with 6 to 20 carbon atoms.

R ₁ may be an alkoxy group having 1 to 10 carbon atoms in which one or more fluorines are substituted, or an aryloxy group having 6 to 20 carbon atoms in which one or more fluorines are substituted. Specifically, it may be an alkoxy group having 1 to 10 carbon atoms in which one or more fluorines are substituted. and, more specifically, it may be an alkoxy group having 1 to 5 carbon atoms substituted with one or more fluorines, and even more specifically, it may be CF ₃ O-, CF ₃ CF ₂ O-, or CF ₃ CH ₂ O-. More specifically, it may be CF ₃ CH ₂ O- in terms of easy formation of the cathode SEI film.

R ₂ and R ₃ may be independently hydrogen, an alkyl group with 1 to 10 carbon atoms, or an aryl group with 6 to 20 carbon atoms, and specifically hydrogen or an alkyl group with 1 to 5 carbon atoms, more specifically, a stable reaction during formation of the SEI film. In terms of purpose, it may be an alkyl group having 1 to 5 carbon atoms, and more specifically, a methyl group.

Specifically, the compound represented by Formula 1 may include at least one selected from the group consisting of a compound represented by Formula 2, a compound represented by Formula 3, and a compound represented by Formula 4. In terms of being able to easily form an SEI film containing an inorganic component such as LiF on the cathode, it may include a compound represented by the following formula (2).

[Formula 2]

[Formula 3]

[Formula 4]

The first additive is added to the non-aqueous electrolyte in an amount of 0.01% to 10% by weight, specifically 0.1% to 2% by weight, more specifically 0.2% to 1% by weight, and even more specifically 0.5% to 1% by weight, More specifically, it may be included at 0.7% by weight to 1% by weight. When the content of the compound represented by Formula 1 satisfies the above range, it is desirable in terms of providing sufficient durability to the SEI film and preventing an increase in resistance of the lithium secondary battery due to excessive addition and a corresponding decrease in life performance.

Meanwhile, the second additive includes lithium difluorophosphate. The lithium difluorophosphate can form an SEI film containing an organic component on the cathode by reaction with an organic solvent (eg, ethylene carbonate, etc.).

The second additive is added to the non-aqueous electrolyte in an amount of 0.01% to 10% by weight, specifically 0.1% to 2% by weight, more specifically 0.2% to 1% by weight, and even more specifically 0.8% to 1% by weight. may be included. When the content of the second additive satisfies the above range, it is advantageous to improve resistance characteristics while providing sufficient flexibility to the SEI film, and is desirable in terms of preventing an increase in the resistance of the lithium secondary battery due to excessive addition and a corresponding decrease in life performance. do.

The weight ratio of the first additive and the second additive is 10:90 to 90:10, specifically 20:80 to 80:20, more specifically 32:68 to 70:30, and even more specifically 35:65 to 60: 40, more specifically, 53:47 to 60:40, and the above-mentioned weight ratio is preferred because the flexibility and durability of the SEI film can be simultaneously improved to a desirable level.

The additive may further include additional additives along with the first and second additives. The additional additive may be included in the non-aqueous electrolyte to prevent decomposition of the non-aqueous electrolyte in a high-power environment, causing cathode collapse, or to improve low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, and battery expansion inhibition at high temperatures.

Specifically, the additional additives include vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, propane sultone, propene sultone, and succino. Nitrile (succinonitrile), Adiponitrile (Adiponitrile), ethylene sulfate, LiODFB (Lithium difluorooxalatoborate), LiBOB (Lithium bis-(oxalato)borate), TMSPa (3-trimethoxysilanyl-propyl-N-aniline), and It may be at least one selected from the group consisting of TMSPi (Tris(trimethylsilyl) Phosphite), and specifically may be vinylene carbonate.

The additional additive may be included in the non-aqueous electrolyte in an amount of 0.1% to 15% by weight.

Lithium secondary battery

Additionally, the present invention provides a lithium secondary battery containing the above-described non-aqueous electrolyte.

Specifically, the lithium secondary battery includes a positive electrode; a cathode opposite the anode; a separator interposed between the anode and the cathode; and the non-aqueous electrolyte described above.

At this time, the lithium secondary battery of the present invention can be manufactured according to a common method known in the art. For example, the anode, the cathode, and the separator between the anode and the cathode are sequentially stacked to form an electrode assembly, and then the electrode assembly can be manufactured by inserting the inside of the battery case and injecting the non-aqueous electrolyte according to the present invention. .

(1) anode

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.

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 include at least one selected from the group consisting of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, and aluminum-cadmium alloy, preferably aluminum.

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 negative 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 layer may include a positive electrode active material.

The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and specifically, a lithium transition metal complex oxide containing lithium and at least one transition metal consisting of nickel, cobalt, manganese, and aluminum, Preferably, it may include a transition metal containing nickel, cobalt, and manganese, and a lithium transition metal complex oxide containing lithium.

For example, the lithium transition metal complex oxide includes lithium-manganese oxide (e.g., LiMnO ₂ , LiMn ₂ O ₄ , etc.), lithium-cobalt oxide (e.g., LiCoO _{2 ,} etc.), and lithium-nickel. oxide (for example, LiNiO ₂ etc.), lithium-nickel-manganese oxide (for example, LiNi _1-Y Mn _Y O ₂ (where 0<Y<1), LiMn _2-z Ni _z O ₄ (here, 0<Z<2), etc.), lithium-nickel-cobalt-based oxide (for example, LiNi _1-Y1 Co _Y1 O ₂ (here, 0<Y1<1), etc.), lithium-manganese -Cobalt-based oxides (for example, LiCo _1-Y2 Mn _Y2 O ₂ (where 0<Y2<1), LiMn _2-z1 Co _z1 O ₄ (where 0<Z1<2), etc.), lithium -Nickel-manganese-cobalt oxide (for example, Li(Ni _p Co _q Mn _r1 )O ₂ (where 0<p<1, 0<q<1, 0<r1<1, p+q+ r1=1) or Li(Ni _p1 Co _q1 Mn _r2 )O ₄ (where 0<p1<2, 0<q1<2, 0<r2<2, p1+q1+r2=2), etc.), or Lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni _p2 Co _q2 Mn _r3 M _S2 )O ₂ (where M is Al, Fe, V, Cr, Ti, Ta, Mg and It is selected from the group consisting of Mo, and p2, q2, r3 and s2 are each independent atomic fraction of elements, 0 < p2 < 1, 0 < q2 < 1, 0 < r3 < 1, 0 < s2 < 1, p2 +q2+r3+s2=1), etc.), and any one or two or more of these compounds may be included. Among these, in that the capacity characteristics and stability of the battery can be improved, the lithium transition metal composite oxide is LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , lithium nickel-manganese-cobalt oxide (for example, Li(Ni _0.6 Mn _0.2 Co _0.2 )O ₂ , Li(Ni _0.5 Mn _0.3 Co _0.2 )O ₂ , Li(Ni _0.7 Mn _0.15 Co _0.15 )O ₂ or Li(Ni _0.8 Mn _0.1 Co _0.1 )O ₂ etc.), or lithium nickel cobalt aluminum oxide (e.g. For example, it may be Li (Ni _0.8 Co _0.15 Al _0.05 )O ₂ , etc.), and considering the remarkable improvement effect due to control of the type and content ratio of the constituent elements forming the lithium transition metal complex oxide, the lithium transition metal The complex oxide is Li(Ni _0.6 Mn _0.2 Co _0.2 )O ₂ , Li(Ni _0.5 Mn _0.3 Co _0.2 )O ₂ , Li(Ni _0.7 Mn _0.15 Co _0.15 )O ₂ or Li(Ni _0.8 Mn _0.1 Co _0.1 )O ₂ etc., and any one or a mixture of two or more of these may be used.

More specifically, the positive electrode active material is a lithium transition metal complex oxide and may contain 60 mol% or more of nickel based on the total number of moles of transition metals contained in the lithium transition metal complex oxide. Specifically, the positive electrode active material is a lithium transition metal complex oxide, and the transition metal includes nickel; and at least one selected from manganese, cobalt, and aluminum, and may contain 60 mol% or more, specifically 60 mol% to 90 mol%, of nickel based on the total number of moles of the transition metal. When this lithium transition metal complex oxide using a high content of nickel is used together with the above-mentioned non-aqueous electrolyte, it is preferable in that it can reduce by-products in the gas phase generated by structural collapse.

Additionally, the positive electrode active material may include a lithium complex transition metal oxide represented by the following formula (5).

[Formula 5]

Li _1+x (Ni _a Co _b Mn _c M _d )O ₂

In Formula 5, M is 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 1+x, a, b, c and d are the atomic fractions of independent elements, 0≤x≤0.2, 0.50≤a<1, 0<b≤0.25, 0<c≤0.25, 0≤d≤0.1, a+b+c+d=1.

Preferably, a, b, c and d may be 0.70≤a≤0.95, 0.025≤b≤0.20, 0.025≤c≤0.20, and 0≤d≤0.05, respectively.

Additionally, a, b, c, and d may be 0.80≤a≤0.95, 0.025≤b≤0.15, 0.025≤c≤0.15, and 0≤d≤0.05, respectively.

Additionally, a, b, c, and d may be 0.85≤a≤0.90, 0.05≤b≤0.10, 0.05≤c≤0.10, and 0≤d≤0.03, respectively.

The positive electrode active material may be included in the positive electrode active material layer at 80% to 99% by weight, preferably 92% to 98.5% by weight, in consideration of sufficient capacity of the positive electrode 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, Ketjen black, channel black, Paneth black, lamp black, and 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 30㎛ to 400㎛, preferably 40㎛ to 110㎛.

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 faces the anode.

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.

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 ㎛.

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. Alternatively, the negative electrode active material may include a carbon-based active material and a (semi-)metal-based active material.

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 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 98% 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.

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, Ketjen black, channel black, Paneth black, lamp black, and 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 10㎛ to 100㎛, preferably 50㎛ to 80㎛.

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

In addition, 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 from the same polyolefin polymer can be used alone or by laminating them, or conventional porous nonwoven fabrics, such as high melting point glass fibers, polyethylene terephthalate fibers, etc., can be used. It is not limited. 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.

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

Hereinafter, the present invention will be described in more detail through specific examples. However, the following examples are only examples to aid understanding of the present invention and do not limit the scope of the present invention. It is obvious to those skilled in the art that various changes and modifications are possible within the scope and technical spirit of the present description, and it is natural that such changes and modifications fall within the scope of the appended patent claims.

Examples and Comparative Examples

Example 1

(Preparation of non-aqueous electrolyte)

As an organic solvent, a mixture of ethylene carbonate (EC) and ethylmethyl carbonate (EMC) in a volume ratio of 30:70 was used.

A non-aqueous electrolyte was prepared by adding LiPF ₆ as a lithium salt to the organic solvent, a compound represented by the following formula (2) as a first additive, lithium difluorophosphate as a second additive, and vinylene carbonate (VC) as an additional additive.

The LiPF ₆ was included in the non-aqueous electrolyte at a concentration of 1.2M.

The compound represented by Formula 2 was included at 0.5% by weight in the non-aqueous electrolyte, the lithium difluorophosphate was included at 0.8% by weight in the non-aqueous electrolyte, and the vinylene carbonate was included at 0.5% by weight in the non-aqueous electrolyte. included.

[Formula 2]

(Lithium secondary battery manufacturing)

Cathode active material (LiNi _0.90 Co _0.06 Mn _0.03 Al _0.01 O ₂ ): conductive material (carbon black): binder (polyvinylidene fluoride) was mixed with the solvent N-methyl-2-pyrrolidone ( NMP) was added to prepare a positive electrode mixture slurry (solid content: 60% by weight). The positive electrode mixture slurry was applied to one side of a positive electrode current collector (Al thin film) with a thickness of 13.5 ㎛, and dried and roll pressed to prepare a positive electrode.

Negative active material (graphite and SiO mixed at a weight ratio of 90:10): Conductive material (carbon black): Binder (styrene-butadiene rubber/carboxymethyl cellulose) is added to distilled water as a solvent at a weight ratio of 97.6:1.6:0.8. A negative electrode mixture slurry (solid content: 60% by weight) was prepared. The negative electrode mixture slurry was applied to one side of a negative electrode current collector (Cu thin film) with a thickness of 6 ㎛, and dried and roll pressed to prepare a negative electrode.

A lithium secondary battery was manufactured by interposing a polyethylene porous film separator between the prepared positive electrode and the negative electrode in a dry room, and then injecting the prepared non-aqueous electrolyte.

Example 2

A non-aqueous electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the compound represented by Formula 2 as a first additive was included in the non-aqueous electrolyte at 0.1 wt% instead of 0.5 wt%.

Example 3

A non-aqueous electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the compound represented by Formula 2 as the first additive was included in the non-aqueous electrolyte at 1 wt% instead of 0.5 wt%.

Example 4

A non-aqueous electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 1, except that 0.5 wt% of lithium difluorophosphate as a second additive was included in the non-aqueous electrolyte instead of 0.8 wt%.

Example 5

A non-aqueous electrolyte and a lithium secondary battery were prepared in the same manner as in Example 1, except that lithium difluorophosphate as a second additive was included in the non-aqueous electrolyte at 1% by weight instead of 0.8% by weight.

Comparative Example 1

A non-aqueous electrolyte, lithium secondary battery was manufactured in the same manner as Example 1, except that the first additive was not added.

Comparative Example 2

A non-aqueous electrolyte, lithium secondary battery was manufactured in the same manner as Example 1, except that the first and second additives were not added.

Comparative Example 3

Non-aqueous electrolyte was prepared in the same manner as in Example 1, except that the second additive was not added and the compound represented by the following formula 6 was added at 0.5% by weight instead of the compound represented by the formula 2 as the first additive to the non-aqueous electrolyte. Electrolyte and lithium secondary battery were manufactured.

[Formula 6]

Comparative Example 4

A non-aqueous electrolyte, lithium secondary battery was manufactured in the same manner as Example 1, except that the second additive was not added.

Experiment example

Experimental Example 1: Evaluation of capacity retention rate after high temperature storage

A formation process was performed on the lithium secondary batteries manufactured in the above examples and comparative examples, and then constant current/constant voltage (CC/CV) charging (0.05C cut off) was performed up to 4.2V at a rate of 0.33C at 25°C. Then, the initial discharge capacity was measured by constant current (CC) discharge to 2.80V at a rate of 0.33C.

Thereafter, the lithium secondary battery was fully charged to SOC 100% under the above charging conditions and stored at high temperature (60°C) for 8 weeks. Afterwards, it was transferred to a charger and discharger at room temperature (25°C), and the discharge capacity was measured by discharging under the above discharge conditions. The capacity retention rate was calculated using the formula below, and the results are shown in Table 1 below.

Capacity maintenance rate (%) = (discharge capacity after high temperature storage/initial discharge capacity) × 100

Experimental Example 2: Evaluation of resistance increase rate after high temperature storage

A formation process was performed on the lithium secondary batteries manufactured in the above examples and comparative examples, and then constant current/constant voltage (CC/CV) charging (0.05C cut off) was performed up to 4.2V at a rate of 0.33C at 25°C. And the initial resistance was measured by constant current (CC) discharge to 2.80V at a rate of 0.33C.

Thereafter, the lithium secondary battery was fully charged to SOC 100% under the above charging conditions and stored at high temperature (60°C) for 8 weeks. Afterwards, it was transferred to a charger and discharger at room temperature (25°C), the resistance was measured, the resistance increase rate was calculated using the following equation, and the results are shown in Table 1 below.

Resistance increase rate (%) = {(resistance after high temperature storage - initial resistance) / (initial resistance)} × 100

	Experimental Example 1	Experimental Example 2
	Capacity retention rate when stored at high temperature (%, 8 weeks)	Resistance increase rate when stored at high temperature (%, 8 weeks)
Example 1	91.14	-8.86
Example 2	90.58	-3.42
Example 3	91.33	-10.17
Example 4	90.31	-5.51
Example 5	91.24	-8.72
Comparative Example 1	90.39	-1.32
Comparative Example 2	89.45	+8.42
Comparative Example 3	87.85	+22.50
Comparative Example 4	89.45	+8.10

Referring to Table 1, the lithium secondary batteries of Examples 1 to 5 using a non-aqueous electrolyte containing the first additive and the second additive according to the present invention have high temperature storage life performance compared to the lithium secondary batteries of Comparative Examples 1 to 4. It can be seen that it is excellent and the resistance increase rate is low.

Claims (10)

1. lithium salt;

   organic solvent; and

   Contains additives;

   The additive includes a first additive and a second additive,

   The first additive includes a compound represented by the following formula (1),

   The second additive is a non-aqueous electrolyte comprising lithium difluorophosphate:

   [Formula 1]

   

   In Formula 1, R ₁ is an alkoxy group having 1 to 10 carbon atoms substituted with one or more fluorines or an aryloxy group having 6 to 20 carbon atoms with one or more fluorine substituted, and R ₂ and R ₃ are independently hydrogen and carbon atoms. It is an alkyl group with 1 to 10 carbon atoms or an aryl group with 6 to 20 carbon atoms.
2. In claim 1,

   The compound represented by Formula 1 is a non-aqueous electrolyte comprising at least one selected from the group consisting of a compound represented by Formula 2, a compound represented by Formula 3, and a compound represented by Formula 4:

   [Formula 2]

   

   [Formula 3]

   

   [Formula 4]

   

   .
3. In claim 1,

   The first additive is included in the non-aqueous electrolyte in an amount of 0.1% to 10% by weight.
4. In claim 1,

   The second additive is included in the non-aqueous electrolyte in an amount of 0.1% to 10% by weight.
5. In claim 1,

   A non-aqueous electrolyte wherein the weight ratio of the first additive and the second additive is 10:90 to 90:10.
6. 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 At least one selected from the group consisting of SO ₃ , LiFSI (LiN(SO ₂ F) ₂ ), LiCH ₃ SO ₃ , LiCF ₃ CO ₂ , LiCH ₃ CO ₂ and LiBETI (LiN(SO ₂ CF ₂ CF ₃ ) ₂ ) A non-aqueous electrolyte containing.
7. In claim 1,

   The lithium salt is included in the non-aqueous electrolyte at a molar concentration of 0.5 M to 5.0 M.
8. In claim 1,

   The organic solvent is a non-aqueous electrolyte comprising at least one selected from the group consisting of a cyclic carbonate-based organic solvent, a linear carbonate-based organic solvent, a linear ester-based organic solvent, and a cyclic ester-based organic solvent.
9. In claim 1,

   The additives include vinylene carbonate, vinylethylene carbonate, fluoroethylene carbonate, propane sultone, propene sultone, succinonitrile, adiponitrile, ethylene sulfate, LiBOB (Lithium bis-(oxalato)borate), LiODFB (Lithium difluorooxalatoborate). , 3-trimethoxysilanyl-propyl-N-aniline (TMSPa), and Tris(trimethylsilyl) Phosphite (TMSPi).
10. anode;

    a cathode opposite the anode;

    a separator interposed between the anode and the cathode; and

    A lithium secondary battery comprising the non-aqueous electrolyte according to claim 1.